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Biomedical subjects

V Candas

Publications and source records attributed to V Candas.

At least 55 records · Page 3Linked to original sources
PubMed1986

Temperature regulation during intermittent exercise with progressive dehydration.

Effects of dehydration (3% of initial body weight) on temperature regulation were investigated in 5 men during intermittent exercise of 4 h duration at a dry air temperature of 34 degrees C. Relative mechanical work load was 50% of the subject's steady state heart rate, which was 170 beats . min-1. During rehydration from the 70th min to the end of the exercise, the subjects drank, every 10 min in equal portions, an amount of water (20 degrees C) totaling up to 80% of the body weight loss recorded during dehydration runs. Continuous measurements were made of rectal (Tre) and mean skin (Tsk) temperatures and of whole body weight loss. Chest sweating rate (msw) was measured from a capsule located under a local thermal clamp (36 degrees C). Blood samples were obtained during rest periods and after the 1st and the 4th hour of exercise. Compared to dehydration runs, water intake did not always cause an increase of msw while body temperatures always decreased. Dehydration resulted in a decrease in plasma volume and in increases of plasma osmolality, [Na+] and [K+]. Water intake induced a thermoregulatory response whose intensity largely differs from one body area to another. The change in the slope of the relation of msw to Tre features a decrease in the sensitivity of the thermoregulatory system with dehydration. The whole body water loss is significantly correlated with the change in plasma volume and body temperatures (Tre, Tsk). This suggests that the reduced sweating response observed during dehydration can be related to plasma hypovolemia.

Adult↗
PubMed1986

Sweat gland response to local heating during sleep in man.

In order to assess whether the fluctuations in the sweating response occurring during sleep are related to changes in central drive or in peripheral sweat gland reactivity, 4 healthy male subjects spent 6 non-consecutive nights in a climatic chamber. Air temperature was 25 degrees C, dew-point temperature was 10 degrees C and air velocity was 0.3 m X s-1, while wall temperature was either 38 degrees C, 46 degrees C or 48.7 degrees C giving 3 levels of operative temperature (To = 30, 33 or 34 degrees C). During the whole night, 2 local sweating rates on the right and the left sides of the upper chest were continuously recorded from 12 cm2 area capsules using a dew-point hygrometer technique, while applying local thermal clamps, a constant 2 degrees C difference in local skin temperatures being imposed between the two symmetrical skin areas. Continuous measurements were made of rectal temperature, 10 local skin temperatures, 2 EEGs, 2 EOGs, 1 EMG and 1 ECG. Results show that the multiplicative relationship between the peripheral influence of local skin temperature and the central drive for sweating described in waking subjects, is still valid in sleeping subjects. No peripheral change appears in sweat gland reactivity between the different sleep stages. Changes in the sensitivity of the thermoregulatory system occurring during sleep cannot be explained by a local factor acting at the sweat gland level.

Body Temperature Regulation↗
PubMed1985

Thermoregulatory adjustments in squirrel monkeys exposed to microwaves at high power densities.

The present study was undertaken to investigate the thermal adjustments of squirrel monkeys exposed in a cold environment to relatively high energy levels of microwave fields. The animals (Saimiri sciureus) were equilibrated for 90 min to a cool environment (Ta = 20 degrees C) to elevate metabolic heat production (M). They were then exposed for brief (10-min) or long (30-min) periods to 2,450-MHz continuous-wave microwaves. Power densities (MPD) were 10, 14, 19, and 25 mW/cm2 during brief exposures and 30, 35, 40, and 45 mW/cm2 during long exposures (rate of energy absorption: SAR = 0.15 [W/kg]/[mW/cm2]). Individual exposures were separated by enough time to allow physiological variables to return to baseline levels. The results confirm that each microwave exposure induced a rapid decrease in M. In a 20 degree C environment, the power density of a 10-min exposure required to lower M to approximate the resting level was 35 mW/cm2 (SAR = 5.3 W/kg). During the long exposures, 20 min was needed to decrease M to its lowest level. Cessation of irradiation was associated with persistence of low levels of M for periods that depended on the power density of the preceding microwave exposure. Vasodilation, as indexed by changes in local skin temperature, occurred at a high rate of energy absorption (SAR = 4.5 W/kg) and was sufficient to prevent a dramatic increase in storage of thermal energy by the body; vasoconstriction was reinstated after termination of irradiation. Patterns of thermophysiological responses confirm the influence both of peripheral and of internal inputs to thermoregulation in squirrel monkeys exposed to microwaves in a cool environment.

Animals↗
PubMed1984

Endocrine concomitants of sweating and sweat depression.

The effect of humid heat (Ta = 43 degrees C, Pa = 32 Torr) on sweat rate, plasma renin activity and plasma levels of aldosterone and antidiuretic hormone (ADH) was studied in four male subjects before and after repeated heat exposures. Over-sweating and sweat drippage followed by hidromeiosis were observed in three subjects during initial heat exposure. With repeated humid heat exposures increased sweat rates were accompanied by a more intense sweat depression (hidromeiosis) in all four subjects. In our conditions, no changes in plasma levels of aldosterone and ADH or plasma renin activity were observed with hidromeiosis. Plasma renin activity was slightly depressed by repeated exposures, whereas plasma volumes were enhanced, with no significant changes in plasma Na or K. The results suggest that neither ADH nor the components of the renin-angiotensin aldosterone system are involved in the hidromeiotic phenomenon.

