Variability of normal sleep patterns in 40 consecutive ambulatory sleep-wakefulness records.

Sleep-wakefulness (S-W) patterns were recorded continuously for 40 consecutive 24 h using subcutaneous chronic electrodes and an ambulatory cassette recorder in a healthy 57-year-old volunteer. Variability of sleep patterns was assessed in steady-state conditions and in the course of a scientific journey encompassing flights in both west/east and south/north directions. Data were compared with findings from age-matched laboratory control records. Polysomnographic evaluation of our sleep data shows: (1) Stability of the first 3 sleep cycles and variability of the remaining sleep period with respect to both duration and structure. Vulnerability of REM sleep to environmental interference. (2) Stability of the WASO/drowsiness cluster as an intraindividual biological trait independent of social interactions. The clinical relevance of ambulatory serial recording is stressed. (3) The role of the first sleep cycle structure in the chronobiological adaptation process is documented. Apparently travelling in south/north directions may have similar or even more polygraphic implications than west/east transfer.