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Publication AbstractsPower Spectral Analysis Imperfectly Informs Changes in Sympathetic Traffic During Acute Simulated MicrogravityWilliam H. Cooke, M.A., Ph.D., and Mandy M. Dowlyn, B.S.Aviat Space Environ Med 2000; 71:1232-8 AbstractThe purpose of this study was to investigate the value of frequency-domain analysis of autonomic rhythms as a simple, non-invasive technique for the study of immediate neural adjustments to simulated microgravity. We continuously recorded the electrocardiogram, non-invasive beat-by-beat arterial pressure, and muscle sympathetic nerve activity (MSNA) during 5-min periods of controlled frequency breathing (15 breaths · min-1) with subjects (n = 10) in supine, and 10° head-down tilt positions. We estimated changes in fluid volume with lower leg circumference measurements. We analyzed data in the frequency domain with fast Fourier-based power spectral analysis, and calculated the ratio of normalized low-to-respiratory frequency RR-interval spectral power as an index of sympathetic activity. Head-down tilt significantly reduced lower leg volume, MSNA, and MSNA oscillations at the respiratory frequency (p < 0.05). Head-down tilt did not change RR-interval, arterial pressure, or their power spectra (p > 0.05). We conclude that non-invasive frequency-domain estimates do not adequately reveal subtle changes in sympathetic traffic during acute, simulated microgravity.Keywords: head-down tilt, muscle sympathetic nerve activity, autonomic rhythms. Information on subscribing, and on obtaining copies of an article or of an entire issue. Table of Contents for Volume 71, Number 12 of the ASME journal.
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