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At least 271 records · Page 15Linked to original sources
PubMed1989

Arterial gas tensions and hemoglobin concentrations of the freely diving Weddell seal.

Heart rate, body temperature, arterial blood gas tensions, pHa and hemoglobin concentrations were measured during and after free diving of the Weddell seal (Leptonychotes weddelli), beneath the fast ice of McMurdo Sound, Antarctica. To examine arterial nitrogen tensions (PaN2), 47 samples of arterial blood were obtained from 4 seals diving up to 23 min to depths of 230 m. Peak arterial nitrogen tensions between 2000 and 2500 mmHg were recorded at depths of 40-80 m during descent, indicating that the seal's lung collapses by 25-50 m. Then arterial blood nitrogen tensions slowly decreased to about 1500 mmHg near surfacing. Thus during diving alveolar collapse and redistribution of blood nitrogen allow the seal to avoid nitrogen narcosis and decompression sickness. The arterial PO2 (PaO2) at rest (78 +/- 13 mmHg, mean +/- SD) increased with diving compression to a maximum measured value of 232 mmHg and then rapidly decreased to 25-35 mmHg. The lowest diving PaO2 was 18 mmHg just before the seal surfaced from a 27-min dive. A consistent increase of arterial hemoglobin concentrations occurred during each dive. We suggest that an extension of the sympathetic outflow of the diving reflex caused profound contraction of the Weddell seal's spleen.

Animals↗
PubMed1987

Decompression after repeated dives.

Seventy-six men and 7 women performed a 2nd dive in a pressure chamber under dry conditions after intervals at the surface of 10, 30, 90, or 120 min. Of these, 35 persons performed a 3rd dive after an interval of 20 or 90 min (118 repeated dives). Air was the breathing gas during all phases of the tests. During exposure to overpressure the divers exercised on a bicycle-ergometer. The decompressions for dives 2 and 3 were the same as for the first dive. After the 2nd or 3rd dive, certain symptoms of decompression sickness of the skin occurred in 5 of the 118 exposures, and 1 diver complained of muscular aches. These results suggest that no general sensitization occurred after the 1st dive. We concluded that a slightly more conservative decompression with regard to ascent velocity and profile is feasible for repeated dives.

Adult↗
PubMed1985

Analyses of variables underlying U.S. Navy diving accidents.

U.S. Navy diving logs were examined to determine the most frequently occurring diving accidents and to identify significant underlying factors. Of the 1174 incidents reported during the course of 706,259 dives, decompression sickness and barotraumas were the most prevalent. Mishap incidence increased significantly with dive depth. Dives for selection or experimental purposes, as well as saturation diving and surface decompressions among decompression schedule types, were at an elevated risk of terminating in an accident. Older divers were disproportionately assigned to deep dives. Eighty-one percent of diving mishaps ended in complete relief for the diver while 18% terminated in substantial relief.

Accidents, Occupational↗
PubMed1995

Balance testing in saturation diving.

UNLABELLED: The literature is sparse and equivocal concerning the possible influence of hyperbaric exposure on postural control and the vestibular system. HYPOTHESIS: Deep heliox diving may influence postural control and the vestibular system. METHOD: Multiple objective measurements of postural control were made in four divers by means of a static balance platform before, during and after an onshore experimental saturation heliox chamber dive of 32 d duration. Saturation pressure was 4.6 MPa, corresponding to a depth of 450 m of seawater (msw). Downward excursions to 470 msw were also performed. Clinical ENT and otoneurological examination, including bithermal caloric vestibular testing with electronystagmography (ENG) was performed before and after the dive. RESULTS: Reduced postural control was detected by the balance platform test in all four divers from approximately 200 msw and deeper. Body sway showed a distinct increase during compression, reaching a maximum value during the bottom phase. The Romberg index was not suitable for describing shifts in postural stability. All sway parameters returned to pre-dive values after surfacing. Immediately post-dive, most caloric responses were reduced, compared to the pre-dive results. CONCLUSION: We conclude that deep heliox diving influences postural control and the vestibular system. Computerized stabilometry is a convenient and sensitive method of monitoring postural control during saturation diving. The path length of the center of pressure (COP) seems to be suitable as a monitoring parameter.

Adult↗
PubMed1996

Divers' pulmonary function after open-sea bounce dives to 10 and 50 meters.

