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This is to certify that the

thesis entitled

POSTURAL SWAY ANALYSIS

presented by

DAVID BIALSKI ;

has been accepted towards fulfillment
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Masters Large Animal

degree in

 

Clinical Sciences

 

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6/01 e/CIRCJDateDuepss-nts

POSTURAL SWAY ANALYSIS 1N HORSES

By

David Elyezer Bialski

AN ABSTRACT OF A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Large Animal Clinical Sciences

2001

Professor Hilary Clayton

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ABSTRACT
POSTURAL SWAY ANALYSIS IN HORSES
By

David Elyezer Bialski

Postural sway analysis offers an objective method of assessing a horse’s balance.
The objectives of this study were to measure postural sway in normal horses and to assess
the effects of detomidine (10 ug/kg and 20 ug/kg) on the horse’s balance at 15 minute
intervals for 120 minutes. Horses stood with four hooves on the force platform, while
force data (1,000 Hz) were collected for 10 5 periods, with five repetitions .per condition.
Summary statistics were used to quantify the center of pressure (COP) movements and
the effects of the drug on the horse’s balance. Mediolateral COP movements, COP area
and mean COP radius returned to no sedation values (0.94 i 0.21 cm, 0.72 i 0.22 cmz,
0.34 i 0.05 cm, respectively) within 15 minutes after 10 ug/kg and within 30 minutes
after 20 ug/kg of detomidine. Mean COP velocity returned to the no sedation value (0.91
i 0.07cm/S) in both levels of sedation after 30 minutes. Craniocaudal COP movements
returned to the no sedation value (1.15 i 0.11 cm) after 60 minutes and 90 minutes for 10
ug/kg and 20 ug/kg, respectively. It is concluded that the horse should not be moved,
have its limbs manipulated or collect postural sway data for 30 minutes after

adminiStration of detomidine.

DEDICATION

This work is dedicated to Israel‘l’, Clara‘t, José‘l’, Bellal', Terezaf, Alzira, Helio, Adrianne,
Berenice‘t, Bernardo, Dayana, Claudio, Daniel, Juliana, James, Alessandra, Andrea,
Victor, Igor and Clarinha, because without your help, love and comprehension I would
never be the person I am today and I would never had accomplished this.

Thank you.

ACKNOWLEDGMENTS

0 First of all I would like to thank God for being my mentor through life.

0 I would like to thank my advisor Professor Hilary M. Clayton and also the members
of my committee Dr. Harold Schott, Dr. Susan Ewart, Dr. Robert Bowker, and Dr.

George Bohart for all the help and advice during my program.

0 My sincerest appreciation is also expressed to Joel Lanovaz, who is the research
coordinator at the Mary Anne McPhail Equine Performance Center, for his technical
and intellectual assistance and also for his unconditional help through my research;
and all the graduate students at the Mary Anne McPhail Equine Performance Center,
particularly Wesley Singleton for assistance with my project and Molly Nicodemus

for all the intellectual input.

9 I would like to express my sincere gratitude to Sarah Fox, Acacia Wilson, Sergey
Balinskiy and Cara O’ Connor for all the help during the collection of data, also I

would like to thank Cathy Berney and Susan W. Ebehart for facilitating my research .

This research was supported by the Mary Anne McPhail Endowment

iv

TABLE OF CONTENTS

LIST OF TABLES... ............................................................................. viii
LIST OF FIGURES ................................................................................. x
1. INTRODUCTION ................................................................................ 1
1.1. Research objectives .......................................................................... 6
2. LITERATURE REVIEW ...................................................................... 7
2.1. BALANCE .................................................................................... 9
2.1.1. Somatosensory, vestibular and visual systems ................................ 11
2.2. POSTURAL SWAY ANALYSIS ....................................................... 1.3
2.2.2. Previous studies in humans ....................................................... 15
2.2.3. Previous studies in quadrupeds .................................................. 19
2.2.4. Postural sway analysis in horses ................................................ 20
2.3. EFFECTS OF THE USE OF DRUGS ON POSTURAL SWAY ................... 22
3. METHOD OF INVESTIGATION .................................................... 24
3.1. SUBJECTS ................................................................................. 24
3.2. DATA COLLECTION ................................................................... 25
3.2.1. Force data ............................................................................ 25
3.2.2. Kinematic data ...................................................................... 26
3.3. DRUG ADMINISTRATION ............................................................ 29

3.4.

3.5.

4.1.

4.2.

4.3.

DATA ANALYSIS ........................................................................ 31

3.4.1. Force data analysis ................................................................ 31
3.4.2. Kinematic data analysis .......................................................... 3S
STATISTICAL ANALYSIS ............................................................ 41
RESULTS .................................................................................. 43
Postural sway variables ................................................................... 43
4.1.1. Mediolateral range of COP motion ............................................. 44
4.1.2. Craniocaudal range of COP motion ....... I ...................................... 46
4.1.3. Mean COP radius .................................................................. 48
4.1.4. Area of the COP ................................................................... 50
4.1.5. Mean COP velocity ............................................................... 52
4.1.6. Data collection time ............................................................... 54
Kinematic variables ....................................................................... 55
4.2.]. Height of the head .................................. I ................................ 56
4.2.2. Spatial kinematic variables ......................................................... 58
Observations ................................................................................ 61
DISCUSSION .............................................................................. 62
CONCLUSION ........................................................................... 75
6.1. Future applications .................................................................... 76
GLOSSARY ............................................................................... 77

10.

ll.

12.

13.

APPENDIX A .............................................................................. 79

APPENDIX B .............................................................................. 80
APPENDIX c .............................................................................. 81
APPENDIX D .............................................................................. 82
APPENDIX E .............................................................................. 83
REFERENCES ................. 86

 

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8.1

Table 3.1.

Table 3.2.

Table 4.1.

Table 4.2.

Table 4.3.

Table 4.4.

Table 4.5.

Table 4.6.

Table 4.7.

Table 4.8.

A.l.

B.l.

LIST OF TABLES

Morphological characteristics of the horses ................................... 24
Data collection schedule ......................................................... 30

Mean and standard deviation for mediolateral range of COP motion for the
three treatments ................................................................... 45

Mean and standard deviation for craniocaudal range of COP motion for
the three reatrnents ................................................................ 47

Mean and standard deviation for mean COP radius for the three
treatments ........................................................................... 49

Mean and standard deviation for area of the COP for the three treatments
........ 51

Mean and standard deviation for mean COP velocity for the three
treatments .......................................................................... 52

Mean and standard deviation for total time for the three treatments ...... 54

Mean and standard deviation for head height for the three

treatments ........................................................................... 57
Mean iSD values for the no significant variables ........................... 60
Information sheet log ............................................................. 79

Doses of detomidine for each individual horse no sedation (placebo), light
sedation (10 ug/kg) or heavy sedation (20 ug/kg) ............................. 80

 

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C.1.

D.l.

D.2.

E.l.

F.1.

F2

F3.

F.4.

F.5.

F.6.

Log for data collection ............. ’ .............................................. 8]

Parameters used to access the level of sedation during the data
collection ........................................................................... 82

Classification of the grade of sedation based on the parameters from table

D.1 ................................................................................... 82
Overall mean 1*: SD for 6 horses within 3 levels of sedation ............... 77
Grade of sedation for horse 210 ................................................. 83
Grade of sedation for horse 211 ................................................. 83
Grade of sedation for horse 212 ................................................. 84
Grade ofsedation for horse 213 ............. 84
Grade of sedation for horse 214 ................................................. 85
Grade of sedation for horse 215 ................................................. 85

 

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PI

PI

Pi,

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Figure 1.1.
Figure 2.1.
Figure 3.1.
Figure 3.2.
Figure 3.3.
Figure 3.4.
Figure 3.5.
Figure 3.6.
Figure 3.7.

Figure 3.8.

Figure 3.9.
Figure 3.10.

Figure 3.11.

- LIST OF FIGURES

Horse standing on a force platform ............................................... 3
Foot placement during Romberg’s test ........................................ 14
Scheme of the handler position during data collection ....................... 25
Comer of the force platform ..................................................... 26
Triangle calibration ............................................................... 27
Schematic view of the data collection area .................................... 28
Camera and illumination set up ................................................. 29
Saline solution and detomidine .................................................. 30
Stabilograrn ........................................................................ 32

Representation of the coordinate system to measure mediolateral and

' craniocaudal range of COP motion ............................................. 33
Graphic representation of the Delaunay triangulation ........................ 34
Graphic representation of the calculation of the limb angles ............... 37
Representation of the head marker ............................................. 38

 

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Figure3. 12.

Figure 3.13.

Figure 3.14.

Figure 4.1.

Figure 4.2.

Figure 4.3.

Figure 4.4.

Figure 4.5.

Figure 4.6.

Figure 4.7.

Figure 4.8.

Representation of the longitudinal and tranverse angles when correcting
forelimbs angles ................................................................... 39

Representation of the area of the base of support and center of the base of
support .............................................................................. 40

Graphic representation of Heron’s theorem showing how the area of the
base of support was calculated ................................................... 41

Stabilograms under the no sedation condition at times 0, 15, 30 and 120
minutes .............................................................................. 44

Graphic representation of the mediolateral range of COP motion ......... 46 '

Graphic representation of the craniocaudal range of COP motion .........48

Graphic representation of the mean COP radius .............................. 51
Graphic representation ofthe area ofthe COP ........... 53
Graphic representation of the mean COP velocity ........................... 55
Graphic representation of the total time ........................................ 55
Graphic representation of the head height ..................................... 58

1. INTRODUCTION

Biomechanics applies mechanical principles to the study of living systems. With
the use of biomechanics we can better understand how the different systems within the
horse normally fimction and how the locomotor system reacts to development, change
and human intervention (Lanovaz, 1997). Horses perform a wide. repertoire of gaits
including the walk, trot, pace, canter, gallop and other more specialized gaits. Training
transforms ordinary gaits into elegant movements such as piaffe and pirouettes. Horses
move differently when carrying a rider than when they are performing at liberty (van
Weeren, 2000). They also have lighter ground reaction forces especially in the forelimbs
(Clayton, et al., 1999), which may increase the risk of injury. Injuries of the locomotor
system me by far the most common problem in equine athletes (Jeffcott et al., 1985). The
necessity to understand the mechanics of injury prevention has been cited in the literature
since the 17th century (reviewed by van Weeren, 2000).

The unportance of “balance” of the horse is well recognized in relation to athletic
performance (Schamhardt et al., 1992), although data defining balance in horses are
scarce. Balance is the ability to maintain a state of equilibrium while at rest or in motion
(Kirby et al., 198 7). The body counteracts both internal and external forces that are
disruptive to equilibrium by a dynamic system of sensory input, motor responses and
cognitive processes that work together to maintain the body’s center of gravity over its

base of support. Balance is not only a reactive response to disruptive forces but can also

be proactive and adaptive based on prior experience and intended movement (Horak et
al., 1997).

Winter (1990) describes the center of gravity (COG) as an imaginary point where
body weight is concentrated. The line of gravity is a vertical line through the COG. When
a horse is standing in a balanced position the line of gravity contacts the ground within
the base of support, which is circumscribed by the four hooves that are in contact with the
ground. The nervous system maintains the COG above the base of support. Each hoof
exerts a force against the ground and the ground exerts a force against each hoof that is
called the ground reaction force (GRF). The GRF is equal in magnitude and opposite in
direction to the force exerted by the hoof against the ground, and it represents the force of
the ground on the body. A force platform is a device that measures the total GRF over its
entire surface and locates its point of application. When a horse has more than one hoof
in contact with a force platform, it cannot distinguish between the individual hooves, and
the center of pressure (COP) is the centroid of the total force distributed on its surface
(Figure l. 11).: If the horse stands perfectly still with all four. hooves on the force platform
the GRF vector is superimposed on the line of gravity. Even during quiet standing,
however, small adjustments of muscle tension are reflected by movements of the COP
(Winter, .1990). These movements are described as postural sway. In normal standing
there is alwaysls’ome postural Way and the amount of sway is an indicator of the stability
of the COP (Winter, 1990).

Somatosensory, vestibular and visual pathways provide feedback for the
maintenance of balance (Jeka et al., 1998). During a clinical neurological examination,

several observations and manipulative tests of balance are performed. These assess head

position and coordination of head movements: normal horses maintain the head in a
typical vertical position and are able to perform certain acts, such as prehension of food.
Some neurological diseases, such as vestibular disease, cause changes in head position
and stability (Smith, 1992). Balance is evaluated during the neurological examination by
determining the horse’s response to manipulations that include elevating the horse’s head
or pulling the horse’s tail to one side as the horse walks in a straight line. Responses are
assessed subjectively and interpretation depends on the experience of the clinician
(MacKay and Mayhew, 1991). Postural sway analysis offers an objective method of

assessing a horse’s balance.

