The respiratory properties of the blood of two diving rodents, the beaver and the water vole.
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Acid-Base Equilibrium↗
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Results for “Diving physiology”
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Breathing pattern and ventilatory response to carbon dioxide in divers.
The breathing pattern and ventilatory response to carbon dioxide of 10 experienced divers was compared with that of 10 nondivers of similar age and build. Breathing pattern was described by the equation VE = M (VT - K) and the response to carbon dioxide by VE = S(PCO2 - B). The divers exhibited a value form 27% lower than the nondivers; S was 33% lower. The difference was significant (P less than 0.05) in both cases. B was significantly higher (P less than 0.05) in the divers than nondivers. These differences are not attributable to age, build, or vital capacity. S was well correlated with M when all subjects were considered a single group. Within the diving group no correlation of S and M with diving experience was found.
Adaptation, Physiological↗
Ascent exhalations of Antarctic fur seals: a behavioural adaptation for breath-hold diving?
Novel observations collected from video, acoustic and conductivity sensors showed that Antarctic fur seals consistently exhale during the last 50-85% of ascent from all dives (10-160 m, n > 8000 dives from 50 seals). The depth of initial bubble emission was best predicted by maximum dive depth, suggesting an underlying physical mechanism. Bubble sound intensity recorded from one seal followed predictions of a simple model based on venting expanding lung air with decreasing pressure. Comparison of air release between dives, together with lack of variation in intensity of thrusting movement during initial descent regardless of ultimate dive depth, suggested that inhaled diving lung volume was constant for all dives. The thrusting intensity in the final phase of ascent was greater for dives in which ascent exhalation began at a greater depth, suggesting an energetic cost to this behaviour, probably as a result of loss of buoyancy from reduced lung volume. These results suggest that fur seals descend with full lung air stores, and thus face the physiological consequences of pressure at depth. We suggest that these regular and predictable ascent exhalations could function to reduce the potential for a precipitous drop in blood oxygen that would result in shallow-water blackout.
Adaptation, Physiological↗
Effect of pharmacological blockade on cardiovascular responses to voluntary and forced diving in muskrats.
Neural control of free and forced diving bradycardia and peripheral resistance was studied in the muskrat (Ondatra zibethicus) by means of acute pharmacological blockade with the muscarinic blocker atropine, the alpha-adrenergic blocker phentolamine and the beta-adrenergic blockers nadolol and propranolol. Saline injection was used as a control. Heart rate in control animals increased before voluntary dives and dropped markedly as soon as the animals submerged. Heart rate started increasing towards the end of voluntary dives and reached pre-dive values within the first 5 s of recovery. Pre-dive and post-dive tachycardia were reduced in beta-blocked animals, emphasizing the role of the sympathetic system during the preparatory and recovery periods of voluntary dives. Diving bradycardia and the acceleration in heart rate before surfacing were abolished by atropine and unaffected by nadolol, demonstrating the importance of vagal efferent activity during diving. The results after blockade with nadolol suggest that there is an accentuated antagonism between the two branches of the autonomic nervous system during diving, so that parasympathetic influences on the heart predominate. Propranolol-treated muskrats had a higher diving heart rate than saline- and nadolol-treated animals, which may be due to a sedative effect caused by propranolol crossing the blood-brain barrier, a blockade of central catecholaminergic pathways or a peripheral neural effect, due to the anaesthetic properties of propranolol. Phentolamine did not affect diving bradycardia, indicating that diving bradycardia occurs independently of peripheral vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)
Adrenergic alpha-Antagonists↗
[Medical aspects of diving--a sport for both women and men].
As interest in scuba diving is increasing in both sexes, doctors need to be aware of the risks encountered when diving and about gender-related differences in these risks. Individuals prone to panic attacks, claustrophobia or reckless risk-taking should avoid diving. In tolerating cold, muscle mass is more important than the amount of subcutaneous fat. The risk of decompression disease seems to be slightly greater among women, probably due to their fat distribution. Pregnant women are recommended not to dive, because the risk of birth defects seems to be greater among those who do, and there is a serious risk of fetal decompression disease. All participants in the sport must be responsible for their own diving safety.
Adaptation, Physiological↗
[Dehydration--a risk factor for the decompression-accident in diving].
We report on a decompression-accident with neurological manifestation in an experienced recreational diver. As no obvious omission against the prescribed rules of decompression could be observed, dehydration due to intense jogging prior to the dive was identified as a risk-factor. Hyperbaric treatment resulted in a complete restitution. The physiological aspects are discussed and recommendations for the fluid-intake before diving are given.
Decompression Sickness↗
A possible physiological basis for the term urinator, "diver".
