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At least 163 records · Page 9Linked to original sources
PubMed2005

Physiological control of diving behaviour in the Weddell seal Leptonychotes weddelli: a model based on cardiorespiratory control theory.

Despite being obligate air breathers, many species of marine mammal are capable of spending most of their lives submerged in water. How they do this has been a subject of intense interest to physiologists for over a century, yet we still do not have a detailed understanding of the physiological mechanisms underlying this behaviour. What are the proximate mechanisms that trigger the 'decisions' to submerge and return to the surface? The present study proposes a model intended to address this question, based on fundamental concepts of cardiorespiratory control. Two basic hypotheses are examined by computer simulation, using a mathematical model of the mammalian cardiorespiratory control system with parameter values for an adult Weddell seal: (1) that the control of diving can be considered to be a respiratory control problem, and (2) that dives are initiated and maintained by disfacilitation of respiratory drive, not inhibition. Computer simulations confirmed the plausibility of these hypotheses. Simulated diving behaviour and physiological responses (ventilation, cardiac output, blood and tissue gas tensions) were consistent with published data from freely diving Weddell seals. Dives up to the estimated aerobic dive limit (ADL, 18-25 min) could be simulated without the need for active inhibition of breathing in this model. This theoretical analysis suggests that the most important physiological adjustments occur during the surface interval phase of the dive cycle and include hyperventilation accompanied by high cardiac output, appropriate regulation of cerebral blood flow and central chemoreceptor threshold shifts. During dives, cardiac output, distribution of peripheral blood flow, splenic contraction and peripheral chemoreflex drives were found to modulate physiological and behavioural responses, but were not essential for simulated dives to occur. The main conclusion from this study is that the central chemoreceptor may be an important mechanism involved in the regulation of diving behaviour, implying that CO2, not O2, is the key regulatory variable in this model. This model includes and extends the ADL concept and suggests an explicit mechanism by which the respiratory control system may play a central role in the regulation of diving behaviour. It is likely that respiratory mechanisms are an important component of a hierarchical behavioural control system and further studies are required to test the qualitative and quantitative validity of the model.

Animals↗
PubMed1986

Diving behaviour and heart rate in tufted ducks (Aythya fuligula).

Diving behaviour and heart rate were monitored in tufted ducks diving under circumstances which simulated various environmental conditions such as feeding under ice in winter. When distance to food was increased on a covered outdoor pond, dive duration increased proportionately, but it was calculated that time available for feeding was reduced during the longer-distance 'extended' dives. There was a gradual reduction in heart rate to 77.3 +/- 13.8 beats min-1, which is significantly lower than the resting value of 121.1 +/- 14.1 beats min-1, during the course of extended dives, suggesting that the ducks could gradually switch over to a 'classical' oxygen-conserving response during these prolonged voluntary dives. The duration of the pre-dive preparatory period was positively correlated with dive distance. When the ducks were briefly unable to resurface during an otherwise normal feeding dive in an indoor tank, a situation which may occur if they become disoriented under ice, there was an immediate switch to a full bradycardia. Reduction in heart rate during these 'enclosed' dives occurred only when the ducks were apparently aware of the situation and the rate of onset of bradycardia was very similar to that previously observed during involuntary submersion of tufted ducks. Minimum heart rate was the same at 46 beats min-1 after 15 s of enclosed dives and after 30 s of involuntary submersions, despite the differences in levels of activity in the two situations.

Animals↗
PubMed1994

Gas exchange of captive freely diving grey seals (Halichoerus grypus).