 

Figure 1.1- Horse standing still and square on a force platform which is outlined in white.
The arrow pointing vertically downwards represents the line of gravity and the dot on the
force platform represents the center of pressure (COP). The three mutually perpendicular
arrows indicate the coordinate system of the force platform.

 

 

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The balance mechanism is such that the COP is allowed to drift a short distance
before being corrected. More specifically, over short term an open-loop control scheme is
utilized by the postural control system, in which the body drifts away from its
equilibrium position. Over longer time intervals closed loop control mechanisms are
called into play, in which the body drifts away then returns to its equilibrium (Collins and
De Luca, 1993). These drifts and corrections are measured by postural sway analysis. The
results of postural sway analysis are indicative of the horse’s innate ability to balance.

Preliminary studies of postural sway (Clayton et al., 1999) encountered
difficulties in making horses Stand still and square on a force platform for long enough to
collect useful data. This problem may be overcome using sedation. A sedative that is
commonly used in horses is detomidine (Dormosedan, Pfizer, New York, NY). This
study measures the effects of sedation with detomidine on postural sway analysis. The
results will indicate whether detomidine is likely to have an adverse effect on the horse’s
ability to balance during procedures such as shoeing, clipping and traveling.

Sedatives are used on a daily basis in veterinary practice to provide chemical
restraint during a diverse range of procedures. Their use has resulted in improved safety
both for the horses and for the people who work with them. Previous studies have
examined the physiological response of horses to specific drugs and have identified
suitable drugs to facilitate various procedures in equine medicine. However, the effects of
those drugs on the horse’s balance have not been studied objectively.

Nonopioid analgesics include a large number of drugs used for their anti-
inflammatory properties to combat pain. Most of those drugs can be categorized as

nonsteroidal anti-inflammatory drugs (N SAID) or nonopioid analgesics such as

 

 

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detomidine and xylazine (Muir and Hubbell, 1991). These drugs belong to a much larger
group of sedative analgesics called alphaz adrenoceptor agonists, which act directly on
the central nervous system (Jéchle, 1984).

Detomidine was chosen for this study because it is frequently used by equine
practitioners, has. a long duration of action, and has obvious effects on the horse’s balance
(ataxia) shortly after administration. It is commonly used as a chemical restraint for
procedures such as bronchoscopy or nasogastric intubation, and to provide pain relief for
minor surgical procedures and colic. It usually induces decreased heart rate, profound
lethargy, and reduced sensitivity to environmental stimuli. Paradoxically some horses
have an extreme response to external stimuli after detomidine sedation even when they
look deeply sedated (Muir and Hubbell, 1991). A short time after administration, horses
Show incoordination and a fixed base-wide stance. Occasionally, side effects include a
partial atrioventricular block. The use of atropine may prevent the occurrence of
arhythrnias (Allen et al., 1993). The respiratory rate slows initially but after 5 minutes
returns to normal. Salivation, penile prolapse and sweating may be seen as well. Duration
of sedation following detomidine administration is dose dependent lasting fi'om 30
minutes to 2 hours. This study will apply postural sway analysis to assess the efi’ects of

detomidine on the horse’s balance.

1.1. Research Objectives

1. To measure postural sway in a group of sound horses.

2. To determine the effects of light sedation with detomidine (10 ug/kg IV) on balance
of horses at selected intervals after administration.

3. To determine the effects of heavy sedation with detomidine (20 jig/kg IV) on balance

of horses at selected intervals after administration.

2. LITERATURE REVIEW

The horse has had a very close relationship with man in the 7000 years Since it
was domesticated. Since the early days after its domestication, the horse has been used as
a sport and competition animal and also as a pet, which creates a bond of affection
between horse and man. Thus, horses have always had a unique relationship with people
that has ensured the horse’s survival even after mechanization (Van Weeren, 2000).

Unlike almost all other species, the horse was domesticated for its locomotor
capabilities rather than as a supplier of food or clothing materials. As a result of this
important role in transportation, combined with its closeness to man, the horse was a
focus of attention as veterinary science developed in the ancient societies and later as it
became a prospering branch of science during the Greek and Roman civilizations.
Subsequently, interest in equine veterinary medicine and equine locomotion has kept
pace with public recognition of the importance of the horse (van Weeren, 2000).

After World War 11 horses became less important due to advances in
mechanization. However, interest in the species reappeared at the end of the 1960’s and
in the early 1970’s when equestrian sports developed a tremendous popularity that
continues to increase today (van Weeren, 2000).

Advances in technology, especially in photographic techniques facilitated the
study of equine locomotion. At the end of the 19th century, Marcy and Muybridge took
advantage of new technology to further acquire knowledge of equine locomotion. Later

in the twentieth centm'y, as the interest in horses for sports and recreation increased, the

incredible development of computer technology facilitated complex computational tasks
making this area of research much more accessible.

The study of locomotion is closely associated with biomechanics, the science of
investigating the effects of internal and external forces upon living bodies. The science of
biomechanics can be divided into biostatics and biodynamics. Biostatics is applied to
study systems with no accelerated motion, in which the sum of the external forces acting
on the system is zero: the forces are balanced. Biostatics is more related to study of
tissues, tendons bone and cartilage. Biodynamics is the study of unbalanced systems of
forces on the body, which result in movement. When the horse is moving freely in three
dimensional space the position of any part of the body can be located using a cartesian
coordinate system (x, y and z coordinates). The study of biodynarnics includes kinematics
and kinetics. Kinematics describes the geometry of movement with no regard for the
forces producing motion. Kinetics is concerned with the forces that initiate and alter
motion (Winter, 1990).

There are no easy methods to produce athletic success in horses, but descriptions
of exercise physiology and sport biomechanics, provide some guidelines to trainers,

veterinarians and owners (Dalin and Jeffcott, 1994).

2. l . BALANCE

During quiet standing, balance is maintained by small adjustments in muscular
tension that are reflected by movements of the center of pressure (COP). These
movements are referred to as postural sway and reflect the stability of balance in an
animal. Balance is measured by tracking the movements of the COP on a force platform.
Previous studies in human subjects have shown that postural sway changes with age
(Sinclair et al., 1990; Panzer et al., 1995), loss of visual proprioception (Kollegger et al.,
1992) and development of neurological diseases (Nakamura et al., 1997; Rand et al.,
1998). In horses the effect of age has not been investigated, but it seems likely that
postural stability may develop at a relatively young age due to the precocious
development of locomotion capabilities in this species. In a previous study of normal
horses COP velocity did not change due to loss of visual proprioception (Bialski et al.,
2000), though the findings may be different in horses with neurological disease.

Panzer et al. (1995) studied the effect of aging on balance using the Romberg Test
to assess subjectively the balance in a group of 24 normal people ranging in age fi'orn 21-
77 years old. The results showed that in normal aging there was an increase in variability
in the craniocaudal movements of the center of mass (COM) without a corresponding
increase in variability of total COM displacement.

Smith et a1. (1997) studied the cumulative neurological effects of JP-8 jet fuel

vapor from an aircrafi on postural sway stability. The results showed that exposure to JP-

8 caused a deficit in balance. Two groups were studied (low exposure and high exposure)
and in both groups the amount of postural sway was higher after exposure.

Collins et al., (1995) studied the effects of spaceflight on open loop and closed-
loop postural control mechanisms, and found that there may be in-flight adaptations to
higher level descending postural control pathways. This change may also be a
consequence of a compensatory. postural control strategy which is adopted by the
astronauts to compensate for post flight unsteadiness.

Maintenance of a stable posture is important for all animals. For humans,
maintaining balance is more challenging due to the narrow bipedal base of support.
Approximately two thirds of body mass is precariously balanced some distance from the
ground (Winter, et al., 1990). The importance of “balance” of the horse is well
recognized in. relation to athletic performance (Schamhardt et al., 1992), though data
defining balance are scant.

Stability is achieved using a combination of visual and vestibular input, combined
with somatosensory information from all four limbs. A deficiency in any of these inputs
can lead to instability. Light touching of a stable target close to the person’s body
decreases postural sway in people of all ages. Hewever, finger contact with a target at a
greater distance from the body led to an increase of postural sway (Reginella et al., 1999)

To better understand how the central nervous system (CNS) adapts to different
environmental conditions, it is important to understand postural control and the role of
sensory perception. It has been shown that translating the body with different fi'equencies
requires changes in the coordination patterns of the head, trunk and legs to accommodate

the different forces acting on the body. Translating the body at different frequencies also

10

moves the sensory system outside the optimal operational ranges (Buchanan and Horak,
1999)

The influence of moving visual fields on postural sway stability depends, not only
on the characteristics of the visual environment, but also on the characteristics of the
support surface. Humans and cats with profound loss of vestibular function show
normally coordinated postural responses in the limbs with perturbations at the surface,
but responses in head kinematics and electromyo graphic (EMG) responses are
exaggerated and more variable. The CNS increased COP amplitude to counter higher
forces associated with increasing translation frequency. There was a clear adaptation with
repeated exposure even when the frequencies were presented in random order. Control of
the head and trunk is a critical strategy for balance at all translation frequencies because
the trunk represents a large percentage of body mass and also serves as a platform for the

vestibular and visual organs located in the head (Buchanan and Horak, 1999).

2.1.1. Somatosensory, vestibular and visual systems

The subsystems that make up the postural control system involve sensory input
from the vestibular, visual and somatosensory system, and the CNS.

The somatosensory system, which consists of muscle, joint and cutaneous
receptors, provides information about the state of the effector system in relation to the
environment. It uses receptors in the joints, ligaments, muscles and skin to provide
information about muscle length, tension, and contraction, and also about temperature,

pain, pressure and joint position.

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The vestibular system gives information about the body orientation in the inertial
frame of reference and accelerations of the body. It provides information about the
position of . the head with respect to gravity and inertial forces. The otoliths, which
respond to slow head movements, detect two kinds of motion: linear acceleration and tilt
angle of the head. The resulting information describes the head movement and orientation
with respect to the gravity.

The visual system is also a proprioceptive system because it not only provides
information about the environment but also about the orientation and movement of the
body (Winter et al., 1990). Visual proprioception provides information about the
verticality of the head with respect of the surrounding environment and adjusts head
position when necessary. It also provides information for proactive postural control by
allowing the individual to accommodate to the environment. Visual input is. not necessary
for standing, however, because an individual can stand upright with closed eyes (Winter
et al., 1990).

On a stable surface the principal system used for balance is the somatosensory
system, while the visual system is more important on less stable surfaces such. as sand.
When responses from the somatosensory and visual systems are present the vestibular
system plays a minor role, but without somatosensory and visual input it plays critical
role (Shurnway-Cook and Wollacott, 1995).

Humans use several strategies to maintain posture such as: the ankle strategy
(moving the ankles to the side to achieve balance), hip strategy (swaying the hips to the

side or fiont to back to achieve balance) and stepping strategy.

12

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Maintenance of balance depends on the visual, somatosensory, and vestibular
systems, which provide input to inform the CNS about the location of the COM and the
ability to use the appropriate strategy to maintain posture. Strategies used by horses to

maintain balance include weight shift, body sway and limb stepping.
2.2. POSTURAL SWAY ANALYSIS

The early tests of postural sway involved subjective assessments and were not
very sensitive. Romberg developed a test to subjectively assess postural sway in people
(figure 2.1). The subject’s stood with their feet together and arms folded. Breaking stance
in less than a minute defined failure (Romberg, 1851). Mitchell and Lewis (1886)
positioned subjects in front of a grid pattern and observed the amount of sway. Hinsdale
(1887) attached a flat record sheet to a subject’s head and recorded impressions made by
a stationary stylus on the sheet. This procedure offered a graphic record of sway and was
used later by many other investigators. Later in the same year, Hinsdale introduced a
method'of recording the sway in a kymograph through using a stylus attached by a pulley
system to the subject’s head. Moss (1931), used an unstable platform, which moved upon
a central pivot as the subject shifted weight to measure sway. Hellebrandt (1938) used the
same platform to quantify forward and lateral sway. Thomas and Whitney (1959) used a
suspended platform in which horizontal motion was elastically restrained to measure foot
center of pressure location and the horizontal ground reaction forces. Many investigators
tracked head movements photographically (e.g. Goldberg, 1943; Borman and Jalavisto,

1953). More recently force platforms have been accepted as the standard method for

13

 

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and
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collecting postural sway data (Kilbum et al., 1994). A force platform measures the
vertical ground reaction force (GRF) and provides a means of computing the COP by
measuring force at three or more points on the platform or by measuring the torque
around its horizontal axes (Goldie et al., 1989).

