Equus caballus papillomavirus 8 (EcPV8) associated with multiple viral plaques, viral papillomas, and squamous cell carcinoma in a horse.

BACKGROUND: Equus caballus papillomavirus 8, a recently discovered virus, has been reported to cause generalised papillomavirus in horses. OBJECTIVES: To describe a case in which multiple viral plaques, viral papillomas, squamous cell carcinoma (SCC) in situ and invasive squamous cell carcinoma (ISCC) were associated with EcPV8 in a horse. STUDY DESIGN: Case report. METHODS: A 16-year-old mixed breed horse presented with dozens of raised crusted papular to nodular lesions over a course of 4 years. Masses had been surgically excised four times and cisplatin beads and emulsion were implanted on three different occasions; however new masses continue to develop in sites of previous masses as well as new sites. RESULTS: Multiple viral plaques, viral papillomas, SCC in situ and ISCC, localised to the inguinal region, were diagnosed via histopathology. EcPV8 DNA was detected via PCR. MAIN LIMITATIONS: Since only a few cases have been reported, we do not know the incidence of EcPV8 nor how often it may be associated with SCC in situ or ISCC without further study. CONCLUSIONS: This is the fourth reported case of viral papillomatosis in the context of an EcPV8 infection in a horse. This is the first case in which SCC has been associated with EcPV8.

Considerations for pacing of the cricoarytenoid dorsalis muscle by neuroprosthesis in horses.

REASONS FOR PERFORMING STUDY: The success rate of prosthetic laryngoplasty is limited and may be associated with significant sequelae. Nerve muscle pedicle transplantation has been attempted but requires a year before function is restored. OBJECTIVE: To determine the optimal parameters for functional electrical stimulation of the recurrent laryngeal nerve in horses. METHODS: An experimental in vivo study was performed on 7 mature horses (2-21 years). A nerve cuff was placed on the distal end of the common trunk of the recurrent laryngeal nerve (RLN). In 6 horses the ipsilateral adductor branch of RLN was also transected. The electrodes were connected to programmable internal stimulator. Stimulation was performed using cathodic phase and then biphasic pulses at 24 Hz with a 0.427 ms pulse duration. Stimulation-response experiments were performed at monthly intervals, from one week following implantation. The study continued until unit failure or the end of project (12 months). Two of the horses were stimulated continuously for 60 min to assess onset of fatigue. RESULTS: Excellent arytenoid cartilage abduction (mean arytenoid angle of 52.7 degrees, range 48.5-56.2 degrees) was obtained in 6 horses (laryngeal grades I or II (n = 3) and III (n = 2). Poor abduction was obtained in grade IV horses (n = 2). Arytenoid abduction was maintained for up to a year in one horse. Technical implant failure resulted in loss of abduction in 6 horses at one week to 11 months post operatively. Mean tissue impedance was 1.06 kOhm (range 0.64-1.67 kOhm) at one week, twice this value at 2 months (mean 2.32, range 1.11-3.75 kOhm) and was stable thereafter. Maximal abduction was achieved at a stimulation range of 0.65-7.2 mA. No electrical leakage was observed. Constant stimulation of the recurrent laryngeal nerve for 60 min led to full abduction without evidence of muscle fatigue. CONCLUSIONS: Functional electrical stimulation of the recurrent laryngeal nerve leading to full arytenoid abduction can be achieved. The minimal stimulation amplitude for maximal abduction angle is slightly higher than those for man and dogs. CLINICAL RELEVANCE: This treatment modality could eventually be applicable to horses with recurrent laryngeal neuropathy.

Racing performance after combined prosthetic laryngoplasty and ipsilateral ventriculocordectomy or partial arytenoidectomy: 135 Thoroughbred racehorses competing at less than 2400 m (1997-2007).

