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PubMed1992

Metabolic rates of freely diving Weddell seals: correlations with oxygen stores, swim velocity and diving duration.

The metabolic rates of freely diving Weddell seals were measured using modern methods of on-line computer analysis coupled to oxygen consumption instrumentation. Oxygen consumption values were collected during sleep, resting periods while awake and during diving periods with the seals breathing at the surface of the water in an experimental sea-ice hole in Antarctica. Oxygen consumption during diving was not elevated over resting values but was statistically about 1.5 times greater than sleeping values. The metabolic rate of diving declined with increasing dive duration, but there was no significant difference between resting rates and rates in dives lasting up to 82 min. Swimming speed, measured with a microprocessor velocity recorder, was constant in each animal. Calculations of the aerobic dive limit of these seals were made from the oxygen consumption values and demonstrated that most dives were within this theoretical limit. The results indicate that the cost of diving is remarkably low in Weddell seals relative to other diving mammals and birds.

Animals↗
PubMed1997

Aetiology and occurrence of diving injuries. A review of diving safety.

This paper examines multifaceted aspects of diving entries into water which are the cause of many critical injuries (costed at $A150 million) and therefore have important safety ramifications. Wedge and compression fractures are most commonly found in the cervical area of the spine with off-centre impacts with the pool or sea bottom. Diving-related injuries range from 2.3 in a South African study to 21% of spinal cord injuries in Poland. Alcohol and diving do not mix because of diminished awareness and information processing. Children aged under 13 years suffer fewer cervical injuries (1 to 4%), but complication rates are relatively high for this group. Sports trauma (diving-related in particular) is one of the more prevalent causes of spinal cord injury in children aged 6 to 15 years. The highest incidence occurs among those aged 10 to 14, followed by the group aged 5 to 9 years. This contradicts the common perception that 15-to 19-year-olds comprise the highest risk group. Boys are more frequently injured, and swimming pools are more common as an injury location then is the case with adults. The role played by water depth has been conclusively ascertained; technique, and therefore education, appear to be more important considerations in injury prevention. Although 89% of injuries occur in water < 1.52m, injuries are rare in water of 0.46 to 0.61m. Care with pool design to avoid sudden depth changes and the resultant "spinal wall' is necessary. Minimum depth values for diving vary from 1 to 1.52 m. Velocities and angles of entry are considered to ascertain the body's decelerative capacity upon entry. The scoop, racing start dive has been shown to require at least 1.22 m of water even when practised by trained divers; the risks involved must therefore be weighed against the fact that it may be no faster than more conventional dives. While it may be safe to perform kneeling and crouching dives into shallowers water, standing dives by untrained divers require a greater margin of error. Lack of education is an issue which needs to be addressed and this paper makes recommendations for safety practices such as steering up to the surface, head protection with the arms and only diving when absolutely necessary.

Adult↗
PubMedDate not supplied

Probability of decompression sickness in no-stop air diving and subsaturation diving.

Probabilistic models allow estimation of the probability (Pdcs) that decompression sickness (DCS) will occur in any particular dive. Our objective is to provide Pdcs estimates for no-stop diving instructions used by the U.S. Navy and various other navies. To do so, we develop statistics-based (probabilistic) and intuition-based (deterministic) models using dive-outcome data from the U.S. Navy Decompression Database. We give special attention to subsaturation dives (defined as no-stop dives shallower than 40 fswg with bottom times between 4 hr and one day), for which experimental dives are scarce. According to our models, probability of DCS is 2% or less for current U.S. Navy no-stop air dive schedules and near 1% for the navies of Great Britain, Canada, and France; also the current U.S. Navy prescriptions for subsaturation dives seem to be appropriate. Our probabilistic models fail for deep dives; they do not avoid observed DCS cases in the calibration dataset and provide longer no-stop times than allowed by tables used operationally; we advocate prescriptions by our deterministic model for deep no-stop dives.

Algorithms↗
PubMed2003

Diving experience and the aerobic dive capacity of muskrats: does training produce a better diver?