In the Romberg test, the standing patient performs tasks of increasing difficulty,
while the tester observes the response to positional stress, displacement or loss of visual
input. This test is usually performed before any kind of balance tests, but today is also

used as a way to measure postural sway with the patient standing on a force platform.

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5 I V‘ H I , =.;,:42<‘ i '.,
I -I \ "a i (\- '\ I;
3 ‘, I '. ‘\ I. ; “‘/
; I )‘l ‘ “ E. ,1. IN,»
\ .' i . ' i
r i . -._,x I * . - .35,
”r. i K \‘i
/ : l
1 2 a!" ’1‘ l- .'
\ .
1‘: ’
i i
i I
r I.
‘v’

Figure 2.1- Foot placements used during the Romberg test.
l-Feet comfortably apart
2-Feet together
3-Feet semi-tandem (heel-to-instep)
4-Feet tandem (heels -to-toe)
During the test the patient performs tasks that include raising the arms, crossing

the arms in front of the chest and behind the back. The same tasks are performed sighted
and blindfolded. There are many variables to be observed during this test, such as:
mediolateral range of COP motion, craniocaudal range of COP motion, mean velocity of

the COP, mean radius of the COP and area and many others.

14

2.2.1. Previous studies in humans

Postural sway has been studied extensively in humans since the seventeenth
century. Postural sway analysis is now used as part of the examination in sports and
orthopedic clinics all over the world. The Romberg test, which was described earlier, is a
subjective test to assess postural sway. This is in contrast to the objective assessment of a
person’s balance using a force platform.

Postural stability is the ability of the balance system to return the body close to its
equilibrium point when exposed to a perturbation. For humans to remain upright it is
crucial to know the position of the different body segments relative to the environment.
During normal standing'the mediolateral (ML) sway is mainly controlled by using a load-
unload strategy. Control of craniocaudal (CC) movement is by a strategy called the ankle
strategy (Horak and Nashner, 1986) that uses the flexor and extensor muscles of the ankle
to change the forces between the foot and the ground. Information about standing balance
in humans has provided insights into basic mechanisms of neurological integration into
biomechanics in health and disease. People affected by neurological diseases employ a
variety of different foot positions to adjust the standing balance, postural sway and mean
position of the COP.

Karlsson (2000) studied the accuracy of using of the force plate to analyse
postural sway and to assess the vertical force that acts during standing. He found that
cardiac activity affects the vertical force component. The beating of the heart perturbs

human standing resulting in vertical body oscillations.

15

Mochizuki et a1. (1999) analyzed the effect of different bases of support in the
analysis of postural sway and concluded that craniocaudal and mediolateral sway can be
independent in case of instability.

Yardley et a1. (1999) determined that postural sway increases when a person
performs a verbal test of mental arithmetic (backward counting). He also verified that this
increase in postural sway is due to demand for attentional resources, perturbation of
posture by articulation, or a combination of both factors.

The orientation of the body or specific body segments with respect to the vertical
axis is controlled both in quadrupeds and in humans. The head, trunk and leg axes are
oriented relative to the vertical axis during stance and locomotion in both species. In
quadrupeds the trunk axis orientation is parallel to the ground, and the position of the
COG with respect to the base of support would not be under direct central control, but is
controlled indirectly by the control of body geometry. The COP during static position
represents the position of the center of mass (Massion et al, 1998).

Le Clair and Riach (1996) studied postural stability during quiet standing to
determine the variability of the COP and influence of time. They proved that time affects
the measurements of postural sway.

The use of a force platform to assess postural sway analysis (posturography)
comes from the clinical assessment of balance using the Romberg test, which was
performed with the patient standing still with the eyes closed and open and seeing how
much sway happens in those two conditions. The basic assumption underlying postural
sway analysis is that COP represents the vertical projection of the COG in the transverse

plane, and the path of the COP about this point is called the sway path. Healthy young

16

subjects and adults have Similar sway but use different strategies to achieve balance
(Panzer et al., 1995).

During normal standing, proprioceptive input fi'om the legs provides the most
sensitive means of perceiving postural sway. Perception of sway comes from signals
related to position, velocity or acceleration and each sensory system provides different
information aboutthese parameters (Fitzpatrick et al., 1994).

Kilburn et. al. (1994) compared postural sway measured simultaneously with a
force platform and a device that registers head (and trunk) movements in a group of
people who worked in a metal casting plant and assessed the effects of trichloroethylene
(TCE) and polychlorinated biphenalys (PCBs) and they found that both tests were
suitable to show that years of exposure to those chemicals cause impaired balance in
people.

J eka and Lackner (1994) proved that contact with external surfaces could modify
proprioceptive inputs to the perception of body orientation. The effect of age, sex, height,
weight, shoe area and grip strength on both measurements were examined. Pe0ple stood
on a force platform with their feet in specified positions and they were instructed to look
at a point in fiont of them. Movements of the COP were recorded a 100 Hz. They found
that the time delays between body sway and fingertip contact forces were much larger
with light touch contact. Their findings suggest that the fingertip is providing information
that allows anticipatory innervation of musculature to reduce body sway.

Experiments in microgravity suggest that there is an internal representation of the

body schema, which is not primarily based on sensory information. It deals with body

17

kinetics and kinematics, body mass, inertia and the orientation of the body with respect to
the vertical (Gurfinkel, 1994).

Even in young healthy subjects, who are trying to stand still, movements of the
COP normally occur and can be followed in a global coordinate system. A plot of the
time varying coordinates of the COP in a horizontal plane is known as a stabilogram. The
majority of investigators tried to analyze the response of the human body to various
external perturbations (Collins and De Luca, 1992).

Macpherson et a1. (1988) studied the effects of initial stance configuration on
automatic postural responses in humans. The subjects were tested in both bipedal and
quadrupedal stance postures. The most significant finding was an asymmetry in the use of
the upper limbs and the lower limbs during postural corrections in quadrupedal stance.
Humans subjects in quadrupedal stance posture used the lower limbs as levers,
protracting or retracting the hips in order to propel the trunk back to its original position
with respect to the hands and feet. Postural responses of the subjects during qudrupedal
stance were remarkably similar to those of cats subjected to similar perturbations of the
supporting surface. Also, the same predominance in lower limb correction is
characteristic for both species.

Kirby et al‘. (1987) collected data with the subjects barefoot, in a quiet room
looking at a point in the distance. Data were collected under different conditions with the
right or left foot in front, with the toes pointing in or out at different angles. The influence
of foot angle and mediolateral and craniocaudal movements were measured for all
conditions. Changes in foot angle resulted in little variation in standing balance except

with the extremes of toeing-in, when the movements of the COP were predominantly to

18

 

the right
and norm
The risk

extreinitj

 

It
to mainte
requires I
remain \t
inflinsica‘
Properly t
in which
maintain

(Fung anc

the right. Disturbances of body balance are common in many diseases, but whether sex
and normal aging have an influence on spontaneous postural sway is still controversial.
The risk of falling is increased not only by cognitive impairment, sedative use and lower

extremity disability, but also by abnormalities of balance and gait.
2. 2. 2. Previous studies in quadrupeds

It is not a simple task, from a physiological point of view, for a terrestrial animal
to maintain posture and orientation through changing terrains. Maintenance of posture
requires not only that the body be supported against gravity, but also that the body’s COG
remain within the limits of support in the horizontal plane. Quadrupeds have an
intrinsically stable musculoskeletal fiamework. Movements of any body segment must be
properly counterbalanced to preserve equilibrium. Stance maintenance is a dynamic task
in which the sensorimotor systems must interact with the external environment, to
maintain stability and proper alignment of the limbs and trunk, and head-neck system.
(Fung and Macpherson, I995).

lnterpaw distance has a significant effect on the forces exerted by the cat during
both quiet stance and perturbation of the support surface, which may have an impact on
trunk stability. It was postulated that with long stance distances, the force constraint
strategy was mechanically useful in preventing bending movements of the spine, whereas
with short stance distances, trunk stability was provided by tonic activation of the epaxial

trunk muscles (Fung and Macpherson, 1995).

19

.m—..

Roberts (1973) performed a behavioral observations in animals, and proposed that
the vestibular and neck reflexes may interact to produce appropriate tonic muscle
activities in the limbs to maintain trunk stability during stance on uneven or inclined
surfaces. These involved either constraining the orientation of the trunk and inclining the
limbs or maintaining a constant vertical alignment of the limbs and changing the
curvature of the spine.

Cats seem to have a very simple strategy to maintain balance in the face of
destabilizing movements of the supporting surface in the horizontal plane. For the hind
limbs a simple choice is made to generate an average horizontal force in one of the
craniocaudal and mediolateral directions. Forelimb participation in the correction of
balance in the horizontal plane was not obligatory (Macpherson, 1988).

The effect of prior experience concerning the direction of postural perturbation on
the balance response of cats to translations of their support surface was studied. It was
determined that the use of the force constraint strategy and the amplitude of the response
were independent of prior experience with direction of translation, as was the amplitude

of the response (Macpherson, 1994).

2. 2.3. Postural sway analvsis in horses
During a clinical neurological examination in horses, several observations and -

manipulative tests of balance are performed. These include head position and

coordination of head movements: normal animals maintain the head in a typical vertical

position and are able to perform certain acts, such as prehension of food. Some

20

neurological diseases, such as vestibular disease, cause changes in head position and
stability (Smith, 1992). Balance is evaluated during the neurological examination by
assessing the horse’s response to manipulations including walking with the head elevated
or pulling the horse’s tail to one side as the horse walks in a straight line. Responses are
assessed subjectively and interpretation depends on the experience of the clinician
(MacKay and Mayhew, ‘ 1991).

- Postural sway analysis is an objective test of a horse’s balance. If performed in a
standard manner, and if normal ranges are determined for postural sway measurements in
horses of different ages and breeds, then it may be possible to quantify disturbances in
balance due to various neurological diseases and different conditions such as use of
sedatives. Furthermore, postural sway may be useful for differentiating neurological
problems from mild lameness and for assessing recovery or response to treatment of
neurological diseases.

Previous studies of postural sway in horses were performed with either the
forelimbs or the hind limbs on the force platform. Since the amount of postural sway
measured is confined within the base of support, the detection of craniocaudal sway is
limited (Clayton et al., 1999). Humans normally show a greater range of postural sway in
the craniocaudal direction than in the mediolateral direction (Jeka et al., 1997). In horses
mediolateral range of motion is influenced by sideways movements of the head and neck,
and a trend toward higher values for mediolateral range in the equine forelimbs than the
hind limbs may reflect the in proximity to the head and neck. When the horses were
blindfolded there was a trend toward smaller mediolateral range of COP motion and

lower mean COP velocity for the forelimbs, possibly indicating that the loss of visual

21

proprioception may increase stability in horses (Bialski et al., 2000). This is contrary to
results in humans (Jeka et al., 1997) and worthy of further study. Head movements can be
regarded as internal perturbations to postural sway, which tend to alter the position of the
COP and require a balance response. In humans, the balance response that produces
postural sway is called an ankle strategy (Jeka et al., 1998) .The mechanics of the equine
response have not been investigated.

Balance is also important during locomotion. According to the Federation
Equestre Internationale (FEI) rules for dressage, the objectives of collection include
development of the horse’s balance and equilibrium, which has been displaced by the
additional weight of the rider (Anon., 1991). Postural stability increases when the horse
has more limbs in the ground at one time because the base of support has a larger area.

In general the average number of limbs supporting the horse during the stride is
inversely related to Speed. At Slower speeds the horse needs to compensate for the loss of
dynamic stability by increasing the number of limbs in contact with the ground (Clayton,

1989).

2.3. EFFECTS OF THE USE OF DRUGS ON POSTURAL SWAY

The use of sedatives might be a solution to facilitate the collection of postural
sway data over longer periods of time in horses. As a prerequisite, the influence of
sedatives on the horse’s balance must be assessed. In human subjects, many investigators
tried to assess postural control in patients with labyrinthine disease who were highly

medicated at the time of data collection. The results indicated that the use of sedatives

22

decreased the craniocaudal range of motion in 80% of patients (Paulus et a1. 1987).
England et al. (1992) tested the effects of different doses of the sedatives used

more frequently by veterinarians for chemical restraint in horses. Detomidine was used at

two dosage rates and within 5 minutes after administration horses showed signs of ataxia.

