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Biomedical subjects

V Candas

Publications and source records attributed to V Candas.

At least 37 records · Page 2Linked to original sources
PubMed1992

Thermal and sweating responses in normal and atopic subjects under internal and moderate external heat stress.

To compare the thermoregulatory responses of normal subjects and patients with atopic dermatitis, the effect of exercise under moderate heat stress was examined in two groups of subjects. Each group of eight subjects (controls or clinical atopics) underwent a 90-min experiment after being equipped with probes for measurement of core and skin temperatures, heart rate and overall and local sweating rates. Sweat surface tension was determined from sweat collection made at the end of the session. The experimental procedure was as follows: 30 min rest at thermoneutrality, 30 min cycling at 90 W at 36 degrees C, followed by 30 min recovery sitting at rest at 36 degrees C on the cycloergometer. None of the registered variables differed significantly between the normal and atopic subjects except for variations in mean skin temperature, core-to-skin temperature difference and sweat surface tension. Since local sweating on non-affected skin under a controlled thermal clamp was not altered by atopy, it can be concluded that the thermoregulatory modifications under heat stress is of vasomotor origin, the benefit of which, in terms of heat dissipation capacity, remains uncertain. There may be alterations in the constituents of sweat, but not in its excretion rate. Local, rather than central, factors are probably involved in this qualitative change, which remains to be investigated.

Adult↗
PubMed1991

Temperature and sweating responses in one-legged and two-legged exercise.

In looking at the thermoregulatory responses resulting from symmetrical or asymmetrical exercise, this paper has focused on the effect of local skin temperature (Tsk,local) on local sweat rates (msw,local) during one-legged (W1) and two-legged (W2) exercise on an ergocycle. Five subjects underwent four 3-h tests at 36 degrees C, each consisting of six 25-min exercise periods alternating with 5-min rest periods. The subjects performed W1 and W2 at 45 and 90 W, respectively, either dehydrated or rehydrated. Body temperatures and total sweat rate were measured as well as four msw,local (on chest and thighs), assessed from sweat capsules under which Tsk,local was maintained at predetermined levels (37.0 degrees C and 35.5 degrees C). The combinations of Tsk,local levels, capsule locations, exercise intensity and hydration level chosen in our protocol led to the following results. The hydration level affected rectal temperature but not total or msw,local. No specific effect of muscle activity was found; msw,local on thighs of resting and working legs were similar. The msw,local were only influenced by exercise intensity, msw,local being more elevated during the higher intensity. No significant effect of Tsk,local on msw,local was found, whatever the experimental condition and/or the location. It was concluded that local thermal effects on msw,local could have been masked by the strong central drive for sweating which has been found to exist in subjects exercising in a warm environment.

Adult↗
PubMed1991

Leg skin temperature and thigh sweat output: possible central influence of local thermal inputs.

To demonstrate whether or not the skin temperature of one lower limb can have an influence on the sweat rate of the contralateral leg, the two legs of five subjects were exposed inside leg-chambers to specific local thermal conditions while sweat rates were measured on both limbs. Three experiments (C I, II, III) of 3 h were carried out: each included two phases A and B. During A, the right leg was not ventilated, while the left leg was (C I) or was not (C II-III) ventilated. During B, the legs were either removed from the leg-chambers (C I) or ventilated inside the chambers at differently controlled levels of leg skin temperature (C II-III). At all times, sweat capsules on both legs measured the sweat rates of local areas of the thigh which were also temperature-controlled. Results showed that, at constant or slightly increased mean skin and core temperatures, the sweat output of one leg could be decreased at constant (C II) or higher local skin temperature (C III) probably due to a decrease in the temperature of the opposite leg. This finding is interpreted as a consequence of a central negative effect, originating from contralateral thermal inputs.

Adult↗
PubMed1991

Sleep changes in fasting rats after chronic glycerol feeding.

