1. ¹Kaiser Permanente Center for Health Research, Portland, OR, USA
2. ²Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins University, Baltimore, MD, USA
3. ³Duke Hypertension Center and Sarah W. Stedman Center for Nutritional Studies, Duke University Medical Center, Durham, NC, USA
4. ⁴Boston University, Boston, MA, USA
5. ⁵Kaiser Permanente Center for Health Research, Honolulu, HI, USA
6. ⁶Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
7. ⁷Division of Epidemiology and Clinical Applications, NHLBI, NIH, Rockville, MD, USA
8. ⁸Pennington Biomedical Research Center, Baton Rouge, LA, USA

Correspondence: Dr WM Vollmer, Center for Health Research, 3800 N. Interstate Ave, Portland, OR 97227-1110, USA. E-mail: william.vollmer@kpchr.org

Received 18 February 2004; Revised 8 April 2004; Accepted 15 June 2004; Published online 9 September 2004.

Abstract

Ambulatory blood pressure monitoring (ABPM) is commonly used in clinical trials. Yet, its ability to detect blood pressure (BP) change in comparison to multiple office-based measurements has received limited attention. We recorded ambulatory and five daily pairs of random zero (RZ) BPs pre- and post-intervention on 321 adult participants in the multicentre Dietary Approaches to Stop Hypertension trial. Treatment effect estimates measured by ambulatory monitoring were similar to those measured by RZ and did not differ significantly for waking vs 24-h ambulatory measurements. For systolic BP, the standard deviations of change in mean 24-h ambulatory BP (8.0 mmHg among hypertensives and 6.0 mmHg among nonhypertensives) were comparable to or lower than the corresponding standard deviations of change in RZ-BP based on five daily readings (8.9 and 5.9 mmHg). The standard deviations of change for mean waking ambulatory BP (8.7 and 6.7 mmHg) were comparable to those obtained using three to four daily RZ readings. Results for diastolic BP were qualitatively similar. Ambulatory monitoring was more efficient (ie, a smaller sample size could detect a given BP change) than three to four sets of daily RZ readings and required fewer clinic visits. The average of 33 ambulatory BP readings during the waking hours had an efficiency comparable to that from the mean of four daily pairs of RZ-BPs. Participants readily accepted the ABPM devices, and their use requires less staff training. ABPM provides a useful alternative to RZ-BP measurements in clinical trials.