Author: Niels Wessel1, Andrej Gapelyuk1, Jonas Weiß2, Martin Schmidt2, Jan F Kraemer1, Karsten Berg1, Hagen Malberg2, Holger Stepan3, Jürgen Kurths1,4,5
Affiliation: <sup>1</sup> Department of Physics, Humboldt-Universität zu Berlin, Berlin, Germany.
<sup>2</sup> Institute of Biomedical Engineering, Technische Universität Dresden, Dresden, Germany.
<sup>3</sup> Division of Obstetrics, Universitätsklinikum Leipzig, Leipzig, Germany.
<sup>4</sup> Potsdam Institute for Climate Impact Research, Potsdam, Germany.
<sup>5</sup> Department of Human and Animal Physiology, Saratov State University, Saratov, Russia.
Conference/Journal: Front Neurosci
Date published: 2020 Sep 24
Other:
Volume ID: 14 , Pages: 547433 , Special Notes: doi: 10.3389/fnins.2020.547433. , Word Count: 351
Spontaneous baroreflex sensitivity (BRS) is a widely used tool for the quantification of the cardiovascular regulation. Numerous groups use the xBRS method, which calculates the cross-correlation between the systolic beat-to-beat blood pressure and the R-R interval (resampled at 1 Hz) in a 10 s sliding window, with 0-5 s delays for the interval. The delay with the highest correlation is selected and, if significant, the quotient of the standard deviations of the R-R intervals and the systolic blood pressures is recorded as the corresponding xBRS value. In this paper we test the hypothesis that the xBRS method quantifies the causal interactions of spontaneous BRS from non-invasive measurements at rest. We use the term spontaneous BRS in the sense of the sensitivity curve is calculated from non-interventional, i.e., spontaneous, baroreceptor activity. This study includes retrospective analysis of 1828 measurements containing ECG as well as continues blood pressure under resting conditions. Our results show a high correlation between the heart rate - systolic blood pressure variability (HRV/BPV) quotient and the xBRS (r = 0.94, p < 0.001). For a deeper understanding we conducted two surrogate analyses by substituting the systolic blood pressure by its reversed time series. These showed that the xBRS method was not able to quantify causal relationships between the two signals. It was not possible to distinguish between random and baroreflex controlled sequences. It appears xBRS rather determines the HRV/BPV quotient. We conclude that the xBRS method has a potentially large bias in characterizing the capacity of the arterial baroreflex under resting conditions. During slow breathing, estimates for xBRS are significantly increased, which clearly shows that measurements at rest only involve limited baroreflex activity, but does neither challenge, nor show the full range of the arterial baroreflex regulatory capacity. We show that xBRS is exclusively dominated by the heart rate to systolic blood pressure ratio (r = 0.965, p < 0.001). Further investigations should focus on additional autonomous testing procedures such as slow breathing or orthostatic testing to provide a basis for a non-invasive evaluation of baroreflex sensitivity.
Keywords: barorecepter reflex sensitivity; blood pressure variability; heart rate variability; rest; slow breathing.
PMID: 33071732 PMCID: PMC7543095 DOI: 10.3389/fnins.2020.547433