Species which do not enter torpor during fasting and which were efficiently able to spare their body proteins during the first two phases of fasting (which are commonly comprised of 3 successive phases) also increase their daily amount of slow-wave sleep (SWS) during the first two phases. Since in fasting animals the ability to spare proteins was reported to be improved when they were previously fed with a diet enriched with glycerol, it was supposed that, after such a diet, food-deprived rats would increase their daily quota of SWS. In addition, the tolerance to food deprivation, defined as the time elapsed to reach the end of phase II, should also be improved since this tolerance is known to be critically modulated by protein utilization. The daily proportions of wakefulness (W), SWS and paradoxical sleep (PS) were thus studied in Wistar rats after 16 weeks of feeding (i.e., when they were 27 weeks old) with an enriched glycerol diet. These daily W and sleep state proportions were then evaluated until the middle of fasting phase II (MII), i.e., when protein catabolism in the rat appears to be at its lowest level. The rats were able to tolerate more than 5 weeks of food deprivation, which represented an increase of 123% of the fasting tolerance previously reported in rats of the same age but which were fed normally before fasting onset. At MII the daily proportion of SWS was significantly (vs. fed state, p less than 0.01) increased (due to an increase in the daily mean episode duration), at the expense of W (due to a lowering in the daily occurrence of W episodes).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Ambient temperatures preferred by young European males and females at rest.

Forty-eight young adults (24 men and 24 women) stayed for three hours in a climatic chamber setting, lightly clothed and seated at rest with no prescribed task; rectal and mean skin temperatures were continuously recorded. During the first hour, the subjects were exposed to an imposed ambient temperature (25.1 degrees C) during which body temperatures stabilized and subjective thermal judgments were collected. For the next two hours they could freely set the ambient temperature at the level(s) they preferred. The subjects spent about one hour seeking a preferred temperature (transition period), which subsequently turned out to be unsteady in most cases. The overall mean of the individual average preferred temperatures (third hour) was 26.6 degrees C (S.D. = 2.6 degrees C). Significant time of day (morning versus afternoon) effects were found on preferred ambient and actual body temperatures. The body temperatures previously recorded at 25.1 degrees C were significantly predictive of the average ambient temperatures preferred between one and two hours later (third hour); the multiple regression equations differed markedly between men and women.

Adult↗
PubMed1990

Growth hormone and prolactin response to rehydration during exercise: effect of water and carbohydrate solutions.

The effect of progressive rehydration with either water or a carbohydrate solution on the plasma growth hormone (GH) and prolactin (PRL) response to exercise was examined together with plasma somatostatin. Five subjects underwent four 3-h experimental sessions at 36 degrees C in which 25-min exercise periods alternated with 5-min rest periods. The sessions were conducted without fluid replacement (DH) or under rehydration with either water or isosmotic carbohydrate solutions AISO (acid) or NISO (neutral). The fluid was given every 10 min after the 1st h of exercise. Plasma GH increased significantly (p less than 0.01) under DH after 2 and 3 h of exercise; this increase was prevented by rehydration with water, AISO and NISO. Plasma glucose was significantly higher following AISO and NISO rehydration compared with DH. This possibly influenced the GH response, but there was no difference between plasma glucose levels under DH and water rehydration at any time. The solutions tended to attenuate the increase in heart rate, rectal temperature and plasma cortisol, suggesting that the lack of GH response under rehydration conditions is a result of decreasing physiological stress levels. The GH response could not be explained by plasma somatostatin, which tended to decline in all sessions. Plasma PRL did not increase in any of the sessions, confirming that exercise without rehydration is a more potent stimulator of GH than of PRL. It is concluded that progressive rehydration with water is sufficient to prevent the exercise-induced increase in plasma GH.

Adult↗
PubMed1990

Physiological effects of dehydration and rehydration with water and acidic or neutral carbohydrate electrolyte solutions.

Five healthy young men exercised on an ergocycle for six 25-min periods separated by 5-min rest intervals in a warm dry environment (36 degrees C). After 1 h of exercise without fluid intake, the subjects continued to be dehydrated or were rehydrated either with water (W) or with isosmotic electrolyte carbohydrate solutions, either acidic (AISO) or close to neutrality (NISO). The average amount of the fluid ingested progressively every 10 min (120 ml) at 20 degrees C was calculated so as to compensate for 80% of the whole body water loss due to exercise in the heat. Dehydration associated with hyperosmotic hypovolaemia elicited large increases in heart rate (HR), and in rectal temperature (Tre), while no decrease was found in either whole body or local sweat rates. Rehydration with water significantly reduced the observed disturbances, except for plasma osmolality and Na+ concentration which were significantly lower than normal. With both AISO and NISO there was no plasma volume reduction and osmolality increase. Although a plasma volume expansion was induced by NISO ingestion, the cardiac cost was not improved, as reflected by the absence of a decrease in HR. With NISO, sweating was not enhanced and Tre tended to remain higher. It is concluded that efficient rehydration requires the avoidance of plasma volume expansion at the expense of interstitial and intracellular rehydration. During rehydration by oral ingestion of fluid, the pH of the drink may be an important factor; its effect remains unclear, however.

