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PubMed1991

Diving and hypothermia.

Hypothermia is not and should not be a prevalent feature of diving, yet many divers become extremely cold and uncomfortable during their work. It is not difficult to provide adequate insulation to protect the torso but if movement and dexterity are to be maintained, the extremities will inevitably suffer. Free swimming divers are limited by duration in cold (5 degrees C), shallow (10 m) water. Six hours is a typical maximum before both core cooling and extremity pain or dysfunction pose a threat. Habituation to cold may be observed in some divers. Surface supplied or bell supported divers, relying on supplementary hot water, need between 500 and 3500 Watts to preserve comfort over the range 10 to 300 m depth. Deep diving, using oxyhelium gas mixtures, can result in high respiratory convective losses in excess of 300 Watts. Heat exchangers are used to prevent damage to the tract. There have been a number of cases where hypothermia has been implicated in the cause of death in diving accidents, but generally the reason is not lack of physiological knowledge but equipment failure and inadequate contingency. Recent developments in diver protection have focused on electrically heated hand wear to preserve performance and prevent the risk of non freezing injury in a relatively inactive diver.

Acclimatization↗
PubMed1998

Mechanism and evolution of hypoxia-tolerance in humans.

To physiologists, the term 'adaptation' usually refers to any trait that is considered advantageous; evolutionary biologists require a more rigorous definition (restricting it to traits arising and maintained under selection). By their definition, many physiological traits may merely reflect inheritance passed on through lineage. In considering the evolution of tolerance to reduced oxygen availability, we examined the issue (of true adaptations versus simple inheritance) in pinnipeds (the two dominant groups, phocids and otariids, with varying diving capacities) and in human lineages exposed for varying generational periods to hypobaric hypoxia. Basic principles of the evolution of complex physiological systems first emerged from an analysis of the diving response. We then analyzed human responses to hypobaric hypoxia in three different lineages: lowlanders, Andean natives (Quechuas) and Himalayan natives (Sherpas). As in the pinniped example, we found 'conservative' and 'adaptable' physiological characters involved in human responses to hypoxia. Conservative characters are clearly dominant and are too numerous to outline in detail; three examples are haemoglobin oxygen-affinities, the organization of muscle into different fibre types and the brain's almost exclusive preference for glucose as a fuel. Most notably, we also found evidence for 'adaptable' characters at all levels of organization examined. At the whole-body level in Quechuas and Sherpas, we found (i) that maximum aerobic and anaerobic exercise capacities were down-regulated, (ii) that the acute effect of hypoxia (making up the energy deficit due to oxygen lack; i.e. the Pasteur effect) expected from lowlanders was blunted, and (iii) that acclimation effects were also attenuated. The biochemical behaviour of skeletal muscles was consistent with lowered reliance on glycolytic contributions to energy supply, thus improving the yield of ATP per mole of carbon fuel utilized. Heart adaptations also seemed to rely upon stoichiometric efficiency adjustments, improving the yield of ATP per mole of oxygen consumed (by using glucose in preference to fatty acids). Most of the biochemical and physiological adaptations we noted (both as acute and as acclimation responses) were similar in Sherpas and Quechuas. These two lineages have not shared a common ancestor for approximately one-third of the history of our species, so it is possible that their similar physiological traits arose independently as hypoxia defence adaptations in two different times and places in our history. As in the evolution of exquisite capacities for management of oxygen down to vanishingly low levels in diving animals, the evolution of human hypoxia-tolerance can be described in terms of how two (conservative versus adaptable) categories of physiological characters are assembled in different human lineages and how the assembly changes through generational time. More recent evidence indicating that our species evolved under 'colder, drier and higher' conditions suggests that these adaptations may represent the 'ancestral' physiological condition for humans.

Adaptation, Physiological↗
PubMed1987

Seadragon VI: a 7-day saturation dive at 31 ATA. V. Cardiovascular responses to a 90 degree body tilt.

Cardiovascular deconditioning (CD) has been reported to occur in weightlessness, bed rest, and head-out water immersion. An expanded intrathoracic blood volume results, at least initially, in all these diverse conditions. Subjects in hyperbaric environments exhibit cephalad redistribution of blood volume, which also occurs in weightlessness, bed rest, and head-out water immersion. This physiologic similarity led us to suspect that CD may also occur as a consequence of hyperbaric exposure. We examined this possibility in 3 young male subjects during a 7-d dry saturation dive at 31 ATA. Changes in blood pressure, heart rate, and stroke volume were measured before and during 15 min of the 90 degree body tilt. These changes, expressed either singly or in combination, provided indications of CD during and immediately after hyperbaric exposure. One of the principal indicators of CD was the inability to exert adequate vasoconstriction. In addition, 1 subject fainted during hyperbaric exposure, whereas no such episode occurred before or after the exposure. These findings suggest that inappropriate orthostatic reflexes may be evoked by hyperbaria and reduced physical activity over the period of confinement. It should be noted, however, that CD was already evident within 24 h of hyperbaric exposure, suggesting that the initial phase of CD was unrelated to physical confinement. We postulate that CD occurs during hyperbaric exposure as an expression of cardiovascular and neurohumoral adaptation to an expanded central blood volume with a reduced total blood volume.

