title: Stability of the noninvasive baroreflex sensitivity assessment using cross-spectral analysis of heart rate and arterial blood pressure variabilities.
abstract: BACKGROUND
  Depressed baroreflex sensitivity (BRS), usually estimated using the invasive phenylephrine method or the nitroprusside test, is significantly and independently associated with an increased risk of malignant ventricular arrhythmias and sudden cardiac death in patients surviving acute myocardial infarction. Several investigators have compared the standard phenylephrine test and different noninvasive methods.
  
  
  OBJECTIVE
  This study evaluated the influence of different body positions with different breathing regimes on cross-spectral baroreflex indices (coherence between the spectral densities of blood pressure and cardiac cycle variabilities) in both low- and high-frequency bands.
  
  
  METHODS
  The data were obtained in 103 patients (73 males, aged 53 +/- 12 years) with coronary artery disease and/or hypertension. Simultaneous electrocardiographic and noninvasive blood pressure recordings were obtained in each subject in both supine and sitting positions during both spontaneous and slow and fast controlled respiration (0.1 and 0.33 Hz).
  
  
  RESULTS
  The results show a significant bias and disagreement between noninvasive baroreflex sensitivity (BRS) indices. The mean values of the baroreflex in low frequency ranged from 5.0 +/- 5.3 to 10.1 +/- 7.9 ms/mmHg, while in high frequency, the mean values ranged from 6.6 +/- 6.1 to 10.1 +/- 7.9 ms/mmHg. The limits of agreement ranged from +/-1.7 to +/-4.1 ms/mmHg with bias from -1.0 to +0.7 ms/mmHg.
  
  
  CONCLUSIONS
  A comprehensive comparison of different methods shows that BRS estimated in low-frequency band in sitting position during spontaneous respiration is the most representative part of the global baroreflex gain.
authors.affiliation: Third Department of Internal Medicine, First Medical School, Charles University, Prague, Czech Republic.
authors.forename: D
authors.initials: D
authors.lastname: Wichterle
authors.forename: V
authors.initials: V
authors.lastname: Melenovsky
authors.forename: L
authors.initials: L
authors.lastname: Necasova
authors.forename: J
authors.initials: J
authors.lastname: Kautzner
authors.forename: M
authors.initials: M
authors.lastname: Malik
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D016683:Supine Position