Administration, Oral↗
PubMed1989

The influence of the initial state of hydration on endocrine responses to exercise in the heat.

This study examines the effect of the initial state of hydration on hormone responses to prolonged exercise in the heat. Five subjects at two initial hydration levels (hypohydrated and hyperhydrated) were exposed to a 36 degrees C environment for 3 h of intermittent exercise. During exercise, the subjects were either fluid-deprived, or rehydrated with water or an isotonic electrolyte sucrose solution (ISO). Both the stress hormones, adrenocorticotropic hormone and cortisol, and the main fluid regulatory hormones, aldosterone, renin activity (PRA) and arginine vasopressin (AVP), were measured in blood samples taken every hour. Prior hyperhydration significantly reduced initial AVP, aldosterone and PRA levels. However, except for AVP, which responded to exercise significantly less in previously hyperhydrated subjects (p less than 0.05), the initial hydration state did not influence the subsequent vascular and hormonal responses when the subjects were fluid-deprived while exercising. Concurrent rehydration, either with water or with ISO, reduced or even abolished the hormonal responses. There were no significant differences according to the initial hydration state, except for PRA responses, which were significantly lower (p less than 0.01) in previously hyperhydrated subjects who also received water during exercise. These results indicate that prior hydration levels influence only slightly the hormonal responses to prolonged exercise in the heat. Progressive rehydration during exercise, especially when extra electrolytes are given, is more efficient in maintaining plasma volume and osmolarity and in reducing the hormonal responses.

Adrenocorticotropic Hormone↗
PubMed1989

Effect of rehydration on atrial natriuretic peptide release during exercise in the heat.

In an attempt to investigate their relationships with plasma volume (PV), heart rate (HR), and other hormonal systems, plasma atrial natriuretic peptide (ANP) levels were determined in response to exercise in the heat, associated with dehydration and rehydration with various fluids. Five normal subjects underwent four 3-h experiments, in a 36 degree C environment, in which 25-min exercise periods on a cycle ergometer at 90 W alternate with 5-min rest periods. Blood samples were collected hourly and ANP, arginine vasopressin (AVP), adrenocorticotropin (ACTH), and cortisol were analyzed in four experimental sessions: without fluid supplement (DH) and with progressive rehydration either with water (W), acid isotonic solution (AISO), or neutral isotonic solution (NISO). Exercise in the heat, accompanied by a decrease in PV and an increase in osmolality, elicited an increase of 28 +/- 1.6 pg/ml in plasma ANP, with concomitant increases in AVP (5.1 +/- 1.4 pg/ml), ACTH (49.6 +/- 12.3 pg/ml), and cortisol (8.4 +/- 2.0 micrograms/100 ml). Progressive rehydration maintained PV and blunted ANP, AVP, ACTH, and cortisol responses. These results demonstrate the importance of rehydration, during exercise in a warm environment, in preventing hormonal increases. They suggest that under our conditions, the PV changes and the inferred atrial pressure changes may not be the primary factors controlling ANP release, as under other physiological conditions. The exercise-related activation of pituitary and adrenals and the stimulation of HR counteract the influence of PV changes due to vascular fluid shifts.

Adrenocorticotropic Hormone↗
PubMed1988

Thermal and circulatory responses during prolonged exercise at different levels of hydration.

