Path taken by gases through the respiratory system of the chicken

Abstract

The path of gases through the avian respiratory system was studied by comparing P_co2 and P_o2 in expired gas and air sacs and P_o2 in left ventricular blood. A respiratory mass spectrometer was used for gas analyses and an o₂ electrode for blood P_o2. Findings were: a) P_co2 and P_o2 in air sacs varied little during the respiratory cycle; they fell when N2 was injected into the sac but returned rapidly to the original level in steps, a step with each inspiration. b) P_o2 of left ventricular blood and air sac gas were essentially the same and varied less than 5% of total Po₂ during the respiratory cycle. c) End-tidal P_co2 and P_o2 were essentially the same as air sac P_co2 and P_o2. The first two findings suggest that gas reaches the air sacs only via the respiratory surfaces of the lung. The third suggests that during expiration gas passes directly from air sacs to mouth without passing again over the respiratory surfaces. The path is therefore mouth-lung-air sacs-mouth, with almost complete valving despite the absence of demonstrable anatomical valves. Submitted on February 9, 1959