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Levenson, DH, Ponganis PJ, Crognale MA, Deegan JF, Dizon A, Jacobs GH.  2006.  Visual pigments of marine carnivores: pinnipeds, polar bear, and sea otter. Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology. 192:833-843.   10.1007/s00359-006-0121-x   AbstractWebsite

Rod and cone visual pigments of 11 marine carnivores were evaluated. Rod, middle/long-wavelength sensitive (M/L) cone, and short-wavelength sensitive (S) cone opsin (if present) sequences were obtained from retinal mRNA. Spectral sensitivity was inferred through evaluation of known spectral tuning residues. The rod pigments of all but one of the pinnipeds were similar to those of the sea otter, polar bear, and most other terrestrial carnivores with spectral peak sensitivities (lambda(max)) of 499 or 501 nm. Similarly, the M/L cone pigments of the pinnipeds, polar bear, and otter had inferred lambda(max) of 545 to 560 nm. Only the rod opsin sequence of the elephant seal had sensitivity characteristic of adaptation for vision in the marine environment, with an inferred lambda(max) of 487 nm. No evidence of S cones was found for any of the pinnipeds. The polar bear and otter had S cones with inferred lambda(max) of similar to 440 nm. Flicker-photometric ERG was additionally used to examine the in situ sensitivities of three species of pinniped. Despite the use of conditions previously shown to evoke cone responses in other mammals, no cone responses could be elicited from any of these pinnipeds. Rod photoreceptor responses for all three species were as predicted by the genetic data.

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McDonald, BI, Ponganis PJ.  2014.  Deep-diving sea lions exhibit extreme bradycardia in long-duration dives. Journal of Experimental Biology. 217:1525-1534.   10.1242/jeb.098558   AbstractWebsite

Heart rate and peripheral blood flow distribution are the primary determinants of the rate and pattern of oxygen store utilisation and ultimately breath-hold duration in marine endotherms. Despite this, little is known about how otariids (sea lions and fur seals) regulate heart rate (f(H)) while diving. We investigated dive f(H) in five adult female California sea lions (Zalophus californianus) during foraging trips by instrumenting them with digital electrocardiogram (ECG) loggers and time depth recorders. In all dives, dive f(H) (number of beats/duration; 50 +/- 9 beats min(-1)) decreased compared with surface rates (113 +/- 5 beats min(-1)), with all dives exhibiting an instantaneous f(H) below resting (<54 beats min(-1)) at some point during the dive. Both dive f(H) and minimum instantaneous f(H) significantly decreased with increasing dive duration. Typical instantaneous f(H) profiles of deep dives (>100 m) consisted of: (1) an initial rapid decline in f(H) resulting in the lowest instantaneous f(H) of the dive at the end of descent, often below 10 beats min-1 in dives longer than 6 min in duration; (2) a slight increase in f(H) to similar to 10-40 beats min(-1) during the bottom portion of the dive; and (3) a gradual increase in f(H) during ascent with a rapid increase prior to surfacing. Thus, f(H) regulation in deep-diving sea lions is not simply a progressive bradycardia. Extreme bradycardia and the presumed associated reductions in pulmonary and peripheral blood flow during late descent of deep dives should (a) contribute to preservation of the lung oxygen store, (b) increase dependence of muscle on the myoglobin-bound oxygen store, (c) conserve the blood oxygen store and (d) help limit the absorption of nitrogen at depth. This f(H) profile during deep dives of sea lions may be characteristic of deep-diving marine endotherms that dive on inspiration as similar f(H) profiles have been recently documented in the emperor penguin, another deep diver that dives on inspiration.

McDonald, BI, Ponganis PJ.  2012.  Lung collapse in the diving sea lion: hold the nitrogen and save the oxygen. Biology Letters. 8:1047-1049.   10.1098/rsbl.2012.0743   AbstractWebsite

Lung collapse is considered the primary-mechanism that limits nitrogen absorption and decreases the risk of decompression sickness in deep-diving marine mammals. Continuous arterial partial pressure of oxygen (P-O2) profiles in a free-diving female California sea lion (Zalophus californianus) revealed that (i) depth of lung collapse was near 225 m as evidenced by abrupt changes in P-O2 during descent and ascent, (ii) depth of lung collapse was positively related to maximum dive depth, suggesting that the sea lion increased inhaled air volume in deeper dives and (iii) lung collapse at depth preserved a pulmonary oxygen reservoir that supplemented blood oxygen during ascent so that mean end-of-dive arterial P-O2 was 74+/-17 mmHg (greater than 85% haemoglobin saturation). Such information is critical to the understanding and the modelling of both nitrogen and oxygen transport in diving marine mammals.

