Electromyographic activity of the stylopharyngeus muscle in exercising horses

REASONS FOR PERFORMING STUDY: There is a need to understand the process which leads to failure of recruitment of the stylopharyngeus muscle in clinical cases of nasopharygeal collapse. We therefore studied the timing and intensity of stylopharyngeus muscle activity during exercise in horses. OBJECTIVE: To measure the electromyographic (EMG) activity of the stylopharyngeus muscle in exercising horses and correlate it with the breathing pattern. METHODS: Five horses were equipped with a bipolar fine wire electrode placed on the stylopharyngeus muscle and a pharyngeal catheter. The horses exercised on a treadmill at speeds corresponding to 50 (HRmax50), 75 and 100% of maximum heart rate, and EMG activity of the stylopharyngeus muscle and upper airway pressures were recorded. The EMG activity of the stylopharyngeus muscle was then correlated to the breathing pattern and the activity quantified and reported as a percentage of the baseline activity measured at HRmax50. RESULTS: There was ongoing activity of the stylopharyngeus muscle throughout the breathing cycle; however, activity increased towards the end of expiration and peaked early during inspiration. Tonic activity was present during expiration. Peak, mean electrical and tonic EMG activity increased significantly (P<0.05) with exercise intensity. CONCLUSION: The stylopharyngeus muscle has inspiratory-related activity and tonic activity that increases with speed. POTENTIAL RELEVANCE: The stylopharyngeus muscle is one of a group of upper airway muscles that function to support and maintain the patency of the nasopharynx during inspiration. Failure of recruitment of the stylopharyngeus muscle during exercise is a potential explanation for clinical cases of dorsal pharyngeal collapse, but further work investigating the activity of the stylopharyngeus muscle in horses affected by this disease is needed.     

Electromyographic activity of the palatinus and palatopharyngeus muscles in exercising horses

REASONS FOR PERFORMING STUDY: Determining the respiratory related activity of the palatinus and palatopharyngeus muscles in exercising horses is relevant because dysfunction of these muscles has been implicated in the pathogenesis of dorsal displacement of the soft palate. OBJECTIVE: To determine if the palatinus and palatopharyngeus muscles have respiratory activity that increases with intensity in exercising horses. METHODS: Electromyographic activity was measured in the palatinus and palatopharyngeus muscles using bipolar fine-wire electrodes while the horses completed an incremental exercise treadmill protocol. RESULTS: Both muscles displayed synchronous expiratory activity that increased significantly (P < 0.05) with exercise intensity. Phasic expiratory activity of the palatinus increased 390 +/- 98%, whereas phasic expiratory activity of the palatopharyngeus increased by 198 +/- 30% as the treadmill speed increased from 6 to 12 m/s. CONCLUSIONS: The palatinus and palatopharyngeus muscles may be important respiratory muscles, functioning to stabilise the position of the soft palate during intense exercise. CLINICAL RELEVANCE: The predominant expiratory activity of these muscles may be associated with specific muscle function related to exercise or distinct upper airway phenomena of an obligate nasal breather, such as the horse.     

Electromyographic activity of the hyoepiglotticus muscle and control of epiglottis position in horses

