Effects of pulmonary embolism on regional myocardial blood flow

The effects of autologous pulmonary embolism and pulmonary artery constriction on regional myocardial blood flow and ventricular hemodynamics were evaluated in 15 trained, awake, spontaneously breathing dogs. RV and LV myocardial blood flows were measured by 8 to 10μ radioactive microspheres. Tension-time index and minute work were calculated for each ventricle to indicate hemodynamic load. Control measurements were compared with those obtained following pulmonary artery constriction and after pulmonary embolism at equal levels of increased afterload. Arterial blood pressure, heart rate, and arterial Po₂ were unchanged throughout the study. Control RV myocardial flow averaged 59 percent of LV myocardial flow. Both pulmonary artery constriction and embolism produced a twofold increase in blood flow to the RV myocardium without corresponding changes in LV myocardial flow. Indices of RV hemodynamic load significantly increased during constriction and embolism without changes in LV values. Both interventions were accompanied by parallel decreases in RV coronary vascular resistance. These data indicate that the compensated RV responds to increased regional work load following either pulmonary artery constriction or pulmonary embolism by local autoregulation producing an increase in RV myocardial blood flow independent of LV hemodynamics or myocardial blood flow.