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 PP02 was about 50 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 acid-base 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.

Cardiovascular responses to diving in the turtle, Pseudemys scripta

“…Graham (1974) has shown that such snakes can get O2 cutaneously during a dive. Seymour and Webster (1975) found no relationship between submergence and heart rate in bea snakcb…”

Cardiovascular responses to diving in the turtle, Pseudemys scripta

“…Therefore, a low O2 content in the inspired air does not impose an immediate threat. Seymour and Webster (1975) found that lung and aortic O2 contents converged until just before voluntary emergence in sea snakes, when the lung PO2 was about 50 torr and the blood PO2 was 34 torr. Thus, only about half of the available O2 had been used; the arterial blood was still 44% saturated.…”

“…Hov/eve*"; Seymour and Webster (1975) found the buffering capacity of sea snake blood to be similar to that of land snakes. Buffering capacity of aquatic turtles is generally higher than in terrestrial tur tles (Robin et al, 1964;Lenfant et al, 1970a).…”

“…Seymour and Webster (1975) found that hemoglobin (Hb) concentration and Hb-02 affinity in sea snakes were no different than for terrestrial snakes, and Mutton (.1958) found no consistent difference in hematocrit or red cell count between semi-aquatic and terrestrial snakes. Moreover, significant concentrations of methemoglobin occasionally observed in reptiles reduce the 0?…”

“…Either a R-L shunt occurs to dilute the pulmonary venous blood entering the arterial system or else there is incomplete equilibrium of the O2 gas in the lung and blood, or both. Calculations indicate that this corresponds to a 50-70% R-L shunt (Heatwole and Seymour, 1975;Seymour and Webster, 1975). Since it is known that cutaneous gas exchange occurs in sea snakes (Graham, 1974), it has been suggested that the shunt serves to keep arterial POglow, thus allowing O2 uptake fran the water when the snake is at or near the surface and preventing O2 loss to water during a deep dive when the lung PO2 increases (Heatwole and Seymour, 1975;Seymour and Webster, 1975).…”