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PubMed2006

Haemodynamic changes induced by submaximal exercise before a dive and its consequences on bubble formation.

OBJECTIVES: To evaluate the effects of a submaximal exercise performed 2 h before a simulated dive on bubble formation and to observe the haemodynamic changes and their influence on bubble formation. PARTICIPANTS AND METHODS: 16 trained divers were compressed in a hyperbaric chamber to 400 kPa for 30 min and decompressed at a rate of 100 kPa/min with a 9 min stop at 130 kPa (French Navy MN90 procedure). Each diver performed two dives 3 days apart, one without exercise and one with exercise before the dive. All participants performed a 40 min constant-load submaximal and calibrated exercise, which consisted of outdoor running 2 h before the dive. Circulating bubbles were detected with a precordial Doppler at 30, 60 and 90 min after surfacing. Haemodynamic changes were evaluated with Doppler echocardiography. RESULTS: A single bout of strenuous exercise 2 h before a simulated dive significantly reduced circulating bubbles. Post-exercise hypotension (PEH) was observed after exercise with reductions in diastolic and mean blood pressure (DBP and MBP), but total peripheral resistance was unchanged. Stroke volume was reduced, whereas cardiac output was unchanged. Simulated diving caused a similar reduction in cardiac output independent of pre-dive exercise, suggesting that pre-dive exercise only changed DBP and MBP caused by reduced stroke volume. CONCLUSION: A single bout of strenuous exercise 2 h before a dive significantly reduced the number of bubbles in the right heart of divers and protected them from decompression sickness. Declining stroke volume and moderate dehydration induced by a pre-dive exercise might influence inert gas load and bubble formation.

Adult↗
PubMed2000

Lung function over the first 3 years of a professional diving career.

OBJECTIVES: To characterise diving exposure and pulmonary function in professional divers at the start of their formal education and during the first 3 years of their professional career. METHODS: The study included 87 men at the start of their education as professional divers. At follow up 1 and 3 years after the school 83 and 81 divers respectively were re-examined. Assessment of lung function included dynamic lung volumes and flows and transfer factor for carbon monoxide (Tl(CO)). RESULTS: 69 Divers had preschool SCUBA diving experience and had a median number of 70 dives (range 2-3000) to a median maximal depth of 40 (range 10-73) metres. During the 15 week introductory diving course, they had 44 dives (range 38-50) in the depth range 10-50 metres. The median number of dives over the follow up period was 95 (range 0-722) to a maximal median depth of 38 (range 0-98) metres. At the start of the diving course there were no differences in forced vital capacity (FVC), forced expired volume in 1 second (FEV(1)), and in Tl(CO) between the 69 pre-exposed divers and the 18 never exposed divers. The FVC was significantly larger than predicted in both groups. At follow up at 3 years there was a significant reduction in mean (SD) FEV(1) of 1.8% (6.5), in forced mid-expiratory flow rate (FEF(25-75%)) of 6.5% (11.7) and in forced expiratory flow at 75% of FVC expired (FEF(75%)) of 10.4% (16. 8). There was no change in FVC. The Tl(CO) was significantly decreased by 4.6% (8.8). No significant effects were found of cumulative diving exposure, including the number of dives, on the relative changes of any of the lung function variables. CONCLUSIONS: The results indicate that divers initially belong to a selected group with large FVC. Exposure to diving may contribute to changes in pulmonary function, mostly affecting small airways conductance.

Adult↗
PubMed1982

Respiratory and cardiovascular control during diving in birds and mammals.

Recent studies on freely diving birds and mammals indicate that, contrary to the classical hypothesis, the majority of dives are aerobic with minimal cardiovascular adjustments (i.e. bradycardia and selective vasoconstriction). It is postulated that during these aerobic dives the cardiovascular adjustments result from the opposing influences of exercise and the classical diving response, with the bias towards the exercise response. It is envisaged that the active muscles, as well as the brain and heart, are adequately supplied with blood to enable them to metabolize aerobically. Intense mental activity, particularly in carnivores seeking their prey, may also attenuate the classical response. Aerobic dives are usually terminated well before the oxygen stores are depleted, and another dive follows once they have been replenished. In this way a series of dives is performed. Prolonged dives are endured as a result of a shift towards the classical response of bradycardia, presumably more intense vasoconstriction, and anaerobiosis. This may be a form of alarm response, particularly in small animals such as ducks and coypus, or it may be a means of allowing the marine birds and mammals that dive deeply for their food to engage in unusually long hunting expeditions. For those that dive under ice, it may also allow long periods of underwater exploration as well as being a safety mechanism should the animal become disoriented.