Adult↗
PubMed1984

Relationship of skin surface area to body mass in the immature rat: a reexamination.

Skin surface area (Ab) was measured in the rat beginning at birth mass and extending over a range of body mass (m) from 5.0 to 49.3 g. Area of each animal was determined using an elastic impression material. The best-fit relationship between Ab and m over the entire range of mass was Ab = 6.88m0.736. Results suggest, however, that the standard mass exponent of two-thirds, for estimating Ab of adult animals, could also be used for immature animals weighing 14 g or more. In rats weighing less than 14 g, the mass coefficient of the Meeh-Rubner equation varies with m, indicating that the two-thirds exponent is inappropriate for use with very young animals.

Animals↗
PubMed1984

Contribution of skin thermal sensitivities of large body areas to sweating response.

The thermal sensitivity of different parts of the body was investigated by heating large areas of the body surface while the mean skin temperature calculated from Hardy and DuBois ' formula (1938) was always kept constant. The right arm sweating responses recorded under a local thermal clamp were related to changes in segmental skin temperatures of the different parts of the body. The results show that: 1) the various local peripheral signals are projected into integrating structures in the central nervous system; 2) the thermal sensitivity is greater for the head-and-trunk area in comparison with other parts of the body. For resting nude subjects, the formula of Hardy and DuBois remains a pertinent way for evaluating the role of skin thermal signals in the central drive for sweating. The peripheral contribution to the central sweating drive depends only on the skin temperature change and on the size of the stimulated area.

Adult↗
PubMed1984

Physiological and perceptual responses to cyclic heat stress variations.

The effect of the time presentation of a given external heat load was examined on five subjects exercising at a constant work load (50 W). The subjects, dressed in briefs, were exposed to cyclic variations for 120 min in air temperatures between 51 degrees C and 23 degrees C, under three different schedules involving heat pulses of 10-min, 20-min and 30-min duration, respectively. The strain induced by each of these conditions was compared in terms of both physiological and perceptual criteria. Results showed that between conditions, there were significant differences in skin temperature levels but not in core temperature levels, body heat storage, or body weight loss. Perception of effort and thermal sensation ratings both exhibited similar changes in all three conditions. Due to the time constant of the sweating response, sweating rates and skin wettednesses at the end of the heat pulses were lower for 10-min heat pulses than for those of 20- and 30-min duration, and these differences were perceived by the subjects. Lower perceived skin wettedness ratings are thus suggested as the main factor to explain why all subjects rated the 10-min heating-cooling cycle as the least strenuous and uncomfortable condition. It is concluded that under the conditions of this study, perceptual criteria associated with physiological criteria represent a useful means of discriminating slight differences in strain.

Adult↗
PubMed1983

Sweating and sweat decline of resting men in hot humid environments.

Time courses of the rates of sweating, drippage and evaporation were studied in hot humid environments. Resting subjects wearing only briefs were exposed to humid conditions, before, during and after humid heat acclimation, so that different levels of skin wettedness could be studied on the entire body. In addition, local sweat rate was measured on the right upper limb, which was enclosed in a highly ventilated arm-chamber. Thus, the arm remained drier than the rest of the body surface. The results confirm that sweating efficiency is related to the skin wettedness level, and that the decline in intensity of sweating is linked to maximal inefficient sweat drippage before the onset of hidromeiosis. Comparison of general and local sweat decreases confirms that hidromeiosis originates from skin hydration. However it is likely that some factor related to blood content acts on the hidromeiotic process, at least after humid heat acclimation.

Acclimatization↗
PubMed1983

Modifications of sweating responses to thermal transients following heat acclimation.

The sweating response was studied before and after passive humid heat acclimation in four resting male subjects who were exposed to slow thermal transients increasing air and wall temperatures from 28 degrees C to 45 degrees C. The slopes of the ambient temperature increases were +0.19 degrees C . min-1; +0.16 degrees C . min-1 or +0.14 degrees C . min-1. Dew-point temperature and air velocity were kept constant (17.5 degrees C; 0.3 m . s-1). Continuous measurements were made of oesophageal temperature, mean skin temperature, whole-body sweat loss and of right upper limb sweating responses. The local sweating response was measured from an arm chamber under a local thermal clamp (Tsk,1 = 38 degrees C). The results confirmed the fact that heat acclimation to humid heat induces a shortening in the time lag of sweat onset and increases the local sweating rates while internal temperature changes are reduced. These modifications are interpreted as a non-linearity in the response of the central controller, involving both a change in the central gain and an upward resetting of the "local sweating rate-body temperature" curves, without any shifting of the hypothalamic set-point temperature as it is currently described. However, a modification of local sweat gland activity occurring with heat acclimation cannot be ruled out.

