Ventilatory pressure loading at constant pulmonary F CO 2 in Gallus Domesticus

Abstract

Seven White Leghorn roosters were unidirectionally ventilated at constant flows and CO 2 concentrations. The birds were awake and stood or crouched in a plethysmograph. A servo system clamped the pressure in the air sacs at constant values from −10 to + 10 cm H 2O in 2 cm H 2O increments. Therefore, the animals could inflate or deflate the air sacs with breathing movements without affecting intrapulmonary pressures. Decreasing air sac pressure less than atmospheric caused inspiratory duration (T I), expiratory duration (T E), total period (T TOT and tidal volume (V R) to decrease, the ratio, T I/T E to increase. Increasing air sac pressures to 6 cm H 2O above atmospheric caused, T E to increase, T I and T I/T E to decrease and V T and T TOT to change very little. After bilateral vagotomy air sac pressure changes caused little or no changes in T I, T E, T TOT or T I/T E, but produced percentage changes in V T similar to before vagotomy. Comparison of end expiratory volumes with apneic volumes (produced by lowering CO 2 in the insulfating gas) over the range of air sac pressures clamped shows: (1) chickens actively exhale at pressures as low as −10 cm H 2O, and (2) the change of mean air sac volume due to imposed pressure is less during breathing than during apnea. These findings, we believe, are due to a reflex initiated by mechanoreceptors with projections in the vagus nerves.