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Results for “Diving physiology”

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PubMed1982

Oxygen affinity of sea turtle blood.

The oxygen binding properties of whole blood in adult sea turtles (green, Chelonia mydas; loggerhead, Caretta caretta) were measured as a function of pH, and carbon dioxide partial pressure using the 'Hemoscan Oxygen Dissociation Analyser' with modifications that improved the performance of the method. Under approximately physiological conditions (25.7 degrees C, PCO2 = 37 Torr; pH 7.45) there is a marked affinity difference between the two species (green, P50 = 29 Torr; loggerhead, 47 Torr). It is suggested that the large affinity difference between blood of green and loggerhead turtles may be related to differences in depths to which they typically dive. The Hill coefficient at 50% saturation is 2.4 in the green under these conditions, and 2.7 in loggerhead. Hill plots of both species curve upward and have significant regions with n approaching 1 at low saturation with the effect that the lower end of the binding curve is more hyperbolic than sigmoidal. The fixed acid and CO2 Bohr effects in both species are strongly saturation dependent, being very low at low saturation and increasing markedly at higher saturation. The fixed acid Bohr effects are similar in the two species but the green is more sensitive to CO2, at constant pH, and so has a larger CO2 Bohr effect. The hyperbolic shape of the lower end of the binding curves, and low pH sensitivity in this region, would tend to favor oxygen loading during a dive, when lung PO2 and blood pH are falling. These properties might therefore favor more complete utilization of the lung oxygen store. We suggest that diving vertebrates can usefully be divided into two groups, those that use the lung as the main oxygen stores and those that use tissue (blood and myoglobin) stores.

Animals↗

PubMed2005

Molecular cloning and expression of leptin in gray and harbor seal blubber, bone marrow, and lung and its potential role in marine mammal respiratory physiology.

Leptin is a multifunctional hormone, produced predominantly in adipocytes. It regulates energy balance through its impact on appetite and fat metabolism, and its concentration indicates the size of body fat reserves. Leptin also plays a vital role in stretch-induced surfactant production during alveolar development in the fetus. The structure, expression pattern, and role of leptin have not previously been explored in marine mammals. Phocid seals undergo cyclical changes in body composition as a result of prolonged fasting and intensive foraging bouts and experience rapid, dramatic, and repeated changes in lung volume during diving. Here, we report the tissue-specific expression pattern of leptin in these animals. This is the first demonstration of leptin expression in the lung tissue of a mature mammal, in addition to its expression in the blubber and bone marrow, in common with other animals. We propose a role for leptin in seal pulmonary surfactant production, in addition to its likely role in long-term energy balance. We identify substitutions in the phocine leptin sequence in regions normally highly conserved between widely distinct vertebrate groups, and, using a purified seal leptin antiserum, we confirm the presence of the leptin protein in gray seal lung and serum fractions. Finally, we report the substantial inadequacies of using heterologous antibodies to measure leptin in unextracted gray seal serum.

Adipose Tissue↗

PubMed2003

Epilepsy and athletics.

It may seem logical to place restrictions on athletes with epilepsy, but there are no studies to suggest that even contact sports exacerbate seizures, and there is ample evidence that exercise reduces seizure frequency and improves well-being. Thus, sports participation should generally be encouraged for epilepsy patients. The risk-benefit analysis for an individual patient is highly dependent on the athletic activity considered; type of seizure, the likelihood that a seizure will occur during the activity, and comorbid conditions. Water sports (scuba diving, swimming, boating), sports performed at heights (piloting, sky diving, climbing, horseback riding), and motor sports require specific considerations.

Athletic Injuries↗

PubMed1980

Thermal responses in humans exposed to cold hyperbaric helium-oxygen.

The relationship of metabolic heat production to skin and core temperatures, cutaneous heat flow, and respiratory heat loss was measured in 10 male subjects cooled in hyperbaric helium at 20.7 ATA and 15 or 20 degrees C for 60-120 min. Under these conditions, metabolic heat production tended to compensate for the sum of convective and radiant heat losses from the skin but did not increase sufficiently to compensate for additional respiratory heat losses. There was a positive correlation between respiratory heat loss and fall in rectal temperature. Individual variability in ventilatory response to cold hyperbaric helium exposure as shown by a wide range of minute ventilation-to-oxygen consumption ratios (VE/VO2) was similar to that reported during cold water immersion. Subjects with high VE/VO2 had low mean physiological shell insulation values and lost more heat through the skin as well as through the respiratory tract than subjects with low VE/VO2.

