Analysis of gas exchange in the avian lung: Theory and experiments in the domestic fowl

Abstract

Gas exchange in the parabronchial lung of birds is analysed in theory using a model suggested by Zeuthen (1942), consisting of a continuously ventilated tube, representing the parabronchi, surrounded by blood-perfused capillaries. Equations describing how partial pressures of CO 2 and O 2 in pulmonary gas and blood depend upon ventilation, perfusion and diffusing capacity are derived. The theory was applied to measurements of gas exchange in unanesthetized White Leghorn hens, of 1.6 kg average weight. In order to confine the pulmonary gas exchange to a P CO 2 and P O 2 range in which the blood dissociation curves were relatively straight, a combination of inspiratory hypoxia and hypercapnia was used ( F i CO 2 = 0.03 , F i O 2 = 0.13 ). Arterial P CO 2 was lower and arterial P O 2 was higher than the corresponding values in end-expired gas. This finding is explainable by the theory. From the experimental data the pulmonary diffusing capacity for O 2 (D LO 2 ) was estimated at 1.1 to 1.5 ml·min −1·mm Hg −1. As the calculations were based on a homogeneous lung model, these values represent a lower limit for d LO 2 .