The head was lowered for 90 minutes at a dose of 10 jig/kg and for longer when a higher

dose of 20 rig/kg was administrated.

Sedation with detomidine was least pronounced and most short-lived at a dose
rate of 10 jig/kg and increased significantly in depth and duration at higher doses, when
the effects could last for more than 4 hours (Hamm et al., 1995)

A study of the effect of detomidine as a pre-anesthetic in a large group of horses
concluded that it is an excellent sedative and analgesic. Side effects such as ataxia,
staggering, sweating and diuresis were not regarded as harmful to the animals
(Szeligowski et al., 1986).

‘A comparison study between romifidine and detomidine determined that
detomidine had a' longer period of ataxia and instability than ronrifidine (Jochle et al.,
1984).

Previous studies using repeated adrrrinistration of detomidine used an interval at
least 72 hours between successive administrations (Muir and Hubbell, 1991 ; Hamm et

aL,1995)

3. METHOD OF INVESTIGATION

3.1. SUBJECTS

Six horses were selected for inclusion in the study, on the basis of being similar in
morphology (Quarter Horse cross) and age (15-21 months old) and having been assessed
clinically to be sound and flee from neurological disease. The horses were weighed and
their height was measured to the highest point of the withers. Shoulder width was
measured as the distance between the greater tubercles on the left and right humeri and
hip width was measured as the distance between the left and right coxal tuberosities’
(Table 3.1).The log sheet used to gather descriptive information for each individual horse

prior to data collection is shown in appendix A.

Table 3.1- Morphological characteristics of horses

 

 

 

 

 

 

 

 

 

 

Horse Weight Height Shoulder Hip width
(#) (kg) (cm) width (cm)
(cm)

210 , 350 150 . 21 51
211 339 146 22 47
212 313 141 20 50
213 359 135 21 48
214 333 142 20 45
215 328 144 23 47
mean 334 141 21 47
SD 16 5 1 2

 

 

 

 

 

 

3.2. DATA COLLECTION PROTOCOL
3.2.1 Force Data

Force data were measured using a force platform (LG6/4/8000, AMTI,

Watertown, Massachusetts) measuring 60 x 120 cm2. Data from the force platform were
collected using a laptop computer (Toshiba Satellite 2535 CD8, New York, NY) and a
12-bit A/D data processor card (DAQ CARDTM—700, National Instruments, Austin, TX).
The horses stood with the four hooves on the force platform and the limbs were oriented
as vertically as feasible when viewed in a frontal plane. A handler stood directly in fi'ont
Of the horse. The lead rope was loose during data collection, without restricting
movements of the head and neck. A helper stood to the side or behind the horse to help
the handler (Figure 3.1). Each recording lasted 10 s with a sampling frequency of 1,000

Hz. Five recordings were made for each horse under each condition.

HELPER POSITION 1
. HANDLER é__ FORCE HELPER POSITION 3
, PLATFORM
HELPER POSITION 2

Figure 3.1. Position of handler and helper relative to the horse and force platform during
data collection. The horse’s head faces toward the handler and the helper stood to one
side or behind the horse during data collection.

25

3.2.2 Kinematic data

Reflective skin markers were placed on the mid dorsal aspect of the hoof, fetlock
and carpus in the forelimbs and hoof, fetlock and tarsus in the hind limbs to measure limb
angles and hoof locations on the force platform. A marker was placed on the head
between the left and right supraorbital forarnina, to measure head height while recording
COP data. On the comers of the force platform four markers were placed, to find the 0,0
location on the force platform (Figure 3.2). To determine the accuracy of the video data, a
triangle calibration with 3 markers placed at known locations was recorded on the force

platform (Figure 3.3).

 

 

 

 

 

 

it c

Figure 3.2. Coordinate system viewed from above, the horse’s head is facing upwards in
the same direction of the big arrow. The Open circle represents the 0, 0 location on the
force platform. The filled circles represents the markers placed on the comers of the force
platform.

 

26

“'9 8'07

 

  

 

 

 

 

C
9

   

 

 

61.3 cm

Figure 3.3. Coordinate system viewed from the side. The filled circles represent the
markers, which were placed in the triangle. The triangle was placed on the middle of the
force platform in an upright position as indicated by the arrow.

During collection of COP data, video recordings were made using two
camcorders (Figure 3.4, 3.5). The camcorders recorded at a sampling frequency of 60 Hz
and were synchronized with each other and with the force data using a numerical counter.
The counter was triggered by the laptop computer, so that it started simultaneously with
the force platform data acquisition. The counter was visible to both camcorders, which
allowed temporal synchronization of the video fiarnes with the force recordings. The
video data were used to measure and correct orientation of the body axes, determined
from the placements of the hooves, relative to the axes of the force platform, and to
account for different limb conformations. The x direction corresponds with the transverse

axis of the force platform and the y direction corresponds with the longitudinal axis of the

force platform.

27

5.38 m
. FORCE
7.35m
5.26 m

 

 

Figure 3.4. Scheme of the data collection. Force data were recorded on a computer
located at the computer station. The 2 camcorders were located at C1, C2.

 

Figure 3.5. Camera and illumination set up for the data collection.

3.3. DRUG ADMINISTRATION

For each horse data were collected under three different conditions, no sedation,
light sedation and. heavy sedation. The order in which the three conditions were recorded
was randomly assigned following a cross over design and an interval of 72 hours elapsed
between data collections in an individual horse. The data collection schedule is shown in
Table 3.2. For the light sedation conditiOn the horses received 10 rig/kg detomidine
(Dormosedan-Pfizer, New York, NY), which is the dose used clinically for light sedation.
For heavy sedation the horses received 20 jig/kg of detomidine (Figure 3.6), which is a
typical pre anesthetic dose. The precise quantity of detomidine or, for the no sedation
condition an equivalent volume of saline sOlution, was administered intravenously (IV) in
the jugular vein (Appendix B). Data collections were made at intervals of 0, 15, 30, 45,

60, 75, 90, 105 and 120 minutes after administration of detomidine or saline solution

29

using a data collection form (Appendix C). During data collection all the reactions of the

horse were recorded in a logbook (Appendix D).

 

Figure 3.6. Saline solution (left) and detomidine (right) administered to the horses.

Table 3.2- Data collection schedule

 

30

3.4. DATA ANALYSIS
3.4.1- F orce data analvsis

The force data for each trial were displayed graphically as a stabilogram, plotting
longitudinal (craniocaudal) position of the COP on the vertical axis against transverse
(mediolateral) position of the COP on the horizontal axis (Figure 3.7). Each data point on
the graph represents a point in time during the 10 s period of data collection, during
which data were recorded at a sampling rate of 1,000 Hz. The centroid of all the points
comprising the stabilogram was located at the point 0,0 on the graph. We determined the
0,0 location of the stabilogram on the force platform, using a calibration fiarne system,
then the area and center of the horse’s base of support were determined using Heron’s
Theorem, which is based on calculation Of the areas of two triangles for which the length

of the sides are known (see section 3.4.2).

31

Mediolateral (cm)

 

 

 

 

 

 

 

0.3
E
a
a
‘5
S
8
O
’E
a
I-
O
-03
03 0.0 ~03

Figure 3.7. Stabilogram showing COP movements in craniocaudal and mediolateral

directions. Each data point on the graph represents the position of the COP at a point in
time during the 10 8 period. The 0,0 location , which is the centroid of all the points, is
located in the intersection of the mediolateral and craniocaudal axes of the stabilogram.

Seven variables were calculated to quantify the movements of the COP:

o mediolateral range of COP motion - the range of motion along the horizontal axis
of the stabilogram, which corresponds with the x axis of the coordinate system
(Figure 3.8). Using a custom software program, the x location for each data point
was determined and the mediolateral range of motion for the entire trial was
calculated from the minimum and maximum x values.

0 craniocaudal range of COP motion - the range of motion along the vertical axis of

the stabilogram, which corresponds with the y axis of the coordinate system

(Figure 3.8). Using a custom software program, the y location for each data point

32

was determined and the craniocaudal range of motion for the entire trial was

calculated from the minimum and maximum y values.

I

 

 

y+

 

 

 

 

Figure 3.8. Coordinate system viewed from above, the horse’s head is facing upwards in
the same direction of the big arrow. The filled circle represents the 0, 0 location on the
force platform. The arrows represents the positive directions of the coordinate system
used to calculate the mediolateral and craniocaudal range of COP motion.

- COP area - area encompassed by the stabilogram. Using a special feature in
Matlab (Matlab 5.3, The Mathworks, Natick, MA) called the Delaunay
triangulation (Figure 3.9), the area of the stabilogram was divided into unique
triangles in which each data point was connected to two other data points in such

a way that there was no overlap between the triangles. The sum of the areas of all

the triangles gave the area encompassed by the stabilogram.

33

 

 

 

 

 

Figure 3.9. Graphic representation of the Delaunay triangulation. Each data point is
connected to two other data points to form a triangle with no overlap between adjacent
triangles.

mean COP radius - the average distance between the centroid of all points on the
stabilogram and each individual data point. Using the custom software the
centroid of all the points comprising the stabilogram was determined as the 0,0
location. The distance from the 0,0 location to each data point on the stabilogram

was measured and the mean value was calculated.

COP velocity - average velocity of the COP between each two successive data
points. The distance between each two successive data points was calculated fiom
the x and y coordinates using Pythagoras theorem. The velocity was calculated

fiom the distance and time.

3.4.2 Kinematic data analysis

The kinematic data were used to check that the limb placements and body orientation
were standardized between trials and between horses. The videotapes were analyzed
using an Ariel Performance Analysis System (APAS, Ariel Dynamics Inc., Trabuco
Canyon, CA). Each video field was grabbed and stored digitally, then the markers on the
horse, corner files and triangle files were manually digitized. The raw data were
transformed using a direct linear transformation technique and smoothed with a fourth
order Butterworth digital filter, with a cut-off frequency of 6 Hz.

The locations of the hooves were determined using custom software (Matlab 5.3, The
Mathworks, Natick, MA). The 0,0 location for the horse and for the force platform were
located, corrected and matched if necessary using the comer files, for both mediolateral
and craniocaudal directions.

The longitudinal axis of the force platform bisects it lengthways and the transverse
axis of the force platform bisects i,t crossways. All horses faced in the same direction
when standing on the force platform. The craniocaudal (y) axis of the horse was defined
as running from the mid point between the two fore hooves to the mid point between the
two hind hooves.The y axis of the horse was approximately aligned with the longitudinal
axis of the force platform and it was positive in the caudal direction of the horse. The
mediolateral (x) axis of the horse was defined as running from the midpoint between the
left fore and hind hooves on one Side to the midpoint between the right fore and hind
hooves on the other side The mediolateral axis of the horse was approximately aligned

with the transverse axis of the force platform, and it was positive to the right of the

35

horse’s body. The locations of the four hooves on the force platform were determined

from the 3D video coordinates of the hoof markers. The accuracy of the video data was

determined using the triangle calibration. (Figure 3.12).

The following kinematic variables were measured:

Hind limb distance - the distance between the hind limbs during data collection
Forelimb distance - the distance between the forelimbs during data collection
Right side distance - the distance between the right fore and right hind limbs of
the horse during data collection

Left side distance - the distance between the left fore and left hind limbs of the
horse during data collection

Right and left limb frontal plane angles — a line connecting the carpal/tarsal and
fetlock markers forms the angle of cannon segment (Figure 3.10). The angle of
this segment is measured relative to a vertical line drawn through the
carpus/tarsus. A positive Sign is assigned when the distal part of the segment

rotates counter clockwise as seen from the front.

:> Carpal marker

   

:> Cannon segment

6 ED Fetlock marker

-'- +

 

 

 

Figure 3.10. Calculation of frontal plane limb angles. The circles represent the markers
placed on the horse limbs. The dashed lines connect the carpus and fetlock in the
forelimbs and tarsus and fetlock in the hind limbs, forming the angle of cannon segment.
The solid lines are drawn through the carpus / tarsus and the angle of cannon segment is
measured relative to this vertical line. Counter clockwise rotation of the distal part of the

cannon segment is positive.

37

0 Height of the head- average height of the head marker above the lefi and right

carpal markers during data collection (Figure 3.1 l).

 

Figure 3.11. Measurements of height of the head. The distance is measured from a
reflective marker on the horse’s forehead (between left and right supraorbital processes)
to the markers on the lefi and right carpi.

0 Transverse orientation angle - the angle between the transverse axis of the force
platform and the mediolateral axis of the horse. A positive angle is assigned if the
rotation of the horse relative to the force platform, viewed from above, occurs in a
counterclockwise direction (Figure 3.12).

