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    Radiographic anatomy of the equine lung : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science, Massey University
    (Massey University, 1982) Sanderson, Garry Neil
    This research project was instigated in an attempt to provide information on the radiographic anatomy of equine thorax which would enable specific interpretative criteria to be developed in the diagnosis of equine pulmonary conditions. In order to accurately characterise the structures in the thorax a number of existing investigative techniques had to be modified for use in equine subjects. In the absence of an existing method at the time, a simple method of performing bronchograms on standing conscious horses was developed. The technique involved insufflation of 100 - 200gms of finely powdered Barium Sulphate mixed with 3-7gms of powdered methyl cellulose from an ether vapouriser connected to an intra tracheal tube and supplied with compressed air from a gas cylinder. Good visualisation of bronchial branches down to the seventh and eighth generations were obtained in all but the most dorsal bronchial branches. Elimination of residual contrast agent was rapid and inflammatory response determined by serial histological studies was minimal. Attempts at pulmonary arterial angiography in the standing horse were abandoned owing to adverse patient reaction in favour of similar technique in anaesthetised animals, however as a resultof difficulties encountered with this technique only a small series of angiograms was performed with mixed results. Fume fixation of the equine lung was performed utilising the hot formalin vapour technique of Wright et.al.,(1974) resulting in the successful production of several sets of "phantom" lungs on which extensive radiological and gross anatomical studies were performed in an attempt to relate the "in vitro" appearances with those of plain radiographs of the thorax of standing horses. Careful examination of the resultant radiographs and correlation of differing appearances provided by the contrast techniques demonstrated a number of important diagnostic points. On the plain radiograph a greater number of generations of pulmonary arteries, veins and bronchi can be accurately identified in the horse compared to other species. In addition, despite a similar subgross and superficial radiographic anatomy to man, the horse demonstrates an arterial and venous branching pattern exactly the reverse in appearance. Thus monopodal branching is a feature of the pulmonary arterial system whereas dichotomous smooth branching is the norm for equine pulmonary veins. Marked between animal variation in the pattern of bronchial branching was also noted however it was not determined if this was a true variation in anatomical branching or the result of widely varying degrees of bronchoconstriction. The latter effect was very marked in some bronchograms when atropine sulphate was not used prior to barium sulphate insufflation during bronchography. Perhaps the most important result of the correlative study was the ability to accurately identify bronchial and vascular branches over the greater point of the lung fields as a result of prior knowledge of their branching patterns obtained from the contrast studies. No attempt was made in this study to relate the radioanatomical findings to known clinically apparent pulmonary conditions. Such research was held to be appropriate for a follow up study.
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    Mechanical and electrical studies on the horse : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1977) Barnes, Geoffrey Robert George
    Muscle forces may have profound influences on stress and strain within the muscle - skeletal system of an animal. These forces have previously been measured by indirect methods often with severe restrictions on the type of movement (if any) that the skeleton was allowed to undergo. A direct method of muscle force (or tendon tension) measurement in the conscious animal was sought which did not necessitate restriction of skeletal movement. This project reports the manufacture and successful in vivo functioning of a tendon tension 'buckle' transducer. The use of the device was demonstrated by correlating tension in the common digital extensor tendon with strain on the lateral and medial aspects of the bone of the walking horse. Strain was monitored by bonding foil electrical resistance strain gauges to the bone surface using a contact cement. The swing and support phases of the forelegs were monitored by switches attached to each forefoot and occasionally monitored by cinematography. Thus it was possible to make a detailed analysis of the lateral bone strain recording in terms of body weight bearing and of muscle action via the monitored tendon. Also considered were the influences of tension in other tendons of the limb and the action of the head and neck during walking. A further application of the tendon tension transducer was its use in monitoring tendon tension during recordings of the electrical activity generated by the corresponding muscle. This activity, which was recorded from intramuscular wire electrodes, was later rectified, integrated and compared with the directly measured force. Experience in electromyography was gained through extensive studies of the equine larynx during which the instrumentation was improved. The early attempts at bonding strain gauges and flanges to living equine bone failed because the epoxy resin flanges which held the lead wires became detached from the bone. The epoxy resin mouldings were consequently screwed in place but this caused slight lameness immediately following surgery. Experiments with a tendon tension transducer proved fruitless until the 'buckle' configuration was adopted. This device, when suitably constructed, did not significantly affect the gait of the animal.
