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At least 19 recordsLinked to original sources
PubMed1990

Splenic contraction during breath-hold diving in the Korean ama.

Major increases of hemoglobin concentration and hematocrit, possibly secondary to splenic contraction, have been noted during diving in the Weddell seal. We sought to learn whether this component of the diving response could be present in professional human breath-hold divers. Splenic size was measured ultrasonically before and after repetitive breath-hold dives to approximately 6-m depth in ten Korean ama (diving women) and in three Japanese male divers who did not routinely practice breath-hold diving. Venous hemoglobin concentration and hematocrit were measured in nine of the ama and all Japanese divers. In the ama, splenic length and width were reduced after diving (P = 0.0007 and 0.0005, respectively) and calculated splenic volume decreased 19.5 +/- 8.7% (mean +/- SD, P = 0.0002). Hemoglobin concentration and hematocrit increased 9.5 +/- 5.9% (P = 0.0009) and 10.5 +/- 4% (P = 0.0001), respectively. In Japanese male divers, splenic size and hematocrit were unaffected by repetitive breath-hold diving and hemoglobin concentration increased only slightly over baseline (3.0 +/- 0.6%, P = 0.0198). Splenic contraction and increased hematocrit occur during breath-hold diving in the Korean ama.

Adult↗
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

Electrocardiogram during deep breath-hold dives by elite divers.

A portable ECG recorder was used during breath-hold dives at sea by 3 elite divers to 65 and 45 m. ECG was also recorded during nonimmersed maximal breath holds in the divers and 8 control subjects. Heart rate in the dives decreased rapidly to 20-24 beats.min(-1). During the surface experiments in the divers, bradycardia was much slower in onset, reaching 28-36 beats.min(-1) at the end of the breath holds. The divers showed a more consistent bradycardial response than the controls. The difference in temporal pattern of bradycardia, in the dives and in the breath holds by the divers, may have been due to face immersion in cold water, chest compression, and/or redistribution of blood into the chest with concomitant stimulation of cardiac and other mechanoreceptors. Arrhythmias, mostly supraventricular and ventricular premature complexes, were observed coincidently with the lowest heart rates, presumably reflecting a high vagal tone. In addition, cardiac distention at depth might have made the heart more prone to arrhythmias, while in the surface breath holds hypoxia might have accounted for a similar effect.

Adult↗
PubMed1991

Alveolar gas composition and exchange during deep breath-hold diving and dry breath holds in elite divers.

End tidal O2 and CO2 (PETCO2) pressures, expired volume, blood lactate concentration ([Lab]), and arterial blood O2 saturation [dry breath holds (BHs) only] were assessed in three elite breath-hold divers (ED) before and after deep dives and BH and in nine control subjects (C; BH only). After the dives (depth 40-70 m, duration 88-151 s), end-tidal O2 pressure decreased from approximately 140 Torr to a minimum of 30.6 Torr, PETCO2 increased from approximately 25 Torr to a maximum of 47.0 Torr, and expired volume (BTPS) ranged from 1.32 to 2.86 liters. Pulmonary O2 exchange was 455-1,006 ml. CO2 output approached zero. [Lab] increased from approximately 1.2 mM to at most 6.46 mM. Estimated power output during dives was 513-929 ml O2/min, i.e. approximately 20-30% of maximal O2 consumption. During BH, alveolar PO2 decreased from approximately 130 to less than 30 Torr in ED and from 125 to 45 Torr in C. PETCO2 increased from approximately 30 to approximately 50 Torr in both ED and C. Contrary to C, pulmonary O2 exchange in ED was less than resting O2 consumption, whereas CO2 output approached zero in both groups. [Lab] was unchanged. Arterial blood O2 saturation decreased more in ED than in C. ED are characterized by increased anaerobic metabolism likely due to the existence of a diving reflex.

Adult↗
PubMed1992

Nitrogen tensions in brachial vein blood of Korean ama divers.

