Equitation and exercise factors affecting dynamic upper respiratory tract function: A review illustrated by case reports

The importance of undertaking appropriate exercise tests for the diagnosis of dynamic upper respiratory tract (URT) obstructions has been previously documented. Dynamic URT collapse is usually most severe during peak exercise; however, there are occasions when an URT collapse appears more severe during the immediate recovery period. In addition, equitation factors such as head and neck flexion and factors relating to the bit and bridle may induce or exacerbate dynamic URT collapse. The purpose of this paper was to review the literature and 5 cases within the authors' experience have also been included.     

Dynamic obstructions of the equine upper respiratory tract. Part 2: comparison of endoscopic findings at rest and during high-speed treadmill exercise of 600 Thoroughbred racehorses

REASONS FOR PERFORMING STUDY: The reliability of diagnoses of obstructive conditions of the upper respiratory tract (URT) based on examinations performed at rest vs. at exercise is controversial. OBJECTIVE: To compare diagnosis of URT by endoscopy at rest with that achieved during high-speed treadmill exercise (HSTE). HYPOTHESIS: Endoscopy of URT at rest, when performed in isolation from other simpler techniques is unreliable in the prediction of dynamic respiratory obstructions. METHODS: Endoscopic findings of 600 Thoroughbred racehorses during quiet breathing were compared with findings during high-speed treadmill exercise. Other parameters were also assessed for their specificity in diagnosis. RESULTS: Endoscopy of the resting horse showed low sensitivity (0.15) in the diagnosis of dorsal displacement of the soft palate (DDSP) and palatal instability (PI). When endoscopy and reported noises were taken together there was still a 35% misdiagnosis rate. Although there was significant association between resting laryngeal function score (LFS) and dynamic vocal cord and/or arytenoid cartilage collapse at exercise, 19% of horses with a grade 4/5 LFS were able to attain and maintain full abduction during exercise and 7% of those with 'normal' grades 1 or 2 LFS at rest showed dynamic laryngeal collapse when exerted. Sensitivity of the diagnostic model was greatly increased (80%) when a history of inspiratory noise and palpable intrinsic muscle atrophy were included. CONCLUSIONS AND POTENTIAL RELEVANCE: Endoscopy of the upper respiratory tract of static horses is unreliable in the diagnosis of dynamic obstructions of the URT and should not be used in isolation in surgical decision-making or in the assessment of horses at the time of sale.     

Clinical trials using a telemetric endoscope for use during over‐ground exercise: A preliminary study

Dynamic collapse of the upper respiratory tract (URT) is a common cause of poor performance in horses. These conditions occur predominantly during strenuous exercise when the URT is unable to maintain dilation in the face of high inspiratory pressures. In most cases, these disorders cannot be accurately diagnosed during a resting endoscopic examination. To date, a definitive diagnosis of dynamic URT obstructions has been possible only by performing an endoscopic examination during high‐speed treadmill exercise. However, recent technological advances now enable URT endoscopy to be performed while the horse is exercising in its normal environment.     

Dynamic respiratory endoscopy without treadmill in 68 performance Standardbred,Thoroughbred and saddle horses under natural training conditions

Reasons for performing study: High speed treadmill endoscopy provides a true assessment and diagnosis of the dynamic obstructions of the upper equine respiratory tract (DO‐URT). However, treadmills do not always allow reproduction of the exact conditions of dynamic collapse of the URT. The availability of on‐board endoscopes, which could be used without a treadmill, would make exercising endoscopy readily available to more equine practices. Objectives: To develop and validate an innovative endoscope which could be used for the examination of the URT at exercise in ridden and harnessed sport horses performing in natural conditions. Methods: Authors worked closely with engineers of a company manufacturing veterinary endoscopes. Over a 2‐year period several prototypes were tested on more than 20 cooperative horses performing either in trot, gallop, jumping or endurance. The final Dynamic Respiratory Scope (DRS) allows real‐time visualisation of the URT and video recordings for post test reviewing and archiving. The DRS was then tested in 2 equine livery yards. Performance horses presented for investigation of abnormal respiratory noises at exercise and/or poor performance were subjected to exercising endoscopy. Endoscopic images of the URT were recorded and video recordings of the URT were reviewed post test. Results: A total of 68 horses were examined: 39 harnessed Standardbred and 29 mounted horses (16 Thoroughbred and 13 saddle horses). Of these, 44 were diagnosed with a URT abnormality. Good quality videos were obtained even at maximum speed in all cases. The innovative insertion tube provided very stable images compared to those obtained with flexible video endoscopes on treadmills. Conclusions: This study validates the safety and the reliability of the DRS for imaging the equine URT during natural exercising conditions. Potential relevance: Most common causes of DO‐URT can be diagnosed easily during any type of performance without a treadmill and the DRS offers a great potential for further URT clinical research.     