Atmospheric Pressure↗

PubMed2000

Role of histidine-related compounds as intracellular proton buffering constituents in vertebrate muscle.

The intracellular non-bicarbonate buffering capacity of vertebrate muscle is mainly supported by the imidazole groups of histidine residues in proteins, free L-histidine in some fish species, and histidine-containing dipeptides such as carnosine, anserine, and balenine (ophidine). The proton buffering capacity markedly differs between muscle types and animal species depending on the ability for anaerobic exercise. The capacity is typically high in fast-twitch glycolytic muscles of vertebrates adapted for anaerobic performance such as burst swimming in fishes, prolonged anoxic diving in marine mammals, flight in birds, sprint running in mammalian sprinters, and hopping locomotion in some terrestrial mammals. A high correlation between buffering capacity, concentration of histidine-related compounds in muscle, and percentage of fast-twitch fibers in all vertebrates adapted for intense anaerobic performance clearly supports the idea that proton buffering is the main physiological function of histidine-related compounds.

Animals↗

PubMed1993

New findings regarding light intensity and its effects as a zeitgeber in the Sprague-Dawley rat.

Circadian rhythmicities are oscillations of physiological cycles designed to create temporal organization. Circadian rhythms ensure that physiological mechanisms are expressed in proper relationship to each other and the 24 hour day. Light is the main zeitgeber ("time giver") for biological clocks. The daily variations in light intensity from dawn to dusk, and seasonally due to the rotation of the earth, act upon organisms to give them photoperiodic information. This entrainment allows them to vary biologically to prepare for reproduction, hibernation, migration and the daily adaptations necessary for survival. In most mammals, the suprachiasmatic nucleus of the anterior hypothalamus has been implicated as the central diving mechanism of circadian rhythmicity. The photic input from the retina, via the retino-hypothalamic tract, and modulation from the pineal gland help regulate the clock. In this study we investigated the effects of low light intensity on the circadian system of the Sprague-Dawley rat. A series of light intensity experiments were conducted to determine if a light level of 0.1 Lux will maintain entrained circadian rhythms of feeding, drinking, and locomotor activity.

Activity Cycles↗

PubMed1996

Responses to underwater exercise in scuba divers differing in trait anxiety.

Fifteen male scuba divers performed underwater leg ergometer exercise in an effort to determine if trait anxiety was related to their physiologic or perceptual responses. Psychologic assessment completed before exercise testing revealed that the sample exhibited positive psychologic profiles. However, five individuals possessed trait anxiety scores above the published mean (M = 46.0). Their responses to exercise were compared with the five participants with the lowest trait anxiety scores (M = 30.6). The exercise task was 20 min of steady-state underwater leg ergometer exercise. Oxygen consumption, CO2 production, minute ventilatory volume, breathing frequency, and heart rate were assessed at rest and every 5 min during exercise. Perception of effort and breathing discomfort were also determined during exercise. Each of the physiologic and perceptual variables increased (P < 0.05) with exercise. The only group main effect (P < 0.05) occurred for respiration rate. The high trait anxious group took 7.4 fewer breaths per minute (13.1 vs. 20.5) compared with low trait anxious group. These results have implications regarding the use of intervention strategies in persons at potential risk of experiencing panic while scuba diving.

Adult↗

PubMed1988

Some effects of sleep loss on vestibular responses.

This study assessed ocular nystagmus and motion experiences of men exposed to both simple (angular acceleration) and complex (Coriolis) vestibular stimulation during approximately 55 h of sleep loss. Control and sleep-deprived groups each comprised 10 young men. Angular accelerations and Coriolis stimulation (30 degrees head movements during CW rotation) were accomplished in darkness in an enclosed Still-Werner rotating device. Nystagmus and motion experiences (turning, "diving," and "climbing") were recorded throughout each session. Tests were given at 0900 and 1300 on each of 3 successive days. Subjects ingested 10-mg of d-amphetamine at 1200 on Day 3. During simple stimulation, the sleep-deprived group showed regular declines across sessions in slow phase and duration measures of nystagmus but fast phase ocular frequency and measures of experienced turning resisted declines until the final predrug session; subjective response latencies increased with sleep loss. Declines during rotation for ocular output and measures of perceived displacement during rightward head tilts ("climbing" sensation) were obtained for the sleep deprived, but both nystagmus and sensations were unaffected by return (leftward) movements of the head ("diving" sensation). d-Amphetamine had no consistent effect on responses of control subjects, but significantly increased nystagmus and elevated (but not significantly) measures of turning experiences for the sleep deprived.

