A DOSE-RESPONSE STUDY OF TOTAL SLEEP TIME AND THE ABILITY TO MAINTAINWAKEFULNESS

The apparent connection between sleep debt, performance decrements and workplace accidents has generated a need for feasible vigilance tests that focus on the quantification of daytime sleepiness in occupationa l settings. The objective of this study was to evaluate the sensitivit y of the Maintenance of Wakefulness Test (MWT) to acute sleep deprivat ion of various doses. Eight healthy female volunteers, mean age 28.9 y ears (range 23-36), participated in this laboratory study. After an ad aptation night, the subjects were assigned to four counterbalanced, ra ndomly ordered night sleep conditions. These four conditions allowed f or a time in bed (TIB) of 0, 2, 4 or 8 h, producing a total sleep time of 0, 113, 218 and 427 min, respectively. The ability to sustain wake fulness was measured after the TIE period at 11.00 and 17.00 hours by the MWT. Analysis of variance with repeated measures was used to study the dependence of MWT sleep latencies on the immediately prior TIE pe riod. Both the latency of stage 1 sleep onset and the appearance of sl ow eye movements reduced significantly with increased sleep loss. The quantitative relationship between the previous total sleep time and th e subsequent MWT sleep latencies followed an exponentially decaying fu nction showing a high sensitivity to acute, severe night sleep loss bu t low sensitivity to less severe sleep restrictions. It is concluded t hat the MWT seems to be a sensitive method for the estimation of acute sleep deprivation. The test results appear, however, non-linearly rel ated to the earlier sleep debt.