Temporal order of sleepiness, performance and physiological indices during 19-h sleep deprivation

Nineteen-hour variation of subjective sleepiness, performance and physiological indices were assessed during sleep deprivation. Longitudinal data of each index had its characteristic curve through which the values changed from day level to night level. A comparison of the time when each curve crossed its mid-range (50% value of its range) showed that those of subjective sleepiness and heart rate were significantly earlier than those of tracking error and coefficient of variation of R-R interval (CV(R-R)), P<0.01. That of rectal temperature was located at between 1:00 and 4:00 am. These temporal relationships were reproducible under two lighting conditions. These results will be useful in considering the occurrence of human errors by night-time workers in the early morning.