Intravascular bubble formation and symptoms of decompression sickness have been reported during repetitive deep breath-hold diving. Therefore we examined the pattern of blood N2 kinetics during and after repetitive breath-hold diving. To study muscle N2 uptake and release, we measured brachial venous N2 partial pressure (PN2) in nine professional Korean breath-hold divers (ama) during a 3-h diving shift at approximately 4 m seawater depth and up to 4 h after diving. PN2 was determined with the manometric Van Slyke method. Diving time and depth were recorded using a backpack computer-assisted dive longer that allowed calculating the surface-to-depth time ratio to derive the effective depth. With the assumption that forearm muscle N2 kinetics follow the general Haldanian principles of compression and decompression, i.e., forearm muscle is a single compartment with a uniform tissue PN2 equal to venous PN2, PN2 data were fitted to monoexponential functions of time. In the early phase of the diving shift, PN2 rapidly increased to 640 Torr (half time = 6 min) and then slowly declined to baseline levels (half time = 36 min) after the work shift. Peak PN2 levels approximated the alveolar PN2 derived from the effective depth. We conclude that forearm muscle N2 kinetics are well described by a Haldanian single-compartment model. Decompression sickness is theoretically possible in the ama; it did not occur because the absolute PN2 remained low due to the shallow working depth of the ama we studied.

Diving↗
PubMed1976

Succinate accumulation in man during exercise.

It has been demonstrated in several diving vertebrates that succinate, a component of the Krebs cycle, accumulates in blood during breath-hold dives. The production of succinate is thought to result from amino acid catabolism. Our purpose was to determine whether succinate accumulation occurs in man during muscular activity requiring anaerobic energy contribution. Experiments using an endurance athlete included apneic work on an underwater ergometer and treadmill running to exhaustion. During 1 min breath-hold "dives" in cold water while exercising at a work rate equivalent to 62% of VO2max, venous succinate increased from 42 mumoles/l (M X 10(-6)) at rest to 125 M X 10(-6). The treadmill run elicited VO2max and increased succinate from a similar resting value to 93 M X 10(-6). Increases in alanine, lactate, and pyruvate were observed for both types of exercise. The findings confirm that succinate accumulation also occurs in man. It was suggested that amino acid catabolism may provide a source of anaerobic energy production in addition to glycolysis. However, the importance of the proposed energy pathway remains to be quantified.

Adult↗
PubMed1989

Mechanism of tolerance to renal ischemia in harbor seal: role of membranes.

Many diving animals are capable of engaging in long breath-hold dives. Investigations were undertaken to compare the active tubular transport of organic ions between kidney slices from harbor seals (Phoca vitulina) and rats (control) under anoxia or low pH or both. Para-aminohippurate (PAH) and tetraethylammonium (TEA) were used as a representative organic anion and cation, respectively. The slice-to-medium concentration ratios (S:M) of PAH (congruent to 2.5) in the harbor seal was not altered (unlike in the rat) after 60 min of incubation in a nitrogen atmosphere but was reduced to congruent to 1.0 in the presence of 10(-4) M 2,4-dinitrophenol. Subsequent studies also demonstrated that PAH uptake in the harbor seal was not influenced by pH of the incubation medium over a range of 6.0 to 7.4. In contrast, PAH uptake was very sensitive to the medium pH in the rat, decreasing significantly with reduction in pH. Although the TEA uptake decreased in anoxia in both species, it decreased considerably less in the harbor seal than in the rat (40 vs. 70%). However, TEA uptake decreased significantly at low pH in both species. The magnitudes of increase in intracellular Na and of decrease in intracellular K in anoxia were consistently less in the harbor seal than in the rat, especially at low pH. On the basis of these and other findings reported in the literature, cellular mechanisms for the remarkable ischemic tolerance of the seal kidney are discussed.

Animals↗
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↗
PubMed1979

Periodic breathing in the crocodile, Crocodylus niloticus: consequences for the gas exchange ratio and control of breathing.

The ventilatory pattern in the Nile crocodile consists of episodes of breathing, interrupted by periods of breath-holding, the latter occupying 80% of total time during normal breathing at 25 degrees C. End-tidal gas composition varied with the periodic breathing but PO2 was always high (PO2 less than 110 torr) and PCO2 low (PCO2 less than 25 torr). The alveolar gas exchange ratio, RE, was very low during the non-ventilatory periods (RE congruent to 0.5), but increased markedly during ventilation. Breathing of hypoxic and hpercapnic gases caused a pronounced decrease in the duration of breath-holds. Hypercapnia decreased breathing frequency during ventilatory periods, but increased tidal volume. The results are discussed in relation to the practice of prolonged breath-holding associated with diving in crocodiles.

Alligators and Crocodiles↗
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↗
PubMed1976

South African underwater diving accidents, 1969-1976.

