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Biomedical subjects

J Bittel

Publications and source records attributed to J Bittel.

At least 19 recordsLinked to original sources
PubMed1995

Acute mountain sickness relates to sea-level partial pressure of oxygen.

The aim of this study was to clarify the relationships between acute mountain sickness (AMS), studied during an expedition in the Andes, and some physiological parameters determined before the expedition, i.e. biometrical characteristics of the subjects [maximal oxygen consumption (VO2max), body fat content, body mass index], functional pulmonary tests (forced vital capacity, forced expiratory volume at the first second), ventilatory or cardiac responses measured at 4,500 m [hypoxic ventilatory responses (HVR) 4,500 and hypoxic cardiac responses (HCR) 4,500, respectively), cold pressor responses. To achieve this objective, 11 subjects were firstly submitted to a hypobaric poïkilocapnic hypoxic test (589 hPa, 4,500 m) at rest and during exercise to study minute volume, respiratory frequency, end tidal partial pressure of O2 (PETO2) and CO2, HVR 4,500, HCR 4,500 and to a cold pressor test of the hand (5 min in 5 degrees C cold water) to study heart rate, blood pressure and skin temperature changes. The AMS was assessed daily by questionnaire during a 12-day expedition in the Andes following both Hackett's method and Environmental Symptoms Questionnaire (modified ESQ II). Maximal AMS-Hackett score, maximal AMS-ESQ score and mean AMS-ESQ score were defined. The quantifications of AMS following the two methods were correlated. No significant relationships were observed between mean AMS-ESQ score and the biometrical characteristics of the subjects, the functional pulmonary tests, HVR 4,500, HCR 4,500 or the cold pressor responses. However, it appeared that the mean AMS-ESQ score was correlated with PETO2 measured at rest and during exercise (50% VO2max) both in hypoxia and normoxia. A closer linear relationship was observed during the exercise in normoxia (r = -0.92, P < 0.0001). These results could suggest that AMS was related to a relative alveolar hypoventilation more in relation to breathing pattern than HVR.

Acute Disease↗
PubMed1992

Reversal of cold induced haemoconcentration.

Classically, cold induced plasma volume reduction is explained by an increased diuresis which is generated by an inhibition of antidiuretic hormone release. However, most of the haemoconcentration appears to be reversible during rewarming. This observation weakens the former statement. The aim of this study was to clarify the mechanisms involved in the reversal of the cold induced haemoconcentration. Six young males, resting in a dorsal reclining position, were exposed successively to a thermoneutral environment (30 min), a cold environment (1 degrees C; cold) or thermoneutrality (control) for 120 min, and during a 60-min recovery period in thermoneutral conditions. During cold stress, a reduction of 15% (i.e. 510 ml) of the plasma volume was observed, and osmolality was unchanged. After the 60-min recovery under thermoneutral conditions, plasma volume variation between the Cold and the Control experiments was reduced and reached 3% (i.e. 100 ml). This volume equalled the increased amount of urine production observed during the cold stress experiment. Haemoconcentration cannot be explained by increased urinary water loss (+/- 100 ml) alone. Therefore a transient shift of plasma water from vascular to interstitial spaces, due to an increase of blood pressure, could be involved in the reduction of plasma volume.

Adult↗
PubMed1992

The different types of general cold adaptation in man.

Different types of general cold adaptation have been described over the last 50 years. Metabolic adaptation (Alacaluf Indians, Arctic Indians Eskimos), insulative adaptation (coastal Aborigines of tropical northern Australia), hypothermic adaptation (bushmen of the Kalahari desert, Peruvian Indians) and insulative hypothermic adaptation (Central Australian Aborigines, nomadic Lapps, Korean and Japanese diving women). These different types of cold adaptation are related to the intensity of the cold stress and to individual factors such as diet, the level of physical fitness and body fat content. Thus, in natural environments, man develops a strategy of adaptation to cold, which takes into account environmental and individual factors. This strategy is susceptible to be modified when these conditions change. Caloric intake deficit could have been responsible for the hypothermic adaptation observed after J.-L. Etienne's journey to the North Pole. Physiological responses were adapted to maintain an acceptable level of energetic reserves with a moderate hypothermia, which was not life threatening for the climatic conditions encountered by the polar explorer.

