Page:Risk of performance errors due to sleep loss, circadian desynchronization, fatigue, and work overload.pdf/12

first and last days of a mission (total 5.6 and 5.7 hours, respectively). Many crew members reported fewer than 5 hours sleep on some nights, and some crew members slept 2 hours or less (Santy et al., 1988, p. 1096). While NASA flight surgeons recommend 8 hours of sleep per day in space, studies on 101 astronauts have found that, in space, they sleep an average of approximately 6 hours per day.

Note that, in the table, the categories of evidence are limited to Category II and Category III. This limitation is due to the nature of space flight, which requires that researchers evaluate a small number of subjects, rendering it practically impossible to truly replicate a Category I when astronauts are on orbit.

Actigraphy and self-reporting are currently measuring to what degree space flight results in disruption of sleep during both short-duration (shuttle) and long-duration (ISS) missions (Barger and Czeisler, 2008). This study will be the largest and most rigorous of its type. To date, 36 subjects on shuttle missions and six subjects on ISS missions have completed the protocol; a total of 20 subjects from ISS missions are planned to take part in the study, and shuttle data collection will continue until the ISS goal is achieved and/or the shuttle is retired. Data are collected at 90 days before launch for 2 weeks (to establish a baseline), from 11 days before launch until launch, in flight (as soon as possible on orbit until the last flight day), and, after landing, for 7 more days. Preliminary analysis, using 23 subjects over nine shuttle missions, estimated that the average total nightly sleep duration (estimated with actigraphy) was 5.9 hours in flight and 6.9 ± 1.0 hours in the first week after flight. Of the 279 nights in flight that were recorded with actigraphy, 52 (18.6%) included fewer than 6 hours of sleep. These findings confirm previous studies that show an incidence of reduced sleep quantity in space.

Further preliminary analysis shows that sleep quantity may be reduced even more prior to undergoing critical mission operations. Evaluations of nine crew members who were performing between one and three EVAs each, across five missions, estimate that the average total amount of sleep that the crew members had the night before the EVAs was 5.6 ± 1.1 hours. As previously discussed, ground-based studies have consistently reported performance impairments under conditions of acute or chronic reduced sleep.

Objective feedback on sleep quantity is important information to provide to flight surgeons and astronauts who are preparing to engage in critical mission activities; this will be particularly true for the more autonomous Exploration missions. Currently, actigraphy data for some missions are being shared among the researcher, the flight surgeon, and the crew member; the flight surgeons and astronauts, who have commented on the benefit of having this information available, support transitioning the Actiwatch (figure 3-4) protocol to an operational tool (flight surgeons G Beven and S Johnston, personal communication, 2008).

A compelling testimony of sleep disturbances in flight is the degree to which sleep medications are used. A 1999 Category III study reviewed records from 79 space shuttle missions: of the 219 records that were obtained (each record representing one person on one flight), 94% indicated medication use during flight; and of the records that indicated medication use, 45% of them indicated that the medications were taken for sleep disturbances and that these were taken consistently for 9 flight days (Putcha et al., 1999). Two examples of astronaut sleep facilities on the ISS are provided in figure 3-5 and 3-6.