LEVEL OF SLEEPINESS AND TOTAL SLEEP TIME FOLLOWING VARIOUS TIME IN BED CONDITIONS

The effects of various time in bed (TIB) conditions on daytime sleepin ess and total sleep time (during a 24-hour enforced bedtime) were inve stigated. Thirty-two healthy male subjects participated in the study. Subjects were assigned to one of four groups to balance average screen ing multiple sleep latency tests (MSLT). Subjects were randomly assign ed to spend 8, 6, 4 or 0 hours time in bed, They underwent the same TI B condition twice with at least 7 days between the two sessions. Follo wing their assigned time in bed conditions, subjects were counterbalan ced to have a standard MSLT and a 24-hour enforced bedtime protocol. T o assess the effect of TIB on the MSLT. the sleep latencies were submi tted to a four (TIB condition) by four (nap test) multivariate analysi s of variance. The sleep latencies were shorter for those subjects in the 0-hours condition when compared to the other three conditions. Als o, the sleep latencies of those subjects in the 4- and 6-hour conditio ns were comparable but different from those of subjects in the 8- and 0-hour TIB conditions. To assess the effect of TIB on the 24-hour enfo rced bedtime, the total sleep time during this period was submitted to a six (4-hour block) by four (TIB condition) multivariate analysis of variance. Subjects slept more following 0 hours TIB when compared to the other three conditions. There were no statistically significant di fferences between the 8-, 6- and 4-hour TIB conditions. Across conditi ons, subjects slept more during the first 4 hours when compared to blo cks 2, 3, 4 and 5. Blocks 1 and 6 were comparable. Subjects slept more in block 2 when compared to blocks 3 and 4 but less when compared to block 6. Subjects' sleep was comparable in blocks 3 and 4 but less whe n compared to blocks 5 and 6. Subjects slept less in block 5 when comp ared to block 6. Finally, trend analyses were used to better define th e quantitative characteristics of the mean MSLT and total sleep times following the various TIB conditions. A significant linear component b ut no quadratic or cubic components were evident in the mean MSLT and total sleep times with decreasing TIB. These results suggest that the propensity to fall asleep and the propensity to stay asleep follow sim ilar response patterns.