Advancements in estimating baroreflex function

Among the modern approaches for evaluating the baroreflex sensitivity (BRS), one of the most frequently employed is the sequence technique. This method is based on the computerized scanning of beat-to-beat series of systolic (S)BP and RRI values in search of spontaneous sequences of three or more consecutive heart beats in which SBP progressively increases and, usually with a one-beat delay, RRI progressively lengthens (RRI+/SBP+ sequences) or, vice-versa, SBP progressively decreases and RRI shortens (RRI-/SBP- sequences). The slope of the regression line between the SBP and RRI values included in each sequence is traditionally taken as a measure of BRS. A large number of these baroreflex sequences spontaneously occurs during daily life activities, thus providing a detailed profile of BRS modulation over time. In this article, we focus on the methodological basis of this technique. In particular, by taking advantage of experimental data collected over the years, we explore the characteristics of the SBP and RRI patterns within each spontaneous sequence. This analysis is followed by methodological considerations aimed at clarifying the perspective from which the sequence technique evaluates BRS, as compared with other techniques. Finally, the latest enhancements of the sequence technique, leading to the quantification of other aspects of baroreflex function apart from BRS, are also described.