Changes in ventilatory flow rate in ducks in response to a single inspiration of air containing 5% CO2.

A single inspiration of 5% CO2 abolished the phasic inspiratory discharge of a population of intrapulmonary chemoreceptors (IPC) in decerebrate ducks. Inspiratory flow rate (V1) was found to increase in 27 of 40 trials in 3 tranquillized ducks, and in 43 of 47 trials in 3 decerebrate ducks. In addition, the abruptness of the transition from inspiration to expiration (dV/dt) increased in response to inspiring 5% CO2 in 32 of 40 trials in the tranquillized animals, and in 45 of 47 trials with the decerebrate animals. It is argued that the VI and dV/dt responses are mediated by the change in inspiratory IPC discharge caused by the inspired CO2. It is concluded that inspiratory IPC discharge inhibits the level of output of central inspiratory neurones moment by moment, and additionally prevents an abrupt cessation or initiation of activity in the antagonistic ventilatory muscles.