Adaptative mechanism of the equilibrative nucleoside transporter 1 (ENT-1) and blood adenosine levels in elite freedivers.

PURPOSE: Long static or intense dynamic apnoea-like high-altitude exposure is inducing hypoxia. Adenosine is known to participate to the adaptive response to hypoxia leading to the control of heart rate, blood pressure and vasodilation. Extracellular adenosine level is controlled through the equilibrative nucleoside transporter 1 (ENT-1) and the enzyme adenosine deaminase (ADA). The aim of this study was to determine the control of adenosine blood level (ABL) via ENT-1 and ADA during apnoea-induced hypoxia in elite freedivers was similar to high-altitude adaptation. METHODS: Ten freediver champions and ten controls were studied. Biological (e.g. ENT-1, ADA, ABL, PaO2, PaCO2 and pH) and cardiovascular (e.g. heart rate, arterial pressure) parameters were measured at rest and after a submaximal dry static apnoea. RESULTS: In freedivers, ABL was higher than in control participants in basal condition and increased more in response to apnoea. Also, freedivers showed an ADA increased in response to apnoea. Finally, ENT-1 level and function were reduced for the free divers. CONCLUSION: Our results suggest in freedivers the presence of an adaptive mechanism similar to the one observed in human exposed to chronic hypoxia induced by high-altitude environment.

Cardiac alterations induced by a fish-catching diving competition.

Cardiac changes induced by repeated breath-hold diving were investigated after a fish-catching diving competition. Eleven healthy subjects carried out repeated breath-hold dives at a mean maximal depth of 20 ± 2.7 msw (66 ± 9 fsw) during 5 h. One hour after the competition, the body mass loss was -1.7 ± 0.5 kg. Most of the breath-hold divers suffered from cold and although the core temperature remained normal, a decrease in cutaneous temperature was recorded in the extremities. Systolic blood pressure was reduced in both upper and lower limbs. Heart rate was unchanged, but left ventricular (LV) stroke volume was reduced leading to a decrease in cardiac output (-20%). Left atrial and LV diameters were significantly decreased. LV filling was assessed on a trans-mitral profile. An increase in the contribution of the atrial contraction to LV filling was observed. Right cavity diameters were increased. The cardiac autonomic alterations were in favor of sympathetic hyperactivity. After a fish-catching diving competition in cold water, alterations suggesting dehydration, contraction in plasma volume and sympathetic hyperactivity were observed. Furthermore, enlargements of right cavities were in favor of right ventricular strains. Repeated apnea and swimming in cold water may account for these alterations.

Ultrasound lung comets induced by repeated breath-hold diving, a study in underwater fishermen.

Pulmonary edema has been reported in breath-hold divers during fish-catching diving activity. The present study was designed to detect possible increases in extravascular lung water (EVLW) in underwater fishermen after a competition. Thirty healthy subjects were studied. They participated in two different 5-h fish-catching diving competitions: one organized in the winter (10 subjects) and one organized in the autumn (20 subjects). A questionnaire was used to record underwater activity and note respiratory problems. An increase in EVLW was investigated from the detection of ultrasound lung comets (ULC) by chest ultrasonography. Complementary investigations included echocardiography and pulmonary function testing. An increase in EVLW was detected in three out of 30 underwater fishermen after the competition. No signs of cardiovascular dysfunction were found in the entire population and in divers with an increase in the ULC score. Two divers with raised ULC presented respiratory disorders such as cough or shortness of breath. Impairment in spirometric parameters was recorded in these subjects. An increase in EVLW could be observed after a fish-catching diving competition in three out of 30 underwater fishermen. In two subjects, it was related to respiratory disorders and impairment in pulmonary flow.

Physiological responses to repeated apneas in underwater hockey players and controls.

The aim of this study was to investigate the effects of short repeated apneas on breathing pattern and circulatory response in trained (underwater hockey players: UHP) and untrained (controls: CTL) subjects. The subjects performed five apneas (A1-A5) while cycling with the face immersed in thermoneutral water. Respiratory parameters were recorded 1 minute before and after each apnea and venous blood samples were collected before each apnea and at 0, 2, 5 and 10 minutes after the last apnea. Arterial saturation (SaO2) and heart rate were continuously recorded during the experiment. Before the repeated apneas, UHP had lower ventilation, higher P(ET)CO2 (p < 0.05) and lower P(ET)O2 than CTL (p < 0.001). After the apneas, the P(ET)O2 values were always lower in UHP (p < 0.001) than CTL but with no difference for averaged P(ET)CO2 (p = 0.32). The apnea response, i.e., bradycardia and increased mean arterial blood pressure, was observed and it remained unchanged throughout the series in the two groups. The SaO, decreased in both groups during each apnea but the post-exercise SaO2 values were higher in UHP after A2 to A5 than in CTL (p < 0.01). The post-apnea lactate concentrations were lower in UHP than in CTL. These results indicate that more pronounced bradycardia could lead to less oxygen desaturation during repeated apneas in UHP. The UHP show a specific hypoventilatory pattern after repeated apneas, as well as a more pronounced cardiovascular response than CTL. They indeed showed no detraining of the diving response.

