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At least 217 records · Page 12Linked to original sources
PubMed2005

Bioenergetics and diving activity of internesting leatherback turtles Dermochelys coriacea at Parque Nacional Marino Las Baulas, Costa Rica.

Physiology, environment and life history demands interact to influence marine turtle bioenergetics and activity. However, metabolism and diving behavior of free-swimming marine turtles have not been measured simultaneously. Using doubly labeled water, we obtained the first field metabolic rates (FMRs; 0.20-0.74 W kg(-1)) and water fluxes (16-30% TBW day(-1), where TBW=total body water) for free-ranging marine turtles and combined these data with dive information from electronic archival tags to investigate the bioenergetics and diving activity of reproductive adult female leatherback turtles Dermochelys coriacea. Mean dive durations (7.8+/-2.4 min (+/-1 s.d.), bottom times (2.7+/-0.8 min), and percentage of time spent in water temperatures (Tw) < or =24 degrees C (9.5+/-5.7%) increased with increasing mean maximum dive depths (22.6+/-7.1 m; all P< or =0.001). The FMRs increased with longer mean dive durations, bottom times and surface intervals and increased time spent in Tw< or =24 degrees C (all r2> or =0.99). This suggests that low FMRs and activity levels, combined with shuttling between different water temperatures, could allow leatherbacks to avoid overheating while in warm tropical waters. Additionally, internesting leatherback dive durations were consistently shorter than aerobic dive limits calculated from our FMRs (11.7-44.3 min). Our results indicate that internesting female leatherbacks maintained low FMRs and activity levels, thereby spending relatively little energy while active at sea. Future studies should incorporate data on metabolic rate, dive patterns, water temperatures, and body temperatures to develop further the relationship between physiological and life history demands and marine turtle bioenergetics and activity.

Animals↗
PubMed1993

Cardiac responses of grey seals during diving at sea.

Heart rate, swimming speed and diving depth data were collected from free-ranging grey seals, Halichoerus grypus, as they foraged and travelled in the sea around the Hebrides Islands off western Scotland. Information was collected on a tracking yacht using a combination of sonic and radio telemetry. Diving heart rate declined as a function of dive duration. In long dives, grey seals employed extreme bradycardia, with heart rates falling to 4 beats min-1 for extended periods, despite the animal being free to breath at will. This extreme dive response is part of the normal foraging behaviour. Seals spent 89% of the time submerged during bouts of long dives; swimming was restricted to ascent and descent. Dive durations exceeded estimated aerobic dive limit, even assuming resting metabolic rates. These results indicate that behavioural, and possibly cellular, energy-sparing mechanisms play an important role in diving behaviour of grey seals. This has implications not only for studies of mammalian energetics but also for our understanding of the foraging tactics and prey selection of marine mammals. If some seals are using energy-sparing mechanisms to reduce metabolic costs while at depth, they may be forced to wait for and ambush prey rather than to search for and chase it.

Animals↗
PubMed1997

Heart rates of northern elephant seals diving at sea and resting on the beach.

Heart rates of northern elephant seals diving at sea and during apnoea on land were monitored to test whether a cardiac response to submergence is an important factor in their ability to make repetitive, long-duration dives. Seven juvenile northern elephant seals were captured at Año Nuevo, CA, instrumented and translocated to release sites around Monterey Bay. Heart rate and dive depth were recorded using custom-designed data loggers and analogue tape monitors during the seals' return to Año Nuevo. Heart rates during apnoea and eupnoea were recorded from four of the seals after they hauled out on the beach. Diving patterns were very similar to those of naturally migrating juveniles. The heart rate response to apnoea at sea and on land was a prompt bradycardia, but only at sea was there an anticipatory tachycardia before breathing commenced. Heart rate at sea declined by 64% from the surface rate of 107 +/- 3 beats min-1 (mean +/- S.D.), while heart rate on land declined by 31% from the eupnoeic rate of 65 +/- 8 beats min-1. Diving heart rate was inversely related to dive duration in a non-linear fashion best described by a continuous, curvilinear model, while heart rate during apnoea on land was independent of the duration of apnoea. Occasionally, instantaneous heart rate fell as low as 3 beats min-1 during diving. Although bradycardia occurs in response to apnoea both at sea and on land, only at sea is heart rate apparently regulated to minimise eupnoeic time and to ration oxygen stores to ensure adequate supplies for the heart and brain not only as the dive progresses normally but also when a dive is abnormally extended.

