Instantaneous Cardiac Baroreflex Sensitivity: xBRS Method Quantifies Heart Rate Blood Pressure Variability Ratio at Rest and During Slow Breathing

To quantify spontaneous baroreflex sensitivity (BRS), many groups use the xBRS method, which calculates the cross-correlation between the systolic beat-to-beat blood pressure and the R-R interval, resampled at 1 Hz, in a 10 s sliding window, with 0-5 s delays for the interval. The delay with the greatest positive correlation is selected and, if significant, the quotient of the standard deviations of R-R intervals and systolic blood pressures are recorded as corresponding xBRS value. In this paper we test the hypothesis that the xBRS method quantifies the causal interactions of spontaneous BRS at rest and is not exclusively dominated by the quotient of heart rate and systolic blood pressure variability (HRV/BPV). Therefore, we retrospectively analyzed 1828 beat-to-beat time series and the corresponding systolic blood pressure at rest. We found a high correlation between the HRV/BPV quotient and the xBRS of r=0.94 (p