title: Analysis of long term heart rate variability:  methods, 1/f scaling and implications.
abstract: The use of spectral techniques to quantify short term heart rate fluctuations on the order of seconds to minutes has helped define the autonomic contributions to beat-to-beat control of heart rate.  We used similar techniques to quantify the entire spectrum (0.00003-1.0 Hz) of heart rate variability during 24 hour ambulatory ECG monitoring.  The ECG from standard Holter monitor recordings from normal subjects was sampled with the use of a phase locked loop, and a heart rate time series was constructed at 3 Hz.  Frequency analysis of the heart rate signal was performed after a nonlinear filtering algorithm was used to eliminate artifacts.  A power spectrum of the entire 24 hour record revealed power that was inversely proportional to frequency, 1/f, over 4 decades from 0.00003 to 0.1 Hz (period approximately 10 hours to 10 seconds).  Displaying consecutive spectra calculated at 5 minute intervals revealed marked variability in the peaks at all frequencies throughout the 24 hours, probably accounting for the lack of distinct peaks in the spectra of the entire records.
authors.affiliation: Harvard-MIT Division of Health Sciences and Technology, Boston, MA, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Saul
authors.forename: P
authors.initials: P
authors.lastname: Albrecht
authors.forename: R D
authors.initials: RD
authors.lastname: Berger
authors.forename: R J
authors.initials: RJ
authors.lastname: Cohen
mesh_terms: D000328:Adult; D000465:Algorithms; D015716:Electrocardiography, Ambulatory / Q000706:statistics & numerical data*; D005583:Fourier Analysis; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D012815:Signal Processing, Computer-Assisted; D013057:Spectrum Analysis; D013997:Time Factors