FACTORS AFFECTING THE NOCTURNAL DECREASE IN BLOOD-PRESSURE - A COMMUNITY-BASED STUDY IN OHASAMA

Objective To investigate factors affecting the nocturnal decrease in b lood pressure. Design A cross-sectional study of 823 community-based u ntreated subjects aged > 20 years. Screening and ambulatory blood pres sures were measured and the effects of age and the ambulatory blood pr essure on the nocturnal decrease were examined. Results The magnitude of the decrease and the percentage decrease in the nocturnal blood pre ssure increased with increasing daytime ambulatory blood pressure and decreased with increasing night-time ambulatory blood pressure. Althou gh the magnitude of the nocturnal decrease in blood pressure increased with increasing daytime blood pressure, the nocturnal blood pressure levels in hypertensives were still higher than those in normotensive s ubjects. The magnitude decreased with increasing age for men but not f or women, whereas the percentage decrease decreased with increasing ag e both for men and for women. The SD of the 24 h blood pressure correl ated strongly to the magnitude of the nocturnal decrease (systolic blo od pressure r = 0.62, P < 0.0001; diastolic blood pressure r = 0.52, P < 0.0001), suggesting that the SD of the 24 h blood pressure is repre sentative of the nocturnal decrease, A minimal nocturnal decrease was observed frequently in elderly normotensive men but infrequently in hy pertensive individuals from the general population. A marked nocturnal decrease was observed frequently in hypertensive women aged > 70 year s. Conclusion Although the magnitude of the nocturnal decrease in bloo d pressure increased with increasing daytime blood pressure, the noctu rnal blood pressure levels increased with increasing daytime ambulator y blood pressure. Therefore, the blood pressure in hypertensive subjec ts should essentially be lowered throughout the 24 h period. A marked nocturnal decrease in blood pressure in some elderly hypertensive wome n was observed without treatment. The nocturnal blood pressure levels of such subjects should be considered during treatment.