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At least 397 records · Page 22Linked to original sources
PubMed2005

Substitution of heat from exercise and digestion by ducks diving for mussels at varying depths and temperatures.

Diving birds can lose significant body heat to cold water, but costs can be reduced if heat from exercising muscles or the heat increment of feeding (HIF) can substitute for thermogenesis. Potential for substitution depends jointly on the rate of heat loss, the rate of heat produced by exercise, and the level of HIF. To explore these interactions, we measured oxygen consumption by lesser scaup ducks (Aythya affinis) diving to depths of 1.2 and 2 m at thermoneutral (23 degrees C) and sub-thermoneutral (18 and 8 degrees C) temperatures. Birds dove while fasted and when feeding on blue mussels (Mytilus edulis). Substitution occurred if HIF or costs of diving above resting metabolic rate (RMR) were lower at 18 or 8 degrees C than at 23 degrees C, indicating reduction in the thermoregulatory part of RMR. For fasted scaup diving to 1.2 m, substitution from exercise heat was not apparent at either 18 or 8 degrees C. At 2 m depth, dive costs above RMR were reduced by 5% at 18 degrees C and by 40% at 8 degrees C, indicating substitution. At 1.2 m depth (with voluntary intake of only 14-17% of maintenance requirements), HIF did not differ between temperatures, indicating no substitution. However, at 2 m (intake 13-25% of maintenance), substitution from HIF was 23% of metabolizable energy intake at 18 degrees C and 22% at 8 degrees C. These results show that even with low HIF due to low intake rates, substitution from HIF can add to substitution from the heat of exercise.

Animals↗
PubMed1999

Thermoregulation during swimming and diving in bottlenose dolphins, Tursiops truncatus.

Heat transfer from the periphery is in important thermoregulatory response in exercising mammals. However, when marine mammals submerge, peripheral vasoconstriction associated with the dive response may preclude heat dissipation at depth. To determine the effects of exercise and diving on thermoregulation in cetaceans, we measured heat flow and skin temperatures of bottlenose dolphins (Tursiops truncatus) trained to follow a boat and to dive to 15 m. The results demonstrated that skin temperatures usually remained within 1 degree C of the water after all exercise levels. Heat flow from peripheral sites (dorsal fin and flukes) increased over resting values immediately after exercise at the water surface and remained elevated for up to 20 min. However, post-exercise values for heat flow from the flukes and dorsal fin decreased by 30-67% when dolphins stationed at 15 m below the surface. The pattern in heat flow was reversed during ascent. For example, mean heat flow from the flukes measured at 5 m depth, 40.10 +/- 2.47 W.m-2, increased by 103.2% upon ascent. There is some flexibility in the balance between thermal and diving responses of dolphins. During high heat loads, heat transfer may momentarily increase during submergence. However, the majority of excess heat in dolphins appears to be dissipated upon resurfacing, thereby preserving the oxygen-conserving benefits of the dive response.

Animals↗
PubMed2006

A single open sea air dive increases pulmonary artery pressure and reduces right ventricular function in professional divers.

After decompression from dives, bubbles are frequently observed in the right ventricular outflow tract and may lead to vascular damage, pulmonary arterial hypertension and right ventricular overload. No data exist on the effect of open sea diving on the pulmonary artery pressure (PAP). Eight professional divers performed an open sea air dive to 30 msw. Before and postdive a Doppler echocardiographic study was undertaken. Systolic pulmonary artery pressure (SPAP) was estimated from measurement of peak flow velocity of the tricuspid regurgitant jet; the ratio between pulmonary artery acceleration times (AccT) and right ventricular ejection time (RVET) was used as an estimate of the mean PAP. No evidence of either patent foramen ovale or intra-pulmonary shunt was found in any subject postdive after performing a Valsalva maneuver. SPAP increased from 25 +/- 3 to 33 +/- 2 mmHg and AccT/RVET ratio decreased from 0.44 +/- 0.04 to 0.3 +/- 0.02 20 min after the dive, respectively. Pulmonary vascular resistance increased from 1.2 +/- 0.1 to 1.4 +/- 0.1 Woods Units. Postdive right ventricle end-diastolic and end-systolic volumes were increased for about 19% (P = 0.001) and 33% (P = 0.001) and right ejection fraction decreased about for 6% (P = 0.001). Cardiac output decreased from 4.8 +/- 0.9 (l min(-1)) to 4.0 +/- 0.6 at 40 min postdive due to decreases in heart rate and stroke volume. This study shows that a single open sea dive may be associated with right heart overload due to increased pressure in the pulmonary artery.