Afferent Pathways↗
PubMed1986

Gas exchange, storage and transport in voluntarily diving Xenopus laevis.

A closed, extracorporeal loop, containing oxygen and carbon dioxide electrodes, was developed in order to make continuous measurements of lung gas PO2 (PAO2) and PCO2 (PACO2) in undisturbed Xenopus laevis. Pulmonary R values (delta PACO2/delta PAO2) are about 0.8 during periods of lung ventilation in resting animals, but they fall very rapidly as a voluntary dive proceeds. In fact, the instantaneous R values for lung eventually fall to zero during a voluntary dive, since PAO2 continues to decline whilst PACO2 (after an initial increase) comes into a steady state as transcutaneous CO2 losses balance metabolic production. These relationships change during spontaneous underwater activity, aquatic hypercapnia or enforced diving, with significantly higher PACO2 levels being found at any PAO2 value than in resting animals. Emergence from such dives is marked by a considerable hyperventilation, leading to lung R values which are 2-3 times higher than those seen during lung ventilation of animals at rest. The lungs of Xenopus are therefore important in eliminating the CO2 stored during a period of breath-holding but not of major importance in forming part of that store themselves. The lungs of Xenopus are, however, important sources of stored oxygen during voluntary dives, the rate of use being clearly related to activity levels and dive durations. There could be sudden changes in the rate of PAO2 depletion during a dive, suggesting that factors additional to the metabolic rate of the cells may be important in determining the way in which the lung store is used. In a parallel series of experiments, O2 and CO2 partial pressures were determined in lung gas samples and in simultaneously drawn samples of blood from the femoral artery (systemic arterial) and left auricle (pulmonary venous) of animals making voluntary dives. These blood/gas data, together with results of previous experiments on Xenopus, have been used to develop an idealized model of O2 exchange, storage and transport during a 30-min voluntary dive. The volume of the O2 stores held in the lungs and various subdivisions of the circulation are shown in the model by plotting the PO2 of the store against its respective O2 capacitance. The model illustrates the overall importance of the lung as a source of oxygen during breath-holding and that early use of a large systemic venous O2 store may be an important basic function for cardiovascular adjustments seen in a dive.

Animals↗
PubMed1997

Post-dive blood lactate concentrations in emperor penguins, Aptenodytes forsteri.

In order to determine an aerobic diving limit (ADL) in emperor penguins (Aptenodytes forsteri), post-dive blood lactate concentrations were measured in penguins foraging at an isolated sea ice hole. Resting lactate concentrations were 1.2-2.7 mmol l-1. Serial samples revealed that lactate level usually peaked within 5 min after dives and that 7-12 min was required for lactate concentrations to decrease from 5-8 mmol l-1 to less than 2.5 mmol l-1. Post-dive lactate level was not elevated above 3 mmol l-1 for dives shorter than 5 min. Two-phase regression analysis revealed a transaction at 5.6 min in the post-dive lactate level versus diving duration relationship. All dives longer than 7 min were associated with lactate concentrations greater than 5 mmol l-1. We conclude that the ADL in emperor penguins ranges between 5 and 7 min. These are the first determinations of post-dive lactate concentrations in any free-diving bird and are currently the only physiological assessment of an ADL in an avian species.

Animals↗
PubMed1998

Distribution of regional cerebral blood flow in voluntarily diving rats.