Exercise testing in the equine athlete

In the last decade there have been significant technological advances and increases in the availability of portable diagnostic equipment for use in the assessment of athletic performance. The design and application of appropriate exercise tests are critical factors for the diagnosis of conditions affecting equine performance and it is therefore necessary for veterinary surgeons using such equipment to develop an understanding of appropriate exercise testing methods. This is the first in a series of three papers covering exercise testing in the equine athlete, interpretation of heart rate and rhythm during exercise and interpretation of dynamic upper respiratory tract function. In this first paper, both performance and clinical exercise testing in the equine athlete are reviewed.     

Dynamic respiratory endoscopy without a treadmill: Initial experiences

There are potential advantages to imaging the upper portion of the respiratory tract (URT) of horses during ridden exercise within their normal environment. With the advent of a wireless endoscope, this is now possible. The following article describes initial experiences using the dynamic respiratory endoscope (DRS) on horses presented for the investigation of poor performance or abnormal respiratory noise and suggests that this technique can be used to diagnose common causes of URT associated with poor performance in horses during normal training. This has substantial implications for future clinical diagnosis, treatment of URT pathology and equine welfare.     

Dynamic respiratory endoscopy in 67 Thoroughbred racehorses training under normal ridden exercise conditions

Reasons for performing study: There are potential advantages to imaging the upper portion of the respiratory tract (URT) of horses during ridden exercise. With the advent of a wireless endoscope, this is now possible. However, there has been no detailed validation of the technique and findings have not been compared to ridden speed. Objectives: To assess the combined use of a Dynamic Respiratory Scope (DRS) and global positioning system (GPS) receiver for examining the URT of a group of Thoroughbred racehorses randomly selected from a single flat racehorse training establishment. Methods: Horses were selected randomly from a population of Thoroughbred horses in training at the same training yard. Endoscopic images of the URT were recorded during a ridden exercise test on an ‘all‐weather‐gallop’ and were reviewed post testing. Speed was measured using a wrist mounted GPS receiver. Results: A total of 67 (34%) of the 195 horses in training were examined. Endoscopic findings included: normal URT function (44 cases); dorsal displacement of the soft palate (DDSP) (13 cases); laryngeal asymmetry (4 cases); and axial deviation of the aryepiglottic folds (3 cases). Maximum speed obtained by individual horses ranged from 41.8–56.3 km/h. Ridden speed was variably affected by DDSP. Conclusions: The DRS provides a safe effective system for imaging the equine URT during ridden exercise at speed. The abnormalities of the URT identified were similar to those observed during treadmill endoscopy studies reported in the literature. The effect of URT abnormalities on ridden speed requires further investigation. Potential relevance: This technique can be used to diagnose common causes of URT associated with poor performance in horses during normal training. This has substantial implications for future clinical diagnosis and treatment of URT pathology.     

