NOCTURNAL BLOOD-PRESSURE FALL ON AMBULATORY MONITORING IN A LARGE INTERNATIONAL DATABASE

A wide range of definitions is used to distinguish subjects in whom bl ood pressure (BP) falls at night (dippers) from their counterparts (no ndippers). In an attempt to standardize the definition of nondipping, we determined the nocturnal BP fall and night-day BP ratio by 24-hour ambulatory monitoring in 4765 normotensive and 2555 hypertensive subje cts from 10 to 99 years old. In all subjects combined, the systolic/di astolic nocturnal fall and corresponding ratio averaged (+/-SD) -16.7/-11.0/-13.6+/-8.1 mm Hg and 87.2+/-8.0%/83.1+/-9.6%, respectively. In normotensive subjects, the 95th percentiles were -0.3/-1.1 mm Hg for the nocturnal fall and 99.7%/98.3% for the night-day ratio. Both the f all and ratio showed a curvilinear correlation with age. The smallest fall and largest ratio were observed in older (greater than or equal t o 70 years) subjects. A higher BP on conventional sphygmomanometry was associated with a larger systolic (partial r=.11) and diastolic (r=.1 2) nocturnal BP fall. The diastolic (r=.08) but not the systolic night -day ratio increased with higher conventional BP. The nocturnal BP fal l was larger and the corresponding night-day ratio smaller in oscillom etric (n=5884) than in auscultatory (n=1436) recordings, in males (n=3 730) than in females (n-3590), and in Europe (n=4556) than in the othe r continents (n=2764). The distributions of the nocturnal BP fall and night day ratio showed considerable overlap among normotensive and hyp ertensive subjects, but the overlap tended to be larger for the ratio than for the fall. Of all subjects, 3.2% had systolic and diastolic ra tios of 100% or more. With adjustments applied for confounders, the pr obability of being a nondipper increased 2.8 times (95% confidence int erval, 2.0-4.0) from 30 to 60 years and 5.7 times (4.4-7.4) from 60 to 80 years. The odds ratios were 1.0 (0.8-1.4) for males versus females , 1.6 (1.2-2.1) for subjects with definite hypertension versus normote nsive subjects, 2.4 (1.2-4.7) for Asians (n=2213, 96% Japanese) versus inhabitants of the other continents, and 2.4; (1.5-3.8) for subjects examined with auscultatory versus oscillometric devices. In conclusion , the mathematical definition of nondipping, ie, having a night-day ra tio of 100% or more for systolic and diastolic BPs; closely approximat ed the 95th percentiles of the night-day ratio in normotensive subject s. The ratio depends less on BP level than the nocturnal BP fall and i s therefore to be preferred in the definition of dipping status. Notwi thstanding the present findings, the reproducibility of nondipping and its prognostic significance need further clarification.