REASONS FOR PERFORMING STUDY: The success of combined prosthetic laryngoplasty with ipsilateral ventriculocordectomy (LPVC) has not been compared to that of partial arytenoidectomy (PA) in a clinical population. HYPOTHESES: In Thoroughbred (TB) racehorses: (1) earnings after LPVC are unaffected by the severity of recurrent laryngeal neuropathy (RLN) (laryngeal grade III vs. grade IV); (2) LPVC and PA yield similar results in the treatment of grade III RLN; (3) performance outcome following PA is independent of diagnosis (RLN vs. unilateral arytenoid chondritis [UAC]); and (4) neither LPVC nor PA returns horses to the level of performance of controls. METHODS: Medical and racing records of 135 TB racehorses undergoing LPVC or PA for the treatment of grade III or IV RLN or UAC were reviewed. Racing records of age and sex matched controls were also reviewed. RESULTS: After LPVC, horses with grade III RLN performed better compared to those with grade IV RLN. Furthermore, horses treated for grade III RLN by LPVC showed post operative earnings comparable to controls. Rate of return to racing were similar for PA and LPVC, although LPVC resulted in higher post operative earnings. Performance after PA was similar regardless of diagnosis (UAC or RLN). Finally, neither LPVC when performed for grade IV RLN, nor PA performed for either diagnosis restored post operative earnings to control levels. CONCLUSIONS: Thoroughbred racehorses treated by LPVC for grade III RLN show significantly better post operative earnings compared to horses treated for grade IV disease. In grade III RLN, LPVC returns earning potential to control levels. PA and LPVC lead to similar success in terms of rate of return to racing, but PA leads to inferior earnings after surgery. POTENTIAL RELEVANCE: Laryngoplasty should be recommended for all TB racehorses with grade III RLN to maximise return to racing at a high level. This contradicts the common approach of waiting for complete paralysis.

Surgical advancement of the larynx (laryngeal tie-forward) as a treatment for dorsal displacement of the soft palate in horses: a prospective study 2001-2004.

REASONS FOR PERFORMING STUDY: Correct placement of sutures ('laryngeal tie-forward') in experimentally created dorsal displacement of the soft palate (DDSP) has been observed to replace the function of the thyrohyoideus muscles and prevent DDSP. HYPOTHESIS: The 'laryngeal tie-forward' procedure would prevent or delay the occurrence of DDSP during exercise in horses with naturally occurring DDSP and therefore improve performance. METHODS: A clinical population (n = 116), mainly of racehorses was presented for treatment of naturally occurring exercise-induced DDSP. All horses underwent the 'laryngeal tie-forward' procedure. The relative position of the thyroid and cricoid cartilage in relation to the caudal aspect of the basihyoid bone was recorded; follow-up was obtained by telephone communication with trainers, owners and/or referring veterinarians. In addition, a performance index and earnings were determined using race records. RESULTS: Preoperatively, the median distance between the caudal aspect of the basihyoid bone and rostral aspect of the thyroid cartilage was 3.5 cm. Post operatively, the thyroid cartilage was moved a median distance of 4 cm rostrally and the larynx was shown to be in a position more rostral and dorsal than in preoperative radiographs. Of 98 horses for which follow-up was available, the performance of 87% was classified as improved, 12% as unchanged and 2% as worse. In 20 horses in which the diagnosis had been confirmed by treadmill videoendoscopy, 80% had a significantly increased performance index and earnings (P = 0.007). For the entire population, there was a significant improvement in performance index and earnings after surgery (82%) (P = 0.0001). CONCLUSIONS: Placing the larynx in a more rostral and dorsal position may have improved the performance in 80-82% of the horses affected with naturally-occurring DDSP. POTENTIAL RELEVANCE: 'Laryngeal tie-forward' is a surgical technique that has a measurable effect on the position of the larynx and offers an alternative therapy for treating horses affected with DDSP. More experience may be needed with this technique prior to its widespread use in horses with a clinical diagnosis of DDSP.

Can an external device prevent dorsal displacement of the soft palate during strenuous exercise?

