S. H. Franklin

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.

Comparisons of overground endoscopy and treadmill endoscopy in UK Thoroughbred racehorses

REASONS FOR PERFORMING STUDY To date there is no information on the comparison of the more recently documented technique of performing endoscopy during ridden exercise in the field, with the more traditional method of endoscopy during high-speed treadmill exercise. OBJECTIVES To compare the results of upper respiratory tract endoscopy in UK Thoroughbred racehorses performed during ridden exercise in the field with those obtained during exercise on the treadmill. METHODS A direct comparison was undertaken in 4 horses whereby both procedures were performed in the same horse within 10 days of each other. An indirect comparison was also undertaken whereby the results of overground endoscopy performed in 50 racehorses was compared to the results obtained during treadmill endoscopy in a further 50 racehorses. Horses were matched for age, gender, use (National Hunt vs. Flat) and presenting complaint (abnormal respiratory noise vs. poor performance). RESULTS Dorsal displacement of the soft palate was diagnosed less frequently during overground endoscopy than during treadmill endoscopy. There was no significant difference in the diagnosis of dynamic laryngeal collapse between the 2 techniques. The treadmill exercise test was performed over longer distances at higher inclines, albeit at lower speeds than the overground test. In contrast to the treadmill test, the overground test was frequently performed in intervals. CONCLUSIONS The results of both the direct and indirect comparisons suggest that dorsal displacement of the soft palate is diagnosed less often during overground endoscopy than during treadmill endoscopy. Strenuous exercise tests may be more easily performed on a treadmill than by performing multiple exercise intervals in the field. POTENTIAL RELEVANCE Care should be taken in interpreting negative findings during both procedures, but particularly during overground endoscopy if racing conditions have not been appropriately replicated.

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.

Assessment of the exercise tests used during overground endoscopy in UK Thoroughbred racehorses and how these may affect the diagnosis of dynamic upper respiratory tract obstructions

REASONS FOR PERFORMING STUDY Overground endoscopy is being performed with increasing frequency in the UK. A previous study has shown that the type of exercise test may affect the diagnosis of upper respiratory tract (URT) obstructions. The successful clinical application of overground endoscopy systems requires understanding of appropriate field exercise testing protocols. OBJECTIVES The aim of this study was to report the exercise test parameters used during overground endoscopy in UK Thoroughbred racehorses and to investigate potential effects of these on the diagnosis of URT obstructions. METHODS The exercise test parameters used and the endoscopic observations of the URT during exercise were recorded for 140 Thoroughbred racehorses referred for the investigation of abnormal respiratory noise and/or poor athletic performance. RESULTS The exercise test parameters varied widely between horses. The presenting complaint was easiest to reproduce in horses with a history of abnormal noise in training and hardest to reproduce in those referred for investigation of poor performance with no abnormal noise. No associations between the presence or not of an URT obstruction and exercise test parameters was identified. For horses referred for abnormal noise during racing DDSP was more likely to be observed when longer distances were performed. CONCLUSIONS It is difficult to standardise exercise tests in the field when multiple premises are used and when training gallops differ markedly to racecourses. It was not possible to establish exercise test protocols which should be used for all Thoroughbred racehorses. Therefore, at present the best advice for horses which make abnormal noise during a race or have poor race performance, can only be to replicate race conditions as closely as possible. For horses that race over longer distances this will require the use of a circular gallops (e.g. racecourse) if only short gallops are available at the trainers premises.

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.

Evaluation of cytokine mRNA expression in bronchoalveolar lavage cells from horses with inflammatory airway disease

