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At least 19 recordsLinked to original sources
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↗
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↗
PubMed1976

The effect of hypercapnia on respiratory characteristics and diving behaviour of freely diving seals.

Three trained young seals, one harp seal, Pagophilus groenlandicus, and two hooded seals, Cystophora cristata, have been used to study the effect of hypercapnia on respiratory characteristics and diving behaviour. The seals were allowed free movements within a circular pool, while diving and respiratory behaviour were recorded. During the experiments the alveolar CO2 tension was continually recorded. There was a significant decrease in duration of dives with increasing Paco2 for all animals. Ve increased significantly with increasing Paco2. This increase was caused by more frequent surfacing rather than by a higher respiratory frequency during the breathing periods. Tidal volume increased from 3 to 43% when inspired CO2 was increased from 0.03 to 9 vol%. The seals were all found to be less sensitive to CO2 than man. A decreased sensitivity to CO2 with age is suggested from the results.

Age Factors↗
PubMed1977

Shallow habitat air dives I and II: human hematologic responses to compressed air saturation diving.

Two subjects each were exposed to pressure equivalents of 50 (SHAD I) and 60 (SHAD II) feet of sea water gauge (FSWG) for 30 and 28 d, respectively. Red blood cell (RBC) count, hemoglobin (Hb) content, and reticulocyte count of venous blood from divers were measured before, during, and after these exposures. RBC count of the divers decreased a maximum of 7.1% in the 50-ft dive and 10.7% in the 60-ft dive compared to surface control values. Hb content fell 7.7% and 11.1% in the 50- and 60-ft dives, respectively, when compared to nondiving subjects. Reticulocyte counts tended to increase late in the pressurization phase and during the recovery. The total month-long responses of Hgb in SHAD I, and RBC, Hgb, and reticulocyte count in SHAD II were significantly altered when compared to those of the surface control subjects. The changes in these factors were directly attributable to the month-long exposure to the total hyperbaric environment. The threshold for hematological effects of chronic exposure to compressed air would seem to lie between 50 and 60 FSWG.

Air↗
PubMedDate not supplied

Daily diving pattern of Korean and Japanese breath-hold divers (ama).

Daily diving patterns and thoracic skin and sea-water temperatures were recorded during the entire work shift of Korean female unassisted (cachido) and Japanese male unassisted and partly assisted (funado) divers using Underwater Physiological Data Loggers developed in Buffalo and Japan. All 3 groups of divers were studied during the summer of 1989 and 1990. Additional studies were conducted during the winter of 1991 on Korean female divers who, unlike Japanese divers, dive all year round. The water temperature of the diving grounds in summer was 24 degrees C in both Korea and Japan, and 10 degrees C during winter in Korea. Both Korean female and Japanese male cachido divers made 113-138 dives a day and stayed in the water a total of 170-200 min.day-1, of which only 52-63 min were spent diving submerged, and the remaining time at the water surface. These diving patterns were not different between female and male cachido divers. Compared with Japanese male divers, Korean female divers dived to a shallower depth (3.7 vs. 6.9 m) with shorter dive time (29 vs. 37 s) and shorter bottom time (14 vs. 18 s). Velocities of descent (0.72 vs. 0.47 m.s-1) and ascent (0.77 vs. 0.56 m.s-1) were also slower in female divers than in male divers. The diving pattern of Korean female divers was similar in both summer and winter. Although all cachido divers wore wet suits and thus were protected from severe cold stress, thoracic skin temperature decreased during a work shift by 7 degrees C in winter (vs. 1 degree C in summer) in Korean divers. Compared with Japanese male cachido divers, Japanese male funado divers stayed in the diving ground (including time in the boat) longer (201 vs. 305 min.day-1) but performed only 23 dives per day. The average diving depth (9.7 m), duration (69 s), and bottom time for each dive (45 s), however, were significantly greater in funados. The velocity of vertical descent (1.0 m.s-1) was also significantly greater in funados because they descend with a weight (8-12 kg). The rate of ascent was not different.

