Evaluation of Factors Affecting the Renal Doppler Waveform with the Use of an Electrical Circuit Model

ABSTRACT

PURPOSE: We have evaluated the influence of several variables such as vascular compliance and resistance and heart rate on the resistive index by the use of an electrical circuit model that simulates renal blood flow. MATERIALS AND METHODS: To analyze the renal artery Doppler waveform, we modeled the renal blood-flow circuit with an equivalent simple electrical circuit containing resistance, inductance and capacitance. The relationship between impedance and resistance and compliance of the circuit was derived from well-known equations including Kirchhoff's current law for an alternating current circuit. Simulated velocitytime profiles for pulsatile flow were generated by the use of Mathematica software (Wolfram Research, Champaign, IL USA) and the influence of resistance, compliance and pulse rate on waveforms and the resistive index were evaluated. RESULTS: Resistance and compliance altered the waveforms independently. The impedance of the circuit increased with increasing proximal compliance, proximal resistance and distal resistance. Impedance decreased with increasing distal compliance. The resistive index of the circuit decreased with increasing proximal compliance and resistance. The resistive index increased with increasing distal compliance and resistance. These results showed no tendency of a positive correlation between the impedance and resistive indices. The pulse rate is an extrinsic factor that also influences the resistive index. CONCLUSIONS: By the use of this simulation study using an electrical circuit model, a better understanding of the Doppler waveform and resistive index was achieved and the study findings may be useful in various clinical settings.