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PubMed1975

Cardiac output and its distribution during diving in the rat.

The diving response was produced by submerging the head of the unanesthetized rat for 60 s, while it was confined in a mesh-wired cone. Heart rate and cardiac output decreased by 73% and 74% from the predive values, respectively, indicating insignificant change in stroke volume. Central systemic arterial blood pressure rose by 22% during diving and a fourfold increase in total peripheral resistance was observed. Blood flow to the coronary, cerebral, and bronchial circulations remained unchanged while a 95% reduction in the intestine and the spleen, a 97% reduction in the kidney, and greater than 99% reduction in the tail and skin were observed during diving. The blood flow reduction from predive values ranged from 50% for liver and skeletal muscle to 75% for the adrenals and 65% for the diaphragm. The redistribution of the drastically reduced cardiac output during head immersion in the rat is similar to that reported for diving mammals. It is suggested that the rat may serve as a useful cardiovascular model for further studies of the diving response in mammals.

Adrenal Glands↗
PubMed1982

Control of diving responses by carotid bodies and baroreceptors in ducks.

The precise role of carotid body chemoreceptors and systemic baroreceptors in cardiovascular responses during experimental diving in ducks is controversial. The diving responses of chronically baroreceptor-denervated, chemoreceptor-denervated, and combined baroreceptor- and chemoreceptor-denervated White Pekin ducks, Anas platyrhynchos, were compared with those of intact and sham-operated birds. All three types of denervation elevated predive heart rates on average by 100-150 beats/min. During submergence, the cardiac rate of the barodenervates quickly dropped and after 60 s stabilized at levels similar to those of submerged intact ducks for the remainder of a 2-min dive. However, arterial blood pressure declined drastically in the barodenervates. Ducks without functional carotid bodies showed significant bradycardia during submergence, although heart rate only fell to the predive rate of intact animals. Birds with combined baroreceptor and chemoreceptor denervation exhibited the same degree of bradycardia as chemoreceptor denervates, and arterial blood pressure rose spectacularly during a dive. It is concluded that during experimental diving in ducks 1) cardiac responses are not baroreflexive in origin, 2) the major portion of bradycardia is due to stimulation of carotid body chemoreceptors, and 3) intact system baroreceptors appear essential for maintenance of blood pressure.

Animals↗
PubMed1998

Circadian rhythms in diving behavior and ventilatory response to asphyxia in canvasback ducks.

Underwater feeding behavior was measured in 10 captive canvasback ducks (Aythya valisineria) for 12 days under a 12:12-h light-dark photoperiod. Feeding activity exhibited a daily rhythm, with 76% of dives occurring at night. In separate experiments on six of these ducks, a circadian rhythm was observed in the duration of voluntary dives. Dives at night (14.7 +/- 0.7 s) were significantly longer than those during the day (10.7 +/- 0.7 s). These day-night differences in diving behavior were accompanied by day-night differences in respiratory responses to progressive asphyxia. In the same six ducks, ventilation increased exponentially as a function of inspired CO2 concentration during rebreathing in a closed-circuit barometric plethysmograph. The exponential rate constant for inspired ventilation was significantly smaller at night (0.23 +/- 0.02) than during the day (0.26 +/- 0.01). We suggest that intermittent apneic exercise is facilitated by reduced respiratory chemosensitivity and that the respiratory and behavioral control systems are synchronized by the circadian timing system in diving ducks.

Animals↗
PubMed1979

Regional blood flow during simulated diving in the conscious Weddell seal.