REASONS FOR PERFORMING STUDY: Dorsal displacement of the soft palate (DDSP) is a common condition in racehorses for which various surgical treatments are often performed. In light of recent findings that suggested the position of the larynx may influence the occurrence of DDSP, we investigated whether a noninvasive mean of affecting the position of the larynx could be effective in the management of DDSP. HYPOTHESIS: An external device (laryngohyoid support; LHS) positioning the larynx in a more rostral and dorsal location and preventing caudal displacement of the basihyoid bone would be effective in preventing DDSP during strenuous exercise. METHODS: Ten horses were exercised on a high-speed treadmill under 4 different treatment conditions: control (n = 10); control with external device (n = 10); after bilateral resection of thyrohyoid (TH) muscles (n = 7); and after bilateral resection of TH muscles with external device (n = 7). Two trials were performed randomly for each of the 4 conditions. In Trial 1, videoendoscopic images of the upper airway, pharyngeal and tracheal static pressures, and arterial blood gases were collected. In Trial 2, airflow measurement combined with mask and tracheal static pressure was obtained, and upper airway impedance calculated. The trials allowed calculation of airway impedance and respiratory frequency, and assessment of ventilation using arterial PO2 and PCO2. RESULTS: Under control conditions, none of the 10 horses developed DDSP. There was no statistically significant effect from the LHS on airway impedance or respiratory frequency, nor on arterial PO2 and PCO2. Seven of the 10 horses developed DDSP during exercise after resection of the TH muscles. None of these 7 horses continued to experience DDSP during exercise with the external device. In the latter group and condition, the LHS significantly improved inspiratory and expiratory flow and impedance. CONCLUSIONS: The LHS helped prevent experimentally induced DDSP at exercise, probably by statically positioning the larynx in a more rostral and dorsal position. POTENTIAL RELEVANCE: Field studies are required to investigate whether the LHS can successfully prevent DDSP in horses with naturally occurring disease.

Do Thoroughbred and Standardbred horses have similar increases in pulmonary vascular pressures during exertion?

To test the hypothesis that the pulmonary vascular pressures of Thoroughbred and Standardbred horses behave similarly during exertion. Measurements were made on 5 Thoroughbred and 5 Standardbred horses on a treadmill at rest and during 3-minute exercise intervals at speeds predicted to produce 75%, 90%, and 100% maximal heart rate. Left forelimb acceleration, heart rate, esophageal pressure, and pulmonary artery pressure were measured continuously. Pulmonary capillary and wedge pressures were measured during intermittent occlusion of the pulmonary artery. Breathing rate and gait frequency were the fundamental frequencies of the esophageal pressure and limb acceleration signals respectively. The ratio of speed:gait frequency gave stride length. The effects of exertion and breed were evaluated using two-way analysis of variance. Exertion produced significant increases in pulmonary artery (P = 0.001), capillary (P = 0.002), and wedge (P = 0.005) pressures. No significant effect of breed was detected on pulmonary artery pressure, but at exertion pulmonary capillary and wedge pressures were 15% (P = 0.03) and 23% (P = 0.04) greater in Thoroughbreds, respectively. Treadmill speed was approximately 12% greater (P = 0.04), stride length was approximately 25% greater (P = 0.0003), gait frequency was approximately 10% less (P = 0.006), breathing rate was approximately 10% less (P = 0.001), and heart rate was approximately 6% less (P = 0.06) for Thoroughbreds. There was no effect of breed on inspiratory or expiratory esophageal pressure although mean esophageal pressure was approximately 2 mmHg greater (P = 0.03) in exercising Standardbreds. In conclusion, pulmonary capillary and wedge pressures are greater in Thoroughbreds than in Standardbreds at similar fractions of maximal heart rate. This is compatible with the higher incidence of exercise-induced pulmonary hemorrhage observed in Thoroughbreds.

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.

An in vitro comparison of cordopexy, cordopexy and laryngoplasty, and laryngoplasty for treatment of equine laryngeal hemiplegia.

