Myocardial blood flow regulation relative to left ventricle pressure and volume in anesthetized dogs

The influence of left ventricle pressure and volume changes on coronary blo od flow was investigated in eight anesthetized dogs. Coronary artery pressu re-flow relationships were determined at two levels of left ventricular pre ssure and volume. The distribution of blood flow within the myocardium was also determined when these relationships varied. Reducing left ventricle pr essures and volumes increased heart rate. Rate-pressure product, diastolic coronary pressure, myocardial O-2 consumption, total, subendocardial and su bepicardial flow decreased. Hematocrit and blood gas data were unchanged. T he pressure-flow relationships were shifted leftward (p = 0.001) but the ra nge of autoregulation was not altered. At low left ventricle pressures and volumes, the lower coronary artery pressure limit was shifted leftward (fro m 75 to 45 mmHg (1 mmHg = 133.3 Pa)), while total, subendocardial, and sube picardial blood flow did not change compared with the control. Below the lo wer coronary artery pressure limit, subendocardial but not subepicardial fl ow decreased, resulting in maldistribution of flow across the left ventricu lar wall. When coronary pressure was reset between control and the lower co ronary artery pressure limit, subendocardial flow was restored. These resul ts show that the lower coronary artery pressure limit can be shifted leftwa rd while the distribution of blood flow across the left ventricular wall is preserved.