When at sea, phocids dive for long periods and spend a high percentage of their time submerged. This behaviour requires some combination of an increased oxygen storage capacity, rapid oxygen loading at the surface and reduced oxygen utilisation when submerged. To assess these adaptations, breath-by-breath ventilation was studied in four adult grey seals (two male, two female, 160-250 kg), freely diving in a large outdoor tank where surface access was restricted to one breathing hole. The dive patterns obtained were similar to those recorded from freely diving wild grey seals. Respiratory frequency during the surface periods was 40% higher than that estimated from allometric relationships (19.4 +/- 0.7 breaths min-1), and tidal volume (6.3 +/- 1.21) was approximately five times higher than that estimated from allometric relationships. These adaptations produce a high minute volume and enable gas exchange to occur at the surface. Mean oxygen consumption rate (VO2, measured for a dive+surface cycle) decreased with increasing dive duration. The aerobic dive limit was estimated as 9.6 min for a 150 kg grey seal (using the overall average VO2 of 5.2 ml O2 min-1 kg-1), which is consistent with results from freely diving wild grey seals (only 6% of dives exceeded 10 min). End-tidal oxygen values varied during a surface period, following a U-shaped curve, which suggests that there is limited oxygen uptake from the lung and/or blood oxygen stores during dives. This result was unexpected and indicates that these seals are utilising substantial physiological responses to conserve oxygen, even during shallow voluntary diving.

Animals↗
PubMed1999

The diving physiology of bottlenose dolphins (Tursiops truncatus). I. Balancing the demands of exercise for energy conservation at depth.

During diving, marine mammals must rely on the efficient utilization of a limited oxygen reserve sequestered in the lungs, blood and muscles. To determine the effects of exercise and apnea on the use of these reserves, we examined the physiological responses of adult bottlenose dolphins (Tursiops truncatus) trained to breath-hold on the water surface or to dive to submerged targets at depths between 60 and 210 m. Changes in blood lactate levels, in partial pressures of oxygen and carbon dioxide and in heart rate were assessed while the dolphins performed sedentary breath-holds. The effects of exercise on breath-hold capacity were examined by measuring heart rate and post-dive respiration rate and blood lactate concentration for dolphins diving in Kaneohe Bay, Oahu, Hawaii. Ascent and descent rates, stroke frequency and swimming patterns were monitored during the dives. The results showed that lactate concentration was 1.1+/-0.1 mmol l(-1) at rest and increased non-linearly with the duration of the sedentary breath-hold or dive. Lactate concentration was consistently higher for the diving animals at all comparable periods of apnea. Breakpoints in plots of lactate concentration and blood gas levels against breath-hold duration (P(O2), P(CO2)) for sedentary breath-holding dolphins occurred between 200 and 240 s. In comparison, the calculated aerobic dive limit for adult dolphins was 268 s. Descent and ascent rates ranged from 1.5 to 2.5 m s(-1) during 210 m dives and were often outside the predicted range for swimming at low energetic cost. Rather than constant propulsion, diving dolphins used interrupted modes of swimming, with more than 75 % of the final ascent spent gliding. Physiological and behavioral measurements from this study indicate that superimposing swimming exercise on apnea was energetically costly for the diving dolphin but was circumvented in part by modifying the mode of swimming.

Aerobiosis↗
PubMed1999

The diving physiology of bottlenose dolphins (Tursiops truncatus). III. Thermoregulation at depth.

During diving, marine mammals initiate a series of cardiovascular changes that include bradycardia and decreased peripheral circulation. Because heat transfer from thermal windows located in peripheral sites of these mammals depends on blood flow, such adjustments may limit their thermoregulatory capabilities during submergence. Here, we demonstrate how the thermoregulatory responses of bottlenose dolphins (Tursiops truncatus) are coordinated with the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water surface, stationed 5-50 m under water and floated at the surface immediately following a dive. The results showed that heat flow ranged from 42.9+/-7.3 to 126.2+/-23.1 W m(-)(2) and varied with anatomical site and diving activity. Upon submergence, heat flow declined by 35 % from the dorsal fin and by 24 % from the flank. An immediate increase in heat flow to levels exceeding pre-dive values occurred at both sites upon resurfacing. Changes in heart rate during diving paralleled the thermoregulatory responses. Mean pre-dive heart rate (102.0+/-2.6 beats min(-)(1), N=26) decreased by 63.4 % during dives to 50 m and immediately returned to near resting levels upon resurfacing. These studies indicate that heat dissipation by dolphins is attenuated during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation is reduced.

Animals↗
PubMed2002

The relative risk of decompression sickness during and after air travel following diving.

