Background : Ambulatory blood pressure assessments have been shown to be associated with subclinical and clinical endpoints even after controlling for the effects of clinic blood pressure.
Objective : To examine the incremental validity of ambulatory over clinic blood pressures using equivalent time periods, equivalent numbers of observations, and comparable measurement instruments across both settings.
Design and Methods : In this cross-sectional study of 216 healthy, community volunteers (ages 50-70 years), we compared three types of assessment in terms of their association with carotid artery atherosclerosis: manual clinic blood pressure (two readings, 10 min interval), automated clinic blood pressure (four readings, 2.5 h interval), and automated ambulatory blood pressure (four readings, 2.5 h interval) using the same type of automated device for the latter two conditions. These measurements were obtained during the morning hours on three separate occasions. Carotid intima-medial thickness and plaque were assessed, by ultrasound, as markers of atherosclerosis.
Results : Greater ambulatory systolic and diastolic blood pressure were associated with increased intima-medial thickness and an increased prevalence of plaque (odds ratios > 3.0), even after statistical adjustment for clinic blood pressure assessments and demographic covariates.
Conclusions : We conclude that the independent utility of ambulatory over clinic blood pressure cannot be attributed to methodological issues that have traditionally confounded these comparisons. These findings highlight the potential importance of behavioral and lifestyle factors in contributing to the incremental value of ambulatory blood pressure.