Page:Risk of performance errors due to sleep loss, circadian desynchronization, fatigue, and work overload.pdf/13

Figure 3-4. Image of an Actiwatch activity monitor that is shown next to a ruler to demonstrate the size of the Actiwatch.

Figure 3-5. With most of his body tucked away in a sleeping bag, astronaut Daniel Tani, Expedition 16 flight engineer, poses for a photograph near two extravehicular mobility unit spacesuits in the Quest Airlock of the ISS.

Figure 3-6. Cosmonaut Vladimir Dezhurov of Rosaviakosmos, Expedition 3 flight engineer, works on a laptop computer in the temporary sleep station in the U.S. Laboratory.

Recent unpublished data from shuttle missions (Barger and Czeisler, 2008) also show a trend of regular use of medication to promote sleep. Of the first 32 crew members studied during 11 missions, 26 (81%) reported taking a sleep-promoting medication in flight. Crew members who used sleep medications reported taking them on approximately half the nights that data were collected aboard the space shuttle; two doses of sleep medication were taken on 7% of the nights when medication was used. The frequent use of sleep medication in flight serves as a strong indication that sleep is disturbed for some crew members.

Sleep structure (i.e., sleep quality) may also be altered in space. A 1997 study (Gundel et al.), which used polysomnography (Category II) to evaluate sleep content, found that latency to the first rapid eye movement (REM) episode was shorter, and slow wave sleep (SWS) was redistributed from the first to the second sleep cycle. Dijk et al. (2001), who also used polysomnography, found a reduction of SWS during the final third of in-flight sleep episodes and post-flight (evaluated at 2, 4, and 5 days post-landing), with an increase in sleep duration and the amount of restorative sleep.