Home blood pressure variability as cardiovascular risk factor in the population of Ohasama

Abstract

Blood pressure variability based on office measurement predicts outcome in selected patients. We explored whether novel indices of blood pressure variability derived from the self-measured home blood pressure predicted outcome in a general population. We monitored mortality and stroke in 2421 Ohasama residents (Iwate Prefecture, Japan). At enrollment (1988-1995), participants (mean age, 58.6 years; 60.9% women; 27.1% treated) measured their blood pressure at home, using an oscillometric device. In multivariable-adjusted Cox models, we assessed the independent predictive value of the within-subject mean systolic blood pressure (SBP) and corresponding variability as estimated by variability independent of the mean, difference between maximum and minimum blood pressure, and average real variability. Over 12.0 years (median), 412 participants died, 139 of cardiovascular causes, and 223 had a stroke. In models including morning SBP, variability independent of the mean and average real variability (median, 26 readings) predicted total and cardiovascular mortality in all of the participants (P≤0.044); variability independent of the mean predicted cardiovascular mortality in treated (P=0.014) but not in untreated (P=0.23) participants; and morning maximum and minimum blood pressure did not predict any end point (P≥0.085). In models already including evening SBP, only variability independent of the mean predicted cardiovascular mortality in all and in untreated participants (P≤0.046). The R(2) statistics, a measure for the incremental risk explained by adding blood pressure variability to models already including SBP and covariables, ranged from <0.01% to 0.88%. In a general population, new indices of blood pressure variability derived from home blood pressure did not incrementally predict outcome over and beyond mean SBP.

Figure 1

Incidence of total and cardiovascular mortality and stroke by quartiles of the mean level (A and C) and variability independent of the mean (B and D) of systolic blood pressure measured at home in the morning (A and B) or evening (C and D) in 2421 participants. Rates given as end points per 1000 person-years were standardized for sex and age by the direct method. The number of end points contributing to the rates is presented. The P values refer to the significance for linear trend across the quartiles.

Figure 2

Kaplan-Meier survival function estimates for cardiovascular mortality by quartiles of the mean level (A and C) and variability independent of the mean (B and D) of systolic blood pressure measured at home in the morning (A and B) or evening (C and D) in 2421 participants. The P values refer to the significance of the log-rank test across quartiles.

Figure 3

Absolute 10-year risk of cardiovascular mortality (A and C) and stroke incidence (B and D) in relation to the mean level of systolic blood pressure measured at home in the morning (A and B) or evening (C and D) in 2421 participants. The analyses were standardized to the distributions (mean or ratio) of sex, age, body mass index, heart rate, smoking and drinking, total cholesterol, diabetes mellitus, history of cardiovascular diseases, and treatment with antihypertensive drugs. In each panel, mean systolic blood pressure along the horizontal axis (SBP) covers the 2.5th to 97.5th percentile interval. Four continuous lines represent the risk independently associated with variability independent of the mean (VIM) equal to 3, 6, 9, and 12 units.P values are for the independent effect of SBP (P_SBP) and VIM (P_VIM). n_p and n_e indicate the number of participants at risk and the number of events.