Time domain cross-correlation analysis of blood pressure and heart rate variability

Beat-to-beat time series of systolic ABP (SAP) and pulse interval (PI) were obtained from 10 healthy volunteers with the Finapres device and the ECG for periods of 5 min. in the supine and standing positions. Cross-correlation functions (CCF) were estimated with a moving window 5 to 15 beats wide. Mean CCF patterns were obtained for each subject and for the whole population. The mean CCF shows a biphasic patttern with highly significant peak (lag 0 or 1) and trough (lag -2 or -3). The CCF pattern and significance of the peak and trough were destroyed by pre-filtering the SAP and PI signals in the VLF range (0.002-0.05 Hz), but the main features were presented by pre-filtering in the LF (0.05-0.20 Hz) and HF (0.20-0.35 Hz) ranges. The CCF pattern and the distribution of P-values of a moving linear regression for 3-beat sequences suggest that the peak value corresponds to 'BRS sequences' whilst the trough at lag = -2 reflects the effect of PI on SAP or the so-called 'non-BRS sequences '.