0 Longitudinal orientation angle - the angle between the longitudinal axis of the
force platform and the craniocaudal axis of the horse. A positive angle is assigned
if the rotation of the horse relative to force platform, viewed from above, occurs

in a counterclockwise direction (Figure 3.12).

 

  
 
 
     
  

RF
0

Craniocaudal axis
(horse) ->

Mediolateral axis
(horse)
+

 
  
  

Transverse axis
(force platform)

LH

Longitudinal axis
(forge platform)

 

 

Figure 3.12. Alignment of the horse relative to force platform as seem from above. The
longitudinal and transverse force platform axes are shown in solid lines. The filled circles
represent the location of the four hooves on the force platform (LF=lefi forelimb,
RF=right forelimb, RH=right hind limb and LH=1eft hind limb). The dashed lines are the
craniocaudal and mediolateral axes of the horse’s body. The angles measured are the

longitudinal and transverse orientation angles. In this case the angles are positive (counter
clockwise rotation as seen from above).

0 Area of the base of support - the area circumscribed by the four hoof placements
(Figure 3.13).
0 Center of the base of support - the geometric center of the base of support was

located at the point where lines connecting diagonal limb pairs intersected (Figure

3.13).

39

Center of the base
of support

Area of the base
of support

 

Figure 3.13. The filled circles represent the hooves. The shaded area is the area of the
base of support. The open circle is the center of the base of support and it is located at the
point where the lines connecting the diagonal pairs of limbs intersect.

The area of the base of support is calculated as the sum of the areas of two
triangles represented by triangle 1 and triangle 2 (Figure 3.14). The lengths of the sides of

the triangles were measured from the video coordinates of the hoof markers and the areas

of the triangles were calculated using Heron’s Theorem.

 

Area = J perimeter( perimeter — sidel)( perimeter — side2)( perimeter — side3)

 

For triangle 1: Area = Js(s — c)(s —d)(s -e) ,
where c, d, e are the lengths of the sides of the triangle and s is the perimeter of the

triangle, s=c+d+e

 

For triangle 2: Area = Js(s — a)(s - b)(s - c) ,
where a, b, c are the lengths of the sides of the triangle and s is the perimeter of the

triangle, s=a+b+c

 

 

Figure 3.14. Diagramatic representation of Heron’s Theorem. The areas of triangles l and
2 were calculated and the sum of both areas is the area of the base of support. The filled
dots are the hooves.

0 Mean longitudinal and transverse displacement of base of support from COP:
distance between location of the COP derived from force data and the geometric
center of the base of support derived from kinematic data measured in the x and y
directions.

0 Total data collection time: total time taken to collect 5 data trials of 10 s duration

under each condition.

3.5. STATISTICAL ANALYSIS

The data were analyzed using SAS software (SAS institute Inc., Cary, NC). This

study had a cross over design and was a randomized and balanced study. For each
variable, the mean value i SD were calculated on a horse by horse basis, under the three

conditions (no sedation, light sedation and heavy sedation) within the nine different time

41

intervals ranging fi'om 0-120 minutes. The mean values for the individuals were used to
determine the group mean i SD.

Before analyzing the data, the assumption of normality and homogenous
variances through factors were checked using PROC UNIVARIATE and residual plots.

PROC MIXED PROCEDURE was used with repeated statement based on the
covariance structure (compound symmetry). The three sedation conditions were the
factors and the nine time intervals were the levels. The time * treatment interaction was
assessed separately for the nine levels within the three factors. The model included order
as a fixed factor, time, treatment, and treatment versus time interaction as a random
factor, horse. Differences between the levels of the factors were determined by LS
MEANS with post hoc TUKEY-KRAMER adjustments in PROC MIXED procedure for

all statistical tests the level of significance chosen was p<0.05 alpha.

42

4. RESULTS

For each variable, the mean value :1: SD were calculated on a horse by horse basis,
under the three conditions (no sedation, light sedation and heavy sedation) within the nine
different time intervals ranging from 0-120 minutes. The three sedation conditions were
the factors and the nine time intervals were the levels and the time * treatment interaction

was assessed separately for the nine levels within the three factors.

4.1 .POSTURAL SWAY VARIABLES

Examples of stabilograms for horse 213 at times 0, 15, 30 and 120 minutes after
detomidine or placebo administration are shown in figure 4.1. The postural sway
variables were measured from the stabilograms to determine how long it took for the
horse’s balance variables to return to the same value as in the no sedation condition
following the administration of the two doses of detomidine (10 lag/kg for the light
sedation and 20 [lg/kg for the heavy sedation). The results for each variable are shown in
tables and graphs. Confidence intervals (99% CI) for the no sedation condition were used

as a further indicator of whether the values were within the normal range.

NS LS HS

 

 

 

 

 

 

 

o no 2&\ 0 minutes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

20
E ' ’
o ,_ A A 4% 15 minutes
V 0 r I\ V
:3 I
:s -20 I
(U
8 i 20
S
cts o , '1, _§€._ 30 minutes
1
-2o 1
20
0 ,3 120 minutes
-20
-2o 0 2o -20 o 20 -2o 0 20
Mediolateral (cm)

Figure 4.1. Sample of stabilograrns of a single horse, for no sedation (placebo), light
sedation ( l O ug/kg detomidine) and heavy sedation (20 rig/kg detomidine) conditions at
times 0, 15, 30 and 120 respectively.

4.1.1. Mediolateral rgrgge of COP motion

For the overall model, the mediolateral (ML) range of COP motion was smaller under

the no sedation condition than in the light and heavy sedation conditions. Differences

between the time intervals for the overall model are shown in table 4.1. The time“

treatment interaction showed time significant differences between no sedation and light

sedation and no sedation and heavy sedation at time 0 (Figure 4.2).

Table 4.1. Mediolateral range of COP motion (cm) for 6 horses within 3 levels of
sedation at 9 periods of time, ranging from O to 120 minutes after no sedation (placebo)
light sedation (10 ug/kg detomidine) or heavy sedation (20 rig/kg detomidine).

 

 

 

 

 

 

 

 

 

 

Time (min) N o sedation fight sedation Heavy sedation
01 0.78 i- 0.08 ' 2.84 i 0.31 " 2.90 i 0.38 "
152 1.05 i 039 1.19 i- 0.14 1.88 : 0.38
303 0.89 i 0.10 0.70 i 0.06 0.90 i 0.10
453 0.82 i 0.08 0.64 :r 0.06 0.72 .4; 0.09
60‘ 0.74 i 0.09 0.57 i 0.07 0.53 :t 0.04
753 9.72 i: 0.09: 0.89 i 0.11 0.66 i 0.08
903 0.98 i 0.10 0.86 i 0.11 0.74 i- 0.10
1052 1.21 i 0.21 0.94 i 0.13 0.80 i- 0.09
1207 132 i 0.25 0.98 :t 0.11 0.93 i 0.11

 

 

 

 

 

 

*Reading across the treatment rows, values with different superscripts letters are
significantly different within each time period (p<0.05).
*Reading down the time column, time periods with different superscripted numbers are
significantly different for the overall model (p<0.05).

In figure 4.2, the mediolateral range of COP motion at time 0 for the light
sedation condition along with times 0 and 15 for heavy sedation, are outside of the 99%

confidence interval for the no sedation condition.

45

4 -O-No sedation
-I-nght sedation
+Heavy sedation

  
  
  

0)

Distance (cm)
to

d

\ ‘ Arr fir,—
‘3‘? I

 

0
0 153045 60 75. 90 105 120
Time(min)

Figure 4.2. Mediolateral range of COP motion. The 99% CI for the no sedation condition
is delineated by the dashed lines.

4.1.2. Crgniocaudal range of COP motion

For the overall model, the craniocaudal range of COP motion was smaller for the
no sedation than the light and heavy sedation conditions. In addition, there were

significant differences between time intervals for the overall model (Table 4.2, Figure

4.3).

Table 4.2. Craniocaudal range of COP motion (cm) for 6 horses within 3 levels of
sedation at 9 periods of time, ranging from 0 to 120 minutes after no sedation (placebo),
light sedation (10 pig/kg detomidine) or heavy sedation (20 ug/kg detomidine).

 

 

 

 

 

 

 

 

 

 

 

Time(min) No sedation LEM sedation Heavy sedation

. 00' 1.02 i 0.07 ' 2.70 i 0.26 b 2.59 i 0.48 b
152 1.19 i 0.13 ' 1.62 i- 0.12 ' 2.10 a: 0.20 "
302 1.02 i- 0.57 1.42 : 0.12 1.62 a 0.12
453 1.14 i 0.09 ' 1.24 i 0.09 1.05 i 0.07
603 1.09 i 0.09 1.24 i 0.10 1.30 i 0.11
7? 1.30 i 0.12 1.16 i 0.07 1.06 i 0.08
903 1.10 i 0.07 1.22 i 0.06 1.20 i 0.07
1052 1.24 i 0.10 1.41 i 0.11 1.21 i 0.10
1202 130 i 0.14 1.50 i- 0.13 1.43 i 0.08

 

 

 

 

 

*Reading across the treatment rows, values with different superscripts letters are
significantly different for each time period (p<0.05)

*Reading down the time column, time periods with different superscripted numbers are
significantly different for the overall model (p<0.05).

The craniocaudal range of COP motion at time 0 was significantly different
between no sedation and light sedation and between no sedation and heavy sedation
conditions. At time 15 minutes there was no significant difference between no sedation
and light sedation but both were different from the heavy sedation condition (Table 4.2).
Time 0 and 15 minutes for light sedation condition and times 0, 15 and 30 minutes for the

heavy sedation condition are outside of the 99% confidence interval for the no sedation

condition (Figure 4.3).

47

-0-No sedation

 

    

4
+Light sedation
3 +Heavy sedation
E
3
g 2
£3
a \ —' 4 r ‘3 ;_
1 I I I I
o l ‘ .. l
0 15 30 45 60 75 90 105 120
Time (min)

V Figure 4.3. Craniocaudal range of COP motion. The 99% CI for the no sedation condition
is delineated by the dashed lines.

4.1.3. Mgarn COP radius

For the overall model the mean COP radius was smaller under the no sedation
condition than in the light or heavy sedation conditions. After injection of detomidine or

saline solution there were significance differences between time intervals for the overall

model (Table 4.3).

Table 4.3. Mean COP radius (cm) for 6 horses within 3 levels ‘of sedation at 9 periods of
time, ranging from 0 to 120 minutes after no sedation (placebo), light sedation (10 rig/kg
detonridine) or heavy sedation (20 ug/kg detomidine).

 

 

 

 

 

 

 

 

 

 

 

Time (min) No sedation Light sedation Heavy sedation
01 0.28 :r 0.03 ' 0.98 i 0.10 b 1.16 i 0.14 "
152 037 i 0.04 0.48 a 0.04 0.68 i 0.10
30, 031 a. 0.02 037 i 0.03 0.43 i 0.03
453 0.31 i 0.03 032 a 0.02 030 4.- 0.02
603 0.29 a» 0.03 030 i 0.02 * 032 i 0.02
753 034 i 0.04 036 i 0.02 030 i 0.03
903 033 i 0.03 . 036 10.03 034 i 0.02
105’ 0.41 :t 0.04 , 0.40 i 0.03 038 :l: 0.03
1202 039 i- 0.04 0.43: 0.04 0.43 :1: 0.03

 

 

 

 

 

*Reading across the treatment rows, values with different superscripts letters are
significantly different for each time period (p<0.05).
*Reading down the time column, time periods with different superscripted numbers are
significantly different for the overall model (p<0.05).

The mean COP radius at time 0 was significantly different between no sedation
and light sedation condition and no sedation and heavy sedation condition (Table 4.3).

The mean COP radius for the light and heavy sedation condition at time 0 and 15 minutes

were outside of the 99% confidence interval for the no sedation condition (Figure 4.4).

49

2 *No sedation

-I-nght sedation
-t- Heavy sedation

E

8.

a:

g 1

S

.2

D

  
  

\L

0 15. 30 45 60 75 90 . 105 120
Time (min)

Figure 4.4. Mean COP radius. The 99% CI for the no sedation condition is delineated by
the dashed lines.
4.1.4. Areg of the COP

For the overall model, the area of the COP was smaller for the no sedation condition

than for the light or heavy sedation. In addition, there were significant differences

between time intervals for the overall model (Table 4.4).