Adult↗

PubMed1999

Medical advice for commercial air travelers.

Family physicians are often asked to advise patients who are preparing to travel. The Air Carrier Access Act of 1986 has enabled more passengers with medical disabilities to choose air travel. All domestic U.S. airlines are required to carry basic (but often limited) medical equipment, although several physiologic stresses associated with flight may predispose travelers with underlying medical conditions to require emergency care. Recommendations for passengers with respiratory, cardiac or postsurgical conditions must be individualized and should be based on objective testing measures. Specific advice for patients with diabetes, postsurgical or otolaryngologic conditions may make air travel less hazardous for these persons. Air travel should be delayed after scuba diving to minimize the chance of developing decompression sickness. Although no quick cure for jet lag exists, several simple suggestions may make travel across time zones more comfortable.

Aerospace Medicine↗

PubMed1989

Hypothermia and cold.

Hypothermia is defined and classified, and the physiology of temperature regulation summarized; fluid balance and the phenomenon of symptomless cooling are considered in more detail. The symptoms and signs of hypothermia are charted, with cautions, and the problems considered of making any diagnosis, including that of death, in hypothermic patients. Recommendations for treatment are complicated by the possible presence of other factors including drowning and the so-called 'diving reflex' phenomenon. There are many methods of rewarming and all are safe if used with intensive care monitoring. However, for field use by the rescue services there are only three practical methods. The traditional explanation of why survivors die after rescue is discarded with an alternative proposed. Since hypothermia is not numerically the most important cause of cold-related deaths, the other dangers are considered. Finally caution is advised when interpreting published papers on hypothermia.

Body Temperature Regulation↗

PubMed1986

[Women and diving].

Explore the source record for details and available documents.

Contraceptives, Oral↗

PubMed1964

THE HYPERBARIC CHAMBER AT THE ROYAL VICTORIA HOSPITAL, MONTREAL.

The single apparent and potential benefit of hyperbaric oxygen is the great increase in the blood content of dissolved oxygen achieved when pure oxygen is breathed at increased pressure. The design of an economical chamber for this purpose is presented. A large number of physiological measurements (cardiac output, electroencephalogram, electrocardiogram, etc.) can be performed on patients or experimental animals within the chamber by use of unique electronic connections in the chamber wall which permits all recording equipment to remain outside. Expected arterial blood oxygen tensions have been achieved in patients studied at 2, 3, and 4 atmospheres. Safety features are emphasized. No complication has resulted in 113 dives over the period January to June 1964, one-half of which were for treatment of patients. The chamber has been used clinically as an adjunct to treatment of shock, certain forms of malignancy, anaerobic infections, coronary occlusion, and problems of ischemia, and for preservation of organs for transplantation.

Animals↗

PubMedDate not supplied

[High density respiratory syndrome: I. Oscillations of flow-volume curves during forced respiration in dense gas media].

33 divers exposed to high pressure have been examined in three series. The dynamics of the forced breathing parameters has been studied: I--helio or neon-oxygen medium under pressure of 1.078-3.53 MPa (11-36 kg/m2) with density to 32.7 kg/m3; II--nitrogen-oxygen medium under 0.274-0.882 MPa (2.8-9.0 kg/m2) with density of 11.7 kg/m3; III--under the same conditions, as II, but using bronchospasmolytics (stimulators of 2-adrenoreceptors: astompent, salbutamol, berotec) under hyperbaria. A new phenomenon: high-density breathing syndrome is revealed. It includes appearance of oscillations of respiratory flows against the background of a decrease of forced breathing rate in dense gas medium and has a common mechanism of appearance both during inhale and exhale. High hydrostatic pressure and narcotic qualities of inert gases can have a modulating effect. Evidences are obtained that tremor phenomena observed during high pressure nervous syndrome can influence the biomechanics of forced breathing at hyperbaria. A high correlation between amplitude modulation of electromyograms of breathing muscles and pneumotachogram oscillations within the range, corresponding to the frequency of physiological tremor, allowed assuming that tremor of breathing muscles induced by high-density gas medium action is one of factors responsible for appearance of respiratory flows oscillations.

