Revisiting the Sequence Method for Baroreflex Analysis.

Luiz Eduardo Virgilio Silva,Rubens Fazan,Carlos Alberto Aguiar Da Silva,Hélio Cesar Salgado,Daniel Penteado Martins Dias

doi:10.3389/fnins.2019.00017

Luiz Eduardo Virgilio Silva, Rubens Fazan + Show 3 more

Open Access

https://doi.org/10.3389/fnins.2019.00017

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Abstract

The sequence method is an important approach to assess the baroreflex function, mainly because it is based on the spontaneous fluctuations of beat-by-beat arterial pressure (for example, systolic arterial pressure or SAP) and pulse interval (PI). However, some studies revealed that the baroreflex effectiveness index (BEI), calculated through the sequence method, shows an intriguing oscillatory pattern as function of the delay between SAP and PI. It has been hypothesized that this pattern is related to the respiratory influence on SAP and/or PI variability, limiting the SAP ramps to 3 or 4 beats of length. In this study, this hypothesis was tested by assessing the sequence method using raw (original) and filtered series. Results were contrasted to the well-established transfer function, estimated between SAP and PI. Continuous arterial pressure recordings were obtained from healthy rats (N = 61) and beat-by-beat series of SAP and PI were generated. Low-pass (LP) and high-pass (HP) filtered series of SAP and PI were created by filtering the original series with a cutoff frequency of 0.8 Hz. Original series were analyzed by either the sequence method or cross-spectral analysis (transfer function) at low- (LF) and high- (HF) frequency bands, while filtered series were evaluated only by the sequence method. Baroreflex sensitivity (BRS) and BEI of original series, calculated by sequence method, was highly (85–90%) determined by HP series, with no significant association between original and LP series. A high correlation (>0.7) was found between the BRS estimated from original series (sequence method) and HF band (transfer function), as well as for LP series (sequence method) and LF band (transfer function). These findings confirmed the hypothesis that the sequence method quantifies only the high-frequency components of the baroreflex, neglecting the low-frequency influences, such as the Mayer waves. Therefore, we propose using both the original and LP filtered time series for a broader assessment of the baroreflex function using the sequence method.

Highlights

The sequence method, first described in the mid-1980s, was a milestone for the analysis of baroreflex function at both clinical and experimental levels (Bertinieri et al, 1985)
In contrast to baroreflex sensitivity (BRS), baroreflex effectiveness index (BEI) reflects the percentage of beat-by-beat arterial pressure (AP) changes that are effectively translated into reflex changes of the heart rate (HR; Di Rienzo et al, 2001)
The current study evaluated the influence of low- and highfrequency oscillations of systolic AP (SAP) and pulse interval (PI) in the sequence method, and compared the BRS calculated using the sequence method to BRS obtained from the cross-spectral analysis

Summary

Introduction

The sequence method, first described in the mid-1980s, was a milestone for the analysis of baroreflex function at both clinical and experimental levels (Bertinieri et al, 1985). In the late 2000s, Laude and coworkers studied more in-depth the parameters of the sequence method to better understand their influence and the best choices for working with mice (Laude et al, 2008, 2009). They reported an intriguing feature: when the BEI is calculated for increasing delays between beat-by-beat systolic AP (SAP) and pulse interval (PI), its value oscillates with a period of 3 to 4 beats. The BRS, assessed with increasing delays, do not show any oscillatory pattern

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