BACKGROUND: Decompression sickness (DCS) can be provoked by post-dive flying but few data exist to quantify the risk of different post-dive, preflight surface intervals (PFSI). METHODS: We conducted a case-control study using field data from the Divers Alert Network to evaluate the relative risk of DCS from flying after diving. The PFSI and the maximum depths on the last day of diving (MDLD) were analyzed from 627 recreational dive profiles. The data were divided into quartiles based on surface interval and depth. Injured divers (cases) and uninjured divers (controls) were compared using logistic regression to determine the association of DCS with time and depth while controlling for diver and dive profiles characteristics. These included PFSI, MDLD, gender, height, weight, age, and days of diving. RESULTS: The means (+/-SD) for cases and controls were as follows: PFSI, 20.7 +/- 9.6 h vs. 27.1 +/- 6.7 h; MDLD, 22.5 +/- 14 meters sea water (msw) vs. 19 +/- 11.3 msw; male gender, 60% vs. 70%; weight, 75.8 +/- 18 kg vs. 77.6 +/- 16 kg; height, 173 +/- 16 cm vs. 177 +/- 9 cm; age, 36.8 +/- 10 yr vs. 42.9 +/- 11 yr; diving > or = 3 d, 58% vs. 97%. Relative to flying > 28 h after diving, the odds of DCS (95% CI) were: 1.02 (0.61, 1.7) 24-28 h; 1.84 (1.0, 3.3) 20-24 h; and 8.5 (3.85, 18.9) < 20 h. Relative to a depth of < 14.7 msw, the odds of DCS (95% CI) were: 1.2 (0.6, 1.7) 14.7-18.5 msw; 2.9 (1.65, 5.3) 18.5-26 msw; and 5.5 (2.96, 1 0.0) > 26 msw. CONCLUSIONS: Odds ratios approximate relative risk in rare diseases such as DCS. This study demonstrated an increase in relative risk from flying after diving following shorter PFSIs and/or greater dive depths on the last day. The relative risk increases geometrically as the PFSI becomes smaller.

Adult↗
PubMed1983

Patterns of wet suit diving in Korean women breath-hold divers.

Work shifts, diving pattern, diving lung volumes, and counterweights were studied in professional Korean women breath-hold divers wearing wet suits. One of the major differences, compared with their diving pattern only a few years ago when wearing cotton suits, is the prolongation of the diving shifts from 70 to 180 min in the summer and 10 to 120 min in the winter. In sustained diving the average dive and surface times in a 5-m dive are 32 and 46 s, and in a 10-m dives, 43 and 85 s, respectively. During a 3-h shift the total bottom time for harvesting is 37 min in 5-m dives and 17 min in 10-m dives. Rates of descent and ascent are 0.55 and 0.84 m/s. The wet suit divers adjust their counterweights to obtain a 12% positive buoyancy at the surface of sea water in contrast to the 8% positive buoyancy of cotton suit divers. The average lung volumes before and after a dive are 79% and 64% of their vital capacities, values similar to those of previous cotton suit divers.

Adaptation, Physiological↗
PubMed1982

Observations on no-stop and repetitive air and oxynitrogen diving.

The historical origins of the respective air decompression schedules of the British and United States Navies are reviewed with particular reference to the repetitive diving rules. No-stop diving is also discussed. A series of single dive and repetitive dive trials of the Royal Navy Air Table is presented. U.S. Navy and Royal Naval Physiological Laboratory (RNPL) 1968 repetitive dive rules were also tested according to their respective tables on a selection of dives. Comparison of the two methods produce a remarkably similar outcome for dives to similar depths. For dives to very dissimilar depths there is no comparison. The RNPL system has commendable simplicity but lacks the flexibility of the U.S. Navy system for use with successive dives to different depths. Observations on the results of a triple no-stop repetitive dive experiment are presented. It is concluded that little would be gained by further practical investigation of no-stop diving times.

Air↗
PubMed1993

Compressed air diving and respiratory disease. A discussion document of the Thoracic Society of Australia and New Zealand.