Adult↗

PubMed1997

Probabilistic gas and bubble dynamics models of decompression sickness occurrence in air and nitrogen-oxygen diving.

Probabilistic models of the occurrence of decompression sickness (DCS) with instantaneous risk defined as the weighted sum of bubble volumes in each of three parallel-perfused gas exchange compartments were fit using likelihood maximization to the subset of the USN Primary Air and N2-O2 database [n = 2,383, mean P(DCS) = 5.8%] used in development of the USN LE1 probabilistic models. Bubble dynamics with one diffusible gas in each compartment were modeled using the Van Liew equations with the nucleonic bubble radius, compartmental volume, compartmental bulk N2 diffusivity, compartmental N2 solubility, and the N2 solubility in blood x compartmental blood flow as adjustable parameters. Models were also tested that included the effects of linear elastic resistance to bubble growth in one, two, or all three of the modeled compartments. Model performance about the training data and separate validation data was compared to results obtained about the same data using the LE1 probabilistic model, which was independently implemented from published descriptions. In the most successful bubble volume model, BVM(3), diffusion significantly slows bubble growth in one of the modeled compartments, whereas mechanical resistance to bubble growth substantially accelerates bubble resolution in all compartments. BVM(3) performed generally on a par with LE1, despite inclusion of 12 more adjustable parameters, and tended to provide more accurate incidence-only estimates of DCS probability than LE1, particularly for profiles in which high fractional O2 gas mixes are breathed. Values of many estimated BVM(3) parameters were outside of the physiologic range, indicating that the model emerged from optimization as a mathematical descriptor of processes beyond bubble formation and growth that also contribute to DCS outcomes. Although incomplete as a mechanistic description of DCS etiology, BVM(3) remains applicable to a wider variety of decompressions than LE1 and affords a conceptual framework for further refinements motivated by mechanistic principles.

Decompression Sickness↗

PubMed2004

Pulmonary pneumaticity in the postcranial skeleton of extant aves: a case study examining Anseriformes.

Anseriform birds were surveyed to examine how the degree of postcranial pneumaticity varies in a behaviorally and size-diverse clade of living birds. This study attempts to extricate the relative effects of phylogeny, body size, and behavioral specializations (e.g., diving, soaring) that have been postulated to influence the extent of postcranial skeletal pneumaticity. One hundred anseriform species were examined as the focal study group. Methods included latex injection of the pulmonary apparatus followed by gross dissection or direct examination of osteological specimens. The Pneumaticity Index (PI) is introduced as a means of quantifying and comparing postcranial pneumaticity in a number of species simultaneously. Phylogenetically independent contrasts (PICs) were used to examine the relationship between body size and the degree of postcranial pneumaticity throughout the clade. There is a high degree of similarity (i.e., clade-specificity) within most anseriform subgroups. As a whole, Anseriformes demonstrate no significant relationship between relative pneumaticity and body size, as indicated by regression analysis of body mass on PI. It is apparent, however, that many clades of diving ducks do exhibit lower PIs than their nondiving relatives. By exclusion of diving taxa from analyses, a significant positive slope is observed and the hypothesis of relatively higher pneumaticity in larger-bodied birds is only weakly supported. However, low correlations indicate that factors other than body size account for much of the variation observed in relative pneumaticity. Pneumaticity profiles were mapped onto existing phylogenetic hypotheses. A reduction in the degree of postcranial pneumaticity occurred independently in at least three anseriform subclades specialized for diving. Finally, enigmatic pneumatic features located in distal forelimb elements of screamers (Anhimidae) result from invasion of bone by a network of subcutaneous air sac diverticula spreading distally along the wings.

Animals↗

PubMed2006

The use of biota sampling for environmental contaminant analysis for characterization of benthic communities in the Aleutians.

