Investigating claims that a clothed person's mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more detail than human studies would permit. Using clothing with different levels of vapor permeability and measuring heat losses from skin controlled at 34 degrees C in ambient temperatures of 10, 20, and 34 degrees C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss (E(mass)) measurement and direct measurement of the extra heat loss by the manikin due to wet skin (E(app)) were compared. A clear discrepancy was observed. E(mass) overestimated E(app) in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34 degrees C, apparent latent heat (lambda(app)) of pure evaporative cooling was lower than the physical value (lambda; 2,430 J/g) and reduced with increasing vapor resistance up to 45%. At lower temperatures, lambda(app) increases due to additional skin heat loss via evaporation of moisture that condenses inside the clothing, analogous to a heat pipe. For impermeable clothing, lambda(app) even exceeds lambda by four times that value at 10 degrees C. These findings demonstrate that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type. The model presented explains human subject data on EVAP that previously seemed contradictive.

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.

The present study investigated the causes of decreases in sweating capacities with age. The hypothesis was that the decrease in local sweat rate in older individuals was associated with deterioration in thermal cutaneous receptor responses leading to weaker signals to the thermoregulatory center (i.e. the hypothalamus). Fifteen older (>60 years), 15 middle-aged (40-50 years) and 15 young (20-30 years) men were exposed for 90 min to a 40 degrees C, 14 degrees C dew point environment. The thermal detection threshold was measured at 9 different cutaneous locations. The results showed a reduced sweat output with age, and that older and middle-aged subjects had higher core and skin temperatures than young subjects. In addition, there was a sensory thermal sensitivity decrease and a correlation between thermal sensitivity and local sweat rate in older and middle-aged subjects, but not in young subjects. The data suggest that the age-related effects on thermoregulatory mechanisms reflect local skin changes rather than central alterations.

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.

Many studies have reported that blind people compensate for their visual deficit by sharpening auditory processes. Here we compare the sensitivity to echo cues between blind and sighted subjects. In the first experiment, the blind subjects were more accurate than the sighted subjects in localizing an object on the basis of echo cues. To ensure that enhanced echolocalization abilities were not only due to the fact that blind individuals are more used to consciously paying attention to echo cues and are more familiar with this kind of tasks than sighted subjects, we tested both groups of subjects in a simple azimuthal localization task of auditory stimuli. In this second experiment, we evaluated the influence of irrelevant echo signals on auditory localization by placing the subjects and the sound sources at different positions in a sound reverberant room. Results revealed that blind subjects exhibit a higher sensitivity to echo signals than sighted subjects.