PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Diving physiology”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMed2004

The diving paradox: new insights into the role of the dive response in air-breathing vertebrates.

When aquatic reptiles, birds and mammals submerge, they typically exhibit a dive response in which breathing ceases, heart rate slows, and blood flow to peripheral tissues is reduced. The profound dive response that occurs during forced submergence sequesters blood oxygen for the brain and heart while allowing peripheral tissues to become anaerobic, thus protecting the animal from immediate asphyxiation. However, the decrease in peripheral blood flow is in direct conflict with the exercise response necessary for supporting muscle metabolism during submerged swimming. In free diving animals, a dive response still occurs, but it is less intense than during forced submergence, and whole-body metabolism remains aerobic. If blood oxygen is not sequestered for brain and heart metabolism during normal diving, then what is the purpose of the dive response? Here, we show that its primary role may be to regulate the degree of hypoxia in skeletal muscle so that blood and muscle oxygen stores can be efficiently used. Paradoxically, the muscles of diving vertebrates must become hypoxic to maximize aerobic dive duration. At the same time, morphological and enzymatic adaptations enhance intracellular oxygen diffusion at low partial pressures of oxygen. Optimizing the use of blood and muscle oxygen stores allows aquatic, air-breathing vertebrates to exercise for prolonged periods while holding their breath.

Adaptation, Physiological↗
PubMed1983

Role of venoconstriction in the cardiovascular responses of ducks to head immersion.

Central venous pressure of ducks rose from resting values of 0.31 +/- 0.16 (SE) to 1.75 +/- 0.20 kPa during forced head immersion. Because a similar increase in mean circulatory pressure (Pmc) was also observed (0.71 +/- 0.16 to 2.15 +/- 0.20 kPa) the rise in central venous pressure was attributed to a venoconstrictor mechanism. When this venoconstrictor-induced rise in central venous pressure was prevented by graded withdrawal of venous blood, then immersion bradycardia was inhibited, and the reduced cardiac output associated with head immersion was largely the result of reduced stroke volume. When compared with normal dives, this intervention resulted in greater myocardial energy requirements, as assessed by the pressure-rate product. It is concluded that venoconstriction increases central venous pressure during head immersion. The increase in central venous pressure alters cardiac function through the Frank-Starling mechanism such that myocardial energy requirements are minimized during this period of low oxygen availability.

Animals↗
PubMed1989

Perspectives in diving and asphyxia.

Animals vary in their ability to tolerate asphyxia. Among aquatic species, some are well adapted to asphyxia associated with the apnea of their diving behavior. The related mechanisms and their regulation are not unique to aquatic animals, rather they are extensions of similar reactions noted in terrestrial species. Our understanding of asphyxia has grown in large part from research on aquatic mammals and birds and by comparing the responses of these natural breath-holding specialists with those of other animals. Studies in nature and in the laboratory have both contributed to this knowledge. The divers have been shown to rely ultimately on oxygen conservation and enhanced anaerobic reserves, producing a strategic retreat into a hypometabolic state.

Adaptation, Physiological↗
PubMed2002

Biochemical aspects of pressure tolerance in marine mammals.

Some marine mammals can dive to depths approaching 2000 m. At these hydrostatic pressures (200 atm), some fish species show alterations in enzyme structure and function that make them pressure-tolerant. Do marine mammals also possess biochemical adaptations to withstand such pressures? In theory, biochemical alterations might occur at the control of enzymatic pathways, by impacting cell membrane fluidity changes or at a higher level, such as cellular metabolism. Studies of marine mammal tissues show evidence of all of these changes, but the results are not consistent across species or diving depth. This review discusses whether the elevated body temperature of marine mammals imparts pressure tolerance at the biochemical level, whether there are cell membrane structural differences in marine mammals and whether whole, living cells from marine mammals alter their metabolism when pressure stressed. We conclude that temperature alone is probably not protective against pressure and that cell membrane composition data are not conclusive. Whole cell studies suggest that marine mammals either respond positively to pressure or are not impacted by pressure. However, the range of tissue types and enzyme systems that have been studied is extremely limited and needs to be expanded before more general conclusions about how these mammals tolerate elevated pressures on a biochemical level can be drawn.