Animals↗
PubMed2002

High feeding costs limit dive time in the largest whales.

Large body size usually extends dive duration in air-breathing vertebrates. However, the two largest predators on earth, the blue whale (Balaenoptera musculus) and the fin whale (B. physalus), perform short dives for their size. Here, we test the hypothesis that the foraging behavior of these two species (lunge-feeding) is energetically expensive and limits their dive duration. We estimated the cost of lunge-feeding in both species using an approach that combined attaching time/depth recorders to seven blue whales and eight fin whales and comparing the collected dive information with predictions made by optimality models of dive behavior. We show that the rate at which whales recovered from a foraging dive was twice that of a non-foraging dive and that the cost of foraging relative to the cost of travel to and from the prey patch was 3.15 in blue whales (95 % CI 2.58-3.72) and 3.60 in fin whales (95 % CI 2.35-4.85). Whales foraged in small areas (<1 km(2)) and foraging bouts lasted more than one dive, indicating that prey did not disperse and thus that prey dispersal could not account for the limited dive durations of the whales. Despite the enormous size of blue whales and fin whales, the high energetic costs of lunge-feeding confine them to short durations of submergence and to areas with dense prey aggregations. As a corollary, because of their limited foraging time under water, these whales may be particularly vulnerable to perturbations in prey abundance.

Animals↗
PubMed2002

Experienced, recreational scuba divers in Australia continue to dive despite medical contraindications.

OBJECTIVE: In Australia, a medical examination is required before undertaking a scuba diving course in order to screen for contraindications to diving. No further medical screening is required, and yet divers may develop diseases during their diving careers. This study aimed to survey experienced recreational scuba divers to determine the prevalence of diseases contraindicated in diving. METHODS: A cross-sectional, postal survey was taken of divers belonging to scuba diving clubs across Australia. RESULTS: Three hundred forty-six divers returned completed questionnaires. Two hundred fifty-four (73.4%) were male, and 258 (74.6%) were aged 31 to 60 years. The mean years of diving equaled 10.6 +/- 9.18 years, and the mean number of dives undertaken was 414 +/- 740 dives. One hundred sixty-two (46.8%) divers were overweight, 45 (13.0%) divers required regular medication, and 39 (11.3%) divers smoked. Thirty-six (10.4%) divers reported a past or present history of asthma, and the same number reported hypertension or coronary heart disease. Eighty-six (24.9%) divers reported past or present psychological symptoms. Forty-two (12.1%) divers reported hearing difficulties, and 81 (23.4%) divers reported past or present tinnitus. Two divers had a past history of epilepsy, 2 had a history of pneumothorax, and I was diabetic. CONCLUSIONS: Experienced, recreational scuba divers continue to dive despite medical contraindications. This raises the questions: Did the divers fail to disclose these conditions at the initial examination, or did these conditions develop subsequently? Is the risk associated with these conditions clinically significant, and should screening examinations be undertaken at regular intervals? The high prevalence of hearing difficulties and tinnitus may be the result of aural barotrauma and requires further research.

Adult↗
PubMed2001

Recreational scuba diving, patent foramen ovale and their associated risks.

