Indicator-Dilution Curves During Methoxamine Infusion jn Patients with Mitral Valvular Disease

This report describes the time-concentration components and the contour of indicator-dilution curves recorded from the femoral artery after injection of radioactive iodinated (I131) human serum albumin into the pulmonary artery before and during methoxamine infusion in nine patients with predominant mitral stenosis, and seven patients with predominant mitral insufficiency. During methoxamine infusion, the changes were as follows: (a) The forward cardiac output was uniformly reduced in both groups. The changes in the total and “central” blood volumes were inconsistent in both groups. In all cases, there was prolongation of the appearance and mean transit times. (b) There was a significantly greater prolongation of the reciprocal of the downslope and the disappearance time in patients with mitral insufficiency than in those with mitral stenosis. By means of a simple formula, we allowed for alteration in forward cardiac output and “central” blood volume during methoxamine infusion, and a satisfactory discrimination between mitral stenosis and mitral insufficiency was achieved by comparing the change in 1/S. Comparison of the ratio of spread time to appearance time (Ts/TA) before and during methoxamine infusion also effected an excellent separation between the two groups. It is postulated that the characteristic changes of the indicator-dilution curves during methoxamine infusion in patients with mitral insufficiency were due to augmentation of regurgitant stroke volume, increase in the force of the regurgitant jet, or both.