Biomedical subjects

J Bittel

Publications and source records attributed to J Bittel.

At least 37 records · Page 2Linked to original sources

PubMed1997

[Travelers exposed to extreme temperatures].

Sudden introduction of the unadapted human into extreme environments can result in serious, sometimes fatal, reactions. Most complications are due either to failure of thermoregulatory system or consecutive to the physiological responses to those environmental conditions. In addition to a number of minor diseases, cold can cause two major accidents, i.e., hypothermia and frostbite which can be enhanced at altitude. Moreover, the main disease in altitude conditions is represented by the acute mountain sickness which can lead to acute pulmonary and cerebral edema. Heat can cause heatstroke, dehydration, syncope, and other minor disorders. Prevention of these manifestations during stays in inhospitable climatic conditions for which the body is not suited requires knowledge of the environment and its dangers. Implementation of suitable measures can greatly reduces the incidence of adverse effects.

Adaptation, Physiological↗

PubMed1996

Pre-adaptation, adaptation and de-adaptation to high altitude in humans: cardio-ventilatory and haematological changes.

The aim of this study was first to investigate cardio-ventilatory and haematological responses induced by intermittent acclimation and second to study de-adaptation from high altitude observed after descent. To achieve these objectives nine subjects were submitted to intermittent acclimation in a low barometric chamber (8 h daily for 5 days, day 1 at 4500 m, day 5 at 8500 m) before an expedition to the Himalayas. Cardio-ventilatory changes were measured during a hypobaric poikilocapnic hypoxic test (4500 m, barometric pressure = 589 hPa) and haematological changes were studied at sea level. These measurements were performed before and after acclimation, after return to sea level, but also 1 and 2 months after the expedition. In addition, partial pressures of oxygen and carbon dioxide in arterial blood (PaO2, PaCO2) and arterial erythropoietin concentration [EPO] were measured at rest during the hypoxic test. Results suggested the pre-adaptation protocol was efficient since an increased PaO2 (+12%, P < 0.05), a smaller difference in alveolo-arterial PO2 ( -63%, P < 0.05) and a lower PaCO2 ( -11%, P < 0.05), subsequent to ventilatory changes, were observed after acclimation with a significant increase in reticulocytes and in sea level [EPO] (+44% and +62% respectively, P < 0.05). De-adaptation was characterized by a loss of these cardio-ventilatory changes 1 month after descent, whereas the haematological changes (increased red blood cells and packed cell volume, P < 0.05) persisted for 1 month before disappearing 2 months after descent. This study would also suggest that acute hypoxia performed after a sojourn at high altitude could induce significantly depressed EPO responses (P < 0.05).

Adaptation, Physiological↗

PubMed1996

Biometrical characteristics and physiological responses to a local cold exposure of the extremities.

The aim of this study was firstly to describe the physiological responses observed in 19 subjects during immersion of the arm up to the elbow in water at 5 degrees C (5 min) followed by a 10-min recovery and secondly, to correlate the observed physiological responses with biometrical characteristics of the subjects (maximal oxygen uptake, VO2max, percentage fat content of whole body, BF, and arm, forearm and hand skinfold thickness). The results showed that the time courses of changes in forearm and hand skin temperature were different compared to those of finger skin temperatures both during local cooling and during rewarming (P < 0.05). Cardiovascular responses (heart rate, systolic and diastolic blood pressures) and finger skin temperatures were not related to the biometrical characteristics of the subjects. However, at the end of the immersion, decreased hand skin temperature was correlated to VO2max (r = 0.45, P < or = 0.05) whereas decreased forearm skin temperature was correlated both to VO2max (r = 0.44, P < or = 0.05) and to skinfold thickness (r = -0.44, P < or = 0.05) but not to BF. During the beginning of the recovery period only, outside, inside forearm and hand skin temperatures were related to VO2max (r = 0.54, P < or = 0.05; r = 0.66, P < or = 0.01 and r = 0.45, P < or = 0.05, respectively) and all the skinfold thicknesses (r = -0.47 to -0.71, P < or = 0.05). It was concluded that the local skin temperature profiles differed according to the upper limb segment both during cooling and during early rewarming. Moreover, VO2max and upper limb skinfold thickness but not BF did influence the forearm and hand skin temperature changes during cooling and early rewarming but not the finger skin temperature changes and cardiovascular responses.

