Are Inter-Beat Intervals From Blood Pressure a Valid Alternative to R-R Intervals for the Multiscale Entropy Analysis of Heart Rate Variability?

When an ECG recording is not available to derive the R-R interval (RRI) series, the heart rate variability (HRV) may be evaluated considering the inter-beat intervals (IBI) from other cardiovascular signals, like the arterial blood pressure (ABP). However, it is unknown how the ABP-derived IBI series quantify the multiscale entropy (MSE) of HRV. Thus our aim is to describe differences between RRI and the ABP-derived IBI in MSE estimates. We recorded the ECG and the finger ABP in 40 volunteers. We derived the RRI series from the ECG (reference IBI) and the series of systolic-systolic intervals (SSI), diastolic-diastolic intervals (DDI), and intervals between maxima of the first- (d'PI) and second- (d“PI) derivative of ABP. For each IBI series, we estimated the MSE at the scale s=1 beat (SampEn), at high-frequency scales (MSE
HF
, for 2≤s≤7 beats) and low-frequency scales (MSE
LF
, for 7HF
and MSE
LF
were underestimated by ABP-derived IBI. The estimates closest to RRI were provided by d'PI (error +11% for SampEn, − 2% for MSE
HF
) and SSI (-2% for MSE
LF
). Thus, the ABP-derived IBI series reflect SampEn components absent in RRI, being d'PI and SSI the closest surrogate for RRI.