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IntroductIon: Very early preterm infants (VPIs) are exposed to unpredictable noise in neonatal intensive care units. Their ability to perceive moderate acoustic environmental changes has not been fully investigated. rESuLtS: Physiological values of the 598 isolated sound peaks (sPs) that were 5-10 and 10-15 dB slow-response a (dBa) above background noise levels and that occured during infants' sleep varied significantly, indicating that VPIs detect them. exposure to 10-15 dBa sPs during active sleep significantly increased mean heart rate and decreased mean respiratory rate and mean systemic and cerebral oxygen saturations relative to baseline. dIScuSSIon: VPIs are sensitive to changes in their nosocomial acoustic environment, with a minimal signal-to-noise ratio (sNR) threshold of 5-10 dBa. These acoustic changes can alter their well-being. MEtHodS: In this observational study, we evaluated their differential auditory sensitivity to sound-pressure level (sPL) increments below 70-75 dBa equivalent continuous level in their incubators. environmental (sPL and audio recording), physiological, cerebral, and behavioral data were prospectively collected over 10 h in 26 VPIs (Ga 28 (26-31) wk). sPs emerging from background noise levels were identified and newborns' arousal states at the time of sPs were determined. changes in parameters were compared over 5-s periods between baseline and the 40 s following the sPs depending on their sNR thresholds above background noise. V ery early preterm infants (VPIs) are exposed to nosocomial environmental stimuli that differ from the stimuli they encounter in utero. This new "naturalistic" milieu, especially loud noise, may interfere with their neurodevelopment and growth (1-4). This has led to specific recommendations for permissible noise criteria levels in the neonatal intensive care unit (NICU) (5-7). These recommendations were based primarily on the evaluation of the effects of noise on the developing auditory system and well-being of newborns. Most studies were experimental. Preterm newborns were exposed to 5 s of high artificial sound (8,9), including sound-pressure levels (SPLs) ranging from 80 to 100 dB (8) and to warbling tones of 100 dB (9). The most prevalent responses were an increase in heart rate (HR) (8,9) proportional to the SPL of the stimulus and a tendency toward a decrease in respiratory rate (RR) (9). Few studies have evaluated the impact of noise in the NICU on newborns' physiological stability. Unfortunately, some of these studies measured the effect of acoustic environments quite different from those in the contemporary NICU (10) or did not include preterm infants (11) or VPIs (10). Moreover, some yielded questionable results because of study design, nonreporting of background noise, and the absence of a well-defined study population (e.g., inclusion of newborns with a wide range of gestational age, GA) (12). Despite these limitations, these studies showed that a high level of environmental noise, >70-75 dB slow response A (dBA) equivalent continuous leve...

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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.

Extensive research has demonstrated that shiftwork produces deleterious effects on health because of the desynchrony it induces in the biological clock. The problem is even more crucial for older workers who present, in addition, various decrements in their cognitive functioning, particularly on attention and memory. The present study assessed whether age was related to task complexity as a function of time of day and time-on-task in a rapid rotating work-rest schedule. 24 subjects (12 juniors: 20-30 years and 12 seniors: 50-60 years) performed either a simple task (visual discrimination) or a complex task (descending subtraction) on three different moments of the day simulating the main shifts (morning, evening, and night). Analysis indicated that an age effect was only present on the more complex task, which was demanding in attentional resources and memory load. Seniors had no deficit in performance on the simple task compared to juniors. The effect of time of day was restricted to the simple task for both age groups. However, some differential strategies appear to distinguish juniors and seniors, specifically on accuracy during the night, suggesting that subjects of different ages cope with cognitive tasks in different ways and that perhaps some adverse effects apparently associated with aging could be counteracted by efficient strategies, but not others.

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When exposed to cold, the hands need to be protected against heat loss not only in order to reduce thermal discomfort, but also to keep their efficiency. Although gloves are usually the most common protection, their thermal insulation is generally unknown. The aim of this study was to measure the heat losses from a gloved hand with a special interest in local variations. Using a calorimetric hand placed in a cold box, several types of gloves were tested. The results indicated that depending on the glove and on the area covered the heat loss reduction may vary from almost 60% to 90%. When the least efficient pair of gloves was excluded, heat exchange coefficients varied from 1.8 to 4.8 W/m2 per degrees C for the palm and from 4.2 to 6.2 W/m2 per degrees C for the back of the hand. The three medium fingers seemed to be equally treated, with a heat exchange coefficient variation of 6.3-9.0 W/m2 per degrees C. The thumb and the little finger, which require better insulation, exhibited higher local heat transfer coefficients of 8.3-12.7 W/m2 per degrees C. Some practical aspects are evoked.

The present experiment was designed to assess daily fluctuations of visual discriminability, a function reflecting the resolution power of the visual sensitivity by measure of a differential threshold. Sixteen subjects underwent a visual discrimination threshold task (using the constant method) in a protocol allowing one point every 2h over the 24h period. The results show that the visual discrimination threshold is low in the morning and increases progressively over the day, reaching a first peak at 22:00. During the night, the same pattern occurs, with low threshold levels at the beginning of the night and high levels at the end. This profile is quite different from that of detection threshold variations, suggesting that the two visual functions are under the control of different underlying mechanisms. Two interpretations could account for this discrepancy. The first relates to different oscillators in the eye for detection and discrimination. The second refers to a possible linkage of visual discriminability with the sleep-wake cycle since threshold measures were systematically low (i.e., high resolution power) after long sleep periods.