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.     

Dynamic respiratory endoscopy of Standardbred racehorses during qualifying races

Reason for performing study: Examination of the equine upper airway during racing has not previously been documented. Objective: To describe the feasibility and appearance of the upper airways by overground respiratory endoscopic examination during racing conditions. Methods: Overground videoendoscopic examinations were performed on 46 Standardbred racehorses during qualifying races. Examined horses' speeds were recorded throughout the race with a portable GPS device. Results: The procedure did not interfere with performance as there were no significant differences in race times between races in which horses were examined with the endoscope in place and prior unexamined races. Airway obstructions during or after the race were documented in 21 horses. Most previously reported causes of upper airway obstruction were observed; surprisingly bilateral ventro‐medial arytenoid displacement (VMAD; n = 5) was seen during exercise as frequently as dorsal displacement of the soft palate (DDSP). Although DDSP (n = 10) was the most common diagnosis made, many displacements (n = 5) occurred after the race. Horses that demonstrated DDSP after the race had slower speeds than unaffected horses during the race. Conclusions: Racing endoscopy permits the diagnosis of upper airway obstructions without affecting performance. The occurrence of DDSP immediately after exercise may be clinically relevant. During racing VMAD may be an important anomaly. Potential relevance: Racing endoscopy could be used to correlate the sensitivity of diagnostic endoscopy during race‐training or treadmill examination. The pathogenesis and significance of VMAD deserves further investigation.     

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.     

Successful treatment of persistent dorsal displacement of the soft palate and evaluation of laryngohyoid position in 15 racehorses

Reasons for performing study: Caudal descent of the larynx has been proposed to be associated with intermittent dorsal displacement of the soft palate (DDSP) as it leads to a loss of the seal between the epiglottis and soft palate but further investigation of this theory is required. Objectives: To evaluate laryngohyoid position of horses with persistent DDSP in comparison to horses with intermittent DDSP and evaluate the outcome of treatment. Hypotheses: Horses with persistent DDSP have a different laryngohyoid position compared to those with intermittent DDSP. Horses with persistent DDSP can be returned successfully to racing with a laryngeal tie‐forward procedure. Methods: Medical records of 15 racehorses presented for persistent DDSP between 2002 and 2007 were reviewed. Age, sex and breed matched horses diagnosed with intermittent DDSP were used as a comparison group. Treatment of all horses was performed by laryngeal tie‐forward, 8/15 horses with persistent DDSP had a subsequent laser staphylectomy. Preoperative laryngohyoid position was compared between the 2 groups using a radiographic reference system. Surgical effect on position was assessed by comparing pre‐ and post operative radiographic measurements. Outcome was assessed by return to racing and comparison of pre‐ and post operative race earnings ($). Results: Thirteen of 15 horses with persistent DDSP returned to racing. Seven of 15 horses were treated with laryngeal tie‐forward alone while 8/15 horses were also treated with a laser staphylectomy. Horses with persistent DDSP had a more caudal larynx (ossification of the thyroid cartilage) (13 mm, P = 0.014), a more caudal (10 mm, P = 0.044) and dorsal (7 mm, P = 0.01) basihyoid bone, and a more dorsal thyrohyoid‐thyroid articulation (10 mm, P = 0.002) than horses with intermittent DDSP. Conclusions and potential relevance: Racehorses with persistent DDSP can be treated successfully by laryngeal tie‐forward or by laryngeal tie‐forward followed by laser staphylectomy. Horses with persistent DDSP have a more caudal larynx and more caudal and dorsal basihyoid bone than horses with intermittent DDSP.     

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.     

Spectrum analysis of respiratory sounds in exercising horses with experimentally induced laryngeal hemiplegia or dorsal displacement of the soft palate

