Characteristics of a community-based distribution of home blood pressure in Ohasama in northern Japan

Objective: To evaluate the distribution, reference values and day-to-day variation of blood pressure of untreated subjects measured at home. Design: Cross-sectional study of a cohort. Setting: General community in northern Japan. Subjects: Blood pressure was measured in 871 subjects (mean±SD age 46.0 ± 19.5 years, range 7-98, constituting 38.7% of the local population of Uchikawama region, Ohasama) who were not receiving antihypertensive medication. Methods: Subjects measured their own blood pressure at home at least three times (mean ± SD 19.718.4) each morning using a semi-automatic oscillometric blood pressure measuring device. Screening blood pressure was measured once. Main outcome measures: Distribution of home blood pressure in the study population as a whole and with respect to age and sex, and the distribution of day-to-day variation of home blood pressure were determined. Results: Mean home blood pressure was 117.3 ± 13.4/69.3 ± 9.7mmHg (95% confidence interval 116.4-118.2/68.7-70.0). The 95th centile value was 143/85 mmHg, mean + SD 131/79 mmHg and mean ± 2SD 144/89 mmHg. Mean screening blood pressure was 126.2 ± 18.9/72.1 ± 11.7 mmHg (95th centile 159/92 mmHg). Age- and sex-specific 95th centile values as well as mean±SD were obtained. Mean + SD, mean + 2SD and the 95th centile values obtained as reference upper limits of home blood pressure from subjects identified as normotensive by screening blood pressure (n = 707) were 125/77, 137/86 and 134/83 mmHg, respectively. Home blood pressure increased gradually with increasing age in both men and women, although blood pressure was significantly higher in men until 50 years of age. Day-to-day variation of home systolic blood pressure also increased with age. Conclusions: Since the distribution of home blood pressure values was affected by age and sex, age- and sex-matched reference values for home blood pressure should be established. Home blood pressure values in elderly subjects should be evaluated carefully, since these exhibit greater day-to-day variation.