Prognostic value of nighttime blood pressure in the elderly: a prospective study of 24-hour blood pressure

Abstract

Although it has been suggested in several reports that 24-h ambulatory blood pressure (BP) is a better predictor than casual BP measured in a clinician's office of the incidence of cardiovascular (CV) events, little information is available concerning the prognostic value of nighttime BP in the elderly population. Therefore, to evaluate the clinical implications of the nighttime BP in the elderly, we prospectively followed-up 324 elderly individuals (mean age, 77.2 +/- 7.0 years) who had undergone ambulatory BP monitoring at an annual health examination over a mean follow-up period of 51.5 +/- 22.0 months, and the relationship between BP and CV events was analyzed using Cox's proportional hazard model. For the analysis, 310 participants, excluding 14 subjects who were withdrawn due to non-CV events, were classed into two groups, one consisting of 134 individuals who were undergoing treatment with an anti-hypertensive drug (medicated group) and another consisting of 176 who were not medicated (nonmedicated group). New cardiovascular events developed in 43 cases in the medicated group and in 14 cases in the non-medicated group during the follow-up period. In the medicated group, a linear relationship was observed between BP and the event rates. The hazard ratio for CV events adjusted for age, sex, and other cardiovascular risks was 1.28 (95% confidence interval [CI], 1.05 to 1.54, p< 0.05) for a 10 mmHg increase of 24-h systolic BP. Corresponding values in 24-h diastolic BP, nighttime systolic BP, and nighttime diastolic BP were 1.71 (1.19 to 2.46, p< 0.01), 1.34 (1.13 to 1.58, p< 0.01), and 1.67 (1.20 to 2.31, p< 0.01), respectively. In the non-medicated group, the event rate was least in the subgroup in the second-lowest quartile for nighttime systolic BP, with a slight non-significant increase in the subgroup of the lowest quartile. It was shown that insufficient control of nighttime BP in the elderly with hypertension is associated with the development of CV complications.