Lengthening of inspiration by intrapulmonary chemoreceptor discharge in ducks

The influence of avian intrapulmonary chemoreceptors (IPC) on inspiratory duration (TI) was tested by experimentally reducing their level of discharge for a single inspiration. The seven major air sacs of decerebrate or anesthetized ducks were cannulated with wide-bore tubing and then connected to a single clamped outlet. In self-ventilating animals, opening the sac line for a single inspiration caused the inspiratory discharge of 17 IPC to disappear and that of a further 7 to fall substantially; no IPC showed a rise in discharge, nor did the 6 presumed respiratory stretch receptors from which recordings were made. The reduction of IPC discharge was accompanied by a fall in TI rather than the rise required if IPC were to resemble mammalian pulmonary stretch receptors in their action on TI. We propose that in eupnea inspiratory IPC discharge prolongs inspiration.