Feasibility of mitral flow assessment by echo-contrast ultrasound, part II: experimental study on a mechanical model of the left heart

Estimation of forward and backward mitral flow using indicator dilution technique: a theoretical feasibility study

A new theoretical algorithm is presented for high-resolution mitral flow determination based on the indicator dilution principle. The algorithm allows forward as well as backward time-dependent mitral flow estimation with a beat-to-beat resolution. Indices of normal/subnormal left heart functioning, including total stroke volume (TSV), cardiac output (CO), total ejection fraction (TEF), mitral regurgitation volume (MRV) and mitral regurgitation fraction (MRF), are determined. Knowledge of left atrium and ventricle indicator concentration versus time dependencies and the end systolic left atrium and ventricle volumes are sufficient to determine the mitral flow pattern. However, the non-dimensional index of the total ejection fraction can be calculated on the basis of only the indicator concentration. The algorithm was validated by applying it to blood flows and heart chamber volumes derived from a computer simulation of the cardiovascular circulation. First left heart concentrations versus time data were obtained by determining the distribution over a cardiovascular tract of an ideal indicator, a bolus of which was intravenously injected into one of the arms. Then the backward problem of finding mitral flow was solved. The accuracy of the mitral flow estimation depends on the accuracy of end systolic left atrium and ventricle volume data. The method is applicable over a wide range of aortic regurgitation, up to 20% of cardiac output, suggesting that the algorithm might become a robust technique of non-invasive mitral flow assessment, replacing traditional techniques such as nuclear radiography.