McDonald, BI, Ponganis PJ.  2013.  Insights from venous oxygen profiles: oxygen utilization and management in diving California sea lions. Journal of Experimental Biology. 216:3332-3341.   10.1242/jeb.085985   AbstractWebsite

The management and depletion of O-2 stores underlie the aerobic dive capacities of marine mammals. The California sea lion (Zalophus californianus) presumably optimizes O-2 store management during all dives, but approaches its physiological limits during deep dives to greater than 300. m depth. Blood O-2 comprises the largest component of total body O-2 stores in adult sea lions. Therefore, we investigated venous blood O-2 depletion during dives of California sea lions during maternal foraging trips to sea by: (1) recording venous partial pressure of O-2 (PO2) profiles during dives, (2) characterizing the O-2-hemoglobin (Hb) dissociation curve of sea lion Hb and (3) converting the PO2 profiles into percent Hb saturation (SO2) profiles using the dissociation curve. The O-2-Hb dissociation curve was typical of other pinnipeds (P-50=28 +/- 2mmHg at pH 7.4). In 43% of dives, initial venous SO2 values were greater than 78% (estimated resting venous SO2), indicative of arterialization of venous blood. Blood O-2 was far from depleted during routine shallow dives, with minimum venous SO2 values routinely greater than 50%. However, in deep dives greater than 4. min in duration, venous SO2 reached minimum values below 5% prior to the end of the dive, but then increased during the last 30-60s of ascent. These deep dive profiles were consistent with transient venous blood O-2 depletion followed by partial restoration of venous O-2 through pulmonary gas exchange and peripheral blood flow during ascent. These differences in venous O-2 profiles between shallow and deep dives of sea lions reflect distinct strategies of O-2 store management and suggest that underlying cardiovascular responses will also differ.

Meir, JU, Robinson PW, Vilchis LI, Kooyman GL, Costa DP, Ponganis PJ.  2013.  Blood oxygen depletion is independent of dive function in a deep diving vertebrate, the northern elephant seal. Plos One. 8   10.1371/journal.pone.0083248   AbstractWebsite

Although energetics is fundamental to animal ecology, traditional methods of determining metabolic rate are neither direct nor instantaneous. Recently, continuous blood oxygen (O-2) measurements were used to assess energy expenditure in diving elephant seals (Mirounga angustirostris), demonstrating that an exceptional hypoxemic tolerance and exquisite management of blood O-2 stores underlie the extraordinary diving capability of this consummate diver. As the detailed relationship of energy expenditure and dive behavior remains unknown, we integrated behavior, ecology, and physiology to characterize the costs of different types of dives of elephant seals. Elephant seal dive profiles were analyzed and O-2 utilization was classified according to dive type (overall function of dive: transit, foraging, food processing/rest). This is the first account linking behavior at this level with in vivo blood O-2 measurements in an animal freely diving at sea, allowing us to assess patterns of O-2 utilization and energy expenditure between various behaviors and activities in an animal in the wild. In routine dives of elephant seals, the blood O-2 store was significantly depleted to a similar range irrespective of dive function, suggesting that all dive types have equal costs in terms of blood O-2 depletion. Here, we present the first physiological evidence that all dive types have similarly high blood O-2 demands, supporting an energy balance strategy achieved by devoting one major task to a given dive, thereby separating dive functions into distinct dive types. This strategy may optimize O-2 store utilization and recovery, consequently maximizing time underwater and allowing these animals to take full advantage of their underwater resources. This approach may be important to optimizing energy expenditure throughout a dive bout or at-sea foraging trip and is well suited to the lifestyle of an elephant seal, which spends >90% of its time at sea submerged making diving its most "natural" state.

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.

