Abstract
Caliber changes in retinal vessels of groups of hypertensive patients were measured after the blood pressure had been lowered by successful renal surgery, posture with adrenergic blocking drugs, and parenteral hydralazine. The small arterioles dilated when the pressure was reduced, whatever means were used. Larger arterioles dilated in three younger hypertensive patients but in the remainder they were unchanged or narrowed by pressure reduction. Inhalation of oxygen constricts normal retinal arterioles but the response in hypertensive patients was much less. A response to oxygen was restored in some small arterioles that dilated when the blood pressure was lowered. As retinal arterioles have no adrenergic vasomotor supply, changes in their caliber probably occur because of autoregulation. Narrowing caused by autoregulation during a rise in systemic arterial pressure may become irreversible in long-standing hypertension because of structural changes in the vessel wall.
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