Disturbances in diurnal rhythms following a night of reduced sleep

Twenty-four healthy young adult males who slept regularly for 7--8 hr completed nonlaboratory appraisals based upon dependent variables which reflected daytime alertness at 4-hr intervals from 8:15 a.m. until midnight once: (a) initially after having experienced disturbed nocturnal sleep and (b) following a control night. A statistically significant 1.8 hr average decrease in total sleep was reported during the disturbed night X = 6.0 hr) versus the control condition (X - 7.8 hr) which primarily resulted from delays and/or difficulties in falling asleep. Following disturbed nocturnal sleep a significant decline in alert wakefulness occurred predominantly at: (a) midday (12:00 noon) and/or (b) in the afternoon (4:00 p.m.) as assessed by 4 of 6 adjective check list scales and lowered body temperature levels. After the disturbed night, compared with the control condition, there was a significant diminution of the amplitude or variability in the diurnal rhythm of: (a) body temperature; (b) Stanford Sleepiness Scale ratings: (c) adjective check list scores on the (i) activation, (ii) fatigue, and (iii) performance efficiency subscales. The amplitude reduction in the diurnal rhythm was associated with a general trough during the middle of the wakefulness cycle which extended from 12:00 noon until 8:00 pm.m when various arousal indices following regular sleep attained maximal values. Subjects subsequently slept significantly longer by 1.3 hr than on the immediately preceding night of reduced sleep. There was a significant negative correlation between relative levels of temperature in the morning and sleep duration reported on the disturbed night. Greater accumulations of sleep reported during the disturbed night occurred when temperature levels corresponded with values in the control condition.