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At least 163 records · Page 9Linked to original sources
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↗
PubMed2001

Diving: what to tell the patient with asthma and why?

Until a decade ago, divers with asthma were uniformly barred from diving with compressed air. This prohibition was based more on theoretical concerns for barotrauma than on actual data. Follow-up studies, although retrospective, do not support a ban on recreational or commercial diving for divers with stable asthma. These studies have noted that, despite the prohibition on diving, many divers with asthma have logged multiple dives without negative consequences. When those who have suffered diving-related barotrauma have undergone physiologic testing, measurements of small airways dysfunction (maximal mid-expiratory flow rates) have been lower than measurements for comparable divers who have never suffered diving accidents. Follow-up studies with long-term commercial divers have shown that a small percentage of individuals who have sufferred diving-related barotrauma also develop abnormal maximal mid-expiratory flow rates and even some airway hyperreactivity. These latter findings correlate with the changes that occur in chronic asthmatic patients, especially those who are not well treated. The decision as to whether an asthmatic patient should be allowed to dive rests on the individual's physiologic function, maturity, and insight into the consequences of poorly managed airway inflammation and bronchospasm.

Asthma↗
PubMedDate not supplied

Blood volume and diving ability of the New Zealand sea lion, Phocarctos hookeri.

We test the hypothesis that the New Zealand sea lion is physiologically better equipped for prolonged, continuous diving than other otariids (fur seals and sea lions) by measuring its blood volume, an important component of its oxygen storage. Mass, hematocrit, and plasma volume were measured and blood volume calculations were completed on 14 adult females and five juvenile females. Plasma volume was determined using the Evans blue dye dilution technique. Mean plasma volume for all subjects was 74 mL kg(-1). Mass-specific plasma volume was significantly higher in adult females (15.3%) than in juveniles (14.6%). Blood volume (150 mL kg(-1)) and hematocrit (51%) were not significantly different between adults and juveniles. The aerobic dive limit can be estimated by dividing the animal's oxygen stores by its metabolic rate. The estimated aerobic dive limit for adult animals was between 5.5 and 7.8 min, depending on the assumed metabolic rate. New Zealand sea lions have the highest blood volume yet reported for an otariid, which supports the hypothesis that they have a physiological capability suited to their unique diving behavior.

Aerobiosis↗
PubMed2006

Optimal diving behaviour and respiratory gas exchange in birds.

This review discusses the advancements in our understanding of the physiology and behaviour of avian diving that have been underpinned by optimal foraging theory and the testing of optimal models. To maximise their foraging efficiency during foraging periods, diving birds must balance numerous factors that are directly or indirectly related to the replenishment of the oxygen stores and the removal of excess carbon dioxide. These include (1) the time spent underwater (which diminishes the oxygen supply, increases carbon dioxide levels and may even include a build up of lactate due to anaerobic metabolism), (2) the time spent at the surface recovering from the previous dive and preparing for the next (including reloading their oxygen supply, decreasing their carbon dioxide levels and possibly also metabolising lactate) and (3) the trade-off between maximising oxygen reserves for consumption underwater by taking in more air to the respiratory system, and minimising the energy costs of positive buoyancy caused by this air, to maximise the time available underwater to forage. Due to its importance in avian diving, replenishment of the oxygen stores has become integral to models of optimal diving, which predict the time budgeting of animals foraging underwater. While many of these models have been examined qualitatively, such tests of predictive trends appear fallible and only quantifiable support affords strong evidence of their predictive value. This review describes how the quantification of certain optimal diving models, using tufted ducks, indeed demonstrates some predictive success. This suggests that replenishment of the oxygen stores and removal of excess carbon dioxide have significant influences on the duration of the surface period between dives. Nevertheless, present models are too simplistic to be robust predictors of diving behaviour for individual animals and it is proposed that they require refinement through the incorporation of other variables that also influence diving behaviour such as, perhaps, prey density and predator avoidance.

Animals↗
PubMed1993

Physiological responses of firefighting students during simulated smoke-diving in the heat.