We have studied pulmonary function before and 2 h after open sea dives to 10 and 50 m and 24 h after the dive to 10 m. Nine trainee divers participated in the dive to 10 m and 17 in the dive to 50 m. Mean time in water was 53 (32-62) min for the 10-m dive and 38 (26-76) min for the 50-m dive. Assessment of lung function included dynamic lung volumes and flows and transfer factor for carbon monoxide (TlCO). There were significant reductions (P < 0.05) in forced vital capacity of 5.8% (SD = 3.9) and 1.8% (SD = 2.8), in forced expired volume in 1 s of 6.6% (SD = 3.5) and 2.7% (SD = 2.4), in forced mid-expiratory flow rate of 10.3% (SD = 7.8) and 5.2% (SD = 6.5), and in TlCO of 11.3% (SD = 7.9) and 12.8% (SD = 5.9) 2 h after the 10- and 50-m dive, respectively. Our results indicate that factors related to submersion and increased breathing resistance contribute to changes in pulmonary function in the first hours after open-sea bounce dives.

Adult↗
PubMedDate not supplied

Impact of externally attached loggers on the diving behaviour of the king penguin.

The impact of relatively small externally attached time series recorders on some foraging parameters of seabirds was investigated during the austral summer of 1995 by monitoring the diving behaviour of 10 free-ranging king penguins (Aptenodytes patagonicus) over one foraging trip. Time-depth recorders were implanted in the abdominal cavities of the birds, and half of the animals also had dummy loggers attached on their backs. Although most of the diving behaviour was not significantly affected by the external loggers (P>0.05), the birds with externally attached loggers performed almost twice as many shallow dives, between 0 and 10 m depth, as the birds without external loggers. These shallow dives interrupted more frequently the deep-diving sequences in the case of birds with external loggers (percentage of deep dives followed by deep dives: 46% for birds with implants only vs. 26% for birds with an external attachment). Finally, the distribution pattern of the postdive durations plotted against the hour of the day was more heterogeneous for the birds with an external package. In addition, these penguins had extended surfacing times between two deep dives compared to birds without external attachments (P<0.0001). These results suggest the existence of an extra energy cost induced by externally attached loggers.

Animals↗
PubMed2026

Adaptations to breath-hold diving: from traditional divers to elite athletes.

Breath-hold diving exposes humans to repeated episodes of profound hypoxia and hypercapnia, eliciting physiological adaptations that enable prolonged underwater performance. This article summarises current knowledge on chronic adaptations in elite breath-hold athletes and traditional diving populations, including the Bajau sea nomads of Southeast Asia and the Korean Haenyeo divers. Evidence indicates that repeated apnoea induces adaptations across multiple physiological systems. Haematological changes include increased spleen size and enhanced splenic contraction, augmenting circulating haemoglobin and oxygen stores during apnoea. In elite divers, structured training can increase resting spleen volume, whereas the Bajau exhibit genetically associated splenic enlargement linked to variants near the PDE10A gene. Cardiopulmonary adaptations include modified pulmonary vascular responses to hypoxia, improved oxygen conservation, and metabolic shifts favoring efficient mitochondrial energy production. Molecular adaptations involve enhanced antioxidant defenses and activation of hypoxia-responsive pathways that may mitigate oxidative stress associated with repeated hypoxia-reoxygenation cycles. Emerging evidence also suggests neural plasticity and possible structural brain adaptations, although the long-term neurological consequences of chronic intermittent hypoxia exposure remain uncertain. Studies of traditional diving populations indicate that both phenotypic plasticity and genetic selection contribute to diving capacity, highlighting interactions between training and evolution. Despite these benefits, breath-hold diving also carries risks, including hypoxic blackout, decompression sickness, and potential neurological injury. Understanding the mechanisms underlying human tolerance to extreme hypoxia may have implications beyond diving physiology, including applications in cardiovascular medicine, hypoxic diseases, and rehabilitation. Further longitudinal, genomic, and mechanistic studies are needed to clarify the limits, benefits, and clinical relevance of these adaptations.

Humans↗
PubMed2001

Can diving-induced tissue nitrogen supersaturation increase the chance of acoustically driven bubble growth in marine mammals?

