Rates of evaporation and sweating were recorded for three acclimatized male subjects in hot humid conditions, the ambient parameters of which were set so that the various imposed evaporative rates required the same skin wettedness at different levels of sweating. Rectal and skin temperatures were measured. Results showed that during steady state occurring during the 2nd h of exposure each subject reached the required evaporative rate by means of increases in skin wettedness regardless of the level of sweating; the sweat evaporative efficiency, defined as the ratio between evaporative rate and sweat rate, decreased as skin wettedness increased, in a range between 0.74 and 1.0 Sweat efficiency fell to 0.67 for fully wet skin. The body temperatures did not increase with time if skin wettedness was less than unity. Evaporative heat transfer coefficient (he), maximum evaporative capacity, and wettedness were estimated on the basis of the observed decrease of sweat efficiency. The relationship between skin wettedness and sweat efficiency was interpreted as a combined effect of differences in local he as well as in local sweat rates.

feed-425 back and augmented REM sleep. Psychophysiology 7 (1970) abstract. 39 Zir, L.M., Smith, R. A,, and Parker, D.C., Human growth hormone release in sleep: effect of daytime exercise. J. clin. Endocr. Metab. 32 (1971) 662-665. 40 Zloty, R.B., Burdick, J.A., and Adamson, J.D., Sleep of distance runners. Activitas nerv. sup. 15 (1973) 217 221.

The purpose of the present study was to analyse the arousing effects of noise on sleep inertia as a function of circadian placement of a one-hour nap. In a first experiment, we measured the effects of sleep inertia in a neutral acoustic environment after a one-hour nap placed either at 0100 or 0400 on response time during a spatial memory test. In a second experiment were analysed the effects of an intense continuous noise on sleep inertia. The results showed that noise produced a total abolition of sleep inertia after an early nap (0000 to 0100). This may be due to the arousing effect of noise; however, results are less clear after a late nap 0300 to 0400 as noise seems to be ineffective. This result is discussed in terms of either a function of time-of-day effect or of prior sleep intensity. Moreover, our data suggest a possible interaction of noise with partial sleep deprivation leading to a slight deleterious effect those subjects who did not sleep at all.

This study assessed clinical and cardiorespiratory responses after an interval training programme in sedentary elderly adults using the ventilatory threshold (Vth) as the index of exercise training intensity. A selection of 22 subjects were randomized into two groups: 11 subjects served as the training group (TG) and the others as controls (CG). Maximal exercise tests were performed on a treadmill before (T0), each month (T1, T2) and after the 3-month interval training programme period (T3). The TG subjects were individually trained at the heart rate corresponding to Vth measured at T0, T1 and T2 as the breakpoint in the oxygen uptake-carbon dioxide production relationship. Their training programme consisted of walking/jogging sessions on a running track twice a week. The sessions consisted of varying durations of exercise alternating with active recovery in such a way that the subjects slowly increased their total exercise time from an initial duration of 30 min to a final duration of 1 h. During training the heart rate was continuously monitored by a cardiofrequency meter. Compared with the daily activities of the controls, no training programme-related injuries were observed in TG. Moreover, programme adherence (73%) and attendance (97.3%) were high. The maximal oxygen uptake and Vth were increased in TG, by 20% (P<0.05) and 26% (P<0.01), respectively. Interval training at Vth also significantly increased maximal O2 pulse (P<0.05) and maximal ventilation (P<0.01). A significant decrease in submaximal ventilation (P<0.05) and heart rate (P<0.01) was also noted. These results would suggest that for untrained elderly adults, an interval training programme at the intensity of Vth may be well-tolerated clinically and may significantly improve both maximal aerobic power and submaximal exercise tolerance.

Before and after heat acclimation, four male resting subjects were exposed to humid heat that caused levels of skin wettedness ranging from 50 to 100%. The physical experimental conditions were chosen so that the same skin wettedness was attained with modification of only the ambient water vapor pressure, at two wind speeds (0.6 and 0.9 m . s-1). The esophageal temperature (Tes), mean skin temperature (Tsk), sweating rate (msw), and dripping sweat rate (mdr) were recorded; the amounts of local drippage in the same thermal conditions before and after acclimation were also determined. The relationship between the evaporative efficiency of sweating (eta sw) and the skin wettedness (w) is reported, as is the influence of the subject's acclimation to humid heat on adjustments of skin wettedness. The effects of the air velocity on the coefficient of evaporation and on sweating efficiency are discussed. Beneficial increases in evaporation were achievable by increasing skin wettedness only when there was a consistent drippage, which differed from one body area to another and from one subject to another. The relation of drift in body temperature to skin wettedness changed with the acclimation of the subjects.

