title: Extreme hypoxemic tolerance and blood oxygen depletion in diving elephant seals.
abstract: 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 (Po(2)) during dives with a Po(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 Po(2) profiles to obtain %Hb saturation (So(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 So(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 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.
authors.affiliation: Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla 92093-0204, USA. jmeir@ucsd.edu
authors.forename: Jessica U
authors.initials: JU
authors.lastname: Meir
authors.forename: Cory D
authors.initials: CD
authors.lastname: Champagne
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Costa
authors.forename: Cassondra L
authors.initials: CL
authors.lastname: Williams
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Ponganis
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001158:Arteries / Q000503:physiopathology; D001522:Behavior, Animal; D001784:Blood Gas Analysis / Q000295:instrumentation / Q000592:standards; D001831:Body Temperature; D002138:Calibration; D004242:Diving; D004567:Electrodes, Implanted; D000860:Hypoxia / Q000097:blood* / Q000503:physiopathology; D017736:Ion-Selective Electrodes; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000378:metabolism*; D010313:Partial Pressure; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D046048:Seals, Earless; D013997:Time Factors; D014680:Veins / Q000503:physiopathology
chemical_list: D010108:Oxyhemoglobins; D010100:Oxygen