The distribution of regional cerebral blood flow (rCBF) was examined in conscious, voluntarily diving rats using the brain blood flow tracer N-[14C]isopropyl-p-iodoamphetamine and quantitative autoradiography. A detailed examination of the regional distribution of cerebral blood flow revealed that almost all brain regions were hyperperfused during diving. During diving, rCBF increased by an average of 1.7-fold in 29 of the 33 brain regions examined, despite a 69.2 % decrease in cardiac output. Only some regions of the basal ganglia (caudate-putamen and globus pallidus) and limbic areas (hippocampus and amygdala) did not increase rCBF significantly during diving. We determined that the increase in rCBF during diving is primarily due to a corresponding 20.9 % decrease in cerebrovascular resistance. A significant increase in perfusion pressure during diving also potentially contributed to the increase in rCBF. Because some brain regions did not increase flow significantly during diving, these results suggest that not all brain regions participate equally in the global cerebrovascular response to diving. This study provides evidence to support the view that the brain is preferentially perfused during conscious voluntary diving in the rat. The mechanism(s) that probably produce the cerebrovascular changes during diving are discussed.

Animals↗
PubMed1999

Development of diving capacity in emperor penguins.

To compare the diving capacities of juvenile and adult emperor penguins Aptenodytes forsteri, and to determine the physiological variables underlying the diving ability of juveniles, we monitored diving activity in juvenile penguins fitted with satellite-linked time/depth recorders and examined developmental changes in body mass (Mb), hemoglobin concentration, myoglobin (Mb) content and muscle citrate synthase and lactate dehydrogenase activities. Diving depth, diving duration and time-at-depth histograms were obtained from two fledged juveniles during the first 2.5 months after their depature from the Cape Washingon colony in the Ross Sea, Antarctica. During this period, values of all three diving variables increased progressively. After 8-10 weeks at sea, 24-41 % of transmitted maximum diving depths were between 80 and 200 m. Although most dives lasted less than 2 min during the 2 month period, 8-25 % of transmitted dives in the last 2 weeks lasted 2-4 min. These values are lower than those previously recorded in adults during foraging trips. Of the physiological variables examined during chick and juvenile development, only Mb and Mb content did not approach adult values. In both near-fledge chicks and juveniles, Mb was 50-60 % of adult values and Mb content was 24-31 % of adult values. This suggests that the increase in diving capacity of juveniles at sea will be most dependent on changes in these factors.

Animals↗
PubMed2001

Diving development in nursing harbour seal pups.

This study investigated physiological and behavioural aspects of diving development in pups of the harbour seal Phoca vitulina. Behavioural data (4280 h, 6027 dives) from time/depth recorders (N=13) deployed on pups aged 0-19 days are presented concomitantly with physiological measurements (N=8, sampled both early and late in the nursing period) of blood oxygen stores and body composition. Pups grew from 12.6+/-1.8 kg (mean age 2 days, total body fat 16+/-4 %) to 22.2+/-2.5 kg (mean age 16 days, total body fat 35+/-5 %; means +/- S.D.) over the duration of the experiment. Pups less than 5 days of age had an elevated haematocrit and reduced plasma volume compared with older pups. Although plasma volume and blood volume increased, mass-specific blood oxygen stores (total haemoglobin) fell during the study period. Simultaneously, the following behavioural indicators of diving ability increased: the proportion of time spent in the water, dive depth, dive duration, bottom time and maximum daily swimming velocity. In addition, the proportion of dives that were identified by cluster analyses as being U-shaped increased significantly with age. On the basis of the measured blood oxygen stores, less than 1 % of the recorded dives exceeded the calculated aerobic dive limit. Thus, development in blood oxygen stores or rates of oxygen consumption did not seem to restrain the rate of neonatal dive development in harbour seals. It appears that behavioural modifications (experience and learning) may be the primary rate-limiting factors for ontogeny of diving skills in neonates of this species.

Animals↗
PubMed2002

Buoyancy and maximal diving depth in penguins: do they control inhaling air volume?

Using a newly developed data logger to measure acceleration, we demonstrate that free-ranging king and Adélie penguins only beat their flippers substantially during the first part of descent or when they were presumed to be chasing prey at the bottom of dives. Flipper beating stopped during the latter part of ascent: at 29+/-9 % (mean +/- S.D.) of dive depth (mean dive depth=136.8+/-145.1 m, N=425 dives) in king penguins, and at 52+/-20 % of dive depth (mean dive depth=72.9+/-70.5 m, N=664 dives) in Adélie penguins. Propulsive swim speeds of both species were approximately 2 m s(-1) during dives; however, a marked increase in speed, up to approximately 2.9 m s(-1), sometimes occurred in king penguins during the passive ascending periods. During the prolonged ascending, oblique ascent angle and slowdown near the surface may represent one way to avoid the potential risk of decompression sickness. Biomechanical calculations for data from free-ranging king and Adélie penguins indicate that the air volume of the birds (respiratory system and plumage) can provide enough buoyancy for the passive ascent. When comparing the passive ascents for shallow and deep dives, there is a positive correlation between air volume and the depth of the dive. This suggests that penguins regulate their air volume to optimize the costs and benefits of buoyancy.

