The sequence technique revised: additional concepts on the assessment of spontaneous baroreflex function.

The sequence technique is commonly employed to estimate the baroreflex sensitivity from the analysis of systolic blood pressure (SBP) and RR Interval (RRI) recordings. Traditionally, the RRI+/SBPand RRI-/SBP+ sequences are excluded from this analysis. In this paper we present a new interpretative model that, through the introduction of the concept of baroreflex SBP set point, proposes a sub-classification of the excluded sequences in "converging" and "diverging" types, depending on whether they point at, or, depart from the SBP set point, respectively. According to the model, also the RRI+/SBPand RRI-/SBP+ "converging" sequences might be associated with the baroreflex control of circulation. As a first test of the model, we estimated the distribution of the "converging" and "diverging" RRI+/SBPand RRI-/SBP+ sequences in a group of 10 healthy subjects at rest in a quiet context, where an enhancement of the baroreflex function could be assumed and a predominance of the "converging" sequences could be expected according to the model. Actually the results confirmed a significant prevalence of "converging" type over the "diverging" type sequences (10.6±6.7 vs. 3.3±2.8, mean±sd) in these recordings. Although future studies are needed to experimentally validate this new classification of the RRI+/SBPand RRI/SBP+ sequences, our results provide a first positive support to the model.