A model of regional ventilation-perfusion inhomogeneity in the avian lung

Abstract

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 P_CO2 and P_O2, and expired P_CO2 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 P_CO2 and observed values was achieved after forcing simulated Pa_O2 to converge on observed Pa_O2 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.