Circadian rhythm of autonomic cardiovascular control during Mars500 simulated mission to Mars

Abstract

Introduction: The Mars500 project was conceived to gather knowledge about the psychological and physiological effects of living in an enclosed environment during the 520 days as would be required for a real mission to Mars. Our objective was to investigate the circadian profile of heart rate variability in the context of the Mars500 study. Methods: 24-h EKG records were obtained before, during and after confinement from the six crew members that participated in the mission. Autonomic activity was evaluated through time and frequency domain indexes of heart rate variability (HRV) analysis. Circadian rhythmicity was assessed both by averaging hourly HRV along wake and sleep scheduled periods and by fitting a 24-hour harmonic to the hourly means. Results: During confinement, wake HRV showed (mean ± SE) a progressive increase in mean RR interval (from 778 ± 24 ms to 916 ± 42 ms), and in the amplitude (values are wavelet power coefficients) of very low (from 13.3 ± 0.3 to 14.1 ± 0.2) and high (from 7.8 ± 0.4 to 8.3 ± 0.3) frequency components. During sleep, the relative amplitude of the high frequency component of HRV decreased (from 11.8 ± 1.6 nu to 9.4 ± 1.8 nu). Overall, sleep-wake differences of HRV showed a progressive decrease of the relative amplitude of the high frequency component. Also, circadian HRV rhythms were dampened during confinement. Discussion: Data revealed diminished amplitude of the rest-activity pattern of autonomic nervous system parasympathetic function. Reduced daylight exposure and mood changes could account for this observation.