The 24Â h blood pressure-R-R interval relation in ambulatory monitoring

In all subjects night, with respect to day, was characterized by R-R interval lengthening and blood pressure lowering. Despite this common pattern, day and night means and SDs, night and day differences, Δy/Δx ratios, a_24 h and b_24 h were different from individual to individual, but they were characteristic and reproducible in 20 out of the 21 subjects in which ABPM was repeated twice. Subjects could thus be classified according to their Δy/Δx ratios and slope (b_24 h). The 24 h blood pressure-R-R interval relation as calculated from ABPM yields individually characteristic indices of circadian sympatho-vagal reciprocity. This novel approach may be helpful in characterizing the 24 h autonomic control of several groups of patients.