Biomedical subjects

V Candas

Publications and source records attributed to V Candas.

At least 19 recordsLinked to original sources

PubMed2006

Rightward shift of the auditory subjective straight ahead in right- and left-handed subjects.

While spatial asymmetries have been extensively investigated in the visual modality and to a lesser degree in the tactile modality, there are no reports on auditory spatial asymmetries in neurologically normal subjects. The subjects in this study performed an auditory midline task in which they had to adjust the level of two sounds that were presented simultaneously in different hemispaces so as to make the perceived fused sound appear to emanate from the midsagittal plane. The results showed that subjects reported a sound to be central when it was lateralized to the left (i.e., more intense at the left ear), as if there were a rightward shift in the perceived location. This rightward shift was more pronounced in left-handed than in right-handed subjects, even though all the subjects had to use both hands to adjust the sound level. Gaze direction significantly modulated the shift of the perceived auditory midline: the rightward shift was maximal when the subjects' gaze direction was central and 30 degrees to the right, while it disappeared when the gaze was directed 30 degrees to the left side. These results are compared with data obtained from neglect patients in previous studies and are discussed in terms of the interaction between asymmetrical hemispheric activations in auditory spatial tasks and an asymmetrical allocation of attention between the left and right hemispaces.

Acoustic Stimulation↗

PubMed2005

Enhanced self-localization by auditory cues in blind humans.

PURPOSE: Investigate the involvement of auditory spatial compensation, which is observed in blind humans, in self-localization processes. METHOD: Sighted and early-blind subjects had to indicate, on a two-dimensional view of the experimental room, the position where they previously sat and had passively listened to auditory spatial cues. Two different environments were distinguished. In a first session, auditory cues (i.e., white broadband sounds) were displayed successively in a dark anechoic room. This condition was defined as a simple acoustic environment. In a second session, four different auditory cues were displayed simultaneously at regular intervals in an experimental room, where echo cues were salient. This condition, which is more reminiscent of the natural situation, was described as a complex acoustic environment. RESULTS: Self-localization capacities were significantly better in early-blind individuals than in sighted subjects, whatever the type of acoustic environment. CONCLUSIONS: Auditory compensation leads to improved self-localization capacities in early-blind humans and indicates that prior visual experience is not essential for the development of spatial competence.

Adolescent↗

PubMed2005

Auditory compensation in myopic humans: involvement of binaural, monaural, or echo cues?

The purpose of this paper is to investigate the involvement of various auditory localization mechanisms in the improvement of auditory spatial sensitivity in the case of partial visual deprivation. We compared sensitivity to binaural, monaural, and echo cues between normal-sighted and myopic subjects. In an auditory task, which depended solely upon binaural processing, myopic and normal-sighted subjects showed an almost equal localization performance. We also found that myopic subjects were no more disturbed than normal-sighted subjects when spectral shape cues were removed. On the other hand, near-sighted subjects exhibited better echolocation skills and a higher sensitivity to echo cues than normal-sighted subjects. We can therefore conclude that an improved auditory spatial sensitivity in myopic subjects may result from the increased use of echo information.

Acoustic Stimulation↗

PubMed2005

Spatial auditory compensation in early-blind humans: involvement of eye movements and/or attention orienting?

Several studies have reported that the early-blind displays higher auditory spatial abilities than the sighted. Although many studies have attempted to delineate the cortical structures that undergo functional reorganization in blind people, few have tried to determine which auditory or non-auditory processes mediate these increased auditory spatial abilities. The aim of this paper is to investigate the role of eye movements and orientation of attention in auditory localization in blind humans. Although we found, in a first experiment, that the influence of eye movements on auditory spatial localization is preserved in spite of congenital visual deprivation, the saccade influence on spatial hearing is not more pronounced in the blind than in the sighted. In a second experiment, early-blind and sighted subjects undertook a task involving discrimination of sound elevation in which auditory targets followed uninformative auditory cues on either side with an intermediate elevation. When sounds were emitted from the frontal hemifield, both groups showed similar auditory localization performance. Although the auditory cue did not affect discrimination accuracy in both groups, early-blind subjects exhibited shorter reaction times than sighted subjects when sound sources were placed at far-lateral locations. Attentional cues, however, had similar effects on both groups of subjects, suggesting that improved auditory spatial abilities are not mediated by attention orienting mechanisms.

