Respiratory,cardiovascular and metabolic adjustments during steady state swimming in the green turtle,Chelonia mydas

Summary Heart rate and pulmonary artery blood flow of resting green turtles,Chelonia mydas, at 29°C increased with lung ventilation (heart rate from 24±5 to 51±8 beats min). When swimming at 0.6 m s^–1 in water at 30°C, oxygen uptake was 2.83 times and respiratory frequency was 2.75 times the resting values. Heart rate was 1.33 times that during ventilation at rest but 2.83 times that at the end of a breath hold at rest. Partial pressures of oxygen and carbon dioxide, lactic acid concentration and pH of arterial blood, when swimming at 0.5 m s^–1, were similar to those soon after ventilation at rest. Pulmonary blood flow did not decline to low levels between breaths, when the animals were swimming, as it did when they were at rest.In active turtles it appears that pulmonary perfusion remains elevated, supplying oxygen to the locomotory muscles at a sufficiently high rate to support the complete aerobic production of energy, and that respiratory frequency is kept as low as possible, as surfacing for air increases the metabolic cost of swimming.