On-line Identification of the Circulatory System Driven by the Left Ventricular Assist Device

A new hemodynamic measurement system was developed by using the left ventricular assist device (LVAD) to estimate the cardiac function of the natural heart. The LVAD was placed between the left atrium and the aorta for the patient with deeply failed left ventricular pump function and driven by the pneumatic drive unit. In the personal computer system, an on-line identification method was implemented to estimate the coefficients of the autoregressive moving average (ARMA) model whose input and output were corresponding to the drive pressure of the drive unit and the pump flow from LVAD, respectively. Two driving modes of LVAD were compared with each other. One is the co-pulsation mode in which the systolic period of LVAD coincides with that of the natural heart, and the other is the counter-pulsation mode in which the systolic period of LVAD is followed by that of the natural heart. This comparison clarified that the capability of cardiac function of the natural heart could be quantitatively evaluated on the basis of the difference between two frequency responses derived from the coefficients of the ARMA model. This implies that the proposed method is useful for making a decision on weaning from LVAD in the clinical case.