Adaptation, Physiological↗

PubMed2004

Effects of steady-state noise and temperature conditions on environmental perception and acceptability.

The combined effects of noise and temperature on environmental perception and acceptability were studied on 18 lightly clothed subjects (0.6 clo), individually exposed for 2 h in a climatic chamber. Three homogeneous climatic conditions were chosen (air temperature at 18, 24 or 30 degrees C, air velocity =0.1 m/s). For each of them, three different noise levels were continuously maintained (35, 60, 75 dBA, recorded fan noise). The 18 subjects were divided into three groups and each group experienced only one single thermal condition, at each level of noise, during three different experimental sessions. Subjective answers about perception and comfort were obtained at t = 30 and 120 min. Main results indicate that acoustic perception decreases when thermal environment is far from thermoneutrality. Although the combined effects of noise and temperature did not influence the physiological data, our results show that whatever the ambient temperature, thermal unpleasantness is higher when noise level increases. Finally, equivalence between acoustic and thermal sensations is proposed for short-term exposure (1 degree C = 2.6 dBA) and for steady state (1 degrees C = 2.9 dBA). In conclusion, this study strongly suggests that interactions between environmental components do exist, right from perceptual level, and might explain some combined effects on cognitive performance.

Acoustics↗

PubMed2003

Effects of a moderate nocturnal cold stress on daytime sleep in humans.

The effects of a nocturnal exposure to a cool environment on daytime recovery sleep was studied in eight young (20-25 years old) healthy volunteers. A set of standardized clothing (KSU ensemble type) was provided to each individual (estimated total thermal resistance: 0.6 clo). The subject kept awake was passively exposed from 22.30 to 07.30 hours to environments perceived as neutral (N) and comfortable or slightly cold (C) and uncomfortable. They were then allowed to sleep ad libitum (light out at 08.00 hours) under thermoneutral conditions (air temperature: 21 degrees C to 22 degrees C; clothing: cotton tee-shirt and pajama-pants; covering: one cotton sheet and one wool blanket). Sleep was recorded and scored according to the Rechtchaffen and Kales standard procedures. Esophageal temperature (T(es)) was recorded from 21.30 hours until the end of sleep. The nocturnal drops in T(es) were significantly different between N and C (p<0.01), this difference disappearing during sleep. No statistical difference was found between conditions for most of the sleep variables. Compared to N however, C resulted in a significant increase in rapid eye movement (REM) sleep duration (+35%, p<0.01) during the subsequent daytime sleep. It is hypothesized that the REM-sleep increase induced by the exposure to moderate cold is due to the thermal discomfort stress consciously perceived by the subject.

Adaptation, Physiological↗

PubMed2000

Thermoregulatory effects of three different types of head cooling in humans during a mild hyperthermia.

