Abstract
Although it is known that reproducibility of ambulatory blood pressure (BP) is superior to office BP in middle-aged subjects, little is known in older age groups. Hence, we compared the long-term reproducibility of ambulatory and office BP readings in subjects over the age of 75 years. A cohort of 72 subjects 75-90 years of age (mean, 82 years at baseline) had repeat office and ambulatory BPs 2 years apart under similar conditions. On the same day, patients underwent office BP measurements by a semi-automated device and then by ambulatory BP monitoring. Awake and sleep periods were divided according to a diary kept by each patient. The agreement between studies was assessed using the standard deviation of the differences (SDD) and Bland-Altman plots. There were minimal mean changes in office, 24-h, and awake and sleep mean BP values between baseline and 2 years later. The SDDs between visits were lower for 24-h BP compared with the office BP (11.7/5.9 mm Hg versus 17.8/9.0 mm Hg, P<0.01). The SDD for 24-h BP was also lower than the SDDs for the awake and sleep BP (P<0.05). Nocturnal BPs defined by absolute values were more reproducible than categories of dippers and non-dippers. These data demonstrate that long-term reproducibility of 24-h BP is superior to office measurements for very elderly subjects. In a clinical trial involving this age group, far fewer subjects would be required if 24-h BP was the primary efficacy endpoint rather than the office BP.