Body Temperature↗
PubMed1992

Cardiovascular responses elicited by simulated diving and their habituation in man.

The cardiovascular responses of 24 subjects were investigated under various simulated diving conditions. Muscle blood flow in forearm and calf, arterial pressure, heart rate and intrathoracic pressure were monitored. Breath holding with face immersion in water at 18 degrees C gave a typical diving response at intrathoracic pressure of 0 and 20 mmHg, (23% bradycardia, greater than 60% muscle vasoconstriction). Breath holding alone at 20 mmHg intrathoracic pressure resulted in vasoconstriction (50%) and bradycardia (4%). Breath holding at 0 mmHg intrathoracic pressure induced a muscle vasoconstriction (5%). These results indicate that both increased intrathoracic pressure and facial immersion can produce a typical diving response individually but that the full 'diving response' requires the presence of both conditions. Diving often activated two responses, the typical 'diving response' and a superimposed defence reaction. Cardiovascular components of the defence reaction (muscle vasodilatation and tachycardia) which was elicited in some divers masked the diving response. In those subjects in whom the diving response was initially absent during repetition of diving manoeuvres the cardiovascular components of the defence reaction were habituated and the characteristic diving response gradually emerged: the initial tachycardia diminished and was replaced by bradycardia, while vasodilatation in the forearm and calf was replaced by vasoconstriction.

Adolescent↗
PubMed1991

High altitude dives from 7000 to 14,200 feet in the Himalayas.

Indian Navy divers carried out no-decompression dives at altitudes of 7000 to 14,200 ft (2134-4328 m) in the Nilgiris and Himalayas from May to July 1988. Seventy-eight dives on air and 22 dives on oxygen were carried out at various altitudes. The final dives were at Lake Pangong Tso (4328 m) in Ladakh, Himalayas, to a maximum of 140 feet of sea water (fsw) [42.6 meters of sea water (msw)] equivalent ocean depth in minimum water temperature of 2 degrees C. Oxygen diving at 14,200 ft (4328 m) was not successful. Aspects considered were altitude adaptation, diminished air pressure diving, hypothermia, and remote area survival. Depths at altitude were converted to depths at sea level and were applied to the Royal Navy air tables. Altitude-related manifestations, hypoxia, hypothermia, suspected oxygen toxicity, and equipment failure were observed. It is concluded that stress is due to effects of altitude and cold on man and equipment, as well as changes in diving procedures when diving at high altitudes. Equivalent air depths when applied to Royal Navy tables could be considered a safe method for diving at altitudes.

Acclimatization↗
PubMed1975

Bradycardia during human diving.

The bradycardial response to the diving reflex, which occurs in man and in diving animals, is thought to be a physiologically protective oxygen-conserving mechanism whereby the animal is kept alive during submergence. The physiology and nervous pathways are not yet fully understood, but several investigators have pointed out the potentially fatal outcome of an accentuated diving reflex. the CO2 content of the peripheral venous blood has been proved variable and unpredictable during the hyperventilation-breath-hold dive cycle in man. A group of 8 male divers (average age 34 years) was investigated during breathhold dives to 3,3 m in a swimming pool. Heart rates were recorded and compared at various stages during breath-hold and SCUBA (self-contained underwater breathing apparatus) dives, viz. when resting on the surface, breath-holding, hyperventilating and swimming underwater. Two divers performed extreme breathhold endurance tests lasting 135 seconds underwater. All divers had a tachycardia after hyperventilation and a bradycardia after breathhold diving, lasting 80-100 seconds. Extrasystoles were recorded during some of the breathhold dives. Prolonged submergence caused extreme bradycardia (24/min) with central cyanosis. Bradycardia during diving may be a physiological )2-conserving reflex or the start of a pathophysiological asphyxial response.

Adult↗
PubMed1977

Converting standard air decompression tables for no-stop diving from altitude or habitat.