Seven healthy young men participated in six trials with three different types of local cooling [cool air breathing (CAB), face skin cooling (FaC), and combined cooling (CoC)] in a warm environment for 90 min while either resting (operative temperature: T(0) = 40 degrees C, dew point temperature: T(dp) = 15 degrees C, air velocity: v(a) = 0.3 m x s(-1)) or exercising on a cycle ergometer with an external work load of 90 W (T(0) = 36 degrees C, T(dp) = 15 degrees C, v(a) = 0.3 m x s(-1)). Cool air (10 degrees C) arrived at the entry point of the hood and/or the mask at a ventilation rate of 12 m x s(-1). Oesophageal temperature was not affected by any kind of cooling, while tympanic temperature was decreased at rest by both FaC and CoC [respectively -0.15 (0.06) and -0.09 (0.03) degrees C, P </= 0.05]. Mean skin temperature was decreased by FaC and CoC at rest [respectively -0.31 (0.07) and -0.27 (0.09) degrees C, P </= 0. 05] and during exercise [respectively -0.64 (0.15) and -1.04 (0.22) degrees C, P </= 0.01]. CAB had no effect on skin temperatures. CoC and FaC reduced head skin temperature during both rest and work (P < 0.001) with no effect on the skin temperature of the rest of the body, except under CoC with exercise (P < 0.05). CAB did not influence local sweating. FaC, however, decreased the more profuse sweat rates (P </= 0.05) at rest, while CoC decreased all sweating rates at rest (P </= 0.05) and only the back, head and leg sweating rates during exercise (P </= 0.05). These results suggest that head skin cooling causes a reduction in heat strain, while CAB does not. This beneficial influence does not, however, appear to be the result of selective brain cooling. Tympanic temperature seems to be a good index of the core thermal inputs to the hypothalamic regulatory system, since variations in that parameter were associated with similarly directed variations in the sweating outputs.

Adult↗

PubMed1997

A short-term poikilothermic period occurs just after paradoxical sleep onset in humans: characterization changes in sweating effector activity.

We examined the changes in sudorific effector activity in five healthy young (21-23 y) subjects just before, during and just after successive paradoxical sleep (PS) phases. Local sweat rates were evaluated minute by minute over the chest (mcs). Previous observations, showing that mcs levels dropped before paradoxical sleep onset was electrophysiologically scored, were confirmed. At the end of this period of mcs depression, which in the present study coincided with paradoxical sleep onset, we show for the first time a short period (3-7 min) (period I) during which sweat production completely disappeared. A second period then followed (period II), at the very beginning of which mcs was re-elicited and thereafter increased in close correlation with paradoxical sleep duration. During period II, the remaining inhibiting influences (maximal during period I) and their releases could be specified by the successive valleys (indicating mcs inhibition) and peaks (indicating release of the mcs inhibition) drawn by the minute by minute mcs changes. These inhibitions became weaker as paradoxical sleep advanced. Given the strategic position of period I (at paradoxical sleep onset) and the total mcs abolition therein observed, it may be assumed that this poikilothermic state is the re-emergence of the 'ancestral' mode of body temperature regulation. From a thermophysiological point of view, period II may be considered as more 'modern' and directly related to the extension of paradoxical sleep in humans. This extension could be underlain by the unique development of our cognitive and/or learning functions.

Adult↗

PubMed1997

Comparison of sweat rate measured by a pouch collector and a hygrometric technique during exercise.

Measurements of local sweat rate (back) determined with a closed-pouch collector made of polyethylene (110 cm2) were compared with those obtained from a ventilated capsule using an infrared photometric hygrometer technique. Eight young male subjects underwent three exercise sessions each for 60 min at 45% VO2max on a cycle ergometer at an ambient temperature of 35 degrees C and 35% relative humidity. When the onset and transient sweating periods (0-20 min) are excluded from calculations, the difference between the mean values obtained by the collector and the sweat capsule during the 20-60 time period is only 0.06 +/- 0.04 mg x cm-2 x min-1 (5%). Although a significant correlation (r = .74, p < .05) was obtained between methods, individual differences in sweat-rate measurements varied on average +/-0.22 mg x cm-2 x min-1 (+/-19%). Designed more specifically for sweat-content analysis, the pouch collector may serve as a satisfactory field method to approximate the local sweat rate and excretion induced by prolonged exercise in a hot environment.

Adult↗

PubMed1996

Alcohol and its variable effect on human thermoregulatory response to exercise in a warm environment.

