Prazosin-induced haemodynamic modification in human hypertension. Evidence from strain-gauge plethysmography. Part II.

Three hypertensive in-patients responsive to a single oral administration of 1 mg prazosin were studied to compare the delays of drug effect on peripheral blood flow (PBF), heart rate (HR) and blood pressure (BP). Arm PBF was measured by venous occlusion strain-gauge plethysmography in a long run session (lasting at least 2 hours) every 5 - 10 minutes. HR and BP were measured accordingly, by conventional methods. The delays of the effect were compared by a cross correlation function of HR, systolic and diastolic BP versus PBF. The results show both advance and delay of HR increase as compared with PBF increase, suggesting some independent mode of action of prazosin at peripheral (vasodilation) and central (HR) level. BP decrease is instead always delayed with respect to PBF increase, by a variable amount (10 - 60 minutes) and with some difference in time response to systolic and diastolic BP, suggesting some independent feed-back loops controlling systolic and diastolic BP adjustment due to primary vasodilation effect.