Effect of a mask and pneumotachograph on tracheal and nasopharyngeal pressures, respiratory frequency, and ventilation in horses.
To investigate the effect of a mask and pneumotachograph on ventilation, respiratory frequency, and tracheal and nasopharyngeal pressures in horses running on a treadmill. 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 pharyngeal inspiratory and expiratory pressures, respiratory frequency, and arterial blood gases were measured. Six Standardbred horses. Oxygen consumption was measured during an incremental exercise test to determine the speed that resulted in maximal oxygen consumption for each horse. Tracheal and pharyngeal pressures were measured, using transnasal tracheal and pharyngeal side-hole catheters connected to differential pressure transducers. Carotid arterial blood samples were collected and PAO2, PaCO2, and pH were measured with a blood gas analyzer. Peak tracheal and pharyngeal inspiratory pressures were 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 PaCO2 was higher and arterial pH and PaO2 were lower (P < 0.05) when horses wore a mask. The mask and pneumotachograph altered upper airway pressures, respiratory frequency, and ventilation in horses running on a treadmill.