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PubMed1982

Respiratory and cardiovascular control during diving in birds and mammals.

Recent studies on freely diving birds and mammals indicate that, contrary to the classical hypothesis, the majority of dives are aerobic with minimal cardiovascular adjustments (i.e. bradycardia and selective vasoconstriction). It is postulated that during these aerobic dives the cardiovascular adjustments result from the opposing influences of exercise and the classical diving response, with the bias towards the exercise response. It is envisaged that the active muscles, as well as the brain and heart, are adequately supplied with blood to enable them to metabolize aerobically. Intense mental activity, particularly in carnivores seeking their prey, may also attenuate the classical response. Aerobic dives are usually terminated well before the oxygen stores are depleted, and another dive follows once they have been replenished. In this way a series of dives is performed. Prolonged dives are endured as a result of a shift towards the classical response of bradycardia, presumably more intense vasoconstriction, and anaerobiosis. This may be a form of alarm response, particularly in small animals such as ducks and coypus, or it may be a means of allowing the marine birds and mammals that dive deeply for their food to engage in unusually long hunting expeditions. For those that dive under ice, it may also allow long periods of underwater exploration as well as being a safety mechanism should the animal become disoriented.

Afferent Pathways↗
PubMed2004

Defining the limits of diving biochemistry in marine mammals.

The field of marine mammal diving biochemistry was essentially untouched when Peter Hochachka turned his attention to it in the mid-1970s. Over the next 30 years, his work followed three main themes in this area: first, most biologists at that time supported the theory that diving mammals utilized enhanced metabolic pathways for hypoxic energy production (glycolysis to lactate) and reduced their metabolic rate while diving. Peter began his work on potential hypoxic adaptations in marine mammals by working out the details of how these pathways would be regulated. By the 1980s, he started to ask how diving mammals balanced the increased demands of exercise with the apparently conflicting demands to reduce aerobic metabolism while exercising underwater. By the 1990s, his work involved complex models of the interplay between the neural, hormonal, behavioral and evolutionary components of diving biochemistry and animal exercise. From a comparative approach, he excelled at bringing themes of hypoxic adaptation from many different types of animals to the field of diving mammal biochemistry. This review traces the history of Peter Hochachka's work on diving biochemistry from the perspective of those of us who spent time with him both inside the laboratory and outside in the field from Antarctica to Iceland.

Adaptation, Physiological↗
PubMed1997

Membrane lipid order of human red blood cells is altered by physiological levels of hydrostatic pressure.

The effect of hydrostatic pressure at levels applied in diving or hyperbaric treatment (thus considered "physiological") on the order of lipid domains in human red blood cell (RBC) membrane was studied. Membrane order was determined by measuring 1) the fluorescence anisotropy (FAn) of lipid probes, 2) the resonance energy transfer from tryptophan to lipid probes, and 3) spectral shifts in Laurdan fluorescence emission. It was found that the application of mild pressure (< 15 atm) 1) increased, selectively, the FAn of lipid probes that monitor the membrane lipid core, 2) increased the tryptophan FAn, 3) increased the resonance energy transfer from tryptophan to lipid probes residing in the lipid core, and 4) induced changes in the Laurdan fluorescence spectrum, which corresponded to reduced membrane hydration. It is proposed that the application of pressure of several atmospheres increases the phase order of membrane lipid domains, particularly in the proximity of proteins. Because the membrane lipid order ("fluidity") of RBCs plays an important role in their cellular and rheological functions, the pressure-induced alterations of the RBC membrane might be pertinent to microcirculatory disorders observed in humans subjected to elevated pressure.

Energy Transfer↗
PubMed1996

Diving energetics in king penguins (Aptenodytes patagonicus).

