Arterial and venous effects of verapamil in normal volunteers

1. The effects of verapamil (120 mg orally) and a placebo on arterial pressure, heart rate, PR interval, arterial flows and diameters of the brachial and carotid arteries (pulsed Doppler technique), forearm vascular resistance, and venous diameter and compliance (cutaneous microstrain gauge and plethysmography) have been compared over a 10-hr period in six healthy volunteers during a double-blind and cross-over study. 2. Verapamil reduced diastolic blood pressure by approximately 10 mm Hg, did not affect heart rate and increased PR interval by approximately 15%. 3. Verapamil significantly increased brachial and carotid arterial blood flows by 56% (P less than 0.01) and 16% (P less than 0.05), respectively, but the diameters of these vessels were not significantly modified (+7 and +4%, respectively, NS). Forearm vascular resistance decreased by 40% (P less than 0.01), indicating that verapamil preferentially dilates small arteries. All these effects peaked at 2 h after drug intake and lasted for 6 h. 4. Verapamil increased hand dorsal vein diameter and flow by 95% (P less than 0.05) and 80% (P less than 0.05), respectively, from 2 to 4 h after drug intake but venous compliance, assessed by the venous diameter/venous flow ratio, was not significantly modified (from 0.71 to 0.69, NS), thus indicating that veins are not directly affected by this drug.