System identification of closed-loop cardiovascular control: effects of posture and autonomic blockade

Abstract

We applied system identification to the analysis of fluctuations in heart rate (HR), arterial blood pressure (ABP), and instantaneous lung volume (ILV) to characterize quantitatively the physiological mechanisms responsible for the couplings between these variables. We characterized two autonomically mediated coupling mechanisms [the heart rate baroreflex (HR baroreflex) and respiratory sinus arrhythmia (ILV-HR)] and two mechanically mediated coupling mechanisms [the blood pressure wavelet generated with each cardiac contraction (circulatory mechanics) and the direct mechanical effects of respiration on blood pressure (ILV-->ABP)]. We evaluated the method in humans studied in the supine and standing postures under control conditions and under conditions of beta-sympathetic and parasympathetic pharmacological blockades. Combined beta-sympathetic and parasympathetic blockade abolished the autonomically mediated couplings while preserving the mechanically mediated coupling. Selective autonomic blockade and postural changes also altered the couplings in a manner consistent with known physiological mechanisms. System identification is an "inverse-modeling" technique that provides a means for creating a closed-loop model of cardiovascular regulation for an individual subject without altering the underlying physiological control mechanisms.

Information-based detection of nonlinear Granger causality in multivariate processes via a nonuniform embedding technique

“…This occurs from X 2 to X 1 , from X 3 to X 1 , and from X 2 to X 3 , with coupling equal to zero (and nonsignificant). The overall picture is in agreement with behaviors that are well explainable in terms of the known cardiovascular physiology: The unidirectional interactions from X 1 to X 2 and from X 1 to X 3 document expected physiological mechanisms whereby respiration affects both the arterial pressure, through mechanical effects, and the heart rate, according to the so-called respiratory sinus arrhythmia phenomenon [32]; moreover, the significance of the coupling from X 3 to X 2 and the simultaneous absence of coupling in the opposite direction from X 2 to X 3 are in agreement with the notion that mechanisms operating in the direction from heart period to arterial pressure may prevail, in the nonsolicited resting condition of the subject, over the baroreflex mechanism describing driving effects from systolic pressure to heart period [33,34]. Results obtained in the upright position after head-up tilt evidence an alteration of the Granger causal relationships among the observed systems [ Fig.…”

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

“…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.…”

Robust efficiency and actuator saturation explain healthy heart rate control and variability

“…In addition to mechanistic physiological models, we also use systems identification techniques (referred to as "black-box" fits in this paper) (25,33,36,37) as intermediate steps to identify parsimonious canonical dynamical input-output models relating HR as an output variable to input disturbances such as workload and ventilation. These techniques establish causal deterministic links between input and output variables, highlight the aspects of time series and dynamic relationships that are explored further, and give some indication of the degree of complexity of their dynamics.…”