Local circulation in heart muscle studied with Na²⁴ clearance method

Neutral, isotonic Na 24 Cl solution was injected into the left ventricular wall of open-chest dogs. The disappearance of local radioactivity was recorded. Individual injections that exceeded 5 mm 3 retarded Na clearance. The rate of Na clearance from individual deposits did not measure coronary flow in absolute terms; however, when one hemodynamic parameter was suddenly changed 50–200 sec after the injection of a radioactive deposit, the changed Na clearance slope reflected directional variations of coronary flow. In ischemic regions of self-perfused hearts, elevation of aortic pressure that was paralleled by increased left ventricular and central coronary pressures did not always result in more rapid Na clearance.