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Diving↗
Physical standards for scuba divers.
Scuba diving has become a popular aquatic sport during the past 2 decades, and family physicians are frequently involved in examining scuba divers and in the decision making that allows them to pursue their training or careers in this sport. The purpose of this article is to review the physiology and gas laws that are involved in diving and to provide guidelines for assessing each diving candidate. The clinical manifestations of decompression sickness are discussed as well as the medical problems that could cause severe morbidity or mortality if diving is attempted.
Athletic Injuries↗
[Reactivity of the physiological system of the connective tissue and immunoglobulin levels in divers of the Arctic Pri-Elbrus regions].
The functional state of the conjunctive tissue system in deep-divers has been evaluated by the Kavetsky-Leshchinsky method. The content of different classes of immunoglobulins in the mucosa of upper respiratory tracts has been studied by the fluorescent antibody method under conditions of the Arctic and highland. The long-term divings cause a decrease in the reactivity of a physiological system of conjunctive tissue and a shift in the parameters of the immunological organism status. These changes are found to be more pronounced in the deep divers with underwater work experience of more than 2,000 hours. The general immunological reactivity of the organism rises significantly after 2.5 months stay under conditions of the Elbrus (height--2100 m). These facts confirm an idea that favourable climatic factors of the highland are expedient to be used in the complex of rehabilitation measures for deep-divers.
Adult↗
Effect of compression rate on use of trimix to ameliorate HPNS in man to 686 m (2250 ft).
Previous man dives, in a series designed to evaluate the physiological effects of helium, nitrogen, and oxygen (trimix), investigated the comparative effects of 5% vs. 10% nitrogen with fast compression (12 h 20 min) to 460 m (1509 ft) and subsequent compression over 2.5 d to 650 m (2132 ft). In 1981 three divers were compressed twice as slowly as for these earlier dives to 650 m over a period of 6 d 8 h using 10% N2 in heliox. An extensive series of studies were made over 4 d 15 h at 650 m before further compression to 686 m (2250 ft) for a stay of 24 h with extensive tests of psychological and neurophysiological performance, pulmonary function, reflex, Doppler, and other studies. High pressure nervous syndrome (HPNS) tremors and EEG theta activity increases were effectively controlled with no nausea, vomiting, or somnolence (microsleep). Some euphoria was present. At 686 m there was a 20% to 30% impairment of concentration and attention; otherwise the physical condition of the divers was fine and they completed all tasks without difficulty. Slow compression prevented the initial large performance decrement of 40% to 50% on Day 1 as found in previous fast-compression dives. Otherwise the performance tests showed much the same decrement of 15% to 20% seen in earlier dives; deeper than 570 m (1870 ft), however, the addition test was worse, with a decrement of 35%. The results are discussed with respect to the previous two dives with faster compression, and the possible nonlinearity of nitrogen antagonism of HPNS is considered.
Adult↗
A theoretical analysis of diving performance in the Weddell seal (Leptonychotes weddelli).
Marine mammals are constrained in their foraging behaviour because, as obligate air breathers, they must undertake regular trips to the water surface to satisfy the need for respiratory gas exchange. Maximum underwater endurance time is determined by O2 supply and demand, but this does not necessarily imply that O2 is the main factor regulating individual dive and surface times. This study presents a theoretical analysis of diving performance that emphasizes a key role for CO2 in the proximate control of diving behaviour. Computer simulations, based on a mathematical model of the mammalian cardiorespiratory control system, are used to investigate the influence of swimming to depth and other energetic stresses (feeding, thermogenesis, sleep) on predicted diving behaviour in an average adult Weddell seal. The plausibility of the proposed model is supported by the study, which replicated published observations of natural diving behaviour in this species. It is suggested that diving behaviour is tuned to oscillations in respiratory drive and that behavioural and physiological factors can alter the dynamic characteristics of the system to achieve a highly adaptable reciprocal interaction that blurs the boundary between physiology and behaviour.
Animals↗
Red blood cell aggregability is enhanced by physiological levels of hydrostatic pressure.
The effect of hydrostatic pressure of up to 15 bars on the aggregability of rat and human red blood cells (RBC), i.e., their capability to form aggregates, was studied using computerized image analysis. The aggregate size distribution was determined under ambient pressure, following application of hydrostatic pressure for various durations up to 2 h. It was found that RBC aggregability markedly increases, up to three-fold, as the pressure which had been applied was increased. Accordingly, higher shear stress is required for dispersing the aggregates of pressure-treated RBC than those of untreated cells. The median size of human RBC aggregates was about three times higher than that of rat RBC, and this ratio was maintained following pressure treatment. RBC aggregability is a major determinant in blood flow, especially in the microcirculation. Pressure at the levels used in this study occurs in physiological states such as hyperbaric treatment or diving. The enhanced aggregability induced by application of such pressure implies that blood flow in microvessels might be altered under conditions associated with elevated hydrostatic pressure.
