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PubMed1996

Pulmonary barotrauma of a diver using an oxygen rebreathing diving apparatus.

A 22-yr-old healthy male diver performed a dive using a closed circuit oxygen rebreathing apparatus according to normal procedure. After the dive he developed clinical symptoms of mediastinal emphysema. A chest X-ray taken 1 d after the dive showed a discrete "tram track" sign in the left paracardial region. Spiral volumetric computed tomography of the chest 4 d postinjury detected a small subpleural emphysematous bulla next to the left ventricle, the pneumomediastinum being absorbed in the meantime. Clinical outcome of pulmonary decompression barotrauma in the case of oxygen rebreathing may be different from that in compressed air diving, due to the altered gas physics. The necessity for computed tomography of the chest is emphasized, preferably using the spiral mode, in any case of suspected pulmonary barotrauma.

Adult↗

PubMed1997

Doppler-echocardiography study of cardiac function during a 36 atm (3,650 kPa) human dive.

To determine the influence of a saturation dive on cardiac function, Doppler-echocardiographic measurements were compared at sea level and during a 36 atm (3,650 kPa) He-O2 dive (gas density: 7 g/liter) in four healthy men. Left ventricular systolic function was studied from time motion measurements. Transmitral flow (E:A ratio) and isovolumetric relaxation time were used to assess left ventricular diastolic function. Cardiac output was derived from systolic pulmonary and aortic valvular flows. Cardiac output decreased 4.4 +/- 0.8 vs. 5.9 +/- 1.2 liter/min at sea level) whereas stroke volume, left ventricular ejection fraction, atria and ventricular diameters remained unchanged. Thus, the decrease in cardiac output was attributed to bradycardia (56 +/- 8 vs. 73 +/- 9 beats/min at sea level) which probably resulted from the slight hyperoxia (PI(O2), 0.4 atm). We found no evidence of left ventricular diastolic dysfunction. nor did we find valvular regurgitation or pulmonary hypertension. We conclude that Doppler-echocardiography can be used safely to investigate cardiac function during human saturation dives. Our results suggest that a 36 atm He-O2 dive does not modify cardiac or systolic and diastolic function except for a slight decrease in cardiac output correlated to bradycardia.

Adult↗

PubMed1997

[Retinal vein occlusion and deep-sea diving].

We report a case of retinal vein occlusion after breath-holding diving. After one hour of diving at a maximal depth of eight meters, each apnea no longer than one minute, the patient complained of a diminution of the visual acuity in the left eye. Ophthalmological examination revealed an occlusion of the superior branch of the central vein of the retina in the left eye. This could be considered as a decompression sickness even if the occlusion could happen fortuitously in water. Secondary to the multiple descents, a bubble would have appeared in the vein leading to an obstruction. The purpose of this paper is to discuss a possible link between the breath-holding diving and this kind of accident. We also report the different ophthalmological features that may occur while diving.

Decompression Sickness↗

PubMed1997

Recurrent pulmonary barotrauma in scuba diving and the risks of future hyperbaric exposures: a case report.

A 27-yr-old male scuba diving student suffered two episodes of pulmonary barotrauma 6 mo. apart after 12-ft training scuba dives. In the interval between these episodes, four uneventful hyperbaric chamber dives occurred. No definite cause or risk factors were identified. A MEDLINE review of diving literature revealed few studies of recurrent pulmonary barotrauma and no studies addressed risks of recurrent pulmonary barotrauma in the hyperbaric oxygen therapy environment following scuba pulmonary barotrauma.

Adult↗

PubMed1998

Diving pattern and work schedule of construction well divers in Taiwan.

Construction well divers in Taiwan reportedly suffer a high prevalence of dysbaric osteonecrosis. We studied five divers working at the same construction site. We recorded their diving methods, diving depths, bottom times, work patterns, water temperatures, and heart rates. We also monitored gas bubbles in the subclavian vein in selected dives. A crude but effective hot-water system protected divers against hypothermia and allowed them to work in 24 degrees-27 degrees C water. Divers worked approximately 6.6 h a day and progressed approximately 3.0 m a day while excavating an average of 148 buckets of sand and rock each weighing 49.5 kg. The divers sustained a heart rate increase of 49%. Sixty percent of their equivalent single dive bottom times exceeded the U.S. Navy's no-decompression limits. Two cases of venous bubbles were detected, and one of these divers showed symptoms of decompression sickness. The prolonged bottom time and lack of a decompression schedule probably contributed to a risk of decompression sickness and dysbaric osteonecrosis.

