Relative Effects of Heart Chambers, Lungs, and Mitral Insufficiency on the Shape of Indicator Dilution Curves

The shape of dilution curves obtained by sampling from different sites was studied in dogs following superior vena caval injections of dye. Synchronous sampling from paired sites enabled observations to be made on the separate effects of the right heart, left ventricle and aorta on the dye dilution curves, with and without mitral insufficiency. The results show that tile left ventricle and aorta have little effect on the final slope of a dilution curve across the lungs in dogs with normal hearts. In the presence of mitral incompetence the final slope across both lungs and heart was slower than in the normal, but these changes were related to cardiac output and increase in lung mixing volume rather than primarily to the incompetence of the valve.