title: Average magnitude of heartbeat fluctuations in healthy subjects after exposure to 4 hours head down bed rest.
abstract: Orthostatic intolerance, induced by microgravity exposure, has been hypothesized to be related to a disorder of the autonomic control of the cardiovascular system. Non-invasive measurement of Heart Rate Variability (HRV) have been used as a valuable tool to characterize the ability of the autonomic system to modulate the cardiovascular function by analyzing the spontaneous fluctuations of arterial pressure and heart period on a beat-to-beat basis. Concerning this, conflicting results have been reported on the heart rate and blood pressure variability responses during exposure to microG. These differences seem to be due to different experimental designes used. Moreover, the different behavior of normal subjects in response to orthostatic stress after HD, i.e. Symptomatic (S) or Non Symptomatic (NS), could play some role in producing these discrepancies [correction of dicrepancies]. In this study we suggest the analysis of "magnitude" or "volatility" as a new method to study HRV variability. The volatility is a measure of the beat-to-beat excursion capability of the heart, regardless to its direction (positive or negative): the higher the volatility, the greater the excursion. The aim of the present study was to examine R-R volatility before and after 4 hours of HD -6 degrees in normal subjects.
authors.affiliation: Centro Biomedicina Spaziale, Fisiopatologia Medica. Dip. Medicina Interna, Universita di Roma "Tor Vergata".
authors.forename: G
authors.initials: G
authors.lastname: Raimondi
authors.forename: C
authors.initials: C
authors.lastname: Michelassi
authors.forename: S
authors.initials: S
authors.lastname: Chillemi
authors.forename: S
authors.initials: S
authors.lastname: Sacco
authors.forename: S
authors.initials: S
authors.lastname: Contini
authors.forename: J M
authors.initials: JM
authors.lastname: Legramante
authors.forename: R
authors.initials: R
authors.lastname: Balocchi
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D005260:Female; D018475:Head-Down Tilt; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007024:Hypotension, Orthostatic / Q000453:epidemiology* / Q000503:physiopathology; D008297:Male; D011237:Predictive Value of Tests; D018667:Tilt-Table Test; D018474:Weightlessness Simulation