Adult↗

PubMed1995

Respiratory and plumage gas volumes in unrestrained diving ducks (Aythya affinis).

Closed-circuit plethysmography and inert gas equilibration analysis were used to measure the volumes of gas in the respiratory system and plumage at the end of voluntary dives in unrestrained lesser scaup (Aythya affinis). Total (respiratory plus plumage) gas volumes were measured by helium dilution and estimated from body mass, body tissue density and buoyant force. These two techniques yielded results that differed by only 2.1 +/- 1.5%. Buoyancy decreased from a maximum of 3.46 +/- 0.16 N at immersion to a minimum of 2.65 +/- 0.16 N at 1.5 m depth at the end of the feeding phase of voluntary dives. At 0.193 +/- 0.013 L BTPS, the respiratory system contributed 52% of the initial buoyancy and 65% of the minimum value. The increasing relative influence of the respiratory system on buoyancy was due to the loss of 47 +/- 5% of the air in the plumage layer during the dive. These data differ significantly from estimates based on restrained ducks, and this has implications for modelling of mechanical costs of diving, oxygen storage capacity and thermal insulation in foraging ducks.

Air↗

PubMed1988

Effect of N2-He-O2 on decompression outcome in rats after variable time-at-depth dives.

No study of decompression sickness has examined both variable gas mixtures and variable time at depth to the point of statistical significance. This investigation examined the effect of N2-He-O2 on decompression outcome in rats after variable time-at-depth dives. Unanesthetized male albino rats were subjected to one of two series of simulated dives: 1) N2-He-O2 dives (20.9% O2) at 175 feet of seawater fsw) and 2) N2-O2 dives (variable percentage of O2; depths from 141 to 207 fsw). Time at depth ranged from 10 to 120 min; rats were then decompressed within 10 s to surface pressure. The probability of decompression sickness (severe bends symptoms or death) was analyzed with a Hill equation model, with parameters for gas potency and equilibrium time for the three gases and weight of the animal. Relative potencies for the three gases were of similar magnitude for bends and statistically different for death in ascending order: O2 less than He less than N2. Estimated gas uptake rates were different. N2 took three to four times as long as He to reach full effect; the rate of O2 appeared to be considerably shorter than that of N2 or He. The large influence of O2 on decompression outcome questions the simplistic view that O2 cannot contribute to the decompression requirement.

Animals↗

PubMed1999

Physiological responses of king penguins during simulated diving to 136 m depth

To evaluate blood N(2) uptake and the role of the respiratory volume (air sacs/lungs) as a N(2) and O(2) reservoir in deep-diving penguins, diving respiratory volume (Vdr), heart rate (fh), venous P(N)(sum), blood volume (V(b)) and hemoglobin (Hb) concentration were measured in king penguins (Aptenodytes patagonicus) during forced submersions and compressions equivalent to depths up to 136 m. Vdr was 69+/-18 ml kg(-)(1) (mean +/- s.d.) in 62 submersions ranging from 4.4 atmospheres absolute (ATA; 1 ATA=101 kPa) (34 m) to 14.6 ATA (136 m). Submersion fh averaged 30+/-7 beats min(-)(1) (N=18), approximately 20 % of pre- and post-submersion values. Venous P(N)(sum) values during and after submersions as deep as 11.2 ATA (102 m) were all less than 2.8 atmospheres N(2) (283 kPa) above ambient pressure, a previously measured threshold for symptomatic bubble formation. Mean V(b) was 83+/-8 ml kg(-)(1) (N=6); [Hb] was 17.6+/-0.7 g dl(-)(1) (N=7). On a mass-specific basis, mean Vdr, and therefore total available N(2), is 41 % of that in shallow-diving penguin species. Total body O(2) stores, calculated from measured Vdr, V(b), [Hb], muscle mass and myoglobin concentration, are 45 ml kg(-)(1), with 23 % in the respiratory system. This small respiratory fraction in comparison with that in shallow-diving penguins suggests a lesser reliance on the respiratory oxygen store for extended breath-holding and also a reduced uptake of nitrogen at depth.

Journal Article↗

PubMed2026

The effect of drysuit diving in warm water on body temperature and post immersion orthostatic hypotension.

