Avian intrapulmonary chemoreceptors: respiratory response to a step decrease in PCO2

The contribution of intrapulmonary chemoreceptors (IPC) to the respiratory response, following a step decrease in PICO2 was assessed in anesthetized and unidirectionally ventilated chickens. Step changes in the PCO2 of the ventilatory gas (PICO2) to a single lung were introduced with PICO2 to the contralateral lung held constant. Respiratory amplitude and frequency were monitored. Experimental series were conducted under conditions such that (I) both systemic chemoreceptors and IPC, (II) systemic chemoreceptors alone and (III) IPC alone contribute to the ventilatory response. The results indicate (1) that a rapid component of the transient response (complete in 25 sec) is eliminated by sectioning the pulmonary nerves (Series II), and (2) within the rapid component, a localized minimum in respiratory amplitude was observed which was not seen in either Series II or Series III experiments. We conclude that the rapid component of the transient response is due to the CO2-sensitive IPC and that intrapulmonary and systemic chemoreceptors are not simply additive in the generation of respiratory amplitude and frequency, but a more complex interaction must be involved.