OBJECTIVE: To determine whether the hyoepiglotticus muscle has respiratory-related electromyographic activity and whether electrical stimulation of this muscle changes the position and conformation of the epiglottis, thereby altering dimensions of the aditus laryngis. ANIMAL: 6 Standardbred horses. PROCEDURE: Horses were anesthetized, and a bipolar fine-wire electrode was placed in the hyoepiglotticus muscle of each horse. Endoscopic images of the nasopharynx and larynx were recorded during electrical stimulation of the hyoepiglotticus muscle in standing, unsedated horses. Dorsoventral length and area of the aditus laryngis were measured on images obtained before and during electrical stimulation. Electromyographic activity of the hyoepiglotticus muscle and nasopharyngeal pressures were measured while horses exercised on a treadmill at 50, 75, 90, and 100% of the speed that produced maximum heart rate. RESULTS: Electrical stimulation of the hyoepiglotticus muscle changed the shape of the epiglottis, displaced it ventrally, and significantly increased the dorsoventral length and area of the aditus laryngis. The hyoepiglotticus muscle had inspiratory activity that increased significantly with treadmill speed as a result of an increase in phasic and tonic activity. Expiratory activity of the hyoepiglotticus muscle did not change with treadmill speed in 4 of 6 horses. CONCLUSIONS AND CLINICAL RELEVANCE: Findings reported here suggest that contraction of the hyoepiglotticus muscle increases dimensions of the airway in horses by depressing the epiglottis ventrally during intense breathing efforts. The hyoepiglotticus muscle may be an important muscle for dilating the airway in horses, and contraction of the hyoepiglotticus muscle may induce conformational changes in the epiglottis.     

Incidence of swallowing during exercise in horses with dorsal displacement of the soft palate

Reasons for performing study: The relationship between dorsal displacement of the soft palate (DDSP) and swallowing is unclear. Objective: To quantify the relationship between DDSP and swallowing in horses at exercise. Hypotheses: The frequency of swallowing increases immediately prior to DDSP in horses at exercise. Methods: Videoendoscopic and upper airway pressure data were collated from horses with a definitive diagnosis of DDSP at exercise. Horses with no upper airway abnormalities were matched by age, breed and sex and used as controls. Sixty‐nine horses were identified with a definitive diagnosis of DDSP during the study interval. Airway pressure data were available for 42 horses. Results: The majority of horses displaced at high exercising speeds while accelerating; a smaller number displaced during deceleration after peak speed had been reached. Horses swallowed significantly more frequently in the 1 min immediately preceding DDSP than in the control horses at equivalent speeds. DDSP at exercise results in a significant increase in tracheal expiratory pressure, a significant decrease in pharyngeal expiratory pressure and a significantly less negative pharyngeal inspiratory pressure compared to matched controls and compared to the pressures during the 1 min interval prior to DDSP. There was no significant difference between any measure of airway pressure before or after a swallow when examined at each time interval in the DDSP population. Conclusions: The frequency of swallowing decreases with increasing speed in normal horses. In contrast, the frequency of swallowing increases immediately prior to onset of DDSP. This is not a result of pharyngeal and tracheal pressure changes. Potential relevance: The increased frequency of swallowing observed prior to DDSP may be related to the aetiology of the disease.     

Treatment of left laryngeal hemiplegia in standardbreds, using a nerve muscle pedicle graft

The efficacy of a nerve muscle pedicle (NMP) graft in restoring upper airway function was evaluated in exercising horses with induced left laryngeal hemiplegia. The NMP graft was created from the first cervical nerve and the omohyoideus muscle and transplanted into the left cricoarytenoideus dorsalis muscle. Seven adult Standardbreds were trained to exercise on a treadmill inclined at 6.38 degrees. With the horses at rest and exercising at 4.2 and 7.0 m/s, the following variables were recorded: peak inspiratory and expiratory transupper airway pressures (defined as the pressure difference between a lateral tracheal catheter and a mask catheter), peak inspiratory and expiratory air flow, inspiratory and expiratory impedance, tidal volume, minute ventilation, heart rate, and respiratory frequency. Measurements were made before left recurrent laryngeal neurectomy (LRLN), 28 days after LRLN, and 12, 24, and 52 weeks after the NMP graft (n = 5) or sham operation (n = 2). Before LRLN, exercise increased inspiratory and expiratory air flow and transupper airway pressure, whereas the impedance was unchanged. After LRLN, transupper airway inspiratory pressure and impedance were significantly greater and inspiratory air flow was significantly less than baseline values at 7.0 m/s. The sham operation did not improve airway function. Twelve weeks after insertion of the NMP graft, inspiratory impedance and inspiratory air flow were significantly different (improved) from LRLN values. Twenty-four weeks after insertion of the NMP graft, inspiratory impedance was not significantly different from LRLN values.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of a tongue-tie on upper airway mechanics during exercise following sternothyrohyoid myectomy in clinically normal horses