Since 1969 a survey of diving accidents involving South African amateur divers was undertaken. The South African Underwater Union diving accident report form was used, and various State agents (SA Police and inquest courts) and individual divers and club instructors were questioned. This survey covers the period up to the end of June 1976. Data acquired during the 8-year period 1969 - 1976 are compared. A conservative estimate from the number of certificates issued to club divers indicates a 25% increase in diver population, while the number of fatilities has decreased from 0,1% in 1971 to 0,016% in 1976, indicating the importance of accident reporting in determining safety trends. In general, a change in pattern is observed during the last 4 years, showing more SCUBA than breath-hold fatalities. The formation of the Decompression Sickness and Diving Accidents Investigation Panel as a further measure to decrease fatal diving accidents is discussed.

Accidents↗
PubMedDate not supplied

[Inner ear injuries in breath-holding divers].

Five breath-hold divers with inner ear barotrauma due to the diving to 10 meters of depth have been treated at the Department of Otorhinolaryngology, Pula Medical Centre during 1990. Because of eustachian tube dysfunction, a negative middle ear pressure is transmitted into the inner ear over the round and oval window causing a lower hydrostatic pressure of the inner ear fluids and consequent delay in microcirculation of the inner auditory artery. Together with a hypoxia in apnea the oxygen demand is increased and the inner ear neuroepithelium damage is more severe. All treated divers had irreversible sensorineural hearing loss of the attacked ear on frequency range higher than 2000 Hz to 70-80 dB.

Adult↗
PubMed1991

[The usefulness of diving reflex--the effect on PSVT].

We attempted to use the diving reflex to treat PSVT in five patients, in whom carotid-sinus massage had failed to terminate, PSVT. In three cases PSVT converted to normal sinus rhythm. The patient was seated comfortably, and a pan of ice and water (4 degrees C) was placed on the table in front of the patient. He then took a deep breath and, without expiration, submerged his face in the cold ice and water for about 30 seconds. In case 1, a 68-year-old male, PSVT stopped after facial immersion of 11 seconds. Subsequently, sinus arrest with junctional or ventricular contractions continued for 7 seconds followed by conversion to the sinus rhythm. The duration of facial immersion was 18 seconds. In case 2, a 51-year-old male, PSVT converted to the sinus rhythm in the same way. The duration of facial immersion was 23 seconds. Case 3 was a 27-year-old female with WPW syndrome. PSVT converted to the sinus rhythm after a 6.6 seconds facial immersion. Case 4 and 5 were respectively 72 and 73-year-old males, whose attacks did not respond to the diving reflex for the reason that they could not maintain breath-holding for a sufficient time to activate the reflex adequately. We postulated that apnea might effect the termination of PSVT in case 1 and 2 because relatively long duration of about 20 seconds was necessary to convert PSVT to the sinus rhythm. On the other hand, in case 3, cold water stimulation on the face might play an important role because PSVT converted to the sinus rhythm immediately.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Facial cold receptors and the survival reflex "diving bradycardia" in man.

We measured heart rate (HR), stroke volume (SV), systemic arterial blood pressure (BP), and mean arterial pressure (MAP) in 7 healthy volunteers in response to face immersion in water with concomitant breath-holding at different lung volumes. The subjects were at rest in the prone position. During breath-holding at total lung capacity (TLC), baseline HR (70 to 75 beats/min) fell by 10% within fractions of a second, both in the control preimmersion state when the head was surrounded by room air, and when it was immersed in water of 33 degrees C. This response was associated with rises in MAP and in SV. Immersion of the face in 10 degrees C water while breath-holding, was associated with a strong, negative chronotropic effect (22% fall in HR), which developed within 10 s. Breath-holding at functional residual capacity (FRC) reduced HR substantially only in 10 degrees C water, and in contrast to that at TLC, the response was slowly developing with a latency of 10-15 s. All these reductions in HR were significant and accompanied by increases in BP and MAP. The strong, negative chronotropic effect of cold water was typically linked to a rise in SV. The study identified two temporal components of HR reduction to face immersion: a fast parasympathetic response dependent on the input from the high pressure baroreceptors, and a late response mediated, in all likelihood, by sympathetic efferent activity. Facial receptors sensitive to cold seem to be vital in the largest responses observed. The fast response to breath-holding with the face in water of neutral temperature was equal to that in air. Thus "diving bradycardia" is in fact a basic survival response independent of water.

Adult↗
PubMed1977

Heart rate response to breath holding at 18.6 ATA.