OBJECTIVE: To record respiratory sounds in exercising horses and determine whether spectrum analysis could be use to identify sounds specific for laryngeal hemiplegia (LH) and dorsal displacement of the soft palate (DDSP). ANIMALS: 5 Standardbred horses. PROCEDURE: Respiratory sounds were recorded and pharyngeal pressure and stride frequency were measured while horses exercised at speeds corresponding to maximum heart rate, before and after induction of LH and DDSP. RESULTS: When airway function was normal, expiratory sounds predominated and lasted throughout exhalation. After induction of LH, expiratory sounds were unaffected; however, all horses produced inspiratory sounds characterized by 3 frequency bands centered at approximately 0.3, 1.6, and 3.8 kHz. After induction of DDSP, inspiratory sounds were unaffected, but a broad-frequency expiratory sound, characterized by rapid periodicity (rattling) was heard throughout expiration. This sound was not consistently detected in all horses. CONCLUSIONS AND CLINICAL RELEVANCE: The technique used to record respiratory sounds was well tolerated by the horses, easy, and inexpensive. Spectrum analysis of respiratory sounds from exercising horses after experimental induction of LH or DDSP revealed unique sound patterns. If other conditions causing airway obstruction are also associated with unique sound patterns, spectrum analysis of respiratory sounds may prove to be useful in the diagnosis of airway abnormalities in horses.     

Dorsal displacement of the soft palate in 92 horses during high-speed treadmill examination (1993-1998)

OBJECTIVE: To evaluate the occurrence of dorsal displacement of the soft palate (DDSP) during high-speed treadmill (HSTM) exercise in racehorses, and determine treatment efficacy relative to the endoscopic findings observed during resting and HSTM endoscopic examination. STUDY DESIGN: Retrospective study. Animals-Ninety-two racehorses (74 Thoroughbreds, 18 Standardbreds). METHODS: The signalment, history (clinical and race), treatments, and video recordings made during resting and HSTM endoscopy were reviewed in 92 racehorses that developed DDSP during HSTM exercise. Only horses that completed 3 starts before and after HSTM examination were included in performance-outcome analysis. Statistical associations were made between the independent variables (the historical findings and the resting and HSTM endoscopic findings) and performance outcome. RESULTS: Forty-five horses (49%) displaced their palate in an uncomplicated manner, whereas the other horses either had another upper-respiratory abnormality in association with DDSP (35) or displaced after swallowing (12). Although respiratory noise was not recorded during HSTM exercise, only 57 horses (62%) that developed DDSP during HSTM examination had a history of abnormal upper-respiratory noise. For the 45 horses that met the criteria for performance outcome analysis, there were no independent variables recorded during resting or HSTM endoscopy that had a significant association with performance outcome. Treatment for DDSP varied by clinician. Overall, 29 horses (64%) had improved average earnings per start after diagnosis and treatment. CONCLUSIONS: Thirty-five horses (38%) that had DDSP during HSTM endoscopy had no previous history of abnormal upper-respiratory noise, and 74 (80%) had no structural abnormalities noted on resting endoscopic examination. CLINICAL RELEVANCE: HSTM examination is an excellent tool for diagnosis of DDSP and the manner in which it occurs. DDSP did not occur similarly in all horses, and was often associated with another upper-respiratory abnormality. Thus, it is unlikely that a single treatment can be applied effectively for all horses that experience DDSP. Both surgical and medical treatments can be beneficial in improving a horse's performance after a diagnosis of DDSP is made. Neither resting nor HSTM endoscopic findings were clearly prognostic.     

Transendoscopic Nd:YAG Laser Surgery for Treatment of Epiglottal Entrapment and Dorsal Displacement of the Soft Palate in the Horse

Transendoscopic neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used to treat 12 standing horses with epiglottic entrapment (EE) or dorsal displacement of the soft palate (DDSP), or both. In four horses, transendoscopic laser staphylectomy was performed. The most common presenting complaints were respiratory stridor, cough, and exercise intolerance. Ten horses with EE healed without epiglottic complications; in one horse, partial adhesion of the aryepiglottic fold to one side of the epiglottis was corrected surgically through a laryngotomy incision. One horse with DDSP had no further signs, one continued to have continual DDSP, and two had induced DDSP. Transendoscopic Nd:YAG laser proved to be a feasible means of correcting EE and selected cases of DDSP.     

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.     