Scuba diving has become a popular leisure time activity with distinct risks to health owing to its physical characteristics. Knowledge of the behaviour of any mixture of breathable gases under increased ambient pressure is crucial for safe diving and gives clues as to the pathophysiology of compression or decompression related disorders. Immersion in cold water augments cardiac pre- and afterload due to an increase of intrathoracic blood volume and peripheral vasoconstriction. In very rare cases, the vasoconstrictor response can lead to pulmonary oedema. Immersion of the face in cold water is associated with bradycardia mediated by increased vagal tone. In icy water, the bradycardia can be so pronounced, that syncope results. For recreational dives, compressed air (i.e., 4 parts nitrogen and 1 part oxygen) is the preferred breathing gas. Its use is limited for diving to 40 to 50 m, otherwise nitrogen narcosis ("rapture of the deep") reduces a diver's cognitive function and increases the risk of inadequate reactions. At depths of 60 to 70 m oxygen toxicity impairs respiration and at higher partial pressures also functioning of the central nervous system. The use of special nitrogen-oxygen mixtures ("nitrox", 60% nitrogen and 40% oxygen as the typical example) decreases the probability of nitrogen narcosis and probably bubble formation, at the cost of increased risk of oxygen toxicity. Most of the health hazards during dives are consequences of changes in gas volume and formation of gas bubbles due to reduction of ambient pressure during a diver's ascent. The term barotrauma encompasses disorders related to over expansion of gas filled body cavities (mainly the lung and the inner ear). Decompression sickness results from the growth of gas nuclei in predominantly fatty tissue. Arterial gas embolism describes the penetration of such gas bubbles into the systemic circulation, either due to pulmonary barotrauma, transpulmonary passage after massive bubble formation ("chokes") or cardiac shunting. In recreational divers, neurological decompression events comprise 80% of reported cases of major decompression problems, most of the time due to pathological effects of intravascular bubbles. In divers with a history of major neurological decompression symptoms without evident cause, transoesophageal echocardiography must be performed to exclude a patent foramen ovale. If a cardiac right-to-left shunt is present, we advise divers with a history of severe decompression illness to stop diving. If they refuse to do so, it is crucial that they change their diving habits, minimising the amount of nitrogen load on the tissue. There is ongoing debate about the long term risk of scuba diving. Neuro-imaging studies revealed an increased frequency of ischaemic brain lesions in divers, which do not correlate well with subtle functional neurological deficits in experienced divers. In the light of the high prevalence of venous gas bubbles even after dives in shallow water and the presence of a cardiac right-to-left shunt in a quarter of the population (i.e., patent foramen ovale), arterialisation of gas bubbles might be more frequent than usually presumed.

Atrophy↗
PubMed2001

Decrease in platelet count during saturation diving.

BACKGROUND: The change in platelet count (PC) occurring during saturation diving has rarely been discussed. We set out to clarify the details of this change in PC, and its relationship with: i) the storage depth and duration of the saturation dive, and ii) the presence of decompression bubbles. METHODS: In a total of 42 divers, the change in PC was measured in 8 simulated saturation dives (1992-1998) using a Deep Diving Simulator with decompression procedures based on the modified DUKE-GKSS schedule. Blood samples were taken before the dive, at the bottom (twice), during decompression, on surfacing, and about 1 wk after surfacing. Decompression bubbles were examined by ultrasonic M-mode echocardiography. RESULTS: PC (mean +/- SD x 10(4) x microl(-1)) was 23.9 +/- 4.85, 24.9 +/- 4.9, 24.2 +/- 4.8, 19.2 +/- 4.4*, 20.1 +/- 4.5*, 25.0 +/- 5.1 on the occasions listed above (*= p < 0.05 vs. pre-dive). The PC showed no correlation with either storage depth or dive duration. Decompression bubbles were detected during decompression in only 2 divers (4.8%), and the bubbles disappeared immediately after surfacing. In these 2 divers the decreases in PC values from baseline to the middle of decompression and on surfacing were 2 and 2.7 x 10(4) x microl(-1), and 3.4 and 1.7 x 10(4) x microl(-1) respectively. No diver complained of decompression sickness. CONCLUSION: The magnitude of the decrease in PC (< 5 x 10(4) x microl(-1)) and the time to recover to the pre-dive value (< 1 wk) suggests that changes in PC during saturation diving should not cause any clinical problems. The mechanisms underlying the decrease in PC remain unclear.

Adult↗
PubMed2002

Comparative data from 2250 male and female sports divers: diving patterns and decompression sickness.

