Receptive fields of intrapulmonary chemoreceptors in the Pekin duck

Reflex experiments indicate a uniform distribution of CO₂ chemosensitivity in avian lungs, but neural recording experiments suggest a non-uniform distribution of intrapulmonary chemoreceptor (IPC) endings. To reconcile these observations, blood gases and PE_CO2 were measured while recording discharge frequencies, recorded from the left vagus, were determined while ventilating the perfused left lung with caudocraminal and craniocaudal flows of 1% CO₂ in air, and then while ventilating the unperfused left lung with known levels of CO₂ in air. Lung P_CO2 profiles were predicted using an eight-compartment computer model of cross-current gas exchange with log-normal ventialtion-perfussion inequality and shunt. The P_CO2 profiles and IPC discharge frequencies were used to calculate receptor location. At the 99% confidence limit, estimates of IPC location changed significantly in all but 7 IPC when the ventilation was reversed, indicating many IPC have multiple endings. Eighteen of 32 IPC had receptive fields extending at least 50% of the parabronchial length, which may explain the uniform reflex chemosensitivity to intrapulmonary CO₂ noted by others.