Model-based causal closed-loop approach to the estimate of baroreflex sensitivity during propofol anesthesia in patients undergoing coronary artery bypass graft

Abstract

Cardiac baroreflex is a fundamental component of the cardiovascular control. The continuous assessment of baroreflex sensitivity (BRS) from spontaneous heart period (HP) and systolic arterial pressure (SAP) variations during general anesthesia provides relevant information about cardiovascular regulation in physiological conditions. Unfortunately, several difficulties including unknown HP-SAP causal relations, negligible SAP changes, small BRS values, and confounding influences due to mechanical ventilation prevent BRS monitoring from HP and SAP variabilities during general anesthesia. We applied a model-based causal closed-loop approach aiming at BRS assessment during propofol anesthesia in 34 patients undergoing coronary artery bypass graft (CABG) surgery. We found the following: 1) traditional time and frequency domain approaches (i.e., baroreflex sequence, cross-correlation, spectral, and transfer function techniques) exhibited irremediable methodological limitations preventing the assessment of the BRS decrease during propofol anesthesia; 2) Granger causality approach proved that the methodological caveats were linked to the decreased presence of bidirectional closed-loop HP-SAP interactions and to the increased incidence of the HP-SAP uncoupling; 3) our model-based closed-loop approach detected the significant BRS decrease during propofol anesthesia as a likely result of accounting for the influences of mechanical ventilation and causal HP-SAP interactions; and 4) the model-based closed-loop approach found also a diminished gain of the relation from HP to SAP linked to vasodilatation and reduced ventricular contractility during propofol anesthesia. The proposed model-based causal closed-loop approach is more effective than traditional approaches in monitoring cardiovascular control during propofol anesthesia and indicates an overall depression of the HP-SAP closed-loop regulation.

Cardiovascular control in women with fibromyalgia syndrome: do causal methods provide nonredundant information compared with more traditional approaches?

“…The BRS and the gain of the feedforward mechanical pathway were estimated by the methodology reported by Porta and colleagues (1,9,18). Briefly, after identification of the coefficients of the M-variate autoregressive model with M ϭ 3 in ⍀ ϭ {HP, SAP, RESP}, the baroreflex feedback arm, from SAP to HP, was described by the regression of HP on past SAP values, whereas the regression of SAP on past HP values described the mechanical feedforward arm, from HP to SAP.…”

“…However, these approaches to the quantification of BRS have many methodological drawbacks. The most relevant one is the inability to account for causality, thus merging the feedforward pathway from HP to SAP, which is related more to the mechanical properties of the heart and dynamical properties of circulatory system, to the feedback pathway, which is more related to cardiac baroreflex (18,23).In an attempt to overcome this issue, model-based causal closed-loop methods (1, 9, 13, 28), and more recently, a Granger causality approach have been proposed (18,20,22). These methods have been shown to provide complementary information to that obtained by traditional indices about the cardiovascular autonomic regulation.…”

“…However, these approaches to the quantification of BRS have many methodological drawbacks. The most relevant one is the inability to account for causality, thus merging the feedforward pathway from HP to SAP, which is related more to the mechanical properties of the heart and dynamical properties of circulatory system, to the feedback pathway, which is more related to cardiac baroreflex (18,23).…”

“…In an attempt to overcome this issue, model-based causal closed-loop methods (1, 9, 13, 28), and more recently, a Granger causality approach have been proposed (18,20,22). These methods have been shown to provide complementary information to that obtained by traditional indices about the cardiovascular autonomic regulation.…”

Validity and variability of xBRS: instantaneous cardiac baroreflex sensitivity

“…2010; Porta et al. 2013) and ultimately the correlation is just positive, not even significant, then still do the numbers not change importantly: the average xBRS remains the same, so does the coefficient of variation (geometric SD/geometric mean). The number of detected xBRS estimates increases to 90% of the time in the baseline recordings and under clonidine or propranolol, less for atropine blockade or atropine + propranolol blockade.…”