Autonomic Recovery after Long-duration Spaceflight
- Paper number
IAC-08.A1.2.5
- Author
Mr. Kurt Couckuyt, K.U. Leuven, Belgium
- Coauthor
Dr. Bart Verheyden, Belgium
- Coauthor
Prof. André Aubert, University Hospital Gasthuisberg, Belgium
- Year
2008
- Abstract
Spaceflight induces changes in cardiovascular regulation. These can affect the astronaut’s ability to stand upright after return to earth. Previous studies of the impact of exposure to weightlessness during short-duration missions of 10 days in space have shown a altered cardiovascular autonomic respons to orthostatic stress. The first days after return, vagal modulation is decreased resulting in a sympathetic dominance. After 9 days this control is almost completely recovered, although the effect on heart rate is visible up to 25 days after spaceflight. In this study, the recovery of cardiovascular autonomic modulation after long-duration spaceflight (6 months) is evaluated over a period of 30 days. A comparison is made with the alterations in cardiovascular autonomic modulation after a 10 day period of weightlessness. It is expected that cardiovascular recovery after spaceflight takes longer when the time spent in weightlessness is extended. Six male astronauts who spent 6 months in space participated in the study. ECG and continuous blood pressure were measured for 10 minutes both in standing and supine position. The astronauts were asked to pace their breathing at 12 breaths per minute, guided by an audio stimulus with visual feed-back, in order to eliminate the possible influence of different breathing frequencies during different measurements. Measurements toke place 30 days before spaceflight (L-30) and on day 1 (R+1), day 5 (R+5), day 10 (R+10) and day 30 (R+30) after return from space. None of the astronauts experienced difficulties to stand upright after landing. For each subject, postflight arterial blood pressure was comparable with preflight pressure and was maintained stable during standing indicating an adequate compensatory elevation in vascular resistance. First day after landing, in standing position, both low frequency and high frequency powers of RRI oscillations were depressed compared to preflight conditions (p<0.05). In supine position, only high frequency oscillations were depressed (p<0.05). In standing position, heart rate was significantly higher after return (103±14 bpm at R+1 ; 75±7 bpm at L-30 ; p<0.05) but restored quickly to preflight values (88±16 bpm at R+1 ; 75±7 bpm at L-30 ; p=NS). However, differences in heart rate and high frequency power of RRI oscillations were already recovered at R+5, postflight baroreflex sensitivity was decreased compared to preflight values until R+10 (5.9±1.6 ms/mmHg at L-30 ; 2.8±0.6 ms/mmHg at R+1 ; 3.5±1.2 ms/mmHg at R+5 ; 3.5±1.1 ms/mmHg at R+10 ; p<0.05 for each postflight measurement compared to L-30). Low frequency oscillation in systolic blood pressure were increased from day 1 after landing up to 30 days after landing suggesting a sustained elavation of sympathetic modulation (14.8±11.8 mmHg² at L-30 ; 32.4±14.7 mmHg² at R+1 ; 32.6±14.7 mmHg² at R+5 ; 32.7±14.6 mmHg² at R+10 ; 28.0±12.4 mmHg² at R+10 ; p<0.05 for each postflight measurement compared to L-30) It can be concluded that changes in cardiac autonomic control at day 1 after spaceflight are comparable between short-duration and long-duration spaceflight. While standing, vagal withdrawal and sympathetic dominance result in higher heart rates. Surprisingly, recovery of vagal control and heart rate after long duration spaceflight at R+5 seems to be faster than after short duration spaceflight (R+9). This may be the result of differences in exercise and countermeasures against cardiovascular deconditioning during the time spent on board of the spacecraft.
- Abstract document
- Manuscript document
(absent)