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Dynamic adaptation of cardiac baroreflex sensitivity to prolonged exposure to microgravity: data from a 16-day spaceflight

¹Polo Tecnologico, Fondazione Don Carlo Gnocchi, ONLUS, Milano, Italy; ²Dipartimento di Medicina Interna, Universita' di Roma "Tor Vergata," and IRCCS San Raffaele Pisana, Roma, Italy; ³IRCCS San Raffaele Pisana, Roma, Italy; ⁴Centro di Terapia Neurovegetativa, Polo L. Sacco-Universita di Milano, Milano, Italy; ⁵Department of Clinical Medicine and Prevention, University of Milano-Bicocca, and Department of Cardiology, San Luca Hospital, IRCCS, Istituto Auxologico Italiano Milan, Italy; and ⁶Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands

Submitted 9 May 2008 ; accepted in final form 13 August 2008

This study explored the process of arterial baroreflex adaptation to microgravity, starting from the first day of flight, during the 16-day STS-107 Columbia Space Shuttle mission. Continuous blood pressure (BP), ECG, and respiratory frequency were collected in four astronauts on ground (baseline) and during flight at days 0–1, 6–7, and 12–13, both at rest and during moderate exercise (75 W) on a cycle ergometer. Sensitivity of the baroreflex heart rate control (BRS) was assessed by sequence and spectral alpha methods. Baroreflex effectiveness index (BEI); low-frequency (LF) power and high-frequency (HF) power of systolic BP (SBP), diastolic BP (DBP), and R-R interval (RRI); the RRI LF/HF ratio; and the RRI root mean square of successive differences (RMSSD) index were also estimated. We found that, at rest, BRS increased in early flight phase, compared with baseline (means ± SE: 18.3 ± 3.4 vs. 10.4 ± 1.2 ms/mmHg; P < 0.05), and it tended to return to baseline in subsequent days. During exercise, BRS was lower than at rest, without differences between preflight and in-flight values. At rest, in the early flight phase, RMSSD and RRI HF power increased (P < 0.05) compared with baseline, whereas LF powers of SBP and DBP decreased. No statistical difference was found in these parameters during exercise before vs. during flight. These findings demonstrate that heart rate baroreflex sensitivity and markers of cardiac vagal modulation are enhanced during early exposure to microgravity, likely because of the blood centralization, and return to baseline values in subsequent flight phases, possibly because of the fluid loss. No deconditioning seems to occur in the baroreflex control of the heart.

arterial baroreflex; heart rate variability; blood pressure monitoring

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				M Di Rienzo, G Parati, A Radaelli, and P Castiglioni Baroreflex contribution to blood pressure and heart rate oscillations: time scales, time-variant characteristics and nonlinearities Phil Trans R Soc A, April 13, 2009; 367(1892): 1301 - 1318. [Abstract] [Full Text] [PDF]