Using the phase equilibration theory of Hills (1966), as modified by Hennessy and Hempleman (1977), it is possible to predict formulas for converting standard air decompression tables for no-stop diving at altitude or from a normoxic habitat, breathing air. For diving following equilibration at altitude, the Royal Navy, Royal Naval Physiological Laboratory, and Haldane-type rules appear to be too conservative, with the opposite result for diving after excursion to altitude. Predictions in the latter case are in fair agreement with the Swiss (Boni, Schibli, Nussberger, and Bühlmann 1976) no-stop altitude tables. In the case of habitats, close agreement is found between the Hamilton, Kenyon, Freitag, and Schreiner (1973) normoxic tables for no-stop downward excursions and indefinite dive upward-excursions on air. In the case of flying directly after no-stop diving, the US Navy rule of using repetitive group D appears to be conservative for dives less than 50 fsw, and possibly unsafe for dives over 50 fsw. It is concluded that for no-stop diving a single tissue and single safe ascent pressure formula are all that is necessary to generate equivalent air dives. This enforces the hypothesis that it is the volume of gas released on ascent that governs marginal type I bends, and that in a no-stop ascent, all excess dissolved gas is released in the worst case.

Aerospace Medicine↗
PubMed1975

Gas transport and blood acid-base balance in diving sea snakes.

The values of hemoglobin concentration, Hb-O2 affinity and buffering capacity of the blood of six sea snake species considerably overlap values from terrestrial squamates. Decreased blood pH had little effect on the P50 but increased the n-value of Hb-O2 equilibrium curves. The O2 saturation of blood in the dorsal aorta varied between about 30 and 70% during voluntary diving in Acalyptophis peronii and Lapemis hardwickii. Voluntary dives ended when the lung PP02 was about 50 mm Hg and the arterial PO2 about 30 mm Hg indicating that roughly half of the O2 reserves had been used. In conjunction with relatively stable blood lactate concentration and pH, this indicates that voluntary dives occurred largely aerobically. In contrast, forced dives resulted in depletion of O2 reserves and large changes in blood acid-base balance. Long recovery periods following forced dives are inconsistent with field observations and thus suggest that extensive anaerobic metabolism does not normally occur in sea snakes. Bradycardia was not evident during forced dives. Large differences in PO2 between the lung and dorsal aorta indicated considerable right to left shunting either in the heart or in the lung. Venous blood represented over 50% of the systemic flow when there was considerable O2 in the lung. Therefore blood PO2 may remain relatively low despite elevated lung PO2 resulting from diving. In view of substantial capability for extra-pulmonary gas exchange, high shunting reduces the possibility of losing O2 through the skin and also may help prevent decompression sickness following deep dives.

Acid-Base Equilibrium↗
PubMed1977

Acute otitis externa in divers working in the North Sea: a microbiological survey of seven saturation dives.

Saturation diving is an important and widely used technique in the Offshore Oil Industry. During 1974-5 two saturation dives in the North Sea were terminated because of outbreaks of incapacitating otitis externa, and others were disrupted. Pseudomonas aeruginosa was consistently isolated from the ears of affected divers. Because complex work schedules were threatened seven subsequent dives were subjected to microbiological monitoring and control. Colonization of ear canal with P. aeruginosa or with other gram-negative bacilli occurred in 39 (67%) of the 58 divers studied, usually within 7 days of starting the dive. Data obtained by serotyping this isolations of P. aeruginosa suggested that a single infected diver may be the source of organisms which rapidly spread to his colleagues and throughout the living chambers, that the living chambers may constitute a reservoir of infection during and between dives, and that certain serotypes of P. aeruginosa are more likely than others to colonize the ear canal in the conditions of a saturation dive. The control measures used during the dives were only partially effective, but none of the divers suffered severe pain and all the dives were an operational success.

Corynebacterium↗
PubMed2026

Adaptations to breath-hold diving: from traditional divers to elite athletes.

