Asymmetry Assessment of Cardiac and Sympathetic Arms of the Baroreflex

Pharmacological challenges allowed the characterization of the cardiac baroreflex (cBR) asymmetry, defined as the difference of cBR sensitivity (cBRS) in response to arterial pressure (AP) rises and fallings. Asymmetry of the sympathetic baroreflex (sBR) has never been explored. Two recently proposed analytical methods for cBRS and sBR sensitivity (sBRS) estimation, i.e. the sequence (SEQ) and the bivariate phase rectified signal averaging (PRSA) methods, allow the noninvasive assessment of cBR and sBR asymmetry, respectively, from the spontaneous fluctuations of heart period in response to systolic AP changes and from spontaneous variability of sympathetic discharge in response to diastolic AP variations. In the present study we applied SEQ and PRSA methods with the aim at evaluating the cBR and sBR asymmetry in young healthy subjects during incremental head-up tilt. We found that sBRS computed by the SEQ method over negative diastolic AP changes was significantly more negative than that computed over positive AP diastolic changes. Asymmetric cBR behavior was not observed. In addition, we confirmed the superiority of the SEQ method compared to the PRSA one in assessing the asymmetry of baroreflex control. We conclude that in physiological conditions baroreflex asymmetry is a peculiar characteristic of sBR and not of the cBR.