A simple four-tube arteries-microvessels-veins system which simulates a more realistic loading for human circulation was built using transmission line network. Hemodynamic data from literature are used in the fluid-circuit analogy, and the flow leakage and viscoelastic properties of the blood vessels have been considered. The effect of veins on the input impedance spectrum was found to be negligibly small above 0.5 Hz. The predicted input impedance spectra agree reasonably well with the published measurements both in shape and magnitude. Parametric analysis shows that the changes of vascular properties in the lower body affect the first minimum, and the changes in the upper body influence the second minimum. The blood flow in and out of kidney and liver dominates the aortic impedance from 0 to 5 Hz. Decreasing capacitance (i.e., increasing arterial stiffness due to aging), reducing the lumen area, or decreasing the length of blood vessels result in an increase in the impedance modulus, and the first minimum shift to a higher frequency which agree well with experiments. In the current model, the pressure, flow waveform, and local impedance can be predicted at any location along the circulatory tree. The characteristic of arterial pulse propagation resembles published measurements.
A viscoelastic four-tube arteries-micro-vessels-veins model has been built using transmission line network. Hemodynamic data from literature are used in the fluid-circuit analogic model. The predicted input impedance spectra agree reasonably well with the published measurements. Parametric analysis shows that the changes in the vascular properties in different portions of the body cause fluctuations of the maxima or minima of the impedance spectrum. In general, the changes of vascular properties in the lower body affect the first minimum, and the changes in the upper body influence the second minimum. Decreasing capacitances (i.e., increasing arterial stiffness due to aging), reducing the lumen area, or decreasing the length of blood vessels result in an increase of the impedance modulus, and the shift of the first minimum to a higher frequency, which agree well with experiments. The changes of peripheral resistances of all terminations affect the magnitude of impedance modulus maxima only. The current model uses simple physiological data directly; it can be used to simulate the effect of pharmacologic manipulation on the impedace spectra of the patients.
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