Factors associated with intra-individual visit-to-visit variability of blood pressure in four countries: the INTERMAP study.

Several studies demonstrated that visit-to-visit variability of blood pressure (BP) predicted future events of total death, stroke and cardiovascular disease. Little is known about factors associated with visit-to-visit BP variability in different countries. We recruited participants aged 40-59 years from four countries (Japan, the People's Republic of China [PRC], the United Kingdom [UK] and the United States [US]). At each study visit, BP was measured twice by trained observers using random zero sphygmomanometers after five minutes resting. We defined visit-to-visit BP variability as variation independent of mean (VIM) by using average systolic BP of 1st and 2nd measurement across four study visits. Data on 4680 men and women were analyzed. Mean ± standard deviation of VIM values among participants in Japan, the PRC, the UK and the US were 5.44 ± 2.88, 6.85 ± 3.49, 5.65 ± 2.81 and 5.84 ± 3.01, respectively; VIM value in the PRC participants was significantly higher. Sensitivity analyses among participants without antihypertensive treatment or past history of cardiovascular disease yielded similar results. Higher VIM value was associated with older age, female gender, lower pulse rate and urinary sodium excretion and use of antihypertensive agents such as angiotensin converting enzyme inhibitors, beta blockers and calcium channel blockers. The difference of visit-to-visit BP variability between PRC and other countries remained significant after adjustment for possible confounding factors. In this large international study across four countries, visit-to-visit BP variability in the PRC was higher than in the other three countries. Reproducibility and mechanisms of these findings remain to be elucidated.