OBJECTIVE: To examine the effect of cordopexy, laryngoplasty, and cordopexy combined with a modified laryngoplasty on airway mechanics. STUDY DESIGN: Experimental airway mechanics were determined by subjecting equine cadaveric larynges to airflows similar to inspiratory airflow of exercising horses. ANIMALS OR SAMPLE POPULATION: Twenty equine larynges. METHODS: Using cadaveric larynges, we developed and tested a new technique of arytenoid cartilage abduction. All larynges had the right arytenoid cartilage abducted to mimic the degree of arytenoid abduction that occurs at maximal exertion in live horses. Three surgical techniques were used to stabilize the left arytenoid cartilage of treated larynges; the left arytenoid cartilage was not stabilized in control larynges. Technique 1: Cordopexy--a suture was placed between the vocal ligament and the lamina of the thyroid cartilage. Technique 2: Standard laryngoplasty--a suture was placed between the muscular process of the arytenoid cartilage and the caudomedial aspect of the cricoid cartilage. Technique 3: Cordopexy plus modified laryngoplasty--the cordopexy suture was placed with a second suture between the horizontal ridge rostral to the muscular process of the left arytenoid cartilage and the lamina of the thyroid cartilage. Translaryngeal impedances (TI) were determined for each surgical technique by subjecting the larynges to increasing airflows and measuring the translaryngeal pressure differences. The arytenoid right to left angle quotient (RLQ) and the glottic cross-sectional area (CSA) were also measured. RESULTS: At maximal airflow, the adjusted means for the arytenoid RLQ and the TI for the cordopexy plus modified laryngoplasty (1.48 +/- 0.04, 0.69 +/- 0.05 cm H2O/L/s) and the standard laryngoplasty (1.39 +/- 0.04, 0.78 cm H2O/L/s) were different (P < .05) from values obtained after cordopexy alone (2.74 +/- 0.37, 1.76 +/- 0.48 cm H2O/L/s) or in control larynges (3.66 +/- 0.54, 4.16 +/- 0.96 cm H2O/L/s). Overall, a cordopexy plus modified laryngoplasty (9.69 cm2), a standard laryngoplasty (9.34 cm2), and a cordopexy alone (9 cm2) resulted in an increased glottic CSA greater than that for control larynges (6.94 cm2; P = .0001). CONCLUSIONS: Cordopexy alone did not improve airflow in a left laryngeal hemiplegic model. Cordopexy plus modified laryngoplasty was as efficacious as the standard laryngoplasty in alleviating the effects of left laryngeal hemiplegia on TI, glottic CSA, and arytenoid RLQ. CLINICAL RELEVANCE: Fixation of the vocal cord (cordopexy) in addition to a laryngoplasty procedure may prove useful in the surgical treatment of equine laryngeal hemiplegia.

Effects of extrathoracic airway obstruction on intrathoracic pressure and pulmonary artery pressure in exercising horses.

OBJECTIVE: To determine whether dorsal displacement of the soft palate (DDSP) results in pulmonary artery hypertension and leads to increases in transmural pulmonary artery pressure (TPAP); to determine whether pulmonary hypertension can be prevented by prior administration of furosemide; and to determine whether tracheostomy reduces pulmonary hypertension. ANIMALS: 7 healthy horses. PROCEDURE: Horses were subjected to 3 conditions (control conditions, conditions after induction of DDSP, and conditions after tracheostomy). Horses were evaluated during exercise after being given saline (0.9% NaCl) solution or furosemide. RESULTS: Controlling for drug, horse, and speed of treadmill, DDSP-induced increase in intrathoracic pressure was associated with a significant increase in minimum (36 mm Hg), mean (82 mm Hg), and maximum (141 mm Hg) pulmonary artery pressure, compared with values for control horses (30, 75, and 132 mm Hg, respectively). Increases in pulmonary artery pressure did not induce concomitant increases in TPAP. Tracheostomy led to a significant reduction of minimum (53 mm Hg), and mean (79 mm Hg) TPAP pressure, compared with values for control horses (56 and 83 mm Hg, respectively). When adjusted for horse, speed of treadmill, and type of obstruction, all aspects of the pulmonary artery and TPAP curves were significantly decreased after administration of furosemide, compared with those for horses given saline (0.9% NaCl) solution. CONCLUSIONS: DDSP was associated with increases in pulmonary artery pressure but not with increases in TPAP. CLINICAL RELEVANCE: Expiratory obstructions such as DDSP are likely to result in pulmonary hypertension during strenuous exercise, but may not have a role in the pathogenesis of exercise-induced pulmonary hemorrhage.

