Assessment of the trough/peak ratio and smoothness index as a marker of stable antihypertensive effects

Twenty-four-hour ambulatory blood pressure monitoring was carried out before and after treatment with the long-acting calcium channel blocker barnidipine in hypertensive patients, and the trough/peak (T/P) ratio and smoothness index (SI) were calculated in 239 patients to assess the durability of the antihypertensive effects of the drug. A mean T/P ratio of -1130/0 ± 1973% SD for systolic blood pressure (SBP) was calculated after averaging the trough and peak values determined in each patient. When the T/P ratio was calculated after extrapolation of 24-h and 12-h Fourier curves, the mean ratio of barnidipine was 0.45 ± 0.8 for SBP and 0.43 ± 0.7 for diastolic blood pressure (DBP). When patients were classified into the low ambulatory (low-range) or high ambulatory (high-range) blood pressure group based on pretreatment measurements, a reasonable T/P ratio of 57% for SBP and 51% for DBP was calculated for patients in the high-range group, suggesting that barnidipine had a stable and long-acting antihypertensive effect in these patients. When patients in the high-range group were further divided into dippers and non-dippers, based on the diurnal variation in blood pressure, the mean T/P ratio of non-dippers was estimated to be 63% for SBP and 64% for DBP, suggesting that a constant blood pressure-lowering effect was achieved over a 24-h period in these patients. The low-range group had a low SI in both SBP and DBP (0.33/0.28), and the high-range group had a high SI (0.96/0.77). Although the T/P ratio did not change with the barnidipine dose, the SI increased dose-dependently, suggesting that the SI reflects not only the homogeneity of the antihypertensive effect but also the intensity of the blood pressure lowering.