THE RELATIVE IMPORTANCE OF THE SYSTOLIC AND THE DIASTOLIC BLOOD PRESSURE IN MAINTAINING THE CORONARY CIRCULATION

Abstract

It is generally known that the coronary circulation is greatly influenced by changes in blood pressure. This was well illustrated by the experiments of Markwalder and Starling.¹ In some instances they obtained 100 per cent increase in the rate of coronary flow by elevating the blood pressure from 80 to 110 mm. of mercury. The relative importance of the two phases of the blood pressure in maintaining the coronary circulation, however, has not been determined. In the study of the coronary circulation in the tortoise, the blood was observed to flow very rapidly during the diastolic phase, whereas during the height of the systolic period the smaller arteries were closed and the blood came to a standstill in the larger vessels.² It would thus seem that the rate of coronary flow is to a large extent dependent on the height of the diastolic pressure. It is therefore not improbable that