Blood oxygen depletion during rest-associated apneas of northern elephant seals (Mirounga angustirostris)

• Published in: Journal of Experimental Biology
• Main Authors: Stockard, T. K., Levenson, D. H., Berg, L., Fransioli, J. R., Baranov, E. A., Ponganis, P. J.
• Format: Text
• Language: English
• Published: Company of Biologists 2007
• Subjects: Research Article; Elephant Seals
• Online Access: http://jeb.biologists.org/cgi/content/short/210/15/2607; https://doi.org/10.1242/jeb.008078

Blood gases ( P O 2, P CO 2, pH), oxygen content, hematocrit and hemoglobin concentration were measured during rest-associated apneas of nine juvenile northern elephant seals. In conjunction with blood volume determinations, these data were used to determine total blood oxygen stores, the rate and magnitude of blood O 2 depletion, the contribution of the blood O 2 store to apneic metabolic rate, and the degree of hypoxemia that occurs during these breath-holds. Mean body mass was 66±9.7 kg (± s.d.); blood volume was 196±20 ml kg–1; and hemoglobin concentration was 23.5±1.5 g dl–1. Rest apneas ranged in duration from 3.1 to 10.9 min. Arterial P O 2 declined exponentially during apnea, ranging between a maximum of 108 mmHg and a minimum of 18 mmHg after a 9.1 min breath-hold. Venous P O 2 values were indistinguishable from arterial values after the first minute of apnea; the lowest venous P O 2 recorded was 15 mmHg after a 7.8 min apnea. O 2 contents were also similar between the arterial and venous systems, declining linearly at rates of 2.3 and 2.0 ml O 2 dl–1 min–1, respectively, from mean initial values of 27.2 and 26.0 ml O 2 dl–1. These blood O 2 depletion rates are approximately twice the reported values during forced submersion and are consistent with maintenance of previously measured high cardiac outputs during rest-associated breath-holds. During a typical 7-min apnea, seals consumed, on average, 56% of the initial blood O 2 store of 52 ml O 2 kg–1; this contributed 4.2 ml O 2 kg–1 min–1 to total body metabolic rate during the breath-hold. Extreme hypoxemic tolerance in these seals was demonstrated by arterial P O 2 values during late apnea that were less than human thresholds for shallow-water blackout. Despite such low P O 2s, there was no evidence of significant anaerobic metabolism, as changes in blood pH were minimal and attributable to increased P CO 2. These findings and the previously reported lack of lactate accumulation during these breath-holds are consistent with the maintenance of aerobic ...