Rapid ventilatory responses to changes in insufflated CO2 in awake roosters

The ventilatory responses to pulses or steps in the fraction of CO2 in the insufflated gas stream (FICO2) in awake, unidirectionally ventilated White Leghorn roosters (Gallus domesticus) were studied. Within 0.2-0.5 s of the change in FICO2 at the syrinx, a change in inspiratory or expiratory flow occurred. Increases in FICO2 increased flow and tidal volume (VT), whereas decreases in FICO2 decreased flow and VT. Expiratory duration (TE) was markedly prolonged by decreases in FICO2 and shortened by increases. Inspiratory duration was affected little by FICO2 changes. The TE response to pulses of FICO2 (0.2-0.4 s duration) revealed a time dependency such that a maximum effect occurred when the pulses arrived at the syrinx at approximately midexpiration. The magnitudes of the responses were approximately proportional to the amplitude and duration of the FICO2 changes, but decreases in FICO2 had greater effects than increases. A likely receptor site for these responses is the intrapulmonary chemoreceptors, which appear to function in a reflex controlling airflow and timing of the ongoing breath.