Effect of dorsal displacement of the soft palate on ventilation and airflow during high-intensity exercise.

Dorsal displacement of the soft palate (DDSP) is one of the most common obstructive conditions of the upper respiratory tract in the racehorse. The present study was conducted to determine the effects of intermittent dorsal displacement of the soft palate (DDSP) on ventilation and respiratory airflow during high intensity exercise. Videoendoscopic recordings were made of the nasopharynx and larynx simultaneously with measurements of airflow and respiratory gas exchange, during high-speed treadmill exercise in 9 horses with confirmed intermittent DDSP admitted for clinical investigation of poor racing performance. In all horses, DDSP resulted in a reduction in minute ventilation (VE) (P<0.001), associated with a decrease in tidal volume (VT) (P<0.01) with no change in breathing frequency (f) and a reduction in oxygen consumption (VO2) (P<0.01). Further, DDSP resulted in reduction of expiratory flow parameters, including peak expiratory flow (PEF), EF50, EF25 and EF125 (P<0.01), with no alteration of inspiratory flow. These results confirm that naturally-occurring intermittent DDSP creates a flow-limiting expiratory obstruction. The associated impairment of athletic performance is probably caused, at least in part, by the accompanying decrease of oxygen uptake.