Exercising Blood Gas Analysis, Dynamic Upper Respiratory Tract Obstruction, and Postexercising Bronchoalveolar Lavage Cytology—A Comparative Study in Poor Performing Horses

Respiratory abnormalities are common causes of decreased performance in horses presumably because of impaired pulmonary gas exchange. The objectives of the present study were to describe respiratory abnormalities in poorly performing horses and to investigate the relationships between dynamic upper respiratory tract (URT) videoendoscopy, postexercising bronchoalveolar lavage (BAL) cytology, and exercising arterial blood gas analysis. Medical records of 93 horses with exercise intolerance, which presented for treadmill evaluation, were reviewed. Relationships between horse demographics, treadmill endoscopic findings, exercising blood gas values, and BAL cytology results were examined. A total of 25 (27%) horses had a URT obstruction and 91 (98%) horses had abnormal BAL cytology; 73 (78%) had evidence of inflammatory airway disease (IAD) and 83 (89%) had exercise-induced pulmonary hemorrhage (EIPH). In all, 39 (42%) horses had abnormal blood gas values. Dynamic URT obstruction was significantly associated with exercising hypoxemia (P = .036). There were no significant relationships between gas exchange and IAD or between EIPH. Out of 24 (26%) horses with combined URT obstruction and abnormal BAL, horses with URT obstruction and EIPH were more likely to be hypoxic during exercise (P = .037). It was concluded that horses with dynamic URT abnormalities are likely to have exercising hypoxemia. Although IAD and EIPH were commonly indentified in poor performers, they were not significantly associated with abnormal exercising blood gas analysis.     

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.     

Spectral analysis of respiratory noise in horses with upper airway disorders

REASONS FOR PERFORMING STUDY: It has long been recognised that the production of abnormal respiratory sounds by horses during exercise is frequently associated with upper airway obstructions. Respiratory acoustic measurements have shown promise in investigation of upper airway disorders in man and, more recently, in horses with experimentally-induced obstructions. OBJECTIVES: To evaluate sounds from exercising horses with naturally occurring dynamic obstructions of the upper respiratory tract and to compare these with those from normal horses in order to determine whether different obstructions produce characteristic spectral patterns. METHODS: The audio signal, airflow and videoendoscopic images were recorded simultaneously during an incremental exercise test on a high-speed treadmill. RESULTS: Spectral analysis of the audio signal showed marked differences between control and clinically afflicted horses. Dorsal displacement of the soft palate was characterised by a narrow low frequency (20-80 Hz) peak during expiration. Horses with dynamic laryngeal collapse produced inspiratory sounds characterised by a broad band high frequency spectral component in the range 1.1-2.7 kHz. CONCLUSIONS AND POTENTIAL RELEVANCE: Spectral analysis of respiratory sounds in horses has potential as a diagnostic technique for field use especially when facilities for high-speed treadmill assessment are not practicable.     

Prevalence of Bordetella bronchiseptica in cats attended by a veterinary practice in the Manawatu region

AIMS: To determine the prevalence by isolation of Bordetella bronchiseptica infection in healthy cats and in cats showing signs of upper respiratory tract (URT) disease attended by a veterinary practice in the Manawatu region. METHODS: The nasal cavity and oropharynx of 100 cats of mixed sex and age were swabbed and the swabs cultured for B. bronchiseptica. The population of cats surveyed was that attended by the Massey University Veterinary Teaching Hospital, and included healthy cats, cats with clinical signs of URT disease, cats with a recent history of URT disease, cats from single cat households, cats from multiple-cat households, and cats from a colony. RESULTS: Bordetella bronchiseptica was recovered from 7 cats (5 from pharyngeal samples and 2 from nasal samples). Five of the 7 cats appeared to be healthy at the time of sampling, whilst 2 showed clinical signs of URT disease. Six of the 7 culture-positive cats were from a cat colony. The prevalence of B. bronchiseptica in healthy cats sampled was 7% and in cats with URT disease was 8%. CONCLUSION: This study confirms that B. bronchiseptica infection is present, but the prevalence of infection is low, in both healthy cats and in cats with URT disease attended by the Massey University Veterinary Teaching Hospital. It is unlikely that B. bronchiseptica infection is a frequent cause of feline URT disease of cats in this region.     

