Slow-release nifedipine: effect on the circadian rhythm of blood pressure in essential hypertension.

The aim of this study was to investigate the effect of orally administered, slow-release, nifedipine tablets on the circadian rhythm of blood pressure and heart rate, in hospital patients with clinical diagnosis of hypertension validated by a chronobiologic inferential statistic method. A group of 14 patients (nine women and five men, 47 to 71 years old) with clinical diagnosis of "essential hypertension" underwent automatic blood pressure and heart rate monitoring in a hospital room for 48 hours. Measurements were taken every 15 min by an oscillometric instrument with automatically inflated cuff. The patients received no treatment during the two proceeding weeks and the first day of the study. On the second day, slow-release nifedipine tablets were administered, one at 10 a.m. and one at 10 p.m. A highly significant circadian rhythm was documented for systolic and diastolic blood pressure, mean arterial pressure and heart rate, both in basal conditions and after nifedipine. Blood pressure mesors were higher than reference standards in basal conditions, and were lowered (average decrease = 20 mmHg for systolic and 9 mmHg for diastolic mesor) by nifedipine. A significant, though minor, elevation of heart rate mesor (from 70 to 75 b.p.m.) was also noted during treatment. The circadian amplitudes of blood pressure and heart rate did not differ significantly before and during treatment. In conclusion, the circadian rhythm of blood pressure is still present with the same amplitude after slow-release nifedipine, but is set at a lower pressure level. Heart rate rhythm is also preserved, with only a minor elevation of its mesor.