Journal
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
Volume 297, Issue 4, Pages R927-R939Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpregu.00247.2009
Keywords
PO2; aerobic metabolism; %Hb saturation; O-2-Hb dissociation curve; hypoxia
Categories
Funding
- National Science Foundation [IOS-0641801]
- Scripps Institution of Oceanography Halliday Student Field Research Award
- National Defense Science and Engineering
- Los Angeles Achievement Rewards for College Scientists fellowship
- Philanthropic Educational Organization (P. E. O.)
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Meir JU, Champagne CD, Costa DP, Williams CL, Ponganis PJ. Extreme hypoxemic tolerance and blood oxygen depletion in diving elephant seals. Am J Physiol Regul Integr Comp Physiol 297: R927-R939, 2009. First published July 29, 2009; doi: 10.1152/ajpregu.00247.2009.-Species that maintain aerobic metabolism when the oxygen (O-2) supply is limited represent ideal models to examine the mechanisms underlying tolerance to hypoxia. The repetitive, long dives of northern elephant seals (Mirounga angustirostris) have remained a physiological enigma as O-2 stores appear inadequate to maintain aerobic metabolism. We evaluated hypoxemic tolerance and blood O-2 depletion by 1) measuring arterial and venous O-2 partial pressure (PO2) during dives with a PO2/temperature recorder on elephant seals, 2) characterizing the O-2 hemoglobin (O-2-Hb) dissociation curve of this species, 3) applying the dissociation curve to PO2 profiles to obtain %Hb saturation (SO2), and 4) calculating blood O-2 store depletion during diving. Optimization of O-2 stores was achieved by high venous O-2 loading and almost complete depletion of blood O-2 stores during dives, with net O-2 content depletion values up to 91% (arterial) and 100% (venous). In routine dives (>10 min) Pv(O2) and Pa-O2 values reached 2-10 and 12-23 mmHg, respectively. This corresponds to SO2 of 1-26% and O-2 contents of 0.3 (venous) and 2.7 ml O-2/dl blood (arterial), demonstrating remarkable hypoxemic tolerance as PaO2 is nearly equivalent to the arterial hypoxemic threshold of seals. The contribution of the blood O-2 store alone to metabolic rate was nearly equivalent to resting metabolic rate, and mean temperature remained near 37 degrees C. These data suggest that elephant seals routinely tolerate extreme hypoxemia during dives to completely utilize the blood O-2 store and maximize aerobic dive duration.
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