Pulmonary ventilation: perfusion relationships in terrestrial and aquatic chelonian reptiles

Pulmonary ventilation and perfusion have been measured directly in unanaesthetized turtles (Pelomedusa subrufa) and tortoises (Testudo pardalis) during normal air breathing and during the inspiration of both hypoxic and hypercapnic gases. Lung ventilation in air was intermittent in both species and particularly in the turtle was accompanied by transient increases in pulmonary perfusion. Hypercapnia (4% CO2 in air) elicited a twofold to threefold increase in pulmonary perfusion but a sixfold increase in pulmonary ventilation in both species. Consequently the ventilation:perfusion ratio more than doubled in value. Unlike the hypercapnic responses, hypoxia (5% O2 in N2) increased pulmonary perfusion by two to five times but increased pulmonary ventilation by less than two times, and so the ventilation:perfusion ratio fell by one-half during hypoxic exposure. These data are interpreted in terms of intermittent breathing and processes of O2 and CO2 transport.