Asymmetry Assessment of Cardiac and Sympathetic Arms of the Baroreflex

Beatrice De Maria1, Vlasta Bari2, Beatrice Cairo3, Emanuele Vaini2, Elisabeth Lambert4, Murray Esler5, Mathias Baumert6, Sergio Cerutti7, Laura Dalla Vecchia8, Alberto Porta9
1IRCCS Istituti Clinici Scientifici Maugeri, Istituto di Milano; Department of Electronics Information and Bioengineering, Politecnico di Milano, 2Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, 3Department of Biomedical Sciences for Health, University of Milan, 4Faculty of Health, Arts and Design, Swinburne University of Technology, 5Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute, 6School of Electrical and Electronic Engineering, University of Adelaide, 7Department of Electronics Information and Bioengineering, Politecnico di Milano, 8IRCCS Istituti Clinici Scientifici Maugeri, Istituto di Milano, 9Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato; Department of Biomedical Sciences for Health, University of Milan


Abstract

The cardiac baroreflex (cBR) asymmetry, defined as the difference in cBR sensitivity (cBRS) in response to arterial pressure (AP) rises and fallings, has been observed in pharmacological studies. This aspect has never been explored over sympathetic baroreflex (sBR). Two analytical methods for cBRS and sBR sensitivity (sBRS) estimation, namely sequence (SEQ) and bivariate phase rectified signal averaging (PRSA) methods, allowed the separate computation of cBRS and sBRS in response to positive and negative AP changes from the spontaneous variability, respectively, of heart period and systolic AP, and of muscle sympathetic nerve activity (MSNA) burst rate and diastolic AP. The aim of this study is to test the cBR and sBR asymmetry via SEQ and PRSA methods in young healthy subjects. We recorded electrocardiogram (ECG), invasive AP and MSNA in 12 young healthy subjects for ten minutes at supine resting and during head-up tilt at 20°, 30°, 40° and 60°. HP was derived as inter-beat interval from the ECG, while SAP and DAP as AP maximum and minimum in the current HP, respectively. The variation of the number of MSNA bursts within a window of 5 s was taken as MSNA variability series. SEQ and PRSA methods were applied to sequences of 300 consecutive HP, SAP, DAP and MSNA burst rate values over each experimental condition. After pooling together all the data, cBRSs derived from positive and negative SAP changes were similar regardless of the method. Conversely, sBRS computed by SEQ method over positive DAP changes was different from that computed over negative DAP variations (-0.072±0.026 vs -0.099±0.062 bursts·s-1·mmHg-1). No sBRS differences were observed using PRSA method. This study suggests that in physiological conditions baroreflex asymmetry is a peculiar characteristic of sBR and not of the cBR and the SEQ method is more powerful than the PRSA technique in characterizing it.