INTRODUCTION: Warm-water diving can limit heat dissipation, particularly when performed in fully encapsulating protective gear, leading to substantial thermal and cardiovascular strain that may impair diver safety. Following immersion, removal of hydrostatic support combined with heat-induced vasodilation may reduce central blood volume and increase susceptibility to orthostatic intolerance during egress and recovery. The extent to which this thermal strain impairs post-immersion orthostatic tolerance remains unknown. METHODS: Four randomised, crossover immersion trials were conducted at 28°C, 33°C, 38°C without precooling (38°C), and 38°C with precooling (38°C + Cool), with subjects wearing fully encapsulating dive gear. Subjects walked for up to 60 minutes at approximately 50% of O2max heart rate (HR) or until core temperature (Tc) reached 38.5°C, or they voluntarily stopped. Tc, HR, and perceptual measures were recorded every 10 minutes. Orthostatic tolerance was assessed after immersion via a 70° head-up tilt test. RESULTS: Eight healthy adults completed all aspects of the study. Tc and HR were higher during both 38°C conditions compared with 28°C and 33°C (all P < 0.01) with no differences between 38°C and 38°C + Cool. Sweat loss exceeded 1.2 (SD 0.67) L⋅h-1 in both 38°C conditions compared with ≤ 0.3 (0.32) L⋅h-1 at 28°C and 33°C (P < 0.01). Survival analysis showed orthostatic tolerance decreased with increasing thermal stress (log-rank P = 0.027; trend P = 0.003). Precooling did not reduce peak Tc or HR, nor did it improve tolerance time in 38°C water. CONCLUSIONS: Encapsulated warm-water diving causes heat stress and cardiovascular strain that persists after immersion, impairing orthostatic tolerance. Precooling does not significantly reduce these outcomes.

Humans↗

PubMed2005

Structure and biomechanical properties of the trachea of the striped dolphin Stenella coeruleoalba: evidence for evolutionary adaptations to diving.

This study analyzes the structure and mechanical properties of the trachea of the striped dolphin Stenella coeruleoalba, one of the most common cetacean species. The cetacean trachea is made up of closed or semiclosed cartilaginous rings without a paries membranaceus. Our results indicate that the inner lining of the trachea contains erectile tissue in which several venous lacunae permeate the mucosa. We also observed and described the presence of peripheral neurons containing nitric oxide along the rim of the venous lacunae. Data obtained from compression and tensile tests and comparison with the pig and goat tracheas indicate a higher stiffness and a different, higher breaking point for the dolphin trachea. On the whole, our data suggest that the trachea of the striped dolphin possesses structural properties that allow rapid filling with blood, possibly in relation to dive activities, and also allow modifications due to increased pressure and immediate return to the original shape without risks of permanent bending or rupture, as would happen in a terrestrial mammal. As the organ undergoes intense pressure difference during descent to optimal foraging depth and subsequent rapid ascent to surface, especially in deep dives of hundreds of meters, the specific structural and biomechanical peculiarities of the trachea of the striped dolphin may represent an evolutionary adaptation to life in the water and to diving.

Animals↗

PubMed1975

Some anatomical aspects of the cardiovascular system of Antarctic seals and their possible functional significance in diving.

The hearts and ascending aortae of 11 Weddell seals, Leptonychotes weddelli, three adult Crabeater seals, Lobodon carcinophagus, two adult Ross seals, Ommatophoca rossi, and one adult Leopard seal, Hydrurga leptonyx, were examined for comparison with terrestrial forms. The Weddell seal specimens were from animals ranging in age from midterm in fetal development to mature adults. All specimens were collected in 1971, 1972, and 1973, from McMurdo Sound and the Ross Sea, Antarctica. The phocid hearts were characteristically broader and flatter than those of other carnivore families and they tended toward bifid apices. The heart form indices (height/circumference) averaged 31.5 compared to 39.0 for felids. The right ventricular chambers of the Antarctic seals were found to average longer in Weddells and narrower in all, than those reported for four other carnivore families. An elastic enlargement was present in the ascending aortae of all seals. The largest diameter of the aortic bulb averaged 25.5 mm more than the base of the aorta in the adult Weddell seals which represented an increase of 72.5% over the base. It is suggested that the general heart form, and especially the ascending aortae, are anatomical adaptations to diving. The compressed heart makes possible unimpaired function when the chest is compressed during deep dives. The aortic bulb maintains mean arterial blood pressure and perfusion of the brain and cardiac tissue during diving bradycardia.

