Accuracy of the HVAD Pump Flow Estimation Algorithm

Controller algorithms are an important feature for assessment of ventricular assist device performance. Flow estimation is one algorithm implemented in the HeartWare continuous-flow ventricular assist device pump system. This parameter estimates flow passing through the pump and is calculated using speed, current, and hematocrit. In vitro and in vivo studies were conducted to assess the algorithm accuracy. During in vitro testing, three pumps were tested in four water–glycerol solutions at 37°C with viscosities equivalent to hematocrits of 20, 30, 40, and 50%. By using a linear regression model, a correlation coefficient of >0.94 was observed between measured and estimated flow for all conditions. In vivo studies (n = 9) were conducted in an ovine model where a reference flow probe was placed on the outflow graft and speed was adjusted from 1,800 to 4,000 revolutions per minute. During in vivo experiments, estimated pump flow (mean, minimum, and maximum) was compared with measured pump flow. The best-fit linear regression equation for the data is y = 0.96x + 0.54, r = 0.92. In addition, waveform fidelity was high (r > 0.96) in normal (i.e., nonsuction) cases where flow pulsatility was >2 L/min. The flow estimation algorithm demonstrated strong agreement with measured flow, both when analyzing average waveform magnitude and fidelity.