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  • Title: Nonlinear coupling among heart rate, blood pressure, and respiration in patients susceptible to neuromediated syncope.
    Author: Censi F, Calcagnini G, Strano S, Bartolini P, Barbaro V.
    Journal: Ann Biomed Eng; 2003 Oct; 31(9):1097-105. PubMed ID: 14582612.
    Abstract:
    The aim of this study is to evaluate the degree of coupling between the cardiovascular variability series and the respiration in subjects susceptible to neurally mediated syncope. Twenty-one informed patients susceptible to syncope and ten sex- and age-matched control subjects were enrolled in the study. ECG, respiration activity, and arterial blood pressure were simultaneously recorded at rest (controlled and free breathing) and during the 70 degrees head-up TILT test (free breathing). The degree of nonlinear coupling among heart rate variability (HRV), blood pressure variability (BPV), and respiration was quantified by means of two indices according to a multivariate embedding-based approach. Eleven patients developed syncope during the TILT test. We found that during the late TILT phase, the TILT-positive group experienced a significant increase in nonlinear coupling respect to the mid TILT phase (p < 0.01, Wilcoxon nonparametric test for pair data) while the TILT-negative group did not (p < 0.01, Mann-Whitney U-test). If the proposed nonlinear coupling indexes can be considered expression of the coupling mechanisms involved in the vagal regulation of the cardiovascular system, an increase in vagal tone accompanied by a decrease in sympathetic activity seem to occur before a vasovagal event.
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