Air↗
PubMed2006

A survey of diving behaviour and accidental water ingestion among Dutch occupational and sport divers to assess the risk of infection with waterborne pathogenic microorganisms.

Divers may run a higher risk of infection with waterborne pathogens than bathers because of more frequent and intense contact with water that may not comply with microbiologic water quality standards for bathing water. In this study we aimed to estimate the volume of water swallowed during diving as a key factor for infection risk assessment associated with diving. Using questionnaires, occupational and sport divers in the Netherlands were asked about number of dives, volume of swallowed water, and health complaints (nausea, vomiting, diarrhea, and ear, skin, eye, and respiratory complaints). Occupational divers, on average, swallowed 9.8 mL marine water and 5.7 mL fresh surface water per dive. Sport divers swallowed, on average, 9.0 mL marine water; 13 mL fresh recreational water; 3.2 mL river, canal, or city canal water; and 20 mL water in circulation pools. Divers swallowed less water when wearing a full face mask instead of an ordinary diving mask and even less when wearing a diving helmet. A full face mask or a diving helmet is recommended when diving in fecally contaminated water. From the volumes of swallowed water and concentrations of pathogens in fecally contaminated water, we estimated the infection risks per dive and per year to be as high as a few to up to tens of percents. This may explain why only 20% of the divers reported having none of the inquired health complaints within a period of 1 year. It is highly recommended that divers be informed about fecal contamination of the diving water.

Bacterial Infections↗
PubMed2000

A trial to determine the risk of decompression sickness after a 40 feet of sea water for 200 minute no-stop air dive.

BACKGROUND: The USN93 probabilistic model of decompression sickness (DCS) predicts a DCS risk of 3.9% after a 40 ft of seawater (fsw) for 200 min no-stop air dive, although little data is available to evaluate the accuracy of this prediction. Based on an analysis of Navy Safety Center data from diving on U.S. Navy standard air decompression tables, the observed incidence of DCS for this type of dive is 0.11%. Knowing the true incidence of the dive is important for deciding whether or not to adopt proposed probability based decompression procedures for U.S. Navy diving. HYPOTHESIS: The risk of DCS after a 40 fsw for 200 min no-stop air dive is 3.9%. METHODS: We conducted a closed sequential trial to determine the DCS incidence on this dive. RESULTS: Of 30 military divers who completed 91 dives, there were 2 cases of DCS (2.2%, 95% CI: 0.27 7.7%). The study was terminated early after the second DCS case because of the presence of neurological symptoms and signs. CONCLUSIONS: This study demonstrates that the incidence of DCS in a laboratory setting is higher than observed in fleet diving. Use of the 40 fsw for 200 min schedule in a decompression computer is likely to result in DCS incidence 2.5- to 70-fold greater than that observed in U.S. Navy diving using table-based procedures.

Adult↗
PubMed2001

The energetic costs of diving in Aedes aegypti and Aedes albopictus pupae.

Undisturbed mosquito pupae rest at the water surface and respond to passing shadows or vibrations by diving. Pupae do not feed and rely solely on energy stored from the larval stage. The ability of a newly emerged adult mosquito to survive, and therefore to transmit disease, depends on these energy reserves. Earlier studies of diving behavior in Aedes aegypti, Ae. albopictus, and Ae. triseriatus pupae provided evidence that pupae sense their state of buoyancy and modify their diving behavior accordingly. With strong stimulation pupae tend to dive to a depth where they become neutrally or negatively buoyant and commonly rest on the bottom. This behavior, as well as the tendency to rest when not disturbed, may logically be viewed as energy-conserving. The results of these studies also generated the hypothesis that the diving behavior displayed by these container-breeding mosquitoes helps them avoid being washed from their container by overflowing water during rainfall. Rainfall stimulates diving and logically, prolonged, heavy rainfall stimulates excessive diving, a likely drain on energy reserves. Our objectives were to determine, in Ae. aegypti and Ae. albopictus, the energetic costs associated with resting behavior, with frequent diving, and with buoyancy reduction. Using survival rate, mean survival after adult emergence, and measurement of total calories, we found a clear energetic cost associated with frequent diving. In contrast, relative to diving, essentially no energy cost was associated with buoyancy reduction, that is, pupae behave in response to variations in buoyancy in a way that does not impact significantly on energy reserves.

