Using nine 2-h delays to achieve a 6-h advance disrupts sleep, alertness, and circadian rhythm.

UNLABELLED: 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 nine consecutive 2-h phase delays, as would be recommended by NASA's Appendix K guidelines.
METHODS: A 16-d (384-h) mission was simulated in 10 subjects (5 men, 5 women, mean age: 41.2 yr), studied singly or in pairs. After 14 d on a 23:00-07:00 sleep/wake cycle, the subject entered the laboratory. After a 4-d baseline segment, repeated 2-h phase delays were then required on each of the next nine successive nights of the study (i.e., bedtimes at 01:00, 03:00, 05:00, etc.), resulting in an eventual movement of bedtimes to an 18-h phase delayed (equivalent to a 6-h phase advanced) position with bedtime at 17:00. Measures taken throughout the laboratory study included polysomnographically measured sleep, circadian rhythms in rectal temperature, and subjective ratings of mood and alertness.
RESULTS: Circadian dysfunction and sleep disruption were not avoided by trickling in the phase shift. The circadian pacemaker appeared to delay its phase by an average of about 1 h later per night, rather than the 2 h later per night required by the imposed routine. This resulted in a progressive decrease in circadian temperature rhythm amplitude, a progressive disruption in sleep, and a progressive lowering in subjective ratings of alertness.
CONCLUSION: Doubt must be cast on the assertion that circadian dysfunction and sleep loss can be avoided by limiting repeated phase delays in routine to 2 h.