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At least 433 records · Page 24Linked to original sources
PubMed1987

Failure of heparin, superoxide dismutase, and catalase to protect against decompression sickness.

The effects of heparin (HEP), superoxide dismutase (SOD), and catalase (CAT) on the course of decompression sickness (DCS) were studied in anesthetized dogs (Canis familiaris). Animals were divided into 4 groups: a drug assay group (n = 4) received HEP + SOD or HEP + SOD + CAT but were not dived; a control group (n = 14) was dived without drug treatment; a HEPSOD group (n = 11) received HEP + SOD predive and postdive; and a HEPSODCAT group (n = 15) received HEP + SOD + CAT before diving. All dived animals were subjected to repetitive air dives to 10 ATA until pulmonary artery pressure at least doubled within 10 min postdive. Physiologic variables were measured for 3 h postdive or until death. Animals were not recompressed. More early deaths occurred in the HEPSOD (7/11) and HEPSODCAT (8/15) groups than in the control group (5/14). All dived animals developed pulmonary hypertension, systemic hypotension, hemoconcentration, acidosis, hypoxemia, and interstitial pulmonary edema postdive. Drug therapy did not alter these responses to decompression. We conclude that without recompression, treatment with either HEP + SOD OR HEP + SOD + CAT does not improve the outcome of severe DCS in this animal model.

Animals↗
PubMed1996

Cancer and stress.

Chronic stress in humans can cause psychological and physiological reactions. Emotional withdrawal may be accompanied by biochemical changes in a cell that turns it to anaerobic metabolism instead of aerobic respiratory metabolism. These are both aquatic defence mechanisms which whales, as well as humans, can use as part of the diving reflex to escape from stress. The cell now metabolizes anaerobically in the presence of adequate oxygen (the Warburg effect, present in virtually all cancer cells). The oxygen is toxic and causes DNA damage. An ATPase enzyme, normally useful in phosphorylation of sugar, reverts to its former function as part of the SOS 'error-prone' DNA repair system and attempts to repair the damaged DNA by sending in new DNA that causes such mutations in the chromosomes that the cell acts like an anaerobic microbe, reproducing immortally and eventually metastasizing. Chronic stress can be lessened in the treatment of cancer.

Aerobiosis↗
PubMed2006

Ontogeny of diving behaviour in the Australian sea lion: trials of adolescence in a late bloomer.

1. Foraging behaviours of the Australian sea lion (Neophoca cinerea) reflect an animal working hard to exploit benthic habitats. Lactating females demonstrate almost continuous diving, maximize bottom time, exhibit elevated field metabolism and frequently exceed their calculated aerobic dive limit. Given that larger animals have disproportionately greater diving capabilities, we wanted to examine how pups and juveniles forage successfully. 2. Time/depth recorders were deployed on pups, juveniles and adult females at Seal Bay Conservation Park, Kangaroo Island, South Australia. Ten different mother/pup pairs were equipped at three stages of development (6, 15 and 23 months) to record the diving behaviours of 51 (nine instruments failed) animals. 3. Dive depth and duration increased with age. However, development was slow. At 6 months, pups demonstrated minimal diving activity and the mean depth for 23-month-old juveniles was only 44 +/- 4 m, or 62% of adult mean depth. 4. Although pups and juveniles did not reach adult depths or durations, dive records for young sea lions indicate benthic diving with mean bottom times (2.0 +/- 0.2 min) similar to those of females (2.1 +/- 0.2 min). This was accomplished by spending higher proportions of each dive and total time at sea on or near the bottom than adults. Immature sea lions also spent a higher percentage of time at sea diving. 5. Juveniles may have to work harder because they are weaned before reaching full diving capability. For benthic foragers, reduced diving ability limits available foraging habitat. Furthermore, as juveniles appear to operate close to their physiological maximum, they would have a difficult time increasing foraging effort in response to reductions in prey. Although benthic prey are less influenced by seasonal fluctuations and oceanographic perturbations than epipelagic prey, demersal fishery trawls may impact juvenile survival by disrupting habitat and removing larger size classes of prey. These issues may be an important factor as to why the Australian sea lion population is currently at risk.