BACKGROUND: The aim of the study was to compare the diving habits and histories of men and women in recreational scuba diving. METHODS: More than 10,000 questionnaires were circulated to recreational divers in the United Kingdom. Retrospective, broad-based information was requested concerning general health, smoking, alcohol, recreational drug use, diving habits and histories, and physician-confirmed and self-diagnosed episodes of decompression sickness (DCS). Data relating only to women were also gathered. Questionnaires were anonymous. RESULTS: Over four years, 2250 divers responded, 47% of whom were women. Of the 458,827 dives reported, 310% were by women. Differences in diving habits were observed between men and women, which included number of dives per annum, maximum depths dived, and dives with extra stops. When the level of experience was taken into account in this study group, the estimated rate of DCS in men was 2.60 times greater than for women. CONCLUSIONS: In this study, comparison between men and women in recreational diving differed from the initial evaluation when underlying factors were taken into account. Future studies should attempt to control for underlying factors in the data gathering and data analysis.

Adolescent↗
PubMed1991

High altitude dives from 7000 to 14,200 feet in the Himalayas.

Indian Navy divers carried out no-decompression dives at altitudes of 7000 to 14,200 ft (2134-4328 m) in the Nilgiris and Himalayas from May to July 1988. Seventy-eight dives on air and 22 dives on oxygen were carried out at various altitudes. The final dives were at Lake Pangong Tso (4328 m) in Ladakh, Himalayas, to a maximum of 140 feet of sea water (fsw) [42.6 meters of sea water (msw)] equivalent ocean depth in minimum water temperature of 2 degrees C. Oxygen diving at 14,200 ft (4328 m) was not successful. Aspects considered were altitude adaptation, diminished air pressure diving, hypothermia, and remote area survival. Depths at altitude were converted to depths at sea level and were applied to the Royal Navy air tables. Altitude-related manifestations, hypoxia, hypothermia, suspected oxygen toxicity, and equipment failure were observed. It is concluded that stress is due to effects of altitude and cold on man and equipment, as well as changes in diving procedures when diving at high altitudes. Equivalent air depths when applied to Royal Navy tables could be considered a safe method for diving at altitudes.

Acclimatization↗
PubMed1989

Behavior of freely diving animals.

While diving animals are capable of both long-duration and deep dives, their normal behavior does not routinely approach these limits of time and depth. Studies of the physiologic and biochemical capabilities of diving species have defined the maximum limits of their underwater periods. However, by also studying their diving behavior, we can examine how diving animals most efficiently work within those limits. If we assume for example that the behavioral goal of a foraging seal is to spend as much time underwater as possible, then it must also minimize time at the surface and make many repetitive dives instead of single, longer dives that require long surface recovery periods. To understand the efficiency of bout diving, we must study the physiologic impact of many repetitive dives and how the seal manipulates its behavior to both stay within its physiologic limits and to maximize time underwater.

Animals↗
PubMed1986

Balancing conflicting metabolic demands of exercise and diving.

During enforced diving, aquatic animals activate a set of physiological reflexes (apnea, bradycardia, peripheral vasoconstriction), which are termed the diving response and are in effect the first line of defense against hypoxia. At least in the Weddell seal, this strategy is now known also to be used in voluntary diving at sea, but the response is necessarily modified to accommodate potentially conflicting demands of diving and swimming exercise. The main modification appears to involve skeletal muscles used in swimming, which, because of their high energy requirements, must be powered by aerobic metabolism. Thus they must remain perfused at rates porportional to swimming velocity (which is why heart rates are adjusted to swimming velocity). The required regulation of O2 delivery is achieved at least in part by a well-paced release of oxygenated red blood cells, stored at the beginning of the dive apparently in the spleen. The main metabolic difference between laboratory and voluntary diving is that, in the latter, working muscles serve as a sink for lactate and thus the entry rates of lactate into the plasma can be balanced by exit rates from the plasma; the maintenance of this balance means that no excess lactate remains for a lactate washout in postdiving exercise except under long, exploratory diving. Even in the latter long dives, however, the amount of lactate formed is far less than would be expected if the energetic shortfall caused by hypoperfusion and O2 lack were made up by anaerobic glycolysis (Pasteur effect). Consequently, during diving, hypoperfused tissues necessarily sustain a metabolic arrest of variable degrees as a mechanism of defense against hypoxia.

