Respiration and gas exchange during recovery from exercise in the American alligator

Low respiratory exchange ratios (R) occur in reptiles. In crocodilians they have been attributed to the loss of respiratory CO2 into the urine and to the immediate exercise-history of an animal. In this study, expired ventilation (V(E)), oxygen consumption (V(O2)), and carbon dioxide excretion (V(CO2)) were measured during recovery from treadmill-exercise in the American alligator. Both V(O2) and V(CO2) decreased exponentially during recovery, but the decrease of V(CO2) was greater than that of V(O2). By 55 min into recovery R fell to 0.3 +/- 0.02 (mean +/- S.E.M). These low values of R may be partially attributable to hyperventilation that occurred during exercise. These data suggest that both hyperventilation during exercise and a metabolic acidosis deplete blood bicarbonate stores, contributing to a low R during recovery. We propose that the right to left cardiac shunt could facilitate restoration of these alkaline reserves and blood pH.