Cooke W H, Ames JE I V, Crossman A A, Cox J F, Kuusela T A, Tahvanainen K U, Moon L B, Drescher J, Baisch F J, Mano T, Levine B D, Blomqvist C G, Eckberg D L
Center for Biomedical Engineering, Michigan Technological University, Houghton, Michigan 49931, USA.
J Appl Physiol (1985). 2000 Sep;89(3):1039-45. doi: 10.1152/jappl.2000.89.3.1039.
We studied three Russian cosmonauts to better understand how long-term exposure to microgravity affects autonomic cardiovascular control. We recorded the electrocardiogram, finger photoplethysmographic pressure, and respiratory flow before, during, and after two 9-mo missions to the Russian space station Mir. Measurements were made during four modes of breathing: 1) uncontrolled spontaneous breathing; 2) stepwise breathing at six different frequencies; 3) fixed-frequency breathing; and 4) random-frequency breathing. R wave-to-R wave (R-R) interval standard deviations decreased in all and respiratory frequency R-R interval spectral power decreased in two cosmonauts in space. Two weeks after the cosmonauts returned to Earth, R-R interval spectral power was decreased, and systolic pressure spectral power was increased in all. The transfer function between systolic pressures and R-R intervals was reduced in-flight, was reduced further the day after landing, and had not returned to preflight levels by 14 days after landing. Our results suggest that long-duration spaceflight reduces vagal-cardiac nerve traffic and decreases vagal baroreflex gain and that these changes may persist as long as 2 wk after return to Earth.
