title: Instant power spectrum analysis of heart rate variability during orthostatic tilt using a time-/frequency-domain method.
abstract: BACKGROUND
  Spectral analysis of heart rate (HR) variability (HRV) requires, as a rule, some level of stationarity and, as a result, is inadequate to quantify biological transients. A time-/frequency-domain method (TF) was developed to obtain an instant spectral power (SP) of HRV during tilt.
  
  
  RESULTS
  HR was recorded by Holter monitoring in volunteers and analyzed with a TF, the smoothed pseudo-Wigner-Ville transformation (SPWVT), with the table inclination randomly set or continuously increased while the table rotated in head-up position. (1) The SPWVT assesses, beat by beat, the instant center frequency (ICF) of the SP. ICF correlates better with instant HR than the ratio of low- (LF) to high-frequency (HF) oscillations. The transient effect of tilt is better characterized as a shift of SP toward lower frequencies than by changes in amplitudes. (2) The method evidences variations of HR from one second to another. During the passage to head-up position, the vagal withdrawal and the sympathetic activation occur nearly simultaneously, as indicated by the instant changes in both LF and HF amplitudes and ICF. (3) The averaged results of the SPWVT give results similar to those previously obtained with autoregressive algorithms.
  
  
  CONCLUSIONS
  The SPWVT is a new tool to explore HR transitions such as periods before episodes of arrhythmias on a time scale of one beat and allows quantification of an instant frequency index (ICF) that closely reflects the instantaneous relationship between sympathetic and vagal modulations.
authors.affiliation: U127-INSERM, Paris, France.
authors.forename: S
authors.initials: S
authors.lastname: Jasson
authors.forename: C
authors.initials: C
authors.lastname: Médigue
authors.forename: P
authors.initials: P
authors.lastname: Maison-Blanche
authors.forename: N
authors.initials: N
authors.lastname: Montano
authors.forename: L
authors.initials: L
authors.lastname: Meyer
authors.forename: C
authors.initials: C
authors.lastname: Vermeiren
authors.forename: P
authors.initials: P
authors.lastname: Mansier
authors.forename: P
authors.initials: P
authors.lastname: Coumel
authors.forename: A
authors.initials: A
authors.lastname: Malliani
authors.forename: B
authors.initials: B
authors.lastname: Swynghedauw
mesh_terms: D000328:Adult; D015716:Electrocardiography, Ambulatory; D005260:Female; D005583:Fourier Analysis; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D018667:Tilt-Table Test; D013997:Time Factors