Adaptation, Physiological↗
PubMed1989

Adaptations to deep breath-hold diving: respiratory and circulatory mechanics.

Respiration and circulation in diving mammals are characterized by interrelated adaptations of structure, function, and behavior that are incompletely described and understood. This speculative survey touches some of them. a) Arterial blood flow can be controlled by vasoconstriction not only in arterioles but also in large arteries. The latter physiology is not well known. b) Mechanisms that might regulate and limit nitrogen uptake are not clear, although Scholander's suggestion that airspaces become gas-free during deep dives is still accepted. c) Systemic arterial retes may be able to store oxygenated blood in some diving mammals. If so, O2 in the lung might be "skimmed off" early in a dive, leaving the N2 behind. d) Variable clusters of interdependent adaptations in diving mammals include compliant chest walls that avoid thoracic squeeze; inspiratory breath holds that maintain high lung volumes; large tidal volumes that nearly empty the lung at end-expiration (so there is near-complete turnover of lung gas with each breath); airways that are "armored" by cartilage rings all the way out to the airspaces (so that they do not close and trap gas in the lung and do permit high expiratory flow rates even at very low lung volumes); submucosal vascular retes that may prevent airway squeeze; a puzzling difference in the cross-sectional areas of trachea and bony nares; and very large lungs in shallow divers (sea otters). Study of mammalian adaptations to deep diving promises to illuminate basic issues in physiology.

Adaptation, Physiological↗
PubMed1980

Observations on Baiji (Lipotes vexillifer) and finless porpoise (Neophocaena asiaeorientalis) in the lower reaches of the Chang Jiang.

Lipotes usually occurs in pairs or in small loose groups. The calves are born in March-April. The Finless porpoises are usually seen in groups of five or six individuals. The blow of Lipotes lasts 0.2-0.6 sec and that of Neophocaena 0.2-0.5 sec. In Lipotes, a short dive would take 10-20 sec and a long dive up to 1-2 min (average value being 31 sec). In Neophocaena a long dive would reach a maximum of 65 sec with an average of 17.5 sec. Lipotes has a pair of functional eyes. The selective secondary atrophy of a number of eye muscles and nerves and the position of the eyes in the head correspond with the physical conditions of the environments, so that the field of vision is directed forwards and upwards. When pursued by motor boat, both species react with a long dive and a change of direction under water. With the Baiji this would occasionally cause fatal injuries by the propeller of the ship. Such a case seems much less often with Neophocaena. The population of Lipotes is at present very small. In the stretch of the river (between Nanjing and Taiyangzhou) under exploration, we found scarcely more than one dolphin per 4 km. The cause for its scarcity is mostly due to accidents or wounds caused by propellers.

Adaptation, Physiological↗
PubMed1994

Cardiovascular responses elicited by different simulated diving manoeuvres.

It has been documented that placing an ice-bag on the forehead causes similar cardiac and vascular responses as face immersion. There has been disagreement concerning the contribution of separate cold stimulation on the face and breathholding in the diving response. This study set out to unravel the extent to which these two factors contribute individually to the observed cardiovascular changes during the combined manoeuvre. It further aimed to reveal whether peripheral vascular responses to these stimuli are different in forearm and calf. We observed a significant rapid increase in the RR-interval, which was maintained until the end of the 25-s observation period and a homogeneous vasoconstriction in forearm and calf, despite minor changes in arterial blood pressure, during breathholding, placing the icebag on the forehead and the combined stimuli. Cardiac and peripheral vascular responses to the combined manoeuvre did not differ significantly from the responses elicited by the two stimuli separately. This test is another example that illustrates the heterogeneous cardiovascular response involving both parasympathetic and sympathetic activation. Moreover, since the icebag on the forehead test is technically easy to perform and does not require the active co-operation of the patient, it may be a valid method to replace a full face immersion test accompanied by breathholding.

