Anatomic and Physiologic Considerations in Measurements of Myocardial Blood Flow

heart disease has provided a powerful stimulus for the development of new and bet-ter methods for the study of the coronary circulation. In the animal laboratory, the elec-tromagnetic flowmeter has replaced the rotam-eter as the standard method of measuring coronary blood flow. Flowmeter probes can be implanted around a dog's coronary artery and utilized to study the coronary circulation during exercise in an intact unanesthetized animal. ' These excellent methods cannot, for obvious reasons, be applied to the study of patients, and therefore clinical investigators have been forced to develop other methods for the study of patients with ischemic heart disease. The coronary circulation can be defined as a peripheral circulatory bed, and therefore any discussion of the method of measuring myo-cardial blood flow should logically begin with a consideration of the simplest kind of periph-eral circulatory bed as diagrammed in figure 1. The artery and vein are both accessible, and an indicator can be injected into the blood flowing in through the artery and its concentration measured in venous blood leav-ing the bed, and there is no pathway whereby it can recirculate. The indicator substance may be identified by virtue of its color, its chemical properties, or its radioactivity. If a radioactive indicator is used, and a scintillation probe is placed over the vascular bed, a con-centration time plot can be obtained by mean