We tested the hypothesis that the body oxygen stores, aerobic dive limit (ADL) and dive performance of muskrats can be enhanced by dive-conditioning in a laboratory setting. We compared several key variables in 12 muskrats trained to swim a 16 m underwater course to a feeding station ('divers') with those of 12 animals precluded from diving but required to travel identical distances in water to feed ('surface swimmers'). Acclimated muskrats assigned to each group were trained concurrently over a 9-11 week period. We observed significant gains in the haematocrit (P=0.0005) and blood haemoglobin concentration (P=0.015) of 'divers', but not 'surface swimmers'. The post-training blood O(2) store calculated for 'divers' (22.9 ml O(2) kg(-1)) was nearly 26% higher than that (18.2 ml O(2) kg(-1)) derived for 'surface swimmers' (P=0.03). Dive-conditioning had no apparent effect on lung volume, whole blood and plasma volumes, nor on the glycogen level and buffering capacity of skeletal muscles. Cardiac and skeletal muscle myoglobin levels were also similar in both test groups following training. The mean total body oxygen store of 'divers' (37.8ml O(2) STPD kg(-1)) was 13.5% higher (P=0.037) than for 'surface swimmers' (33.3 ml O(2) STPD kg(-1)), an increase attributed entirely to the gain in blood O(2) storage capacity of the former group. However, owing to a slightly higher estimate of diving metabolic rate in dive-conditioned animals, the calculated ADL for this group (61.3 s) was indistinguishable from that of 'surface swimmers' (61.8 s). Few differences were observed in the post-training dive behaviour of 'surface swimmers' and 'divers', a finding consistent with the strong similarity in their calculated aerobic dive capacities.

Animals↗
PubMed2002

Body oxygen stores, aerobic dive limits and diving behaviour of the star-nosed mole (Condylura cristata) and comparisons with non-aquatic talpids.

The dive performance, oxygen storage capacity and partitioning of body oxygen reserves of one of the world's smallest mammalian divers, the star-nosed mole Condylura cristata, were investigated. On the basis of 722 voluntary dives recorded from 18 captive star-nosed moles, the mean dive duration (9.2+/-0.2 s; mean +/- S.E.M.) and maximum recorded dive time (47 s) of this insectivore were comparable with those of several substantially larger semi-aquatic endotherms. Total body O(2) stores of adult star-nosed moles (34.0 ml kg(-1)) were 16.4 % higher than for similarly sized, strictly fossorial coast moles Scapanus orarius (29.2 ml kg(-1)), with the greatest differences observed in lung and muscle O(2) storage capacity. The mean lung volume of C. cristata (8.09 ml 100 g(-1)) was 1.81 times the predicted allometric value and exceeded that of coast moles by 65.4 % (P=0.0001). The overall mean myoglobin (Mb) concentration of skeletal muscles of adult star-nosed moles (13.57+/-0.40 mg g(-1) wet tissue, N=7) was 19.5 % higher than for coast moles (11.36+/-0.34 mg g(-1) wet tissue, N=10; P=0.0008) and 54.2 % higher than for American shrew-moles Neurotrichus gibbsii (8.8 mg g(-1) wet tissue; N=2). The mean skeletal muscle Mb content of adult star-nosed moles was 91.1 % higher than for juveniles of this species (P<0.0001). On the basis of an average diving metabolic rate of 5.38+/-0.35 ml O(2) g(-1) h(-1) (N=11), the calculated aerobic dive limit (ADL) of star-nosed moles was 22.8 s for adults and 20.7 s for juveniles. Only 2.9 % of voluntary dives by adult and juvenile star-nosed moles exceeded their respective calculated ADLs, suggesting that star-nosed moles rarely exploit anaerobic metabolism while diving, a conclusion supported by the low buffering capacity of their skeletal muscles. We suggest that a high mass-specific O(2) storage capacity and relatively low metabolic cost of submergence are key contributors to the impressive dive performance of these diminutive insectivores.

Aerobiosis↗
PubMed2004

The diving paradox: new insights into the role of the dive response in air-breathing vertebrates.

When aquatic reptiles, birds and mammals submerge, they typically exhibit a dive response in which breathing ceases, heart rate slows, and blood flow to peripheral tissues is reduced. The profound dive response that occurs during forced submergence sequesters blood oxygen for the brain and heart while allowing peripheral tissues to become anaerobic, thus protecting the animal from immediate asphyxiation. However, the decrease in peripheral blood flow is in direct conflict with the exercise response necessary for supporting muscle metabolism during submerged swimming. In free diving animals, a dive response still occurs, but it is less intense than during forced submergence, and whole-body metabolism remains aerobic. If blood oxygen is not sequestered for brain and heart metabolism during normal diving, then what is the purpose of the dive response? Here, we show that its primary role may be to regulate the degree of hypoxia in skeletal muscle so that blood and muscle oxygen stores can be efficiently used. Paradoxically, the muscles of diving vertebrates must become hypoxic to maximize aerobic dive duration. At the same time, morphological and enzymatic adaptations enhance intracellular oxygen diffusion at low partial pressures of oxygen. Optimizing the use of blood and muscle oxygen stores allows aquatic, air-breathing vertebrates to exercise for prolonged periods while holding their breath.

