Publications

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2011
Ponganis, PJ, Meir JU, Williams CL.  2011.  In pursuit of Irving and Scholander: a review of oxygen store management in seals and penguins. Journal of Experimental Biology. 214:3325-3339.   10.1242/jeb.031252   AbstractWebsite

Since the introduction of the aerobic dive limit (ADL) 30 years ago, the concept that most dives of marine mammals and sea birds are aerobic in nature has dominated the interpretation of their diving behavior and foraging ecology. Although there have been many measurements of body oxygen stores, there have been few investigations of the actual depletion of those stores during dives. Yet, it is the pattern, rate and magnitude of depletion of O(2) stores that underlie the ADL. Therefore, in order to assess strategies of O(2) store management, we review (a) the magnitude of O(2) stores, (b) past studies of O(2) store depletion and (c) our recent investigations of O(2) store utilization during sleep apnea and dives of elephant seals (Mirounga angustirostris) and during dives of emperor penguins (Aptenodytes forsteri). We conclude with the implications of these findings for (a) the physiological responses underlying O(2) store utilization, (b) the physiological basis of the ADL and (c) the value of extreme hypoxemic tolerance and the significance of the avoidance of re-perfusion injury in these animals.

2010
Meir, JU, Ponganis PJ.  2010.  Blood temperature profiles of diving elephant seals. Physiological and Biochemical Zoology. 83:531-540.   10.1086/651070   AbstractWebsite

Hypothermia-induced reductions in metabolic rate have been proposed to suppress metabolism and prolong the duration of aerobic metabolism during dives of marine mammals and birds. To determine whether core hypothermia might contribute to the repetitive long-duration dives of the northern elephant seal Mirounga angustirostris, blood temperature profiles were obtained in translocated juvenile elephant seals equipped with a thermistor and backpack recorder. Representative temperature (the y-intercept of the mean temperature vs. dive duration relationship) was 37.2 degrees +/- 0.6 degrees C (n=3 seals) in the extradural vein, 38.1 degrees +/- 0.7 degrees C (n=4 seals) in the hepatic sinus, and 38.8 degrees +/- 16 degrees C (n=6 seals) in the aorta. Mean temperature was significantly though weakly negatively related to dive duration in all but one seal. Mean venous temperatures of all dives of individual seals ranged between 36 degrees and 38 degrees C, while mean arterial temperatures ranged between 35 degrees and 39 degrees C. Transient decreases in venous and arterial temperatures to as low as 30 degrees-33 degrees C occurred in some dives >30 min (0.1% of dives in the study). The lack of significant core hypothermia during routine dives (10-30 min) and only a weak negative correlation of mean temperature with dive duration do not support the hypothesis that a cold-induced Q(10) effect contributes to metabolic suppression of central tissues during dives. The wide range of arterial temperatures while diving and the transient declines in temperature during long dives suggest that alterations in blood flow patterns and peripheral heat loss contribute to thermoregulation during diving.

2009
Meir, JU, Champagne CD, Costa DP, Williams CL, Ponganis PJ.  2009.  Extreme hypoxemic tolerance and blood oxygen depletion in diving elephant seals. American Journal of Physiology-Regulatory Integrative and Comparative Physiology. 297:R927-R939.   10.1152/ajpregu.00247.2009   AbstractWebsite

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 (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(O2) and Pa(O2) 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 PaO(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.

2008
Ponganis, PJ, Kreutzer U, Stockard TK, Lin PC, Sailasuta N, Tran TK, Hurd R, Jue T.  2008.  Blood flow and metabolic regulation in seal muscle during apnea. Journal of Experimental Biology. 211:3323-3332.   10.1242/jeb.018887   AbstractWebsite

In order to examine myoglobin (Mb) function and metabolic responses of seal muscle during progressive ischemia and hypoxemia, Mb saturation and high-energy phosphate levels were monitored with NMR spectroscopy during sleep apnea in elephant seals (Mirounga angustirostris). Muscle blood flow (MBF) was measured with laser-Doppler flowmetry (LDF). During six, spontaneous, 8-12 min apneas of an unrestrained juvenile seal, apneic MBF decreased to 46 +/- 10% of the mean eupneic MBF. By the end of apnea, MBF reached 31 +/- 8% of the eupneic value. The t(1/2) for 90% decline in apneic MBF was 1.9 +/- 1.2 min. The initial post-apneic peak in MBF occurred within 0.20 +/- 0.04 min after the start of eupnea. NMR measurements revealed that Mb desaturated rapidly from its eupenic resting level to a lower steady state value within 4 min after the onset of apnea at rates between 1.7 +/- 1.0 and 3.8 +/- 1.5% min(-1), which corresponded to a muscle O(2) depletion rate of 1-2.3 ml O(2)kg(-1) min(-1). High-energy phosphate levels did not change with apnea. During the transition from apnea to eupnea, Mb resaturated to 95% of its resting level within the first minute. Despite the high Mb concentration in seal muscle, experiments detected Mb diffusing with a translational diffusion coefficient of 4.5 x 10(-7) cm(2) s(-1), consistent with the value observed in rat myocardium. Equipoise P(O2) analysis revealed that Mb is the predominant intracellular O(2) transporter in elephant seals during eupnea and apnea.