Exercising upper respiratory videoendoscopic evaluation of 100 nonracing performance horses with abnormal respiratory noise and/or poor performance

Reasons for performing study: Although well documented in racehorses, there is paucity in the literature regarding the prevalence of dynamic upper airway abnormalities in nonracing performance horses. Objective: To describe upper airway function of nonracing performance horses with abnormal respiratory noise and/or poor performance via exercising upper airway videoendoscopy. Methods: Medical records of nonracing performance horses admitted for exercising evaluation with a chief complaint of abnormal respiratory noise and/or poor performance were reviewed. All horses had video recordings of resting and exercising upper airway endoscopy. Relationships between horse demographics, resting endoscopic findings, treadmill intensity and implementation of head and neck flexion during exercise with exercising endoscopic findings were examined. Results: Dynamic upper airway obstructions were observed in 72% of examinations. Head and neck flexion was necessary to obtain a diagnosis in 21 horses. Pharyngeal wall collapse was the most prevalent upper airway abnormality, observed in 31% of the examinations. Complex abnormalities were noted in 27% of the examinations. Resting laryngeal dysfunction was significantly associated with dynamic arytenoid collapse and the odds of detecting intermittent dorsal displacement of the soft palate (DDSP) during exercise in horses with resting DDSP was only 7.7%. Exercising endoscopic observations were different from the resting observations in 54% of examinations. Conclusions: Dynamic upper airway obstructions were common in nonracing performance horses with respiratory noise and/or poor performance. Resting endoscopy was only helpful in determining exercising abnormalities with recurrent laryngeal neuropathy. Potential relevance: This study emphasises the importance of exercising endoscopic evaluation in nonracing performance horses with abnormal respiratory noise and/or poor performance for accurate assessment of dynamic upper airway function.     

Correlation of resting and exercising endoscopic findings for horses with dynamic laryngeal collapse and palatal dysfunction

Reasons for performing study: To correlate resting and exercising endoscopic grades of laryngeal function in horses undergoing high‐speed treadmill endoscopy (HSTE) using the Havemeyer grading system. To correlate dorsal displacement of the soft palate (DDSP) seen at rest with palatal function during exercise. Methods: Records of horses that underwent HSTE examination (1999–2009) were reviewed. Resting laryngeal function score and other abnormalities noted on resting endoscopy were recorded as were results of HSTE. Results of resting and exercising endoscopic findings were correlated. Results: 281 horses underwent HSTE. There was significant correlation between grade of laryngeal function at rest (grades 1–4) and exercise (ρ= 0.53, P<0.001) and between resting subgrades 3.1, 3.2 and 3.3 and exercising grades of laryngeal function (ρ= 0.43, P = 0.0017). DDSP was observed at rest significantly more often in horses that developed DDSP during HSTE than those without DDSP during HSTE (RR = 4.1, P<0.001). The sensitivity and specificity of DDSP seen during resting endoscopy as a test for DDSP occurring during exercise were 25.5 and 95.1% respectively (positive predictive value 0.57, negative predictive value 0.83). Conclusions and potential relevance: The results of the current study support the use of the Havemeyer system for grading laryngeal function in the resting horse, and corroborate findings of previous studies correlating resting and exercising palatal abnormalities. Studies that use the presence of spontaneous DDSP during resting endoscopic examination as an inclusion criterion for investigating efficacy of treatments for DDSP are likely to have a low proportion of horses with false positive diagnoses.     

Effects of stylopharyngeus muscle dysfunction on the nasopharynx in exercising horses

REASONS FOR PERFORMING STUDY: Nasopharyngeal collapse has been observed in horses as a potential cause of exercise intolerance and upper respiratory noise. No treatment is currently available and affected horses are often retired from performance. OBJECTIVE: To determine the effect of bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction on nasopharyngeal function and airway pressures in exercising horses. METHODS: Endoscopic examinations were performed on horses at rest and while running on a treadmill at speeds corresponding to HRmax50, HRmax75 and HRmax, with upper airway pressures measured with and without bilateral glossopharyngeal nerve block. RESULTS: Bilateral glossopharyngeal nerve block caused stylopharyngeus muscle dysfunction and dorsal nasopharyngeal collapse in all horses. Peak inspiratory upper airway pressure was significantly (P = 0.0069) more negative at all speeds and respiratory frequency was lower (P = 0.017) in horses with bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction compared to control values. CONCLUSIONS: Bilateral glossopharyngeal nerve anaesthesia produced stylopharyngeus muscle dysfunction, dorsal pharyngeal collapse and airway obstruction in all horses. POTENTIAL RELEVANCE: The stylopharyngeus muscle is probably an important nasopharyngeal dilating muscle in horses and dysfunction of this muscle may be implicated in clinical cases of dorsal nasopharyngeal collapse. Before this information can be clinically useful, further research on the possible aetiology of stylopharyngeus dysfunction and dysfunction of other muscles that dilate the dorsal and lateral walls of the nasopharynx in horses is needed.     