Adaptation, Physiological↗
PubMed2000

Risk reduction in diving spinal cord injury: teaching safe diving skills.

Thirty-four recreational swimmers underwent an intervention program to improve diving skills. Participants with low diving skills completed seven 10-minute sessions which emphasised locking thumbs and holding arms extended beyond the head, and steering and gliding skills. Various dive entries were video-recorded and maximum depth reached was used as the criterion measure. A one-way repeated measures analysis of variance was conducted for each dive condition. Maximum depth decreased for all dives. Velocity at maximum depth was greater for the Treadwater, Deck and Block conditions. Improved streamlining and increased 'spring' were evident in more confident participants. Hands separated in 71% of pre-intervention dives but only in 3% of post-intervention dives. Preintervention, arms were pulled backward before. or at, maximum depth in 30% of participants but none did this post-intervention. Diving skills were improved following participation in the intervention program.

Adult↗
PubMed2003

Evaluation of decompression safety in an occupational diving group using self reported diving exposure and health status.

BACKGROUND: Many occupational diving groups have substantially different diving patterns to those for which decompression schedules are validated. AIMS: To evaluate tuna farm occupational diving practice against existing decompression models and describe a method for collecting and modelling self reported field decompression data. METHODS: Machine readable objective depth/time profiles were obtained from depth/time recorders worn by tuna farm occupational divers. Divers' health status was measured at the end of each working day using a self administered health survey that produces an interval diver health score (DHS) with possible values ranging from 0 to 30. Depth/time profiles were analysed according to existing decompression models. The contribution of diving exposure and between diver variability to DHS was evaluated using linear regression. RESULTS: The mean risk of decompression sickness was calculated as 0.005 (SD 0.003, n = 383). The mean DHS following diving was 3 (SD 2, n = 383) and following non-diving activities was 1 (SD 1, n = 41). After accounting for between diver variability in intercept, DHS was found to increase one unit for every 1% increase in the risk of decompression sickness. CONCLUSIONS: A method has been established for the collection and analysis of self reported objective decompression data from occupational diving groups that can potentially be used as the basis for development of purpose designed occupational diving decompression schedules.

Decompression↗
PubMedDate not supplied

NIHSS applied to cerebral neurological dive injuries as a tool for dive injury severity stratification.

BACKGROUND: Evaluation via National Institutes of Health Stroke Scale (NIHSS) upon presentation in hospital triage following ischemic stroke is predictive of recovery or progression to neurological deficits. Cerebral injuries sustained while diving have symptoms similar to stroke. Applying the NIHSS to dive injuries may successfully summarize neurological dive injuries, providing a standardized tool for study of dive injury data. METHODS: We retrospectively determined NIHSS scores for a diverse population of 192 divers presenting to the University of Hawaii recompression chamber from 1983-2002, both prior to initial treatment and after all treatment. Spinal and vestibular decompression sickness cases were excluded. RESULTS: The performance of the NIHSS among this diving population was similar to its performance as an accepted tool in evaluation of ischemic stroke, although results are influenced by the abundance of mild injury cases in the data set. The estimated C-statistic with NIHSS predicting no observable deficit was 0.88, and predicting post NIHSS of 0-1 was 0.85 (vs. 0.86 when applied to stroke). Sensitivity for predicting recovery (NIHSS 0-1) at discharge was 0.99 (vs. 0.97 for stroke). CONCLUSIONS: The NIHSS applied to cerebral dive injuries has adequate predictive ability and correlates with other measures of dive injuries, while providing a standardized, more graduated scale. The NIHSS may be useful as a standardized measurement for evaluation of treatment regimens and adjunctive therapy for diving injuries.

Adolescent↗
PubMed1987

Habituation of the cardiac response to involuntary diving in diving and dabbling ducks.