OBJECTIVE: To determine the effect of a tongue-tie on upper airway mechanics in clinically normal horses exercising on a treadmill following sternothyrohyoid myectomy. ANIMALS: 6 Standardbreds. PROCEDURE: Upper airway mechanics were measured with horses exercising on a treadmill at 5, 8, and 10 m/s 4 weeks after a sternothyrohyoid myectomy was performed. Pharyngeal and tracheal inspiratory and expiratory pressures were measured by use of transnasal pharyngeal and tracheal catheters connected to differential pressure transducers. Horses were fitted with a facemask and airflow was measured by use of a pneumotachograph. Horses underwent a standardized exercise protocol on a treadmill at 5, 8, and 10 m/s with and without a tongue-tie in a randomized cross-over design. Inspiratory and expiratory airflow, tracheal pressure, and pharyngeal pressure were measured, and inspiratory and expiratory resistances were calculated. RESULTS: We were unable to detect an effect of a tongue-tie on any of the respiratory variables measured. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that a tongue-tie does not alter upper airway mechanics following sternothyrohyoid myectomy in clinically normal horses during exercise.     

Identification and categorization of the vascular patterns to muscles of the thoracic limb, thorax, and neck of dogs.

Vascular patterns to thoracic limbs, thorax, and neck muscles were studied in 10 dogs (20 limbs) to identify muscles most suitable for transposition in the treatment of large wounds. Gross dissection of injected specimens and angiography were used to identify vascular pedicles. Size and location of pedicles were generally consistent, and any variations would not interfere with most muscle transfers. The cutaneous trunci, latissimus dorsi, sternothyroideus, sternohyoideus, deep pectoral, anconeus, ulnaris lateralis, and ulnar head of flexor carpi ulnaris muscles were identified as suitable for transfer. The cranial trapezius, caudal omotransversarius, cleidobrachialis, and caudal sternocephalicus muscles also had potential for use. Other muscles, because of inaccessibility or unfavorable vascular pattern, were not suitable candidates for transfer.     

Influence of age of horse on results of quantitative electromyographic needle examination of skeletal muscles in Dutch Warmblood horses

OBJECTIVE: To determine the influence of age on results of quantitative analysis of electromyographic (EMG) needle examination in the subclavian, triceps, and lateral vastus muscles of Dutch Warmblood horses. ANIMALS: 7 healthy young Dutch Warmblood horses (range, 13 to 18 months old), 7 healthy adult Dutch Warmblood horses (range, 4 to 10 years old), and 7 healthy elderly Dutch Warmblood horses (range, 18 to 21 years old). PROCEDURE: An EMG needle examination was performed to evaluate insertional activity, spontaneous activity, and motor unit action potential (MUAP) variables. Although all horses were conscious, young horses were sedated prior to examination. RESULTS: Mean insertional activity in young horses was significantly lower than in elderly horses. Pathologic spontaneous activity was rarely found in young and adult horses but was frequently evident in all muscles in all elderly horses. The MUAP duration and amplitude were significantly lower in all muscles of young horses, compared with values for adult and elderly horses. The MUAP duration and number of phases and turns were significantly lower in adult horses than in elderly horses. Group differences for percentages of polyphasic and complex MUAPs were also found. The 95% confidence intervals for MUAP duration, MUAP amplitude, and number of phases and turns for the subclavian, triceps, and lateral vastus muscles were significantly lower in young horses than in adult or elderly horses. CONCLUSIONS AND CLINICAL RELEVANCE: Age of the horse being examined should be considered when EMG examination is performed.     

Observations on the mechanism of functional obstruction of the nasopharyngeal airway in the horse.

