Conway Reactive Hyperemia Resistance and Blood Pressure

T HE increased peripheral resistance associated with hypertension has been demonstrated for the circulation as a whole by measurements of blood pressure and cardiac output.l 2 The site of this resistance has not been precisely identified but it is believed to reside in the smallest arteries and arterioles.3'4 Since the activity of the smooth muscle in these vessels is readily affected by humoral and neurogenic stimuli, it has been assumed that there is an increased level of vasoconstrictor tone in this disease, but no evidence has yet been obtained for this assumption. On the other hand, there is considerable evidence in man affected by hypertension that the blood vessels themselves show exaggerated responses to vasoconstrictor drugs,5-9 although this may not be readily demonstrated when these drugs are given intravenously.10 13 Paradoxically, however, Folkow and associates14 have shown that under the influence of the powerful vasodilator stimuli of heat and reactive hyperemia the blood vessels maintain a greater level of resistance in hypertensive than in normal subjects. These facts suggest that whatever abnormal vasoconstrictor stimuli may be operative in hypertension, the function of the blood vessels themselves may also be abnormal. A study has, therefore, been undertaken to determine the presence of a vascular abnormality of the blood vessels in hypertension and to relate it to the severity of the disease in a large group of patients.