Changes in regional blood flow during simulated normobaric diving were studied in the conscious Antarctic Weddell seal (Leptonychotes weddelli) by injecting 25-microns radioactive microspheres into the left ventricle. Injections were performed before and 8--12 min after submersion of the head in iced seawater. Diving was associated with a fall in cardiac output from a mean control value of 39.8 +/- 10.2 to 5.6 +/- 3.4 l/min (mean +/- SD) and in heart rate from 52 +/- 15 to 15 +/- 4 beats/min. Blood flow to the splanchnic and peripheral vascular bed was reduced by more than 90%, cerebral blood flow was unchanged, right and left ventricular blood flow decreased by 85%, and adrenal blood flow decreased by 39%. The pulmonary fraction of the injected microsphere dose increased from 7.9 to 29.9% during diving. This may signify a large increase of peripheral arteriovenous shunting during the dive and/or increased bronchial artery blood flow. It is concluded that blood flow during diving is directed to organs and tissues according to their metabolic requirements.

Animals↗
PubMed1980

Responses of fetal sheep to simulated no-decompression dives.

The effect of simulated standard no-decompression dives to 60 and 100 ft of seawater was tested in 12 near term sheep carrying 16 fetuses. In the immediate postdive period there were no significant changes in fetal blood pressure or fetal placental or renal blood flow, but the maternal blood pressure was elevated and the maternal placental blood flow was depressed. Six surgically prepared fetuses were dived to 100 ft. Five died within 20 min of ascent and the sixth suffered severe cardiac arrhythmia and hypotension. At autopsy all fetuses were observed to have massive bubbling in the arterial system and heart. Five fetuses were dived to 100 ft without surgery. Two were alive 3 h later and no bubbles were present at autopsy, and three were born alive at term. With the 60-ft dives, three fetuses were subjected to surgery and all suffered massive bubbling. Two fetuses were dived to 60 ft without surgery; one was alive after 3 h and the other was born alive at term. We conclude that surgery and monitoring result in the formation of postdive gas bubbles that would not otherwise appear.

Animals↗
PubMed1982

Control of heart rate by carotid body chemoreceptors during diving in tufted ducks.

Previous work has shown that during forcible submersion of domestic ducks there is a gradual reduction in heart rate to 10-20% of its predive value after 45-60 s. Bilateral denervation of the carotid body chemoreceptors abolishes most of this bradycardia. By use of implanted radio transmitters it has been shown that in free-swimming tufted ducks, Aythya fuligula, there is an immediate reduction in heart rate, on spontaneous diving, from an elevated predive level. It then increases for a few seconds before it stabilizes at a level similar to that recorded when the duck is swimming fairly vigorously. The present study has shown that, following bilateral denervation of the carotid bodies, there is a significant increase in mean dive duration but no effect on the immediate reduction in heart rate on submersion. Heart rate is, however, significantly higher toward the end of spontaneous dives after carotid body denervation. Unlike the situation in mallards and their domesticated varieties, carotid body denervation has no effect on heart rate in tufted ducks during the first 40 s of forced dives. The carotid bodies therefore do not play the dominant role in cardiac control during submersion of diving ducks that has been suggested by work involving the forcible submersion of the mallard duck and its domesticated varieties.

Animals↗
PubMed1986

Respiratory mechanics in men following a deep air dive.

The mechanical properties of the lungs were measured in 10 men before and after a simulated air dive to 285 ft of seawater (87 m). The objective was to determine whether a dive likely to produce pulmonary bubble emboli would alter lung mechanics. Lung function was measured predive and at 1, 2, 3, 6, 7, and 23 h postdive. Measurements of lung function were also made at identical times on a control day when no dive was made. Each set of measurements included precordial Doppler signals, pulmonary resistance, quasistatic lung compliance, forced vital capacity (FVC), forced expired volume after 1.0 s (FEV 1.0), the ratio of FEV 1.0 to FVC (FEV 1.0/FVC%), and maximal airflow after 50 and 75% of the vital capacity had been expired (Vmax50 and Vmax75, respectively). Base-line measurements of pulmonary resistance and quasistatic compliance were normal in all subjects. FVC and FEV 1.0 were greater than predicted for most subjects and were increased proportionately so that the FEV 1.0/FVC% was normal. Following the dive, bubble signals were heard in four subjects, and two subjects had mild symptoms of decompression sickness. No subject demonstrated any alteration in lung function that could be attributed to the dive. We concluded that stressful decompressions capable of producing "silent" pulmonary bubble emboli do not alter lung mechanics.