Table 4.4. Area of the COP (cmz) for 6 horses within 3 levels of sedation at 9 periods of
time, ranging fi‘om 0 to 120 minutes after no sedation (placebo), light sedation (10 rig/kg

detonridine) or heavy sedation (20 rig/kg detomidine).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time (min) No sedation Light sedation Heavy sedation
00I 0.55 i 0.12 ' 5.20 i 0.84 " 8.70 i: 1.94 b
152 0.91 i 0.29 1.35 i 0.21 334 i 0.94
303 0.55 i 0.06 0.62 i 0.07 0.93 i 0.13
45j 0.62 i 0.10 0.48 i- 0.06 0.52 i- 0.11
60‘ 0.53 i 0.10 0.45 i 0.07 0.44 i 0.06
75I 0.56 i 0.09 0.63 i 0.07 0.47 i- 0.09
903 0.70 i 0.12 0.68 i 0.11 0.55 i 0.10
1053 0.97 i- 0.18 0.90 i 0.17 0.60 i 0.08
1205 1.12 :t 031 1.11 i 0.21 0.85 i 0.14

 

 

*Reading across the treatment rows, values with different superscripts letters are
significantly different for each time period (p<0.05).

*Reading down the time column, time periods with different superscripted numbers are
significantly different for the overall model (p<0.05).

  
 

 
 
  

9 -0-No sedation
8 -I-Light sedation
7 +Heavy sedation
A I
NE 6
3
,, 5 ,
g -;
4'5 4 l
E’ 3 t
2 1
O

   

15 30 45 60 75 90 105 120
Time (min)

O

Figure 4.5. Area of the COP. The 99% confidence interval is delineated by the dashed
lines.

51

The area of the COP at time 0 was significantly different between no sedation and
light sedation condition and no sedation and heavy sedation condition (Table 4.3). At
time 0 and 15 nrinutes the values for light and heavy sedation conditions were outside of

the 99% confidence interval for the no sedation condition (Figure 4.4).
4.1.5. Mean COP velocity:

For the overall model the mean COP velocity was slower for the no sedation
condition than the light and heavy sedation conditions, it was also slower under light
sedation than heavy sedation. The differences within the time intervals are shown in table
4.5.

Table 4.5. Mean COP velocity (cm/s) for 6 horses within 3 levels of sedation at 9 periods

of time, ranging from 0 to 120 minutes after no sedation (placebo), light sedation (IO
rig/kg detomidine) or heavy sedation (20 11ng detomidine). .

 

 

 

 

 

 

 

 

 

 

 

Time (min) N o sedation Light Sedation Heavy Sedation
00' 0.89 i 0.04: 1.74 i 0.12” 1.90 i 0.22"
152 0.99 :006 0.92 i 0.04 139 i:- 0.18
303 0.87 i 0.03 0.78 i 0.03 0.94 i 0.07
453 0.87 i 0.04 0.70 :1: 0.02 0.74 i- 0.04
60r 0.83 i 0.04 0.69 i 0.02 0.70 i 0.03
75‘ 0.84 i 0.04 0.70 a 0.03 0.66 i- 0.02
903 0.90 at 0.04 0.72 i 0.03 0.67 i 0.02
1053 1.00 i 0.06 0.89 :t 0.06 0.69 :t 0.02
1202 1.03 i 0.06 1.12 i 0.11 0.78 i 0.04

 

 

 

 

 

*Reading across the treatment rows, values with different superscripts letters are
significantly different for each time period (p<0.05).

*Reading down the time column, time periods with different superscripted numbers are
significantly different for the overall model (p<0.05).

52

 

 

Mean COP velocity at time 0 was significantly different between no sedation and
light and heavy sedation conditions and both sedated conditions are above of the 99%
confidence interval for the no sedation condition. In addition mean COP velocity for the
heavy sedation was outside of the 99 % CI for the no sedation condition at time 15
minutes. The mean COP velocity showed a trend from time 45 to time 90 for the light

sedation and from time 45 to time 105 afier heavy sedation (Figure 4.6).

    

2 . +No sedation
-I-Light sedation
. +Heavy sedation
’5‘
3 I I I I I I I I I I I I I I I I I I I
31
c
a
4.0
.2 I I I I I I I I
a

0:15 30 4560 75 90 105 120
Time(min)

Figure 4.6. Mean COP velocity. The 99% CI for the no sedation condition is delineated
by the dashed lines. .

4.1.6. Data collection time

When the horses were sedated, it was much easier to keep them standing still and
quiet on the force platform (Figure 4.7 and Table 4.6). There were significance
differences between time intervals for the overall model (Table 4.7). Total time taken to
collect data was considerably shorter when the horses were sedated at all times except

120 minutes. The differences were not significant different however due to large standard

deviations.

Table 4.6. Total time for data collection (5) for 6 horses within 3 levels of sedation at 9
periods of time, ranging fiom O to 120 minutes after no sedation (placebo), light sedation

(10 rig/kg detomidine) or heavy sedation (20 [lg/kg detomidine).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time No sedation Light sedation Heavy sedation
001 556 1r 648 325 i 125 390 _+_ 118
151 276 i 305 143 i 99 182 i 83
301 3612*: 140 134 4.- 67 127 i- 98
452 358 i 230 137 i 35 104 i 52
602 352 i 183 164 i- 87 120 i 39
757 415 i 206 185 i 116 202 i 167
902 348 i 147 252 i 138 200 i 82

1057‘ 384 i 248 287 i- 202 167 :1: 106
1203 192 it 120 322 i 320 337 i 248

 

*Reading across the treatment rows, values with different superscripts letters are

significantly different for each time period (p<0.05).

*Reading down the time column, time periods with different superscripted numbers are

significantly different for the overall model (p<0.05).

 

+No sedation +Light sedation +I-ieavy sedation

 

o 15 30 45 60 75 .90 105 120
Time (min)

Figure 4.7. Total time to collect data.
Under the no sedation condition the time taken to collect data was highest at time
0 and then decreased which reflects habituation by the horses. During the period from 15

to 60 minutes after sedation, data collection time was short for both conditions.
4.2.KINBMATIC VARIABLES

The kinematic variables were used to check if the horses were standing in the
same position within and between treatments. The kinematic variables measured were:
height of the head, limb angles, right side distance, left side distance, forelimb distance,
hind limb distance, longitudinal angle, transverse angle, craniocaudal difference,
mediolateral difference and area of the base of support.

The overall distances and angle for the triangle calibration were calculated on

each day of data collection. The average distances and angle for the 9 days were

55

calculated and it showed that the average length error was 1 cm in 61.3 cm for side 1 and
0.57 cm in 40.8 cm for side 2, and 0.6 degrees in the 90 degrees angle in between the two

sides, showing that the video data were accurate and coherent.
4. 2. 1. Height of the head

The height of the head was measured for comparison with the results of previous
physiological studies, in which ataxia and lowering of the head were reported after
administration of detomidine, and also to assess the effects of the height of the head on
the horse’s balance

For the overall model, the head was significantly higher in the no sedation than in
the light and heavy sedation conditions and there were significant differences between
time intervals. Differences between conditions persisted until time 90 minutes after

detomidine administration (Table 4.7).

Table 4.7. Height of the head (cm) for 6 horses within 3 levels of sedation at 9 periods of
time, ranging from 0 to 120 minutes after no sedation (placebo), light sedation (10 rig/kg

detomidine) or heavy sedation (20 rig/kg detomidine).

 

 

 

 

 

 

 

 

 

 

Time(min) No sedation Lijht Sedation Heavy Sedation

001 129.1 : 2.5‘ 84.6 : 3.8 " 86.07 : 2.9 "
151 129.4 : 1.7 ' 79.9 : 3.2 " 80.03 : 2.5 "
302 134.0 : 1.7 ‘ 91.5 : 43 " 81.29 : 2.9 b
453 129.3 : 1.9 ‘ 96.3 : 4.0 " 92.89: 3.2 b

60‘ 130.9 : 2.5 ‘ 104.3 : 3.8 " 9638: 3.5 b

755 136.5: 2.6 ' 117.1 : 3.0 ' 110.12 : 3.1 "
90‘ 136.6 : 1.9 ‘ 126.0 : 2.8 ' 110.49: 3.0 "
105‘ 133.1 : 2.5 130.2 : 23 119.80 : 2.7
1202 137.2 : 2.4 133.4 : 2.2 123.21 : 3.2

 

 

 

 

 

 

*Reading across the treatment rows, values with different superscripts letters are
significantly different for each time period (p<0.05).

*Reading down the time column, time periods with different superscripted numbers are
significantly different for the overall model (p<0.05).

Immediately after administration of detomidine the head was lowered by 40-50
cm. After light sedation, the head height increased gradually from 30 minutes, returning
to the no sedation height by 75 minutes. After heavy sedation, the horses did not begin
raising their heads until 45 minutes after sedation, returning to normal at time 105
minutes. The head was below the lower limit of the 99 % CI for the no sedation condition

through out the period of the study for the heavy sedation and until 90 minutes after

administration of detomidine for the light sedation condition (Figure 4.8).

57

 

Distance (cm)

1 4O
60
40
20 No sedation -I-Light sedation +Heavy sedation
0
0 1 5 30 45 60 75 90 1 05 1 20

Time (min)

Figure 4.8. Height of the head. The 99% CI for the no sedation condition is delineated by
the dashed lines. '

4. 2. 2. Spatial kinematic variables

The distances between the forelimbs and hind limbs and area of the base of
support did not change in response to light or heavy sedation. The area of the base of
support showed a small but insignificant change after 45 rrrinutes. Generally between the
time 45 and time 60 minutes the horses were moved off of the force platform to urinate.
When the horses returned to the force platform, they were encouraged to stand in the
same position as they were before being moved. However, they tended to use a smaller
base of support after being moved. There were no significant differences between times
in the limb angles, limb distances, longitudinal or transverse angles and mediolateral or
craniocaudal range of COP motion relative to center of the base of support (Table 4.8).

The fact that the linear variables were not significantly different after sedation in

this group of normal horses showed that the horses were standing with their limbs in the

58

same position during the different data collections. Therefore, stance did not affect the
postural sway measurements. The fact that the area of the base of support and the angular
variables did not differ significantly between treatments showed that this study did not
introduce systematic errors by having horses standing in a particular way during data
collection. The order in which. the sedation conditions were evaluated had no influence on

the postural sway' measurements.

59

 

Table 4.8. Mean i SD for 6 horses within 3 levels of sedation at 9 periods of time,
ranging from 0 to 120 minutes after no sedation (placebo), light sedation (10 rig/kg
detomidine) or heavy sedation (20 rig/kg detonridine).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

No sedation Light sedation Heavy sedation
Mediolateral
difference (cm) 1.00 i 0.10 0.58 i' 0.07 1.30 i- 0.11
Craniocaudal
difference (cm) -4.39 i- 0.28 -5.03 i- 0.17 -4.80 i 0.06
Area of the base
of support (cm’) 2281.4 : 17.0 2204.5 : 12.4 2391.6 : 13.4
Longitudinal 7
angli(degrees) -0.54 i- 0.11 0.53 :t 0.13 0.25 i 0.08
Transverse
angle (degges) -0.95 i- 0.20 -0.03 i 0.13 -0.90 i 0.25
Right fore
aggge (degrees) -1.03 i 0.09 -1.26 i 0.06 -l.73 i 0.12
Left fore
angle (degrees) 3.23 :1: 0.16 2.97 i 0.10 3.16 i 0.11
Right hind
angle ((1ng) -1.02 i 0.09 -1.22 i 0.18 -l.12 i 0.16
Left hind
angleflegrees) 0.86 i 0.09 1.50 i 0.10 1.70 i 0.19
Forelimb
distance gm) 24.4 i 0.2 24.6 i 0.2 26.7 i 0.1
Hind limb
distance (cm) 27.7 10.2 27.7 i 0.2 27.9 i- 0.2
Right side
distance (cm) 88.2 i 0.3 85.4 i 0.4 88.7 i 2.5
Left side
distance (cm) 88.1 $0.3 85.2 i 0.3 88.0 i 0.2

 

 

 

 

*No significant difference between conditions.

 

- 4.3.0BSERVATIONS

A degree of penile prolapse was first noted 5 to 30 minutes after of the injection
of detomidine in both rates. Sweating was noted in all horses, which varied from a damp
coat to profuse sweating. Urination was noted with equal frequency in all the horses
usually occuning 45-60 minutes after drug administration. Trembling, locking and
unlocking joints, shifting weight and obvious swaying were consistently noted in all
horses during the first 10 to 15 minutes after the administration of the drug in both levels
of sedation. ’

The grade of sedation assessed for each horse at each time for each condition are

shown in appendix E.

