Anterior vena caval oxygen profiles in a deep-diving California sea lion: arteriovenous shunts, a central venous oxygen store and oxygenation during lung collapse.

Abstract

Deep-diving California sea lions (Zalophus californianus) can maintain arterial hemoglobin saturation (SO2 ) above 90% despite lung collapse (lack of gas exchange) and extremely low posterior vena caval SO2 in the middle of the dive. We investigated anterior vena caval PO2and SO2 during dives of an adult female sea lion to investigate two hypotheses: (1) posterior vena caval SO2 is not representative of the entire venous oxygen store and (2) a well-oxygenated (arterialized) central venous oxygen reservoir might account for maintenance of arterial SO2 during lung collapse. During deep dives, initial anterior vena caval SO2 was elevated at 83.6±8.4% (n=102), presumably owing to arteriovenous shunting. It remained high until the bottom phase of the dive and then decreased during ascent, whereas previously determined posterior vena caval SO2 declined during descent and then often increased during ascent. These divergent patterns confirmed that posterior vena caval SO2 was not representative of the entire venous oxygen store. Prior to and early during descent of deep dives, the high SO2 values of both the anterior and posterior venae cavae may enhance arterialization of a central venous oxygen store. However, anterior vena caval SO2 values at depths beyond lung collapse reached levels as low as 40%, making it unlikely that even a completely arterialized central venous oxygen store could account for maintenance of high arterial SO2 These findings suggest that maintenance of high arterial SO2 during deep dives is due to persistence of some gas exchange at depths beyond presumed lung collapse.