Gas transport and blood acid‐base balance in diving sea snakes

Abstract

The values of hemoglobin concentration, Hb-O₂ affinity and buffering capacity of the blood of six sea snake species considerably overlap values from terrestrial squamates. Decreased blood pH had little effect on the P₅₀ but increased the n-value of Hb-O₂ equilibrium curves. The O₂ saturation of blood in the dorsal aorta varied between about 30 and 70% during voluntary diving in Acalyptophis peronii and Lapemis hardwickii. Voluntary dives ended when the lung Po₂ was about mm Hg and the arterial Po₂ about 30 mm Hg indicating that roughly half of the O₂ reserves had been used. In conjunction with relatively stable blood lactate concentration and pH, this indicates that voluntary dives occurred largely aerobically. In contrast, forced dives resulted in depletion of O₂ reserves and large changes in blood acidbase balance. Long recovery periods following forced dives are inconsistent with field observations and thus suggest that extensive anaerobic metabolism does not normally occur in sea snakes. Bradycardia was not evident during forced dives. Large differences in Po₂ between the lung and dorsal aorta indicated considerable right to left shunting either in the heart or in the lung. Venous blood represented over 50% of the systemic flow when there was considerable O₂ in the lung. Therefore blood Po₂ may remain relatively low despite elevated lung Po₂ resulting from diving. In view of substantial capability for extra-pulmonary gas exchange, high shunting reduces the possibility of losing O₂ through the skin and also may help prevent decompression sickness following deep dives.