The potential for acoustically mediated causes of stranding in cetaceans (whales and dolphins) is of increasing concern given recent stranding events associated with anthropogenic acoustic activity. We examine a potentially debilitating non-auditory mechanism called rectified diffusion. Rectified diffusion causes gas bubble growth, which in an insonified animal may produce emboli, tissue separation and high, localized pressure in nervous tissue. Using the results of a dolphin dive study and a model of rectified diffusion for low-frequency exposure, we demonstrate that the diving behavior of cetaceans prior to an intense acoustic exposure may increase the chance of rectified diffusion. Specifically, deep diving and slow ascent/descent speed contributes to increased gas-tissue saturation, a condition that amplifies the likelihood of rectified diffusion. The depth of lung collapse limits nitrogen uptake per dive and the surface interval duration influences the amount of nitrogen washout from tissues between dives. Model results suggest that low-frequency rectified diffusion models need to be advanced, that the diving behavior of marine mammals of concern needs to be investigated to identify at-risk animals, and that more intensive studies of gas dynamics within diving marine mammals should be undertaken.

Animals↗
PubMed2002

Precocial diving and patent foramen ovale in bearded seal (Erignathus barbatus) pups.

In this study we used a Doppler ultrasonic device, in combination with a sonographic contrast medium, to test whether free-living bearded seal (Erignathus barbatus) pups have a closed (anatomically or functionally) foramen ovale. A total of 17 examinations were performed on 12 individual pups with a body mass range of 29-103 kg (0-21 days old). These examinations showed that young bearded seal pups dive with a patent foramen ovale (PFO), and that this structure starts to close, at least functionally, during the 2nd week of life. The wide range in the timing of closure (one animal 21 days old still had a PFO) indicates that a closed foramen ovale is not crucial for the diving that these seals perform at this age. The primary function of diving during the 1st week of life is to avoid surface predation and only moderate diving ability is sufficient to achieve this goal. However, some of the diving performed by bearded seal pups with a PFO would likely be sufficient to create intravenous bubble formation during breath-hold diving in humans. Special adaptations in the seals, such as collapsible lungs and diving with minimal lung air volume, probably prevent this from happening.

Animals↗
PubMed2005

Changes in erythropoietin and haemoglobin concentrations in response to saturation diving.

A reduction in haemoglobin concentration is consistently reported after deep saturation dives. This may be due to a downregulation of erythropoietin (EPO) concentration or to a toxic effect of the hyperoxia associated with the dives resulting in an increased destruction rate of erythrocytes. In this study haemoglobin concentration, blood cell counts, serum ferritin, bilirubin, haptoglobin and EPO concentrations were measured before, during and after a 19 day saturation dive to 240 m. The partial pressure of oxygen (PO(2)) was 35-70 kPa during the 7 day compression and bottom phase, and 30-50 kPa during the 12 day decompression phase. There was a reduction in EPO concentration from 8.4+/-1.4 (mean +/- 1SD) to 6.3 +/- 1.9 U.L(-1) on Dive day 2. On Dive days 7 and 17 EPO concentrations were not significantly different from baseline despite the continued exposure to hyperoxia. Immediately after the dive and return to a normoxic environment there was an increase in the EPO concencentration to 14.5 +/- 4.7 U.L(-1). Haemoglobin concentration, erythrocyte and reticulocyte counts were decreased at the end of the dive, and there was an increase in serum ferritin. There were no changes in bilirubin or haptoglobin concentrations indicative of haemolysis. It appears that the change in PO(2), rather than the sustained exposure to a hyperoxic environment, induces the changes in the EPO concentrations and erythropoietic activity.

Adult↗
PubMed2004

Defining the limits of diving biochemistry in marine mammals.

The field of marine mammal diving biochemistry was essentially untouched when Peter Hochachka turned his attention to it in the mid-1970s. Over the next 30 years, his work followed three main themes in this area: first, most biologists at that time supported the theory that diving mammals utilized enhanced metabolic pathways for hypoxic energy production (glycolysis to lactate) and reduced their metabolic rate while diving. Peter began his work on potential hypoxic adaptations in marine mammals by working out the details of how these pathways would be regulated. By the 1980s, he started to ask how diving mammals balanced the increased demands of exercise with the apparently conflicting demands to reduce aerobic metabolism while exercising underwater. By the 1990s, his work involved complex models of the interplay between the neural, hormonal, behavioral and evolutionary components of diving biochemistry and animal exercise. From a comparative approach, he excelled at bringing themes of hypoxic adaptation from many different types of animals to the field of diving mammal biochemistry. This review traces the history of Peter Hochachka's work on diving biochemistry from the perspective of those of us who spent time with him both inside the laboratory and outside in the field from Antarctica to Iceland.