Fibreoptic endoscopy was used to study the movements of the larynx and pharynx during nasal occlusion in 10 horses, which showed signs consistent with functional pharyngeal obstruction (FPO) on exercise. Cine-endoscopic films were made on 3 such horses. Consideration of the anatomy of the region indicates that FPO may best be regarded as a subluxation of the nasopharyngeal and larygneal airways and it was found that a constant component of the movements which brought about this subluxation was a marked caudal retraction of the larynx. It is suggested that this caudal retraction of the larynx occurred as a result of the action of th sternothyrohyoid and omohyoid muscles and that removal of a portion of these muscles might prevent subsequent airway subluxation in horses prone to FPO on exercise.     

Effect of commercially available nasal strips on airway resistance in exercising horses

OBJECTIVE: To determine the effect of a commercially available nasal strip on airway mechanics in exercising horses. ANIMALS: 6 horses (5 Standardbreds and 1 Thoroughbred). PROCEDURE: Horses exercised on a treadmill at speeds corresponding to 100 and 120% of maximal heart rate with and without application of a commercially available nasal strip. Concurrently, tracheal pressures, airflow, and heart rate were measured. Peak inspiratory and expiratory tracheal pressures, airflow, respiratory frequency, and tidal volume were recorded. Inspiratory and expiratory airway resistances were calculated by dividing peak pressures by peak flows. Endoscopic examination of the narrowest point of the nasal cavity (ie, nasal valve) was performed in 1 resting horse before, during, and after application of a nasal strip. RESULTS: During exercise on a treadmill, peak tracheal inspiratory pressure and inspiratory airway resistance were significantly less when nasal strips were applied to horses exercising at speeds corresponding to 100 and 120% of maximal heart rate. Application of the nasal strip pulled the dorsal conchal fold laterally, expanding the dorsal meatus. CONCLUSIONS AND CLINICAL RELEVANCE: The commercially available nasal strip tented the skin over the nasal valve and dilated that section of the nasal passage, resulting in decreased airway resistance during inspiration. The nasal strip probably decreases the amount of work required for respiratory muscles in horses during intense exercise and may reduce the energy required for breathing in these horses.     

Investigations into the role of the thyrohyoid muscles in the pathogenesis of dorsal displacement of the soft palate in horses

REASONS FOR PERFORMING STUDY: Contributes to the understanding of the pathogenesis of dorsal displacement of the soft palate during exercise so that management of this condition could be enhanced. HYPOTHESIS: That the thyrohyoid muscles play an important role in the stability of the laryngo-palatal relationship and that dysfunction of these muscles leads to dorsal displacement of the soft palate (DDSP) during exercise. METHODS: Ten horses were exercised on a high-speed treadmill under 4 different treatment conditions: control conditions (n = 10), after resection of thyrohyoid muscles (TH, n = 10), after sham-treatment (n = 5), or after restoration of function of the thyrohyoid muscles with surgical sutures (prosthesis-treatment, n = 6). During trials, the following determinations were made: videoendoscopy of the upper airway, gait frequency and pharyngeal and tracheal static pressures. RESULTS: None of the 10 horses developed DDSP during 2 separate treadmill-exercise trials under the control conditions. Seven of the 10 horses developed DDSP after resection of the TH muscles, 4 of 5 of these horses still experienced DDSP after sham-treatment, but 5 of 6 horses no longer experienced DDSP at exercise after the prosthesis-treatment. There were significant anomalies in airway pressures, respiratory frequency, and occurrence of DDSP in both the TH resection and sham-treatment conditions compared to control conditions. In contrast, no statistical differences were noted in any of the parameters measured between the prosthesis-treatment and control conditions. CONCLUSIONS: That the function of the TH muscles is important to the stability of the laryngo-palatal relationship and plays a role in the pathophysiology of exercise-induced DDSP. POTENTIAL RELEVANCE: Management of horses with DDSP could be enhanced by restoring the function of the TH muscles.     