Dive duration in wild king penguins and the energetic cost of swimming in a 30m long swim channel were determined at Ile de la Possession, Crozet Archipelago, using external data loggers and respirometry, respectively. Calibrated electronic data loggers equipped with a pressure sensor were used to determine dive durations: 95% of dives were less than 6 min long and 66% of dives were less than 4 min long. Dive patterns show that king penguins may intersperse long dive durations (4-6.3 min) with short ones (1.5-3 min) and make surface pauses of variable duration between them (0.5-3.5 min), or dive regularly (for up to 5 h) with long dive durations (5 min) and constant interdive surface intervals (1.5 min). The latter indicates that the aerobic dive limits (ADL) of this species could be higher and oxygen consumption lower than previously reported. Assuming that king penguins dive within their aerobic limit, different approaches to the analysis of the data obtained in the swim channel are discussed to derive the ADL. Swimming speeds observed in the channel ranged from 0.9 to 3.4 m s-1. Transport costs were lowest between 1.8 and 2.2 m s-1. Although at 2.2 m s-1 king penguins used only 10.3 Wkg-1 over a dive+surface cycle (minimal transport costs of 4.7 J kg-1 m-1), we speculate that tisse oxygen consumption during submergence may be as low as 0.23 ml O2 kg-1 s-1 (2.1 times standard metabolic rate, SMR) or perhaps lower (which gives an ADL of 4.2 min). During surface phases, oxygen uptake would be increased to at least 1 ml O2kg-1 s-1 (9.3 times SMR). This implies that at least 70% of all dives are aerobic. Potential physiological mechanisms allowing king penguins to partition O2 consumption between submergence and surface periods remain, however, unclear.

Animals↗
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↗
PubMed1990

Hormonal and cardiorespiratory changes following simulated saturation dives to 4 and 11 ATA.

Professional divers were compressed with trimix to 4 ATA (2 persons, aged 35 and 26) and to 11 ATA (3 persons, aged 34, 26, and 23) for saturation dives with durations of 48 and 50 h, followed by 33 and 109 h of decompression, respectively. Pre- and postdive cardiorespiratory reactions to a step test--heart rate (HR) and ventilation (VE)--and concentrations of growth hormone, corticotropin, cortisol, insulin, lutotropin, folitropin, triiodothyronine (T3), thyroxine (T4), thyrotropin, and testosterone in serum were studied. All divers developed postdecompression tachycardia (90-108 beats/min), which persisted 24 h after surfacing. Physical fitness assessed by steady state HR and VE during a step test was lowered 24 h after decompression compared with the predive values in 4 divers and enhanced in 1. These data provide evidence for hindered and delayed readaptation of the cardiorespiratory system to a normobaric environment. T3, T4, and testosterone were significantly decreased postdive. Hormonal responses were found to exhibit a very individual pattern from which it was possible to estimate the adaptive reactions after hyperbaric exposure. Professional divers with a lower level of physical fitness showed more pronounced hormonal responses to hyperbaric environments.

Adaptation, Physiological↗
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↗
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↗
PubMed2005

Energetic costs of diving and thermal status in European shags (Phalacrocorax aristotelis).

Diving is believed to be very costly in cormorants (Phalacrocoracidae) when compared with other avian divers because of their poor insulation and less-efficient foot propulsion. It was therefore suggested that cormorants might employ a behavioural strategy to reduce daily energy expenditure by minimizing the amount of time spent in water. However, European shags (Phalacrocorax aristotelis) have been observed to spend up to 7 h day(-1) diving in water of around 5-6 degrees C. To gain a better understanding of the energetic requirements in European shags, we measured their metabolic rates when resting in air/water and during shallow diving using respirometry. To investigate the effects of water temperature and feeding status on metabolic rate, birds dived at water temperatures ranging from 5 to 13 degrees C in both post-absorptive and absorptive states. In parallel with respirometry, stomach temperature loggers were deployed to monitor body temperature. Basal metabolic rate (BMR) was almost identical to allometric predictions at 4.73 W kg(-1). Metabolic rate when resting on water, during diving and after feeding was significantly elevated when compared with the resting-in-air rate. During diving, the metabolic rate of post-absorptive shags increased to 22.66 W kg(-1), which corresponds to 4.8x BMR. Minimum cost of transport (COT) was calculated at 17.8 J kg(-1) m(-1) at a swim speed of 1.3 m s(-1). Feeding before diving elevated diving metabolic rate by 13% for up to 5 h. There was a significant relationship between diving metabolic rate and water temperature, where metabolic rate increased as water temperature declined. Thermal conductance when resting in air at 10-19 degrees C was 2.05 W m(-2) degrees C(-1) and quadrupled during diving (7.88 W m(-2) degrees C(-1)). Stomach temperature when resting in air during the day was 40.6 degrees C and increased during activity. In dive trials lasting up to 50 min, stomach temperature fluctuated around a peak value of 42.0 degrees C. Hence, there is no evidence that European shags might employ a strategy of regional hypothermia. The energetic costs during shallow diving in European shags are considerably lower than has previously been reported for great cormorants (Phalacrocorax carbo) and are comparable to other foot-propelled divers. The lower dive costs in shags might be the consequence of a more streamlined body shape reducing hydrodynamic costs as well as a greater insulative plumage air layer (estimated to be 2.71 mm), which reduces thermoregulatory costs. The latter might be of great importance for shags especially during winter when they spend extended periods foraging in cold water.