Adult↗
PubMed1987

Dive response of children in relation to cold-water near-drowning.

The strength of the dive response, as judged by the combination of breath-hold duration (BHD) and bradycardia, was compared in 87 children (4-13 yr old) and 68 adults (20-68 yr old) during simulated dives in 29 degrees C water. Mean BHD in children (16.1 s) was only 37.4% (P less than 0.001) of adult BHD (43.0 s). Within children, BHD was significantly (P less than 0.001) dependent on age (A in yr) according to the regression BHD = -1.46 + 2.27A. No age dependency of BHD occurred in adults. Due to the low BHD of children, only 14/87 (16.1%) were able to breath hold for the 25 s necessary to develop full diving bradycardia. For these 14 children, their bradycardia (36.1% reduction) was insignificantly different (P greater than 0.50) from that of adults (36.4%). These experimental findings demonstrate that the dive response of children is extremely weak, due mainly to their very low BHD. Since lower water temperature would probably accentuate the shortness of BHD (according to previous findings for adults), it is concluded that the dive response is unlikely to make a significant contribution to the prolonged resuscitatibility of children who are victims of cold-water near-drowning.

Adult↗
PubMed1993

Contribution of hyperoxia to reduced pulmonary function after deep saturation dives.

Pulmonary function was measured before and after a 28-day saturation dive to a pressure of 0.25 MPa in eight subjects. PO2 was 40 kPa, with periods of 75 kPa for 2 h every 2nd day during the first 14 days, 50 kPa for the next 12 days, and a gradual fall to 21 kPa over the last 2 days in decompression. A 28-day saturation dive with six subjects to a pressure of 0.15 MPa and a PO2 of 21 kPa was used as control. The measurements included static and dynamic lung volumes and flows, transfer factor for carbon monoxide (TLCO), and a cycle ergometer exercise test. There was a significant reduction in TLCO of 9.8 +/- 6.0% (P < 0.001) after the dive when values were corrected for hemoglobin concentration changes. Effective alveolar volume was unchanged. There was a reduction in forced midexpiratory flow rate of 9.8 +/- 7.0% (P < 0.01), but forced vital capacity and forced expired volume in 1 s were unchanged. Peak oxygen uptake was reduced by 10.1 +/- 5.3% (P < 0.001). There were no significant changes in any of the lung function variables after the control dive. Exposure to raised PO2 contributes significantly to the changes in pulmonary function that have been reported after deep saturation dives to pressures of 3.1-4.6 MPa with a similar profile of oxygen exposure. TLCO is apparently a more sensitive index than vital capacity for oxygen toxicity.

Adult↗
PubMed1995

Intrapulmonary distribution of alveolar gas exchange during breath-hold diving in humans.

Expirograms for CO2 and O2 obtained immediately after 75-s breath holds (BHs) in thermoneutral conditions were studied in 10 subjects. BHs were performed at normal atmospheric pressure in dry condition (dry surface BH), at normal atmospheric pressure submerged (wet surface BH), and during a transient increase of ambient pressure to 3 atmospheres absolute submerged (wet BH dive). Cardiac index was estimated by means of impedance cardiography. Phase III (alveolar plateau) slopes for CO2 expirograms were lowest after wet surface BH. The greater slope observed after dry surface BH was attributed mainly to intrapulmonary perfusion heterogeneity and the greater slope seen after wet BH dive to continuing alveolar CO2 exchange during expiration. Cardiogenic oscillations in phase III (evaluated by spectral analysis) were largest after dry surface BH, much reduced by wet surface BH, and further reduced by wet BH dive. This was attributed to more even distribution of pulmonary perfusion during submersion and compression. Terminal changes of the expirograms (phase IV) revealed a less even interregional pulmonary distribution of CO2 and a more even distribution of O2 after wet BH dive compared with wet surface BH. This difference was attributed to improved apical pulmonary perfusion at depth during the wet BH dives.