Meir, JU, Stockard TK, Williams CL, Ponganis KV, Ponganis PJ.  2008.  Heart rate regulation and extreme bradycardia in diving emperor penguins. Journal of Experimental Biology. 211:1169-1179.   10.1242/jeb.013235   AbstractWebsite

To investigate the diving heart rate (f(H)) response of the emperor penguin (Aptenodytes forsteri), the consummate avian diver, birds diving at an isolated dive hole in McMurdo Sound, Antarctica were outfitted with digital electrocardiogram recorders, two-axis accelerometers and time depth recorders ( TDRs). In contrast to any other freely diving bird, a true bradycardia (fH significantly < f(H) at rest) occurred during diving [dive fH (total beats/duration)= 57 +/- 2 beats min(-1), f(H) at rest= 73 +/- 2 beats min(-1) ( mean +/- s. e. m.)]. For dives less than the aerobic dive limit ( ADL; duration beyond which [ blood lactate] increases above resting levels), dive f(H)= 85 +/- 3 beats min(-1), whereas f H in dives greater than the ADL was significantly lower (41 +/- 1 beats min(-1)). In dives greater than the ADL, f(H) reached extremely low values: f H during the last 5 mins of an 18 min dive was 6 beats min(-1). Dive f H and minimum instantaneous f(H) during dives declined significantly with increasing dive duration. Dive f(H) was independent of swim stroke frequency. This suggests that progressive bradycardia and peripheral vasoconstriction ( including isolation of muscle) are primary determinants of blood oxygen depletion in diving emperor penguins. Maximum instantaneous surface interval f(H) in this study is the highest ever recorded for emperor penguins ( 256 beats min(-1)), equivalent to f(H) at V-O2 max., presumably facilitating oxygen loading and post-dive metabolism. The classic Scholander-Irving dive response in these emperor penguins contrasts with the absence of true bradycardia in diving ducks, cormorants, and other penguin species.

Meir, JU, Ponganis PJ.  2009.  High-affinity hemoglobin and blood oxygen saturation in diving emperor penguins. Journal of Experimental Biology. 212:3330-3338.   10.1242/jeb.033761   AbstractWebsite

The emperor penguin (Aptenodytes forsteri) thrives in the Antarctic underwater environment, diving to depths greater than 500m and for durations longer than 23 min. To examine mechanisms underlying the exceptional diving ability of this species and further describe blood oxygen (O(2)) transport and depletion while diving, we characterized the O(2)-hemoglobin (Hb) dissociation curve of the emperor penguin in whole blood. This allowed us to (1) investigate the biochemical adaptation of Hb in this species, and (2) address blood O(2) depletion during diving, by applying the dissociation curve to previously collected partial pressure of O(2) (P(O2)) profiles to estimate in vivo Hb saturation (S(O2)) changes during dives. This investigation revealed enhanced Hb-O(2) affinity (P(50)=28mmHg, pH7.5) in the emperor penguin, similar to high-altitude birds and other penguin species. This allows for increased O(2) at low blood P(O2) levels during diving and more complete depletion of the respiratory O(2) store. S(O2) profiles during diving demonstrated that arterial S(O2) levels are maintained near 100% throughout much of the dive, not decreasing significantly until the final ascent phase. End-of-dive venous S(O2) values were widely distributed and optimization of the venous blood O(2) store resulted from arterialization and near complete depletion of venous blood O(2) during longer dives. The estimated contribution of the blood O(2) store to diving metabolic rate was low and highly variable. This pattern is due, in part, to the influx of O(2) from the lungs into the blood during diving, and variable rates of tissue O(2) uptake.

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.

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Nagy, KA, Kooyman GL, Ponganis PJ.  2001.  Energetic cost of foraging in free-diving emperor penguins. Physiological and Biochemical Zoology. 74:541-547.   10.1086/322165   AbstractWebsite