Acclimatization↗
PubMed1992

Use of a hypobaric chamber for pre-acclimatization before climbing Mount Everest.

Climbing Mount Everest needs an acclimatization period of 3 to 4 weeks between 3000 and 6000 m. In order to reduce this period of time spent in dangerous conditions, an experience of pre-acclimatization was performed with 5 elite alpinists (4 male, 1 female), aged 30 +/- 4 yrs (mean +/- SD), before their attempt to climb Mount Everest. Subjects first remained one week on Mont-Blanc (between 4350 and 4807 m), then spent a total of 38 hours in a hypobaric chamber (in 4 consecutive days) from 5000 to 8500 m standard altitude. Then, they flew to Kathmandu and reached 7800 m five days only after leaving the base camp. The pre-acclimatization period showed a 12% increase in hemoglobin concentration, and no change in ventilatory response to hypoxia. Arterial oxygen saturation at submaximal exercise in hypoxia (FIO2 = 0.115) increased from 75 +/- 4 to 82 +/- 3%, probably because of an efficient ventilatory acclimatization. On Mount Everest, the speed of ascent was very high (5600 m of altitude gain in 6 days), knowing that in conventional expeditions, 12 to 32 days are generally necessary to reach, safe, the same altitude. In conclusion, pre-acclimatization seems to have triggered efficient mechanisms which allowed climbers to save 1 to 3 weeks of time in mountain conditions.

Acclimatization↗
PubMed1992

Factors enhancing cardiac output in resting subjects during cold exposure in air environment.

Six young males, in semi-nude conditions, resting in dorsal reclining position, were exposed successively to a thermoneutral environment (30 min), a cold environment (1 degree C) (Cold) or thermoneutrality (Control) (120 min), and during 60 min recovery in thermoneutral conditions. Cardiac output has been measured using a Dual Beam Doppler. During cold stress a significant increase of heart rate (66.4 +/- 6.4 to 91.0 +/- 14.9 beats.min-1), systolic blood pressure (119.5 +/- 7.8 to 218.7 +/- 18.7 mmHg), diastolic blood pressure (68.1 +/- 11.7 to 114.3 +/- 28.3 mmHg) and cardiac output (5.42 +/- 0.96 to 8.08 +/- 1.28 l.min-1) were observed. On the contrary initial systolic aorta flow acceleration is significantly lowered (1130 +/- 120 to 840 +/- 170 cm.s-2). Systolic ejection volume remained unchanged throughout the whole experiment. Increase in cardiac output during cold air (1 degree C) exposure is thus only imputed to the higher heart rate partly due to hypersecretion of catecholamines. The diminution of the blood flow acceleration could be related to a lesser arterial compliance and/or to the cold induced hemoconcentration. Enhanced heart's mechanical work due to sympathetic stimulation, seems thus to be absorbed by the increase in the peripheral resistance.

Adult↗
PubMed1990

Finger and forearm vasodilatatory changes after local cold acclimation.