Adolescent↗
PubMed2002

Ascent rate, age, maximal oxygen uptake, adiposity, and circulating venous bubbles after diving.

Decompression sickness in diving is recognized as a multifactorial phenomenon, depending on several factors, such as decompression rate and individual susceptibility. The Doppler ultrasonic detection of circulating venous bubbles after diving is considered a useful index for the safety of decompression because of the relationship between bubbles and decompression sickness risk. The aim of this study was to assess the effects of ascent rate, age, maximal oxygen uptake (VO(2 max)), and percent body fat on the production of bubbles after diving. Fifty male recreational divers performed two dives at 35 m during 25 min and then ascended in one case at 9 m/min and in the other case at 17 m/min. They performed the same decompression stops in the two cases. Twenty-eight divers were Doppler monitored at 10-min intervals, until 60 min after surfacing, and the data were analyzed by Wilcoxon signed-rank test to compare the effect of ascent rate on the kinetics of bubbles. Twenty-two divers were monitored 60 min after surfacing. The effect on bubble production 60 min after surfacing of the four variables was studied in 47 divers. The data were analyzed by multinomial log-linear model. The analysis showed that the 17 m/min ascent produced more elevated grades of bubbles than the 9 m/min ascent (P < 0.05), except at the 40-min interval, and showed relationships between grades of bubbles and ascent rate and age and interaction terms between VO(2 max) and age, as well as VO(2 max) and percent body fat. Younger, slimmer, or aerobically fitter divers produced fewer bubbles compared with older, fatter, or poorly physically fit divers. These findings and the conclusions of previous studies performed on animals and humans led us to support that ascent rate, age, aerobic fitness, and adiposity are factors of susceptibility for bubble formation after diving.

Adipose Tissue↗
PubMed2003

The neuropsychology of repeated 1- and 3-meter springboard diving among college athletes.

This study examined the neuropsychological effects of repeated springboard diving. It was hypothesized that the impact velocity, which can range from 20 to 30 mph, and accompanying deceleration in the water may lead to concussions and affect the diver's cognitive function. Six varsity National Collegiate Athletic Association Division 1 springboard divers participated in the study. Each diver performed a total of 50 practice dives from either the 1- or 3-m springboard. After each set of 10 dives, the participants were immediately evaluated at poolside using the Symbol Digit Modalities Test, the Stroop Color Word Test, and the Trail Making Test B. Baseline testing revealed, consistent with their athletic specialty, clear neurocognitive strengths among the divers on tests sensitive to proprioception, motor speed, and visual-spatial organization. Results from the serial assessments indicated no detectable neuropsychological deficits among competitive divers compared to baseline testing. Skilled diving at the collegiate level appears to be a safe sport and water appears to present the perfect medium for gradual deceleration. More studies, however, are warranted for 5-, 7.5-, and 10-m platform diving since the impact velocity of the diver from these heights is higher.

Adult↗
PubMed1985

Diving and chronic spontaneous pneumothorax.

Diving and pneumothorax cannot go together. An air bubble between the visceral and the parietal pleura will change its size according to Boyle's law, and pneumothorax might increase in size during the ascent from a dive. We would like to present the case of a professional diver, who was engaged in active diving for a period of five months during which time he made 80 to 85 dives with pneumothorax. As far as we know, this is the first such case published in the medical literature. We should also like to emphasize the protracted nature of the pneumothorax, which persisted for that time without changing size. This diver had no medical problems with diving, and the deeper he descended, the better he felt. No tension pneumothorax ever occurred and the diagnosis was made by chance.

Adult↗
PubMed1992

[Inner ear decompression sickness following a scuba dive].