Adult↗
PubMed2000

Changes in maximal performance of inspiratory and skeletal muscles during and after the 7.1-MPa Hydra 10 record human dive.

During the 7.1-MPa hydrogen-helium-oxygen record human dive, we tested the hypothesis that the increased ambient pressure would alter the maximal muscle performance, specifically that breathing dense gas would lead to fatigue of the respiratory muscle. A group of hand muscles (adductor pollicis, AP) and the inspiratory muscles (IM) were studied in three professional divers. Maximal voluntary contractions (MVC) of AP and maximal inspiratory pressure (P(i(max))) generated by IM were measured prior to the dive, during compression and decompression, and then 1 and 2 months after the dive. The decrease in MVC (-22%) was significant at 3.1 MPa, i.e. at the beginning of the introduction of hydrogen into the breathing mixture, whereas P(i(max)) fell progressively during the dive and decompression (maximal DeltaP(i(max)) = -55%), a significant reduction still being measured 1 month after the dive. The altered IM function was attributed to the consequences of long-term ventilatory loading, a condition associated with breathing a dense gas. The transient decrease in MVC of the skeletal muscle would indicate a possible effect of the hyperbaric environment, possibly the high partial pressure of hydrogen, on neuromuscular drive.

Diving↗
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

Metabolic regulation in diving birds and mammals.

Ducks, fur seals, Weddell seals and probably most cetaceans seem to be able to dive and remain aerobic for durations that are consistent with their elevated stores of usable oxygen and their metabolic rate while diving being similar to that when they are resting at the surface of the water. Ducks, in fact, have a high metabolic rate while diving, mainly because of their large positive buoyancy, but other species have relatively low buoyancy, are better streamlined and use lift-based rather than drag-based propulsion. However, species such as the larger penguins, grey seals and elephant seals seem to achieve the impossible by performing a substantial proportion of their dives for periods longer than would be expected on the above assumptions, and yet remaining aerobic. The logical conclusion is that during such dives these species reduce their metabolic rate below the resting level (hypometabolism) and, in some of them, there is a regional reduction in body temperature (hypothermia) which may contribute to the reduction in metabolic rate.

Abdominal Cavity↗
PubMed2005

The composition of pulmonary surfactant from diving mammals.

Maintaining a functional pulmonary surfactant system at depth is critical for diving mammals to ensure that inspiration is possible upon re-emergence. The lipid and protein composition of lavage extracts from three pinniped species (California sea lion, Northern elephant seal and Ringed seal) were compared to several terrestrial species. Lavage samples were purified using a NaBr discontinuous gradient. Concentrations of phospholipid classes and molecular species were measured using electrospray ionisation mass spectrometry, cholesterol was measured using high-performance liquid chromatography, surfactant protein A (SP-A) and SP-B were measured using enzyme-linked immunosorbent assays. There were small differences in phospholipid classes, with a lower level of anionic surfactant phospholipids, PG and PI, between diving and terrestrial mammals. There were no differences in PL saturation or SP-A levels between species. PC16:0/14:0, PC16:0/16:1, PC16:0/16:0, long chain PI species and the total concentrations of alkyl-acyl species of PC and PG as a ratio of diacyl species were increased in diving mammals, whereas concentrations of PC16:0/18:1, PG16:0/16:0 and PG16:0/18:1 were decreased. Cholesterol levels were very variable between species and SP-B was very low in diving mammals. These differences may explain the very poor surface activity of pinniped surfactant that we have previously described [Miller, N.J., Daniels, C.B., Schürch, S., Schoel, W.M., Orgeig, S., 2005. The surface activity of pulmonary surfactant from diving mammals. Respir. Physiol. Neurobiol. 150 (2006) 220-232], supporting the hypothesis that pinniped surfactant has primarily an anti-adhesive function to meet the challenges of regularly collapsing lungs.

