Noninvasive Assessment of Temporal Dynamics in Sympathetic and Parasympathetic Baroreflex Responses

Background: The baroreflex system is crucial for cardiovascular regulation and autonomic homeostasis. A comprehensive assessment requires understanding the simultaneous temporal dynamics of its multiple functional branches, which traditional methods often overlook.

Objective: To develop and validate a noninvasive method for simultaneously assessing the temporal dynamics of sympathetic and parasympathetic baroreflexes using pulse contour analysis and the sequence method.

Methods: Beat-to-beat blood pressure and ECG recordings were analyzed from 55 preoperative cardiothoracic surgery patients in the supine position and 21 subjects from the EUROBAVAR dataset in both supine and standing positions. Systolic arterial pressure (SAP), interbeat interval (IBI), cardiac output (CO), myocardial contraction (dP/dt_max), and systemic vascular resistance (SVR) were estimated using pulse contour analysis. Baroreflex sensitivity (BRS) was calculated via the sequence method and correlated with hemodynamic and heart rate variability (HRV) parameters.

Results: Parasympathetic BRS for IBI was correlated with the root mean square of successive differences of ECG RR intervals (RMSSD-HRV) at 0-beat delay. Sympathetic BRS for SVR strongly correlated with SVR, CO, and RMSSD-HRV, particularly at 3-beat delay, and was uniquely associated with SAP at 1-beat delay. Sympathetic BRS for dP/dt_max correlated with dP/dt_max at 1-beat delay. In contrast, BRS for CO correlated with CO and SVR at 0- and 3-beat delays. Postural changes mainly affected parasympathetically-mediated BRS for IBI and, to a lesser extent, the sympathetic vascular and myocardial branches.

Conclusions: This method effectively captures multiple baroreflex responses and their temporal dynamics, revealing distinct autonomic mechanisms and the impact of postural changes. Further validation is warranted.