Hypothesizing that emperor penguins (Aptenodytes forsteri) would have higher daily energy expenditures when foraging for their food than when being hand-fed and that the increased expenditure could represent their foraging cost, we measured field metabolic rates (FMR; using doubly labeled water) over 4-d periods when 10 penguins either foraged under sea ice or were not allowed to dive but were fed fish by hand. Surprisingly, penguins did not have higher rates of energy expenditure when they dove and captured their own food than when they did not forage but were given food. Analysis of time-activity and energy budgets indicated that FMR was about 1.7 x BMR (basal metabolic rate) during the 12 h d(-1) that penguins were lying on sea ice. During the remaining 12 h d(-1), which we termed their "foraging period" of the day, the birds were alert and active (standing, preening, walking, and either free diving or being hand-fed), and their FMR was about 4.1 x BMR. This is the lowest cost of foraging estimated to date among the eight penguin species studied. The calculated aerobic diving limit (ADL(C)), determined with the foraging period metabolic rate of 4.1 x BMR and known O-2 stores, was only 2.6 min, which is far less than the 6-min ADL previously measured with postdive lactate analyses in emperors diving under similar conditions. This indicates that calculating ADL(C) from an at-sea or foraging-period metabolic rate in penguins is not appropriate. The relatively low foraging cost for emperor penguins contributes to their relatively low total daily FMR (2.9 x BMR). The allometric relationship for FMR in eight penguin species, including the smallest and largest living representatives, is kJ d(-1) = 1,185 kg(0.705).

Newsome, LR, Ponganis PJ, Reichman R, Nakaji N, Jaski B, Haltley M.  1992.  Portable percutaneous cardiopulmonary bypass: use in supported coronary angioplasty, aortic valvuloplasty, and cardiac arrest. Journal of Cardiothoracic and Vascular Anesthesia. 6:328-331.   10.1016/1053-0770(92)90151-V   Abstract

Portable cardiopulmonary bypass (CPB) systems consisting of a battery source and charger, centrifugal pump, hollow-fiber oxygenator, pump tubing, and large-bore thin-walled femoral arterial and venous cannulae have been commercially available for the past few years. Modifications of the Seldinger technique to allow percutaneous placement facilitate the expeditious institution of CPB in virtually any hospital setting.‘” As a result of this new technology, “supported” percutaneous transluminal coronary angioplasty (PTCA) and aortic valvuloplasty (AVP), which use the prophylactic institution of percutaneous CPB prior to the beginning of these procedures, were reported in 1990. Additionally, these portable systems have been used at various medical centers to help resuscitate patients suffering from cardiac arrest from a variety of causes. Two case histories representative of the use of such a system in both scenarios and including some anesthetic considerations for the use of such systems, specifically in supported angioplasties, are reported. In addition, the authors’ total experience with portable CPB is described.

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Ponganis, PJ, Ponganis EP, Ponganis KV, Kooyman GL, Gentry RL, Trillmich F.  1990.  Swimming velocities in otariids. Canadian Journal of Zoology-Revue Canadienne De Zoologie. 68:2105-2112.   10.1139/z90-293   AbstractWebsite

Velocities during surface swimming and diving were measured with microprocessor recorders in four otariid species: northern fur seals (Callorhinusursinus), Galapagos sea lions (Zalophuscalifornianuswollebaeki), Galapagos fur seals (Arctocephalusgalapagoensis), and Hooker's sea lions (Phocarctoshookeri). Mean surface swimming velocities ranged from 0.6 to 1.9 m/s. Transit distances to feeding sites (1.2–90 km) were calculated using these velocities. Dive velocities, recorded every 15 s, ranged from 0.9 to 1.9 m/s. These velocities were consistent with calculated minimal cost of transport velocities in the smaller species. Using time partitioning, the metabolic cost of a northern fur seal foraging trip is estimated on the basis of recorded velocities and their calculated energy costs. This value is within 6% of that previously made with doubly labeled water techniques.

Ponganis, PJ, Kooyman GL, Sartoris D, Jobsis P.  1992.  Pinniped splenic volumes. American Journal of Physiology. 262:R322-R325. AbstractWebsite

Splenic volume was measured by computerized axial tomography in three harbor seals (Phoca vitulina) and two California sea lions (Zalophus californianus). Volumes ranged from 228 to 679 ml, representing 0.8-3.0% of calculated percentage body mass. Despite possible variation in the state of splenic contraction during the examination, these values are in the upper range of reported mammalian splenic volumes (as % of body mass). This reinforces the pinniped splenic erythrocyte storage concept.

