Circadian and circaseptan (about-7-day) free-running physiologic rhythms of a woman in social isolation

An investigation into the time structure of rhythms in the absence of a clock during prolonged human social isolation is presented. A clinically healthy woman lived underground and her systolic, mean arterial, and diastolic blood pressure and her heart rate were automatically monitored most of the time during 14 weeks. She also self-measured, several times during wakefulness, her oral and axillary temperature. A circadian period slightly longer than 24 h came to the fore for all variables investigated, both by linear-nonlinear rhythmometry and by chronobiologic serial sections on the data obtained from the middle of the second week of isolation for the ensuing 97 days. In heart rate, an about-seven-day (circaseptan) rhythm was also found, with a confidence interval that did not overlap the precise seven-day trial period, notably during the first seven weeks. Some loose coupling of rhythms in metabolism gauged by core temperature and the heart rate is demonstrated for two components of the physiologic rhythm spectrum, the circadian of several variables and the circaseptan of heart rate.