1. Bradycardia in response to forced submergence was habituated in dabbling (Anas platyrhynchos, Linnaeus) and diving (Aythya americana, Eyton) ducks by repetitively submerging the animals, each day for several days, for periods of 40 and 20 s, respectively. The onset of pronounced bradycardia was delayed with each successive trial, until little or no bradycardia occurred during submergence. Diving bradycardia is driven by chemoreceptors in the dabbler and caused by stimulation of narial receptors in the diver. 2. Mean arterial blood pressure in dives was unchanged from pre-dive levels in both naive and trained dabbling ducks. PaO2, PaCO2 and pHa at the end of a dive were similar before and after habituation training. 3. Bradycardia occurred in dives by habituated dabbling ducks if the animal breathed 15% O2 before submergence. The ventilatory responses to breathing high and low levels of oxygen were unaffected by habituation training. 4. The changes in blood gases during dives by naive and habituated dabbling ducks were the same: therefore, in the absence of a demonstrated decrement in receptor chemosensitivity or efferent potency, the locus of habituation must reside in the central nervous system.

Animals↗
PubMed1992

Screening of children with arrhythmias for arrhythmia development during diving and swimming--face immersion as a substitute for diving and exercise stress testing as a substitute for swimming.

We compared face immersion and exercise stress testing by diving and swimming as screening methods for arrhythmias induced by immersion in water. The subjects were 64 children with various arrhythmias who were tested using 5 methods: diving, swimming, face immersion in 25 degrees C water, face immersion in 6 degrees C water, and a treadmill exercise test. Significant arrhythmias occurred during diving or swimming in 51 children, with 44 developing arrhythmias while diving. Both tachyarrhythmias and bradyarrhythmias were seen during diving, but 17 children who also showed significant arrhythmias while swimming mostly had tachyarrhythmias. A comparison with the incidence of arrhythmias produced by diving showed that face immersion in cold water had a sensitivity of 88.6%, a specificity of 85.0%, a predictive value of 92.9%, and an accuracy of 87.5%. Arrhythmias were alleviated in 12.5%, unchanged in 79.7%, and aggravated in 7.8% of the subjects. Face immersion thus appeared to be a useful and adequate screening substitute for diving. Exercise testing was also compared with swimming (sensitivity, 52.9%; specificity, 100%; predictive value, 100%; and accuracy, 87.5%). Arrhythmias were alleviated in 12.5% and unchanged in 87.5% of patients. Although exercise testing produced many false-negatives, all of the severe arrhythmias were reproduced.

Adolescent↗
PubMed2006

CNS toxicity in closed-circuit oxygen diving: symptoms reported from 2527 dives.

INTRODUCTION: Oxygen toxicity is a problem in diving and can have fatal consequences in the water. Various aspects of oxygen diving have been studied in dry hyperbaric chambers, but there is a lack of information on in-water diving using closed-circuit oxygen apparatus. METHOD: We collected 2527 dive reports from 473 closed-circuit oxygen divers (a mean of 5.2 reports per diver), and analyzed the relationships between various symptoms and their dependence on depth and diving time. RESULTS: No CNS oxygen toxicity-related symptoms were reported at a depth of 2 m seawater (msw), but their proportion increased at depths from 3 to 6 msw. We found that CNS oxygen toxicity-related symptoms appeared in 2.5% of dives conducted at a Po2 of 119 kPa. The main symptoms and signs reported were headache: 4.5%; nausea: 2.6%; hyperventilation: 2.6%; heavy breathing: 2.4%; dizziness: 1.6%; hiccups: 1.5%; bloody sputum: 1.4%; cold shivering: 1.1%; tinnitus: 0.9%; difficulty maintaining a steady depth: 0.9%; disorientation: 0.6%; tiredness: 0.5%; tingling in the limbs: 0.4%; hearing disturbances: 0.4%; a choking sensation: 0.4%; extreme effort: 0.4%; and loss of consciousness: 0.3%. DISCUSSION: Environmental factors, light vs. dark and temperature, had no effect on symptoms. The number of symptoms increased with diving time. Divers who experienced amnesia, facial twitching, hearing disturbances (p < 0.001), and disorientation (p < 0.014) were prone to suffer loss of consciousness. It was found that some divers are more sensitive to oxygen than others (p < 0.0001).

Airway Obstruction↗
PubMed2006

Deep diving mammals: Dive behavior and circulatory adjustments contribute to bends avoidance.

