Functional venous admixture in the lungs of the turtle, Chrysemys scripta

Pulmonary functional venous admixture was determined during forced, unidirectional ventilation with pure O2 and air. At a normal lung volume of 140 ml X kg-1, anatomical shunts (physical bypass of gas exchange surface by the blood) averaged 10% of pulmonary blood flow but it increased to 28% as lung volume declined to 30 ml X kg-1. Diffusion limitation and possibly inhomogeneity in ventilation: perfusion ratio also contributed to a total functional venous admixture of about 25% at normal lung volume.