The association of a simple blood pressure-independent parameter derived from ambulatory blood pressure variability with short-term mortality

Abstract

We explored the predictive ability of the blood pressure variability ratio (BPVR), defined as the ratio of 24-h ambulatory systolic blood pressure variability to diastolic variability, and evaluated its predictable relation with blood pressure and the Ambulatory Arterial Stiffness Index (AASI). A total of 3433 consecutive patients were followed up to 16 years for all-cause mortality. Blood pressure variability was expressed by the standard deviation. BPVR, which is the systolic-on-diastolic slope estimated by a known type of symmetric regression ('reduced major axis'), was compared with other expressions of this slope and with AASI using other regression procedures. Time-dependent Cox proportional hazard models, adjusted for demographics, 24-h mean blood pressure, 24-h pulse pressure and dipping were used to assess the association of BPVR and slope-related parameters with all-cause mortality. We found that Pearson's correlation between BPVR and the symmetric slope was 0.957, and between 1-1/BPVR (an AASI-equivalent expression) and the symmetric version of AASI was 0.973. BPVR was entirely independent of mean arterial pressure (r=0.013). Systolic and diastolic ambulatory blood pressure variability was not significantly associated with mortality. Over 16 years, BPVR predicted all-cause mortality [hazard ratio=1.21 (95% CI 1.05-1.40) per 1 s.d. increase]. In time-dependent models, increased BPVR was strongly associated with an 18-month mortality, weakly related to 7 years mortality, showing no effect thereafter. Thus, the ratio between 24-h systolic and diastolic blood pressure variability, readily available from ambulatory monitoring reports, is an easy-to-calculate systolic-on-diastolic slope. It is a blood pressure-independent measure believed to express an arterial property, with prognostic power similar to that of AASI.