Ventilation-perfusion inequally in avian lungs

We assessed ventilation-perfusion inequality in 8 anesthetized, tidally ventilated geese in terms of continuous V/Q distributions using the multiple inert gas elimination technique modified for cross-current avian lungs (Powell and Wagner, 1982). Thirty-four data sets were collected. Allowing for differences in solubility, high molecular weight gases (Enflurane, SF6) were not retained in the blood to any greater extent than the other gases, suggesting that diffusion in the gas phase is functionally complete. Shunt averaged only 0.4 +/- 0.1% (SEM) of cardiac output and areas of low V/Q were seldom seen. Twenty-nine of the 34 data sets had bimodal V/Q distributions with 10.6 +/- 1.4% of expired ventilation and 0.3 +/- 0.1% of cardiac output in a high V/Q mode; the physiological basis of the high mode is unknown. The log-standard deviation of the main Q mode averaged 0.56 or slightly greater than that for healthy men, dogs, or earlier estimates from unidirectionally ventilated birds. It is predicted that CO2 will be more impaired by such V/Q inequality than O2, but that increased ventilation will overcome the CO2 impairment more easily than that of O2 transport.