title: Heart rate and blood pressure response to short-term head-down bed rest: a nonlinear approach.
abstract: Although it is well-known that prolonged exposure to microgravity environment such as in space travel results in derangements of orthostasis, recent evidence suggests that even short-term exposure may have similar effects and parallels such common examples as prolonged bed rest. Whereas spectral analysis of heart rate and systolic blood pressure have been unable to detect changes, we hypothesized that nonlinear indexes may be better able to uncover such perturbations. Eighteen healthy subjects were exposed to 4-hour head-down tilt, and of these, 4 exhibited fainting. Two nonlinear indexes, mutual information and recurrence quantification were used to analyze the data. Only recurrence quantification was able to detect a "decoupling" of heart rate and systolic blood pressure at rest using discriminant analysis (p < 0.05). These results suggest that orthostatic intolerance may be due to a decoupling of heart rate from systolic blood pressure reflexive activity occurring at rest.
authors.affiliation: CNR, Institute of Clinical Physiology, Pisa. balocchi@ifc.pi.cnr.it
authors.forename: R
authors.initials: R
authors.lastname: Balocchi
authors.forename: A
authors.initials: A
authors.lastname: Di Garbo
authors.forename: C
authors.initials: C
authors.lastname: Michelassi
authors.forename: S
authors.initials: S
authors.lastname: Chillemi
authors.forename: M
authors.initials: M
authors.lastname: Varanini
authors.forename: M
authors.initials: M
authors.lastname: Barbi
authors.forename: J M
authors.initials: JM
authors.lastname: Legramante
authors.forename: G
authors.initials: G
authors.lastname: Raimondi
authors.forename: J P
authors.initials: JP
authors.lastname: Zbilut
mesh_terms: D000328:Adult; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D012815:Signal Processing, Computer-Assisted; D013575:Syncope / Q000503:physiopathology*