Effect of various degrees of systemic arterial hypertension on acute canine myocrdial ischemia

Abstract

There is continuing uncertainty about the effects of various degrees of systemic arterial hypertension on myocardial ischemia. In 46 open-chest anesthetized dogs, intramural CO2 tension (PmCO2) was measured directly with a mass spectrometer during repetitive 10 min coronary artery occlusions separated by 45 min periods of reflow. During each occlusion, transmural regional myocardial blood flow (RMBF) in the ischemic area was quantitated with the injection of radioactive microspheres (7-10 .mu.m). In all dogs the increase in PmCO2 from before to 10 min after the 1st occlusion (.DELTA.PmCO2) exceeded that during subsequent occlusions. In those dogs in which systemic arterial hypertension was not produced (controls), .DELTA.PmCO2 during the 3rd occlusion was similar to that during the 2nd occlusion. When phenylephrine was administered during the 3rd occlusion to increase systemic arterial pressure mildly (diastolic pressure 95-115 mmHg), RMBF to the ischemic myocardium was unchanged and the severity of myocardial ischemia was reduced, as reflected by a fall in .DELTA.PmCO2. When diastolic pressure was elevated moderately (116-140 mmHg), RMBF was augmented, but the extent of myocardial ischemia was neither diminished nor worsened. When diastolic pressure was increased markedly (> 40 mmHg), myocardial ischemic injury was intensified (as reflected by an increase in .DELTA.PmCO2) even though RMBF rose significantly. In the dog with acute coronary artery occlusion,an increase of systemic arterial pressure exerts an influence on the severity of myocardial ischemic injury that is related directly to the magnitude of systemic arterial hypertension: a mild increase of pressure reduces ischemic injury, a moderate increase exerts no consistent effect on ischemia and a marked increase worsens ischemic injury.