To determine the vascular changes induced by local cold acclimation, post-ischaemia and exercise vasodilatation were studied in the finger and the forearm of five subjects cold-acclimated locally and five non-acclimated subjects. Peak blood flow was measured by venous occlusion plethysmography after 5 min of arterial occlusion (PBFisc), after 5 min of sustained handgrip at 10% maximal voluntary contraction (PBFexe), and after 5 min of both treatments simultaneously (PBFisc + exe). Each test was performed at room temperature (25 degrees C, SE 1 C) (non-cooled condition) and after 5 min of 5 degrees C cold water immersion (cooled condition). After the cold acclimation period, the decrease in skin temperature was more limited in the cold-acclimated compared to the non-acclimated (P less than 0.01). The PBFisc was significantly reduced in the cooled condition only in the cold-acclimated subjects (finger: 8.4 ml.100 ml-1.min-1, SE 1.1, P less than 0.01; forearm: 5.8 ml.100 ml-1.min-1, SE 1.5, P less than 0.01) compared to the non-cooled condition. Forearm PBFexe was significantly decreased in the cooled condition only in the cold-acclimated subjects (non-cooled: 7.4 ml.100 ml-1.min-1, SE 1.2; cooled: 3.9 ml.100 ml-1.min-1, SE 2.6, P less than 0.05) indicating that muscle blood flow was also reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1990

Thermoregulation at rest and during exercise in prepubertal boys.

Thermal balance was studied in 11 boys, aged 10-12 years, with various values for maximal oxygen uptake (VO2max), during two standardized sweating tests performed in a climatic chamber in randomized order. One of the tests consisted in a 90-min passive heat exposure [dry bulb temperature (Tdb) 45 degrees C] at rest. The second test was represented by a 60-min ergocycle exercise at 60% of individual VO2max (Tdb 20 degrees C). At rest, rectal temperature increased during heat exposure similar to observations made in adults, but the combined heat transfer coefficient reached higher values, reflecting greater radiative and convective heat gains in the children. Children also exhibited a greater increase in mean skin temperature, and a greater heat dissipation through sweating. Conversely, during the exercise sweating-test, although the increase in rectal temperature did not differ from that of adults for similar levels of exercise, evaporative heat loss was much lower in children, suggesting a greater radiative and convective heat loss due to the relatively greater body surface area. Thermophysiological reactions were not related to VO2max in children, in contrast to adults.

Body Temperature Regulation↗
PubMed1990

Thermal exchanges during sleep in anhidrotic ectodermal dysplasia.

Anhidrotic ectodermal dysplasia is a congenital syndrome characterized by the absence of sweat glands. A sweating test was performed on such a patient and proved his inability to sweat. Thermal exchanges during night sleep were then measured in this patient and compared with data obtained from a healthy control subject. Ambient conditions were as follows: dry bulb temperature 32.2 degrees C, relative humidity 30%-40%, wind speed 0.7 m.s-1. Polysomnographic recordings showed normal sleep patterns in both subjects, but a "first night effect" in the patient. Rectal (Tre) and mean skin (Tsk) temperatures and loss of mass were monitored continuously throughout the 8-h sleep recording. Loss of mass averaged 34.1 g.h-1 in the patient vs 78.1 g.h-1 in the control subject. No relationship with sleep stages was observed in the patient, in contrast to the control subject who experienced a decrease in evaporation during rapid eye movement sleep. Body temperatures varied little in the patient, but decreased until the 6th h of sleep in the control subject. On two occasions there was a 0.3 degrees C fall in the Tre of the patient during two slow wave sleep (SWS) phases, while Tsk and loss of mass did not change. As thermolytic processes had not varied on these two occasions, it was concluded that the fall in Tre indicated a concomitant decrease in metabolic heat production, in agreement with the assumption that SWS represented a state of energy conservation.

Adolescent↗
PubMed1990

[Circadian analysis of sleep, rectal temperature and immunological and endocrinological variables in sleeping sickness: preliminary study].

A multidisciplinary study was conducted in 8 patients with neurological Human African Trypanosomiasis. The sleep-wake cycle followed an ultradian pattern which was more pronounced in patients with more severe symptoms. The EEG trace was consistently interrupted by numerous cyclic activation patterns with K complexes, rapid low amplitude elements and slow high voltage elements. Circadian rhythmicity was also disturbed in other physiological (rectal temperature), immunological (interleukins) or hormonal (cortisol, prolactin) variables, the disturbance being greater in severely hit patients.

Adolescent↗
PubMed1988

Seasonal changes in circadian rhythms of body temperatures in humans living in a dry tropical climate.

