Figure 1. Study protocol to assess daily rhythms under baseline (standard sleep-wake schedules) conditions and endogenous circadian rhythmicity of innate immune response in humans.

This is an example protocol for a participant with a bedtime of midnight. Participants were enrolled in a 7-day (n = 3; A) or 9-day (n = 10; B) inpatient protocol in an environment free of time cues. White bars indicate exposure to ambient room light (~90 lux) and gray bars indicate exposure to dim ambient light (<3 lux). Black bars show scheduled sleep episodes in darkness. The schedule consisted of a 3-day baseline including admission (ADM), with 8:16 h sleep:wake cycle (based on average sleep times in the 7 days prior to study entry) and four meals per 24-hours (filled circles); an initial 40 h (A) or 50 h and 10 min (B) constant routine under dim light, semi-recumbent constant posture, forced wakefulness, and hourly space isocaloric meals (filled circles), a 16 h light exposure day (gray hatched bar); followed by 8 h sleep and then discharge (A) or a second 29 h 50 min constant routine followed by an 8 h sleep episode and then discharge (D/C) (B). In the present study data were analyzed from the baseline and initial CR components only using blood samples collected at 4 h intervals shown by the red lines.