Non-invasive evaluation of abdominal aortic properties: lumped circuit model and estimation of its parameters.

To non-invasively determine abdominal aortic properties, a five-element lumped circuit model was adopted. The model consists of resistance due to blood viscosity (R1), inertia of blood flow, compliances of the vessel (C1, C2), resistance of the peripheral arteries (R2) and the impedance of the of the femoral arteries (termination). Patterns of the central velocity of the upper abdominal aorta and the femoral artery are measured by pulsed Doppler echocardiography, and contours of flow volume rates are calculated. The pressure pattern of the lower limb is recorded by a pulse wave transducer and corrected according to sphygmomanometer values. Contours are transformed into respective Fourier transform components. The current transfer function is described theoretically and calculated from the acquired Fourier components. Values of every element are evaluated by the nonlinear least squares method. In 94 subjects (17-92 years), the values of each element are estimated. R2 values are greater in the elderly group than in the young group and r1 (R1/cm) increased with age. This model demonstrates that vessel compliance (C1 + C2 (C1 + C2/cm)) decreases with age, and it is suggested that this may be a useful marker of arteriosclerosis.