Histologic evaluation of nerve muscle pedicle graft used as a treatment for left laryngeal hemiplegia in standardbreds.

A nerve muscle pedicle (NMP) graft was placed in the cricoarytenoideus dorsalis (CAD) muscle of 6 horses with induced left laryngeal hemiplegia. The NMP graft was created by use of the first cervical nerve and omohyoideus muscle. In 1 horse (control), the first cervical nerve was transected after placement of the NMP graft. One year after the surgical procedure, horses were examined endoscopically and then anesthetized. While the larynx was observed endoscopically, the first cervical nerve was stimulated. Horses were subsequently euthanatized, and the larynx was harvested. Prior to anesthesia, the endoscopic appearance of the larynx of all horses was typical of laryngeal hemiplegia. During anesthesia, stimulation of the first cervical nerve produced vigorous abduction of the left arytenoid in principal horses but not in the control horse. The right cricoarytenoideus lateralis and CAD muscles were grossly and histologically normal. Also, the left cricoarytenoideus lateralis was atrophic in all horses as was the left CAD muscle of the control horse. In contrast, the left CAD muscle harvested from principal horses had evidence of reinnervation with type 1 or type 2 fiber grouping. One year after the NMP graft procedure, horses with left laryngeal hemiplegia had reinnervation of the left CAD muscle. In another study, reinnervation was sufficient to allow normal laryngeal function during exercise. Combined, these data suggest that the NMP graft procedure is a viable technique for the treatment of left laryngeal hemiplegia in horses.     

Respiratory mechanics of horses during stepwise treadmill exercise tests, and the effect of clenbuterol pretreatment on them

Normal Standardbred horses were given an incremental exercise test on a horizontal treadmill to evaluate the influence of exercise on gas exchange, resistance, dynamic compliance and inertance of the respiratory system. The exercise test consisted of 2 min exercise steps at each of the following speeds: 2.4 m/sec (walk), 4.5 m/sec (slow trot), 7.0 m/sec (fast trot) and 10 m/sec (gallop). At rest and after 1 min of exercise at each step, airflow, tidal volume, respiratory frequency, pharyngeal, mid-oesophageal and transdiaphragmatic pressures and arterial blood gas tensions were measured. The same horses were subsequently treated intravenously with clenbuterol (0.8 microgram/kg) and an identical exercise test and measurement performed 10 min after clenbuterol injection. In response to exercise, there were large increases in tidal volume, respiratory frequency, airflow and pressures. Exercise was associated with a decrease in upper airway resistance but total pulmonary resistance was unchanged. Exercise did not alter inertance or dynamic compliance, horses became hypoxaemic, and at 10 m/sec (galloping) also developed hypercarbia. Treatment with clenbuterol did not alter any of these measurements in response to exercise. These data suggest that dilation of upper airways occurs during exercise, and that inertial forces are important in strenuously exercising horses and may influence the accuracy of dynamic compliance determinations at high exercise intensities.     

Electromyographic activity of cubital joint muscles in horses during locomotion

Electromyographic (EMG) activity of 4 muscles of the cubital joint and the strain of forelimb hooves were recorded telemetrically in 4 Thoroughbreds (with and without a rider) standing, walking, trotting, and cantering. Bipolar fine wire electrodes were inserted into the muscles, and strain gauges were attached to the hoof wall. Motion pictures (16 mm), synchronized with EMG tracings, were taken to obtain kinematic data. When horses were standing, the biceps brachii had tonic activity, but the brachialis and the caput longum and the caput laterale of the triceps brachii had no EMG activity. The biceps brachii had EMG activity during the stance phase. The brachialis had EMG activity from the end of the stance phase to the middle of the swing phase. Unlike the biceps brachii, the brachialis acted as a flexor muscle of the cubital joint during locomotion. The EMG activity of the caput longum of the triceps brachii was detected from midswing phase to early stance phase. The EMG activity of the caput laterale of the triceps brachii began in midswing or late-swing phase and ceased in early stance or midstance phase. During locomotion, caput longum EMG activity always preceded caput laterale activity. When horses were cantering, the brachialis and the caput longum (acting mainly in the swing phase) had an EMG activity phase different from those in leading and trailing forelimbs. These 4 muscles had similar EMG activity patterns during locomotion in horses with and without a rider.     