Ponganis, PJ, Van Dam RP, Levenson DH, Knower T, Ponganis KV, Marshall G.  2003.  Regional heterothermy and conservation of core temperature in emperor penguins diving under sea ice. Comparative Biochemistry and Physiology a-Molecular & Integrative Physiology. 135:477-487.   10.1016/s1095-6433(03)00133-8   AbstractWebsite

Temperatures were recorded at several body sites in emperor penguins (Aptenodytes forsteri) diving at an isolated dive hole in order to document temperature profiles during diving and to evaluate the role of hypothermia in this well-studied model of penguin diving physiology. Grand mean temperatures (+/-S.E.) in central body sites during dives were: stomach: 37.1 +/- 0.2 degreesC (n = 101 dives in five birds), pectoral muscle: 37.8 +/- 0.1 degreesC (n = 71 dives in three birds) and axillary/brachial veins: 37.9 +/- 0.1 degreesC (n = 97 dives in three birds). Mean diving temperature and duration correlated negatively at only one site in one bird (femoral vein, r = -0.59, P < 0.05; range < 1 degreesC). In contrast, grand mean temperatures in the wing vein, foot vein and lumbar subcutaneous tissue during dives were 7.6 +/- 0.7 degreesC (n = 157 dives in three birds), 20.2 +/- 1.2 degreesC (n = 69 in three birds) and 35.2 +/- 0.2 degreesC (n = 261 in six birds), respectively. Mean limb temperature during dives negatively correlated with diving duration in all six birds (r = -0.29 to -0.60, P < 0.05). In two of six birds, mean diving subcutaneous temperature negatively correlated with diving duration (r = -0.49 and -0.78, P < 0.05). Sub-feather temperatures decreased from 31 to 35 T during rest periods to a grand mean of 15.0 +/- 0.7 degreesC during 68 dives of three birds; mean diving temperature and duration correlated negatively in one bird (r = -0.42, P < 0.05). In general, pectoral, deep venous and even stomach temperatures during diving reflected previously measured vena caval temperatures of 37-39 degreesC more closely than the anterior abdominal temperatures (19-30 degreesC) recently recorded in diving emperors. Although prey ingestion can result in cooling in the stomach, these findings and the lack of negative correlations between internal temperatures and diving duration do not support a role for hypothermia-induced metabolic suppression of the abdominal organs as a mechanism of extension of aerobic dive time in emperor penguins diving at the isolated dive hole. Such high temperatures within the body and the observed decreases in limb, anterior abdomen, subcutaneous and sub-feather temperatures are consistent with preservation of core temperature and cooling of an outer body shell secondary to peripheral vasoconstriction, decreased insulation of the feather layer, and conductive/convective heat loss to the water environment during the diving of these emperor penguins. (C) 2003 Elsevier Science Inc. All fights reserved.

Ponganis, PJ, Meir JU, Williams CL.  2010.  Oxygen store depletion and the aerobic dive limit in emperor penguins. Aquatic Biology. 8:237-245.   10.3354/ab00216   AbstractWebsite

The aerobic dive limit (ADL), dive duration associated with the onset of post-dive blood lactate elevation, has been widely used in the interpretation of diving physiology and diving behavior. However, its physiological basis is incompletely understood, and in most studies, ADLs are simply calculated with an O(2) store/O(2) consumption formula. To better understand the ADL, research has been conducted on emperor penguins diving at an isolated dive hole. This work has revealed that O(2) stores are greater than previously estimated, and that the rate of depletion of those O(2) stores appears to be regulated primarily through a diving bradycardia and the efficiency of swimming. Blood and respiratory O(2) stores are not depleted at the 5.6 min ADL determined by post-dive blood lactate measurements. It is hypothesized that muscle, isolated from the circulation during a dive, is the primary source of lactate accumulation. To predict this 5.6 min ADL for these shallow dives at the isolated dive hole with the classic O(2) store/O(2) consumption formula, an O(2) consumption rate of 2x the predicted metabolic rate of a penguin at rest is required. In contrast, if the formula is used to calculate an ADL that is defined as the time for all consumable O(2) stores to be depleted, then a 23.1 min dive, in which final venous partial pressure of oxygen (P(O2)) was 6 mm Hg (0.8 kPa), represents such a maximum limit and demonstrates that an O(2) consumption rate of about 0.5x the predicted rate of an emperor penguin at rest is required in the formula.