Adult↗
PubMedDate not supplied

Body cooling and its energetic implications for feeding and diving of tufted ducks.

Wintering in a temperate climate with low water temperatures is energetically expensive for diving ducks. The energy costs associated with body cooling due to diving and ingesting large amounts of cold food were measured in tufted ducks (Aythya fuligula) feeding on zebra mussels (Dreissena polymorpha), using implanted heart rate and body temperature transmitters. The effects of diving depth and food ingestion were measured in two sets of experiments: we measured body cooling and energy costs of six tufted ducks diving to different depths in a 6-m-deep indoor tank; the costs for food ingestion and crushing mussel shells were assessed under seminatural winter conditions with the same ducks feeding on mussels in a 1.5-m-deep outdoor pond. Body temperature dropped during feeding bouts and increased gradually during intermittent resting periods. The temperature drop increased linearly with dive duration. The rate of body cooling increased with feeding depth, but it was lower again at depths below 4 m. Half of the increment in energy costs of diving can be attributed to thermoregulatory heat production, of which approximately 50% is generated after diving to warm up the body. The excess costs for ducks feeding on large-sized mussels could be entirely explained by the estimated energy cost necessary to compensate the heat loss following food ingestion, suggesting that the heat production from shell crushing substituted for thermoregulation. Recovery from heat loss is probably a major component of the activity budget of wintering diving ducks.

Adaptation, Physiological↗
PubMed1989

Arctic life adaptation--III. The function of whale (Balaenoptera acutorostrata) hemoglobin.

1. The oxygen binding properties of the hemoglobin from the Lesser Rorqual, Balaenoptera acutorostrata, has been investigated with respect to the possible effects of organic phosphates on gas transport in arctic environments. 2. The intrinsic oxygen affinity of the hemoglobin is high and strongly modulated by the effects of organic phosphates. 3. In the absence of organic phosphates, the temperature sensitivity of oxygen binding expressed by the heat of oxygenation, delta H, is -16.2 kcal/mol when corrected for the heat of oxygen in solution. 4. In the presence of organic phosphates there is a marked decrease in the temperature sensitivity delta H approximately -5 kcal/mol). 5. This feature is of great importance for oxygen unloading in the flippers and the tail, where the temperature is lower than the trunk of the whale. 6. Furthermore the organic phosphates strongly increase the Bohr coefficient, delta log P50/delta pH, from less than -0.3 in stripped hemoglobin to about -1.5 when the hemoglobin is saturated with P6-inositol. 7. This feature may be of great physiological importance by reducing the CO2 tension and acidosis after a prolonged dive.

Adaptation, Physiological↗
PubMed1981

Functional consequences of expanded aortic bulb: a model study.

An investigation of the mechanical effects and physiological functions of the dilated ascending aorta of diving mammals was undertaken with mathematic modeling methods. A mathematical model of a prototype (canine) arterial system was constructed and was evaluated by comparing model-predicted pressure and flow wave forms at four vascular locations with published accounts of experimental measurements. The prototype model was modified to serve as a model of the diving mammal arterial system by changing peripheral vascular parameters and by changing the dimensions of the ascending aorta section of the model. This modified model gave a very good simulation of pressure and flow behavior in diving mammal arteries during a dive. Various distribution patterns of compliance addition to the prototype aortic pattern were evaluated as to the effect of these patterns on aortic input properties. It was concluded that the geometric distribution pattern found in diving mammal arteries was optimal with respect to reducing aortic impedance and peak systolic pressure development and thus favored the function of the left ventricle. This mechanical function could represent an important part of the total picture of adaptation to prolonged ischemia.

Animals↗