Pulmonary capillary pressure in horses undergoing alteration of pleural pressure by imposition of various upper airway resistive loads.

We hypothesized that changes in pleural pressure induced by resistive breathing would affect transmural pulmonary artery, pulmonary capillary, and pulmonary wedge pressures. Seven horses were assigned to exercise with each of 4 upper respiratory resistive loads in random order at intervals of at least 2 days: 1) control--no added resistive loads; 2) inspiratory resistive load (Iobst)--left laryngeal hemiplegia; 3) expiratory resistive load (Eobst)--one-way valve in the right nostril; and 4) combined inspiratory and expiratory resistive loads (CIEobst)--left nostril occlusion. On each occasion, the horses performed an incremental exercise protocol consisting of exercise episodes of 3 min duration at 75, 90, and 100% of maximal heart rate (HRmax). Pulmonary artery and oesophageal pressures were recorded continuously. Subsequent analysis was carried out on the pulmonary arterial pressure signal with the oesophageal pressure signal subtracted, hence the pulmonary vascular pressures in this paper approximate transmural pressures. Pulmonary vascular pressures, heart rate, and arterial blood gas tensions were measured at each level of exercise. Pulmonary capillary and pulmonary wedge pressures were determined from the pulmonary artery waveform after dynamic occlusion of a branch of the pulmonary artery. During exercise, peak expiratory oesophageal pressure was more positive in horses with Eobst and CIEobst (adjusted means = 43, and 39 mmHg, respectively) compared with control (adjusted mean = 23 mmHg) (P = 0.0001). Peak inspiratory oesophageal pressure was more negative in horses at exercise with Iobst and CIEobst (adjusted means = -42 and -39 mmHg, respectively) compared with control (adjusted mean = -26 mmHg) (P = 0.0012). Eobst was associated with an increase in mean oesophageal pressure while Iobst was associated with a decrease in mean oesophageal pressure. There were significant increases in mean pulmonary artery pressure in horses with CIEobst (adjusted means = 82 mmHg) and in pulmonary wedge pressure in horses with CIEobst and Iobst (adjusted means = 51, and 55 mmHg, respectively) when compared to control (73 and 42 mmHg, respectively) (P = 0.0001). Pulmonary capillary pressure was significantly increased in horses with CIEobst or Iobst (adjusted means = 61 mmHg, 63 mmHg, respectively) when compared to control (adjusted mean = 50 mmHg)(P = 0.0001). At maximal exercise intensity with inspiratory obstruction, the mean oesophageal (pleural) pressure was -17 mmHg while the mean pulmonary capillary pressure was 77 mmHg. The latter exceeds the reported 75 mmHg threshold for capillary failure in horses. We conclude that inspiratory resistive breathing can lead to a significant increase in transmural pulmonary capillary pressure which may contribute to loss of capillary integrity and rupture.

Effects of frusemide on pulmonary capillary pressure in horses exercising on a treadmill.