OBJECTIVE: To review the pathophysiology and respiratory complications of compressed air diving, and to formulate guidelines for assessing respiratory fitness to dive so that diving candidates can be advised of the risks associated with respiratory disease, in particular asthma. DATA SOURCES: Specialist medical journals in the areas of respiratory medicine, physiology and diving medicine. Morbidity and mortality statistics were obtained from international diving bodies, diving medicine scientific meetings, and papers. SYNTHESIS: The major complications of underwater diving in subjects with compromised respiratory function are drowning, pulmonary barotrauma and arterial gas embolism. Diving candidates with a history of asthma, pneumothorax, obstructive or restrictive lung disease, lung cysts or thoracic trauma should be advised not to dive in view of these risk factors. CONCLUSIONS: Several respiratory diseases carry an increased risk of morbidity and mortality from compressed air diving. An accurate history and measurement of lung function are an essential part of assessing fitness to dive, both to advise potential divers appropriately and to reduce risks associated with this increasingly popular recreational activity.

Asthma↗
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↗
PubMed2007

[Oxygen therapy in diving accidents].

Diving accidents represent a departure from the routine practice of emergency physicians. The incidence of non-fatal diving accidents is reported as 1-2 per 10,000 dives. Apart from adequate intravenous hydration, oxygen is the only medication with a proven effect in the treatment of diving accidents. After a typical diving accident, administration of oxygen at an inspired concentration (F(I)O(2) 1.0) as high as possible is recommended. Many divers bring along their own oxygen administration systems to the diving sites and these are often better suited for the treatment of diving accidents than the oxygen systems of many emergency responders. Pressure regulators supplying low constant flow oxygen, nasal prongs and inhalation masks are inappropriate. When using artificial ventilation bags with face masks, an oxygen flow of at least 15 l/min should be used. Demand regulators are simple to use and able to deliver a F(I)O2 of 1.0. Their ease of use has earned them high marks in the emergency management of diving accidents and their similarity to standard diving equipment has also aided relatively widespread acceptance. Circulation breathing systems are more technologically complex oxygen delivery systems which permit CO2 absorption and re-breathing at low oxygen flow. In contrast to the demand modules, the likelihood of mistakes during their usage is higher. In diving accidents, the administration of normobaric oxygen, already begun in the field, is the most important therapy and should not be interrupted. Presented with an inadequate supplemental oxygen supply, the inspired oxygen concentration should not be decreased, rather the duration of the oxygen administration should be reduced. Hyperbaric oxygen therapy should be the mainstay of further treatment.

Accidents↗
PubMed1997

Effects of a single saturation dive on lung function and exercise performance.

We studied the effects of an experimental saturation dive to 360 and 450 m in a simulation chamber on spirometric lung function, diffusing capacity, pulmonary compliance, and exercise performance in eight professional divers (age 22-40 years). To assess intraindividual variability, all parameters were measured on 2 days before and on 2 consecutive days immediately after the dive. For the group as a whole there was a significant increase in vital capacity and alveolar volume, and a decrease in Krogh factor and specific compliance (P < 0.01). These changes were reduced on the 2nd day after the dive. All subjects showed lowered exercise performance after the dive. Arterial pressure of oxygen and ventilation during exercise increased (P < 0.01), whereas arterial pressure of carbon dioxide, oxygen uptake, and anaerobic threshold decreased (P < 0.01). Exercise parameters showed only a slight trend towards pre-dive values on the 2nd day after a dive. The individual analysis revealed that after the dive two subjects showed a marked decrease in diffusing capacity and a more than average decrease in Krogh factor (TLCO/VA). One of them had signs of mild decompression sickness and the other, signs of pre-existing obstructive airways disease. Our data are compatible with the hypothesis that the effects of a single deep saturation dive on pulmonary function and exercise performance are the results of counteracting mechanisms. We suggest that lung volumes increase due to the enhanced work of breathing during a deep saturation dive and that these changes could mask an impairment in gas exchange. Furthermore, a saturation dive can induce an apparent deterioration of pulmonary function.

Adult↗
PubMed1998

Changes in fibrinolytic activity in diving grey seals.

