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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.
Content:
Peer Reviewed
Note:
This article was supported by the German Research Foundation (DFG) and the Open Access Publication Fund of Humboldt-Universität zu Berlin.
In:
Lausanne : Frontiers Research Foundation, 14
Language:
English
DOI:
10.3389/fnins.2020.547433
URN:
urn:nbn:de:kobv:11-110-18452/22946-4
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