After a control experiment under initial normal hydration (N), five healthy unacclimated subjects were studied to investigate the effects of initial hypo- and hyperhydration on cardiovascular and thermo-regulatory responses to prolonged intermittent exercise in the heat (To = 36 degrees C; Tdp = 10 degrees C; Va = 0.6 m.s-1). Prior hydrohydration (O) was obtained by diuretics and prior hyperhydration (R) by ingestion of 0.5 L of isotonic (ISO) electrolyte sucrose solution 30 min before the experiments (4 h) started. Exercise (70 W) lasted 3 hours, and was periodically interrupted by resting periods (5-10 min). Three dehydration (D) runs were thus performed under the three initial hydration states (O,N,R) without fluid replacement during the exercise period. Four additional rehydration runs were carried out: 2 in each initial hydration level (O, R) included ingestion (at 36 degrees C) of water or ISO-solution during the first 3 hours. Physiological measurements were continuously recorded and hourly blood samples (15 ml) were obtained. Results showed that dehydration increased core temperature and heart rate and provoked blood hypovolemia and hyperosmolarity, the latter being somewhat prevented by prior ISO-ingestion. Dehydration reduced significantly the overall sweat rate only in hypohydrated subjects and the large hyperosmolarity seemed to be responsible for this. The significant Tcore rise during dehydration is unlikely to be the result of a decrease in evaporative heat transfer, which was found only in the case of initial hypohydration. Rehydration during exercise with water or ISO-solution induced different dynamic responses depending on the initial hydration level, but it never restored plasma volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Local sweating responses of different body areas in dehydration-hydration experiments.

Five subjects performed intermittent exercise on a bicycle ergometer (25 min work, 5 min rest cycles for 2 hours, and 20 min work, 10 min rest cycles for a further hour) in a hot environment (air and wall temperatures = 36 degrees C; dew-point temperature = 10 degrees C; air velocity = 0.6 m.s-1). The relative mechanical work load was of 70 W (30% of the maximal aerobic capacity). Seven experimental tests were carried out in order to induce a plasma hypovolemia associated with either a plasma hypo- or hyperosmolarity. The preexercise level of body hydration was also manipulated by giving a diuretic, or by ingestion of 500 ml of isotonic electrolyte sucrose solution before the start of exercise. Continuous measurements were made of rectal and mean skin temperatures. The sweating responses of the chest and of the thigh (over the active muscles of the leg) were monitored from 4 sweat collection capsules highly ventilated. On each of these body areas, the local skin temperatures under one of the 2 capsules was kept at a constant level (37 degrees C). The effects of the level of body hydration on the sweating response only appear when a high local thermal clamp is imposed beneath the capsule. This local effect is particularly strong over the active muscles of the thigh. The influence of the preexercise hydration appears during dehydration tests. This effect is not significant when fluid is given to the subject during the exercise. The change in the sensitivity of the thermoregulatory system is more strongly associated with plasma osmolarity than hypovolemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Prediction of mean skin temperature in warm environments.

The data collected by the authors in four experimental series have been analysed together with data from the literature, to study the relationship between mean skin temperature and climatic parameters, subject metabolic rate and clothing insulation. The subjects involved in the various studies were young male subjects, unacclimatized to heat. The range of conditions examined involved mean skin temperatures between 33 degrees C and 38 degrees C, air temperatures (Ta) between 23 degrees C and 50 degrees C, ambient water vapour pressures (Pa) between 1 and 4.8 kPa, air velocities (Va) between 0.2 and 0.9 m.s-1, metabolic rates (M) between 50 and 270 W.m-2, and Clo values between 0.1 and 0.6. In 95% of the data, mean radiant temperature was within +/- 3 degrees C of air temperature. Based on 190 data averaged over individual values, the following equation was derived by a multiple linear regression technique: Tsk = 30.0 + 0.138 Ta + 0.254 Pa-0.57 Va + 1.28.10(-3) M-0.553 Clo. This equation was used to predict mean skin temperature from 629 individual data. The difference between observed and predicted values was within +/- 0.6 degrees C in 70% of the cases and within +/- 1 degrees C in 90% of the cases. It is concluded that the proposed formula may be used to predict mean skin temperature with satisfactory accuracy in nude to lightly clad subjects exposed to warm ambient conditions with no significant radiant heat load.

Adult↗
PubMed1987

Sweating responses and body temperatures during nocturnal sleep in humans.