Breath-hold diving exposes humans to repeated episodes of profound hypoxia and hypercapnia, eliciting physiological adaptations that enable prolonged underwater performance. This article summarises current knowledge on chronic adaptations in elite breath-hold athletes and traditional diving populations, including the Bajau sea nomads of Southeast Asia and the Korean Haenyeo divers. Evidence indicates that repeated apnoea induces adaptations across multiple physiological systems. Haematological changes include increased spleen size and enhanced splenic contraction, augmenting circulating haemoglobin and oxygen stores during apnoea. In elite divers, structured training can increase resting spleen volume, whereas the Bajau exhibit genetically associated splenic enlargement linked to variants near the PDE10A gene. Cardiopulmonary adaptations include modified pulmonary vascular responses to hypoxia, improved oxygen conservation, and metabolic shifts favoring efficient mitochondrial energy production. Molecular adaptations involve enhanced antioxidant defenses and activation of hypoxia-responsive pathways that may mitigate oxidative stress associated with repeated hypoxia-reoxygenation cycles. Emerging evidence also suggests neural plasticity and possible structural brain adaptations, although the long-term neurological consequences of chronic intermittent hypoxia exposure remain uncertain. Studies of traditional diving populations indicate that both phenotypic plasticity and genetic selection contribute to diving capacity, highlighting interactions between training and evolution. Despite these benefits, breath-hold diving also carries risks, including hypoxic blackout, decompression sickness, and potential neurological injury. Understanding the mechanisms underlying human tolerance to extreme hypoxia may have implications beyond diving physiology, including applications in cardiovascular medicine, hypoxic diseases, and rehabilitation. Further longitudinal, genomic, and mechanistic studies are needed to clarify the limits, benefits, and clinical relevance of these adaptations.

Humans↗
PubMed1991

Impedance measurement in divers during a scuba-diving training programme.

An assessment of the strain on the tympanic membrane caused by diving was performed using impedance measurement of the middle ear in 21 untrained young men going through a scuba-diving training programme (scuba, self-contained under-water breathing apparatus). Tympanometry was carried out just before and after diving. The divers made 104 dives between them (median 5 each, range 2-7) at depths from 2 to 12 m (median 6 m). The results showed a significant increase in middle ear compliance on diving. The increase in compliance was significant at different depths, was transient, and fell to the initial level between the dives. We conclude that the strain exerted on the tympanic membrane and middle ear from barotrauma due to diving results in a reversible impairment of the recoiling capacity of the elastic fibrils of the tympanic membrane. This transient increase in compliance, we think, is the first measurable change in elasticity of the tympanic membrane. If barotrauma continue the changes could be irreversible.

Acoustic Impedance Tests↗
PubMed1992

Baroreflex control of arterial blood pressure during involuntary diving in ducks (Anas platyrhynchos var.).

The dynamic role of arterial baroreceptors in control of mean arterial blood pressure (MAP), heart rate (HR), cardiac output (CO), hindlimb vascular (HLVR) and total peripheral (TPR) resistance responses to forced dives was investigated in acutely and chronically barodenervated ducks. To activate the baroreflex, the proximal end of one aortic nerve was stimulated electrically with bipolar electrodes that had been implanted under pentobarbital sodium anesthesia. Predive nerve stimulation caused CO to fall (by reducing HR; stroke volume remained constant), producing a decrease in MAP to half the prestimulation level. During diving (for 2.5-min periods) nerve stimulation did not affect HR and MAP after the first minute of submersion. Neither HLVR nor TPR contributed to the fall in MAP during aortic nerve stimulation before or during diving. The effects of nerve stimulation on HR and MAP were maintained to the end of dives in animals given 100% O2 to breathe before diving. In separate experiments, increasing arterial chemoreceptor input by perfusing one vascularly isolated carotid body with venous blood caused a reduction in the effects of aortic nerve stimulation on MAP. Arterial baroreceptors may thus act on HR to alter MAP early in the dive, but as the dive progresses the baroreflex is attenuated by an increase in peripheral chemoreceptor drive.

