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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.

Wright, AK, Ponganis KV, McDonald BI, Ponganis PJ.  2014.  Heart rates of emperor penguins diving at sea: implications for oxygen store management. Marine Ecology Progress Series. 496:85-98.   10.3354/meps10592   AbstractWebsite

Heart rate (f(H)) contributes to control of blood oxygen (O-2) depletion through regulation of the magnitude of pulmonary gas exchange and of peripheral blood flow in diving vertebrates such as penguins. Therefore, we measured H during foraging trip dives of emperor penguins Aptenodytes forsteri equipped with digital electrocardiogram (ECG) recorders and time depth recorders (TDRs). Median dive f(H) (total heartbeats/duration, 64 beats min(-1)) was higher than resting H (56 beats min(-1)) and was negatively related to dive duration. Median dive f(H) in dives greater than the 5.6 min aerobic dive limit (ADL; dive duration associated with the onset of a net accumulation of lactic acid above resting levels) was significantly less than the median dive f(H) of dives less than the ADL (58 vs. 66 beats min(-1)). f(H) profile patterns differed between shallow (<50 m) and deep dives (>250 m), with values usually declining to levels near resting f(H) in shallow, short-duration dives, and to levels as low as 10 beats min(-1) during the deepest segments of deep dives. The total number of heartbeats in a dive was variable in shallow dives and consistently high in deep dives. A true bradycardia (f(H) below resting levels) during segments of 31% of shallow and deep dives of emperor penguins is consistent with reliance on myoglobin-bound O-2 stores for aerobic muscle metabolism that is especially accentuated during the severe bradycardias of deep dives. Although f(H) is low during the deepest segments of deep dives, the total number and distribution of heartbeats in deep, long dives suggest that pulmonary gas exchange and peripheral blood flow primarily occur at shallow depths.

Ponganis, PJ, Kooyman GL, Sartoris D, Jobsis P.  1992.  Pinniped splenic volumes. American Journal of Physiology. 262:R322-R325. AbstractWebsite

Splenic volume was measured by computerized axial tomography in three harbor seals (Phoca vitulina) and two California sea lions (Zalophus californianus). Volumes ranged from 228 to 679 ml, representing 0.8-3.0% of calculated percentage body mass. Despite possible variation in the state of splenic contraction during the examination, these values are in the upper range of reported mammalian splenic volumes (as % of body mass). This reinforces the pinniped splenic erythrocyte storage concept.