Animals↗
Pulmonary air embolism.
Pulmonary air embolism is a well-known consequence of surgery, trauma, diving, and aviation. This article reviews the physiological effects, means of detection and methods of prevention and treatment of pulmonary air embolism. The primary physiological effects are elevated pulmonary artery pressures, increased ventilation-perfusion inhomogeneity, and right ventricular failure. The degree of physiological impairment depends on the volume of gas entrained, the rate of entrainment, the type of gas entrained, and the position of the patient when the embolism occurs. Transesophageal echocardiography is the most sensitive method of detection, but it is invasive. Precordial Doppler ultrasound is almost as sensitive and poses no risk to the patient. End-tidal carbon dioxide monitoring is used on all patients and is a moderately sensitive method of detection, which is useful during surgeries that have a low incidence of air embolism. For high-risk procedures, precordial Doppler ultrasound and a multi-orifice right heart catheter should be used to detect and treat pulmonary air embolism. Prevention measures include volume expansion, careful positioning, positive end-expiratory pressure, military anti-shock trousers, and jugular venous compression. Treatment of pulmonary air embolism includes flooding the surgical site with saline, controlling sites of air entry, repositioning the patient with the surgical site below the right atrium, aspiration of air from a central venous catheter, cessation of inhaled nitrous oxide, and resuscitation with oxygen, intravenous fluids, and inotropic agents. Some hypotheses on the effects of air in the pulmonary vasculature and investigational treatment options are discussed.
Aerospace Medicine↗
Stresses imposed on diving vertebrates during prolonged underwater exposure.
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Adaptation, Physiological↗
[Deep immersion in the light of current scientific knowledge].
Physiological and technical problems related to deep diving are discussed. Starting from a brief summary of fundamental data, the Author deals with breathing mixture, the diver protection, copression rates and other various problems the principal syndromes originated by gases at high pressure in hyperbaric conditions. An analysis of the most important physical factors which can interfere with the tolerability for long period in such artificial athmospheres has been conducted.
Atmospheric Pressure↗
Cardiovascular and thermal responses to SCUBA diving.
Recreational SCUBA diving exposes individuals to environmental stresses not often encountered in other types of activity. These stresses include increased ambient pressure, raised partial pressure of O(2), increased resistance to movement, added weight and drag of diving equipment, cold stress, and a higher breathing resistance. One means to understand how such stresses affect a diver is to employ the stress-strain-adaptive response model. Physiologic adaptations, like an increase in VO(2) in response to cold stress, will minimize the strain placed on thermal balance. Nonphysiologic adaptive responses include those behavioral and equipment interventions that isolate the diver from a particular stress. Self-contained underwater breathing apparatus (SCUBA) isolates the diver from the inability to extract O(2) from the water; dive garments minimize the stress of cold water immersion. This review will focus on cardiorespiratory and thermal responses to SCUBA diving, using the stress-strain-adaptive response model to illustrate the interaction between diver and environment. Some responses like hyperventilation, cardiac arrhythmias, or cold injury due to vasoconstriction are not considered adaptive but are realistic possibilities in diving environments.
Adaptation, Physiological↗
Bloodparameters of the southern elephant seal (Mirounga leonina, Linn.) in relation to diving.
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Adaptation, Physiological↗
Somatic-evoked brain responses as indicators of adaptation to nitrogen narcosis.
Two 2-week experimental pressure chamber exposures to nitrogen-oxygen breathing mixtures afforded an opportunity to study adaptation to nitrogen narcosis. Somatic-evoked brain responses induced by electrical stimulation of the median nerve in the wrist were processed on-line with a signal averager. The N1P2 interval was seen generally to be reduced in amplitude as a result of exposure to increased nitrogen partial pressure. Compressions with air were made from sea level and saturation to 200, 250 and 300 ft of sea water (fsw) equivalent (61, 76, and 91m). The decrement was found to be less, for equivalent exposures, in subjects who had been saturated at the pressure of 90 and 120 fsw (27 and 36 m); we interpret this as evidence of a nonspecific "adaptation." Less adaptation was seen from 30 and 60 fsw (9 and 18 m). These results are consistent with performance tests on the same exposures, and with subjective impressions. Saturation with 3 0r 4 atm of nitrogen may permit somewhat deeper diving without serious narcosis, than is possible from sea level.
Adaptation, Physiological↗