Animals↗
PubMed2000

Continuous monitoring of haemodynamic parameters in humans during the early phase of simulated diving with and without breathholding.

This study examined the integrative changes of blood pressure (BP) and stroke volume (SV) leading to the initial biphasic heart rate (fc) response (first 15 s) in simulated diving manoeuvres with and without breathholding (BH). Simulated diving was studied in ten young healthy volunteers by application of a gel-filled pack at 0 degree C and 18 degrees C on the forehead with and without BH. Beat-by-beat and second-to-second fc, BP, SV, and total peripheral vascular resistance (TPR) were followed by continuous non-invasive monitoring. In all conditions (BH with forehead cooling at 0 degree and 18 degrees C) there was an early rise in BP triggering the first tachycardial response (fc acceleration) which was immediately counteracted by the concurrent further increase of SV leading to the second phase of early bradycardic response (fc deceleration). Furthermore, the continuous beat-by-beat and second-to-second monitoring allowed the documentation of a highly significant increase of TPR within the first few seconds of the manoeuvres. Our data further indicated that the differences in haemodynamics observed during the stimuli at different temperatures was overruled by BH. Detailed comparisons of the beat-by-beat and second-to-second analyses were unable to show that one method was better than the other. Using continuous non-invasive monitoring of haemodynamic variables during simulated diving manoeuvres it was possible to provide better insights into the physiological principles and meaning of the diving reflex in humans.

Adult↗
PubMed2003

Diversity in and adaptation to breath-hold diving in humans.

Several features of potential adaptation to breath-hold diving in diving populations and extreme divers are reviewed. Thermal adaptation consists of an improvement in cold tolerance, as witnessed by a decrease in critical water temperature, and implies an elevation of the shivering threshold associated with a greater body insulation. This is indicative of either a strong peripheral vasoconstriction or a more effective countercurrent heat exchange. Respiratory adaptation consists of a blunted ventilatory response to carbon dioxide and an enlargement of lung volumes. Finally, the occurrence of a diving response has been demonstrated. An extreme peripheral vasoconstriction is associated with a dramatic increase in arterial blood pressure. The consequent stimulation of arterial baroreceptors causes an extreme drop of heart rate. Bradycardia is not compensated by a higher stroke volume, with consequent decrease in cardiac output. This decrease, however, is not such as to undermine perfusion to vital organs. Redistribution of blood flow occurs, and some organs such as skeletal muscle may become unperfused, as indicated by the high blood lactate concentrations at low metabolic rate. It is not possible to state, however, whether these changes reflect genetic adaptations or an adaptive response to a prolonged environmental stress.

Adaptation, Physiological↗
PubMed1984

The QT interval during reflex cardiovascular adaptation.

We examined the relationship between changes in heart rate and the measured QT interval of the electrocardiogram in healthy subjects after exercise and during breath holding, hyperventilation, the dive reflex, the Valsalva maneuver, and the cold-pressor test. The tachycardia of exercise was accompanied by the familiar shortening of the QT interval, but substantial heart rate changes encountered in other more "sedentary" maneuvers were accompanied by very small changes in QT. Calculating the corrected QT in the latter instances, therefore, yielded spurious results. The data suggest very little, if any, direct effect of heart rate on the QT interval. The length of the interval in healthy subjects appears to be determined largely by reflexly elicited discrete autonomic influences. Those associated with exercise result in QT shortening but, during neurally mediated cardiovascular adjustments that do not involve exercise, QT is maintained within narrow limits.

