CUMULATIVE SLEEPINESS, MOOD DISTURBANCE, AND PSYCHOMOTOR VIGILANCE PERFORMANCE DECREMENTS DURING A WEEK OF SLEEP RESTRICTED TO 4-5 HOURS PER NIGHT

To determine whether a cumulative sleep debt (in a range commonly expe rienced) would result in cumulative changes in measures of waking neur obehavioral alertness, 16 healthy young adults had their sleep restric ted 33% below habitual sleep duration, to an average 4.98 hours per ni ght [standard deviation (SD) = 0.57] for seven consecutive nights. Sub jects slept in the laboratory, and sleep and waking were monitored by staff and actigraphy. Three times each day (1000, 1600, and 2200 hours ) subjects were assessed for subjective sleepiness (SSS) and mood (POM S) and were evaluated on a brief performance battery that included psy chomotor vigilance (PVT), probed memory (PRM), and serial-addition tes ting. Once each day they completed a series of visual analog scales (V AS) and reported sleepiness and somatic and cognitive/emotional proble ms. Sleep restriction resulted in statistically robust cumulative effe cts on waking functions. SSS ratings, subscale scores for fatigue, con fusion, tension, and total mood disturbance from the POMS and VAS rati ngs of mental exhaustion and stress were elevated across days of restr icted sleep (p = 0.009 to p = 0.0001). PVT performance parameters, inc luding the frequency and duration of lapses, were also significantly i ncreased by restriction (p = 0.018 to p = 0.0001). Significant time-of -day effects were evident in SSS and PVT data, but time-of-day did not interact with the effects of sleep restriction across days. The tempo ral profiles of cumulative changes in neurobehavioral measures of aler tness as a function of sleep restriction were generally consistent. Su bjective changes tended to precede performance changes by 1 day, but o verall changes in both classes of measure were greatest during the fir st 2 days (P1, P2) and last 2 days (P6, P7) of sleep restriction. Data from subsets of subjects also showed: 1) that significant decreases i n the MSLT occurred during sleep restriction, 2) that the elevated sle epiness and performance deficits continued beyond day 7 of restriction , and 3) that recovery from these deficits appeared to require two ful l nights of sleep. The cumulative increase in performance lapses acros s days of sleep restriction correlated closely with MSLT results (r = -0.95) from an earlier comparable experiment by Carskadon and Dement ( 1). These findings suggest that cumulative nocturnal sleep debt had a dynamic and escalating analog in cumulative daytime sleepiness and tha t asymptotic or steady-state sleepiness was not achieved in response t o sleep restriction.