The aim of this study was to observe the effect of alcohol ingestion on body temperature and local sweat rate during endogenous and exogenous heat stress. After ingesting either alcohol (1.2 g alcohol/kg of body weight) or a placebo drink, 8 subjects exercised for 60 minutes at 45% VO2max in a warm environment (35 degrees C, 45% RH). Varying patterns of response were observed in these subjects, with no consistent effect on the thermoregulatory response seen. The absence of any significant change in skin and body temperature and in sweat rate suggests that the capacity of the body to struggle against exogenous and endogenous heat is not fundamentally altered by alcohol ingestion. The difference in individual response observed in our experiment is in accord with the previous lack of clearcut effect of alcohol reported in the literature.

Body Temperature Regulation↗

PubMed1996

Effects of local restriction of evaporation and moderate local ventilation on thermoregulatory responses in exercising humans.

Ten healthy young men participated in two series of three trials: series 1 (C1) with, or without, local restriction of evaporation (either on the trunk or on the legs) and series 2 (C2) with, or without, local moderate nitrogen ventilation (40 l.min-1) under an impermeable garment (trunk or leg ventilation). After 60-min rest in a thermoneutral environment, the subjects exercised in a warm environment [30 degrees C, 47% relative humidity (rh) during C1 and 29% rh during C2] on a cycle ergometer for 60 min at 70 W during C1 or at 60 W during C2. During C1, local covering with plastic foil did not increase internal temperature, but increased the mean skin temperature with a higher effect in the case of leg restriction. The trunk skin temperature was affected by the leg covering while the leg skin temperature was not changed by the trunk covering. Only the local sweat rate of the trunk was increased by the two restriction conditions. During C2, internal temperature was decreased by local ventilation while mean skin temperature was reduced only by trunk ventilation. The local ventilation affected only trunk skin temperature with a greater decrease during trunk ventilation. Trunk ventilation did not influence the skin temperature of the legs while ventilation of the legs decreased trunk skin temperature. In addition, leg ventilation decreased the sweat rate of the legs. The impermeable suit worn during C2 led to a greater physiological strain compared to the plastic film worn during C1 even with local ventilation under the impermeable garment. As expected, limiting sweat evaporation led to an increase in physiological strain. Microclimate ventilation at a rate of 40 l.min-1 was not sufficient to allow total heat dissipation but allowed 60-min exercise in a warm environment to be completed without excessive heat accumulation. It would appear that ventilation of the trunk locally was the best solution because of the smaller increase in skin temperature and higher sweating capacity of the trunk.

Adult↗

PubMed1995

Influence of alcohol on the hydromineral hormone responses to exercise in a warm environment.

Alcohol consumption at rest is associated with disturbed water and salt regulation reflected by changed responses in the hydromineral hormones. This study investigated the effect of alcohol on endocrine systems involved in body fluid and electrolyte regulation under conditions of physical exercise in the heat, a situation in which under normal circumstances, the hydromineral hormones are stimulated in an attempt to preserve physiological homeostasis. Eight healthy male volunteers participated in two trials, which differed only in the presence or absence of alcohol (1.2 g alcohol.kg-1 body mass) in a cocktail drink. After consuming the cocktail, the subjects exercised for 60 min on a cycle ergometer (45% maximal oxygen consumption) at 35 degrees C. Compared to the control situation alcohol consumption (maximal plasma concentrations reaching about 1.08 g.l-1) produced an increase in body fluid loss (P < 0.05), but did not induce significant differences in plasma volume changes. Plasma volume decreased in both sessions during exercise (P < 0.01) and a significant rebound (P < 0.001) occurred during recovery. Osmolality was significantly higher (P < 0.001) during rest, exercise and recovery periods compared to the placebo trials, but no effect of alcohol on plasma Na+ and K+ concentrations was observed. In the alcohol test conditions, the arginine vasopressin (AVP) response to exercise was significantly dampened (P < 0.05). In contrast, alcohol had no effect on aldosterone or atrial natriuretic peptide (ANP). These results demonstrated that alcohol ingestion augmented body fluid losses due to a suppressive effect on AVP during physical exercise conducted in a warm environment. The increase in osmolality due to alcohol did not influence the aldosterone and ANP responses, which would suggest that total osmolality does not play a major role in the regulation of these hormones.