Ponganis, PJ, Kooyman GL, Baranov EA, Thorson PH, Stewart BS.  1997.  The aerobic submersion limit of Baikal seals, Phoca sibirica. Canadian Journal of Zoology-Revue Canadienne De Zoologie. 75:1323-1327.   10.1139/z97-756   AbstractWebsite

An aerobic dive limit (ADL), the diving duration beyond which postdive lactate concentration increases above the resting level, has been estimated theoretically for many species. Such calculations have been based on an oxygen store/diving metabolic rate (MR) equation. Until now, an ADL has been determined empirically from measurements of blood lactate concentration only in the Weddell seal, Leptonychotes weddellii. We measured post-submergence plasma lactate concentrations during spontaneous voluntary submersions of three captive adult Baikal seals (Phoca sibirica). Two-phase regression analysis revealed a transition in the lactate concentration - submersion duration relationship after the animal had been diving for 15 min. Data collected in prior studies on oxygen stores and submersion metabolic rates of Baikal seals yielded a calculated aerobic limit of 16 min. As in Weddell seals, the empirically determined aerobic limit was very similar to the theoretical limit. Furthermore, most diving durations recorded during recent studies of free-ranging Baikal seals are under this limit. These data support the concept of an ADL and its estimation by means of an oxygen store/diving MR calculation.

Ponganis, PJ, Stockard TK, Levenson DH, Berg L, Baranov EA.  2006.  Cardiac output and muscle blood flow during rest-associated apneas of elephant seals. Comparative Biochemistry and Physiology a-Molecular & Integrative Physiology. 144:105-111.   10.1016/j.cbpa.2006.02.009   AbstractWebsite

In order to evaluate hemodynamics and blood flow during rest-associated apnea in young elephant seals (Mirounga angustirostris), cardiac outputs (CO, thermodilution), heart rates (HR), and muscle blood flow (MBF, laser Doppler flowmetry) were measured.. Mean apneic COs and HRs of three seals were 46% and 39% less than eupneic values, respectively (2.1 +/- 0.3 vs. 4.0 +/- 0.1 mL kg(-1) s(-1), and 54 6 vs. 89 14 beats min(-1)). The mean apneic stroke volume (SV) was not significantly different from the eupneic value (2.3 +/- 0.2 vs. 2.7 +/- 0.5 mL kg(-1)). Mean apneic MBF of three seals was 51% of the eupneic value. The decline in MBF during apnea was gradual, and variable in both rate and magnitude. In contrast to values previously documented in seals during forced submersions (FS), CO and SV during rest-associated apneas were maintained at levels characteristic of previously published values in similarly-sized terrestrial mammals at rest. Apneic COs of such magnitude and incomplete muscle ischemia during the apnea suggest that (1) most organs are not ischemic during rest-associated apneas, (2) the blood O-2 depletion rate is greater during rest-associated apneas than during FS, and (3) the blood O-2 store is not completely isolated from muscle during rest-associated apneas. (c) 2006 Elsevier Inc. All rights reserved.

Ponganis, PJ, Kreutzer U, Sailasuta N, Knower T, Hurd R, Jue T.  2002.  Detection of myoglobin desaturation in Mirounga angustirostris during apnea. American Journal of Physiology-Regulatory Integrative and Comparative Physiology. 282:R267-R272. AbstractWebsite

H-1 NMR solution-state study of elephant seal (Mirounga angustirostris) myoglobin (Mb) and hemoglobin (Hb) establishes the temperature-dependent chemical shifts of the proximal histidyl NdeltaH signal, which reflects the respective intracellular and vascular PO2 in vivo. Both proteins exist predominantly in one major isoform and do not exhibit any conformational heterogeneity. The Mb and Hb signals are detectable in M. angustirostris tissue in vivo. During eupnea M. angustirostris muscle maintains a well-saturated MbO(2). However, during apnea, the deoxymyoglobin proximal histidyl NdeltaH signal becomes visible, reflecting a declining tissue PO2. The study establishes a firm methodological basis for using NMR to investigate the metabolic responses during sleep apnea of the elephant seal and to secure insights into oxygen regulation in diving mammals.

