Lack of placebo effect in exercise response of hypertensive patients

The administration of placebo (a pharmacologically inactive substance) is justified in clinical trials of antihypertensive drugs in order to exclude the placebo effect. The evaluation of antihypertensive treatments during exercise is an interesting end point, since aerobic exercise is part of antihypertensive treatment. The aim of this study is to determine the placebo effect on blood pressure, heart rate and catecholamine secretion profiles during exercise testing.

10 patients with untreated mild to moderate essential hypertension participated in a single blind study consisting of two successive submaximal exercise tests (85% of maximal predicted heart rate), separated by a single oral administration of placebo. Blood pressure and heart rate were measured after 10 minutes of rest and at the end of each effort step (2 min, 20 Watts), both before and after placebo. Blood samples (5 ml) were collected at rest and during maximal exercise before and after placebo, in order to determine the effect of placebo on circulating catecholamines.

There were no significant difference between the "control" and after placebo exercise tests, neither in blood pressure or heart rate profiles, nor in values of circulating catecholamines (noradrenaline at rest: 1.88 +/- 0.96, effort: 6.43 +/- 1.93 nm/l before placebo, 1.65 +/- 0.83 nm/l and 5.71 +/- 2.12 nm/l after placebo respectively [NS]).

The placebo effect, which is generally determined from blood pressure at rest by sphygmomanometry, seems devoid of any influence on blood pressure, heart rate or catecholamine profiles during exercise in patients with mild to moderate essential hypertension. Thus, antihypertensive treatments can be evaluated during exercise by comparison to baseline cardiovascular parameters without need of a placebo group.