Aldosterone↗

PubMed1995

Clothing, assessment and effects on thermophysiological responses of man working in humid heat.

This paper presents the relative importance of the different factors to be taken into account when predicting thermal exchanges when man is wearing garments while being exposed to warm environments. Factors considered are the thermal insulation of clothing (CLO), the thermal efficiency of clothing (Fcl), the clothing area factor (fcl), the pumping coefficient (p), the vapour permeation efficiency factor (Fpcl). As Fpcl depends on CLO, Fcl,fcl and p factors, physiological assessments of this factor appears to be necessary for the calculation of the maximum evaporative capacity (Emax) in clothed subjects. In this paper, comparisons of body temperatures, whole body and local sweating were made from data obtained on both unclothed and then clothed subjects working at 50 watts on a cycloergometer in warm environments (Ta = Tr = Tsk), with increasing ambient humidity levels (Pa). Results showed that clothed subjects sweated more than unclothed man for the same Pa increases and hidromeiosis occurring on the skin of unclothed man seemed to be responsible for this. Sweat accumulation in the clothes confirms that the decrease in the evaporative sweat efficiency for clothed subjects was closely associated with the threshold for occurrence of core temperature drift. However the less important slope in the Tcore vs delta Pa relationship for clothed subjects compared to that for unclothed implies a more efficient body cooling thanks to clothing, which does not lead to as great a physiological disadvantage as expected. Pumping effect and additional concurrent evaporation could account for this phenomenon: the ISO model (Required sweat rate) which includes an additional air velocity as a function of metabolism allows us to consider this beneficial influence of increased Emax in clothed subjects. However this effect should not be considered when the model is used for unclothed subjects.

Adult↗

PubMed1994

Local sweating responses during recovery sleep after sleep deprivation in humans.

Changes in the central control of sweating were investigated in five sleep-deprived subjects (kept awake for 40 h) during their recovery sleep under warm ambient conditions [operative temperature (T(o)) was either 35 or 38 degrees C]. Oesophageal (T(oes)) and mean skin (Tsk) temperatures, chest sweat rate (msw,ch), and concomitant electro-encephalographic data were recorded. Throughout the night at 35 or 38 degrees C T(o), msw,ch changes were measured at a constant local chest skin temperature (Tch) of 35.5 degrees C. The results showed that body temperatures (T(oes) and Tsk) of sleep-deprived subjects were influenced by thermal and hypnogogic conditions. The msw,ch levels correlated positively with T(oes) in the subjects studied during sleep stage 1-2 (light sleep: LS), sleep stage 3-4 (slow wave sleep: SWS) and rapid eye movement (REM) sleep. Contrary to what has been reported in normal sleep, firstly, the T(oes) threshold for sweating onset differed between REM sleep and both LS and SWS, and, secondly, the slopes of the msw,ch versus T(oes) relationships were unchanged between REM and non-REM (i.e. LS or SWS) sleep. The changes observed after sleep deprivation were hypothesized to be due to alterations in the functioning of the central nervous system controller.

Adult↗

PubMed1994

Validity of the Wescor's sweat conductivity analyzer for the assessment of sweat electrolyte concentrations.

The purpose of this study was to compare the "NaCl equivalent" values determined by the Wescor's sweat conductivity analyzer (Sweat-Chek) with the sweat Na+ and Cl- concentration values measured by conventional methods. The sweat was induced by 60-min exercise and collected by a closed-pouch collector. The "NaCl equivalent" values determined by the sweat conductivity analyzer (mean: 75 mmol.L-1, range: 38 - 122, n = 72) were significantly (P < 0.05) greater than Na+ concentration values (mean: 71 mmol.L-1, range: 24 - 123, n = 72) measured by flame photometry and Cl-concentration values (mean: 61 mmol.L-1, range: 18 - 100, n = 48) measured by coulometric titration. The difference were most accentuated for low concentration values. The 95% confidence-agreement intervals around the mean differences between methods were 11 mmol.L-1 (14%) for both Na+ and Cl-. The Sweat-Chek conductivity analyzer is a portable instrument which approximates the actual Na+ and Cl- concentrations in sweat but with a positive bias probably due to the other unmeasured anions present in sweat.

