title: Power spectral and time based analysis of heart rate variability following 15 days head-down bed rest.
abstract: Power spectral and time based analyses were applied to the cardiac inter-beat interval (RRI) of 8 healthy men before and after 15 d of bed rest in the 6 degrees head-down tilt position (HDT) to determine changes in indices of cardiac parasympathetic and sympathetic activity after this exposure. At 24 h prior to HDT and on HDT day 15, a minimum of 256 RRI's were obtained from an electrocardiogram (ECG) while the subjects were in the supine position. RRI was subjected to power spectral and two methods of time-based analyses. Power spectral analysis demonstrated that the index of cardiac vagal activity was reduced (95.2 +/- 28.5 to 48.2 +/- 17.4 ms2) without affecting the index of cardiac sympathetic activity (1.18 +/- 0.7 to 0.69 +/- 0.4). The two methods of time-based analyses, time series and standard deviation analyses, further demonstrated a reduction of cardiac vagal activity post-HDT (5.5 +/- 4 to 4.8 +/- 0.6 ms2; and 42.8 +/- 4.8 to 33.9 +/- 3.3 ms, respectively). These data suggest that exposure to 15 d of HDT reduces cardiac vagal activity, while changes in cardiac sympathetic activity were indistinguishable.
authors.affiliation: Department of Physiology, Texas College of Osteopathic Medicine, Fort Worth.
authors.forename: C G
authors.initials: CG
authors.lastname: Crandall
authors.forename: K A
authors.initials: KA
authors.lastname: Engelke
authors.forename: J A
authors.initials: JA
authors.lastname: Pawelczyk
authors.forename: P B
authors.initials: PB
authors.lastname: Raven
authors.forename: V A
authors.initials: VA
authors.lastname: Convertino
mesh_terms: D000328:Adult; D001510:Bed Rest; D003627:Data Interpretation, Statistical; D004562:Electrocardiography; D018475:Head-Down Tilt / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D012815:Signal Processing, Computer-Assisted; D013026:Space Flight; D013564:Sympathetic Nervous System / Q000502:physiology; D013997:Time Factors; D014630:Vagus Nerve / Q000502:physiology