Analysis of Variance↗
PubMed2003

Activation of brainstem catecholaminergic neurons during voluntary diving in rats.

Underwater submergence produces a complex autonomic response that includes apnea, a parasympathetically-mediated bradycardia, and a sympathetically-mediated increase in total peripheral resistance (TPR). The present study was designed to identify brainstem catecholaminergic neurons that may be involved in producing the increased TPR during underwater submergence. Twelve male Sprague-Dawley rats were trained to voluntarily dive 5 m through an underwater maze. On the day of the experiment the rats were randomly separated into a Diving group that repetitively dived underwater, a Swimming group that repetitively swam on the surface of the water, and a Control group that remained in their cages. After the experiment the brainstems of the rats were immunohistologically processed for Fos as an indicator of neuronal activation, and for tyrosine hydroxylase (TH) as an indentifier of catecholaminergic neurons. Neurons labeled with both Fos and TH identified activated catecholaminergic neurons. In Diving rats there was increased Fos+TH labeling in A1, C1, A2, A5, and sub-coeruleus, as well as globosa neurons in the lateral A7 region compared with Control rats, and in A1, C1 and A5 compared with Swimming rats. In Swimming rats Fos+TH labeling was significantly increased in caudal A1, A5, sub-coeruleus and globosa neurons compared with Control rats. These data suggest that selective groups of catecholaminergic neurons within the brainstem are activated by voluntary underwater submergence, and some probably contribute to the sympathetically-mediated increase in vascular tone during diving.

Animals↗
PubMed1989

The influence of diving variables on perceptual and cognitive functions in professional shallow-water (abalone) divers.

Shallow-water diving is regarded as a hazardous occupation due to such dangers as decompression sickness and carbon monoxide poisoning. Recent studies have demonstrated impairments in the neurological and neurobehavioral functioning of professional shallow-water divers, yet the reasons for these deficits are not clear. In this study 80 professional abalone divers were studied using a range of neurobehavioral tests and questioned closely on their diving experience. Multiple linear regression analysis was then performed to determine the extent to which characteristics of the diver's occupation influenced neurobehavioral impairment. The results demonstrated that divers who were at greatest risk of decompression sickness due to their diving technique showed the clearest functional impairments. In particular problems of visual function, psychomotor abilities, and short-term memory were most evident. It appears that professional shallow-water diving is not necessarily a hazardous occupation provided that safe diving practices are observed. However, divers who fail to observe these practices and put themselves at risk of decompression sickness are likely to have impairments in neurobehavioral function which affect their everyday life, and more importantly their responses in emergency situations.

Adult↗
PubMed2001

The oxygen gain of diving insects.

The gas gill of diving insects allows gas exchange with the surrounding water, thus extending diving time. Incompressible gas gills can potentially last indefinitely underwater, but compressible gas gills have a definite lifetime. Theoretical models of a dive event have reached opposite conclusions about the oxygen gain (G, the ratio between the duration of the diving event and the time that the initial oxygen content of the bubble would allow the insect to stay underwater). While some authors claim that G has a fixed value independently of the parameters of the dive (e.g. oxygen consumption rate) others claim the contrary. However, these claims are based on numerical solutions of the models. In this study we offer an analytical solution to the problem. The analysis of a model with constant area for gas exchange demonstrates that G cannot have a fixed value, for a fixed gain would imply in a P(O(2)) inside the bubble different from the one occurring as a result of physical constraints of the gas exchange process.

