Regression dilution of systolic and diastolic blood pressure in patients with established cerebrovascular disease.

BACKGROUND AND OBJECTIVE: Blood pressure (BP) is a major risk factor for stroke and cardiovascular events. To quantify its effect, it is necessary to correct for regression dilution bias (RDB). RDB has been estimated from repeated measurements of BP in population-based studies, but there are no data in patients with established vascular disease. METHOD: We analyzed repeat measurements of BP from three large studies of patients with cerebrovascular disease: UK-TIA trial (n=2098), Dutch TIA trial (n=2953), and the European Carotid Surgery Trial (n=2646). The regression dilution ratio (RDR) was estimated by parametric and nonparametric methods at follow-up intervals ranging from 4 months to 6 years. RESULTS: After an interval of only 4-5 months, nonparametric RDRs of 0.56, 0.40, and 0.45 for systolic BP and 0.45, 0.33, and 0.31 for diastolic BP were observed in the three studies, respectively. These values are much smaller than those reported in population-based studies, indicating greater within-person variability in BP. CONCLUSION: RDRs from population-based studies cannot necessarily be applied to cohorts with established vascular disease