We hypothesised that frusemide would decrease pulmonary capillary pressure in horses during strenuous exercise. Seven horses were tested after receiving saline or frusemide (2 mg/kg bwt) in random order with an interval of at least one week. Measurements were made with the horses standing, exercising at 75, 90 and 100% HRmax (maximal heart rate), and then walking 2 min after cessation of 100% HRmax. The exercise tests lasted for approximately 3 min with an interval of walking between them. Pulmonary artery and oesophageal pressures were recorded continuously and subsequent analysis of the pulmonary artery pressure signal was carried out after subtraction of the oesophageal pressure signal. Pulmonary arterial pressure, pulmonary capillary pressure, pulmonary artery wedge pressure, breathing rate, heart rate and arterial blood gas tensions were recorded at each level of exercise. Pulmonary arterial wedge and pulmonary capillary pressures were determined from the pulmonary arterial waveform after dynamic occlusion of a branch of the pulmonary artery. The resulting decay in pressure was submitted to exponential curve fitting and the amplitude on this curve at the moment of occlusion was recorded as pulmonary capillary pressure. When adjusted for horse and exercise intensity, horses receiving frusemide had lower pulmonary capillary and wedge pressures (adjusted least-squares means = 36 mmHg and 28 mmHg, respectively) when compared with control values (adjusted least-squares means = 41 mmHg (P = 0.042) and 35 mmHg (P = 0.002), respectively). Pulmonary arterial pressure, breathing rate, heart rate and arterial blood gas tensions did not differ between treatments at any exercise intensity. We conclude that frusemide reduces pulmonary capillary and wedge pressures. This is compatible with reduced transcapillary filtration and, therefore, reduced accumulation of lung water at exercise. It may also account for the putative protective effect of frusemide against exercise-induced pulmonary haemorrhage.

Oral nitroglycerin paste did not lower pulmonary capillary pressure during treadmill exercise.

We hypothesised that 22.5 mg of oral nitroglycerin would cause pulmonary vasodilation and therefore decrease pulmonary capillary pressure in horses during strenuous exercise. Six horses were assigned to exercise twice, once with no medication (control) and once with nitroglycerin (22.5 mg orally) in random order. Horses were exercised for 3 min each at 75, 90 and 100% of maximal heart rate (HRmax) with a 2 min period of walking between each period of exertion. Pulmonary artery and oesophageal pressures were recorded continuously. Subsequent analysis was carried out on the pulmonary arterial pressure signal with the oesophageal pressure subtracted, hence pulmonary vascular pressures reported in this paper approximate transmural pressures. Pulmonary arterial pressure, pulmonary arterial wedge pressure, pulmonary capillary pressure, heart rate and arterial blood gas tensions were determined for each level of exercise. Pulmonary arterial wedge and pulmonary capillary pressures were determined from the pulmonary artery waveform after dynamic occlusion of a branch of the pulmonary artery. The resulting decay in pulmonary artery pressure was submitted to an exponential curve fitting and the amplitude at the moment of occlusion on this curve was recorded as pulmonary capillary pressure. The effects of nitroglycerin on the various parameters were evaluated using a 3-way ANOVA blocked on horse treatment, and exercise intensity, followed by Tukey's multiple comparison procedure. Resting pulmonary artery pressure decreased from mean +/- s.e. 34.0 +/- 5.5 mmHg to 24.0 +/- 3.9 mmHg 5 min after administration of nitroglycerin (P < 0.05) but there were no significant effects on pulmonary capillary or wedge pressures. Nitroglycerin at this dose resulted in no significant differences in pulmonary artery, pulmonary capillary, and pulmonary wedge pressure, heart rate, arterial oxygen tension or arterial carbon dioxide tension at 75, 90 and 100% of HRmax. This dose of nitroglycerin does not appear significantly to protect the pulmonary vascular bed from exercise-induced hypertension. These data do not support the use of this dose of oral nitroglycerin in the prevention of EIPH.

Effects of airway obstruction on transmural pulmonary artery pressure in exercising horses.

