The purpose of this study was to evaluate the efficacy of captopril-retard (C-R) and captopril (C) chronobiologically in patients with essential hypertension. Doses of C-R of 18.75mg twice a day and C of 12.5-25mg three times a day were administered at least 6wk in each of 9 patients. The blood pressure (BP) monitoring was repeated before and after the treatment for 48hr every 30 min with an ambulatory instrument (ABPM-630, Nippon Colin, Japan). These data were analyzed with conventional

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... ical and cosinor methods. The hyper-and hypobaric indices of BP were calculated based on our reference limits. The least square fit of a cosine curve with a period of 24hr was calculated to obtain a midline estimating statistic of rhythm (MESOR), amplitude, and acropase. A circadian rhythm cycle of about 24hr was found in the BP in all cases. C-R lowered MESOR of systolic BP (SBP) and diastolic BP (DBP) from 134.6+9.7mmHg to 129.9+9.9mmHg and 77.4+4.3mmHg to 70.2+5.7mmHg (P<0.01), and C decreased