Effect of placebo on office and on 24 hour noninvasive ambulatory blood pressure measurements

Elevated BP in the clinical but not during daily activities (white coat hypertension) is a well recognised problem encountered in the diagnosis of mild hypertension. The aim of this study is to evaluate this phenomenon with a study population of 90 mild hypertensive patients subjected to 24h BP measurement, and to assess the effect of placebo on both the office and the daytime continual BP monitored values. For this purpose, 90 patients were evaluated after four weeks of single-blind placebo (Phase I) and, of these, 27 patients were evaluated after a further four weeks of double-blind placebo administration (Phase II). During Phase I treatment the mean office SBP (163.9 mmHg) and the mean office DBP (104.5 mmHg) were significantly higher than the average of the six readings obtained during the first two hours of automatic continual BP monitoring (158.6 and 98 mmHg respectively, P<0.001) (white coat effect). These differences were much more pronounced when the comparison was made between office measurements and the average daytime values (SBP 152.8 mmHg, DBP 93.1 mmHg). At the end of Phase II, the average values of BP measurements obtained both in the office and from continual monitoring were significantly lower (placebo effect). However, the difference between the office and the daytime values persisted. Thus, notwithstanding the reduction in the BP measurements following placebo administration, the white coat effect persists.