Continuous Cardiac Output Estimation Under Left Ventricular Assistance

Abstract

Sufficient cardiac output is the main goal of ventricular assist device therapy. To date, there is no adequate method to estimate the combined amount of blood the heart and an continuous-flow assist device pump through the circulatory system. This paper presents an approach to estimate the cardiac output based on the signals provided by optical pressure sensors mounted on the inlet and outlet of an Impella CP pump. An extended Kalman filter for joint estimation of the aortic flow rate and the hydraulic resistance of the aortic valve is introduced. It uses a third order nonlinear state-space model of the aortic valve, aortic arch and systemic circulation with six parameters. The accuracy of the estimated cardiac output is investigated in an animal study with two sheep suffering from acute ischemic heart disease supported by a left ventricular assist device. The extended Kalman filter with joint parameter and state estimation yields an error of 0.47 ± 0.32 L · min−1. It is compared to an extended Kalman filter without parameter identification which achieves a comparable error of 0.49 ± 0.26 L · min−1. The errors are in the same order of magnitude as the accuracy of the clinical gold standard for invasive blood flow diagnostics. The introduced method enables cardiac output to be used as the control variable of a physiological control strategy for closed-loop ventricular assist device therapy.