A model of regional ventilation-perfusion inhomogeneity in the avian lung. Implications for gas exchange and intrapulmonary chemoreceptor microenvironment.

We recorded discharge frequencies of 32 intrapulmonary chemoreceptors (IPC) during caudocranial and craniocaudal ventilation in the perfused duck lung. Blood gases, ventilatory gas flow, inspired PCO2 and PO2, and expired PCO2 measured simultaneously were used to predict regional CO2 and O2 gradients within the lung. Gas exchange was modelled in 7 log normal ventilation-perfusion compartments using mass balance differentials with an adjustable step size. CO2 and O2 interactions during exchange were modelled using the Bohr effect, P50, blood acid-base status, and the CO2 dissociation relationship. Close agreement (+/- 1.0 Torr) between simulated arterial and expired PCO2 and observed values was achieved after forcing simulated PaO2 to converge on observed PaO2 by an iterative adjustment of the perfusive shunt or the log standard deviation of the ventilation-perfusion distribution. Using the IPC static CO2 sensitivity measured in the non-perfused lung and the CO2 gradients generated by the model, we have found evidence for a distributed multi-ending receptor system in the duck lung.