Age-related changes in phase-space distribution of ABPM data in normotensive and hypertensive patients

The data collected by ambulatory blood pressure monitoring have been studied in the phase-space of R–R interval and blood pressure and their individual distribution quantified by the slope of the regression line through 24-h values. This slope has been termed “ambulatory autonomic reciprocity index” and abbreviated as AARIs and AARId, the “s” and “d” indicating the relation with systolic and diastolic blood pressure respectively. Ambulatory monitoring was performed in 200 normotensive (NT: 135 females) and 200 untreated hypertensive patients (HT: 59 females). The AARIs was: NT: −6.04 ± 2.7 and HT: −4.69 ± 2.4 ms/mm Hg, respectively (p < 0.001); the AARId was: −7.04 ± 2.9 for NT and −5.79 ± 2.8 for HT subjects (p < 0.001). When distributed by decades of life the steepest AARIs occurred at the 20–29 decade, while the flattest at the 60–69 decade. At the 60–69 decade and above, the AARIs was similar in both groups (ANOVA o.w. NT: p < 0.001; HT: p < 0.01). AARIs and AARId were strongly correlated with 24-h variability of R–R interval, either 24-h standard deviation or coefficient of variation (p < 0.001), and poorly correlated with 24-h variability of blood pressure. These data suggest that the AARI, when seen in the context of the “Autonomic Space”, may be viewed as a 24-h period index of centrally driven cardiovagal function. Being based on both blood pressure and heart rate measurements, the AARI may become clinically useful to address life style changes and pharmacological treatment of hypertensive patients towards optimal results.