EFFECT OF A MASK AND PNEUMOTACHOGRAPH ON TRACHEAL AND NASOPHARYNGEAL PRESSURES, RESPIRATORY FREQUENCY, AND VENTILATION IN HORSES

Objective-To investigate the effect of a mask and pneumotachograph on ventilation, respiratory frequency, and tracheal and nasopharyngeal pr essures in horses running on a treadmill. Design-Six horses ran at 50, 75, and 100% of the speed that resulted in maximum oxygen consumption , with and without a mask and pneumotachograph. Tracheal and pharyngea l inspiratory and expiratory pressures, respiratory frequency, and art erial blood gases were measured. Animals-Six Standardbred horses. Proc edure-Oxygen consumption was measured during an incremental exercise t est to determine the speed that resulted in maximal oxygen consumption for each horse. Tracheal and pharyngeal pressures were measured, usin g transnasal tracheal and pharyngeal side-hole catheters connected to differential pressure transducers. Carotid arterial blood samples were collected and Pa-O2, Pa-CO2, and pH were measured with a blood gas an alyzer. Results-Peak tracheal and pharyngeal inspiratory pressures wer e significantly more negative, peak tracheal and pharyngeal expiratory pressures were significantly more positive, and respiratory frequency was significantly lower (all P < 0.05) at all speeds when horses wore a mask. The Pa-CO2 was higher and arterial pH and Pa-O2 were lower (P < 0.05) when horses wore a mask. Conclusions-The mask and pneumotacho graph altered upper airway pressures, respiratory frequency, and venti lation in horses running on a treadmill.