Cognitive performance during a simulated climb of Mount Everest: implications for brain function and central adaptive processes under chronic hypoxic stress.

High altitude is characterized by hypoxic environmental conditions and is well known to induce both physiological and psychological disturbances. In the present study, called "Everest-Comex 97", the authors investigated the effects of high altitude on the psychosensorimotor and reasoning processes of eight climbers participating in a simulated climb from sea level to 8,848 m over a 31-day period of confinement in a decompression chamber. Tests of visual reaction time, psychomotor ability, and number ordination were used. The climbers' data were compared with data from a similar laboratory study at sea level in control subjects. Continued testing of the control subjects at sea level clearly led to learning effects and improvement of performance in psychomotor ability and number ordination. In the climbers, similar learning effects occurred up to an altitude of 5,500­6,500 m. With further increases in altitude, the climbers' psychomotor performance and mental efficiency deteriorated progressively, leading to significant differences in psychomotor ability and mental efficiency between control subjects and climbers (9 and 13% respectively at 8,000 m and 17.5 and 16.5% respectively at 8,848 m). Three days (72 h) after the climbers had returned to sea level, their mental and psychomotor performances were still significantly lower than those of control subjects (by approximately 10%). In contrast, visual reaction time showed no significant changes in either climbers or control subjects. It is suggested that chronic hypoxic stress could alter selectively mental learning processes, i.e. explicit, rather than implicit (stimulus-response learning processes) memory and cortico-limbic rather than basal ganglia-sensorimotor system function.

T wave changes in humans and dogs during experimental dives.

Electrocardiogram (ECG) analysis was performed in three human divers studied at 21 and 23.5 ATA while they breathed various gas mixtures containing H2 and/or He (COMEX HYDRA IX experiment) and in five dogs exposed to 91 ATA of He-O2 or He-N2-O2. In all cases, the O2 partial pressure was slightly higher than its physiological value. These human and animal studies reveal that elevated pressure of different inert gases did not change the resting heart rate or its respiratory fluctuation. However, the T wave amplitude increased in proportion to the gas density in the three divers; this was also found in four of the five dogs studied. Changes in peak T wave configurations were also observed in the dog experiments. Positional changes in QRS or T vectors cannot explain these T wave changes.

Personality factors, stoicism and motivation in subjects under hypoxic stress in extreme environments.

Previous studies on the physiological and psychological adaptation of subjects to survival conditions involving high-altitude hypoxia (>6,500 m) have shown that personality factors are important in this adaptation. We, therefore, proposed personality traits assessments in two groups of subjects engaged in sporting activities under extreme hypoxic environmental conditions: a group of mountaineers at high altitudes (>5,500 m) and a group of free-lung divers at great depths (<30-60 m). These subjects were compared with two control groups: a group of subjects practicing no sport and another one practicing various competitive athletic activities involving speed constraints. The personality traits assessed concerned mainly the subjects' attitudes and their propensities to act out their feelings and fantasies; they were assessed using projective procedures, the Hand Test and Clark's Situational Pain Questionnaire based on the Sensory Decision Theory. Subjects trained in mountaineering and free-lung diving under extreme environmental conditions displayed a high degree of stoicism. These individuals shared some personality traits with other sportsmen, particularly aggressive tendencies and introversion although not to an extent which interfered with normal interpersonal relationships. However, at least when practicing these extreme sports, the subjects did retreat from society. One of our questions concerns the grounds for this social withdrawal, that is, whether it derives from a inner compulsion founded on personality factors or if it is merely an artifact of our perceptions of the subjects, created by the confluence of the individualistic nature of these sports and the extreme environments in which they are performed.

Heart rate responses during a breath-holding competition in well-trained divers.

The diving response elicited by breath-holding (BH) and immersion mainly consists of bradycardia, decreased cardiac output, and peripheral vasoconstriction. These responses reduce oxygen consumption and thereby prolong the duration of the dive. They may also lead to cardiac arrhythmias or hypoxia, however, which in turn may play a role in the occurrence of syncope during BH. The aim of the present study was to analyze the cardiac responses to prolonged breath-holding in elite divers during a competition. Heart rate behaviour and the incidence of arrhythmia were recorded in 16 well-trained breath-hold divers (BHD) using a cardio-frequency meter (for 15 divers) and a Holter (for one diver) during maximal static breath-holding. Anthropometric, spirometric, and training characteristics such as percentage of body fat, pulmonary volumes and years of BH training were also determined. Forced vital capacity (FVC) and forced expiratory volume in one second (FEV (1)) were higher than the predicted values (+7.7%, p<0.05 and+6.6%, p<0.05, respectively). During the static BH, divers presented apneic bradycardia (-44%) correlated with static BH times (p<0.05); this was associated with cardiac arrhythmias (supraventricular extrasystoles and ventricular extrasystoles) in the Holter-equipped subject. These results are in agreement with those obtained in laboratory conditions and confirm the existence of cardiac arrhythmias in well-trained BHD.

