Long-term exposure to space’s microgravity alters the time structure of heart rate variability of astronauts

Kuniaki Otsuka; Germaine Cornelissen; Satoshi Furukawa; Yutaka Kubo; Mitsutoshi Hayashi; Koichi Shibata; Koh Mizuno; Tatsuya Aiba; Hiroshi Ohshima; Chiaki Mukai

doi:10.1016/j.heliyon.2016.e00211

Heliyon (Dec 2016)

Long-term exposure to space’s microgravity alters the time structure of heart rate variability of astronauts

Kuniaki Otsuka,
Germaine Cornelissen,
Satoshi Furukawa,
Yutaka Kubo,
Mitsutoshi Hayashi,
Koichi Shibata,
Koh Mizuno,
Tatsuya Aiba,
Hiroshi Ohshima,
Chiaki Mukai

Affiliations

Kuniaki Otsuka: Executive Medical Center, Totsuka Royal Clinic, Tokyo Women’s Medical University, Tokyo, Japan
Germaine Cornelissen: Halberg Chronobiology Center, University of Minnesota, Minneapolis, MN, USA
Satoshi Furukawa: Space Biomedical Research Group, Japan Aerospace Exploration Agency, Tokyo, Japan
Yutaka Kubo: Department of Medicine, Tokyo Women's Medical University, Medical Center East, Tokyo, Japan
Mitsutoshi Hayashi: Department of Medicine, Tokyo Women's Medical University, Medical Center East, Tokyo, Japan
Koichi Shibata: Department of Medicine, Tokyo Women's Medical University, Medical Center East, Tokyo, Japan
Koh Mizuno: Space Biomedical Research Group, Japan Aerospace Exploration Agency, Tokyo, Japan
Tatsuya Aiba: Space Biomedical Research Group, Japan Aerospace Exploration Agency, Tokyo, Japan
Hiroshi Ohshima: Space Biomedical Research Group, Japan Aerospace Exploration Agency, Tokyo, Japan
Chiaki Mukai: Space Biomedical Research Group, Japan Aerospace Exploration Agency, Tokyo, Japan

DOI: https://doi.org/10.1016/j.heliyon.2016.e00211
Journal volume & issue: Vol. 2, no. 12

Abstract

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Background: Spaceflight alters human cardiovascular dynamics. The less negative slope of the fractal scaling of heart rate variability (HRV) of astronauts exposed long-term to microgravity reflects cardiovascular deconditioning. We here focus on specific frequency regions of HRV. Methods: Ten healthy astronauts (8 men, 49.1 ± 4.2 years) provided five 24-hour electrocardiographic (ECG) records: before launch, 20.8 ± 2.9 (ISS01), 72.5 ± 3.9 (ISS02) and 152.8 ± 16.1 (ISS03) days after launch, and after return to Earth. HRV endpoints, determined from normal-to-normal (NN) intervals in 180-min intervals progressively displaced by 5 min, were compared in space versus Earth. They were fitted with a model including 4 major anticipated components with periods of 24 (circadian), 12 (circasemidian), 8 (circaoctohoran), and 1.5 (Basic Rest-Activity Cycle; BRAC) hours. Findings: The 24-, 12-, and 8-hour components of HRV persisted during long-term spaceflight. The 90-min amplitude became about three times larger in space (ISS03) than on Earth, notably in a subgroup of 7 astronauts who presented with a different HRV profile before flight. The total spectral power (TF; p < 0.05) and that in the ultra-low frequency range (ULF, 0.0001–0.003 Hz; p < 0.01) increased from 154.9 ± 105.0 and 117.9 ± 57.5 msec2 (before flight) to 532.7 ± 301.3 and 442.4 ± 202.9 msec2 (ISS03), respectively. The power-law fractal scaling β was altered in space, changing from -1.087 ± 0.130 (before flight) to -0.977 ± 0.098 (ISS01), -0.910 ± 0.130 (ISS02), and -0.924 ± 0.095 (ISS03) (invariably p < 0.05). Interpretation: Most HRV changes observed in space relate to a frequency window centered around one cycle in about 90 min. Since the BRAC component is amplified in space for only specific HRV endpoints, it is likely to represent a physiologic response rather than an artifact from the International Space Station (ISS) orbit. If so, it may offer a way to help adaptation to microgravity during long-duration spaceflight.

Published in Heliyon

ISSN: 2405-8440 (Online)
Publisher: Elsevier
Country of publisher: United Kingdom
LCC subjects: Science: Science (General); Social Sciences: Social sciences (General)
Website: https://www.cell.com/heliyon/home

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