Day-by-Day Variability of Blood Pressure and Heart Rate at Home as a Novel Predictor of Prognosis: The Ohasama Study

Abstract

Day-by-day blood pressure and heart rate variability defined as within-subject SDs of home measurements can be calculated from long-term self-measurement. We investigated the prognostic value of day-by-day variability in 2455 Ohasama, Japan, residents (baseline age: 35 to 96 years; 60.4% women). Home blood pressure and heart rate were measured once every morning for 26 days (median). A total of 462 deaths occurred over a median of 11.9 years, composing 168 cardiovascular deaths (stroke: n=83; cardiac: n=85) and 294 noncardiovascular deaths. Using Cox regression, we computed hazard ratios while adjusting for baseline characteristics, including blood pressure and heart rate level, sex, age, obesity, current smoking and drinking habits, history of cardiovascular disease, diabetes mellitus, hyperlipidemia, and treatment with antihypertensive drugs. An increase in systolic blood pressure variability of +1 between-subject SD was associated with increased hazard ratios for cardiovascular (1.27; P =0.002) and stroke mortality (1.41; P =0.0009) but not for cardiac mortality (1.13; P =0.26). Conversely, heart rate variability was associated with cardiovascular (1.24; P =0.002) and cardiac mortality (1.30; P =0.003) but not stroke mortality (1.17; P =0.12). Similar findings were observed for diastolic blood pressure variability. Additional adjustment of heart rate variability for systolic blood pressure variability and vice versa produced confirmatory results. Coefficient of variation, defined as within-subject SD divided by level of blood pressure or heart rate, displayed similar prognostic value. In conclusion, day-by-day blood pressure variability and heart rate variability by self-measurement at home make up a simple method of providing useful clinical information for assessing cardiovascular risk.