While wearing a self-contained breathing apparatus and fire-protective clothing, 35 healthy firefighting students aged 19-27 years performed smoke-diving (entry into a smoke-filled room) during a simulated shipboard fire. The mean (+/- SD) ambient temperature inside the simulator was 119 +/- 12 degrees C, and the task lasted 17 +/- 4 min. All subjects were fit according to their maximal oxygen consumption, which was 52.4 +/- 5.2 mL/min/kg (4.08 +/- 0.45 l/min). During the smoke-diving the average heart rate was 150 +/- 13 beats/min (79 +/- 6% of maximal heart rate attained in a cycle-ergometer test), and the peak heart rate was 180 +/- 13 beats/min (95 +/- 6% of maximal heart rate). The estimated oxygen consumption was 2.4 +/- 0.5 L/min (60 +/- 12% of maximal oxygen consumption). Neither ability to tolerate stress (as determined by the instructors) nor previous experience in smoke-diving tasks seemed to influence the heart rate or estimated oxygen consumption during experiment. Smoke-diving was physically very demanding even for the young and fit subjects, showing the importance of regular evaluation of the health and physical fitness of every firefighter who has to carry out smoke-diving tasks.

Adult↗
PubMed2001

Effects of training on forced submersion responses in harbor seals.

In several pinniped species, the heart rates observed during unrestrained dives are frequently higher than the severe bradycardias recorded during forced submersions. To examine other physiological components of the classic 'dive response' during such moderate bradycardias, a training protocol was developed to habituate harbor seals (Phoca vitulina) to short forced submersions. Significant changes were observed between physiological measurements made during naive and trained submersions (3-3.5 min). Differences were found in measurements of heart rate during submersion (naive 18+/-4.3 beats min(-1) versus trained 35+/-3.4 beats min(-1)), muscle blood flow measured using laser-Doppler flowmetry (naive 1.8+/-0.8 ml min(-1) 100 g(-1) versus trained 5.8+/-3.9 ml min(-1) 100 g(-1)), change in venous P(O(2)) (naive -0.44+/-1.25 kPa versus trained -1.48+/-0.76 kPa) and muscle deoxygenation rate (naive -0.67+/-0.27 mvd s(-1) versus trained -0.51+/-0.18 mvd s(-1), a relative measure of muscle oxygenation provided by the Vander Niroscope, where mvd are milli-vander units). In contrast to the naive situation, the post-submersion increase in plasma lactate levels was only rarely significant in trained seals. Resting eupneic (while breathing) heart rate and total oxygen consumption rates (measured in two seals) were not significantly different between the naive and trained states. This training protocol revealed that the higher heart rate and greater muscle blood flow in the trained seals were associated with a lower muscle deoxygenation rate, presumably secondary to greater extraction of blood O(2) during trained submersions. Supplementation of muscle oxygenation by blood O(2) delivery during diving would increase the rate of blood O(2) depletion but could prolong the duration of aerobic muscle metabolism during diving. This alteration of the dive response may increase the metabolic efficiency of diving.

Animals↗
PubMed2003

Pulmonary oedema in SCUBA divers: pathophysiology and computed risk analysis.

SCUBA diving has become a popular sport, with an increasing number of people participating in it. Although it is an essentially very safe activity, several specific medical problems are associated with diving. The present paper addresses diving-related pulmonary oedema, which is a rarely reported condition. It has been described mostly in cold water diving, and its occurrence in warm water has not been documented before. We delineate the pathophysiology of this condition and its treatment, and use a novel computational model to analyse further the mechanisms leading to diving-related pulmonary oedema. A better understanding of diving-related pulmonary oedema may lead to earlier recognition and treatment, and, potentially, to its prevention. The physiological mechanisms likely to lead to diving-related pulmonary oedema are well recognized. Consequently, we could design and construct a bio-mechanical computer model of the alveolar septa to explore the pathophysiology of diving-related pulmonary oedema and the vulnerability of individual divers as they relate to some mechanical characteristics of their lung structure. The physiological mechanisms of diving-related pulmonary oedema and the results provided by the computational model successfully delineated the process. The model predicted that the risk of injury is significantly increased in individuals who have a stiffer lung parenchyma or lower lung compliance values.

