Fast estimation of arterial vascular parameters for transient and steady beats with application to hemodynamic state under variant gravitational conditions

Numerous parameter estimation techniques exist for characterizing the arter ial system using electrical circuit analogs. These techniques are often lim ited by requiring steady-state beat conditions and can be computationally e xpensive. Therefore, a new method was developed to estimate arterial parame ters during steady and transient beat conditions. A four-element electrical analog-circuit was used to model the arterial system. The input impedance equations for this model were derived and reduced to their real and imagina ry components. Next, the physiological input impedance was calculated by co mputing fast Fourier transforms of physiological aortic pressure (AoP) and aortic flow. The approach was to reduce the error between the calculated mo del impedance and the physiological arterial impedance using a Jacobian mat rix technique which iteratively adjusted arterial parameter values. This te chnique also included algorithms for estimating physiological arterial para meters for nonsteady physiological AoP beats. The method was insensitive to initial parameter estimates and to small errors in the physiological imped ance coefficients. When the estimation technique was applied to in vivo dat a containing steady and transient beats it reliably estimated Windkessel ar terial parameters under a wide range of physiological conditions. Further, this method appears to be more computationally efficient compared to time-d omain approaches. (C) 1999 Biomedical Engineering Society. [S0090-6964(99)0 1404-6].