Ponganis, PJ, Kooyman GL.  1999.  Heart rate and electrocardiogram characteristics of a young California gray whale (Eschrichtius robustus). Marine Mammal Science. 15:1198-1207.   10.1111/j.1748-7692.1999.tb00885.x   AbstractWebsite

Electrocardiogram (ECG) analyses of Holter monitor recordings from a young California gray whale were performed to determine ECG waveform characteristics, evaluate the heart rate pattern for sinus arrhythmia, obtain resting heart rates at known body masses as the whale increased in size, and compare those heart rates with predicted heart rates from allometric equations. The PR and QRS intervals (475 +/- 35 msec, 208 +/- 24 msec, respectively, n = 20) support the concept (Meijler et al. 1992) that atrioventricular transmission and ventricular excitation times do not increase linearly in very large mammals. A sinus arrhythmia pattern at rest (apneic heart rates of 15-25 beats per min [bpm] and eupneic heart rates of 34-40 bpm) is consistent with a relative eupneic tachycardia and apneic bradycardia during diving activity of whales. The heart rate-body mass measurements (35-24 bpm at body masses of 3,531-8,200 kg) in this study (1) extend the range of allometric heart rate and body mass data in mammals a full order of magnitude, to almost 10,000 kg, (2) support the use of allometric equations (based primarily on mammals <1,000 kg in body mass) in estimating resting heart rates in whales, and (3) demonstrate that previously reported heart rates in large whales are not representative of resting heart rate, probably secondary to circumstances during measurement.

Ponganis, PJ, McDonald BI, Tift MS, Gonzalez SC, DaValle B, Gliniecki RA, Stehman CC, Hauff N, Ruddick B, Howard R.  2017.  Effects of inhalational anesthesia on blood gases and pH in California sea lions. Marine Mammal Science. 33:726-737.   10.1111/mms.12388   AbstractWebsite

Despite the widespread use of inhalational anesthesia with spontaneous ventilation in many studies of otariid pinnipeds, the effects and risks of anesthetic-induced respiratory depression on blood gas and pH regulation are unknown in these animals. During such anesthesia in California sea lions (Zalophus californianus), blood gas and pH analyses of opportunistic blood samples revealed routine hypercarbia (highest P-CO2 = 128 mm Hg [17.1 kPa]), but adequate arterial oxygenation (P-O2 > 100 mm Hg [13.3 kPa] on 100% inspiratory oxygen). Respiratory acidosis (lowest pH = 7.05) was limited by the increased buffering capacity of sea lion blood. Amarkedly widened alveolar-to-arterial P-O2 difference was indicative of atelectasis and ventilation-perfusion mismatch in the lung secondary to hypoventilation during anesthesia. Despite the generally safe track record of this anesthetic regimen in the past, these findings demonstrate the value of high inspiratory O-2 concentrations and the necessity of constant vigilance and caution. In order to avoid hypoxemia, we emphasize the importance of late extubation or at least maintenance of mask ventilation on O-2 until anesthetic-induced respiratory depression is resolved. In this regard, whether for planned or emergency application, we also describe a simple, easily employed intubation technique with the Casper zalophoscope for sea lions.

Ponganis, PJ, Stockard TK, Meir JU, Williams CL, Ponganis KV, Van Dam RP, Howard R.  2007.  Returning on empty: extreme blood O-2 depletion underlies dive capacity of emperor penguins. Journal of Experimental Biology. 210:4279-4285.   10.1242/jeb.011221   AbstractWebsite

