Adapting to phase shifts, I. An experimental model for jet lag and shift work

An experimental model was developed to measure various behavioral and physiological parameters in a laboratory paradigm mimicking phase shifts that could occur in time-zone transitions and shift work rotas. Volunteers were exposed to 9-h pulses of bright light (1,200 lx) as follows: day (D)1: 1800-0300 h, D2: 2100-0600 h, and D3, 4, 5: 2400-0900 h, each period followed by 8 h darkness. Immediately following the last treatment, subjects resumed their baseline sleep/wake schedule in a normal environment, thus experiencing a rapid 9-h advance phase shift of local time cues. During the gradual delay shift, a progressive delay shift in the rhythms of urinary 6-sulphatoxymelatonin (aMT6s), temperature and alertness was evident (maximum shift: 9.13 +/- 0.83 h, 9.09 +/- 1.06, and 10.62 +/- 0.96 h, mean +/- SD, respectively). There were no important detrimental effects on behavioral variables. After the rapid 9-h phase advance, sleep patterns, temperature amplitude, aMT6s acrophase, alertness, and performance took at least 5 days to reestablish normal baseline patterns. This model provides an effective and inexpensive model to study adaptation strategies in real life.