Effects of airway obstruction on transmural pulmonary artery pressure in exercising horses.

OBJECTIVE: To determine whether laryngeal hemiplegia would increase transmural pulmonary artery pressure (TPAP). ANIMALS: 6 horses. DESIGN: Horses were studied under 5 conditions: control conditions, after induction of left laryngeal hemiplegia, during obstruction of the left nostril, after placement of an instrumented tracheostomy, and after placement of an open tracheostomy. Horses were evaluated after being given saline solution and after being given furosemide. PROCEDURES: Horses were exercised on a high speed treadmill, using a maximum speed of 13 m/s. During each exercise, airway pressures, airflow, esophageal and pulmonary artery pressures, and blood gas partial pressures were measured. RESULTS: When adjusted for horse, speed, and obstruction condition, mean TPAP (pulmonary artery pressure-esophageal pressure) and minimum TPAP were significantly lower after administration of furosemide than after administration of saline solution. In horses given saline solution, respiratory obstruction that increased intrapleural pressure significantly increased mean TPAP, and respiratory obstruction that decreased intrapleural pressure significantly decreased minimum TPAP. CONCLUSIONS: Changes in intrapleural pressure appear to play an important role in pulmonary artery pressure and TPAP. CLINICAL RELEVANCE: Because induction of laryngeal hemiplegia did not increase TPAP, laryngeal hemiplegia is unlikely to contribute to development of exercise-induced pulmonary hemorrhage.

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 development 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 measurement of tracheal and pharyngeal pressures were used in 14 clinically normal horses and 19 horses with intermittent DDSP. The pressure signals were superimposed on the videoendoscope image, and both images were saved simultaneously on a videocassette for slow motion analysis to determine the instant displacement occurred in the respiratory cycle. Horses were submitted to an escalating 8-minute high-speed test with a maximal 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 during inspiration, 4 horses displaced it during expiration, and 7 displaced it by swallowing. Some horses displaced the soft palate at the beginning of the exercise trial, before reaching maximal speed, some horses displaced it at the peak speed, and some horses displaced it when slowing down. Epiglottic size in horses with DDSP was within normal limits, ruling out epiglottic hypoplasia as a cause of DDSP during exercise. Airway pressures were significantly (P < 0.002) altered after DDSP. Pharyngeal and tracheal inspiratory pressures were less negative, whereas pharyngeal expiratory pressure became less positive and tracheal expiratory pressure became more positive after displacement, suggesting a decrease in airflow and an increase in expiratory resistance in the upper airway.

Measurement of tracheal static pressure in exercising horses.

A nasotracheal catheter for measuring tracheal static pressure in exercising horses was designed according to aerodynamic engineering principles. Small ports near the end of the catheter transmitted pressure fluctuations to the recording apparatus. Accuracy was determined by the size, number, and location of pressure sensing holes on the catheter, and by the position of the catheter in the trachea. The catheter had adequate frequency response to 33 Hz, was insensitive to movement artifacts, was easily introduced, was tolerated well by horses, and resulted in small ventilatory impairment at maximal exertion.