Aging↗
PubMed1964

CIRCULATORY ADAPTATION TO DIVING IN THE FRESHWATER TURTLE.

The heart of the freshwater turtle has a functional ventricular septal defect. In ambient air there is some shunting of blood from the left to the right ventricle through the defect. During prolonged diving or N(2) inhalation, the shunt is reversed and blood from the tissues bypasses the lung and enters the aorta directly. This adaptation appears to be based on the exclusive use of anaerobic glycolysis as an energy source during prolonged diving.

Acclimatization↗
PubMed1977

Hana Kai II: a 17-day dry saturation dive at 18.6 ATA. I. Objectives, design, and scope.

The dive (Hana Kai II) described in these papers was designed to determine the effects on man of a prolonged exposure to a dry helium-oxygen hyperbaric environment. Comprehensive studies on energy balance, body fluid balance, cardiorespiratory functions, maximal oxygen uptake, psychological performance, and physiological responses to cold were performed at a simulated depth of 580 ft (18.6 ATA) over a 30-day period in March-April 1975. Following a 3-day predive control period at 1 ATA air (period 1), 5 male divers spent 17 days at 18.6 ATA in a helium-oxygen environment (periods 2-6), and returned to 1 ATA air after 7 days of decompression (periods 7-8). They stayed an additional 3 days inside the chamber for postdive control measurements (period 9). The chamber temperature was maintained at 25-27 degrees C during periods 1 and 9, 30-31 degrees C during periods 2-5, and 27-28 degrees C during period 6. At 18.6 ATA, the PO2 and PCO2 of the chamber gas were maintained at approximately 225 and 2 mmHg, respectively. In this introductory paper, physical and physiological characteristics of individual subjects, the major daily activity schedule, and the scope of investigation are presented.

Activities of Daily Living↗
PubMed1994

[Cardiovascular system reactions and bioenergy metabolism in relation to adaptation to apnea].

Responses of the cardio-vascular system and bioenergetic metabolism were studied in the heart tissue in apnoea in naturally adapted to diving musk-rats and unadapted rats and mice. A sharp bradycardia was shown to develop in former animals in arresting a breathing as well an increase in the neutrophils contents in the blood. The data obtained suggest that release of the necessary oxygen and antiradical defence functions can be related to the catalase activity.

Adaptation, Physiological↗
PubMed1975

Factors in 171 navy diving decompression accidents occurring between 1960-1969.

Comparisons were made between the incidence of specific factors in U.S. Navy decompression accidents and the incidence of these factors in routine (nonexperimental) U.S. Navy operational dives. It was found that decompression accidents are disproportionately high among a) air dives less than 140 ft which have bottom times of 30 min or less and air dives greater than 140 ft which have bottom times of more than 15 min, b) Divers First Class, c) older divers, and d) dives which do not involve work or divers which require heavy work. Repetitive dives have a lower decompression accident rate than expected. Decompression accidents were not disproportionately high for any category of body build. These results indicate that the present U.S. Navy decompression tables are extremely safe (5 decompression accidents/10,000 dives), and do not appear to require modification. Future decompression research may be directed toward analyzing the relationship of work and aging to physiological processes involved in decompression. In addition, the present findings should be cross-validated using more recent accident and operational diving data.

Accidents↗
PubMed1996

Human red blood cell shape and volume are changed by physiological levels of hydrostatic pressure.

Application of hydrostatic pressure of several atmospheres (atm), such as that applied in diving or hyperbaric treatment, has been previously shown to induce the release of membrane components into the extracellular medium. As the shape of red blood cells (RBC) is sensitive to membrane composition, this might imply a subsequent change in RBC shape and volume. The present study demonstrates that application of hydrostatic pressure of up to 15 atm changes the shape of RBC from the normal discoids to stomatocytes (cup-shaped) and accordingly increases their volume. Changes in RBC shape and volume are known to impair physiological and cellular function. Thus, these changes might be pertinent to hemodynamic and physiological disorders observed in humans subjected to elevated pressure.

Cell Size↗
PubMed2000

Effects of physical and apnea training on apneic time and the diving response in humans.