Adult↗
PubMed2004

Trigeminocardiac reflex. A clinical phenomenon or a new physiological entity?

The trigemino-cardiac reflex (TCR) is defined as the sudden onset of parasympathetic dysrhythmia, sympathetic hypotension, apnea or gastric hypermotility during stimulation of any of the sensory branches of the trigeminal nerve. The sensory nerve endings of the trigeminal nerve send neuronal signals via the Gasserian ganglion to the sensory nucleus of the trigeminal nerve, forming the afferent pathway of the reflex arc. This afferent pathway continues along the short internuncial nerve fibers in the reticular formatio to connect with the efferent pathway in the motor nucleus of the vagus nerve. Clinically, the trigemino-cardiac reflex has been reported to occur during craniofacial surgery, balloon-compression rhizolysis of the trigeminal ganglion, and tumor resection in the cerebellopontine angle. Apart from the few clinical reports, the physiological function of this brainstem-reflex has not yet been fully explored. From experimental findings, it may be suggested that the trigemino-cardiac reflex represents an expression of a central neurogenic reflex leading to rapid cerebrovascular vasodilatation generated from excitation of oxygen-sensitive neurons in the rostral ventrolateral medulla oblongata. By this physiological response, the adjustments of the systemic and cerebral circulations are initiated to divert blood to the brain or to increase blood flow within it. As it is generally accepted that the diving reflex and ischemic tolerance appear to involve at least partially similar physiological mechanisms, the existence of such endogenous neuroprotective strategies may extend the actually known clinical appearance of the TCR and include the prevention of other potentially brain injury states as well. This may be in line with the suggestion that the TCR is a physiological, but not a pathophysiological entity.

Afferent Pathways↗
PubMed1990

Paradoxical hypertension after repair of coarctation of the aorta: a review of its causes.

Correction of a coarctation of the aorta, an apparent simple cause of hypertension, paradoxically can provoke two hypertensive responses, one of which is potentially fatal. The first, limited to the first 24 hours, occurs in nearly one half of the patients. This is likely due to the high set of the carotid baroreceptors. The second, which may be associated with abdominal pain and, in some, with necrosis of the small bowel as a result of severe arteritis confined to arteries arising from the aorta below the coarctation, develops in about one half of the first responders. Norepinephrine excretion greatly increases for several days, whereas angiotensin levels are elevated for 3 to 4 days. The hypertension responds to beta-blockers, to arterial smooth muscle relaxants, and to angiotensin converting enzymes. A theory is advanced to explain the second response. It is the adaptation gone awry that ensures adequate flow to exercising muscles below the coarctation, above and beyond that delivered by increasing the systolic pressure. It could be a regionally controlled mechanism similar to the rationing of blood flow in diving mammals.

Adaptation, Physiological↗
PubMed2002

Kinetic and dynamic models of diving gases in decompression sickness prevention.

Decompression sickness is a complex phenomenon involving gas exchange, bubble dynamics and tissue response. Relatively simple deterministic compartmental models using empirically derived parameters have been the mainstay of the practice for preventing decompression sickness since the early 1900s. Decades of research have improved our understanding of decompression physiology, and the insights incorporated in decompression models have allowed people to dive deeper into the ocean. However, these efforts have not yet, and are unlikely in the near future, to result in a 'universal' deterministic model that can predict when decompression sickness will occur. Divers using current recreational dive computers need to be aware of their limitations. Probabilistic models based on the estimation of parameters using modern statistical methods from large databases of dives offer a new approach and can provide a means of standardisation of deterministic models. Future improvements in decompression practice will depend on continued improvement in understanding the kinetics and dynamics of gas exchange, bubble evolution and tissue response, and the incorporation of this knowledge in risk models whose parameters can be estimated from large databases of human and animal data.

Decompression Sickness↗
PubMed1999

High aerobic capacities in the skeletal muscles of pinnipeds: adaptations to diving hypoxia.

