The extended Kalman filter as a pulmonary blood flow estiṁator

Pulmonary blood flow is represented as a time-varying parameter in a simple model of the bodily uptake of gases that are soluble in blood. The pulmonary blood flow is estimated on-line using Ljung's modification of the extended Kalman filter. The experimental technique for estimation of pulmonary blood flow is based on Zwart's soluble gas method, modified to permit time-varying ventilation and pulmonary perfusion, and also to permit binary dynamic forcing of the inhaled soluble gas. Computer simulations were performed to determine the convergence time and to choose values of algorithmic parameters. Experiments done in humans gave agreement to within the accuracy of that measured invasively by a thermal dilution technique. The method shows promise for use in many biomedical applications, including patient monitoring, physiological experimentation, and clinical heart function tests.