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 developm ent 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 measure ment of tracheal and pharyngeal pressures were used in 14 clinically n ormal horses and 19 horses with intermittent DDSP. The pressure signal s were superimposed on the videoendoscope image, and both images were saved simultaneously on a videocassette for slow motion analysis to de termine the instant displacement occurred in the respiratory cycle. Ho rses were submitted to an escalating 8-minute high-speed test with a m aximal 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 duri ng inspiration, 4 horses displaced it during expiration, and 7 displac ed it by swallowing. Some horses displaced the soft palate at the begi nning of the exercise trial, before reaching maximal speed, some horse s displaced it at the peak speed, and some horses displaced it when sl owing down. Epiglottic size in horses with DDSP was within normal limi ts, ruling out epiglottic hypoplasia as a cause of DDSP during exercis e. Airway pressures were significantly (P < 0.002) altered after DDSP. Pharyngeal and tracheal inspiratory pressures were-less negative, whe reas pharyngeal expiratory pressure became less positive and tracheal expiratory pressure became more positive after displacement, suggestin g a decrease in airflow and an increase in expiratory resistance in th e upper airway.