Regional coronary blood flow in canine hemorrhagic shock.

This study examined circumferential, apex-to-base, and transmural distribution of coronary blood flow at rest and in hemorrhagic shock in a canine model. In addition, animals subjected to identical anesthesia and instrumentation were not hemorrhaged and served as controls. Regional coronary blood flow was measured by the radioactive microsphere technique, using 15-microns diameter microspheres in both control and shocked dogs. Circumferential variation in flow occurred at rest with the left ventricular free wall blood flow higher than septal flow and the anterior region better perfused than the posterior region. In addition, the endocardium was favored over epicardium as indicated by an endocardial-epicardial flow ratio greater than one. Early shock altered the regional distribution of coronary flow, resulting in better perfusion in some areas of the heart than in others. Two hours of sustained shock (mean arterial blood pressure at 30 mm Hg) oblated differences in circumferential as well as apex-to-base distribution of flow, resulting in global hypoperfusion. Transmural distribution of flow was also altered with a significantly greater fall in endocardial compared to epicardial flow. The greater vulnerability of the endocardium to low-flow injury in shock was confirmed by the presence of hypercontraction lesions and necrosis in the papillary muscle and endocardial regions, but not in the epicardial region. Injury was homogenous, as indicated by the uniformed distribution of lesions and necrosis across the anterior and posterior regions, as well as the free wall and septum of the left ventricle. Two hours of anesthesia alone did not significantly alter the transmural or circumferential distribution of coronary blood flow. While there was a tendency for total coronary flow to fall over the experimental period, this did not achieve statistical difference. Our study confirms a significant relationship between reduced coronary perfusion and hypercontraction injury in canine hemorrhagic shock.