Sensorless estimation of pressure head and flow of a continuous-flow artificial heart

The present study has proposed a new method for estimating the pressure head (P(t)[mmHg]) and flow (Q(t)[L min^-1]) of a centrifugal pump by using voltage (V(t)[V]), current (I(t)[A]) and rotational speed (N(t)[k(rpm)]) of the DC motor for the pump without any additional sensors. Two auto-regressive exogeneous (ARX) models are employed in the proposed estimation method. One ARX model has one output: P(t) or Q(t), and three inputs: VI(t) = V(t)I(t), N(t) and the gain constant (K) of the system from VI(t) to N(t). It can be regarded that K may include the information on viscosity of blood. The coefficient parameters of this ARX model are identified in an off-line fashion before implantation of the pump. After implantation, P(t) or Q(t) is estimated by the same ARX model with the pre-identified parameters. The other ARX model is used to identify K on the basis of VI(t) and N(t) in an on-line fashion every time the viscosity of blood may change. In the experiment, a mock circulatory system consisting of a centrifugal pump and a reservoir with glycerin 37% or water was employed. The root mean square error between measured Q and its estimate obtained from the proposed method was 1.82 L min^-1. On the other hand, the different method based on a single ARX model with inputs of VI(t) and N(t) but without the additional input of K yielded the corresponding estimation error of 2.38 L min^-1. This means that the proposed method can reduce its estimation error in comparison with the method that cannot cope with the change in blood viscosity.