Inner ear decompression sickness (IEDCS) is one form of Type II decompression sickness. Most cases of IEDCS have been associated with saturation dives, so there are very few reports of occurrence following shallow scuba dives. We present here the case of a diver who suffered from IEDCS following a shallow scuba dive (30m), and was successfully treated by the protocol outlined in U.S. Navy treatment table 6. This case suggests that there is the possibility of occurrence of IEDCS, even following a shallow scuba dive, if proper decompression procedures are not adhered to. In addition, detailed analysis of diving profiles should be used to distinguish the inner ear dysfunction seen in some divers from inner ear barotrauma which may be attributable to IEDCS.

Adult↗
PubMed1993

Pulmonary function one and four years after a deep saturation dive.

The pulmonary function of 24 Norwegian divers who had participated in a deep saturation dive to pressures of 3.1-4.6 MPa was reevaluated one and four years later. Twenty-eight divers performing ordinary saturation diving to pressures of 0.8-1.6 MPa and followed over a three-year period served as referents. A significant reduction in forced expiratory volume in 1 s (FEV1.0) of 210 (SD 84) ml (P < 0.001) occurred the first year after the dive. Thereafter the annual reduction in FEV1.0 was 28 (SD 62) ml.year-1; this value did not differ from the 35 (SD 80) ml.year-1 of the referents. The forced midexpiratory flow rate and forced expiratory flow rates at low lung volumes were also significantly reduced one year after the deep dive, and the closing volume was increased. No significant changes occurred in forced vital capacity. The results agree with those of cross-sectional studies on divers' lung function and indicate the development of airflow limitation in relation to diving exposure.

Adult↗
PubMed2005

The role of radiology in dive-related disorders.

Recreational scuba diving has continued to grow in popularity in the past several decades, and military diving remains an integral part of ship husbandry, explosives and ordinance disposal, and special warfare. Although relatively uncommon, disorders such as decompression sickness and arterial gas embolism can be fatal, whereas disorders such as ear baro-trauma and dysbaric osteonecrosis are not fatal but can cause significant morbidity. An extensive literature search was performed to comprehensively examine the current role of diagnostic radiology with respect to diving medicine. In selected cases, diagnostic imaging can be of potential benefit for evaluation. Diagnostic imaging plays a useful role in the screening of certain individuals for future fitness to dive. Radiological imaging has also been of paramount importance in postmortem evaluation of dive casualties.

Barotrauma↗
PubMed1999

[Medical aspects of diving--a sport for both women and men].

As interest in scuba diving is increasing in both sexes, doctors need to be aware of the risks encountered when diving and about gender-related differences in these risks. Individuals prone to panic attacks, claustrophobia or reckless risk-taking should avoid diving. In tolerating cold, muscle mass is more important than the amount of subcutaneous fat. The risk of decompression disease seems to be slightly greater among women, probably due to their fat distribution. Pregnant women are recommended not to dive, because the risk of birth defects seems to be greater among those who do, and there is a serious risk of fetal decompression disease. All participants in the sport must be responsible for their own diving safety.

Adaptation, Physiological↗
PubMed1999

[Pregnancy and scuba diving: what precautions?].

Scuba diving is a leisure activity increasingly popular amongst women. Many women are concerned about the risks associated with diving and a known or planned pregnancy. In order to advise these young women, we have reviewed the literature concerning women and diving as well as animal studies on the subject. The different international federations and the Undersea and Hyperbaric Medical Society advise against scuba diving for pregnant women or those planning a pregnancy, but no randomized trials or trials provide a solid scientific basis. The fetal circulation is characterized by the exclusion of the pulmonary circulation by 2 right to left shunts. As the lung appears to act as a filter against the progression of micro-bubbles to the main circulation, the fetus may be therefore particularly exposed to gas emboli. However, the placenta could play this role in certain animal species. Nitrox diving appears to be particularly promising, but studies on the subject are still insufficient to recommend it for pregnant women.

Accidents↗