Seven volunteers (3 females and 4 males; 3 Caucasians and 4 Africans) participated in two 24 h sessions during the cool dry (CD) and the hot dry (HD) seasons of the sahelian tropical climate. Body temperatures were taken on portable cassette recorders for 24 h. Rectal (Tre) and mean skin (Tsk) temperatures decreased in the HD compared to the CD conditions, meeting one of the criteria for adaptation to heat. No ethnic differences in thermal responses were found. Males and females differed in their body temperature rhythms and in their reactions to heat. Body temperatures were higher in females than in males. Males reacted to heat with a decrease in Tre, without change in the Tre-Tsk gradient. Females showed a decrease in both Tre and Tsk, more marked for Tsk, with an increase in the Tre-Tsk gradient. It was concluded that males showed seasonal acclimatization to heat via a decrease in metabolism confirmed by a decrease in plasma levels of thyroid stimulating hormone (TSH) in the HD condition. Females showed a mixed metabolic and thermolytic type of acclimatization, with an absence of variation in plasma TSH levels. In conclusion, the steady rise in temperature between the CD and HD conditions was sufficient to trigger an acclimatization to heat similar in Caucasian and African subjects, although exposure to the external climate differed widely.

Acclimatization↗
PubMed1988

Body temperature and plasma prolactin and norepinephrine relationships during exercise in a warm environment: effect of dehydration.

The effects of euhydration (Eh) and light (Dh1) and moderate (Dh2) dehydrations on plasma prolactin (PRL) levels were studied in 5 young male volunteers at rest and during exercise to exhaustion (50% of VO2max) in a warm environment (Tdb = 35 degrees C, rh = 20-30%). Light and moderate dehydrations (loss of 1.1 and 1.8% body respectively) were obtained before exercise by controlled hyperthermia. Compared to Eh, time for exhaustion was reduced in Dh1 and Dh2 (p less than 0.01) and rectal temperature (Tre) rose faster in Dh2 (p less than 0.05). Both venous plasma PRL and norepinephrine (NE) increased during exercise at any hydration level (p less than 0.05). Plasma PRL reached higher values after 40 and 60 min in Dh2 and Dh1 (p less than 0.05). Plasma NE values were higher in Dh2 at rest and at the 40th min during exercise (p less than 0.05). Plasma PRL was linearly correlated to Tre and plasma NE (p less than 0.001) but unrelated to plasma volume variation and osmolality. Our results provide further evidence for the major effect of body temperature in exercise-induced PRL changes. Moreover, the plasma PRL-NE relationship suggests that these changes may result from central noradrenergic activation.

Adult↗
PubMed1983

[Confinement].

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Air Pollution↗
PubMed1979

Thermogenesis and thermolysis during sleeping and waking in the rat.

Thermogenesis (VO2), sensible heat loss and subcutaneous back temperature were recorded simultaneously during sleeping and waking in both intact and depilated rats at Ra ranging from 21--28 degrees C. VO2 increased during wakefulness (W), decreased and plateaued during slow wave sleep (SWS) and then decreased 10% with each paradoxical sleep (PS) phase. Sensible heat loss, which represented about 90% of the heat production, increased and plateaued during SWS, decreased in W and generally rose abruptly (+40%) during PS. After removal of the fur the mean levels of VO2 and sensible heat loss were increased by 20--50% and returned to normal values within two weeks, although their variations related to stages of sleep were unchanged. These results concerning thermogenesis and thermolysis are in agreement with the variations of body temperature (brain excluded) during sleeping and waking.

Animals↗
PubMed1979

Thermal strain resulting from protective clothing of an armored vehicle crew in warm conditions.

