Key result
Long-duration microgravity linked to ~37% increase in HRV slow-frequency oscillation, reflecting an adaptive brain response.
Why the study?
Does long-duration space flight alter heart rate variability and cardiovascular regulatory system adaptation in healthy astronauts?
Observational (n=8)
Does long-duration space flight alter heart rate variability and cardiovascular regulatory system adaptation in healthy astronauts?
Answers are grounded in this paper and cite their sources.
Brain functional networks and the circadian clock may assist in the adaptation of the cardiovascular regulatory system to microgravity during long-duration space flights.
It is critical that the regulatory system functions well in space's microgravity. However, the "intrinsic" cardiovascular regulatory system (β), estimated by the fractal scaling of heart rate variability (HRV) (0.0001-0.01 Hz), does not adapt to the space environment during long-duration (6-month) space flights. Neuroimaging studies suggest that the default mode network (DMN) serves a broad adaptive purpose, its topology changing over time in association with different brain states of adaptive behavior. Hypothesizing that HRV varies in concert with changes in brain's functional connectivity, we analyzed 24-hour HRV records from 8 healthy astronauts (51.8 ± 3.7 years; 6 men) on long (174.5 ± 13.8 days) space missions, obtained before launch, after about 21 (ISS01), 73 (ISS02), and 156 (ISS03) days in space, and after return to Earth. Spectral power in 8 frequency regions reflecting activity in different brain regions was computed by maximal entropy. Improved β (p < 0.05) found in 4 astronauts with a positive activation in the "HRV slow-frequency oscillation" (0.10-0.20 Hz) occurred even in the absence of consciousness. The adaptive response was stronger in the evening and early sleep compared to morning (p = 0.039). Brain functional networks, the DMN in particular, can help adapt to microgravity in space with help from the circadian clock.
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Otsuka et al. (2018) conducted an observational in Adaptation to microgravity (n=8). Microgravity (long-duration spaceflight) vs. Pre-flight (Earth gravity) was evaluated on Change in HRV slow-frequency oscillation (B2 power, 0.10-0.20 Hz) during ISS03 compared to pre-flight in Group A (p=0.022). Exposure to microgravity during long-duration spaceflight increased HRV slow-frequency oscillation by 36.9% in half of the astronauts, reflecting an adaptive brain response.
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