Biomechanical Phenomena↗
PubMed2001

Diving beyond the limits.

Some free-ranging birds and mammals dive for periods that substantially exceed those for which their usable O(2) stores are estimated to last. The mechanisms that extend the duration of aerobic diving include marked reductions in blood flow (and hence O(2) delivery) to certain organs and tissues, passive gliding and, most probably, regional hypothermia.

Adaptation, Physiological↗
PubMed2006

Stomach temperature telemetry reveals temporal patterns of foraging success in a free-ranging marine mammal.

1. We studied feeding frequency in free-ranging grey seals using stomach temperature telemetry to test if previously reported sex differences in the diving, movement and diet were reflected in the temporal pattern of foraging success. 2. Data were retrieved from 21 of 32 grey seals from 1999 to 2001, totalling 343 days and 555 feeding events, with individual record length varying from 2 to 40 days (mean: 16.33 +/- 2.67 days/seal). 3. Seals fed on 57.8 +/- 6.46% of days sampled and had an average of 1.7 +/- 0.26 meals per day, but individual variability was apparent in the temporal distribution of feeding as evidenced by high coefficients of variation (coefficient of variation = 69.0%). 4. Bout analysis of non-feeding intervals of six grey seals suggests that feeding intervals of individuals were varied and probably reflect differences in prey availability. Grey seals tended to have many single feeding events with long periods separating each event, as would be expected for a large carnivore with a batch-reactor digestive system. 5. We found significant sex differences in the temporal distribution of feeding. The number of feeding events per day was greater in males (2.2 +/- 0.4 vs. 1.0 +/- 0.2), as was time associated with feeding per day (56.6 +/- 5.8 min vs. 43.9 +/- 9.4 min). 6. The number of feeding events varied with time of day with the least number occurring during dawn. Feeding event size differed significantly by time of day, with greater meal sizes during the dawn and the smallest meals during the night. 7. The length of time between meals increased with the size of the previous meal, and was significantly less in males (541.4 +/- 63.5 min) than in females (1092.6 +/- 169.9 min). 8. These results provide new insight into the basis of sex differences in diving and diet in this large size-dimorphic marine predator.

Animals↗
PubMedDate not supplied

Mechanism of the human diving response.

The diving response in human beings is characterized by breath-holding, slowing of the heart rate (diving bradycardia), reduction of limb blood flow and a gradual rise in the mean arterial blood pressure. The bradycardia results from increased parasympathetic stimulus to the cardiac pacemaker. The reduction in limb blood flow is due to vasoconstriction resulting from increased activity of the sympathetic nerves supplying arteries in the arms and legs. Essentially the response is produced by the combination of water touching the face and either voluntary or involuntary (reflex) arrest of breathing. The nervous inputs and outputs for the response are coordinated in the brain stem by the respiratory, vasomotor and cardioinhibitory "centers." The diving response in human beings can be modified by many factors but the most important are water temperature, oxygen tension in the arterial blood and emotional factors.

Cardiovascular Physiological Phenomena↗
PubMed1998

Cardiovascular change in elderly male breath-hold divers (Ama) and their socio-economical background at Chikura in Japan.

The Ama have existed for more than 2000 years in Japan and Korea. They have been diving for seaweed and molluscs. Their traditional way of fishing, with goggles or a mask, but without a wetsuit, is still practised as a result of laws against overfishing. We investigated cardiovascular diving responses, expressed as heart rate (HR) reduction, peripheral vasoconstriction indicated by skin blood flow (SkBF) and mean arterial blood pressure (MAP) during breath-hold face immersion in a group of eight elderly male Ama at Chikura, Japan. Their data were compared to those from three other groups: a) elderly non-divers; b) young divers and c) young non-divers. Our previous studies have shown that young divers show a more pronounced bradycardia than young non-divers. The present study of elderly Ama and elderly non-divers was performed to investigate if this difference persists in old age. We found that, in spite of many years of diving experience, HR reduction of the elderly professional divers observed during face immersion did not differ from that of elderly non-divers, but it was much less pronounced than in the two younger groups. We conclude that even if a well-developed diving response at young age has been reduced to the level of non-divers, the Ama are still able to continue their work of diving in old age. Ama that has been a traditionally female occupation, is mostly practised by men at Chikura today. No young have been recruited for this profession. Therefore, the present Ama are senior and the traditional breath-hold diving will probably cease to exist in the near future. The probable reasons for these changes are discussed.