Adaptation, Physiological↗
PubMed2004

Cardiovascular responses to head-out water immersion in Korean women breath-hold divers.

Head-out water immersion (HOI) increases cardiac output (CO) for a given oxygen consumption. To investigate whether professional breath-hold divers show a similar response, cardiovascular responses to HOI were compared between six Korean women breath-hold divers, six non-diving housewives and six non-diving young women at rest and while performing leg cycle exercise of moderate intensity (Deltametabolic rate = approximately 100 W m(-2)) in water at a thermoneutral temperature (34.5 degrees C). In all three groups, HOI increased CO markedly due to a rise in stroke volume, with no significant change in heart rate (HR) and arterial blood pressure (BP). Thus, total peripheral resistance (TPR) and arterio-venous oxygen content difference fell significantly. During dynamic exercise in water CO increased mainly due to a rise in HR. The arterial systolic BP rose slightly with no significant change in diastolic BP, and the TPR fell 20-40% with similar responses among the three groups of subjects. This study showed that both at rest and during exercise, cardiovascular responses to immersion do not vary significantly with age and water immersion experience.

Adaptation, Physiological↗
PubMed1996

Cardiorespiratory synchrony in turtles.

Many reptiles, particularly diving species, display characteristic cardiovascular changes associated with lung ventilation (cardiorespiratory synchrony). Previous studies on freshwater turtles show that heart rate and pulmonary blood flow rate (Qpul) increase two- to fourfold during ventilation compared with breath-holding, and some studies report concomitant decreases in systemic blood flow rate (Qsys). The primary aim of this study was to provide a detailed description of cardiorespiratory synchrony in free-diving and fully recovered turtles (Trachemys scripta). During breath-holds lasting longer than 5 min, Qpul averaged 15 ml min-1 kg-1 and increased more than threefold to a maximum value of 50 ml min-1 kg-1 during ventilation. Qsys also increased during ventilation compared with during breath-holds lasting longer than 5 min (from 44 to 73 ml min-1 kg-1 during ventilation). Neither Qpul nor Qsys was affected by the number of breaths in the ventilatory periods. Changes in Qpul and Qsys were accomplished entirely through a significant increase in heart rate during ventilation, while total stroke volume (systemic+pulmonary) remained constant. Irrespective of the ventilatory state, Qsys exceeded Qpul by 20-30 ml min-1 kg-1. Nevertheless, because Qpul increased relatively more than Qsys during ventilation, Qpul/Qsys increased from 0.29 during apnoea to 0.80 during lung ventilation. This study confirms cardiorespiratory synchrony in the turtle Trachemys scripta but, in contrast to earlier studies, a net right-to-left cardiac shunt prevailed regardless of ventilatory state.

Animals↗
PubMedDate not supplied

[Cardiovascular function in man during experimental dives at 26 ATA (helium-nitrogen-oxygen mixture)].

During two human experimental dives at 26 ATA (helium-nitrogen-oxygen gaz mixture; PIO2 = 400 mbar), the cardiac frequency (Fc) and radial arterial pulse were continuously recorded, at rest and during periods of maximal expiratory (Valsalva) or inspiratory (Müller) manoeuvres, used to increase or decrease the intrathoracic pressure, respectively. Cardiovascular variables were measured at 1 and 26 ATA in resting individuals and during the maximal respiratory manoeuvres. Discontinuous measurement of arterial blood pressure using a sphygomanometer allowed to calculate the mean arterial pressure. The value of mean arterial pressure was maintained against the membrane of a radial pulse sensor. This procedure, proposed by Posey et al. (1969), gives a continuous approximation and recording of arterial blood pressure and its components. The present results did not show significant variation in the values of Fc nor systolic or diastolic blood pressures measured at rest or during Müller manoeuvres performed at 1ATA at the maximal depth. On the other hand, Valsalva manoeuvres performed at depth induced significant variations in circulatory variables compared to the normobaric response. The most important effect was an enlargement of differential pressure due to a marked decrease in the diastolic blood pressure. These observations are discussed in terms of enlarged sensitivity of the baroreflex arch under hyperbaric condition.

Adult↗