Assessment of the efficacy of composite surgery for the treatment of dorsal displacement of the soft palate in a group of 53 racing Thoroughbreds (1990-1996)

REASONS FOR PERFORMING STUDY: There has been no objectively assessed case-control study of the efficacy of surgery to correct dorsal displacement of the soft palate (DDSP) previously reported. HYPOTHESIS: Composite surgery has a beneficial result on racing performance in horses affected with DDSP as compared to a matched control population. METHODS: Race records were obtained for 53 racing Thoroughbreds which underwent composite staphylectomy, sternothyrohyoideus myectomy and ventriculectomy for correction of idiopathic DDSP at the University of Bristol between 1990 and 1996. Each surgical case was matched for age, sex and training yard with 2 control horses. The racing performance, based on prize money won, of surgical cases and control horses were compared for 3 races run before and after the date of surgery. RESULTS: Ninety-two percent of the surgical cases returned to racing after surgery. There was a significant increase in earnings of the surgical group before and after surgery (P = 0.011), but there was no significant difference in earnings of the control group before and after the date of surgery (P = 0335). Sixty percent of the surgical group had higher earnings after surgery than before, compared to 40% of controls. When horses which underwent surgery were ranked relative to their 2 matched controls, surgical cases did not significantly change in rank (P = 033), whereas control horses significantly decreased in rank (P = 0.012). Additionally, horses within the surgical group were more likely (P < 0.01) to start in 3 post operative races than those in the control group. CONCLUSIONS AND POTENTIAL RELEVANCE: Composite surgery had a beneficial effect on racing performance of horses afflicted with idiopathic DDSP, and further studies to evaluate objectively the usefulness of other surgical techniques are warranted.     

The displaced equine soft palate as a source of abnormal respiratory noise during expiration

REASONS FOR PERFORMING STUDY: To develop the technique of respiratory sound analysis for the diagnosis of dorsal displacement of the equine soft palate. OBJECTIVES: To show that 1) the displaced soft palate can spontaneously vibrate in the presence of expiratory airflow; 2) the observed frequency of vibration can be detected in respiratory sound recordings; and 3) the frequency of vibrations measured in cadaveric specimens are similar to those obtained from audio spectra in exercising horses with DDSP. METHODS: Palatal movements and respiratory sounds were recorded from artificially ventilated cadaveric heads. The fundamental mode of palate vibrations calculated from high-speed videoendoscopic recordings was compared with frequencies detected in the audio spectra and with data collected from exercising horses with DDSP. RESULTS: Palate vibrations occurred when air was blown through the trachea. The fundamental mode of vibrations was present in the audio spectra and was not significantly different from those recorded in vivo. CONCLUSIONS: Vibrations of the soft palate are the probable source of expiratory sounds recorded in horses with DDSP. POTENTIAL RELEVANCE: This study strengthens the case for the application of respiratory sound analysis in the diagnosis of DDSP in exercising horses.     

The effect of palatal dysfunction on measures of ventilation and gas exchange in Thoroughbred racehorses during high intensity exercise

Reason for performing study: The effect of palatal instability (PI) on measures of ventilation and gas exchange is not well understood. Objectives: To assess to what degree different severities of naturally occurring palatal dysfunction affect ventilation and gas exchange during strenuous exercise. Methods: A retrospective study was performed using data collected from 40 Thoroughbred racehorses diagnosed with naturally occurring dynamic palatal dysfunction during high speed treadmill exercise. Upper airway videoendoscopic recordings were made concurrently with measurements of ventilation and gas exchange. Three categories of soft palate dysfunction were formed: mild palatal instability; moderate to severe palatal instability; and dorsal displacement of the soft palate (DDSP). Minute ventilation, tidal volume, breathing frequency, end‐tidal carbon dioxide and oxygen concentrations, oxygen consumption and carbon dioxide production were calculated during the last 10 s of the exercise test, when airway obstruction was at its worst. Results: There was a trend for minute ventilation, tidal volume, oxygen consumption and carbon dioxide production to decrease with increasing degree of palatal dysfunction, although statistically significant differences were only seen with DDSP. End‐tidal carbon dioxide increased and end‐tidal oxygen decreased with increasing obstruction, with both parameters showing significant differences between mild PI and moderate to severe PI. Conclusions: The results suggest that PI has a negative effect on certain respiratory parameters, although this is not as great as that associated with DDSP. Potential relevance: Palatal instability may be detrimental to athletic performance even when progression to DDSP does not occur.     

