DETERMINANTS OF CIRCADIAN BLOOD-PRESSURE VARIATION - A COMMUNITY-BASED STUDY IN OHASAMA

We investigated factors affecting the nocturnal decline in blood press ure (BP). A cross sectional study was done in 706 community-based untr eated subjects greater than or equal to 20 years of age. Screening and ambulatory BPs mere measured and the effects of age and the ambulator y BP on the nocturnal decline were examined. Bivariate analysis demons trated that the magnitude of the decline and the percent decline in th e nocturnal BP increased with increase in daytime ambulatory BP and de creased with increase in nighttime ambulatory BP. Although the magnitu de of the nocturnal decline in BP increased with increasing daytime BP ; the nocturnal BP in hypertensives was still higher than those in nor motensives. The magnitude decreased with increasing age in men belt no t in women, while the percent decline decreased with increasing age in both men and women. Since bivariate analysis demonstrated that the da ytime BP, nighttime BP, and standard deviation of the 24-hour BP stron gly correlated with the magnitude of the nocturnal decline, these para meters mere excluded as independent variables from the multivariate an alysis. In the multivariate analysis the nighttime pulse pressure was negatively and daytime pulse pressure was positively associated with t he magnitude of the decline and the percent decline in the nocturnal B P. A non-dipping circadian variation was frequently observed in elderl y normotensive men but the rate of nondipper was rather low in hyperte nsive individuals in the general population A marked dipping pattern w as frequently observed in hypertensive women greater than or equal to 70 years of age. The nocturnal BP levels in subjects with daytime hype rtension are higher than those in subjects with daytime normotension. Therefore, BP must ideally be lowered over 24-hour period in hypertens ive subjects. The diminished magnitude of the decline and the decrease in the percent decline in the nocturnal BP in the elderly may be medi ated by the disturbed baroreflex function due to the decrease in compl iance of large elastic artery. However, in some elderly hypertensive w omen, excess nocturnal decline in BP is observed. In such subjects, ar e should take care of the nocturnal BP levels during treatment. (C) 19 97 Tohoku University Medical Press.