The aim of this investigation was to study separately the effects of physical training and apnea training on the diving response and apneic time in humans. Both types of training have been suggested to lead to prolonged apneic time and an increased "diving response" (i.e., regional vasoconstriction and bradycardia). The study was also designed to examine the effects of these two types of training on the characteristics of the increase in apneic time with repeated apneas. Simulated diving tests were performed before and after the different training programs. The test format was one apnea and five apneas with facial immersion in cold water at 2-min intervals. An increase in apneic time was observed after physical training (n = 24), and this was attributable to an increased time beyond the physiological breaking point. The other parameters that were measured remained unaffected. After apnea training (n = 9), however, apneic time was increased by a delay in the physiological breaking point, which is mainly determined by the arterial tension of CO2. The diving response had increased, and the effect of repeated apneas on apneic time tended to be larger after apnea training. These results may explain the pronounced diving responses and long apneas observed in trained apneic divers.

Adult↗
PubMed2004

Neutrophil tolerance to oxidative stress induced by hypoxia/reoxygenation.

Repetitive episodes of hypoxia/reoxygenation induce cellular adaptations resulting in a tolerance process against oxidative stress. We studied the effects of chronic episodes of hypoxia/reoxygenation on neutrophil antioxidant defenses, neutrophil oxidative capability, and oxidative damage induced in neutrophils and plasma. Seven professional apnea divers participated in the study. Blood samples were taken under basal conditions, after a diving apnea session, and under basal conditions after five consecutive days of diving apnea sessions (basal post-diving). Chronic episodes of hypoxia/reoxygenation increased malondialdehyde (MDA), carbonyl derivates and creatine kinase (CPK) in plasma. Neutrophil catalase (CAT) levels were higher in basal post-diving. Neutrophil oxidative burst was maintained after diving, although the maximum response was delayed in basal post-diving. Neutrophil thioredoxin reductase (TR) activity increased in basal post-diving, and glutathione reductase (GR) activity was maintained. Chronic, repetitive episodes of diving apnea induce neutrophil adaptations in order to delay the oxidative burst response and to facilitate protein reduction. Diving apnea could be a good model to study tolerance to the oxidative stress generated by hypoxia/ reoxygenation.

Adaptation, Physiological↗
PubMed2002

[Children and scuba diving. How to start?].

Contra-indications to scuba diving are now well defined. The number of children practicising this sport is increasing. However, no consensus nor prospective study exists that allows to determine an age under which physicians should advise against scuba diving. This paper reviews many different approaches and, considering physiopathology and intellecual development, suggests a practical attitude.

Accident Prevention↗
PubMed1995

A field study of the ventilatory response to ambient temperature and pressure in sport diving.

This study reports on the relationship between minute ventilation (VE) and environmental variables of temperature (T) and pressure (P) during open water diving. The author conducted a total of 38 dives involving either a light (20 dives) or a moderate (18 dives) level of physical activity. Within each of these groups, P and T taken together accounted for about two thirds of the variance in the VE data. A very significant increase in VE was observed as T decreased (1 < T(degrees C) < 22), and the magnitude of this increase at a given pressure level was similar in the 'light' and the 'moderate' data sets. A second order observation, particularly notable at lower temperature, was the decrease in VE with increasing pressure under conditions of light work. Empirical functions of the from VE = A+B/P n[1 + exp(T - 8)/10], where A, B, and n are adjustable variables, could accommodate both data sets over the whole range of T and P. These results are the first obtained under actual diving conditions to provide evidence for interactions between P, T, and VE. Understanding the physiological mechanisms by which these interactions occur would assist in appreciation of the limitations imposed on scuba divers by the environmental conditions as they affect their ventilatory responses.

Adult↗
PubMed1986

Effect of intravascular bubbles on perfusate flow and gas elimination rates following simulated decompression of a model tissue.

This study deals with the monitoring of the elimination rates of gases from a porous cylindrical model of the human tissue during simulated single-stop decompression schedules. The data suggest the presence of an optimal decompression stop for each dive at which the gas elimination rate is maximum. The effect of varying the flow rate and the viscosity of the liquid perfusing the tissue model on the elimination rate is determined for different diving conditions. Although this study has been carried out on a single tissue model, it provides means for explaining some of the physiological phenomena observed in human tissues.

Decompression Sickness↗