IMPROVED BAROREFLEX SENSITIVITY IN ELDERLY HYPERTENSIVES ON LISINOPRIL IS NOT EXPLAINED BY BLOOD-PRESSURE REDUCTION ALONE

Objective: The major goals of this study were to determine whether lisinopril and nifedipine lowered blood pressure and improved carotid baroreflexes in older hypertensives. Design: The effects of lisinopril at 10-40 mg/day versus nifedipine gastrointestinal therapeutic system (GITS) at 30-90 mg/day on blood pressure and baroreflex sensitivity were studied after 3 weeks each on (1) single-blind placebo, (2) double-blind assignment to either lisinopril or nifedipine, (3) single-blind placebo, and (4) crossover to double-blind lisinopril or nifedipine. Measurements at the end of the four phases included 24-h blood pressure using the Accutracker, laboratory hemodynamics with the Dinamap and impedance cardiography, baroreflex sensitivity with the pneumatic neck chamber, and plasma samples for neurohumoral and metabolic activity. Patients: Thirteen patients aged 55 years or older (mean +/- SEM 65 +/- 1 years) with mild-to-moderate hypertension completed the study. Main outcome measures: The primary data for analysis across the four study phases included ambulatory blood pressure values, laboratory hemodynamics, and baroreflex sensitivity. Results: Compared with the preceding placebo, lisinopril and nifedipine lowered 24-h blood pressure significantly. In the laboratory, the effects of both compounds on blood pressure, cardiac output, calculated total systemic resistance, and the stroke volume-pulse pressure relationship, an index of arterial compliance, were similar. Lisinopril was associated with a relative increase in the standing systolic blood pressure compared with nifedipine (P < 0.05). This coincided with an enhanced heart-rate (R-R interval) response to neck pressure, which also decreased carotid transmural pressure, with lisinopril versus nifedipine (P < 0.05). Conclusions: Lisinopril and nifedipine were both effective as monotherapy for controlling blood pressure in these elderly patients. Despite similar effects on blood pressure and systemic hemodynamics, baroreflex sensitivity in response to a reduction in carotid transmural pressure was greater with lisinopril than with nifedipine.