61

S-DISCUSSION

Balance is considered to be important in athletic horses in which a high level of
motor coordination is required. Some horses are naturally better balanced than others,
though the trainer assesses this subjectively. Horses, just like in humans are stronger on
one side the other, which is called by trainers the “stiff” and the “hollow” sides. The left
side is usually the “stiff” side, due to the fact that in the beginning of the training, the
majority of young horses prefer to travel crooked with their left hind limb tracking
toward the midline of the body. Later in training and also while performing movements
that require strength and balance, such as piaffe; they prefer to use the left hind limb for
support.

Certain diseases are associated with loss of coordination and balance and
veterinarians use a number of tests to assess a horse’s balance clinically. These include
proprioception tests, complementary and observation tests, the interpretation of which
relies on the experience of the clinician. Disturbances of balance accompany many
neurological diseases in horses, such as equine protozoa] myeloencephalitis, equine
degenerative myeloencephalopathy, vestibular disease and cervical vertebral
malfonnation-malarticulation, commonly known as “wobblers” (MacKay and Mayhew,
1991). Advanced neurological diseases with profound loss of balance are easy to detect,
but the subtle signs are more difficult to assess.

During a neurological examination several tests of balance are performed that

involve the head and cranial nerves, palpation and observation of movement of the neck,

62

forelimbs, back, hind limbs and anus (MacKay and Mayhew 1991). Questions are asked
about the horse’s behavior and recent changes in behavior or mental status (patient’s state
of awareness or consciousness is verified). Examination of the head includes palpation of
the forarnina, detection of edema or swelling, evaluation of head posture and
coordination. Normal animals maintain the head in a certain posture and are able to
perform certain acts, such as prehension of food. Some neurological diseases (e. g. EPM)
can cause changes in this posture and incapacity to perform normal functions, other
diseases (e. g. bilateral vestibular disease) can cause continuous movements of the head or
incapacity to keep the head in a normal position. Each of the twelve pairs of cranial
nerves has its own function, and these functions are tested fiorn the most rostral . nerves
proceeding caudally. Abnormalities discovered during examination of the ftmction of the
cranial nerves are most helpful in diagnosing brainstem lesions. Gait and posture are
evaluated for the presence .of weakness, ataxia, hypometria or hypermetria. All of these
tests are assessed subjectively.

Postural sway analysis is an objective test of a horse’s balance that may prove
useful in detection of disturbances in balance due to neurological diseases, in
differentiating neurological problems from mild lameness, and in assessing balance
changes in horses after the administration of a specific drug.

Due to morphological differences between species it is difficult to compare
postural sway variables recorded in horses with those recorded in people. In humans the
trunk acts as a platform that supports the vestibular and visual receptors. The postural
reflexes attempt to maintain the orientation of the head in relation to the environment

(Buchanan and Horak, 1999). Humans are bipeds with about 2/3 of their mass located 2/3

of body height from the ground (Winter et al., 1990). In horses the visual and vestibular
organs in the head are located at a considerable distance in front of the trunk, rather than
immediately above it. The entire head and neck, which account for 14% of the total body
weight are used to maintain and change a horse’s balance: movements to the side shift the
COM to that side, stretching forward shifts the COM towards the forelimbs, retraction
shifts the COM towards the hind limbs and lowering results in a slight lowering of the
COM. Lowering the head and neck does not change the COP location in a horizontal
plane unless it is accompanied by a forward shift in the COM of the head and neck.

Horses are quadrupeds, but the ability to measure postural sway with all four
hooves on the force platform simultaneously depends on having a large force platform.
Previous studies of postural sway have focused on people and cats, both of which have a
much smaller base of support and therefore require a much smaller force platform than
horses. In these species a considerable body of literature is available. Horses do not
appear to have been studied previously, except for the pilot studies in our laboratory. This
is probably due to the need for a large force platform to accommodate the large base of
support of a horse, which is not available in other laboratories.

The force platform used in this study measm'ed 60 x 120 cm2, which proved
adequate for collecting data with all four hooves placed on the force platform
comfortably for this group of horses that ranged in height from 135 cm to 150 cm and
ranged in weight fiom 313 kg to 350 kg. In these relatively small horses, the average limb
separations on the right side (87.44 cm) and left side (87.13 cm), and the distances
between the forelimbs (25.20 cm) and hind limbs (27.76 cm) were easily accommodated

by the dimensions of the force platform. In larger horses it might be possible to measure

postural sway separately for forelimbs and hind limbs, but the accmacy and reliability of
these data have not been evaluated and compared with those from horses standing with
all four hooves on the force platform.

Mean COP velocity and craniocaudal range of COP motion showed less
variability than the other postural sway variables, indicating that these might be the
variables of choice to assess postural sway in a clinical setting. However, craniocaudal
range of COP motion took longer to return to non-sedated levels making it less suitable
for assessing horse’s balance after detomidine administration.

Barbelini and Macpherson (1998) studied the kinematic and kinetic responses to
different head positions in cats: neutral position, head up, head down, head left, head
right. Large changes in head orientation were associated with changes in forelimb
kinematics and static joint torques, especially at the shoulder and elbow joints. Hind limb
kinematics did not change, and head position had no consistent effect on static ground
reaction forces or COP, indicating that the stance and balance were maintained with
different head positions. The dynamic postural response to translation of the surface
showed movement of the COM in the direction opposite to that of translation. When the
postural response was evoked, the COM trajectory slowed and reversed its direction.
Neither the distance or the direction of trajectory (spatial) nor the response time
(temporal) were affected by head position. The main change was observed in joint
torques at the forelimbs evoked by perturbation. Electromyography showed changes in
the amplitude of the evoked response of muscles in the proximal forelimb and cranial
trunk, but not in their temporal or spatial response. Information regarding the location of

the head in space is provided by vestibular proprioceptors and information about the

65

position of the head and neck relative to the trunk is provided by neck proprioceptors.
Vestibular and neck proprioceoptors interact closely to provide an important reference
signal for postural equilibrium (Barbelini and Macpherson, 1998).

Standing cats do not show changes in COP response to change in head and neck
position, which reflects the fact that cats compensate easily by adjusting the forces
exerted by the limbs. In horses even after sedation with detomidine the lowering of the
head and neck did not appear to be responsible for changes in postural sway variables,
since these variables returned to the resting values before the head was raised to its
normal level.

People can use light contact of their fingers with a stationary object to improve
their balance, but horses and other quadrupeds do not have this option since they already
have the four hooves in contact with the ground. Horses are not thought to use tactile
receptors on the side of the head for balance due. to the fact that this area does not have a
particularly good supply of proprioceptive receptors (De Lahunta, 1983). Therefore, it
seems unlikely that gentle restraint applied to the side of the halter would change postural
sway patterns to any great extent. Even so, there is a possibility that horses may derive
support from a person holding the halter, especially when sedated, therefore the horse’s
head movements were not restrained during this study.

There are major differences in the area and shape of the base of support between
horses and humans, which partially explain the different strategies used to maintain
balance in the two species. In people the craniocaudal base of support is determined by
the length of the feet and the mediolateral dimension is determined by the separation of

the feet. In standard tests of postural sway in people, several foot placements are used:

66

the feet are placed together, one foot in front of the other, toe in, toe out or 15 to 45 cm
apart depending of the size of the force platform. In horses we do not have the option of
using different stance positions. Instead the goal is to standardize the standing position
according to each horse’s conformation by having the horses stand straight and square on
the force platform, to facilitate comparison between different evaluations. The kinematic
variables were used to check consistency of limb placements and the fact that there were
no significant differences between conditions confirms that this was achieved. In human
subjects it has been shown that the foot position significantly affects the mean position of
the center of pressure and postural sway (Kirby et. al., 1987). The area of the base of
support depends on the type of positioning adopted, but the base of support is wider
mediolaterally than craniocaudally, which gives greater stability fi'om side to side than
from fi'ont to back. This is in contrast to the situation in quadrupeds in which the
craniocaudal dimension (between the forelimbs and hind limbs) exceeds the mediolateral
dimension (between the left and right limbs). This gives the animal greater stability fi'om
head to tails than from side to side. In this study the mean length of the base of support
was 75 cm craniocaudally and 23 cm mediolaterally suggesting much greater stability in
the head to tail direction. It might have been expected that the horses would use a wider
base of support to keep their balance when sedated, but this was not the case: the
dimension and area of the base of support were not significantly different after sedation.
If the amount of sway is expressed as the percentage of the length of the base of
support then horses have relatively less sway craniocaudally than mediolaterally. This is
contrast to the situation in humans who have relatively more sway mediolaterally than

craniocaudally. These findings support the suggestion that stability is directly related to

67

the size of the base of support rather than to the absolute amount of sway (Goldie et al.,
1989).

Trunk orientation is maintained above the base of support using proprioceptive
receptors in the trunk. These receptors are located in the muscles of the vertebral column
as well as the joint receptors (De Lahunta, 1983). They detect the forces acting on the
trunk including compressive and gravitational forces. This information is used to
maintain the spatial orientation of the trunk and to keep appropriate intralimb geometry
of the four limbs. The most important considerations are to maintain the trunk height and
orientation relative to the support surface (Macpherson et al., 1995). For example, cats
have an optimal stance distance, and an optimal postural orientation that are related to
energetics and morphometrics, such as length of the torso and limb segments. During
galloping, cats maintain a constant trunk orientation by changing the linib orientation
(Macpherson et al., 1995).

The distance between the limbs has a great effect on the mechanics of quiet stance
and on the dynamic reaction to translation of the support surface (Macpherson et al.,
1994). Remarkable differences were observed when cats were positioned with their limbs
separated by long and short distances. At long distances each limb exerted a force
outward along the diagonals during quiet stance. At short distances, the force vectors
during quiet stance had a more convergent orientation in the craniocaudal direction.

One of the prerequisites in our protocol for the collection of equine postural sway
data was that the horses must be standing still and square on the force platform to avoid
changes in balance associated with different postures. During the data collection the

posture and placement of the horse on the force platform was always carefully observed

and corrected with the hoof placement and limb angles being aligned visually. This
method of placement appeared to be adequate based on the kinematic variables that were
recorded to check the consistency of the horse’s stance between different recordings.
There were no significant differences between the data recording sessions in craniocaudal
distance between the fore and hind limbs, the mediolateral distance between the right or
left limbs, the angles of the four limbs or in the longitudinal or transverse angle in
relation to the force platform. This consistency in limb kinematics removes a potential
source of error in the postural sway data. These findings suggest that in future studies, if
horses are placed carefully on the force platform; it should not be necessary to measure
limb kinematics. Since this is a time-consuming part of the procedure, its omission will
greatly facilitate the use of postural sway in horses in a clinical setting.

This study showed the feasibility of measuring postural sway in normal horses
under non sedated and sedated conditions. In this first study of the effects of sedation on
postural sway, we chose to use the sedative detomidine. This is a potent, non-narcotic
tranquilizer/analgesic that is used frequently in horses. Chemically detomidine is an
irrridazole hydrochloride. Alpha; receptors exist pre-synaptically and post-synaptically in
both the central nervous system and in the peripheral nervous system. Stimulation of the
central pre-synaptic alpha; adrenergic receptors inhibits the release of noradrenalin,
leading to a decrease in cortical neuron activity, which results in sedation (Jochle, 1984).
The physiological effect of detomidine on horses has been studied quite extensively
(Jochle, 1984; England, et.al., 1992, Short et al., 1986; Hamm et al., 1995 and Jiichle and
Hamm, 1986). It has been shown to be a safe pre-anesthetic medication for horses (Short

et al., 1986), but an interval of at least 30 minutes should elapse after adrrrinistration,

69

before proceeding with induction of anesthesia, to allow stabilization of the
cardiovascular parameters and reduce the risk of injuries during intubation.

In a study comparing various sedatives for horses, detomidine was used at doses
of 10, 20, 40 and 80 jig/kg (England et. al., 1992). Detomidine administration was
associated with a considerable degree of ataxia the duration of which was dose
dependent. Ataxia lasted for approximately 15 minutes at the lowest dosage rate
increasing to one hour at the highest dosage rate. The response to stimuli was slower
within 5 to 10 minutes of detomidine administration at all doses. The heart rate decreased
rapidly and was significantly depressed within 1 minute after administration and did not
start to increase until 90 minutes later. Horses that received 10 rig/kg of detomidine,
recovered rapidly and by 90 minutes were considered normal, whereas at the highest
doses it took 160 minutes for horses to return to the normal parameters (England et. al.,
1992).

