Comparison between Cardiac Baroreflex Sensitivity Estimates Derived from Sequence and Phase Rectified Signal Averaging Techniques During Head-up Tilt

Abstract

The cardiac baroreflex (cBR), the physiological control mechanism that modulates heart rate in response to arterial pressure (AP) changes, is activated by both AP increases and decreases. The sequence method, widely utilized to evaluate cBR sensitivity (cBRS) from spontaneous heart period (HP) and systolic AP (SAP) variations allows the separated computation of cBRS from positive and negative SAP variations. Conversely, the recently proposed bivariate phase rectified signal averaging (PRSA) method was successfully applied in prognostic studies exclusively on positive SAP variations. We extended PRSA method to compute cBRS over negative SAP variations as well and we compared results with those derived from the sequence method in 18 healthy subjects undergoing head-up tilt test with a table inclination of 90° (HUT). As expected, regardless of the sign of the SAP changes and methods, cBRS moved toward 0 during HUT. The PRSA-based cBRS measure derived from positive SAP changes was extremely correlated with that derived from negative AP variations and the correlation was significantly higher than that obtained from correspondent sequence-based cBRS estimates. In conclusion, the two methods cannot be considered interchangeable in computing cBRS.