Adult↗

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↗

PubMed1995

Influence of hyperthermia on cochlear micromechanical properties in humans.

We investigated the effect of body temperature on transient evoked otoacoustic emissions (TEOAEs) in humans. Hyperthermic conditions were obtained in adults in a climatic chamber. During hyperthermia up to an average temperature of 38.4 degrees C, significant falls were found in total amplitude and peak values of TEOAEs: by 1.3 dB SPL/degree C and 2.3 dB/degree C, respectively. This inhibition affected all spectrum components equally. These findings indicate that the outer hair cell micromechanical activity that is presumed to be measured by TEOAEs is not independent of variations in body temperature. The reduction found in hyperthermia suggests that temperature-dependent mechanisms are involved in the generation of TEOAEs.

Adult↗

PubMed1995

Evaluation of the Lake Louise acute mountain sickness scoring system in a hypobaric chamber.

This study evaluated the relevance of the Lake Louise acute mountain sickness (AMS) scoring system in comparison with other AMS scoring systems. To achieve this objective nine subjects were submitted to a 9-hr exposure to hypoxia in a hypobaric chamber (altitude 4500-5500 m) that led to the development of AMS. AMS was scored at the end of this exposure period both by questionnaires (Hackett AMS questionnaire, Lake Louise AMS self-report questionnaire, Environmental Symptoms Questionnaire ESQ II and ESQ IV) and by a clinical investigation following the Lake Louise AMS clinical and functional AMS assessment. The AMS scores were between 0 and 9 for the Hackett AMS score, 0 and 38 for the ESQ II AMS score, 0 and 13.7 for the ESQ IV AMS score, 0 and 10 for the Lake Louise AMS self-report, 0 and 2 for the Lake Louise AMS clinical assessment score, and between 0 and 2 for the Lake Louise functional score. All the AMS questionnaire scores were related to the clinical AMS assessment score (p < 0.05) without significant differences between them. The Lake Louise AMS self-report score appeared highly correlated to other AMS scoring systems (Hackett, ESQ II and ESQ IV) (p < 0.05). Suggestions were proposed to improve the sensitivity and the specificity of the Lake Louise AMS scoring questionnaire but also the Lake Louise AMS clinical assessment. In conclusion, this study suggests the relevance of the Lake Louise AMS self-report questionnaire to assess and score AMS with simplicity and rapidity.

Adult↗

PubMed1994

Effect of ingestion pattern on rehydration and exercise performance subsequent to passive dehydration.

Six male volunteers performed three tests, each comprising a passive heating session to obtain dehydration (loss of 2.6% body mass), followed by exercise on a treadmill until exhaustion (50% of maximal oxygen consumption) in a warm environment (dry bulb temperature 35 degrees C, relative humidity 20%-30%). In one test, the subjects exercised without rehydration (Dh). In the two other tests, 50% of the fluid lost in the dehydration session was replaced by drinking mineral water given either in one amount [913 (SEM 23) ml] before the exercise (Rh1) or divided into four equal portions [228 (SEM 5) ml] before the exercise and on three occasions at 15-min intervals during exercise (Rh4). Rehydration increased exercise duration in Rh1 compared to Dh [112 (SEM 7) min and 82 (SEM 3) min, respectively; P < 0.05]. The difference was not significant with Rh4 [103 (SEM 9) min]. A restoration of the time course of changes in plasma volume, plasma osmolality, heart rate and rectal temperature occurred immediately in Rh1 and as delayed in Rh4 until after 60 min of exercise. Our results demonstrated that the swift replacement of the fluid loss in the dehydrated subjects was beneficial to exercise performance by rapidly correcting the disturbances in body fluid balance.

Adult↗

PubMed1994

Cold thermoregulatory changes induced by sleep deprivation in men.

