Level of Sleepiness and Total Sleep Time Following Various Time in Bed Conditions

The effects of various time in bed (TlB) conditions on daytime sleepiness and total sleep time (during a 24-hour enforced bedtime) were investigated. Thirty-two healthy male subjects participated in the study. Subjects were assigned to one offour groups to balance average screening multiple sleep latency tests (MSLT). Subjects were randomly assigned to spend 8, 6, 4 or a hours time in bed. They underwent the same TlB condition twice with at least 7 days between the two sessions. Following their assigned time in bed conditions, subjects were counterbalanced to have a standard MSLT and a 24-hour enforced bedtime protocol. To assess the effect ofTlB on the MSLT, the sleep latencies were submitted to a four (TIB condition) by four (nap test) multivariate analysis of variance. The sleep latencies were shorter for those subjects in the a-hours condition when compared to the other three conditions. Also, the sleep latencies of those subjects in the 4-and 6-hour conditions were comparable but different from those of subjects in the 8-and a-hour TlB conditions. To assess the effect of TlB on the 24-hour enforced 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 a hours TlB when compared to the other three conditions. There were no statistically significant differences between the 8-, 6-and 4-hour TlB conditions. Across conditions, subjects slept more during the first 4 hours when compared to blocks 2, 3, 4 and 5. Blocks I 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 when compared to blocks 5 and 6. Subjects slept less in block 5 when compared to block 6. Finally, trend analyses were used to better define the quantitative characteristics of the mean MSL T and total sleep times following the various TlB conditions. A significant linear component but no quadratic or cubic components were evident in the mean MSL T and total sleep times with decreasing TlB. These results suggest that the propensity to fall asleep and the propensity to stay asleep follow similar response patterns.