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    The pathology of laryngeal hemiplegia in the horse : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University
    (Massey University, 1985) Cahill, Jennifer Irene
    A review of the literature on equine laryngeal hemiplegia indicated that further investigations were warranted, in order to define more clearly the underlying pathogenic processes. This investigation was undertaken on one Standardbred and fourteen Thoroughbred horses, of which four were clinically affected with laryngeal hemiplegia, five subclinically affected and six were apparently normal. Their left and right recurrent laryngeal nerves were examined in detail, as were hindlimb nerves from two of the clinically affected animals. A variety of histological techniques were employed, including light and electron microscopy of resin embedded nerve, and single teased fibre preparations. Quantitative data obtained from these investigations was evaluated statistically. Some intrinsic laryngeal muscles, and the extenson digitonum longus muscle were investigated. In addition, the motor nucleus of the recurrent laryngeal nerve fibres, the nucleus ambiguus, and long central nerve fibre tracts were examined. The results demonstrated that the neuropathy of equine laryngeal hemiplegia is characteristic of a distal axonopathy. Rather than being a disease of the left recurrent laryngeal nerve, as it has previously been considered, a generalised neuropathological process affecting long and large diameter nerve fibres was found. The primary site of the lesion was shown to be the axon rather than the myelin sheath. Distal axonal atrophy was demonstrated. As well as the involvement of peripheral nerve fibres in the disease process, some evidence for the involvement of long fibres of the central nervous system was found. In addition, an investigation of the pathology associated with stringhalt, another nervous condition of horses, was performed on one animal. It was demonstrated that this was also a distal axonopathy, although a number of differences from idiopathic laryngeal hemiplegia were observed. It was an acute rather than a chronic process, and lacked any involvement of central fibres. In conclusion, it was suggested that a number of previously postulated causes for equine laryngeal hemiplegia could be dismissed, on the basis of the finding of a generalised distal axonopathy. This included those which suggested mechanical damage to the left recurrent laryngeal nerve, such as stretch or compression. In light of the findings, the most likely aetiology underlying the pathology of equine laryngeal hemiplegia was considered to be an acquired or inherited metabolic defect affecting energy production in the axon, with the resultant inability to support the distal areas of long, large diameter nerve fibres.
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    A study of some muscles of the equine larynx and soft palate : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Surgery
    (Massey University, 1984) Anderson, Laurence John
    The purpose of this study was to determine the age of onset, incidence and severity of neurogenic disease in the intrinsic laryngeal muscles of a single breed of competitive horse, the New Zealand Thoroughbred. Some palatal muscles from these horses were also studied to ascertain whether neurogenic disease occurred in them. The left and right dorsal cricoarytenoid, lateral cricoarytenoid, transverse arytenoid, ventricular, vocal, cricothyroid, hyoepiglottic, palatopharyngeal, palatine levator, palatine, and palatine tensor muscles were collected from some or all of 53 Thoroughbred horses. Forty-six of the horses had no history of upper respiratory tract abnormalities, six had suffered from idiopathic laryngeal hemiplegia and one from laryngo-palatal dislocation. For comparative purposes similar muscles from three ponies were also studied. The muscles were weighed and then frozen sections were prepared from them. Some of these were stained with haematoxylin and eosin and others to demonstrate the activity of myosin adenosine triphosphatase, succinate dehydrogenase and glycogen phosphorylase. These sections were then studied to determine the muscle fibre types present and their proportions. The mean sizes of the groups of myosin adenosine triphosphatase low reacting fibres were measured as were the mean cross sectional areas of the fibres. Abnormal staining characteristics of the fibres were noted along with histological signs of denervation and reinnervation. Where possible this information was analysed to determine the significance of the differences observed between the measured mean values. A difference in weight between some of the left and right laryngeal muscles was found to be very common in Thoroughbred horses with no history of upper respiratory tract abnormalities. The left lateral cricoarytenoid muscle was lighter than the right in approximately half of these horses. This difference was significant between the muscles of these horses over three years of age and was most obvious in the muscles of the geldings. The left and right dorsal crico-arytenoid muscles showed similar but not such marked differences. These differences were more obvious in the laryngeal hemiplegic horses. The fibres of the intrinsic laryngeal muscles were predominantly highly reactive for the enzyme myosin adenosine triphosphatase with the ventricular and vocal muscles having the highest proportions of these fibres and the cricothyroid and hyoepiglottic muscles the lowest. Glycogen phosphorylase reactivity in these muscles was again predominantly high, and the fibres were almost exclusively, highly reactive for succinate dehydrogenase. Neurogenic disease appeared to have an influence on the proportions of fibre types present in affected muscles. The incidence of larger groups of myosin adenosine triphosphatase low reacting fibres in some of the left than right intrinsic laryngeal muscles was also very common in Thoroughbred horses with no history of upper respiratory tract abnormalities. Eighty percent of these horses over three years of age had larger groups in their left than right lateral cricoarytenoid muscles and the youngest horse where this difference was noted was six weeks Old. The adductor muscles showed more evidence of this side difference in group size than the abductor muscles. The mean cross sectional area of the fibres of the intrinsic laryngeal muscles studied increased till approximately the end of the third year of a horse's life. Neurogenic disease eventually reduced the cross sectional area of the fibres of affected muscles but early in its course it may have produced an increase in the mean cross sectional area of fibres. This increase occurred in mildly affected and also in some unaffected muscles. The latter may have been required to increase their activity to compensate for inefficient function in atrophied muscles. The histological signs of denervation and reinnervation were also very common in the intrinsic laryngeal muscles supplied by the left recurrent laryngeal nerve. These signs were noted in almost 70% of the left lateral cricoarytenoid muscles from horses over one year of age, with no history of upper respiratory tract abnormalities. The incidence of these signs in the dorsal cricoarytenoid muscle was lower but they appeared suddenly and severely in the left muscles of horses during adolescence and early adult life. In the cricothyroid muscle which is not supplied by the recurrent laryngeal nerve, the only histological signs of this nature appeared in the muscles of a few of the aged horses. In the palatal muscles examined there was no evidence of a difference in weight between the left and right muscles and most of their fibres were highly reactive for the three enzymes studied. There was no evidence of fibre type grouping resulting from denervation and reinnervation and none of the other histological signs resulting from severe neurogenic disease were noted.