Psycho-sensorimotor performance in divers exposed to six and seven atmospheres absolute of compressed air.

In the present study, we investigated the psycho-sensorimotor abilities of divers exposed to 6 ATA (50 m of sea water; corresponding to legal limit for occupational diving in North America, United Kingdom, and Northern Europe), or 7 ATA (60 m; the legal limit in France and Southern Europe) of compressed air (1 ATA = 100,000 Pa), using psychometric tests of manual dexterity, visual choice reaction time, and number ordination. The results of the present study showed that abilities in these tests were not significantly altered by pressure exposure to 6 ATA of compressed air. However, data obtained at 7 ATA showed slight but significant decreases in performance. Nevertheless, a few subjects presented large decreases in performance ranging from -20% to -25% of control. Finally, our results supported the ergonomic point of view that the laws limiting occupational diving to 6 ATA (50 m) are better adapted to reality and the requirements of underwater activity.

[Cardiovascular function in man during experimental dives at 26 ATA (helium-nitrogen-oxygen mixture)]. / Etude de la fonction cardio-vasculaire chez l'Homme au cours de plongées expérimentales à 26 ATA (mélange hélium-azote-oxygène).

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.

Electrocardiogram changes during positive pressure breathing in rabbits.

Positive pressure breathing produced by mechanical ventilation with an expiratory threshold load (ETL) may modify electrocardiogram (ECG) complexes independently of any recording artefact due to lung volume changes. Anaesthetized, paralyzed rabbits were treated for about 2 h, then killed. In intact then vagotomized animals two situations were studied successively. Firstly, positive inspiratory pressure breathing, and secondly, positive inspiratory plus expiratory pressure breathing by adding ETL to mechanical ventilation. Arterial blood gases were measured and held constant throughout the challenge. Oesophageal pressure, giving indirect measurement of intrathoracic pressure, arterial blood pressure, blood flows in abdominal aorta and inferior vena cava and standard ECG recordings were made at baseline condition during mechanical ventilation, then at the end of a 10-min period of ETL breathing. The ETL breathing decreased arterial blood pressure significantly and reduced arterial and venous blood flows in the same proportion. No change in the duration of ECG complexes was noticed. However, ETL markedly reduced the amplitude of P- and T-waves, but not that of R-wave, an effect significantly accentuated after vagotomy. The ETL breathing increased the T-vector angle, with no associated change in QRS vector angle. The present animal investigations revealed that positive pressure breathing modifies the ECG independently of the consequences of ETL-induced lung volume changes. We speculate that the changes in P- and T-wave amplitude may have resulted from a reduced transmural pressure gradient between the epicardium and endocardium.

An anxiety, personality and altitude symptomatology study during a 31-day period of hypoxia in a hypobaric chamber (experiment 'Everest-Comex 1997').

Extreme environmental situations are useful tools for the investigation of the general processes of adaptation. Among such situations, high altitude of more than 3000 m produces a set of pathological disorders that includes both cerebral (cAS) and respiratory (RAS) altitude symptoms. High altitude exposure further induces anxiety responses and behavioural disturbances. The authors report an investigation on anxiety responses, personality traits, and altitude symptoms (AS) in climbers participating in a 31-day period of confinement and gradual decompression in a hypobaric chamber equivalent to a climb from sea-level to Mount Everest (8848 m altitude). Personality traits, state-trait anxiety, and AS were assessed, using the Cattell 16 Personality Factor questionnaire (16PF), the Spielberger's State-Trait Anxiety Inventory (STAI), and the Lake Louise concensus questionnaire. Results show significant group effect for state-anxiety and AS; state-anxiety and AS increased as altitude increased. They also show that state-type anxiety shows a similar time-course to cAS, but not RAS. Alternatively, our results demonstrate a significant negative correlation between Factor M of the 16PF questionnaire, which is a personality trait that ranges from praxernia to autia. In contrast, no significant correlation was found between personality traits and AS. This suggests that AS could not be predicted using personality traits and further support that personality traits, such as praxernia (happening sensitivity), could play a major role in the occurrence of state-type anxiety responses in extreme environments. In addition, the general processes of coping and adaptation in individuals participating in extreme environmental experiments are discussed.