Animals↗
PubMedDate not supplied

Diving injuries to the inner ear.

Most of the previous literature concerning otologic problems in compressed gas environments has emphasized middle ear barotrauma. With recent increases in commercial, military, and sport diving to deeper depths, inner ear disturbances during these exposures have been noted more frequently. Studies of inner ear physiology and pathology during diving indicate that the causes and treatment of these problems differ depending upon the phase and type of diving. Humans exposed to simulated depths of up to 305 meters without barotrauma or decompression sickness develop transient, conductive hearing losses with no audiometric evidence of cochlear dysfunction. Transient vertigo and nystagmus during diving have been noted with caloric stimulation, resulting from the unequal entry of cold water into the external auditory canals, and with asymmetric middle ear pressure equilibration during ascent and descent (alternobaric vertigo). Equilibrium disturbances noted with nitrogen narcosis, oxygen toxicity, hypercarbia, or hypoxia appear primarily related to the effects of these conditions upon the central nervous system and not to specific vestibular end-organ dysfunction. Compression of humans in helium-oxygen at depths greater than 152.4 meters results in transient symptoms of tremor, dizziness, and nausea plus decrements in postural equilibrium and psychomotor performance, the high pressure nervous syndrome. Vestibular function studies during these conditions indicate that these problems are due to central dysfunction and not to vestibular end-organ dysfunction. Persistent inner ear injuries have been noted during several phases of diving: 1) Such injuries during compression (inner ear barotrauma) have been related to round window ruptures occurring with straining, or a Valsalva's maneuver during inadequate middle ear pressure equilibration. Divers who develop cochlear and/or vestibular symptoms during shallow diving in which decompression sickness is unlikely or during compression in deeper diving, should be placed on bed rest with head elevation and avoidance of maneuvers which result in increased cerebrospinal fluid and intralabyrinthine pressure. With no improvement in symptoms after 48 hours, exploratory tympanotomy and repair of a possible labyrinthine window fistula should be considered. Recompression therapy is contraindicated in these cases...

Action Potentials↗
PubMed1975

Factors in 171 navy diving decompression accidents occurring between 1960-1969.

Comparisons were made between the incidence of specific factors in U.S. Navy decompression accidents and the incidence of these factors in routine (nonexperimental) U.S. Navy operational dives. It was found that decompression accidents are disproportionately high among a) air dives less than 140 ft which have bottom times of 30 min or less and air dives greater than 140 ft which have bottom times of more than 15 min, b) Divers First Class, c) older divers, and d) dives which do not involve work or divers which require heavy work. Repetitive dives have a lower decompression accident rate than expected. Decompression accidents were not disproportionately high for any category of body build. These results indicate that the present U.S. Navy decompression tables are extremely safe (5 decompression accidents/10,000 dives), and do not appear to require modification. Future decompression research may be directed toward analyzing the relationship of work and aging to physiological processes involved in decompression. In addition, the present findings should be cross-validated using more recent accident and operational diving data.

Accidents↗
PubMed1991

The effect of microinjection of amino acids into the nucleus tractus solitarius on the diving bradycardia in the rat.

The role of nucleus tractus solitarius (NTS) in the diving bradycardia was studied in anesthetized rats. The floor of the 4th ventricle of the medulla was exposed and 0.1 microliters of the test agent was injected into NTS bilaterally. The simulated diving (head immersion) for 30 sec was performed before and after the injection. Blood pressure and heart rate were monitored. Before the treatment, heart rate decreased by 51% and blood pressure rose by 23% during the diving in the pooled data (n = 35). Injection of glutamate (0.1-1 mM) or CaCl2 (100 mM) into NTS attenuated the diving bradycardia, but that of GABA (0.1 mM), glycine (0.1 mM), KCl (100 mM) or saline solution did not affect the diving bradycardia significantly. Lesions of NTS also attenuated the diving bradycardia. These data suggest that NTS may play a role in modulation of the diving response.

Amino Acids↗