Figure 4

Power spectra of long-term heart rate variability of 7 astronauts on the ISS in the frequency range of 0.0001–0.01 Hz (periods of 2.8 h to 1.6 min). Left and right: cardiovascular fractal dynamics assessed by the slope of fractal scaling β before spaceflight and during spaceflight (days 24 ± 5 of flight). Top, middle, and bottom row: 24-h span, sleep span, and awake span. Figure reproduced from Fig. 3 of Ref.¹².