Inflammatory airway disease (IAD) is a common disorder of performance horses and is associated with poor performance and accumulation of mucus and inflammatory cells in lower airway secretions. Horses with IAD frequently have increased relative counts of neutrophils in bronchoalveolar lavage fluid (BALF); less commonly relative counts of eosinophils and/or mast cells may be increased. The aetiopathogenesis of IAD is unknown and may involve innate and/or acquired immune responses to various factors including respirable dust constituents, micro-organisms, noxious gases and unconditioned air. The molecular pathways and role of the immune system in the pathogenesis of IAD remain poorly defined and it is unknown whether polarised T cell responses occur in the disease, as have been reported to occur in equine recurrent airway obstruction and asthma in humans. Elucidating cytokine responses that develop in horses with IAD may allow a greater understanding of the possible aetiopathological pathway(s) involved and could contribute to development of novel treatments. We compared the mRNA expression of tumour necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin (IL)-1β, IL-2, IL-4, IL-8, IL-13, IL-17 and IL-23 in cell pellets extracted from BALF of horses with IAD (n=21) and horses free of respiratory tract disease (n=17). Horses with IAD had significantly increased levels of TNF-α, IL-1β and IL-23 mRNA; no significant differences in the other cytokine mRNAs were detected. The results of this study indicate that IAD of horses is associated with increased mRNA expression of pro-inflammatory cytokines in BALF cells, which may reflect stimulation of the innate immune responses to inhaled antigens. There was no evidence of a polarised T-cell cytokine response suggesting hypersensitivity responses may not be involved in the aetiopathogenesis of IAD.

A systematic review of the efficacy of interventions for dynamic intermittent dorsal displacement of the soft palate.

There are numerous treatments for correction of dorsal displacement of the soft palate (DDSP). However, the efficacy of these treatments is controversial and there is little consensus on how best to treat this condition. The aims of this study were to systematically review the literature and to assess the evidence on the clinical effects of interventions for dynamic intermittent DDSP. A secondary objective was to assess whether factors relating to study quality affected reported success rates. Twenty-three studies were included, covering a wide number of interventions but also differing widely is terms of study design, sample size, method of diagnosis, outcome measure and the number lost to follow-up. The assessment of adverse effects was severely limited because of lack of reporting. The way in which success is measured appears to have a great effect on the reported results. Research synthesis has been severely limited because of the heterogeneity in the included studies. The low level of evidence makes it difficult to draw firm conclusions as to the efficacy of procedures for DDSP. Hence it is currently not possible to determine which procedure is the most appropriate. This systematic review highlights the difficulties of studying palatal dysfunction and suggests areas where improvements can be made in future studies.

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.

Effect of Head Position on Radiographic Assessment of Laryngeal Tie‐Forward Procedure in Horses

OBJECTIVE To assess the effect of head position on relative position of the larynx and hyoid apparatus in horses with palatal dysfunction, and to define a standard position for radiographic assessment of laryngeal tie-forward. STUDY DESIGN Prospective clinical study. ANIMALS Adult horses (n=9) with palatal dysfunction. METHODS Left lateral radiographs of the larynx were obtained pre and postoperatively for 3 different head positions (flexed=90 degrees ; neutral=100 degrees ; extended=115 degrees ). Distance between thyrohyoid bone and thyroid cartilage was measured. Data were analyzed to investigate differences between head positions, and to compare differences between pre- and postoperative measurements. RESULTS Head position had a significant effect on relative position of the larynx and hyoid apparatus preoperatively. There was no significant difference in postoperative measurements of the 3 head positions. A significant difference between pre- and postoperative measurements was found with the head in the neutral or extended position whereas there were no significant differences between pre- and postoperative measurements using the flexed position. CONCLUSIONS Head position affects the relationship between the hyoid apparatus and larynx preoperatively, with greatest distance occurring when the head is extended. In a flexed position, it is not possible to ascertain whether laryngeal position has changed postoperatively. CLINICAL RELEVANCE A standardized head position is necessary when assessing the laryngeal tie-forward procedure radiographically. An extended head position is most useful for this assessment.

Poor performance associated with equine gastric ulceration syndrome in four Thoroughbred racehorses

Summary Equine gastric ulceration syndrome (EGUS) is commonly recognised in Thoroughbred racehorses. Although EGUS has previously been associated with reduced athletic performance, no objective studies have been reported. This case report describes 4 racehorses referred for investigation of poor athletic performance where EGUS was the only abnormal finding during a thorough investigation of all body systems. All horses showed considerable improvement in performance following treatment with omeprazole. Therefore, this is the first report in which evidence is presented suggesting a direct link between EGUS and decreased performance, other causes of poor performance having been excluded.