AN EXPERIMENTAL EVALUATION OF THE INDICATOR DILUTION TECHNIQUE FOR THE MEASUREMENT OF MITRAL REGURGITATION *

Abstract

The indicator-dilution technic has been widely applied in the detection of mitral regurgitation. Regurgitation was produced in 15 open-chest dogs by an external polyvinyl shunt between the left ventricle and left atrium. Regurgitant flow was measured through a side arm and reservoir set at left auricular level. Cardiac output was measured using radioactive iodinated human serum albumin as the indicator. Injections were made into the left auricle or pulmonary artery, and interrupted samples at one second intervals taken from the femoral artery. Regurgitant flow varied between 20 and 38% of forward flow (mean 27%). There was no significant difference between the forward output with or without the shunt being open. There was a good correlation between cardiac output and central blood volume (r = .87) but none between slope and cardiac output. In the same dog, the curve obtained with the shunt open could always be separated from the control curve with the shunt closed by using any simple analysis such as slope or disappearance time. However, when the data from the 15 dogs were pooled, none of the currently used analyses involving slope, time and/or concentration ratios would completely separate the control group from that with insufficiency. Using the interrupted sample method for obtaining dye dilution curves in this experimental preparation, it can be said that given a control dye curve for comparison, the method is sensitive enough to detect 20-38% regurgitation. However, with one isolated measurement the presence of mitral regurgitation cannot always be determined.