Robert Elsner

Diving and asphyxia : a comparative study of animals and man

Preface 1. The biological setting 2. Metabolic conservation by cardiovascular adjustments 3. Cellular tolerances and adaptations to asphyxia 4. Human divers 5. Control mechanisms 6. Perinatal asphyxia and survival, 7. Medical implications References Index.

Diving seals: are they a model for coping with oxidative stress?

The diving lifestyle of seals depends upon cardiovascular adjustments that result in frequent vasoconstriction of numerous organs. With the first post-dive breath, reperfusion allows for eliminating accumulated carbon dioxide (CO(2)) and reloading oxygen (O(2)) stores. Reintroduction of oxygenated blood raises the potential for production of reactive oxygen species (ROS) and the possibility that they may overwhelm the antioxidant defenses. This study addresses the question of possible adaptive responses that allow ringed seal (Phoca hispida) tissues to tolerate repeated cycles of ischemia and reperfusion, and thus protect them from oxidative insult. We obtained samples of ringed seal heart, muscle and kidney through the cooperation of native subsistence hunters at Barrow, Alaska. Samples were subjected to oxidative stress by addition of xanthine oxidase. Production of superoxide radical (O(2)(.-)), lipid peroxidation (as determined by the presence of thiobarbituric acid reactive substances, TBARS) and antioxidant capacity (AOX) were quantified by spectrophotometric analysis. Similarly treated pig tissues were anticipated to be more susceptible to oxidative stress. Contrary to expectations, pig tissues revealed less O(2)(.-) and TBARS compared with ringed seal tissues. These results show that ringed seal muscle, heart and kidney can be induced in vitro to generate ROS, and suggest that the living seals protective defenses may depend upon O(2)(.-) production, similar to the protective effect of experimental preconditioning, or on enhanced intermediate scavenging, as evidenced by the larger AOX found in ringed seal tissues.

Diving seals, ischemia-reperfusion and oxygen radicals

The cardiovascular adaptations of seals that contribute to their ability to tolerate long periods of diving asphyxial hypoxia result in episodic regional ischemia during diving and abrupt reperfusion upon termination of the dive. These conditions might be expected to result in production of oxygen-derived free radicals and other forms of highly reactive oxygen species. Seal organs vary during dives with respect to the degree and persistence of ischemia. Myocardial perfusion is reduced and intermittent; kidney circulation is vigorously vasoconstricted. Heart and kidney tissues from ringed seals (Phoca hispida) and domestic pigs (Sus scrofa) were compared in reactions to experimental ischemia. Resulting production of hypoxanthine, indicative of ATP degradation, was higher in pig than in seal tissues. Activity of superoxide dismutase (SOD), an oxygen radical scavenger, was higher in seal heart. We suggest that these results indicate enhanced protective cellular mechanisms in seals against the potential hazard of highly reactive oxygen forms. SOD activity was unexpectedly higher in pig kidney.

Coping with physiological oxidative stress: a review of antioxidant strategies in seals

While diving, seals are exposed to apnea-induced hypoxemia and repetitive cycles of ischemia/reperfusion. While on land, seals experience sleep apnea, as well as prolonged periods of food and water deprivation. Prolonged fasting, sleep apnea, hypoxemia and ischemia/reperfusion increase oxidant production and oxidative stress in terrestrial mammals. In seals, however, neither prolonged fasting nor apnea-induced hypoxemia or ischemia/reperfusion increase systemic or local oxidative damage. The strategies seals evolved to cope with increased oxidant production are reviewed in the present manuscript. Among these strategies, high antioxidant capacity and the oxidant-mediated activation of hormetic responses against hypoxia and oxidative stress are discussed. In addition to expanding our knowledge of the evolution of antioxidant defenses and adaptive responses to oxidative stress, understanding the mechanisms that naturally allow mammals to avoid oxidative damage has the potential to advance our knowledge of oxidative stress-induced pathologies and to enhance the translative value of biomedical therapies in the long term.

Blood viscosity in phocid seals: possible adaptations to diving

Summary1.Mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) of phocid seal red blood cells (RBC) are elevated compared to those of most terrestrial mammalian species. The influence of these characteristics on blood flow was revealed by viscosity (VIS) measurements.2.RBC morphology and VIS of whole blood from 7 harbor seals and 5 northern elephant seals were compared with blood of the domestic pig. Samples were analysed for RBC count, white blood cell (WBC) count, total plasma proteins, hematocrit (HCT), MCV and MCHC. Viscosity measurements were made at shear rates from 11.5 to 230.4 s−1 on a Wells-Brookfield cone-plate viscometer at 37°C.3.Mean values for HCT (%), MCV (μm3) and MCHC (%) were, respectively: elephant seal: 57, 176, 44; harbour seal: 53, 105, 38; domestic pig: 28, 54, 34. Pig blood was reconstituted to match seal blood HCTs. VIS determinations showed that seal and pig blood conform to the general mammalian dependence of VIS upon shear rate and HCT.4.Seal blood VIS was 28% (harbour seal) and 16% (elephant seal) less than pig blood VIS at low shear (P<0.05). Seal blood carried more hemoglobin per unit volume than did pig blood reconstituted to the same HCT. Fewer, larger RBC with higher MCHC, and hence elevated oxygen storage, accompanied by reduced VIS and reduced flow resistance near stasis suggests that this feature of phocid seal blood is an adaptation to circulatory redistribution during long dives.

