Cardiopulmonary volumes and blood volume expansion in experimental acute myocardial infarction with and without shock

Abstract

The effects of acute myocardial infarction on hemodynamics and cardiopulmonary volumes were studied in two groups of anesthetized closed-chest dogs: a non-shock group (intracoronary thrombus obstruction) and a shock group (intracoronary microspheres). Moderate blood volume expansion was carried out with donor dog blood and the effects were compared with those in a group of normal dogs. The shock dogs had greater decreases in cardiac output and left ventricular work than the non-shock group. In neither were true cardiopulmonary volume or LV end-diastolic volume increased over controls at two hours. With moderate blood volume expansion, improvement in Frank-Starling performance occurred in the infarct dogs with no significant changes in cardiac output or work among the normal dogs. In experimental myocardial infarction, blood volume expansion therefore improved cardiac performance independent of prior reductions in ventricular or central blood volume as a result of infarction. However, such benefits must be weighed against the threat of pulmonary edema with rising LV end-diastolic pressures and possible increased oxygen costs accompanying the increases in cardiac output and left ventricular work.