Correlation between baroreflex gain and 24-h indices of heart rate variability

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 a and HRV indices. Results Significant correlations were observed between index a and SDNN (r = 0.30; P < 0.02) and PNN50 (r= 0.48; P < 0.001), and between index a 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. (C) 2002 Lippincott Williams Wilkins.