Effect of a tongue-tie on upper airway mechanics in horses during exercise

OBJECTIVE: To determine the effect of a tongue-tie on upper airway mechanics in exercising horses. ANIMALS: 5 Standardbreds. PROCEDURE: Peak inspiratory and expiratory tracheal and pharyngeal pressures and airflow were measured while horses exercised on a treadmill with and without a tongue-tie. Respiratory rate was also measured. Horses ran at speeds that corresponded to 50 (HR50), 75, 90 (HR90), and 100% of maximal heart rate. The tongue-tie was applied by pulling the tongue forward out of the mouth as far as possible and tying it at the level of the base of the frenulum to the mandible with an elastic gauze bandage. Peak inspiratory and expiratory tracheal, pharyngeal, and translaryngeal resistance, minute ventilation, and tidal volume were calculated. Data were analyzed by use of 2-way repeated-measures ANOVA. For post hoc comparison of significant data, the Student-Newman-Keuls test was used. RESULTS: We were unable to detect significant differences between groups for peak inspiratory or expiratory tracheal or pharyngeal resistance, peak pressure, peak expiratory flow, tidal volume, respiratory rate, or minute ventilation. Horses that ran with a tongue-tie had significantly higher peak inspiratory flows, compared with horses that ran without a tongue-tie. In the post hoc comparison, this effect was significant at 4 m/s, HR50, and HR90. CONCLUSION AND CLINICAL RELEVANCE: Application of a tongue-tie did not alter upper respiratory mechanics in exercising horses and may be beneficial in exercising horses with certain types of obstructive dysfunction of the upper airways. However, application of a tongue-tie does not improve upper airway mechanics in clinically normal horses.     

Comparison of nociceptive withdrawal reflexes and recruitment curves between the forelimbs and hind limbs in conscious horses

OBJECTIVE: To compare nociceptive withdrawal reflexes (NWRs) evoked from the distal aspect of the left forelimb and hind limb in conscious standing horses and to investigate NWR recruitment for graded electrical stimulation intensities. ANIMALS: 20 adult horses. PROCEDURE: Surface electromyographic (EMG) activity evoked by transcutaneous electrical stimulation of the digital palmar (or plantar) nerve was recorded from the common digital extensor and cranial tibial muscles. Stimuli consisted of 25-millisecond train-of-5 constant current pulses. Current intensity was gradually increased until NWR threshold intensity was reached. The EMG signal was analyzed for quantification of the NWR. Behavioral responses accompanying the reflex were scored (scale, 0 to 5). The NWR recruitment curves were determined at 0.9, 1.1, 1.2, and 1.3 times the NWR threshold intensity. RESULTS: The NWR threshold was significantly higher for the hind limb (median value, 6.6 mA; range, 3 to 10 mA) than the forelimb (median, 3 mA; range, 1.7 to 5.5 mA). The NWR of the hind limb had a significantly longer latency (median, 122.8 milliseconds; range, 106 to 172 milliseconds), compared with the forelimb (median, 98 milliseconds; range, 86 to 137 milliseconds), and it was associated with significantly stronger behavioral reactions. Gradual increase of NWR amplitude was evident at increasing stimulation intensities and supported by the behavioral observations. CONCLUSIONS AND CLINICAL RELEVANCE: We documented NWRs evoked from the forelimb and hind limb and their recruitment with stimuli of increasing intensity in horses. These results provide a basis for use of NWRs in studies on nociceptive modulation in horses.     

