Migeotte PF; Prisk GK; Paiva M
Biomedical Physics Laboratory, Université
We studied heart rate (HR), heart
rate variability (HRV), and respiratory sinus arrhythmia (RSA) in four male
subjects before, during, and after 16 days of spaceflight. The
electrocardiogram and respiration were recorded during two periods of 4 min
controlled breathing at 7.5 and 15 breaths/min in standing and supine postures
on the ground and in microgravity. Low (LF)- and high
(HF)-frequency components of the short-term HRV (< or =3 min) were computed
through Fourier spectral analysis of the R-R intervals. Early in microgravity,
HR was decreased compared with both standing and supine positions and had
returned to the supine value by the end of the flight. In microgravity, overall
variability, the LF-to-HF ratio, and RSA amplitude and phase were similar to
preflight supine values. Immediately postflight, HR
increased by approximately 15% and remained elevated 15 days after landing.
LF/HF was increased, suggesting an increased sympathetic control of HR
standing. The overall variability and RSA amplitude in supine decreased postflight, suggesting that vagal
tone decreased, which coupled with the decrease in RSA phase shift suggests
that this was the result of an adaptation of autonomic control of HR to
microgravity. In addition, these alterations persisted for at least 15 days
after return to normal gravity (