A mathematical model was created that predicted blood and tissue N(2) tension (P(N2)) during breath-hold diving. Measured muscle P(N2) from the bottlenose dolphin after diving repeatedly to 100 m (Tursiops truncatus [Ridgway and Howard, 1979, Science, 4423, 1182-1183]) was compared with predictions from the model. Lung collapse was modelled as a 100% pulmonary shunt which yielded tissue P(N2) similar to those reported for the dolphin. On the other hand, predicted muscle P(N2) for an animal with a dive response, reducing cardiac output by 66% from surface values (20.5 to 6.8l x min(-1)), also agreed well with observed values in the absence of lung collapse. In fact, modelling indicated that both cardiovascular adjustments and dive behaviour are important in reducing N2 uptake during diving and enhancing safe transfer of tissue and blood N2 back to the lung immediately before coming to the surface. In particular, diving bradycardia during the descent and bottom phase together with a reduced ascent rate and increase in heart rate reduced mixed venous P(N2) upon return to the surface by as much as 45%. This has important implications as small reductions in inert gas load (approximately 5%) can substantially reduce decompression sickness (DCS) risk by as much as 50% (Fahlman et al., 2001, J. Appl. Physiol. 91, 2720-2729).

Acclimatization↗
PubMed1982

Effect of diving and diving hoods on the bacterial flora of the external ear canal and skin.

The bacterial flora of the external ear canals and posterior auricular skin surfaces were investigated in a group of 26 divers after 25 dry-suit dives in harbor water and 20 dry-suit dives in clear test tank test. A control group of 16 divers wore rubber hoods 19 times for a similar period (25 to 30 min) but did not dive. The protective effect of 2% acetic acid was tested by instilling it in the left ear of 14 divers and 8 nondivers. Staphylococcus epidermidis, Propionibacterium acnes, alpha-hemolytic streptococci, and enteric gram-negative rods were the predominant isolates from skin and ear samples. After the divers dove or after they wore hoods without going in the water, there was a substantial increase in the number of these organisms on the skin (46.9%) or in the external ears (43.8%) of the divers. However, an increase in the bacterial counts in the external ear canals occurred in only 13.6% of the individuals treated prophylactically with acetic acid drops. Although no gram-negative rods were recovered from the skin or external ear canals of divers in clear tank water, 23 strains were isolated after the dives in harbor water. Identical gram-negative isolates also were recovered from the harbor water. Gram-negative organisms also were recovered from three newly acquired skin lacerations, where they persisted for at least 24 h. Our data show the acquisition of gram-negative rods when dives were made in polluted water. The data also demonstrate the increase in bacterial counts that occurs when rubber diving rods are worn (in or out of water) and that this increase can be controlled by pretreatment of ears with acetic acid.

Acetates↗
PubMed2006

Post-dive bubble formation in rats: effects of exercise 24 h ahead repeated 30 min before the dive.

INTRODUCTION: Recent studies have shown that a nitric oxide releasing agent or a single bout of high-intensity exercise 20-24 h before a dive can prevent bubble formation following decompression. The aim of this study was to determine whether high-intensity exercise immediately prior to a dive eliminates the protective effect of a single bout of high-intensity exercise 24 h before the dive. METHODS: Twelve female Sprague-Dawley rats were randomly divided into two equal groups. Group 1 performed 90 min of exercise twice, beginning 24.5 h and again 2.0 h before compression. Group 2 performed 90 min of exercise beginning at 25.5 h before compression. The standardized exercise protocol was 7 x 8 min at 85-90% maximal oxygen uptake (Vo2max) followed by 2 min at 50% Vo2max for a total of 90 min including a 20 min warm-up at 40-50% of Vo2max. All rats were exposed to a pressure of 700 kPa (7 ATA) for 45 min in a dry hyperbaric chamber followed by decompression to the surface at 100 kPa (1 ATA) at a rate of 50 kPa x min(-1) (0.5 atm x min(-1)) breathing air. RESULTS: Bubble formation was significantly higher in rats that had exercised 24 h and 30 min prior to dive than rats that had only exercised 24 h prior to the dive (median bubble grade 4.5 vs. 0.5). CONCLUSION: This study demonstrated that acute exercise prior to a dive eliminated the protection against bubble formation found 24 h after high-intensity exercise in rats.

Animals↗