Sensitivity of avian intrapulmonary chemoreceptors to venous CO2 load

To investigate the response of individual intrapulmonary chemoreceptors (IPC) to venous CO2 loads approximating moderate muscular exercise, we recorded vagal discharge from 33 IPC arising from the left lungs of 9 anesthetized, unidirectionally ventilated Pekin ducks. Each IPC was studied during control conditions (PECO2 = 29.0 +/- 0.8 Torr, PVCO2 = 30.2 +/- 0.6 Torr) and during venous CO2 load (PECO2 = 29.5 +/- 0.7 Torr, PVCO2 = 51.5 +/- 1.4 Torr). Venous loading was produced by increasing the percentage of CO2 in the gas ventilating the right lung from 0 to 9-25% CO2. The flow of 1% CO2 through the left lung was adjusted to keep the left lung PECO2 constant. During venous loading, discharge frequencies indicated that the PCO2 at the receptive sites fell, on the average, 1.6 +/- 0.8 Torr.