Nine months in space: effects on human autonomic cardiovascular regulation.
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.
Cooke
W H
WH
Center for Biomedical Engineering, Michigan Technological University, Houghton, Michigan 49931, USA. whcooke@mtu.edu
Ames JE
I V
IV
Crossman
A A
AA
Cox
J F
JF
Kuusela
T A
TA
Tahvanainen
K U
KU
Moon
L B
LB
Drescher
J
J
Baisch
F J
FJ
Mano
T
T
Levine
B D
BD
Blomqvist
C G
CG
Eckberg
D L
DL
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