The aim of this study was to evaluate the thermoregulatory changes induced by 27-h of sleep deprivation (SD) in men at rest both in a comfortable ambient temperature and in cold air. A group of 12 male subjects were placed in a comfortable ambient temperature (dry bulb temperature, Tdb = 25 degrees C, relative humidity, rh = 40%-50%, clothing insulation = 1 clo) for 1 h and then they were submitted to a standard cold air test in a climatic chamber for 2 h (Tdb = 1 degree C, rh = 40%-50%, wind speed = 0.8 m.s-1, nude), before and after 27 h of sleep deprivation. Thermoregulatory changes (rectal temperature, Tre; mean skin temperature. Tsk; metabolic heat production M) were monitored continuously. At comfortable ambient temperature, no significant change was observed after SD for Tre, Tsk and M. During the cold test, Tre did not change but Tsk and M were higher after SD (P < 0.05). Increased M (+ 6%, P < 0.05) was related to earlier and higher shivering, with a possible increase in the sensitivity of the thermoregulatory system as shown by the shorter time to onset of continuous shivering (d): 8.66 (SEM 1.33) min versus 28.20 (SEM 1.33) min (P < 0.001) and by a higher Tsk observed at d: 27.60 (SEM 1.40) degrees C versus 21.40 (SEM 0.60) degrees C (P < 0.001). These results were associated with higher cold sensations and shivering following SD. They also suggested that SD modified thermoregulatory responses at a central level especially in a cold environment.

Adult↗

PubMed1994

Physiological changes induced by pre-adaptation to high altitude.

To study the physiological effects of pre-adaptation to high altitude, seven subjects were submitted to acclimatization at 4350 m followed by intermittent acclimation in a low barometric pressure chamber (5000 m to 8500 m). The subjects then spent 25 days in the Himalayas. Ventilatory and cardiac responses were studied during a hypobaric poikilocapnic hypoxic test performed both at rest and during exercise (100 W) in normoxia and in hypoxia (barometric pressure: 589 hPa, altitude: 4500 m). Haemoglobin, erythrocytes, reticulocytes, packed cell volume, 2,3-diphosphoglycerate (2,3-DPG) and erythropoietin (EPO) were measured. All variables were studied before pre-adaptation to high altitude (A), after the acclimatization period (B), after the acclimation period (C) and after the expedition (D). The ventilatory and cardiac responses were characterized by an increased tidal volume in hypoxia (+33% during exercise in B, P < 0.05; +100% at rest and +33% during exercise in C, P < 0.05) without any change in respiratory frequency, whereas an increased systolic blood pressure was only observed in C during exercise in hypoxia [+23 mmHg (3.07 kPa), P < 0.01]. Arterial O2 saturation was higher in hypoxia in C and D, both at rest (+8.2% and +4.7%, P < 0.01, respectively), and during exercise (+6.3% and +6.3%, P < 0.01, respectively). Erythrocytes, haemoglobin and packed cell volume did not vary significantly. The number of reticulocytes was higher in B (+172%, P < 0.05) and in C (+249%, P < 0.05). EPO and 2,3-DPG increased only in C (+770%, P < 0.01 and +23%, P < 0.05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1994

Regional specificity of the long-term variation of tyrosine hydroxylase protein in rat catecholaminergic cell groups after chronic heat exposure.

The present study was carried out to investigate the effect of chronic heat exposure on tyrosine hydroxylase (TH) protein content in catecholaminergic rat brain-stem areas such as the anterior (LCA) and posterior (LCP) locus coeruleus, the substantia nigra (SN), the ventral tegmental area, and the dorsomedial (DMM) and the ventrolateral medulla and in the adrenal gland (AG). Male Sprague-Dawley rats were exposed to 34 degrees C during 3, 7, or 14 days. Controls were kept at 25 degrees C for the same period. In the LCA, TH content was decreased on day 7 (-34%) and 14 (-37%) of heat exposure. In the SN, TH protein content was decreased on day 7 (-25%) and 14 (-20%) after 34 degrees C. In the DMM cell group, 14 days at 34 degrees C produced a decrease (-20%) of TH content. In all of these structures, TH content variations were correlated with body temperature variations. In the AG, TH content increased progressively to peak (+31%) after 14 days of chronic heat exposure. This increase was also associated with body temperature modification. The selective and body temperature-related response to long-term TH protein content variations following chronic heat exposure observed in the LCA, SN, DMM, and AG could represent an adaptive physiological response of these catecholaminergic cells.

Adrenal Glands↗

PubMed1993

[Induction of a "triiodothyronine polar syndrome" in man under laboratory conditions].

To precise the thyroid hormonal changes (TH) during an acute cold exposure, 8 subjects were subjected to a cold air test (2 h, 1 degrees C nude, at rest) in a climatic chamber before and after a local cold acclimation. After cold acclimation the thyroid hormonal changes could suggest the presence of a "T3 polar syndrome" in laboratory conditions. This syndrome was up to now described only after a stay in natural cold environment.

Acclimatization↗

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↗