Abstract An exceptionally large blood O 2 store underlies the remarkable dive performance of elephant seals. However, elevated carboxyhemoglobin (COHb) concentrations in these seals complicate estimations of blood O 2 content and O 2 depletion rates, and may also affect monitoring of brain oxygenation in seals with new non-invasive near-infrared (NIR) recorders. Using hemoximetry analyses of blood samples during sleep apneas of juvenile northern elephant seals ( Mirounga angustirostris ), we constructed in vivo Hill plot equations and O 2 –Hb dissociation curves (ODCs). We found: (a) COHb and methemoglobin (both of which do not bind O 2 and increase hemoglobin (Hb) affinity for O 2 ) comprised 8% of Hb, (b) an in vivo P 50 (partial pressure of O 2 at 50% Hb saturation, an index of O 2 affinity of Hb) of 27.1 mm Hg that was Hg 3.4 mm Hg less than that previously determined with an in vitro laboratory approach, and (c) when the in vivo and in vitro Hill plot equations were applied to arterial, hepatic sinus and extradural vein P O2 profiles during sleep apneas, the resulting differences in blood O 2 content and apneic blood O 2 depletion rates were minor despite higher Hb saturations calculated with the in vivo approach. We conclude that prior blood O 2 contents and depletion rates determined with the in vitro technique during dives are accurate. The range of arterial Hb saturations calculated from the in vivo and in vitro approaches represents the most realistic Hb saturation data available for evaluation of NIR monitors of arterial Hb saturation in seals.
Ponganis et al. (Sat,) studied this question.