Similarly, Hamm et a1. (1995) studied the effects of detomidine at several dosages
at time intervals of 15 minutes until 165 minutes after the administration of the drug.
Horses receiving detomidine at a dose of 10 rig/kg showed less ataxia than those
receiving 20 jig/kg, with instability being short lived and lasting 30 to 45 minutes. The
physiological effects of sedation with detomidine at doses ranging from 20 to 80 jig/kg
persisted for 4 hours (Jéchle and Hamm, 1986).

To facilitate comparison between the effects of detomidine on the horse’s balance
with previous physiological studies, the same post-administration sampling frequency
was used in this study as those described above (England et al., 1992, Hamm, et al.,

1995). Postural sway can be used to quantify ataxia after the administration of medication

70

and the results confirm that ataxia persists for longer periods under heavy sedation.

The results of this study showed that instability was relatively short lived after
detomidine administration. For the light sedation condition the COP variables were
within the 99 % CI for the no sedation condition values by 15 minutes after
administration of detomidine. For the heavy sedation condition the COP variables
returned to within the 99 % CI of the no sedation condition by 30 minutes after
administration of detomidine, with exception of the craniocaudal range of COP motion,
which returned to the same rate as the no sedation after 45 minutes for both light and
heavy sedation. The time required for the postural sway variables to return to the non-
sedated values correlates quite well with the subjective assessment of the duration of
ataxia (J6chle, 1984; England, et.al., 1992, Short et al., 1986; Hamm et al., 1995 and
Jiichle and Hamm, 1986). This study assessed balance dming stance but did not assess
the effects of sedation on the horse’s balance druing locomotion. Normal gait involves
spinal reflexes that may respond differently to sedation than the postural reflexes used
during stance. Therefore it cannot be assumed that normal locomotor patterns are restored
at the same time as normal balance patterns.

Some of the postural sway variables had large standard deviations, which made it
difficult to detect significant differences between conditions in the ANOVA tests. The
use of confidence intervals assisted in indicating when the variables were within the
range recorded for the non-sedated condition. If postural sway analysis is used clinically
to detect abnormal sway patterns in horses with neurological disease, then a range of
“normal” values must be established for comparison. The confidence interval is a suitable

range for this purpose.

71

 

Several studies have shown that detonridine is an excellent drug to be used
routinely in clinics and hospitals under controlled doses and appropriate handling for
sedation in horses (Jéchle, 1984; England, et.al., 1992, Short et al., 1986; Hamm et al.,
1995 and Jiichle and Hamm, 1986). Sedatives and tranquilizers are sometimes used to
facilitate minor procedures that are stressful to some horses, such as: trailering, clipping
and shoeing horses. The results presented have suggested that detomidine is not the best
choice of sedative for clipping due to the constant sweating. It is important to allow
sufficient time for stabilization before proceeding with activities that require the horse to
maintain its balance, such as trailering and shoeing. However, it should not be assumed
that these manipulations are risk-free for the handler. Horses sedated with detomidine
have been reported to show sudden and unpredictable movements, such as kicking, in
response to handling (Jéchle, 1984).

The original motivation for performing this study was to seek a method of
facilitating data collection for postural sway analysis in horses by reducing the time taken
to collect data in horses that were reluctant to stand still on the force platform for long
enough to collect representative data. In humans, data. are normally collected for 30
seconds. A long period of data collection is necessary for statistical analysis using
fractional Brownian motion. The general driving principle of this method of statistical
mechanics is that although the outcome of an individual random event is unpredictable, it
is still possible to obtain definite expressions of the probabilities of various aspects of
stochastic process or mechanism (Collins and De Luca, 1993). People can be instructed
to stand in a required position for a given length of time, making it easy to collect

postural sway data for prolonged periods.

72

Pilot studies in horses indicated that it was not realistic to expect horses to stand
motionless for 30 s and 10 s was more feasible. Therefore, equine studies of postural
sway have used five repetitions, each for 10 5 recording interval. It usually required
several minutes in a quiet environment to collect data and the first data collection, which
is the one used in a clinical evaluation, usually requires more time than subsequent data
collections due to the novelty of the situation for the horses. This effect is clearly obvious
in the time required for data collection in the no sedation condition: the first recording
required the longest time. The presence of distractions (flies, other horses, etc) cause
further increases in the time required to collect data. With the aid of sedation it might be
possible to collect data for an extended (30 s) period of time even in horses that are
normally reluctant to stand still. This would allow the use of the more sophisticated
statistical methods designed by Collins and De Luca (1993). However, the effects of
sedation on postural sway variables in normal horses and in horses with neurological
diseases needs to be quantified before using sedation to facilitate data collection. This
study has shown that sedation with 10 jig/kg of detomidine reduces the time required for
data collection by . about two thirds, with representative postural sway values being
recorded by 30 minutes after administration in normal horses except for the craniocaudal
range of COP motion.

Thus, for horses that are reluctant to stand still on the force platform during data
collection, it may be useful to administer detomidine (10 rig/kg) and then wait 30-45
minutes before collecting data In the long term, this may save time, effort and frustration

in the process of data collection. However, this study used normal horses that were

73

assessed to be free of neurological diseases. If sedation is to be used to facilitate postural
sway analysis as a diagnostic tool in horses with neurological diseases, it will be
necessary to evaluate the effects of sedation on postural sway in horses with neurological

diseases.

74

6- CONCLUSIONS

The postural sway variables for normal horses have been quantified. COP velocity
and craniocaudal range of COP motion have relatively low variability, which suggests
they may be suitable for detecting abnormal sway patterns in horses with neurological
diseases.

If horses are positioned on the force platform carefully in a standardized position, it is
not necessary to measure kinematic variables.

Lowering of the head when the horses were sedated did not change the location of the
COP in relation to the location of the center of the base of support.

Detonridine affects postural sway measurements with mediolateral range of COP
motion, mean COP radius, COP area and mean COP velocity returning to the non
sedated values within 15 minutes after administration of 10 jig/kg of detomidine and
within 30 minutes after administration of 20 jig/kg of detomidine. Craniocaudal range
of COP motion takes longer to return to the non sedated values: 45 minutes after
administration of 10 rig/kg of detomidine and 60 minutes after administration of 10
jig/kg of detomidine.

This study confirmed that detomidine can be used to facilitate collection of postural
sway data, but data collection should not be commenced until 30 to 45 minutes
following administration at which time most of the postural sway variables have

stabilized.

75

6.1. Future applications

If postural sway analysis is performed in a standard manner, and normal ranges are
determined for postural sway measurements in horses of different ages and breeds,
then it may be possible to quantify disturbances in balance due to various
neurological diseases. Furthermore, postural sway may be usefirl for differentiating
neurological problems from mild lameness and assessing recovery from neurological
diseases or response to treatment of such diseases

Detomidine can be used safely to sedate horses for trailering or shoeing but it is not
recommended for clipping because sweating was noted in all the horses ranging from
a damp coat to a profuse sweating. An interval of 30 minutes should elapse before
performing procedures that require good balance

In the fixture, it would be useful to combine postural sway analysis with
electromyography to determine which muscles are firing to maintain the horse’s

balance.

76

APAS

C1

C2

CC

CI

cm

CNS

COG

COM

COP

EMG

FEI

GRF

HEAD MOV.

IV
kg
LEAFORW
LEANBACK
ML

NSAID

7. GLOSSARY

Number

Ariel Performance Analysis System
Camera 1

Camera 2

Craniocaudal range of motion
Confidence interval

centimeters

Central nervous system

Center of gravity

Center of mass

Center of pressure
Electromyography

Federation Equestre Internationale
Ground reaction forces

Head movements

Intravenous

kilogram

Leaning forwards

Leaning backwards

Mediolateral range of motion

Nonesteroidal anti-inflammatory drugs

77

PCBs
SD .
SHAK
SHIFT
TCE
TREM

UNLO

Polychlorinated biphenalys
Standard deviation
Shaking

Shifting weight

' Trichloroethylene

Tremors

Unlocking joints

78

8. APPENDIX A

A. 1 . Information log sheet, which that was completed for each horse prior to data
collection

Date:
1

. Personnel:

 

Owner’s name:

 

l
l
i

1 Animal name:

 

 

Description:

; Age:

 

 

E Weight:
E

 

Height:
1
1 Breed:

l

 

' Utility:

1

j Horse MEPC ID:

 

 

 

E VTH ID:

1 Shoulder width:
1
E Hip width:

 

 

l
l
1

Comments or requests:

 

 

 

 

 

79

9. APPENDIX B

8.1. Volume of detomidine or saline solution injected intravenous into each individual
horse for the no sedation (placebo), light sedation (lO pig/kg detonridine) or heavy
sedation (20 rig/kg detonridine) conditions.

 

Horse placebo 10 ugkg 20 jig/kg
210 0.35 ml 0.35 ml 0.70 ml

21 l 0.68 ml 0.34 ml 0.68 ml
212 0.62 ml 0.31 ml 0.62 ml
213 0.72 ml 0.36 ml 0.72 ml
214 0.33 ml 0.33 ml 0.66 ml
215 0.66 ml 0.33 ml 0.66 ml

 

 

 

 

 

 

 

 

 

 

 

 

10. APPENDIX C

C. l . Log used to record trials and different behaviors or reactions during data collection.

 

 

DATE: NAME:
SEDATED NON SEDATED

TIME 0 15 30 45

DOSE long/kg

BASELINE

' Information

HORSE MEPC ID:
PRE-ANESTHETIC TOTAL TIME
60 75 90 120
long/kg

Heart rate . (25-50)

 

” Rctioeans

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/ '

Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

' Tre/Shak/Shift/Unlo/

Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

Tre/Shak/Shifthnlo/
Leaforw/Leanback

 

Tre/Shak/Shift/Unlo/
Leaforw/Leanback

 

 

 

 

81

 

 

11. APPENDIX D

D. 1. Parameters used to assess the level of sedation during the data collection.

— ATAXIA

   

  
   

0 no change

 

l a little sway

2 swaying and leaning

3 swaying and leaning or unlocking for a better
10 0 SitiOn

— HEIGHT or THE HET if I

0 head are same posron 3

l muzzle going down i

2 muzzle below the levelof the carmrs
16 levl

0 no response to stimuli
E lslow response to stimuli
E 2‘ medium response to stimuli
3 raid rest-rise stimuli

 
 

 

 
      

          
   
 

 

   

   

  
    

     
   

   
  
   

D.2. Classification of the grade of sedation based on the parameters fi'om table D. l .

Classification
Etax ia 2- 3
Heavily sedated eight of the head 2- 3
timuli 0-1
taxE ia 2
Deeply sedated eight of the head 1-2
timuli 1
taxra 1-2

Moderate sedated Eeight of the head 1-2
uli 1-2

 

taxia 0-1
Lightly sedated eight of the head 0-1

 

 

 

82

12. APPENDIX E

E. 1. Grade of sedation at the 9 time intervals under the three conditions for horse 210.

 

 

 

 

 

 

 

 

Horse 210 No sedation Light sedation '(10 Heavy sedation (20
(placebo) detomidine detorrridine

0 5 5 5

15 5 3 2

30 5 l 1
45 5 2 l

60 5 2 1

75 5 3 l

90 5 4 4
105 5 4 4
120 5 5 4

 

 

 

E.2. Grade of sedation at the 9 time intervals under the three conditions for horse 211.

l 3‘ H211 Light sedatio(10 , Heavy sedation (20
E (placebo) ; ; detomidine . ; . ; detomidine
0 5 A 5 5

15

 

 
  

 

 

 

 

 

 

 

 

UIMMMMMUIM

 

 

 

th-bbJNh—I-Iwb)

    

E.3. Grade of Eedation at the 9 time intervals under the three conditions for horse 212.

Horse 212 No 0 Heavy (20

 

E.4. Grade of sedation at the 9 time intervals 'under the three conditions for horse 213.

Horse 213 No sedation Light sedation (10 Heavy sedation (20

5
5
5
5
5
5
5

AAh-v—-r—-Nui

Ur

 

E.5. Grade of sedation at the 9 time intervals under the three conditions for horse 214.

if * Horse214 _Lghitsedatlon(10 _ Heavy sedation
i (placebo) 5 ; . ; detomidine ; . ; detomidine
j 0 5 5 5

15

 

 

  
  

    
 

 

 

 

 

 

 

 

 

 

    

‘ M M M {II LII {It M M
LII A u U) N N F" U)

 

 

 

 

 

 

 

 

 

 

 

 

MMMMMMMM
lM-hAWNNNU)
AAA—HHNN

 

85

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