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.     

Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty for treatment of dorsal displacement of the soft palate in 102 thoroughbred racehorses

Objective— To compare racing performance before and after sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty in Thoroughbred racehorses with intermittent dorsal displacement of the soft palate (DDSP).
Study Design— Retrospective study.
Animals— Thoroughbred racehorses (n=102) with DDSP.
Methods— Retrieved data included signalment, primary complaint, and upper respiratory tract endoscopic finding. Lifetime race records were compared for earnings per start before and after surgery, days to 1st start, and races won postoperatively.
Results— Comparing mean earnings per start for 3 races before ($2792) and after ($3806) surgery, racing performance improved significantly after surgery in 63% (46/73) of horses that competed in at least 1 race before and after surgery ( P =.02). Mean and median days to 1st start after surgery were 109 and 69 days, respectively. Of horses that raced postoperatively 65% (60/92) won at least 1 race, and 77% (71/92) raced in >5 races after surgery.
Conclusions— Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty significantly improved racing performance in experienced Thoroughbred racehorses with performance limiting DDSP, and overall had a similar outcome to other reported surgical techniques for treatment of DDSP.
Clinical Relevance— Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty should be considered as a surgical approach to correction of DDSP in Thoroughbred racehorses; however, it is possible that staphylectomy may not be necessary to achieve a desirable outcome.     

Dynamic obstructions of the equine upper respiratory tract. Part 1: observations during high-speed treadmill endoscopy of 600 Thoroughbred racehorses

REASONS FOR PERFORMING STUDY AND OBJECTIVE: To review the prevalence of single and complex forms of dynamic airway obstructions within a large group of Thoroughbred horses in training referred for investigation of poor performance. METHODS: Video-endoscopic recordings of the upper respiratory tract made during a standardised treadmill exercise test of 600 Thoroughbred racehorses were reviewed and analysed in real time and slow motion to identify dynamic collapse by the tissues bordering onto the pharyngeal and laryngeal airways. RESULTS: Dynamic collapse within the nasopharynx or larynx was confirmed in 471 of the 600 horses. Dorsal displacement of the soft palate (DDSP; 50%) and palatal instability (33%) were the disorders most frequently identified. It was concluded that deglutition is not a significant event in the triggering of DDSP. Complex forms of dynamic collapse were present in 30% of the horses with upper respiratory tract obstructions. A significant influence of age on the prevalence of DDSP and dynamic laryngeal collapse was identified. There was an increased risk of DDSP in younger horses, and of laryngeal collapse in older horses. No association with gender or format of racing was identified. CONCLUSIONS AND POTENTIAL RELEVANCE: Palatal instability and DDSP comprised the most frequently encountered forms of dynamic collapse within the upper respiratory tract of the Thoroughbred racehorses in this study and are probably expressions of the same nasopharyngeal malfunction. Complex obstructions, i.e. where more than one structure collapses into the airway, occur frequently and therefore treatments that address solitary disorders may often be unsuccessful. Younger horses were found to be at greater risk of sustaining DDSP while older horses seemed more at risk to vocal cord collapse but not to collapse of the arytenoid cartilage itself.     

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.     

Sternothyroideus Tenectomy Combination Surgery: Treatment Outcome in 95 Thoroughbred Racehorses (1996–2006)

This retrospective case series reports on the clinical experiences of a group of Thoroughbred racehorses in training that were treated surgically for intermittent dorsal displacement of the soft palate (DDSP) using sternothyroideus tenectomy in combination with soft palate surgery. The 95 horses included in the study were Thoroughbred racehorses in training referred for surgical treatment of intermittent DDSP over a 10-year period. Return to racing was 94% (89/95). Total earnings increased for up to three starts before and after surgery in 65% of horses (62/95, P= .0006). Of the 58 horses that raced in three or more races before and after surgery, 71% (41/58) improved their total earnings. Mean days to first start were 106 days. Performance index improved in 64% of these horses (37/58). Sixty of the 95 horses (63%) raced in six or more races after surgery. Sternothyroideus tenectomy combination surgery had a good prognosis for improving earnings and performance index after surgery in this group of horses that were treated for a working diagnosis of intermittent DDSP.