Animals↗
PubMed1986

Health risks of diving among U.S. Navy officers.

The objectives were to compare hospitalization, medical board, and mortality rates of diving-related disorders and stress-induced diseases between U.S. Navy male diving officers (n = 1977) and a matched sample of nondiving officers (n = 1973). Less experienced diving officers had significantly higher hospitalization rates than more experienced diving officers for total admissions, stress-related disorders (primarily alcoholism), and cardiovascular disease. Diving officers had significantly higher hospitalization rates than controls for nervous system diseases and joint disorders; none of these hospitalized diving officers had a recorded incident of decompression sickness. To ensure the safety and overall excellent health status of diving officers, it is necessary to promote and continue adherence to the procedures developed for safe diving in the U.S. Navy diving community.

Administrative Personnel↗
PubMed1975

Bradycardia during human diving.

The bradycardial response to the diving reflex, which occurs in man and in diving animals, is thought to be a physiologically protective oxygen-conserving mechanism whereby the animal is kept alive during submergence. The physiology and nervous pathways are not yet fully understood, but several investigators have pointed out the potentially fatal outcome of an accentuated diving reflex. the CO2 content of the peripheral venous blood has been proved variable and unpredictable during the hyperventilation-breath-hold dive cycle in man. A group of 8 male divers (average age 34 years) was investigated during breathhold dives to 3,3 m in a swimming pool. Heart rates were recorded and compared at various stages during breath-hold and SCUBA (self-contained underwater breathing apparatus) dives, viz. when resting on the surface, breath-holding, hyperventilating and swimming underwater. Two divers performed extreme breathhold endurance tests lasting 135 seconds underwater. All divers had a tachycardia after hyperventilation and a bradycardia after breathhold diving, lasting 80-100 seconds. Extrasystoles were recorded during some of the breathhold dives. Prolonged submergence caused extreme bradycardia (24/min) with central cyanosis. Bradycardia during diving may be a physiological )2-conserving reflex or the start of a pathophysiological asphyxial response.

Adult↗
PubMed1983

Comparison of diving experience factors between divers classified as positive and negative for bone cysts.

Official U.S. Navy diving records for enlisted divers who were 35 years of age and older were examined for differences in diving experience between those who were classified as positive or negative for bone cysts. One-third of the divers (n = 31) were classified as positive, and two-thirds (n = 62) as negative, for bone cysts. Diving experience factors included total years of diving experience, frequency of dives between 15 and 31 m, frequency of dives deeper than 31 m, number of saturation dives, number of dives involving decompression, and number of cases of decompression sickness. None of these factors differed significantly between the two groups. While previous findings showed that bone cysts are twice as prevalent among divers as among a comparison group of Navy enlisted men matched to divers for age, rank, and occupational specialty, these results indicate that this high prevalence rate does not appear to be related to specific types of diving exposure. Other environmental factors such as long-bone injury, disease, or exposure to hazardous or toxic substances may account for differences in the prevalence of bone cysts between the two groups.

Adult↗
PubMed1980

Scuba diving and fetal well-being: a survey of 208 women.

Scuba diving is an increasingly popular sport among women of childbearing age. It causes physiological changes that are possibly lethal or teratogenic to the fetus. The subject of diving during pregnancy is seldom mentioned in diving courses, however, and few obstetricians are familiar with the physiology of diving. The study employed mailed questionnaires for description and comparison of the extent of diving and obstetric and fetal outcome of 208 women divers, 136 of whom dived during one or more pregnancies. Depths to which these women dived averaged 42.6 ft; 24 women, however, reported dives deeper than 99 ft during the first trimester. I analyzed the prevalence of six specific fetal complications and found that the frequency of birth defects was significantly greater among children from pregnancies during which women dived (P < 0.05) but was within the range for the general population.

