Calculation of arterial characteristic impedance: a comparison using different blood flow models

Within the concept of pulse wave analysis, arterial pressure and flow curves over a whole cardiac cycle are analysed. Characteristic impedance is obtained as ratio of pressure to flow when waves are not influenced by reflections. The aim of this work is to evaluate the effects of different blood flow models on the determination of the characteristic impedance compared to flow curves gained from ultrasound measurements. Beside a simple triangular and an averaged flow, a new blood flow model based on Windkessel theory is used. In a study population of 148 patients for the evaluation of the different models, the characteristic impedance is calculated in the frequency domain. The results indicate that the characteristic impedance strongly depends on the accuracy of the used flow model. While the averaged and the ARCSolver flow provide good estimates for impedance, the triangular flow curve seems to be too simplistic for getting accurate values.