Keeping premature newborns warm is crucial for their survival. Their ability to prevent excessive heat loss to the environment and to control their body temperature is limited. The risk of hypothermia is particularly important for low-birth-weight newborns with a large body surface area in relation to their mass of heat-producing tissues. The present study was performed to assess the body heat loss difference between small and large body-size premature newborns using two anthropomorphic thermal manikins of premature newborns of 900 g and 1,800 g (respective body surface areas of 0.086 and 0.150 m2). The dry heat loss from the six body segments of the small manikin (S) was measured and compared with that of the large manikin (L). The two manikins were exposed to five different environmental temperatures ranging between 29 and 35 degrees C in a single-walled, air-heated closed incubator. The magnitudes of heat loss decreased significantly by 20.4% between the two manikins [small manikin 110.1 (44.3) W/m2 vs large manikin 87.6 (25.8) W/m2, mean values with one standard deviation]. The results obtained from the comparison of the heat loss measures from the two manikins confirm the fact that the heat loss increases with an increase in the ratio of the body surface area to body mass. The thermal manikin appears to provide an accurate method for the assessment of thermal conditions in neonatal care.

549 IN NEONATES, THE INCIDENCE OF APNEA DEPENDS ON A VARIETY OF FACTORS, SUCH AS BIRTH WEIGHT, 1 SEX, 2 GESTATIONAL AGE, 3 AND POSTNATAL AGE. 3,4 Central apnea is generally reported as occurring more frequently during active sleep than during quiet sleep. 2,3,[5][6][7] Many authors have pointed out that apnea incidence is also closely related to ambient temperature in both full-term [8][9][10] and preterm neonates 9,11,12 and that the rate of apneic events is increased by warm exposure (i.e., thermal drive). Although preterm neonates are more often exposed to cool stress than to warm stress, little is known about the influence of cool exposure on the incidence of apnea in the different sleep states. Bader et al 11 reported a lower rate of central apnea during transient decreases in incubator temperature from warm (29°C) to thermoneutral conditions (24°C) over 30 minutes, although this was only seen during quiet sleep for preterm infants and during active sleep for term infants.The mechanism linking thermal stress and apnea is unknown and thus warrants further investigation. On the basis of the above-cited studies, it can be supposed that suprapontine influences modify respiratory control, which must be considered as a multiple-interaction system. Abnormal functional interaction among the respiratory system, thermoregulatory system, and sleep processes may alter compensatory responses to autonomic cardiovascular or respiratory challenge and increase the likelihood of life-threatening events later in life. 13 The effect of thermal stress is usually assessed by monitoring the body's internal temperature (generally esophageal or rectal temperatures, which supposedly represent the core temperature) and/or mean skin temperature. 14 However, the central controller of the thermoregulatory system receives thermal inputs from thermosensitive structures distributed throughout the body. The regulated variable therefore results from a weighted sum of different body temperatures. 15 Hence, to fully understand the thermal influence on apnea incidence in cool environments, it is essential to quantify the magnitude of body cooling that is proportional to the radiant, convective, conductive, and evaporative heat losses (i.e., body heat loss) on the other. Any failure to maintain thermal balance stimulates the body's thermal control mechanisms and thus triggers regulatory adjustments. This approach may help clarify a hypothesis raised by Perlstein et al, 9 whereby apnea is not specifically induced by changes in air temperature but, rather, through processes controlling the overall body heat loss (BHL). Hence, in the present study, the role of thermal drive in the mechanisms underlying the genesis of central apnea in the sleeping neonate was assessed by taking into account BHL during mild warm and cool thermal exposures.Central apneic events were monitored in a group of 22 nearterm neonates. Indeed, there are few published studies on these infants, who are generally considered to be physiologically similar to term infants, even t...

Wrapping low-birth-weight neonates in a plastic bag prevents body heat loss. A bonnet can also be used, since large amounts of heat can be lost from the head region, but may provide too much thermal insulation, thus increasing the risk of overheating. We assessed the time required to reach warning body temperature (t38 degrees C), heat stroke (t40 degrees C), or extreme value (t43 degrees C) in a mathematical model that involved calculating various local body heat losses. Simulated heat exchanges were based on body surface temperature distribution measured in preterm neonates exposed to 33 degrees C air temperature (relative air humidity: 35%; air velocity: <0.1 m/s) and covered (torso and limbs) or not with a transparent plastic bag. We also compared metabolic heat production with body heat losses when a bonnet (2 or 3.5 mm thick) covered 10%, 40%, or 100% of the head. Wrapping neonates in a bag (combined or not with a bonnet) does not induce a critical situation as long as metabolic heat production does not increase. When endogenous heat production rises, t38 degrees C ranged between 75 and 287, t40 degrees C between 185 and 549, and t43 degrees C between 287 and 702 min. When this increase was accompanied by a fall in skin temperature, overheating risk was accentuated (37