Adaptation, Physiological↗
PubMed2005

Patent foramen ovale and diving.

Patency of the foramen ovale is a risk factor for DCS in SCUBA divers, even if they adhere to the currently accepted and used decompression tables. The primary cause of DCS, however, is the nitrogen bubble, not the PFO. There are a number of techniques any diver can use to minimize the occurrence of nitrogen bubbles after a dive. The authors current practice is to inform civilian sports divers of the increased risk and to advise them to adopt conservative dive profiles. This can be achieved by selecting a more conservative dive computer, performing only dives that do not require obligatory decompression stops, or using oxygen-enriched breathing gas mixtures("nitrox") while still diving on "air profiles" [56].Dive-safety organizations are currently under-taking studies aimed at proposing changes in the decompression algorithms to produce low-bubble dive tables [12]. In the meantime, PFO remains a reason for caution. Whether all divers should be screened for PFOis an ongoing discussion [50] in view of methodologic and practical issues outlined in this article. Any definitive recommendations can be made only after a careful, prospective evaluation of the real relative risk for DCS and long-term cerebral damage.

Decompression Sickness↗
PubMed2000

Diving physiology of birds: a history of studies on polar species.

Our knowledge of avian diving physiology has been based primarily on research with polar species. Since Scholander's 1940 monograph, research has expanded from examination of the 'diving reflex' to studies of free-diving birds, and has included laboratory investigations of oxygen stores, muscle adaptations, pressure effects, and cardiovascular/metabolic responses to swimming exercise. Behavioral and energetic studies at sea have shown that common diving durations of many avian species exceed the calculated aerobic diving limits (ADL). Current physiological research is focused on factors, such as heart rate and temperature, which potentially affect the diving metabolic rate and duration of aerobic diving.

Animals↗
PubMed2005

Diving-induced venous gas emboli do not increase pulmonary artery pressure.

Venous gas emboli are frequently observed in divers even if proper decompression procedures are followed. This study was initiated to determine if pulmonary artery pressure increases in asymptomatic divers, which could increase the risk of arterial embolization due to passage of venous gas emboli from the right to the left side of the heart. Recordings of venous gas emboli and estimation of pulmonary artery pressure by non-invasive transthoracic echocardiography were applied in 10 recreational scuba diving volunteers before and 20, 40, 60, and 80 min after simulated dives to 18 m (80 min bottom time) in a hyperbaric chamber. The ratio between pulmonary artery acceleration time and right ventricular ejection time was used as an estimate of pulmonary artery pressure. None of investigated divers had signs of decompression sickness. Despite the post-dive presence of the venous gas emboli, measured in the region of the pulmonary valve annulus (mean=1.71 bubbles.cm-2, 40 min after dive), the ratio between pulmonary artery acceleration time and right ventricular ejection time did not decrease, but actually increased (from 0.43+/-0.06 to 0.49+/-0.06, 40 min after dive; p<0.05), suggesting a decrease in pulmonary artery pressure after the dive. We conclude that diving-induced venous gas bubbles do not cause significant changes in the central circulation which could increase the risk of arterial embolization.

Adult↗
PubMed2006

Diving behaviour of whale sharks in relation to a predictable food pulse.

We present diving data for four whale sharks in relation to a predictable food pulse (reef fish spawn) and an analysis of the longest continuous fine-resolution diving record for a planktivorous shark. Fine-resolution pressure data from a recovered pop-up archival satellite tag deployed for 206 days on a whale shark were analysed using the fast Fourier Transform method for frequency domain analysis of time-series. The results demonstrated that a free-ranging whale shark displays ultradian, diel and circa-lunar rhythmicity of diving behaviour. Whale sharks dive to over 979.5 m and can tolerate a temperature range of 26.4 degrees C. The whale sharks made primarily diurnal deep dives and remained in relatively shallow waters at night. Whale shark diving patterns are influenced by a seasonally predictable food source, with shallower dives made during fish spawning periods.

Animals↗
PubMed1991

Impedance measurement in divers during a scuba-diving training programme.