Acclimatization↗
PubMed1983

Oral temperature as an index of core temperature during heat transients.

Rectal (Tre), oral (Tor) and oesophageal (Tes) temperatures were measured in five exercising subjects exposed for two hours to five conditions (1) a steady condition (WR) involving a constant work load (50 W) at a constant air temperature (Ta = 36.5 degrees C); (2) air temperature variations (delta Ta) between 28 degrees C and 45 degrees C and (3) between 23 degrees C and 50 degrees C at constant work load (50 W); (4) and (5) to work load variations (delta W) between 25 W and 75 W at a constant Ta (= 36.5 degrees C). Oral temperature recordings were taken sublingually and were either continuous or discontinuous. When discontinuous, the time needed for Tor to stabilize after the mouth opening was taken into account. The respective reliability of Tor and Tre as estimates of Tes were compared in each condition. Results showed that the resting (Tor - Tes) difference (+ 0.12 degrees C) was barely modified after two hours of exposure, whereas Tre overestimated Tes by 0.2 degrees C to 0.4 degrees C depending on the condition. The Tor variations were highly correlated with Tes variations under steady condition and under air temperature variations. In these conditions, Tor represented the best estimate of Tes. Under work-load variations, Tor was less closely related to Tes than was Tre. It is suggested that the relative inertia of Tor to step changes in exercise intensity could be ascribed to work induced variations in mouth blood flow.

Adult↗
PubMed1983

REM sleep and ambient temperature in man.

Five young adult males slept two consecutive nights under each of the five ambient temperatures chosen within the usual range: 13 degrees C, 16 degrees C, 19 degrees C, 22 degrees C, and 25 degrees C. Bedding and other ambient parameters were kept constant under all five ambient temperature conditions. The average REM cycle length significantly decreased when the ambient temperature increased from 13 degrees C to 25 degrees C. Other REM sleep characteristics such as total duration of REM sleep, average REM period, and REM sleep latency did not significantly differ from one ambient temperature condition to another.

Adult↗
PubMed1982

Cortisol as a sensitive index of heat-intolerance.

The relationship between plasma cortisol levels, core temperatures, heat storage and the appearance of subjective manifestations of heat intolerance were investigated in two groups of 4 and 3 men, respectively. The first group underwent 4 randomized experimental sessions: a control session and three heat-exposure sessions (A: 48 degrees C, 34 Torr, 80 min; B: 55 degrees, 15 Torr, 120 min; C: 48 degrees C, 15 Torr, 180 min). During control periods, the subjects were maintained in a thermoneutral climate (28 degrees C, 10.5 Torr). The second group of subjects was studied before and after five successive daily exposures to hot and humid conditions (D: 43 degrees C, 32 Torr, 165 min). Signs of subjective discomfort in experiments A and B were accompanied by an increase in cortisol values over control day values, and this increase began at a mean rectal temperature of about 38 degrees C. Condition C was well tolerated, the plasma cortisol remained at basal levels and mean rectal temperature averaged 38 degrees C at the end of the exposure. Repeated exposures in condition D improved heat tolerance with a lesser effect on plasma cortisol levels and a lower body temperature at the end of exposure. Circulating cortisol is shown to be a very sensitive index of heat stress heralding the onset of poor tolerance of severe climates. The relation between concomitant levels of cortisol and rectal temperatures, in fit men, is affected by additional factors (hypotension, uncomfortable posture). These reduce tolerance time and are not reflected by body temperatures, but by rapidly increasing cortisol levels.

Adult↗
PubMed1982

Central and peripheral inputs in sweating regulation during thermal transients.

Eight nude resting men were exposed to consecutive heating-cooling cycles of air and wall temperatures varying from 28 to 45 degrees C in a sawtooth pattern using one of the following slopes: +/- 3.40, +/- 2.27, +/- 1.70, +/- 1.42, or +/- 1.13 degrees C . min-1. Ambient vapor pressure and air velocity were kept constant at 20.0 mbar and 0.9 m . s-1, respectively. Continuous measurements were made of rectal, esophageal, and mean skin temperatures. Local upper limb sweating response was measured from an arm chamber under a local thermal clamp. The results point out the insufficiency of an explantation based on a simple additive function of core and skin temperatures for describing the sweating regulation. During transient thermal loads, a multiplicative interaction of mean skin and core temperatures must also be taken into account for describing the central drive for local sweating response. The interindividual differences observed in the sweating regulation mechanism seem to be linked to a nonlinearity in the response of the thermoregulatory system.

Adult↗
PubMed1982

Thermophysiological responses to humid heat: sex differences.

1. Thermophysiological responses of four men and four pre- and postovulatory women were compared in humid heat conditions. Responses of pre- and postovulatory women are similar except for body temperature levels, which were significantly higher after ovulation. 2. Pronounced sex-related differences were observed in sweating rate and in body temperature variations. For the same evaporation, the sweat rate in men was higher than in women; as a consequence of this, the dripping rate was larger in men and thus the sweat decline was more important. Body temperature increases were larger in men in function of time and therefore temperature regulation in women was considered to be more efficient.

Adult↗