Prevalence of Bordetella bronchiseptica in cats attended by a veterinary practice in the Manawatu region

dAims:To determine the prevalence by isolation of Bordetella bronchiseptica infection in healthy cats and in cats showing signs of upper respiratory tract (URT) disease attended by a veterinary practice in the Manawatu region.

dMethods: The nasal cavity and oropharynx of 100 cats of mixed sex and age were swabbed and the swabs cultured for B. bronchiseptica. The population of cats surveyed was that attended by the Massey University Veterinary Teaching Hospital, and included healthy cats, cats with clinical signs of URT disease, cats with a recent history of URT disease, cats from single cat households, cats from multiple-cat households, and cats from a colony.

dResults: Bordetella bronchiseptica was recovered from 7 cats (5 from pharyngeal samples and 2 from nasal samples). Five of the 7 cats appeared to be healthy at the time of sampling, whilst 2 showed clinical signs of URT disease. Six of the 7 culture-positive cats were from a cat colony.The prevalence of B. bronchiseptica in healthy cats sampled was 7% and in cats with URT disease was 8%.

dConclusion: This study confirms that B. bronchiseptica infection is present, but the prevalence of infection is low, in both healthy cats and in cats with URT disease attended by the Massey University Veterinary Teaching Hospital. It is unlikely that B. bronchiseptica infection is a frequent cause of feline URT disease of cats in this region.     

Use of videoendoscopy during exercise for determination of appropriate surgical treatment of laryngeal hemiplegia in a colt

Videoendoscopy of the larynx during treadmill exercise was used to determine the surgical treatment of upper airway obstruction in a Standardbred colt. Surgical correction of right-sided laryngeal hemiplegia, first by laryngoplasty, then subtotal arytenoidectomy, was ineffective. Videoendoscopy indicated, and upper airway flow mechanics confirmed, that the laryngeal opening was adequate at rest, but obstruction occurred during exercise. On the basis of the appearance of the larynx during high airflow rates on slow-motion playback of the videorecording, total arytenoidectomy was performed, which permitted the horse to race successfully. Videoendoscopy of the upper airway during exercise accurately predicted airflow impedance and permitted salvage of this racehorse, indicating that this is a practical, useful technique that will improve evaluation of upper airway obstructions in the horse.     

Relative prevalence of upper respiratory tract obstructive disorders in two breeds of harness racehorses (185 cases: 1998-2006)

Reasons for performing study: Two genetically and phenotypically distinct horse breeds are used for harness racing in Scandinavia: the Standardbred (SB) and Coldblooded Trotter. These racehorses have identical environmental, management and racing conditions. Therefore, this study was undertaken to identify and compare the relative prevalence of upper respiratory tract (URT) obstructive disorders in these 2 breeds. Objectives: To determine whether these 2 phenotypically different breeds of harness racehorses have different predispositions for URT disorders. Methods: Retrospective study of 88 Norwegian Coldblooded Trotters (NCT) and 97 SBs referred to this hospital for URT evaluation between 1998 and 2006. Case records of all horses diagnosed with an URT disorder during resting endoscopy, and all horses undergoing high‐speed treadmill videoendoscopy (HSTV) with one or more periods of induced poll flexion were evaluated. The relative prevalence of URT disorders between the 2 breeds was analysed using a Fisher's exact test. Results: There was a significant (P<0.05) breed predisposition regarding 6 URT disorders. Bilateral dynamic laryngeal collapse associated with poll flexion and flaccid epiglottis was significantly more frequent in the NCT. Alar fold collapse and nasopharyngeal collapse were significantly more frequent in SBs. Epiglottic entrapment and nasal flutter were only diagnosed in the SBs. Dynamic disorders were more common than resting disorders in both breeds. Conclusion: URT obstructive disorders (dynamic laryngeal collapse associated with poll flexion, flaccid epiglottis, pharyngeal collapse, alar fold collapse, nasal flutter and epiglottic entrapment) are breed related, indicating an anatomic or functional cause. Periods of induced poll flexion during HSTV was essential to declare harness racehorses free of URT disorders. Potential relevance: Further anatomic or physiological studies comparing these breeds could potentially provide insight into the pathogenesis of certain URT obstructive disorders. Induced poll flexion should be included in routine HSTV examinations of all harness racehorses.     

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.     

