Monitoring desynchronization of the circadian timing system in space and during isolation and confinement

Given the increasing duration of space flights problems associated with changes of the circadian rhythm might be increasingly prominent during future exploratory missions. Therefore, technological advances for simple and accurate monitoring of circadian rhythm are clearly needed. Furthermore, such technology would provide the basis for countermeasures and direct treatment for proper reentrainment and synchronization of the circadian system to maintain proper physical and mental wellbeing and performance. In the present study it was shown that during 50 days of bed-rest no changes in circadian rhythm can be observed. It is suggested that both strength and exposure to external 'Zeitgeber' during bed-rest account for these findings. First, all subjects were exposed to various constant social routines such as strict wake-up schedules, regular meals and experimental schedules. In particular, the presence of changing light and dark cycles during the entire study is likely to explain the lack of any significant changes in circadian rhythm. Due to the small sample size, however, these results need to be interpreted with caution. These findings are well in accordance with research from Antarctic missions, stressing the importance of photonic cues for the entrainment of circadian rhythm. The second aim of the present study was to investigate the accuracy of determining circadian rhythm of core body temperature using a new, non-invasive heatflux sensor located at the head (Double Sensor) compared to rectal temperature measurements. The second aim of the present study was to investigate the accuracy of determining circadian rhythm using a new, non-invasive heatflux sensor located at the head (Double Sensor) based temperature recordings compared to rectal temperature measurements. No significant differences could be found for acrophase, mesor, and amplitude. This confirms our previous findings and we conclude that temperature profiles using the Double Sensor technology is well suitable for determining circadian rhythm under thermoneutral conditions. In conclusion, the present results confirm the validity of the Double Sensor technology to determine circadian rhythm and support the implementation of this approach in future space missions to i) better understand the time course and basic principles of the adaptations pertaining to the human autonomic nervous system in space, ii) to adjust more adequately physical exercise as well as rest- and work shifts, and iii) to foster adequate workplace illumination in the sense of occupational healthcare for humans in space.