Physiological sleep tendency on a simulated night shift: adaptation and effects of triazolam.

Daytime sleep and nocturnal sleepiness were examined in 18 normal sleepers (9 young adults, 9 middle-age adults) for 5.5 days following acute sleep/wake schedule inversion. Triazolam and placebo were compared in a counterbalanced, crossover design. Triazolam improved daytime sleep, but did not produce significant changes in sleep tendency at night. Physiological sleep tendency in the early morning hours (0200 to 0600) was profound, but decreased significantly within 3 to 4 days following sleep/wake inversion, irrespective of treatment condition. Nocturnal performance data generally were consistent with changes in physiological sleep tendency. We conclude that extending daytime sleep by an average of approximately 50 min per day via administration of a hypnotic does not appear to significantly reduce circadian sleep tendency in the early morning hours. Further, considerable adaptation, in terms of sleep tendency, occurred within a weak of simulated night shift despite a relatively constant daytime sleep pattern.