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At least 127 records · Page 7Linked to original sources
PubMed2005

The human diving response, its function, and its control.

The purpose of this review is to outline the physiological responses associated with the diving response, its functional significance, and its cardiorespiratory control. This review is separated into four major sections. Section one outlines the diving response and its physiology. Section two provides support for the hypothesis that the primary role of the diving response is the conservation of oxygen. The third section describes how the diving response is controlled and provides a model that illustrates the cardiorespiratory interaction. Finally, the fourth section illustrates potential adaptations that result after regular exposure to an asphyxic environment. The cardiovascular and endocrine responses associated with the diving response and apnea are bradycardia, vasoconstriction, and an increase in secretion of suprarenal catecholamines. These responses require the integration of both the cardiovascular system and the respiratory system. The primary role of the diving response is likely to conserve oxygen for sensitive brain and heart tissue and to lengthen the time before the onset of serious hypoxic damage. We suggest that future research should be focused towards understanding the role of altered ventilatory responses in human breath-hold athletes as well as in patients suffering from sleep-disordered breathing.

Bradycardia↗
PubMed2000

Human Sleep Apneas and Animal Diving Reflexes: The Comparative Link.

Adaptations to survive periods of limited access to oxygen should have been favored along the evolution of vertebrates. Paradigmatic examples of this adaptation are the diving animals, which can sustain prolonged and repetitive periods of anoxia. These animals support what would be considered a severe gas imbalance in their internal environment thanks to three main strategies: increased oxygen stores, resistance to asphyxia, and reduced metabolic expenditure during the apneic intervals. However, diving animals developed their abilities from very old life-sustaining responses that should have been used on many other occasions. Humans with sleep apneas perhaps share many physiological adaptations with diving animals. We review here the extent of such similarities and offer clear evidence of its existence and suggest possible research lines that could improve the clinical knowledge about this condition.

Journal Article↗
PubMed2003

The maximum tissue half-time for nitrogen elimination from divers' body.

Both the longest tissue half-time (T1/2max) and the maximum allowable pressure gradient (deltaP) define the safe rate of decompression (DR) after saturation expositions. The mathematical relation between them (DR = -k x deltaP, where: k = ln(2)/(T1/2max)) suggests that experimentally established decompression rate can be hypothetically described by the infinite number of T1/2max and deltaP combinations. The observed number of decompression sickness after saturation decompressions forced to change those parameters subsequently and finally led to values far outside physiological range. Therefore the aim of this study was to compare values of the longest tissue half-time of nitrogen desaturation from diver's body published since 1908 in order to present the evolution of opinions concerning desaturation process. Non-physiological values of T1/2max (from 75 to 1280 minutes) have been published during historical evolution of decompression tables and systems. The currently accepted values of T1/2max (in the range of 320-480 minutes) for saturation and non-saturation air and nitrox divings and hypobaric decompressions, still need to be precised. The discrepancy between T1/2max values obtained using isobaric decompression method and decompressions after diving indicates different physiological phenomena during nitrogen elimination in both methods.

Decompression↗
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↗
PubMed2001

Diving development in nursing harbour seal pups.

This study investigated physiological and behavioural aspects of diving development in pups of the harbour seal Phoca vitulina. Behavioural data (4280 h, 6027 dives) from time/depth recorders (N=13) deployed on pups aged 0-19 days are presented concomitantly with physiological measurements (N=8, sampled both early and late in the nursing period) of blood oxygen stores and body composition. Pups grew from 12.6+/-1.8 kg (mean age 2 days, total body fat 16+/-4 %) to 22.2+/-2.5 kg (mean age 16 days, total body fat 35+/-5 %; means +/- S.D.) over the duration of the experiment. Pups less than 5 days of age had an elevated haematocrit and reduced plasma volume compared with older pups. Although plasma volume and blood volume increased, mass-specific blood oxygen stores (total haemoglobin) fell during the study period. Simultaneously, the following behavioural indicators of diving ability increased: the proportion of time spent in the water, dive depth, dive duration, bottom time and maximum daily swimming velocity. In addition, the proportion of dives that were identified by cluster analyses as being U-shaped increased significantly with age. On the basis of the measured blood oxygen stores, less than 1 % of the recorded dives exceeded the calculated aerobic dive limit. Thus, development in blood oxygen stores or rates of oxygen consumption did not seem to restrain the rate of neonatal dive development in harbour seals. It appears that behavioural modifications (experience and learning) may be the primary rate-limiting factors for ontogeny of diving skills in neonates of this species.

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↗
PubMed1987

Personality and demographic variables related to individual responsiveness to diving stress.