Algorithms↗
PubMed1999

Respiratory pattern after wet and dry chamber dives to 0.6 MPa ambient pressure in healthy males.

The purpose of this study was to evaluate respiratory effects of wet and dry hyperbaric chamber dives to 0.6 MPa ambient pressure in healthy males. There were 19 and 22 subjects who participated in two series of dives with a bottom time of 15 min and decompression times of 28 and 17 min, respectively. Airways conductance, residual volume, forced vital capacity, forced expiratory volume in 1 sec, mid expiratory flow at 25, 50 and 75% of FVC, and diffusion capacity for CO were measured before the dives, after 3 h, and after 24 h. Multivariate analysis of covariance revealed no statistically significant effects of time or the interaction between time and dry or wet environment on the measured lung function parameters. These findings suggest first that even deep air dives may not necessarily affect pulmonary function, and second, that factors related to the particular wet environment do not seem to contribute to lung function changes after dives.

Adult↗
PubMedDate not supplied

Diving and hyperbaric ophthalmology.

Exposure of the human body to ambient pressures greater than that at sea level may result in various disorders, some of which have ocular manifestations. Additionally, some eye disorders and postoperative states may be adversely affected by the underwater environment or other hyperbaric exposures. The prevalence of recreational, military, and commercial diving, as well as the medical use of hyperbaric oxygen therapy, requires that ophthalmologists be familiar with the effects of the hyperbaric environment on the normal and diseased eye. The ophthalmology and diving medical literatures were surveyed for publications relating to the ophthalmic aspects of diving and hyperbaric exposures. Underwater optics, underwater refractive correction, and ophthalmic aspects of a fitness-to-dive evaluation are summarized. The evaluation and management of ocular manifestations of decompression sickness and arterial gas embolism are reviewed and guidelines for diving after ocular surgery are proposed.

Barotrauma↗
PubMed2002

Comparison between the antioxidant status of terrestrial and diving mammals.

Many diving mammals are known for their ability to deal with nitrogen supersaturation and to tolerate apnea for extended periods. They are all characterized by high oxygen-carrying capacity in blood together with high oxygen storage in their muscle mass due to large myoglobin concentrations. The above properties theoretically also imply a high tissue antioxidant defenses (AD) to counteract reactive oxygen species (ROS) generation associated with the rapid transition from apnea to reoxygenation. Different enzymatic (superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, and glutathione S-transferase), and non-enzymatic (levels of glutathione) AD as well as cellular damage (thiobarbituric acid-reactive substances contents, as a measure of lipoperoxidation) were measured in blood samples obtained from anesthetized animals, and also in blood obtained from recently dead diving mammals, and compared to some terrestrial mammals (n=5 in both groups). The results confirmed that diving mammals have, in general, higher antioxidant status compared to non-diving mammals. Apparently, to avoid exposure of tissues to changing high oxygen levels, and therefore to avoid an oxidative stress condition related to antioxidant consumption and increased ROS generation, diving mammals possess constitutive high levels of antioxidants in tissues. These data are in agreement with short-term AD adaptations related to torpor and to animals that experience large daily changes in oxygen consumption. These data are similar to the long-term adaptations of animals that undergo hibernation, estivation, freezing-thawing and dehydration-rehydration processes. In summary, animals that routinely face high changes in oxygen availability and/or consumption seem to show a general strategy to prevent oxidative damage by having either appropriate high constitutive AD and/or the ability to undergo arrested states, where depressed metabolic rates minimize the oxidative challenge.

Animals↗
PubMed1980

Spinal cord injuries due to diving.

One hundred and fifty patients with spinal cord lesions due to diving accidents were admitted to Stoke Mandeville Hospital between 1944--77. Most of the patients were young men, 65 had dived into the sea, 48 into swimming pools, 21 into rivers and 3 into lakes. Injuries due to diving into the deep end of swimming pools appear to have been eliminated in Great Britain but injuries due to diving into the shallow end of swimming pools and into the sea continue to occur. The public need further education about the dangers of diving.