Adaptation, Physiological↗

PubMed1996

Effects of water and ambient air temperatures on human diving bradycardia.

Upon apnoeic face immersion, humans develop a diving response resembling that found in diving mammals. There have been contradictory reports regarding the influence of water temperature on the magnitude of the resulting bradycardia. This study examined the influence of both water and ambient air temperatures on human diving bradycardia. A group of 23 volunteers performed three series of apnoeic episodes after 60 min exposure to air at temperatures of 10, 20 or 30 degrees C. Oral and skin temperatures were measured during this exposure and during the subsequent test on 5 subjects. At 20 degrees C air temperature oral and skin temperatures were measured on 10 subjects. Heart rate (HR) was recorded for the 23 subjects during apnoea in air and apnoea with the face immersed in water of 10, 20 or 30 degrees C, at each air temperature. We found that both air and water temperatures had significant effects on immersion bradycardia, but in opposite directions. Face immersion in cold water after exposure to a high ambient air temperature induced the most pronounced bradycardia. We further observed that exposure to different ambient air temperatures resulted in different patterns of HR response to water temperature. The range in which the response was positively correlated to water temperature differed at 30 degrees C ambient air from that at 10 and 20 degrees C ambient air. We concluded from these studies that human bradycardia resulting from apnoeic face immersion is inversely proportional to water temperature within a range which is determined by the ambient air temperature. Thus, the interval in which the response to cold stimulation varies with temperature, would appear to be determined by the ambient temperature before stimulation.

Adult↗

PubMed1986

Effects of CO2 inhalation on acid-base balance and thermal recovery following cold water dives by the muskrat (Ondatra zibethicus).

Thermoregulatory, cardiac, and blood gas responses of muskrats to CO2 inhalation were examined during recovery from controlled dives in 3 degrees C water. It was shown that CO2 levels previously recorded in the winter lodges of this species are sufficient to reduce postdive oxygen consumption and rate of rewarming in unrestrained animals. Postdive exposure to 5-10% CO2 reduced recovery of abdominal and subcutaneous temperature (Tb) in the middorsal lumbar region, but did not affect interscapular warming overlying brown adipose tissue. Depressed recovery of deep Tb was matched by a prolonged acidosis in restrained muskrats breathing 5-10% CO2 following 90-s submergence in 3 degrees C water. This occurred despite a comparatively high whole body buffer value (delta H+/delta PaCO2) of 0.53 nM X l-1 X mmHg-1. Protracted recovery of arterial pH did not appear to involve retention of CO2 accumulated during diving, since in all trials, PaCO2 returned to the predive baseline within 5 min of surfacing. Perturbations in PaO2, like PaCO2, were restored within 5 min of surfacing, irrespective of inspired gas mixture. Predive exposure to 5-10% CO2 had no discernible effect on establishment of bradycardia in diving muskrats. Compared to predive values, postimmersion heart rate was significantly reduced in 5-10% CO2, but not in control runs.

Acid-Base Equilibrium↗

PubMed1989

Electrocardiographic aspects of skin diving.

Electrocardiographic (ECG) aspects of skin diving were monitored by means of continuous ECG recording in a pool 15 m deep. Ten regularly trained divers with different levels of experience divid a minimum of three consecutive times, holding their beath, reaching depths of 6 m, 9 m, and 12 or 15 m. The water temperature was 28 degrees C. During the ascending part of these dives, bradycardia was observed in all skin-divers. Minimal heart rate correlated negatively with the diver's experience (number of dives previously performed). In six divers cardiac arrhythmia was observed. Atrial arrhythmias were sometimes isolated occurrences, but more frequently they were multiple. Ventricular arrhythmias tended to be bigeminal. Apparently, forced expiration through the snorkel when surfacing precipitated these rhythmic disorders.

Adult↗

PubMedDate not supplied

Mechanism of the human diving response.

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

Cardiovascular Physiological Phenomena↗

PubMed2001

The development of diving in marine endotherms: preparing the skeletal muscles of dolphins, penguins, and seals for activity during submergence.

