title: Nine months in space: effects on human autonomic cardiovascular regulation.
abstract: 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.
authors.affiliation: Center for Biomedical Engineering, Michigan Technological University, Houghton, Michigan 49931, USA. whcooke@mtu.edu
authors.forename: W H
authors.initials: WH
authors.lastname: Cooke
authors.forename: I V
authors.initials: IV
authors.lastname: Ames JE
authors.forename: A A
authors.initials: AA
authors.lastname: Crossman
authors.forename: J F
authors.initials: JF
authors.lastname: Cox
authors.forename: T A
authors.initials: TA
authors.lastname: Kuusela
authors.forename: K U
authors.initials: KU
authors.lastname: Tahvanainen
authors.forename: L B
authors.initials: LB
authors.lastname: Moon
authors.forename: J
authors.initials: J
authors.lastname: Drescher
authors.forename: F J
authors.initials: FJ
authors.lastname: Baisch
authors.forename: T
authors.initials: T
authors.lastname: Mano
authors.forename: B D
authors.initials: BD
authors.lastname: Levine
authors.forename: C G
authors.initials: CG
authors.lastname: Blomqvist
authors.forename: D L
authors.initials: DL
authors.lastname: Eckberg
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D012119:Respiration; D013026:Space Flight; D013997:Time Factors; D014630:Vagus Nerve / Q000502:physiology