OBJECTIVE: To determine whether laryngeal hemiplegia would increase transmural pulmonary artery pressure (TPAP). ANIMALS: 6 horses. DESIGN: Horses were studied under 5 conditions: control conditions, after induction of left laryngeal hemiplegia, during obstruction of the left nostril, after placement of an instrumented tracheostomy, and after placement of an open tracheostomy. Horses were evaluated after being given saline solution and after being given furosemide. PROCEDURES: Horses were exercised on a high speed treadmill, using a maximum speed of 13 m/s. During each exercise, airway pressures, airflow, esophageal and pulmonary artery pressures, and blood gas partial pressures were measured. RESULTS: When adjusted for horse, speed, and obstruction condition, mean TPAP (pulmonary artery pressure-esophageal pressure) and minimum TPAP were significantly lower after administration of furosemide than after administration of saline solution. In horses given saline solution, respiratory obstruction that increased intrapleural pressure significantly increased mean TPAP, and respiratory obstruction that decreased intrapleural pressure significantly decreased minimum TPAP. CONCLUSIONS: Changes in intrapleural pressure appear to play an important role in pulmonary artery pressure and TPAP. CLINICAL RELEVANCE: Because induction of laryngeal hemiplegia did not increase TPAP, laryngeal hemiplegia is unlikely to contribute to development of exercise-induced pulmonary hemorrhage.

The effect of exercise on diaphragmatic activation in horses.

Horses chronically-instrumented with costal diaphragmatic electromyographic electrodes were studied during exercise while unencumbered by a breathing mask. Exercise-associated changes in esophageal (Pes), gastric (Pga) and transdiaphragmatic (Pdi) pressures were measured and related to diaphragmatic electromyographic activity (CS EMG) and to left forelimb impact. In all breaths examined, CS EMG always coincided with decrements in Pes. For all exercise trials, linear increases in CS EMG, Pga and Pdi and linear decreases in Pes, as a function of exercise intensity, always occurred. During all gaits, breathing frequency (fR) was entrained with stride frequency (fS) one for one. However, a constant phase-coupling relationship between fR and fS, observed when horses cantered and galloped, was absent when horses walked or trotted. We conclude that biomechanical forces contribute minimally to ventilation in exercising horses, that the diaphragm is always phasically active during each breath and its total electrical activity and mechanical output are proportional to the exercise hyperpnea.

Spinal accessory nerve biopsy as an ante mortem diagnostic test for equine motor neuron disease.

The effectiveness of spinal accessory nerve branch biopsy evaluation as a means to confirm the diagnosis of equine motor neuron disease (EMND) was investigated. Sixteen horses with histories and clinical signs suggestive of EMND and 16 control horses with neither histories nor clinical signs of any neurological disorder, were subjects of the study. Biopsy samples of the ventral branch of the spinal accessory nerve were obtained either surgically, under general anaesthesia or post mortem immediately after euthanasia. Evaluation was done on the spinal cord of all horses to serve as the definitive diagnostic indicator of EMND. Results indicate that biopsy of the ventral branch of the spinal accessory nerve is a reliable ante mortem diagnostic test for EMND. Histological evidence of the degeneration of myelinated axons is present in both acute and arrested cases. The ventral branch of the spinal accessory nerve is easy to approach surgically and biopsy of the nerve causes no disfigurement of the sternocephalicus muscle. The use of semi-thin Epon sections is an excellent method of sample preparation. Formalin fixation and routine paraffin embedment may prove more accessible and provide good quality preparations for reliable interpretation. In the hands of an experienced pathologist, the sensitivity and specificity reliability coefficients for spinal accessory nerve branch biopsy are 94%, making this technique an extremely valuable diagnostic tool for the ante mortem diagnosis of EMND.

Measurement of upper airway pressures in exercising horses with dorsal displacement of the soft palate.

To determine whether abnormal airway pressures have a role in development of dorsal displacement of the soft palate (DDSP), measurements of tracheal and pharyngeal pressures were correlated with nasopharyngeal morphology in exercising horses. Exercising videoendoscopy and measurement of tracheal and pharyngeal pressures were used in 14 clinically normal horses and 19 horses with intermittent DDSP. The pressure signals were superimposed on the videoendoscope image, and both images were saved simultaneously on a videocassette for slow motion analysis to determine the instant displacement occurred in the respiratory cycle. Horses were submitted to an escalating 8-minute high-speed test with a maximal speed of 14 m/s. Compared with clinically normal horses, horses with intermittent DDSP did not have excessively negative inspiratory pressures during exercise. Eight horses displaced the soft palate during inspiration, 4 horses displaced it during expiration, and 7 displaced it by swallowing. Some horses displaced the soft palate at the beginning of the exercise trial, before reaching maximal speed, some horses displaced it at the peak speed, and some horses displaced it when slowing down. Epiglottic size in horses with DDSP was within normal limits, ruling out epiglottic hypoplasia as a cause of DDSP during exercise. Airway pressures were significantly (P < 0.002) altered after DDSP. Pharyngeal and tracheal inspiratory pressures were less negative, whereas pharyngeal expiratory pressure became less positive and tracheal expiratory pressure became more positive after displacement, suggesting a decrease in airflow and an increase in expiratory resistance in the upper airway.