Blood gas analyses from emperor penguins (Aptenodytes forsteri) at rest, and intravascular P-O2 profiles from free-diving birds were obtained in order to examine hypoxemic tolerance and utilization of the blood O-2 store during dives. Analysis of blood samples from penguins at rest revealed arterial P(O2)s and O-2 contents of 68 +/- 7 mmHg (1 mmHg= 133.3 Pa) and 22.5 +/- 1.3 ml O-2 dl(-1) (N= 3) and venous values of 41 +/- 10 mmHg and 17.4 +/- 2.9 ml O-2 dl(-1) (N= 9). Corresponding arterial and venous Hb saturations for a hemoglobin (Hb) concentration of 18 g dl(-1) were > 91% and 70%, respectively. Analysis of P-O2 profiles obtained from birds equipped with intravascular P-O2 electrodes and backpack recorders during dives revealed that (1) the decline of the final blood P-O2 of a dive in relation to dive duration was variable, (2) final venous P-O2 values spanned a 40-mmHg range at the previously measured aerobic dive limit (ADL; dive duration associated with onset of post-dive blood lactate accumulation), (3) final arterial, venous and previously measured air sac P-O2 values were indistinguishable in longer dives, and (4) final venous P-O2 values of longer dives were as low as 1-6 mmHg during dives. Although blood O-2 is not depleted at the ADL, nearly complete depletion of the blood O-2 store occurs in longer dives. This extreme hypoxemic tolerance, which would be catastrophic in many birds and mammals, necessitates biochemical and molecular adaptations, including a shift in the O-2-Hb dissociation curve of the emperor penguin in comparison to those of most birds. A relatively higher-affinity Hb is consistent with blood P-O2 values and O-2 contents of penguins at rest.

Ponganis, PJ, Kooyman GL, Castellini MA.  1995.  Multiple sightings of Arnouxs beaked whales along the Victoria Land coast. Marine Mammal Science. 11:247-250.   10.1111/j.1748-7692.1995.tb00523.x   AbstractWebsite
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Ponganis, PJ, Kooyman GL, Zornow MH.  1991.  Cardiac output in swimming California sea lions, Zalophus californianus. Physiological Zoology. 64:1296-1306. AbstractWebsite

Cardiac output was determined by the thermodilution technique in three California sea lions while resting and while swimming. Metabolic rates increased seven-to ninefold above resting rates during maximal exercise. While the sea lions were at rest, stroke volume was also determined by simultaneously counting heart rate during cardiac output determinations. At rest, cardiac output (2.5-3.0 mL kg-1s-1) and stroke volume (2 mL kg-1) were similar to those of harbor seals and terrestrial mammals of similar mass. During exercise, mean cardiac output increased linearly with work load and surface/submerged intervals were short and frequent. The exercise capacity of swimming sea lions appears similar to that of harbor seals, but the exercise response resembles that of terrestrial mammals more than that of harbor seals.

Ponganis, PJ, Kooyman GL, Castellini MA.  1993.  Determinants of the aerobic dive limit of Weddell seals: analysis of diving metabolic rates, postdive end tidal PO2's, and blood and muscle oxygen stores. Physiological Zoology. 66:732-749. AbstractWebsite

The mean aerobic dive limit (ADL) for Weddell seals was calculated from data collected on diving metabolic rates (VO2) and blood and muscle O2 stores. Mean diving VO2 of adult seals during predominantly exploratory dive patterns was 4.5 mL O2 kg-1 min-1; mean VO2 of a subadult seal engaged in foraging dive bouts was 8.5 mL O2 kg-1 min-1. The adult value was 30% greater than that used in past ADL calculations. Mean plasma volume was 7% body mass (BM); blood volume calculated with the highest hematocrit (Hct) observed (66) was 21% BM. Hemoglobin concentration at such an Hct was 26% by weight. End tidal PO2 (pre- and postdive) justified the use of 95% and 20% arterial O2 saturations in the blood O2 store calculation. Total blood O2 stores were 50% greater than those used in past ADL calculations. Mean myoglobin concentration (5.4% by weight) and more recent anatomical estimates of muscle mass yielded a 35% increase in muscle O2 stores. The mean estimated ADL for a 450-kg seal calculated with these new data was 19.1 min, 2.3 min greater than in past calculations and only 1 min less than the 20-min inflection point of the curve of dive duration versus postdive lactic acid appearance. For the subadult engaged in foraging dives, the mean estimated ADL was about 9 min, again quite similar to past ADL calculations.

Ponganis, PJ, Kooyman GL.  1990.  Diving physiology of penguins. Acta XX Congressus Internationalis Ornithologici, Christchurch, New Zealand, 2-9 December 1990. ( Butler PJ, Jones DR, Eds.).:6., Wellington, N.Z.: New Zealand Ornithological Congress Trust Board Abstract
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