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


CONCLUSIONS
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.
Monk
Timothy H
TH
Clinical Neuroscience Research Center, Western Psychiatric Institute and Clinic, University of Pittsburgh Medical Center, Pittsburgh, PA, USA. monkth@upmc.edu
Buysse
Daniel J
DJ
Billy
Bart D
BD
DeGrazia
Jean M
JM
D000328:Adult; D001288:Attention; D001831:Body Temperature; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010561:Personnel Staffing and Scheduling; D017286:Polysomnography; D012893:Sleep Wake Disorders / Q000209:etiology* / Q000517:prevention & control*; D013026:Space Flight