Continuous transepidermal water loss measurement in sleeping infants.

Transepidermal water evaporation rate was measured continuously in 8 infants with the use of an evaporimeter during one night of polygraphic sleep recording. Evaporation rates were significantly lower during REM than during NREM sleep. In both sleep stages it decreased during the night with the lowest values between 02.00 and 04.00 h. Evaporation values showed cyclic changes which were studied by measuring minute-by-minute differences between the maximum and the minimum values (the "amplitude variability") and the number of evaporation peaks per minute (the "peak density"). Both the "amplitude variability" and the "peak density" were smaller in REM than in NREM sleep. The "amplitude variability" decreased during the night with lowest values seen between 02.00 and 04.00 h. These changes in evaporation rates could reflect autonomic nervous system activity as well as basal metabolic activity and should be taken into account whenever such measurements are performed in sleeping infants.