An assessment of the strain on the tympanic membrane caused by diving was performed using impedance measurement of the middle ear in 21 untrained young men going through a scuba-diving training programme (scuba, self-contained under-water breathing apparatus). Tympanometry was carried out just before and after diving. The divers made 104 dives between them (median 5 each, range 2-7) at depths from 2 to 12 m (median 6 m). The results showed a significant increase in middle ear compliance on diving. The increase in compliance was significant at different depths, was transient, and fell to the initial level between the dives. We conclude that the strain exerted on the tympanic membrane and middle ear from barotrauma due to diving results in a reversible impairment of the recoiling capacity of the elastic fibrils of the tympanic membrane. This transient increase in compliance, we think, is the first measurable change in elasticity of the tympanic membrane. If barotrauma continue the changes could be irreversible.

Acoustic Impedance Tests↗
PubMed2005

A single air dive reduces arterial endothelial function in man.

During and after decompression from dives, gas bubbles are regularly observed in the right ventricular outflow tract. A number of studies have documented that these bubbles can lead to endothelial dysfunction in the pulmonary artery but no data exist on the effect of diving on arterial endothelial function. The present study investigated if diving or oxygen breathing would influence endothelial arterial function in man. A total of 21 divers participated in this study. Nine healthy experienced male divers with a mean age of 31 +/- 5 years were compressed in a hyperbaric chamber to 280 kPa at a rate of 100 kPa min(-1) breathing air and remaining at pressure for 80 min. The ascent rate during decompression was 9 kPa min(-1) with a 7 min stop at 130 kPa (US Navy procedure). Another group of five experienced male divers (31 +/- 6 years) breathed 60% oxygen (corresponding to the oxygen tension of air at 280 kPa) for 80 min. Before and after exposure, endothelial function was assessed in both groups as flow-mediated dilatation (FMD) by ultrasound in the brachial artery. The results were compared to data obtained from a group of seven healthy individuals of the same age who had never dived. The dive produced few vascular bubbles, but a significant arterial diameter increase from 4.5 +/- 0.7 to 4.8 +/- 0.8 mm (mean +/- s.d.) and a significant reduction of FMD from 9.2 +/- 6.9 to 5.0 +/- 6.7% were observed as an indication of reduced endothelial function. In the group breathing oxygen, arterial diameter increased significantly from 4.4 +/- 0.3 mm to 4.7 +/- 0.3 mm, while FMD showed an insignificant decrease. Oxygen breathing did not decrease nitroglycerine-induced dilatation significantly. In the normal controls the arterial diameter and FMD were 4.1 +/- 0.4 mm and 7.7 +/- 0.2.8%, respectively. This study shows that diving can lead to acute arterial endothelial dysfunction in man and that oxygen breathing will increase arterial diameter after return to breathing air. Further studies are needed to determine if these mechanisms are involved in tissue injury following diving.

Adult↗
PubMed2003

The effect of a low-frequency sound source (acoustic thermometry of the ocean climate) on the diving behavior of juvenile northern elephant seals, Mirounga angustirostris.

Changes in the diving behavior of individual free-ranging juvenile northern elephant seals, Mirounga angustirostris, exposed to the acoustic thermometry of the ocean climate (ATOC) sound source were examined using data loggers. Data loggers were attached to the animals and measured swim speed, maximum depth of dive, dive duration, surface interval, descent and ascent rate, and descent and ascent angle along with sound pressure level (SPL). The ATOC sound source was at a depth of 939 m and transmitted at 195 dB re: 1 microPa at 1 m centered at 75 Hz with a 37.5-Hz bandwidth. Sound pressure levels (SPL) measured at the seal during transmissions averaged 128 dB and ranged from 118 to 137 dB re: 1 microPa for the 60-90 Hz band, in comparison to ambient levels of 87-107 dB within this band. In no case did an animal end its dive or show any other obvious change in behavior upon exposure to the ATOC sound. Subtle changes in diving behavior were detected, however. During exposure, deviations in descent rate were greater than 1 s.d. of the control mean in 9 of 14 seals. Dive depth increased and descent velocity increased in three animals, ascent velocity decreased in two animals, ascent rate increased in one animal and decreased in another, and dive duration decreased in only one animal. There was a highly significant positive correlation between SPL and descent rate. The biological significance of these subtle changes is likely to be minimal. This is the first study to quantify behavioral responses of an animal underwater with simultaneous measurements of SPL of anthropogenic sounds recorded at the animal.

Acoustics↗