Aedes↗
PubMed2001

Ocular tear film bubble counts after recreational compressed air diving.

Other authors have demonstrated an increase in tear film bubble counts following dry, compressed air dives. We examined the lower tear film meniscus for the presence of bubbles in 42 divers after compressed air dives on a single day and in 11 divers undergoing repetitive, multi-day diving exposures over 5 days. After diving, bubble counts increased significantly (P < 0.01) from predive values. From a predive median (inter-quartile range) of 0 (0-0.33) bubbles/eye, single-day divers reached a maximum bubble count at 48 h after diving of 1 (0-2.25) bubbles/eye. Similarly, from a predive count of 0.33 (0-1) bubbles/eye, multi-day divers had increased bubble counts from 24 h following their first dive until 24 h following their final dive when counts were 1.67 (0.92-3.08) bubbles/eye. Bubble counts were not significantly correlated with inert gas load, body mass index, age, or diving experience. We confirm that tear film bubble counts are raised after wet compressed air diving as previously described following dry diving.

Adult↗
PubMed2003

Field trials of no-decompression stop limits for diving at 3500 m.

INTRODUCTION: In 1990, Boğaziçi University (Istanbul, Turkey) launched an altitude diving program to develop techniques and safe decompression profiles for diving at high terrestrial altitudes. Following pioneering diving expeditions to lakes at high elevations in 1990-1992, it was deemed necessary to calculate new tables. METHODS: Bottom time limits for dives requiring no decompression stops (no-d) were calculated for 3500 m using linear extrapolation of U.S. Navy M-values decreased by 4 ft of sea water (M4 limits). These limits were tested for 15, 18, 21, 24, 27, and 30 m of depth by diving in the Great Sea Lake at Mt Kaçkar (3412 m) with 10 dives per profile. RESULTS: The mean decompression sickness (DCS) risk estimated from precordial bubble scores (Spencer Scale) ranged from 0.3% to 2.8% per profile. After three expeditions, 165 dives had been achieved with a cumulative bottom time of 3199 min. No DCS occurred in dives that adhered to the M4 no-d limits. However, two cases of Type I and one case of Type II DCS were encountered where the divers accidentally exceeded those limits. DISCUSSION: Considering the estimated risk of DCS and the relatively small number of trials, a more conservative approach was used to develop a final set of high altitude dive tables. This conclusive approach used continuous compartment half-lives. It is based on fitting a surface of allowable supersaturation limits using the empirical M-values from existing tables as well as our altitude diving data, together with an added constraint that forces calculated M-values to stay below the available M-value data.

Adult↗
PubMed2005

Time and temperature effects on body fluid loss during dives with the open hot-water suit.

BACKGROUND: Bodyweight (BW) losses up to 5 kg have been observed during diving with the open hot-water suit (HWS). The objective of these dives was to study the hormonal, hematological, and renal effects of dehydration during shallow HWS diving. METHODS: In series 1, four divers dove for 3.5 h each day for 7 d. In series 2, 12 divers dove to 6-8 msw for 1, 2, and 4 h. Blood and urine samples, BW measurements, oral temperature, and thermal stress indices were collected. RESULTS: Average deltaBW (+/- SD) for the 28 dives in series 1 was 1.5 +/- 0.8 kg, and the largest BW reductions were 3.2 and 3.0 kg, corresponding to 3.7 and 4.7% of BW. Changes in thermal stress, hemoglobin, hematocrit, aldosterone, and electrolyte excretion correlated with BW reduction. In series 2, average BW reductions were 0.46 +/- 0.27, 0.96 +/- 0.38, and 1.55 +/- 0.59 kg during 1-, 2-, and 4-h dives. BW reduction correlated significantly with thermal stress (p < 0.01). Aldosterone increased after 1 and 2 h and plasma renin activity was unchanged. Atrial natriuretic peptide increased in all dives (p < 0.01) and arginine vasopressin increased in the 4-h dives (p < 0.05). The 7.2% decrease in plasma volume, the increases in hemoglobin, hematocrit and serum proteins, and an unchanged plasma osmolality indicate an isotonic dehydration after the 4-h dives. CONCLUSIONS: BW loss during HWS diving is mainly caused by sweating. Dives of 4 h produce an isotonic dehydration and a break for fluid intake is, therefore, recommended.

