Measurement of left ventricular volume by thermodilution: an appraisal of technical errors

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Abstract
An analysis of the technical errors inherent in the determination of left ventricular volume by indicator-dilution methods, particularly thermodilution, is presented. Inaccuracies in the measurement of the true rate of indicator washout from the ventricle are related to valvular regurgitation, heat transfer between ventricular wall and chamber, and a long sensor time constant; variations occur due to heterogeneous indicator mixing in the chamber and at the transducer. It is shown that, whatever the reason for error, it multiplies as the fraction of ventricular emptying becomes smaller. The error is reduced through the use of a sensor with an appropriately short time constant and through the acquisition of multiple dilution curves and stroke volume measurements. An estimate of the relative error in the computed left ventricular volume is possible and only under optimal circumstances is close to that found in the determination of cardiac output. The remaining variation in computed volume is primarily an indication of variable indicator mixing. The conditions required for reliability are extensive and place restrictions on the general usefulness of the method. indicator-dilution technic; end-diastolic volume; residual volume; thermistor Submitted on October 29, 1963

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