The objective was to assess the aerobic capacity of skeletal muscles in pinnipeds. Samples of swimming and nonswimming muscles were collected from Steller sea lions (Eumetopias jubatus, n = 27), Northern fur seals (Callorhinus ursinus, n = 5), and harbor seals (Phoca vitulina, n = 37) by using a needle biopsy technique. Samples were either immediately fixed in 2% glutaraldehyde or frozen in liquid nitrogen. The volume density of mitochondria, myoglobin concentration, citrate synthase activity, and beta-hydroxyacyl-CoA dehydrogenase was determined for all samples. The swimming muscles of seals had an average total mitochondrial volume density per volume of fiber of 9.7%. The swimming muscles of sea lions and fur seals had average mitochondrial volume densities of 6.2 and 8.8%, respectively. These values were 1.7- to 2.0-fold greater than in the nonswimming muscles. Myoglobin concentration, citrate synthase activity, and beta-hydroxyacyl-CoA dehydrogenase were 1.1- to 2. 3-fold greater in the swimming vs. nonswimming muscles. The swimming muscles of pinnipeds appear to be adapted for aerobic lipid metabolism under the hypoxic conditions that occur during diving.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1990

[Structure of the neocortex of the Baikal ringed seal (Pusa sibirica Gm.)].

The sulci and gyri of the neocortex, as well as cyto-, synaptoarchitectonics and neuronal composition of the sensomotor (brain area) have been studied in the Baikal ringed seal. The structure of the sulci and gyri have been found to be similar to that in carnivores. The following specific features have been revealed in the brain of this endemic species: a thick layer I, presence of giant pyramidal cells in the layer III, large mitochondria in the presynaptic parts and dendrites. The results obtained are discussed concerning adaptation to semiaqueous way of life and to diving.

Adaptation, Physiological↗
PubMed2005

Acute effects of a single open sea air dive and post-dive posture on cardiac output and pulmonary gas exchange in recreational divers.

OBJECTIVE: To evaluate the cardiopulmonary effects of open sea scuba air diving to 39 m (30 minutes bottom time) with standard decompression. To account for possible gravity dependent effects of venous gas bubbles, the variables were measured in different post-dive body postures and compared with the baseline values before the dive in the same posture. METHODS: Eight male divers conducted two similar dives on successive days. Their posture before and after the dive was either sitting or supine, in random order. The divers were evaluated before and 30, 60, and 90 minutes after the dive. Venous bubbles were detected by precordial Doppler after the dive in four divers in the supine posture and two divers in the sitting posture. RESULTS: Arterialised oxygen tension had decreased at all times after the dive (-11.3 mm Hg, p = 0.00006), due to decreased alveolar oxygen tension, irrespective of posture. Apart from an increase in the sitting posture 30 minutes after the dive, pulmonary capacity for carbon monoxide diffusion and cardiac index decreased, mostly 60 minutes after the dive (-9%, p = 0.0003 and -20%, p = 0.0002 respectively). The decrease in cardiac index was greater in the supine posture (p = 0.0004), and the physiological dead space/tidal volume ratio increased more in the sitting position (p = 0.006). CONCLUSIONS: Field dives are associated with moderate impairments in cardiac output and gas exchange. Some of these impairments appear to depend on the posture of the diver after the dive.

Adult↗
PubMed2006

The effects of depth, temperature and food ingestion on the foraging energetics of a diving endotherm, the double-crested cormorant (Phalacrocorax auritus).

Avian divers are confronted with a number of physiological challenges when foraging in cold water, especially at depth. Besides the obvious constraint imposed by the necessity to return to the surface for gas exchange, cold water temperatures and a reduction in body insulation due to the increase in pressure with dive depth will elevate the energetic costs of foraging in these endotherm divers. The complex effect that depth has on the diving energetics of aquatic birds has largely been ignored. To date, no study has assessed the impact of depth on diving energetics over a significant depth range, naturally encountered by the diver. We used open-circuit respirometry to study the energetic requirements of a foot-propelled pursuit diver, the double-crested cormorant (Phalacrocorax auritus albociliatus), when diving in a shallow (1 m) and deep (10 m) dive tank and when resting in air and water. We also investigated the modifying effects of air or water temperature and feeding status on the costs associated with diving and resting. Of all factors investigated, dive depth exercised the strongest influence on diving metabolic rate. Diving to 10 m depth increased metabolic rate on average by 22% when compared with shallow diving. Declining temperatures in air and water significantly elevated metabolic rate of cormorants resting in air and water as well as during diving. Feeding before resting in water or diving increased metabolic rate by 5-8% for at least 2 h. Cormorants maintained an elevated stomach temperature (>42 degrees C) when resting in water and during diving, even at cold temperatures. The elevated dive costs during deep diving, when compared with shallow diving, are most likely a consequence of the increased thermoregulatory costs associated with a greater heat loss to the water at depth. Nevertheless, our study shows that dive costs in double-crested cormorants are similar to those of other foot-propelled avian divers.