Electromyographic activity of the longissimus dorsi muscles in horses during trotting on a treadmill

OBJECTIVE: To use electromyography (EMG) to measure physiologic activity of the longissimus dorsi muscles of horses during trotting on a treadmill. ANIMALS: 15 adult horses (5 to 20 years old that weighed 450 to 700 kg) that did not have clinical signs of back pain. PROCEDURE: Data were recorded for each horse during trotting on a treadmill at speeds of 2.6 to 4.4 m/s. Surface electromyography was recorded bilaterally from the longissimus dorsi muscles at the levels of T12, T16, and L3. RESULTS: In each motion cycle, 2 EMG maxima were found at the end of the diagonal stance phases. The EMG activity peaked slightly later at L3 than at T12 and T16. Maximum EMG amplitudes were highest at T12 and decreased caudally, with mean +/- SD values of 4.51 +/- 1.20 mV at T12, 3.00 +/- 0.83 mV at T16, and 1.78 +/- 0.67 mV at L3. Mean minimum EMG activity was 1.30 +/- 0.63 mV at T12, 0.83 +/- 0.35 mV at T16, and 0.80 +/- 0.39 mV at L3. The relative amplitudes (ie, [maximum - minimum]/maximum) were 67 +/- 11% at T12, 66 +/- 8% at T16, and 71 +/- 8% at L3. CONCLUSIONS AND CLINICAL RELEVANCE: Activity of the longissimus dorsi muscles is mainly responsible for stabilization of the vertebral column against dynamic forces. The difference between minimum and maximum activity may allow application of this method as a clinical tool. Data reported here can serve as reference values for comparison with values from clinically affected horses.     

Effect of ventriculectomy versus ventriculocordectomy on upper airway noise in draught horses with recurrent laryngeal neuropathy

Reasons for performing study: Little is known about the efficacy of bilateral ventriculectomy (VE) or bilateral ventriculocordectomy (VCE) in draught horses. Objectives: To compare the effect of VE and VCE on upper airway noise in draught horses with recurrent laryngeal neuropathy (RLN) by use of quantitative sound analysis techniques. Hypothesis: In competitive draught horses with grade 4 RLN, VE and VCE reduce upper airway noise during exercise, but VCE is more effective. Methods: Thirty competitive hitch or pulling draught horses with grade 4 RLN were evaluated for upper airway sound during exercise. Respiratory rate (RR), inspiratory (Ti) and expiratory time (Te), the ratio between Ti and Te (Ti/Te), inspiratory (Sli) and expiratory sound levels (Sle), the ratio between Sli and Sle (Sli/Sle), and peak sound intensity of the second formant (F2) were calculated. Eleven horses were treated with VE and 19 with VCE. After 90 days of voice and physical rest and 30 days of work, the horses returned for post operative upper airway sound evaluation and resting videoendoscopy. Results: VE significantly reduced Ti/Te, Sli, Sli/Sle and the sound intensity of F2. Respiratory rate, Ti, Te and Sle were unaffected by VE. VCE significantly reduced Ti/Te, Ti, Te, Sli, Sli/Sle and the sound intensity of F2, while RR and Sle were unaffected. The reduction in sound intensity of F2 following VCE was significantly greater than following VE. After VE and VCE, 7/11 (64%) and 15/18 (83%) owners, respectively, concluded that the surgery improved upper airway sound in their horses sufficiently for successful competition. Conclusions: VE and VCE significantly reduce upper airway noise and indices of airway obstruction in draught horses with RLN, but VCE is more effective than VE. The procedures have few post operative complications. Potential relevance: VCE is recommended as the preferred treatment for RLN in draught horses. Further studies are required to evaluate the longevity of the procedure's results.     

Epiglottic augmentation by use of polytetrafluoroethylene to correct dorsal displacement of the soft palate in a standardbred horse.

