This study assesses how circadian rhythms of heart rate (HR), HR variability (HRV) and activity change during long-term missions in space and how they relate to sleep quality. Ambulatory 48-h ECG and 96-h actigraphy were performed four times on ten healthy astronauts (44.7 ± 6.9 years; 9 men): 120.4 ± 43.7 days (Before) launch; 21.1 ± 2.5 days (ISS01) and 143.0 ± 27.1 days (ISS02) after launch; and 86.6 ± 40.6 days (After) return to Earth. Sleep quality was determined by sleep-related changes in activity, RR-intervals, HRV HF- and VLF-components and LF-band. The circadian amplitude of HR (HR-A) was larger in space (ISS01: 12.54, P = 0.0099; ISS02: 12.77, P = 0.0364) than on Earth (Before: 10.90; After: 10.55 bpm). Sleep duration in space (ISS01/ISS02) increased in 3 (Group A, from 370.7 to 388.0/413.0 min) and decreased in 7 (Group B, from 454.0 to 408.9/381.6 min) astronauts. Sleep quality improved in Group B from 7.07 to 8.36 (ISS01) and 9.36 (ISS02, P = 0.0001). Sleep-related parasympathetic activity increased from 55.2% to 74.8% (pNN50, P = 0.0010) (ISS02). HR-A correlated with the 24-h (r = 0.8110, P = 0.0044), 12-h (r = 0.6963, P = 0.0253), and 48-h (r = 0.6921, P = 0.0266) amplitudes of the magnetic declination index. These findings suggest associations of mission duration with increased well-being and anti-aging benefitting from magnetic fluctuations.
Bibliographical noteFunding Information:
The authors thank Dr. I. Tayama, S. Ishida and T. Aiba from the Space Biomedical Research Group, Japan Aerospace Exploration Agency (JAXA), for cooperation in our study. The authors also acknowledge the cooperation of the astronauts, the engineers, staff and managers of JAXA and NASA. We thank Yohsuke Kamide, Director of the Rikubetsu Space and Earth Science Museum, Professor Emeritus at Nagoya University, Toshio Ozawa, Professor Emeritus at Kochi University and Honorary Director of Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, and Børre H. Holmeslet, Auroral Observatory of the University of Tromsø, Tromsø, Norway for supporting this study. The help of Larry A. Beaty to improve the English language for greater clarity and readability is greatly appreciated. The JAXA Chronobiology Project was supported by the Japan Aerospace Exploration Agency (S.F., K.M., H.O., C.M.) and the Halberg Chronobiology Fund (G.C., K.O.).
© 2021, The Author(s).
PubMed: MeSH publication types
- Journal Article
- Research Support, Non-U.S. Gov't