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Correlation between baroreflex gain and 24-h indices of heart rate variability
Daniela Lucini1, Stefano Guzzetti, Stefano Casiraghi
1Centro di Ricerca sulla Terapia Neurovegetativa, Istituto Scienze Biomediche, University of Milan, Milan, Italy.
Objective:
To examine the relationship between heart rate variability (HRV) and baroreflex sensitivity (BRS).
Design:
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).
Conclusion:
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.