title: Correlation between baroreflex gain and 24-h indices of heart rate variability.
abstract: OBJECTIVE
  To examine the relationship between heart rate variability (HRV) and baroreflex sensitivity (BRS).
  
  
  METHODS
  An observational study, with no intervention, in 55 volunteers with a wide range of arterial pressure (60-90/115-185 mmHg).
  
  
  METHODS
  Volunteers were studied first in the laboratory, with continuous measurement of systolic arterial pressure and electrocardiogram to obtain a frequency domain measure of baroreflex sensitivity (index alpha). Immediately afterwards, while the individual was ambulant, a Holter recording was obtained in order to compute time domain [standard deviation of consecutive normal R-R intervals (SDNN) and the percentage of successive R-R differences > 50 ms (PNN50)], and frequency domain measures of HRV. Linear correlation was used to test the statistical link between index alpha and HRV indices.
  
  
  RESULTS
  Significant correlations were observed between index alpha and SDNN (r = 0.30; P < 0.02) and PNN50 (r = 0.48; P < 0.001), and between index alpha and total power (r = 0.53; P < 0.001), and absolute powers of the 0.0001-0.04 Hz components of R-R interval variability in 24 h (r = 0.47; P < 0.001).
  
  
  CONCLUSIONS
  The major findings of this study are the clear demonstration of a significant correlation between a laboratory measure of baroreflex sensitivity and 24 h measures of HRV, obtained immediately afterwards. Notably, this correlation was found with both time domain and absolute, but not normalized, spectral measures of R-R interval variability. In addition, different levels of individual activity, as assessed by separate examination of daytime and night-time periods, did not seem to influence this relationship.
authors.affiliation: Centro di Ricerca sulla Terapia Neurovegetativa, Istituto Scienze Biomediche, University of Milan, Milan, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Lucini
authors.forename: Stefano
authors.initials: S
authors.lastname: Guzzetti
authors.forename: Stefano
authors.initials: S
authors.lastname: Casiraghi
authors.forename: Massimo
authors.initials: M
authors.lastname: Pagani
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D017704:Baroreflex / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D015716:Electrocardiography, Ambulatory; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D008875:Middle Aged; D011379:Prognosis