Gas Exchange in the Loggerhead Sea Turtle

Pulmonary CO diffusion capacity ( D L C O ) , lung volume (VL), oxygen uptake (Vo ) and pulmonary blood flow (QL) were measured simultaneously in the loggerhead sea turtle Caretta caretta (Linnaeus) (8—11 kg) using a gas rebreathing technique (syringe pump ventilation). Calculated D L C O and Vo values in the loggerhead turtle are approximately twice those of non-varanid reptiles and about 25 % of values for resting mammals. Evidence based on an estimated lung-capillary 0 2 gradient, APo2, shows that only a small driving gradient is required for O2 conductance across the loggerhead turtle lung. Pulmonary blood flow values are high compared to those for other reptiles; on the basis of the Fick principle, this implies a substantial blood convection requirement. Differences in oxygen transport mechanisms between the loggerhead sea turtle and other highly aerobic but terrestrial reptiles may result from divergent lung structures and breathing patterns. In sea turtles, the coupling of respiration with locomotory behaviour is one factor that may limit aerobic performance. Since sea turtles have only intermittent access to air, they are required to load both arterial and venous blood with O2 before submerging.