Complex dynamic upper airway collapse: associations between abnormalities in 99 harness racehorses with one or more dynamic disorders

Reasons for performing study: Many horses demonstrate dynamic collapse of more than one upper respiratory tract (URT) structure during high‐speed treadmill videoendoscopy (HSTV). Objectives: To report the frequency of complex dynamic URT collapse in harness racehorses and determine if an association exists between occurrence of certain disorders. Methods: Retrospective study of 99 Standardbreds and Coldblooded trotters that had one or more dynamic URT disorders identified during HSTV between 1998 and 2006. The horses underwent HSTV using a protocol that included periods of free head carriage and poll flexion until fully fatigued. Dynamic abnormalities were classified as: dynamic laryngeal collapse (DLC) associated with poll flexion; axial deviation of the aryepiglottic folds (ADAF); dynamically flaccid epiglottis (FE); caudal palatal instability (PI); intermittent dorsal displacement of the soft palate (iDDSP); pharyngeal collapse (PC); alar fold collapse (AFC) and nasal flutter (NF). Cluster analysis and Fisher's exact test was performed between groups. Significance was set at P<0.05. Results: The overall incidence of complex dynamic URT collapse was 69.7%. Axial deviation of the aryepiglottic folds was significantly associated with PI (P<0.0001) and FE (P<0.0001); iDDSP was significantly associated with PI (P = 0.004) only. Dynamic laryngeal collapse associated with poll flexion was significantly associated with FE (P = 0.002). Cluster analysis confirmed strong associations between the above diagnosis groups and weaker associations between others. Conclusion: Caudal PI seems to result in 2 diagnosis groupings: one that leads to ADAF and the other to iDDSP. Dynamic collapse of the margins of the epiglottis was a common finding in this study strongly associated with DLC, PI and ADAF. Potential clinical relevance: The associations between certain dynamic diagnoses identified in this study seems best explained as due to local anatomic and functional weaknesses that influence other structures through the Bernouilli principle, rather than being due to a generalised neurological disorder.     

Examination of the upper and lower respiratory tract relevant to purchase.

The intent and extent of the respiratory tract examination relevant to purchase are dictated by numerous factors, including historical information, signs suggestive of respiratory tract abnormalities, intended use of the horse, and economic considerations. Following a thorough and systematic examination of the horse at rest, evaluation during and following exercise may be warranted. The physical examination should include evaluation of regional symmetry of the head, neck, and thorax; evaluation of nasal airflow and patency; palpation of the nasal septum, larynx, and trachea; examination for surgical scars; and auscultation and percussion. Special examination techniques, including endoscopy, stress evaluation, and radiography, may be indicated. Much has been learned about the URT in recent years, particularly regarding endoscopy of the region and the interpretation of endoscopic findings. The reader is referred to a generous list of references to gain further detailed information regarding the endoscopic diagnosis of other URT conditions.     

Measurement of abnormal respiratory sounds during over-ground exercise

REASONS FOR PERFORMING STUDY: The presence of abnormal respiratory sounds is commonly associated with obstructions of the upper respiratory tract. In order to establish their clinical significance measurements are required of both normal and abnormal respiratory sounds produced by horses exercising over-ground. OBJECTIVES: To determine whether high quality recordings of respiratory sound can be made during over-ground exercise, and to develop a convenient measurement system that can be used to obtain respiratory sounds from horses exercising in field conditions. METHODS: A range of prototypes was evaluated against the requirements that the system must be easy to use under field conditions and produce high-quality recordings of respiratory sound. The chosen design incorporated a miniature microphone and an air-flow direction sensor mounted on a lightweight plastic face mask. The mask was attached to the horse's head using nylon straps secured by velcro fastenings. Sound and flow signals were recorded on a portable minidisc player carried by the jockey. RESULTS: The system fulfilled the design criteria. High quality recordings of respiratory sounds were obtained from Thoroughbred horse exercising on a training gallop under a variety of weather conditions. Intermittently occurring abnormal sounds were readily identified from the data. CONCLUSIONS: High quality measurements of respiratory sounds during over-ground exercise can be made relatively easily. POTENTIAL RELEVANCE: The system enables measurement of respiratory sounds outside a laboratory environment creating new opportunities for scientific research and clinical assessment. The study demonstrated that diagnostic systems based on respiratory sound analysis could potentially be manufactured at relatively low cost and be convenient and simple to use.     

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.