A system identification approach to baroreflex sensitivity estimation

Abstract

-The body contains a bewildering array of regulatory systems which maintain homeostasis. There is considerable difficulty in isolating a single control loop for analysis, due to the interactions with other systems/loops. One important such regulatory loop is the baroreflex, and baroreflex sensitivity is a characteristic open-loop parameter which can help us to assess the health of the baroreflex. A diverse range of methods have been proposed to determine baroreflex sensitivity from experimental data. Unfortunately, there appears to be little consistency of result among the different methods and some explanation can be found in the nature of the problem: In most cases, an attempt is being made to determine open-loop measures from a system operating in closed-loop, subject to poor excitation. In this paper we propose a strict procedure, based on a rigourous mathematical framework, from which reliable estimates of baroreflex sensitivity can be obtained. A comparison with other methods for baroreflex sensitivity estimation, using the EuroBaVar data set, is performed.

CardioRVAR: A New R Package and Shiny Application for the Evaluation of Closed-Loop Cardiovascular Interactions

“…However, during post-tilt, they differ in their magnitudes for the LF band: after visual inspection, it was noticed that around 0.06 Hz, where the maximum coherence level was located, the gain of the transfer function dropped, giving a low estimate for this coherence level, while, at frequencies around 0.1 Hz, the gains computed were of much higher magnitude. Therefore, we attribute this finding to the fact that the maximum coherence level, at which the gain dropped, was not located near the center of the frequency band, a region that is better explored by the Gaussian-averaging method [35], which in this case had gains of greater magnitude. During tilt, the response at the HF band is reduced, but the activity of the LF component is still not predominant.…”

“…[8,33]. This method, however, can be too strict to the point of sometimes not obtaining valid estimates from a particular subject due to low coherence values The method proposed by McLoone and Ringwood [35] was also introduced in our software, which consists of applying a frequency-domain Gaussian window to the transfer function at a specific band before computing the expected values. As both authors point out, with this method, the center of each frequency band is mainly considered for the evaluation of the baroreflex activity [35].…”

“…This method, however, can be too strict to the point of sometimes not obtaining valid estimates from a particular subject due to low coherence values The method proposed by McLoone and Ringwood [35] was also introduced in our software, which consists of applying a frequency-domain Gaussian window to the transfer function at a specific band before computing the expected values. As both authors point out, with this method, the center of each frequency band is mainly considered for the evaluation of the baroreflex activity [35]. Finally, another estimation method, which consists of reporting the value of the transfer function at the maximum coherence value of the bands of interest [36], is also included in our software.…”

“…The second analysis consists of a comparison of estimates produced from the tool from five individual normotensive subjects and seven hypertensive subjects in the context of HUT sessions. In the final analysis, estimates computed with the tool from subjects from the EUROBAVAR data set [34] are compared in the supine and standing positions, a validation strategy already used in other works [16,35,38,39]. For these two last analyses, the normality of distributions in the former analysis and of the difference in distributions in the latter is tested with the Shapiro-Wilk test.…”

“…Table 2 summarizes the obtained results from seven hypertensive and five normotensive subjects from the analysis of recordings from HUT tests. Two methods for the estimation of BRS were used in the analyses: a weighted-averaged BRS without coherence thresholding, as in McLoone and Ringwood's work [35], and BRS indices obtained at the maximum coherence level for each frequency band. Significant differences are found for both bands in the supine position, and for the LF band during HUT; however, disagreement between the estimation methods is detected at the LF band in the supine position.…”