The heart rate (HR) responses to breath-holding (BH) with the without face immersion (FI) in 31 or 27 degrees C water was studied in 1 ATA air and hyperbaric He-O2 environments in 4 male subjects during a dry saturation dive to simulated depth of 580 ft (18.6 ATA). When a 60 sec BH or FI was performed while leaning forward, there was a significant linear correlation between the maximal bradycardial response (delta HRmax) and ambient pressure for simple BH (r-0.08, P less than 0.05) and 31 degrees C FI (r = 0.91, P less than 0.01), but not for 27 degrees C FI. A similar trend was seen during 30 sec BH's while seated erect. The facial cold-dependent component of the FI bradycardia was not significantly altered by pressure. In general, there were significant correlations between the initial HR and the initial thoracic conductive volume (TCV; measured by the four-electrode Minnesota impedance cardiograph), and between the initial TCV and delta HRmax observed during seated erect BH's. Since the TCV was generally higher at depth, it is suggested that a mechanical effect due to increased TCV at depth, possibly related to increased gas density, is at least partly responsible for the pressure dependence of BH bradycardia.

Atmospheric Pressure↗
PubMed1990

Cardiac output and heart rate in man during simulated swimming while breath-holding.

We measured stroke volume (SV), heart rate (HR), cardiac output (Q), arterial pressure and intrapulmonic (mouth) pressure in four healthy, male subjects during simulated swimming (i.e., performing crawl movements with the legs continuously at a constant rhythm) with and without apnea (water temperature: 31 degrees C). We wanted to see whether the exercise tachycardia response persisted, or whether the HR decreased during apnea, just as in the "diving response" of diving animals. The SV and the Q fell to half its value in the control phase (i.e., swimming with normal breathing), when the 15-s apnea was performed at a high mouth-pressure; at low mouth-pressure, SV and Q hardly changed. These results are replicates of our previous findings in man during rest in air. Due to the light work, HR increased slightly from rest, but the exercise HR did not change much during apnea with or without high mouth-pressure. The results show that man tends to preserve his exercise HR response, and does not react as an oxygen-conserving animal, whether he is in air or in water under these conditions. However, man, as well as diving animals, may well have a "diving response" as an emergency reaction, which may not be restricted to only the water environment.

Adult↗
PubMed1990

Cardiac output and stroke volume in swimming harbor seals.

Cardiac output was measured by the thermodilution method in three young harbor seals, at rest and while swimming up to the maximum effort for which they could be trained. Stroke volume was determined by counting heart rate simultaneously with determination of cardiac output. Cardiac outputs varied widely between surface breathing (7.8 ml.kg-1.s-1) and breath-holding while swimming under water (1.8 ml.kg-1.s-1). Stroke volume while at the surface was almost twice the volume while submerged. Surface cardiac output was always near maximal despite work effort, whereas submerged cardiac output gradually increased at higher work efforts. The cardiovascular performance of seals at the maximum MO2 we could induce from them is equivalent to that of the domestic goat.

Animals↗
PubMed1990

Apnoeic heart rate responses in humans. A review.

Research examining the heart rate response of humans to apnoea and apnoeic immersion in water has tended to produce equivocal results. Controversy exists in relation to the existence and onset, course and ultimate extent of apnoeic bradycardia, either at rest or during exercise. The reduction in heart rate that has been observed in response to apnoea and apnoeic immersion is considered by some to be a component of an oxygen conserving mechanism termed the mammalian dive reflex. Doubt has been expressed, however, as to whether humans do possess the complex cardiovascular response evident in diving mammals. A bradycardial response to apnoea at rest is reasonably well established. Reports conflict with regard to apnoeic responses to exercise in both terrestrial and aquatic environments, and for the temporal onset of apnoeic bradycardia in general, and the time course required for the maximal development of the response. It is suggested that the existing discrepancies with regard to heart rate responses to apnoea are due in part to the large variety of research protocols employed, with, in many cases, a lack of control of those factors said to modify apnoeic heart rates, and in part to a lack of uniformity in the interpretation of the obtained results. Conflicting evidence exists for almost all of the factors said to modify the apnoeic heart rate response in humans. Factors implicated in the phenomenon of apnoeic bradycardia include the influence of temperature and the physical condition of the individual, varying lung volumes, the depth of immersion in water, the body position during the apnoeic episode, and the psychological state of the individual. The influence of the sex and age of the subjects is equally contentious. Finally, the role of breath-holding capacity as it influences the extent of bradycardia remains to be examined further. Additional research requires the adoption of an integrative, holistic approach if a comprehensive understanding of apnoeic heart rate responses is to be achieved.

Adolescent↗