Regulation of respiratory muscle activities during chemoreceptor stimulation in adult horses.

We examined the electromyographic activity of the costal portion of the diaphragm and the transverse abdominal and external oblique muscles in 6 chronically instrumented awake adult horses during eupneic breathing, during 2 levels of hypercapnia (fractional concentration of inspired CO2; FICO2 = 0.4 and 0.6), and during 2 levels of hypocapnic hypoxia (FIO2 = 0.15 and 0.12). Using the inert gas technique, we also measured the end-expiratory lung volumes of the 6 horses during eupnea, 6% CO2 challenge, and 12% O2 breathing. During eupneic breathing, phasic electrical activity of these 3 muscles was always present and was preceded by the onset of mechanical flow. At progressive levels of hypercapnia, the magnitude of inspiratory and expiratory electrical activity increased, and for the expiratory muscles, this recruitment coincided with significant (P < 0.05) increases in peak expiratory gastric pressure. However, during hypocapnic hypoxia, differential recruitment patterns of the respiratory muscles were found. The electrical activity of the diaphragm increased in magnitude and occurred sooner relative to the onset of mechanical flow. The magnitude and onset of abdominal expiratory activity failed to increase significantly during these episodes of hyperpnea and this pattern of activity coincided with decrements in peak expiratory gastric pressure. Despite alterations in muscle recruitment patterns during these hyperpneic episodes, end-expiratory lung volume remained unchanged. Thus, we conclude that adult horses respond similarly to awake dogs during peripheral and central chemoreceptor stimulation.

Laparoscopic repair of a bladder rupture in a foal.

Ruptured bladder was diagnosed in a 90-day-old Thoroughbred colt that had suffered a open, comminuted tibial fracture 2 days earlier. The bladder rupture was identified by laparoscopic examination of the abdomen and was repaired using a laparoscopic stapling instrument. This technique provided good visualization and allowed repair of the rupture with minimal intervention. Ten months after surgery, the foal was admitted to a referral surgical practice because of colic and stanguria. A urinary calculus was removed from the penile urethra by urethrotomy. Laparoscopic repair of the bladder with nonabsorbable staples may be contraindicated because of possible urolith formation.

Repeatability and normal values for measurement of pharyngeal and tracheal pressures in exercising horses.

Repeatability of measurements of peak and mean tracheal and pharyngeal pressures in exercising horses was determined. Five athletically fit horses were subjected to repeated (n = 5) standardized exercise trials. Static pressures in the trachea, nasopharynx, and mask were determined. At least 96% of all mean pressure measurements were within 5 cm of H2O of the mean value for any horse. Peak pressure measurements were less repeatable, but at least 96% of all measurements were within 10 cm of H2O of the mean peak measurements for any horse. In 10 horses galloping at 14 m/s, the 95% confidence interval for peak tracheal and pharyngeal inspiratory pressures ranged from -40 to -50 cm of H2O and -20 to -26 cm of H2O, respectively. During expiration, the 95% confidence interval for peak tracheal and pharyngeal pressure at the same speed ranged from 15 to 28 cm of H2O and 10 to 24 cm of H2O respectively. During inspiration, horses with induced laryngeal hemiplegia had static pressure measurements generally outside that range. We conclude that determination of tracheal and pharyngeal pressures is a potentially useful adjunct for assessment of the proximal portion of the respiratory tract.