In order to test the hypothesis that enhanced fibrinolytic activity is a factor which prevents the blood of diving seals from clotting, we instrumented two female grey seals (Halichoerus grypus) with subcutaneous electrodes for measurements of heart rate (HR) and an extradural intravertebral venous catheter for collection of blood samples before, during and after simulated dives of 10 min duration. Blood samples were used for in vitro determination of clot lysis time (CLT), which is a measure of the level of fibrinolytic activity, and for analyses of plasma levels of cortisol, noradrenaline and adrenaline (A). The seals displayed profound diving bradycardia indicative of a substantial reduction in blood flow rates (pre-dive HR: 78 (63-98) bpm; dive HR: 8 (7-10) bpm; (median (range); n = 2)) and elevated catecholamine levels (pre-dive A: 121 (98-184) pg.ml-1; peak dive/post-dive A: 3510 (447-6181) pg.ml-1), both of which are factors which promote blood coagulation. Nevertheless, we found that CLT always increased in connection with diving (pre-dive CLT: 436 (356-568) min; peak CLT during diving: 1380 (640-1800) min), which implies a reduced, rather than enhanced, fibrinolytic activity in this situation. These results show that enhanced fibrinolytic activity is not part of the defence system which prevents fatal clotting from occurring in diving grey seals.

Animals↗
PubMed2000

On the direction and velocity of blood flow in the extradural intravertebral vein of harp seals (Phoca groenlandica) during simulated diving.

Ronald et al. (1977) suggested that blood flow in the caudal/lumbar sections of the extradural intravertebral vein (EIV) of seals changes direction from running towards the head before diving, to the opposite during diving. The possible advantage would be that the oxygen-depleted venous effluent from the brain is routed via the EIV to the posterior parts of the hepatic sinuses and the inferior caval vein and, hence, is prevented from mixing with the more oxygen-rich venous blood in their anterior parts. We have re-examined this hypothesis by use of Doppler flowmetry. A catheter-tip flow probe was introduced into the EIV of two similar-sized juvenile harp seals, and flow direction and rate determined before, during and after simulated dives lasting for 5 min, at three positions (caudal, lumbar and thoracic) along the EIV. Regardless of probe position, blood was mainly flowing towards the head in 11 of 13 experiments prior to diving, in 8 of 13 experiments during diving and in 11 of 13 experiments during recovery after diving (and away from the head in the remaining experiments). Flow direction was most variable in the caudal position. Mean blood velocity in the EIV was substantially lower during diving (0.10 +/- 0.22 cm s-1 (n=5) in thoracic position) than in the pre-dive (3.98 +/- 3.32 cm s-1 [n=5]) and post-dive (5.75 +/- 4.07 cm s-1 [n=5]) situations. Thus, the direction and rate of flow in the EIV was variable, particularly during diving, as is to be expected in a system of anastomosing, valveless veins. We conclude that the hypothesis of Ronald et al. (1977) most likely is false.

Animals↗
PubMed2001

Diving after stapedectomy: clinical experience and recommendations.

OBJECTIVES: Much controversy exists concerning the risk of inner ear barotrauma after stapes surgery in scuba and sky divers. Uniform consensus has not been established regarding poststapedectomy barorestrictions. The purpose of this study was (1) to determine the prevalence of adverse auditory and/or vestibular sequelae in patients after stapedectomy related to scuba and sky diving, and (2) to offer recommendations on barometric exposure after stapes surgery. STUDY DESIGN: Survey questionnaires were mailed to 2222 patients who had undergone stapedectomies at a single tertiary otologic referral center between 1987 and 1998. Two hundred eight of the initial 917 respondents (22.7%) had snorkeled, scuba, or sky dived after stapes surgery, and 140 of these responded to a second questionnaire detailing dive protocols, otologic symptoms, and their relationship to the diving activities. Of the 140, 28 had scuba or sky dived. Their survey data were analyzed and their medical records were reviewed. RESULTS: Four of the 22 scuba divers (18.1%) experienced otologic symptoms at the time of diving. These included otalgia on descent (3/22; 13.6%), tinnitus (1/22; 4.5%), and transient vertigo on initial submersion (1/22; 4.5%). One patient had sudden sensorineural hearing loss and vertigo develop 3 months after scuba diving, which he related to noise exposure. He was subsequently found to have a perilymph fistula, which was successfully repaired. Of the 9 patients who sky dived, 2 patients (22.2%) reported otologic symptoms during the dive. No significant diving-related long-term effects indicative of labyrinthine injury were seen in any of the 28 patients. CONCLUSIONS: Stapedectomy does not appear to increase the risk of inner ear barotrauma in scuba and sky divers. These activities may be pursued with relative safety after stapes surgery, provided adequate eustachian tube function has been established.