Thirty U.S. Navy divers were tested for 4 personality and 2 demographic variables. They subsequently were exposed to the stress of being pressurized in a small diving chamber for several hours. Stress responsiveness to this condition was assessed using 3 physiologic and 4 subjective emotionality measures before and after the dive. These physiologic and emotionality measures were factor analyzed and correlated with personality and demographic variables. Difference scores among the physiologic and emotionality measures, indicating responsiveness to stress, correlated significantly with education, diving experience, internality-externality, disinhibition, and socialization. These data indicate that measures of achievement (i.e., diving experience and education), perceived control, sensation seeking, and social adjustment are useful in accounting for individual differences in acute emotional and physiologic responsiveness to stressful diving conditions.

Adult↗
PubMedDate not supplied

[The characteristics of the extreme actions on the bodies of deep-sea divers during saturation dives and the basic task of medical support for these descents].

A novel dive method, namely, saturation diving is presented. Extreme factors affecting the deep divers during such saturation dives are listed. The physiologic parameters of early adaptation, stable adaptation, early disadaptation and readaptation periods of a man during prolonged staying in a hyperbaric artificial gaseous environment are evaluated. The key task of medical monitoring of saturation dives is discussed.

Adaptation, Physiological↗
PubMed1979

The use of the diving reflex to terminate supraventricular tachycardia in a 2-week-old infant.

The use of the diving reflex to terminate a case of paroxysmal supraventricular tachycardia (PST) is described in a 2-week-old infant who presented in severe congestive heart failure with supraventricular tachycardia at a rate of 300. The infant's face was placed in a basin of ice water at 5 degrees C. for 5 seconds with manual occlusion of the infant's nostrils to prevent aspiration. The PST converted to a sinus rhythm of 120 within 3 seconds of facial immersion. The physiology of the diving reflex is reviewed and the uses and hazards of this reflex in terminating attacks of PST in infants is discussed.

Diving↗
PubMed2006

Ontogeny of total body oxygen stores and aerobic dive potential in Steller sea lions (Eumetopias jubatus).

Two key factors influence the diving and hence foraging ability of marine mammals: increased oxygen stores prolong aerobic metabolism and decreased metabolism slows rate of fuel consumption. In young animals, foraging ability may be physiologically limited due to low total body oxygen stores and high mass specific metabolic rates. To examine the development of dive physiology in Steller sea lions, total body oxygen stores were measured in animals from 1 to 29 months of age and used to estimate aerobic dive limit (ADL). Blood oxygen stores were determined by measuring hematocrit, hemoglobin, and plasma volume, while muscle oxygen stores were determined by measuring myoglobin concentration and total muscle mass. Around 2 years of age, juveniles attained mass specific total body oxygen stores that were similar to those of adult females; however, their estimated ADL remained less than that of adults, most likely due to their smaller size and higher mass specific metabolic rates. These findings indicate that juvenile Steller sea lion oxygen stores remain immature for more than a year, and therefore may constrain dive behavior during the transition to nutritional independence.

Age Factors↗
PubMed1999

Development of diving capacity in emperor penguins.

To compare the diving capacities of juvenile and adult emperor penguins Aptenodytes forsteri, and to determine the physiological variables underlying the diving ability of juveniles, we monitored diving activity in juvenile penguins fitted with satellite-linked time/depth recorders and examined developmental changes in body mass (Mb), hemoglobin concentration, myoglobin (Mb) content and muscle citrate synthase and lactate dehydrogenase activities. Diving depth, diving duration and time-at-depth histograms were obtained from two fledged juveniles during the first 2.5 months after their depature from the Cape Washingon colony in the Ross Sea, Antarctica. During this period, values of all three diving variables increased progressively. After 8-10 weeks at sea, 24-41 % of transmitted maximum diving depths were between 80 and 200 m. Although most dives lasted less than 2 min during the 2 month period, 8-25 % of transmitted dives in the last 2 weeks lasted 2-4 min. These values are lower than those previously recorded in adults during foraging trips. Of the physiological variables examined during chick and juvenile development, only Mb and Mb content did not approach adult values. In both near-fledge chicks and juveniles, Mb was 50-60 % of adult values and Mb content was 24-31 % of adult values. This suggests that the increase in diving capacity of juveniles at sea will be most dependent on changes in these factors.

Animals↗
PubMed1984

Modification of the 'dividing bradycardia' by hypoxia or exercise.

The oxygen-conserving efficiency of the physiological adjustments to diving depends on two factors: (1) the rate of onset of reflex action, and (2) the extent to which circulating blood is withdrawn from the organs which are not irreparably damaged by transient hypoxia. We report a study in which either hypoxia or exercise has been imposed as an additional stress on human subjects performing apneic face immersion in order to determine any early changes in the reflex rate of onset and/or the final level of cardiovascular adjustment. It is concluded that the rate of onset of the diving reflex varies with the stresses imposed whereas the final level of adjustment does not.

Adult↗