Abortion, Spontaneous↗
PubMed1995

Diving patterns of ama divers of Hegura Island, Japan.

Daily diving patterns, especially depth-time profiles, were continuously recorded during the entire work shift in four cachido and four funado divers of Hegura Island, Japan. All Hegura divers (cachido and funado alike) were female and habitually wore wet suits. Cachidos dive free and unassisted from a boat or float, whereas funado divers are assisted by weighted descent and during the ascent by being pulled by a partner into a boat on the water surface. Both funado and cachido divers spent 250-280 min/day on the sea at their diving locations; the actual diving time was 100-120 min. The divers made 90-120 dives/day to a depth of 13-22 m, each dive lasting approximately 60 s, considerably longer and deeper than those observed and recorded previously in ama divers in the Chiba and Miura regions. These dive profiles are similar to those reported by Paulev in which he observed apparent signs of decompression sickness when the subject dived to a depth of 15-20 m 100 times in 5 h. The average bottom time for each dive of Hegura funados was 23.6 s which is approximately 10 s longer than that of Korean female ama. The rate of ascent in the funado divers was 1.5 m/s, which is nearly twice that of the cachido divers (0.8 m/s). The dive frequency of Hegura funados (109 dives/day) was greater than the Chiba male funados (23 dives/day). Accordingly, cumulative bottom time of Hegura funado was 48 min/day, whereas that of Chiba funado was 17 min/day.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Asthma and diving.

BACKGROUND: Approximately 10 to 15 million Americans are scuba divers. The prevalence of scuba diving and asthma makes it likely some asthmatics will be interested in scuba diving and some scuba divers will have asthma. Conditions present during scuba diving may provoke airway obstruction in asthmatic patients. Further, asthmatic patients may, in theory, face a greater than normal risk of pulmonary barotrauma from lung overdistension on ascent through the water column. OBJECTIVE: The purpose of this paper is to review the theoretical issues underlying the prohibition against scuba diving for asthmatic patients as advanced by most major diving organizations in the United States and critically examine the relevant accident data. METHODS: All reports that dealt with asthma and diving, and all available American accident data including both fatal and nonfatal accidents were reviewed. RESULTS: Actuarial data on the risk of scuba accidents attributable to asthma do not define several important variables likely to affect accident risk during scuba diving. Despite these limitations, careful review indicates the risks of serious morbidity or mortality during scuba diving appears to be inconsequentially elevated in subjects whose asthma was not characterized. CONCLUSIONS: Additional data are needed to define accurately risks of diving in subjects with different forms of asthma, however, the available data suggest asthmatic patients with normal airway function at rest, and with little airway reactivity in response to exercise or cold air inhalation, have a risk of pulmonary barotrauma similar to that of normal subjects.

Airway Obstruction↗
PubMed1977

Converting standard air decompression tables for no-stop diving from altitude or habitat.

Using the phase equilibration theory of Hills (1966), as modified by Hennessy and Hempleman (1977), it is possible to predict formulas for converting standard air decompression tables for no-stop diving at altitude or from a normoxic habitat, breathing air. For diving following equilibration at altitude, the Royal Navy, Royal Naval Physiological Laboratory, and Haldane-type rules appear to be too conservative, with the opposite result for diving after excursion to altitude. Predictions in the latter case are in fair agreement with the Swiss (Boni, Schibli, Nussberger, and Bühlmann 1976) no-stop altitude tables. In the case of habitats, close agreement is found between the Hamilton, Kenyon, Freitag, and Schreiner (1973) normoxic tables for no-stop downward excursions and indefinite dive upward-excursions on air. In the case of flying directly after no-stop diving, the US Navy rule of using repetitive group D appears to be conservative for dives less than 50 fsw, and possibly unsafe for dives over 50 fsw. It is concluded that for no-stop diving a single tissue and single safe ascent pressure formula are all that is necessary to generate equivalent air dives. This enforces the hypothesis that it is the volume of gas released on ascent that governs marginal type I bends, and that in a no-stop ascent, all excess dissolved gas is released in the worst case.

Aerospace Medicine↗