Adolescent↗
PubMed1984

Biochemical and mood responses predictive of stressful diving performance.

Measures of six self-reported moods (assessed using the Mood Questionnaire), serum cholesterol levels, and serum uric acid (SUA) levels were obtained from 26 divers attending the Saturation Diver Training (SDT) course, the most sophisticated and arduous diving course offered by the U.S. Navy. These measures were correlated with various types of diving activity that occurred during the seven years following graduation from the SDT course. Multiple regression analyses showed that two moods, Fear and Happiness, from the Mood Questionnaire, were independently related to years of subsequent diving experience, while mood Fear and cholesterol levels were associated with total number of dives made during this period. The number of dives made to depths of over 100 feet of sea water was related independently to cholesterol levels and mood Happiness. A high frequency of saturation diving (i.e., dives that last for periods in excess of 12 hours) was found for divers with high SUA levels and low scores on mood Fear. Variations in significant mood and biochemical measures across the different types of diving criteria are discussed in terms of the level of stress involved, prior diving experience, psychological traits including perceived control and achievement motivation, and attitudes formed toward diving during the SDT course.

Achievement↗
PubMed2000

The indigenous fisherman divers of Thailand: diving practices.

Diving practices of a group of indigenous people living on Thailand's west coast were investigated. Village chiefs were first interviewed using a questionnaire. Three hundred and forty-two active divers were then interviewed by health care workers using a second questionnaire. Field observation was used to further develop information and confirm diving practices. Divers in 6 villages, whose basic means of making a living is from diving for marine products such as fish and shellfish, have diving patterns that put them at substantial risk of decompression illness. Breathing air from a primitive compressor through approximately 100 m of air hose, these divers have long bottom times coupled with short surface intervals. Forty-six point two percent of the divers indicated that they would not make a stop during ascent from a long deep dive (40 m for 30 min). When comparing their previous day of diving to the U.S. Navy Standard Air Decompression Table (U.S. Navy, 1993), 72.1% exceeded the no-decompression limits set by the tables. Diving patterns point to a need for more in-depth research into the diving patterns of this indigenous group. Future research should include the use of dive logging devices to record depths and times. There is also a need to provide divers with information and training to reinforce positive practices and strengthen knowledge of the risks associated with their current diving practices.

Adolescent↗
PubMedDate not supplied

Effect of temperature on oxygen stores during aerobic diving in the freshwater turtle Mauremys caspica leprosa.

Oxygen stores available for aerobic diving were studied in the freshwater turtle (Mauremys caspica leprosa) at three constant body temperatures (15 degrees, 25 degrees, and 35 degrees C) and during the thermal transient (30 degrees-15 degrees C) induced by immersion in cold water. The term "aerobic dive limit" has been defined as the maximal duration of the dive before lactate increases. This increase occurs when a critical PO2 value is reached, and it is well characterized at lung level by a sharp increase in the lung apnoeic respiratory quotient. Kinetic analysis of lung gas composition during forced dives at fixed body temperature shows that critical PO2 values rise with temperature and that the postventilatory PO2 at the beginning of a dive decreases, so that the two temperature-dependent factors lead to a significant decrease with temperature in the lung O2 stores available for aerobic diving. During dives with transient body cooling, a natural condition in M. caspica leprosa, temperature equilibration occurs fast enough to expand aerobic scope by bearing the critical PO2 to the same value obtained at a fixed temperature of 15 degrees C. These dives are characterized by reversed CO2 transport (from lung to tissues) and therefore by negative values of the lung respiratory quotient; a decrease in temperature increases CO2 capacitance of tissues, resulting in a fall in PCO2 at constant CO2 content. Because this does not occur in the gas phase, PCO2 difference can lead to diffusion in the direction opposite from normal. This pattern may favour lung-to-tissue O2 transfer, through the Bohr effect. Therefore, the aerobic dive limit is reduced at high temperature not only through a metabolic rate effect but also through a marked decrease in the available O2 stores; fast body cooling (30 degrees-15 degrees C) associated with immersion in cold water extends the O2 stores available for aerobic diving to a level similar to that of immersions at constant body temperatures that are in equilibrium with water temperature.

Animals↗