Adult↗
PubMed2000

The diving behaviour of green turtles at Ascension Island.

For six green turtles, Chelonia mydas, that had nested on Ascension Island in the South Atlantic, we used time-depth recorders to examine their diving behaviour during the subsequent internesting interval (10-12 days). All the turtles performed dives where they remained at a fixed depth for a long period, surfaced briefly and then dived to the same depth again. It is generally believed these dive profiles are caused by the turtles resting on the sea bed. The maximum depth that turtles routinely reached on these resting dives was between 18 and 20 m, with resting dives deeper than 20 m being extremely rare. Resting dive duration increased significantly with deeper dives. From this relationship, and assuming that turtles with fully inflated lungs at the surface need to dive to 19 m to achieve negative buoyancy, we estimated for two turtles that the oxygen consumption during resting dives was 0.016 and 0.020 litres O(2)/kg per h, respectively. This is similar to the value predicted from the allometric scaling relationship for the minimal oxygen consumption of turtles. We calculated that the energy conserved by resting during the internesting period may appreciably increase the reproductive output of females. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1986

Heart rates and gas exchange in the Amazonian manatee (Trichechus inunguis) in relation to diving.

Unrestrained Amazonian manatees (Trichechus inunguis) maintained a constant heart rate during diving and exhibited a slight tachycardia during breathing. 'Forcing' the manatees to dive caused a marked bradycardia. They exhibited a more pronounced tachycardia during breathing after 'forced' dives and hyperventilated during recovery dives. Manatees are capable of dives exceeding 10 min duration without having to resport to anaerobic metabolism, and even after 10 min dives recover within 3-4 short dives. The ability of manatees to make long dives, in spite of relatively poor O2 stores, is due to their low metabolic rate, while the rapid recovery is aided by their high CO2 stores which minimizes CO2 storage in the body. In manatees the changes in alveolar O2 and CO2 pressure (PAO2 and PACO2) in relation to dive time are slower and more variable than in other marine mammals. The lower rate of change is probably due to the manatees' reduced metabolic rate, while the greater variability is due to their breathing pattern, in which both ventilation and body gas stores influence alveolar gases.

Animals↗
PubMed2003

The development of diving bradycardia in bottlenose dolphins (Tursiops truncatus).

Bradycardia is an important component of the dive response, yet little is known about this response in immature marine mammals. To determine if diving bradycardia improves with age, cardiac patterns from trained immature and mature bottlenose dolphins ( Tursiops truncatus) were recorded during three conditions (stationary respiration, voluntary breath-hold, and shallow diving). Maximum (mean: 117+/-1 beats.min(-1)) and resting (mean: 101+/-5 beats.min(-1)) heart rate (HR) at the water surface were similar regardless of age. All dolphins lowered HR in response to apnea; mean steady state breath-hold HR was not correlated with age. However, the ability to reduce HR while diving improved with age. Minimum and mean steady state HR during diving were highest for calves. For example, 1.5-3.5-year-old calves had significantly higher mean steady state diving HR (51+/-1 beats.min(-1)) than 3.5-5.5-year-old juveniles (44+/-1 beats.min(-1)). As a result, older dolphins demonstrated greater overall reductions in HR during diving. Longitudinal studies concur; the ability to reduce HR improved as individual calves matured. Thus, although newly weaned calves as young as 1.7 years exhibit elements of cardiac control, the capacity to reduce HR while diving improves with maturation up to 3.5 years postpartum. Limited ability for bradycardia may partially explain the short dive durations observed for immature marine mammals.

Age Factors↗