Intrapulmonary CO2 receptor discharge at different levels of venous PCO2

It has been suggested that avian intrapulmonary CO2-sensitive receptors (IPC) may be capable of affecting ventilation in response to changes in lung CO2 load. The purpose of this study was to record IPC discharge activity in spontaneously breathing ducks when venous PCO2 was elevated or lowered from resting levels. This was accomplished using an extracorporeal venovenous blood bypass circuit, which included a 0.8-m2 silicone membrane blood oxygenator. Adult male Pekin ducks were anesthetized and tracheostomized. Single-unit activity was recorded from 42 IPC. During venous CO2 loading, there was no difference in the average IPC discharge from control despite an increase in the rate of CO2 excretion (VCO2) to twice the resting level. Venous CO2 unloading decreased VCO2 by one-half but did not significantly affect inspiratory IPC discharge and resulted in only a small increase in expiratory discharge. In contrast, inhalation of 3% CO2 greatly reduced inspiratory discharge. Reflex adjustments in tracheal flow appear to be responsible for maintaining IPC discharge at control levels when venous PCO2 changes.