Effects of Antihypertensive Drugs on Blood Velocity: Implications for Prevention of Cerebral Vascular Disease

The treatment of high blood pressure prevents death from congestive heart failure, hypertensive nephropathy, and encephalopathy, and strokes from cerebral arteriolar disease (lacunes, hemorrhage from microaneurysms). However, atherosclerosis, manifested as coronary artery disease is just as frequent a cause of death in well-controlled hypertensives as in poorly-controlled patients. Increasing evidence suggests that increased blood velocity, by causing turbulence and high shear rates at the endothelial surface of arteries, may be important in the pathogenesis of atherosclerosis. Turbulence has been observed in cerebral berry aneurysms. In order to measure the effects of antihypertensive agents on blood velocity, a new method of analysing Doppler ultrasound velocity recordings has been developed. Studies in Rhesus monkeys show the following: In doses which reduce diastolic pressure by 13-28%, propranolol decreased mean blood velocity (MV) by 17%, clonidine decreased MV by 14%, while methyldopa increased MV 12%, and hydralazine increased MV by 52%. (p less than .00001). It is hypothesized that enlargement of berry aneurysms, the progression of cerebral atherosclerosis, and embolism from carotid lesions might all be decreased by the selection of antihypertensive agents which decrease blood velocity.