Extreme hypoxemic tolerance and blood oxygen depletion in diving elephant seals

1 Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla; and 2 Department of Ecology and Evolutionary Biology, Long Marine Lab, University of California Santa Cruz, Santa Cruz, California Submitted May 5, 2009 ; accepted in...

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Published in:American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2009-10, Vol.297 (4), p.R927-R939
Main Authors: Meir, Jessica U, Champagne, Cory D, Costa, Daniel P, Williams, Cassondra L, Ponganis, Paul J
Format: Article
Language:English
Subjects:
Adaptation, Physiological
Animals
Arteries - physiopathology
Behavior, Animal
Blood
Blood Gas Analysis - instrumentation
Blood Gas Analysis - standards
Body Temperature
Calibration
Diving
Electrodes, Implanted
Hypoxia
Hypoxia - blood
Hypoxia - physiopathology
Ion-Selective Electrodes
Marine mammals
Medical disorders
Metabolism
Oxygen
Oxygen - blood
Oxyhemoglobins - metabolism
Partial Pressure
Regional Blood Flow
Reproducibility of Results
Seals, Earless
Time Factors
Veins - physiopathology
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Summary:1 Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla; and 2 Department of Ecology and Evolutionary Biology, Long Marine Lab, University of California Santa Cruz, Santa Cruz, California Submitted May 5, 2009 ; accepted in final form July 26, 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 (P O 2 ) during dives with a P O 2 /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 P O 2 profiles to obtain %Hb saturation (S O 2 ), 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 O 2 and Pa O 2 values reached 2–10 and 12–23 mmHg, respectively. This corresponds to S O 2 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 Pa O 2 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°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. P O 2 ; aerobic metabolism; %Hb saturation; O 2 -Hb dissociation curve; hypoxia Address for reprint requests and other correspondence: J. U. Meir, SIO/UCSD, 9500 Gilman Dr., La Jolla, CA 92093-0204 (e-mail: jmeir{at}ucsd.edu ).
ISSN:0363-6119
1522-1490
DOI:10.1152/ajpregu.00247.2009