Adolescent↗
PubMed2000

Impact of a deep saturation dive on semen quality.

The demonstration dive 'Aurora' has provided an opportunity to study the impact of extreme hyperbaric conditions on male fertility. This operation involved a 33-day diving programme during which divers were exposed to a maximum pressure of 4.6 Mega Pascals (Mpa) for 7 days. At days - 4, + 27, + 34, + 82 and + 263 relative to the initiation of the dive, semen samples were analysed to determine the quality of spermatogenesis and the functional competence of the spermatozoa. A dramatic fall in semen quality was observed in association with the dive and by day + 82 the potential fertility of the men was seriously compromised as evidenced by oligoasthenoteratozoospermic semen profiles and the poor fertilizing potential of the spermatozoa. These studies indicate, for the first time, that the severe hyperbaric conditions associated with deep saturation dives have a profound effect on male reproductive function.

Diving↗
PubMed2002

Mammary implants: laboratory simulation of recreational diving conditions.

To ascertain whether mammary implants are prone to changes in conformation or structure if they are submitted to recreational dives, eight mammary implants were submitted to 40 simulated dives to imitate an average recreational diving schedule. Matching implants were used as a control group. Photographs were taken before and after completion of the protocol. All implants were observed for changes in volume and checked for integrity. Variations in density were evaluated using a Tc scan. No changes in volume occurred after each dive. None of the implants showed ruptures, and Tc scanning failed to reveal any differences in density between tested and control implants. Cohesive-gel implants submitted to the simulated dives showed some morphological alterations. This study indicates that the mammary implants tested could be implanted in a sports diver, but raises concern about whether the increased exposure to stress could negatively affect their durability.

Breast Implants↗
PubMed2003

Arterial blood gases during diving in elite apnea divers.

Elite apnea divers have considerably extended the limits of dive depth and duration but the mechanisms allowing humans to tolerate the compression- and decompression-induced changes in alveolar gas partial pressures are still not fully understood. Therefore we measured arterial blood gas tensions and acid-base-status in two elite apnea divers during simulated wet dives lasting 3 : 55 and 5 : 05 minutes, respectively. Arterial pO2 followed the compression-(from 13.8/16.9 kPa before the dive to 30 kPa at the start of the bottom time) and decompression-induced (from 13.7/21.0 kPa to 3.3/4.9 kPa immediately after surfacing) variations of ambient pressure, while the arterial pCO2 remained within the physiologic range (3.0/3.9 kPa before diving vs. 5.7/5.9 kPa at the end of the bottom time), probably due to the CO2 storage capacity of the blood. These findings may help to explain why humans can sustain deep and long apnea dives without major increases in respiratory drive.

Acid-Base Equilibrium↗
PubMed1993

Tympanometric evaluation of middle ear barotrauma during recreational scuba diving.

We report the first prospective evaluation of middle ear barotrauma in experienced recreational scuba divers. In this pilot study, tympanometric and otoscopic evaluations were performed daily on two experienced scuba divers engaged in multi-day repetitive diving. Middle ear pressures decreased in proportion to diving frequency, demonstrating eustachian tube dysfunction which promptly reversed upon cessation of diving Otoscopic evidence of traumatic injury to the middle ear occurred in proportion to diving frequency, and also readily reversed upon cessation of diving. Tympanic membrane compliance remained normal, often despite pronounced otoscopic abnormalities. Otologic symptoms and impairment of acuity were not observed. Tympanometry appears to be a valuable modality for the verification of middle ear hemorrhage or tympanic membrane rupture. This preliminary data should assist investigators in planning more comprehensive studies of middle ear barotrauma, including clinical trials of treatment and prophylactic interventions for this common condition.

Acoustic Impedance Tests↗