Hypoxia-Inducible Factor in Ringed Seal (Phoca hispida) Tissues

Tissue hypoxia and ischemia–reperfusion pose a dangerous situation for oxidative stress. However, diving mammals and birds show pronounced resistance to oxidative injury under such conditions, which are a consequence of selective vasoconstriction during a dive. As the function of Hypoxia-Inducible Factor-1α (HIF-1α) in protection against and adaptation to hypoxia has been recognized in terrestrial animals, we have investigated the genomics and expression of this protein in ringed seal (Phoca hispida) in order to determine if it may play a protective role in this diving mammal. PCR studies using primers based on sequences from mouse HIF-1α exons 3, 4, 5, 6, 9, 10, 11, 12 and 15 showed that DNA from seal lung generated PCR products similar to those from mouse DNA. These studies have established that a putative HIF-1α gene exists in the seal genome that appears to have a similar but not identical sequence to the mouse gene. Seal lung and skeletal muscle tissues showed the highest relative levels of HIF-1α protein expression, with heart muscle showing significantly lower levels, and levels of HIF-1β protein expression paralleled this situation. Analysis of oxidized cellular protein levels indicated that seal lung and heart muscle had the lowest levels of oxidized proteins. Thus, as seal lung tissue had the highest level of HIF-1α protein expression and the second lowest level of protein oxidation, this suggests that HIF-1α expression may have an important protective effect in this tissue in diving mammals. Our results support the hypothesis that HIF-1α expression is dependent on both tissue-specific energy requirements and adequate metabolic supply-to-demand ratio. Combined, the evidence available suggests that diving mammals have an overall anticipatory response to avoid the ill effects of dive-associated ischemia–reperfusion which may involve the HIF-1 system.

What diving animals might tell us about blood flow regulation

The ability of air-breathing aquatic mammals and birds to dive for long durations has intrigued physiologists for over 100 years. Much of this capacity results from enhanced oxygen storage and selective vasoconstriction in tissues other than the brain, with consequent conservation of oxygen. However, this view may be too simplistic, since recent studies have revealed a rapid and profound inhibition of the ability of arteries to constrict when subjected to ischemia or pure hypoxia [1, 2]. Nowhere in nature is the apparent conflict between local tissue metabolic needs and survival of the whole organism better demonstrated than in the protection of marine mammals from asphyxia during diving. Central nervous control of tissue blood flow during diving appears, on initial scrutiny, to be at odds with the autoregulatory control of blood flow at the tissue level. These matters raise fundamental and fascinating questions for physiological investigation.

Comparative functional properties of mitochondria from seal and dog hearts.

The harbor seal (Phoca vitulina) is capable of protracted dives resulting in low arterial PO2 levels. The mammalian heart is an aerobic organ depending primarily on mitochondrial oxidations for energy (ATP). Heart mitochondria were isolated from freshly killed seals and the functional data obtained compared to dog heart mitochondria isolated under similar conditions. The percentage yields of mitochondria based on cytochrome oxidase recovery were essentially the same from dog and seal hearts. However, the actual quantity of mitochondrial protein obtained per gram of seal heart tissue was lower than that isolated from dog heart. Phosphorylating rates of respiration (State 3; Q02) and cytochrome content were significantly lower in seal heart mitochondria compared to dog. The data indicate that seal hearts have fewer mitochondria per gram of tissue, lower active respiratory rates and lower cytochrome contents than dog heart.

Seal adaptations for long dives: recent studies of ischemia and oxygen radicals

Some seals species are well adapted to diving asphyxia. These adaptations include prominent cardiovascular responses of bradycardia, reduced cardiac output and selective vasoconstriction in some organs resulting in overall oxygen conservation for the most oxygen-sensitive tissues. Brain perfusion is relatively well maintained, myocardial flow becomes intermittent, while kidney and other visceral circulation ceases entirely or is markedly reduced. The result is an overall conservation of available oxygen and maintenance of essential functions. Ischemia poses a potential threat if circulation is not restored within a critical time. However, another hazard of equal or greater potential may result from the burst of oxygen-derived free radicals and other forms of highly reactive oxygen produced by the post-ischemic re-oxygenation. Seal organs tolerate ischemia and reperfusion better than do those of terrestrial mammals. Studies of isolated arteries reveal some of the controls governing their reactivity. Tissue analyses from harp and ringed seals, Phoca groenlandica and Phoca hispida, show that hypoxanthine, a potential oxygen free radical generator, was produced in ischemic heart and kidney. We suggest that its effects may be blunted in seals by being harmlessly metabolized or recycled.

Voluntary hypometabolism in an indian yogi

Abstract 1. 1. It has been claimed that Indian yogis can voluntarily become hypometabolic (bhoogarbha samadhi) in a sealed underground chamber as a means of remaining in a mediative state for multiday periods. 2. 2. To investigate this claim we obtained cooperation of a practitioner of bhoogarbha samadhi. In an open flow system, we measured his resting rate of oxygen consumption and also his oxygen consumption rate over a 5 h period during which he was requested to display his abilities to become hypometabolic as if he were in bhoogarbha samadhi. 3. 3. The yogis resting O2 consumption was 3.06 ml O2kg-1 min1 and his O2 consumption over a 4h period of meditation was 1.85±0.26 ml O2kg-1min-1, a reduction of 40%. 4. 4. At the beginning of the mediation there was a peripheral vasodilation and a fall in core body temperature of 0.4°C. These events were reversed at the end of the meditation period. 5. 5. This study confirms that Indian yogis can enter a state of self-induced hypometabolism, but the mechanisms remain unknown.