A 2-year-old 400-kg Standardbred colt with a history of exercise intolerance was determined to have dorsal displacement of the soft palate (DDSP). Standing endoscopy revealed a soft, flaccid, and hypoplastic epiglottis and arytenoid cartilages that moved symmetrically and abducted fully. Lateral laryngeal radiography was used to calculate a corrected thyroepiglottic length of 6.48 cm. Videoendoscopy during exercise on a high-speed treadmill at standardized treadmill speeds was performed weekly for 3 consecutive weeks. The soft palate dorsally displaced at each examination. A sternohyoideus/sternothyroideus myectomy was followed by 2 weeks of stall rest and 2 weeks of treadmill training. Because endoscopy during exercise at standardized treadmill speeds caused the horse to dorsally displace the soft palate once a week for 3 weeks after the myectomy, this surgery was deemed ineffective in this horse. Epiglottic augmentation was performed by injecting 7 ml of polytetrafluoroethylene into the ventral submucosal space of the epiglottis. After 21 days of stall rest and 5 weeks of pasture rest, the horse was placed on a 2-month treadmill conditioning program. Using endoscopy at standardized treadmill speeds, exercise efforts to encourage DDSP were unsuccessful, which suggested that epiglottic augmentation by use of polytetrafluoroethylene was an effective surgical treatment to correct dorsal displacement of the soft palate in this horse. It is believed that polytetrafluoroethylene increases the rigidity of the epiglottis, allowing it to maintain the ventral position of the soft palate.     

Endoscopy of the upper respiratory tract during treadmill exercise: a clinical study of 100 horses

SUMMARY: Endoscopy of the upper respiratory tract was performed in 100 horses during high speed treadmill exercise. Reasons for endoscopy were a history of an abnormal noise during exercise in 75 horses, poor performance in 17 horses and to evaluate the results of upper respiratory tract surgery in 8 horses. Of the 75 horses with a history of an abnormal noise during exercise the cause was determined in 67 (89%). Endoscopic abnormalities were detected at rest in 40 of these 75 horses (53%). In these 40 horses, a similar diagnosis as to the cause of the abnormal noise was made at rest and during exercise on the treadmill in 19 cases, while in the remaining 21 the endoscopic findings during exercise varied from that seen at rest. This included 3 horses in which a diagnosis was made at rest but no abnormalities were detected during exercise. Some of the findings during treadmill endoscopy included laryngeal dysfunction, grades 3, 4 and 5 (22 cases), dorsal displacement of the soft palate (20), epiglottic entrapment (8), epiglottic flutter (4), aryepiglottic fold flutter (4), pharyngeal collapse (3), arytenoiditis (3), vocal cord flutter (3), false nostril noise (2), pharyngeal lymphoid hyperplasia (2), soft palate haemorrhage (1) and positional arytenoid collapse (1). More than one abnormality was observed during exercise in 7 horses. A complete and correct diagnosis based on the resting endoscopy findings alone was made in 19 (25%) of these 75 cases. In the 17 horses examined because of poor performance, no abnormalities were detected during treadmill endoscopy that were not evident at rest. None of these 17 horses presented with a history of an abnormal respiratory noise, although one, diagnosed as having grade 4 laryngeal function at rest and exercise, did make a characteristic inspiratory noise during treadmill exercise. Eight horses were evaluated after surgery for correction of laryngeal hemiplegia, as the post-operative performance or the amount of respiratory noise present was considered unsatisfactory. Of these, 3 were found to have a satisfactory airway during exercise and other reasons for poor performance were detected; 3 had insufficient abduction; and 2 had intermittent dorsal displacement of the soft palate. Endoscopy of the upper respiratory tract was found to be a useful technique for evaluating the cause of abnormal respiratory noise in most cases. We concluded that treadmill endoscopy in horses presented for poor performance, without a history of an abnormal respiratory noise, was of little value. The technique, in conjunction with arterial blood gas measurements, was useful in determining the efficacy of surgical treatment of laryngeal hemiplegia.