Chlorides↗

PubMed1994

Humans under showers: thermal sensitivity, thermoneutral sensations, and comfort estimates.

Thirty male subjects participated in four experiments under showers to explore the sensitivities to water temperature and to its slow or rapid fluctuations. After having set the water temperature, at constant flow rate, at either a thermoneutral or a preferred level, subjects were asked to detect thermal changes or to report their thermosensory and affective judgments associated with water temperature changes. Results of water temperature, skin temperature, and subjective estimates showed that skin temperature for thermally neutral sensation under a shower were very similar to those observed in air, and such a thermoneutral level produced no discomfort. Preferred water temperature was slightly warmer and led to slightly elevated skin temperatures, warmth, and pleasantness estimates. Skin sensitivity to water thermal changes was very acute during slow and even more acute during rapid thermal transients. The conclusions of the present study are of value in the production of appropriate equipment to provide thermal comfort to people taking showers.

Adult↗

PubMed1993

Regulation of local sweating in sleep-deprived exercising humans.

Thermoregulatory sweating [total body (msw,b), chest (msw,c) and thigh (msw,t) sweating], body temperatures [oesophageal (T(oes)) and mean skin temperature (Tsk)] and heart rate were investigated in five sleep-deprived subjects (kept awake for 27 h) while exercising on a cycle (45 min at approximately 50% maximal oxygen consumption) in moderate heat (T(air) and T(wall) at 35 degrees C). The msw,c and msw,t were measured under local thermal clamp (Tsk,l), set at 35.5 degrees C. After sleep deprivation, neither the levels of body temperatures (T(oes), Tsk) nor the levels of msw,b, msw,c or msw,t differed from control at rest or during exercise steady state. During the transient phase of exercise (when Tsk and Tsk,l were unvarying), the msw,c and msw,t changes were positively correlated with those of T(oes). The slopes of the msw,c versus T(oes) or msw,t versus T(oes) relationships remained unchanged between control and sleep-loss experiments. Thus the slopes of the local sweating versus T(oes) relationships (msw,c and msw,t sweating data pooled which reached 1.05 (SEM 0.14) mg.cm-2.min-1.degree C-1 and 1.14 (SEM 0.18) mg.cm-2.min-1.degree C-1 before and after sleep deprivation) respectively did not differ. However, in our experiment, sleep deprivation significantly increased the T(oes) threshold for the onset of both msw,c and msw,t (+0.3 degrees C, P < 0.001). From our investigations it would seem that the delayed core temperature for sweating onset in sleep-deprived humans, while exercising moderately in the heat, is likely to have been due to alterations occurring at the central level.

Adult↗

PubMed1993

Qualitative assessment of thermal and evaporative adjustments of human scrotal skin in response to heat stress.

To study scrotal thermoregulation and its efficacy to work against heat accumulation, five subjects were exposed to four experimental conditions under which core and skin temperatures and sweat evaporative responses of various skin surfaces--chest, abdomen and scrotum--were compared. The temperature response of the scrotal area exhibited the largest inertia, and this observation is likely to be the consequence of heat exchange via the vascularization of testes and scrotum which is more efficient than in other parts of the body in limiting local heat storage, thus alleviating heat stress of the testis. The pulsatile nature and the synchronous pattern of the scrotal evaporative heat loss indicate that scrotal sweating takes place, although the gradient response appeared to be less marked than elsewhere in the body. Relatively low and inert scrotal temperature can partly explain this poor local drive for sweating.

Abdomen↗