European isolation and confinement study. Twenty-four hour rhythm of rest/activity and sleep/wakefulness: comparison of subjective and objective measures.

The purpose of this study in the ISEMSI project was to record continuously the rest-activity cycle of the six subjects by ambulatory monitoring. It was planned to record the subjects during approximately 10 days of the pre-isolation period, the 28 days of isolation, and the 6-day post-isolation period. The three following major aims were envisaged: (1) to evaluate the possibility of monitoring the rest-activity cycle and sleep over prolonged time periods under conditions of confinement; (2) to examine the sleep period under the experimental condition in comparison to the pre- and post-experimental periods; and (3) to compare objective and subjective measures of sleep. The activity monitor is enclosed in a small metal case (68 g; 51 x 36.5 x 21 mm), which is worn on the wrist. The monitor is started via an interface; the recording interval was 1 minute. The subjects were instructed to read out their own data into a PC, and to obtain a graphic display within the confinement chambers to supervise the proper functioning of the activity monitors. Subjective data on sleep quality were obtained on a daily basis by means of a morning questionnaire. Once per week, the daytime vigilance states were assessed at 2-hour intervals on visual analogue scales. The activity recordings reflected the tightly controlled sleep-wake cycle during weekdays, and the permissive schedule on weekends. The data revealed no major sleep disturbances, which was in accordance with the subjective data. Most sleep complaints were due to the noise caused by snoring of other subjects. Self-rated tiredness tended to increase during confinement, whereas self-rated tenseness showed no trend. Due to organizational limitations, the data collected in the pre- and post-experimental periods were insufficient for an analysis. Summarizing, motor activity recorded by means of an ambulatory activity monitor proved to be a valuable non-electroencephalographic measure of sleep quality and rest-activity pattern of humans under conditions of long-term confinement. The activity monitor was found to be unobtrusive and reliable. The data read-out by the subjects during the experiment was feasible and contributed to the reduction of data loss. When the objective measures of sleep quality thus obtained were compared with subjective measures of this parameter, a good correspondence was found. Hence it can be said that activity monitoring represents a simple and reliable method for the long-term monitoring of sleep and wakefulness, which is well suited for application under space conditions.