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Tift, MS, Huckstadt LA, Ponganis PJ.  2018.  Anterior vena caval oxygen profiles in a deep-diving California sea lion: arteriovenous shunts, a central venous oxygen store and oxygenation during lung collapse. Journal of Experimental Biology. 221   10.1242/jeb.163428   AbstractWebsite

Deep-diving California sea lions (Zalophus californianus) can maintain arterial hemoglobin saturation (S-O2) above 90% despite lung collapse (lack of gas exchange) and extremely low posterior vena caval S-O2 in the middle of the dive. We investigated anterior vena caval P-O2 and S-O2 during dives of an adult female sea lion to investigate two hypotheses: (1) posterior vena caval S-O2 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 S-O2 during lung collapse. During deep dives, initial anterior vena caval S-O2 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 S-O2 declined during descent and then often increased during ascent. These divergent patterns confirmed that posterior vena caval S-O2 was not representative of the entire venous oxygen store. Prior to and early during descent of deep dives, the high S-O2 values of both the anterior and posterior venae cavae may enhance arterialization of a central venous oxygen store. However, anterior vena caval S-O2 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 S-O2. These findings suggest that maintenance of high arterial S-O2 during deep dives is due to persistence of some gas exchange at depths beyond presumed lung collapse.

Ponganis, PJ, Van Dam RP, Knower T, Levenson DH.  2001.  Temperature regulation in emperor penguins foraging under sea ice. Comparative Biochemistry and Physiology a-Molecular and Integrative Physiology. 129:811-820.   10.1016/s1095-6433(01)00349-x   AbstractWebsite

Inferior vena caval (IVC) and anterior abdominal (AA) temperatures were recorded in seven emperor penguins (Aptenodytes foresteri) foraging under sea ice in order to evaluate the hypothesis that hypothermia-induced metabolic suppression might extend aerobic diving time. Diving durations ranged from 1 to 12.5 min, with 39% of dives greater than the measured aerobic dive limit of 5.6 min. Anterior abdominal temperature decreased progressively throughout dives, and partially returned to pre-dive values during surface intervals. The lowest AA temperature was 19 degreesC. However, mean AA temperatures during dives did not correlate with diving durations. In six of seven penguins, only minor fluctuations in IVC temperatures occurred during diving. These changes were often elevations in temperature. In the one exception, although IVC temperatures decreased, the reductions were less than those in the anterior abdomen and did not correlate with diving durations. Because of these findings, we consider it unlikely that regional hypothermia in emperor penguins leads to a significant reduction in oxygen consumption of the major organs within the abdominal core. Rather, temperature profiles during dives are consistent with a model of regional heterothermy with conservation of core temperature, peripheral vasoconstriction, and cooling of an outer body shell. (C) 2001 Elsevier Science Inc. All rights reserved.