Myoglobin is an important oxygen store for supporting aerobic diving in endotherms, yet little is known about its role during postnatal development. Therefore, we compared the postnatal development of myoglobin in marine endotherms that develop at sea (cetaceans) to those that develop on land (penguins and pinnipeds). We measured myoglobin concentrations in the major locomotor muscles of mature and immature bottlenose dolphins (Tursiops truncatus) and king penguins (Aptenodytes patagonicus) and compared the data to previously reported values for northern elephant seals (Mirounga angustirostris). Neonatal dolphins, penguins, and seals lack the myoglobin concentrations required for prolonged dive durations, having 10%, 9%, and 31% of adult values, respectively. Myoglobin contents increased significantly during subsequent development. The increases in myoglobin content with age may correspond to increases in activity levels, thermal demands, and time spent in apnea during swimming and diving. Across these phylogenetically diverse taxa (cetaceans, penguins, and pinnipeds), the final stage of postnatal development of myoglobin occurs during the initiation of independent foraging, regardless of whether development takes place at sea or on land.

Age Factors↗

PubMed1997

Blood flow in the carotid artery during breath-holding in relation to diving bradycardia.

The present study investigated the mechanism of diving bradycardia. A group of 14 healthy untrained male subjects were examined during breath-holding either out of the water (30-33 degrees C), in heat-out immersion, or in whole-body submersion (27-29 degrees C) in a diving pool. Blood velocity, blood volume flow in the carotid artery, diastolic blood pressure and electrocardiogram were measured and recorded during the experiments. The peak blood velocity increased by 13.6% (P < 0.01) and R-wave amplitude increased by 57.1% (P < 0.005) when the subjects entered water from air. End-diastolic blood velocity (Ved) in the carotid artery increased significantly during breath-holding, e.g. Ved increased from 0.20 (SD 0.02) m.s-1 at rest to 0.33 (SD 0.04) m.s-1 (P < 0.001) at 50.0 s in breath-hold submersion to a 2.0-m depth. Blood volume flow in the carotid artery increased by 26.6% (P < 0.05) at 30 s and 36.6% (P < 0.001) at 40 s in breath-hold submersion to a 2.0-m depth. Diastolic blood pressure increased by 15.4% (P < 0.01) at 60 s during breath-holding in head-out immersion. Blood volume flow, Ved and diastolic blood pressure increased significantly more and faster during breath-holding in submersion than out of the water. There was a good negative correlation with the heart rate: the root mean square correlation coefficient r was 0.73 (P < 0.001). It was concluded that an increased accumulation of blood in the aorta and arteries at end-diastole and decreased venous return, caused by an increase in systemic peripheral resistance during breath-holding, underlies diving bradycardia.

Adult↗

PubMed1990

Diving injuries of the cervical spine.

From 1975 to 1986, 2435 patients were admitted to the Northwestern University-Midwest Regional Spinal Cord Injury Unit. Of these, 220 patients (9.0%) had documented neck fractures from diving accidents, representing the largest series of acute diving injuries yet analyzed. The average age of these patients was 21 years, and males predominated. Two hundred twelve patients (96.4%) were admitted within 48 hours of injury. Associated injuries were rare: none had intracranial mass lesions or systemic injuries, and only nine were near-drowning victims who required endotracheal intubation. The most common levels of injury were C-5 (140 fractures) and C-6 (85 fractures), with 70 patients having fractures at more than one level. Neurological injury was sustained in 154 (70.0%) patients, while 66 (30.0%) patients were neurologically intact. One hundred forty-seven (66.8%) patients underwent posterior cervical fusion, and anterior fusion was performed in 36 (16.4%), allowing for early ambulation and an average hospital stay of 17 days. Hospitalization was relatively uncomplicated, with urinary tract infection in 121 (55.0%), pneumonia in nine (4.1%), and deep vein thrombosis in 24 (10.9%). Long-term follow up averaged 5 years and was obtained in 160 (72.7%) patients. Sixteen (10.0%) improved neurologically, five (3.1%) deteriorated, and 139 (86.9%) were unchanged. Notably, this large study shows that diving accidents occur in a young, healthy population who sustain essentially no other associated intracranial or systemic injuries and have few serious hospital complications. Such patients may be mobilized early in their care after either internal or external stabilization. Subsequent long-term neurological improvement can be expected to occur in about 10% of patients. The importance of water safety and injury prevention is stressed.

Adolescent↗