title: Ambulatory monitoring of the blood pressure in multicenter clinical trials.
abstract: By reducing measurement error associated with clinic (or casual) blood pressure, ambulatory blood pressure measurement (ABPM) potentially enhances the precision of blood pressure estimation. Enhanced precision leads to lower sample size requirements or increased statistical power, or both, in clinical trials. Thus, by virtue of its increased numbers of measurements and improved reproducibility, ABPM can differentiate among active antihypertensive therapies when clinic blood pressure measurements do not. Additional benefits of ABPM can include identification of white-coat hypertensives, removal of observer bias, a marked reduction in placebo effects and evaluation of the circadian blood pressure pattern. By identifying circadian patterns, ABPM aids in the evaluation of the diurnal and nocturnal effects of a therapeutic regimen. ABPM has found more frequent application in the assessment of antihypertensive therapies in multicenter trials in recent years. However, using ABPM in multicenter trials might increase the complexities of the conduct of the trial relevant to the maintenance of homogeneity in study methods. Special concerns for multicenter trials involving ABPM include device use and validation, experience of study coordinators or research technicians and patient compliance. In recent years in the USA, ambulatory blood pressure values have been used to serve as secondary 'cut-off' criteria before random allocation in a trial (after primary entry criteria based on clinical blood pressure values have been satisfied). Sponsors of trials have become highly selective in recruiting study sites with substantial experience in ABPM. These practices may create a more homogeneous cohort in the trial and make the population less representative of the general hypertensive population.
authors.affiliation: Section of Hypertension and Vascular Diseases, Department of Medicine, University of Connecticut School of Medicine, Farmington, Connecticut, USA.
authors.initials: WB
authors.lastname: White
authors.initials: SJ
authors.lastname: Walsh