The changes in the central control of sweating were investigated in five sleeping subjects under neutral and warm conditions [operative temperature (To) = 30, 33, and 34 degrees C; dew-point temperature = 10 degrees C]. Esophageal (Tes) and mean skin (Tsk) temperatures, chest sweat rate (msw,1), and concomitant electroencephalographic data were recorded. Throughout the night, msw,1 was measured under a local thermal clamp of 38 degrees C. Results showed that the thermal environment exerted a strong influence on both the levels and the time patterns of body temperatures. Moreover, local sweating rate correlated positively with Tes, and this relationship varied according to sleep stages. For a given Tes level, there was a sleep stage-related gradation in msw,1 that was higher in slow-wave sleep (SWS) than in stage 1-2 and the lowest in rapid-eye-movement (REM) sleep. This is explained by a change in the excitability or the sensitivity of the thermoregulatory system. The msw,1 differences between stage 1-2 and SWS are accounted for by a decrease in the Tes threshold (Tset) for sweating while the slope of the msw,1-Tes relation remains unchanged. The lower msw,1 in REM sleep is explained by a lesser slope for the msw,1-Tes relation without any Tset change from stage 1-2.

Adult↗
PubMed1986

Hydration during exercise. Effects on thermal and cardiovascular adjustments.

Five young unacclimatised subjects were exposed for 4 h at 34 degrees C (10 degrees C dew-point temperature and 0.6 m X s-1 air velocity), while exercising on a bicycle ergometer: 25 min work--5 min rest cycles for 2 hours followed by 20 min work--10 min rest cycles for two further hours. 5 experimental sessions were carried out: one without rehydration (NO FLUID) resulting in 3.1% mean loss of body weight (delta Mb), and four sessions with 20 degrees C fluid ingestion of spring water (WATER), hypotonic (HYPO), isotonic (ISO) and hypertonic (HYPER) solutions to study the effects of fluid osmolarity on rehydration. Mean final rehydration (+/- SE) after fluid intake was 82.2% (+/- 1.2). Heart rate was higher in NO FLUID while no difference among conditions was found in either delta Mb or hourly sweat rates. Sweating sensitivity was lowest in the dehydration condition, and highest in the WATER one. Modifications in plasma volume and osmolarity demonstrated that NO FLUID induced hyperosmotic hypovolemia, ISO rehydration rapidly led to plasma isoosmotic hypervolemia, while WATER led to slightly hypoosmotic normovolemia. It is concluded that adequate rehydration through ingestion of isotonic electrolyte-sucrose solution, although in quantities much smaller than evaporative heat loss, rapidly restored and expanded plasma volume. While osmolarity influenced sweating sensitivity, the plasma volume changes (delta PV) within the range -6% less than or equal to delta PV + 4% had little effect on temperature adjustments in our conditions.

Adult↗
PubMed1986

Vascular fluid shifts and endocrine responses to exercise in the heat. Effect of rehydration.

This study examines the relationships between vascular changes and endocrine responses to prolonged exercise in the heat, associated with dehydration and rehydration by fluids of different osmolarity. Five subjects were exposed, in a 34 degrees C environment for 4 h of intermittent exercise on a cycle ergometer at 85 +/- 12 Watts (SD). Fluid regulatory hormones and cortisol were analysed in 3 experimental sessions: one without any fluid supplement (NO FLUID), and two with progressive rehydration, either by spring water (WATER) or isotonic solution (ISO), given after 70 min of exercise. Results were expressed in terms of differences between the mean values observed at the end of the exercise and the first hour values taken as references. Dehydration (NO FLUID) elicited a 4.0 +/- 0.8% (SE) decrease in plasma volume (PV) and an increase in osmolarity (8.4 +/- 3.1 mosmol X l-1). Concomitantly, plasma aldosterone (PA), renin activity (PRA), arginin vasopressin (AVP) and cortisol (PC) levels increased greatly in response to exercise in the heat (PA: 37.2 +/- 10.8 ng. 100 ml-1; PRA: 13.4 +/- 2.5 ng X ml-1 X h-1; AVP: 3.8 +/- 1.3 pg X ml-1; PC: 12.2 +/- 2.7 micrograms X 100 ml-1). Rehydration with water led to decreased osmolarity (-8.2 +/- 2.1 mosmol X l-1) with no significant changes in PV. With ISO, PV increased by 6.0 +/- 1.3% and the decrease in osmolarity was-5.8 +/- 1.8 mosmol X l-1. With both modes of rehydration, the increases in PRA, AVP and cortisol were blunted; only ISO prevented the rise in PA.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