Adaptation, Physiological↗
PubMed1994

Cardiovascular and pulmonary responses to breath-hold diving in humans.

Cardiovascular and pulmonary responses to breath-hold diving (breath holding, submersion, and compression) were investigated. In addition, the effects of transitions between dry conditions and head-out immersion during eupnea were studied. Surface breath holds at a large lung volume with relaxed respiratory muscles resulted in a positive esophageal (transthoracic) pressure and a reduced cardiac output. In contrast, the esophageal pressure (relative to ambient pressure) was decreased, and cardiac output was at least partially restored, when lung gas volume was reduced by compression during breath-hold diving. The increased cardiac output that accompanied eupneic transition from dry to immersed conditions was associated with a short-lasting increase of alveolar gas exchange, whereas the decreased cardiac output during immersion-to-dry transition was associated with a long-lasting decrease of alveolar gas exchange, both reflecting changes in the tissue gas stores of the body. Surface breath holds were associated with a decreased O2 uptake from the lung to the blood, and breath-hold dives were associated with a large transient increase of O2 uptake at depth which resulted in a restoration of the time-averaged O2 uptake to the eupneic control level: these changes reflected changes in tissue O2 stores. Compared to surface breath holds, breath-hold dives were associated with larger tissue retention of CO2 during breath holds, and prolonged recovery for CO2 elimination after breath holds. The distribution of pulmonary perfusion, as indicated by expirograms obtained immediately after breath holds, was made more homogeneous by submersion and the distribution was further improved by compression during breath-hold dives. All of these different effects on the gas exchange in breath-hold diving and in eupneic headout immersion can to a large extent be explained by associated changes in cardiac output in combination with redistributions of peripheral blood flow and venous blood volume. Thus, the different components of breath-hold diving have profound cardiovascular and pulmonary effects. Changes in the intrathoracic pressure and in the distribution of venous blood volume induce changes in cardiac output. All of these changes affect the temporal and spatial distributions of pulmonary perfusion and peripheral blood flow. Also, the circulatory changes affect the temporal and spatial distributions of alveolar gas exchange and of tissue gas stores of the body.

Adolescent↗
PubMed2004

The cost of foraging by a marine predator, the Weddell seal Leptonychotes weddellii: pricing by the stroke.

Foraging by mammals is a complex suite of behaviors that can entail high energetic costs associated with supporting basal metabolism, locomotion and the digestion of prey. To determine the contribution of these various costs in a free-ranging marine mammal, we measured the post-dive oxygen consumption of adult Weddell seals (N=9) performing foraging and non-foraging dives from an isolated ice hole in McMurdo Sound, Antarctica. Dives were classified according to behavior as monitored by an attached video-data logging system (recording activity, time, depth, velocity and stroking). We found that recovery oxygen consumption showed a biphasic relationship with dive duration that corresponded to the onset of plasma lactate accumulation at approximately 23 min. Locomotor costs for diving Weddell seals increased linearly with the number of strokes taken according to the relationship: locomotor cost = -3.78+0.04 x stroke number (r(2)=0.74, N=90 dives), where locomotor cost is in ml O(2) kg(-1). Foraging dives in which seals ingested Pleuragramma antarcticum resulted in a 44.7% increase in recovery oxygen consumption compared to non-foraging dives, which we attributed to the digestion and warming of prey. The results show that the energy expended in digestion for a free-ranging marine mammal are additive to locomotor and basal costs. By accounting for each of these costs and monitoring stroking mechanics, it is possible to estimate the aerobic cost of diving in free-ranging seals where cryptic behavior and remote locations prevent direct energetic measurements.

Animals↗