It is increasingly clear that the public, native tribes, and governmental agencies are interested in assessing the well-being of natural resources and ecosystems. This may take the form of understanding species presence, monitoring population status and trends, measuring behavior, or quantifying physiology, biological stresses, or chemical/radiological exposure through biomarkers. Often there is a separation between understanding the biological aspects of species well-being and assessing exposure to contaminants. In this paper we examine the applicability of using scuba sampling aimed primarily at specimen collection for radionuclide analysis to assess species presence/absence and to compare among sampling sites and depths. We were especially interested in whether dive transects could provide information on species presence and potential exposure to environmental contaminants. In June/July 2004 we sampled at 49 depth stations along 19 transects at Amchitka and Kiska Islands in the western Aleutian Islands in the Northern Pacific/Bering Sea region. Amchitka Island, a former World War II U.S. Navy base, was the site of three underground nuclear test shots from 1965 to 1971. Four to six transects were established at three Amchitka sites and two Kiska Sites, and 2 to 4 stations were sampled on each transect. Bottom conditions, weather and currents prevented a complete sampling of all stations. There were interspecific differences in the percent of stations where biota were found and collected, in their occurrence near the three test shots on Amchitka, and in the depth where they were found. There were no significant differences between Amchitka and Kiska Island in the percent of stations where species were found. These data suggest that information gathered incidentally to the collection of specimens for chemical/radiological analysis can prove useful for understanding the presence of benthic organisms along particular transects, at given depths, and at different geographical locations. This information also provides a baseline for the range of organisms that could be exposed to future physical or chemical/radiological stressors. The data are useful for developing future biomonitoring plans to assess biological well-being and chemical/radiological exposure only if they are published and available to the public, public policy makers, and managers. Just as it is critical to select endpoints and bioindicators that are of interest for assessing both human and ecological health, specimens should be collected using a protocol that is useful for both chemical/radiological analysis and biological information.

Alaska↗

PubMed1989

[Conception of a decompression table].

After a given time at bottom, different tissues become saturated to different extents with nitrogen. In diving back to the surface a hydrostatic decompression occurs first, followed by the desaturation process some time later. It is during this time interval that all important events are taking place, namely: either a monophasic desaturation, whereby inert nitrogen gas is given off at the alveolar capillary interface. or a biphasic desaturation takes place, giving rise to gas bubbles in the blood-stream as well as in the tissues. We may then encounter pathologies which are benign incidents or, worse, lead to decompression sickness grade II. Since Paul Bert dedicated his thoughts in 1878 to this problem, numerous authors tried to explain this time delay, for trying to suppress it would be entirely unrealistic. Unfortunately, mathematical reasoning has too often overshadowed physiological thinking in these matters. We also stuck to Haldane's concept of 1908, in incorporating Workman's improvements of 1965. This method is based on two main principles: 1. all calculations were done with several "tissues" in mind. Their anatomical boundaries are of no importance as, only their desaturation half-times are relevant. 2. a natural limit is given by the critical saturation-coefficient (CS). It expresses the ratio between the partial pressure of the dissolved gas and the reduction of hydrostatic pressure during ascent (given as pressure gradient). Through experience we were able to put up tables which were more and more safe, in examining foremost the CS ratio and the desaturation times of certain tissues. Several examples are given, the values of which are statistically highly significant, as they incorporate the results of more than 60,000 air dives.

Decompression↗

PubMed1992

Cardiovascular responses to nasal water flow in rats are unaffected by chemoreceptor drive.

Peripheral chemoreceptors generally play a limited role in the initial development of diving bradycardia in mammals. However, T.F. Huang and Y.I. Peng (Jpn. J. Physiol. 26: 395-401, 1976) reported that peripheral chemoreceptors are very important for manifestation of the diving response in conscious rats. The objectives of this study were to reinvestigate those findings and determine whether the cardiovascular responses to simulated diving in the rat were potentiated during preexisting hypoxia or hypercapnia. Responses to simulated diving were elicited by nasal water flow with concurrent apnea in paralyzed, artificially ventilated Sprague-Dawley rats anesthetized with Innovar. The experiments show that nasal stimulation in the rat results in rapid bradycardia and hypotension and that these responses are not due to laryngeal stimulation. The data also suggest that chemoreceptors do not play a role in the initiation of the responses to simulated diving in rats and that preexisting chemoreceptor drive does not alter the cardiovascular responses. Additionally, we found that concomitant expiratory apnea is necessary to sustain the profound initial cardiovascular changes induced by nasal water flow.

Animals↗