Animals↗
PubMed1985

Oxygen in the treatment of spinal cord decompression sickness.

Twenty-five anesthetized dogs were used to find the optimum Po2 for the delayed treatment of spinal cord decompression sickness (DCS). They were instrumented for the measurement of physiological variables and somatosensory spinal evoked potentials (SEP) given an air dive of 15 min at 10 bar (300 ft) and decompressed in under 6 min. At the surface SEP were observed for signs of DCS. Fifteen minutes after cord DCS was observed in the SEP, the dogs were compressed to 5.0 bar breathing one of 5 gas mixtures giving a Po2 of 1.0, 1.5, 2.0, 2.5, or 3.0 bar. At the start of therapy all groups were in a similar physiological state with a similar loss of SEP. Between 40 and 120 min, recovery was significantly different (P less than 0.05) between the groups, most SEP recovery having occurred within 15 min. The treatments ended with 22, 32, 70, 66, and 42% recovery, respectively. It would appear that the optimum Po2 is around 2.0 bar.

Animals↗
PubMed1990

[Evaluation of a semi-closed underwater breathing apparatus, the "eOBA"].

Semi-closed underwater breathing apparatus has commonly been used among military and commercial divers, but never available for recreational divers because of complicated operations, difficulties of maintenance, and expensiveness. Nippon Sanso K.K. has newly deployed a semi-closed circuit underwater breathing apparatus called the "eOBA". It is especially designed for divers to enjoy shallow (max. 5 m) and short (10 min.) dives. This eOBA was evaluated from manned testing based on physiological requirements for the apparatus. Four male and four female subjects participated in the three test trials. Subjects maintained their position at the depths of 2 m and 4 m for 10 min. and e exercised on the underwater ergometer at the depth of 2.4 m. The pressure at the mouthpiece, tidal volume, breathing rate, the inspired O2 level, CO2 level were monitored on breath-by-breath basis. The inspired O2 level ranged from 45% (at exercise) to 60% (at rest) and the inspired CO2 level were kept less than 1.0% in the most cases. The P-V loop indicated relatively little external work of breathing (less than 0.1 kg.m/l) and allowable peak pressures (less than 25cmH2O). Results show that the eOBA meets the standards sufficiently under the test conditions and is a safe apparatus for recreational divers if it is properly used.

Adult↗
PubMed1990

Temperature modulation of oxygen transport in a diving mammal (Balaenoptera acutorostrata).

The functional properties of haemoglobin from the Lesser Rorqual whale (Balaenoptera acutorostrata) have been characterized as a function of the heterotropic effector concentrations and temperature. The results obtained suggest the existence of sophisticated modulation mechanisms based on the interplay of organic phosphates, carbon dioxide, lactate and temperature. These, together with the very small apparent heat of oxygenation (delta H) of oxygen binding, have been physiologically interpreted on the basis of the specific metabolic needs of this diving mammal.

2,3-Diphosphoglycerate↗
PubMed1982

Hormonal changes and enforced diving in the harbor seal Phoca vitulina. II. Plasma catecholamines.

Plasma epinephrine and norepinephrine concentrations were measured in five harbor seals, Phoca vitulina, during a control period, during a 6-min dive, and during a 30-min postdiving recovery period. Measurements were performed with and without prior glucose administration. Control epinephrine concentrations [189 +/- 118 (SD) pg/ml] and norepinephrine concentrations (340 +/- 191 pg/ml) were similar to resting values in humans. During diving there are dramatic increases in both epinephrine and norepinephrine concentrations, which returned to control values by 30 min of the postdiving recovery period. A similar pattern was found after glucose infusion. The increased catecholamines were not the primary mechanism responsible for arterial constriction during the dive. Persistent diving bradycardia suggests obliteration of the chronotropic effects of catecholamines during the dive. An unchanged stroke volume suggests obliteration of the inotropic effects of catecholamines during the dive. Catecholamines do not appear to be involved in postdiving hyperglycemia and hyperglucogenemia. Neither the regulatory role of increased catecholamines nor the physiological function of increased catecholamines was apparent from the studies. However, dramatic increases in plasma catecholamines during diving appear to be an important component of the hormonal response to prolonged diving in aquatic mammals.

Animals↗