Effects of long-term microgravity exposure in space on circadian rhythms of heart rate variability

Abstract

We evaluated their circadian rhythms using data from electrocardiographic records and examined the change in circadian period related to normal RR intervals for astronauts who completed a long-term (≥6-month) mission in space. The examinees were seven astronauts, 5 men and 2 women, from 2009 to 2010. Their mean±SD age was 52.0±4.2 years (47-59 yr). Each stayed in space for more than 160 days; their average length of stay was 172.6±14.6 days (163-199 days).We conducted 24-hr Holter electrocardiography before launch (Pre), at one month after launch (DF1), at two months after launch (DF2), at two weeks before return (DF3), and at three months astronauts, whereas it decreased in 3 of 7 astronauts and 1 was remained almost unchanged at DF1.During DF3, about 6 months after their stay in space, the HF component of 5 of 7 astronauts recovered from the decrease after launch, with prominent improvement to over 20% in 3 astronauts. 2Although autonomic nervous functions and circadian rhythms were disturbed until one month had passed in space, well-scheduled sleep and wake rhythms and meal times served as synchronizers.

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

“…Some neuropeptides can have more prominent ultradian (with a frequency higher than one cycle per day; e.g., 8-hour periodicity) than circadian changes [24]. We previously showed that the circadian rhythm persisted in space in HR and β [9, 12]. Herein, we confirm the presence in space of 24-, 12-, and 8-hour components in several HRV endpoints by the fit of a model including 4 anticipated components.…”

“…Spaceflight dramatically alters cardiovascular dynamics, as illustrated by changes in HRV [12] and a less negative slope β of the fractal scaling [9] confirmed herein. Kleitman's about 90-min BRAC [20] was found to be amplified about 3-fold in space, notably among astronauts of Group 1, in keeping with a corresponding increase in ULF01/TF (0.0001–0.0003 Hz, i.e., 55–166 min) and corresponding decreases in ULF02/TF and ULF03/TF.…”

“…The measurement procedures and data collection were conducted as previously reported [9, 12]. Briefly, for HRV measurements, QRS waveforms were read from continuous electrocardiographic (ECG) records.…”

“…But, as we reported previously [9], the “intrinsic” cardiovascular regulatory system, reflected by the fractal scaling of HRV [9, 10, 11], did not adapt to the new microgravity environment in space during long-duration (about 6-month) spaceflights. By contrast, after 6 months in space, the circadian rhythm of heart rate had adapted to the new microgravity environment in space [12], an important observation since disruption of circadian rhythms adversely affects human health [13, 14]. As humans plan for long-term space exploration, it is critical to ascertain that the regulatory system can function well in a microgravity environment.…”

Expanded benefits for humanity from the International Space Station

“…Twenty-four-hour ECGs of astronauts were also analyzed to understand the space environment's effect on biological rhythm and cardiac autonomic nervous activity leading to recommendations for maintaining a well-balanced biological rhythm on Earth. One of these recommendations is maintenance of a regular sleep schedule [20]. In studying the sleep patterns of cosmonauts using a miniature device that fits in their pocket [ Figure 8], information is recorded and sent to Earth for analysis of sleep quality.…”