The purpose of the study is to define a method of evaluation of physiological strain resulting from protective garments worn in warm conditions by the armored vehicle crew. A technique is developed evaluating evaporative transfer through clothing by continuous weighing of the active man (accuracy +/- 3/g). An index is defined (Iw) as the ratio of steady-state evaporating rate in clothed conditions to steady-state evaporation of nude subject in the same conditions of work and heat stress. The Iw index is significantly related to physiological strain determined by increased body heat content and reduced tolerance time. The results are compared to other previous findings concerning evaporative transfer through clothing and physiological strain indexes. The technique shows that evaporation through heavy clothing is not negligible. It is suggested that usual static measurements using physical models underestimate the evaporative heat transfer through clothing layers.

Body Temperature↗
PubMed1977

Variations in evaporation and body temperatures during sleep in man.

The thermal balance in man was investigated during nocturnal sleep in neutral and warm environments (from 32 to 39.5 degrees C, 45%rh). Changes of body temperatures and skin evaporation were continuously monitored throughout the whole night. In neutral conditions (32 and 34 degrees C) body temperature and skin evaporation decreased during the night, following the circadian rhythm deltaT sk = -0.34 degrees C; deltaT re = -0.52 degrees C;deltaE = -12 W-m-2. In warm conditions, body temperatures and evaporation remained steady. Marked fluctuations of body temperatures and evaporation occurred synchronously with the rapid eye movement (REM) periods. Each REM period induced phasic increase of Tsk reaching +2 degrees C in some cases, with a cessation of evaporation. Tre showed upward and downward rhythmical waves synchronously with REM sleep occurrence. The nocturnal variations of thermal balance were characterized by two rhythms: a basal circadian rhythm and superimposed on it a rhythm conditioned by occurrence of REM sleep every 80-90 min. The phasic changes of body temperatures and evaporation only appeared with REM's. The results suggest that the nervous integrative function conditioning the patterns of sleep, conditions also the phasic cyclic changes of thermoregulatory function.

Adult↗
PubMed1977

Comparison of indirect calorimetry and direct heat flow discs results in measuring R+C heat loss in burned patients.

This study was carried out on 17 burned patients. Metabolic heat production, rectal and skin temperatures, and heat exchanges by R+C were measured. It was found that R+C heat loss takes into account 60 to 80% of the increased metabolic heat production. Two methods were used to measure R+C heat loss: calculation by indirect calorimetry and direct measurements by using heat flow discs. The direct relationship which exists between the results of these two methods showed the reliability of the use of heat flow discs for measuring R+C heat loss. This fast-responding techniques may allow the elaboration of a thermal setting system which could modulate ambient air temperature, thus limiting exagerated heat loss due to the skin lesions.

Body Temperature Regulation↗
PubMed1975

Comparison of thermal exchanges in men and women under neutral and hot conditions.

1. The thermoregulatory responses in unacclimatized men and women were analysed and compared by means of standard heat exposure tests which allowed evaporative losses, body temperatures, heat storage and the complete thermal balance to be continuously recorded in all subjects. 2. The most pronounced differences were observed in delay before onset of sweating. Sweating always occurred faster with lower body temperatures in men than in women. The period immediately following ovulation was characterized by an increase in onset delay and a decrease in the sensitivity in sweating response compared with the pre-ovulation period. 3. The evaporative rate in the steady state did not change significantly in the post-ovulation period and was found to be higher in men who consequently had lower mean skin temperatures. Skin conductances, different under thermo-neutral conditions, were the same in men and women under hot conditions. 4. Women showed a more definite increase of body temperatures and heat storage than men due to delayed sweating and decreased sweating sensitivity. The body heat content in the steady state increased more markedly in women than in men. Furthermore, the highest heat storage values were found during the post-ovulation period. A high degree of correlation was found between body heat content and absolute onset delay. 5. The sweating kinetics and the transient phase just before the steady state of the thermal balance appeared to be decisive factors in the differentiation of the thermoregulatory behaviour in women before and after ovulation. Heat storage achieved during the transient phase and not made up by adequate evaporation seemed to be the cause of the large increase of body temperatures and heat content shown by women in hot environments.

Adult↗