Using daily 30-min phase advances to achieve a 6-hour advance: circadian rhythm, sleep, and alertness

A ground-based study was undertaken to determine whether circadian and sleep dysfunction could be avoided by "trickling in" a 6-h phase advance in sleep/wake schedule by 12 consecutive 30-min phase advances as per NASA's Appendix K.

We simulated a 16-d (384 h) mission for each of 10 subjects. Temporal cues and light levels approximated those experienced in space. All sleep periods were exactly 8 h. Before the study, for 14 d, subjects were required to live on a schedule with a 23:00 bedtime and 07:00 wake time. Laboratory sessions then started with a 4-d baseline segment on that schedule. The fourth night and the day following it were then taken as baseline. Repeated 30-min phase advances in bedtime were then required on each of the next 12 successive nights, resulting in an eventual movement of bedtimes to a 6-h phase-advanced position (bedtime: 17:00, wake time: 01:00). Polysomnographic sleep, circadian rhythms in urinary free cortisol, urinary volume (every void), and core body temperature (once per minute), and ratings of performance, mood, and alertness (five per day) were measured.

While circadian dysfunction was largely avoided by trickling in the phase shift, there remained slight differences in phase between the endogenous circadian pacemaker and the imposed routine which disrupted sleep and daytime alertness.

Though statistically significant, the disruption was less than we observed from repeated 2-h phase delays reported in a 2004 ASEM paper. Evidence would thus seem to favor repeated 30-min phase advances over repeated 2-h phase delays.