Analog transmission line model for simulation of systemic circulation

A LabVIEW model incorporating an open-loop arterial impedance and a closed-loop circulatory system

While numerous computer models exist for the circulatory system, many are limited in scope, contain unwanted features or incorporate complex components specific to unique experimental situations. Our purpose was to develop a basic, yet multifaceted, computer model of the left heart and systemic circulation in LabVIEW having universal appeal without sacrificing crucial physiologic features. The program we developed employs Windkessel-type impedance models in several open-loop configurations and a closed-loop model coupling a lumped impedance and ventricular pressure source. The open-loop impedance models demonstrate afterload effects on arbitrary aortic pressure/flow inputs. The closed-loop model catalogs the major circulatory waveforms with changes in afterload, preload, and left heart properties. Our model provides an avenue for expanding the use of the ventricular equations through closed-loop coupling that includes a basic coronary circuit. Tested values used for the afterload components and the effects of afterload parameter changes on various waveforms are consistent with published data. We conclude that this model offers the ability to alter several circulatory factors and digitally catalog the most salient features of the pressure/flow waveforms employing a user-friendly platform. These features make the model a useful instructional tool for students as well as a simple experimental tool for cardiovascular research.

Forward electrical transmission line model of the human arterial system

A forward mathematical model of the human arterial system, based on an electrical transmission line analogy, has been developed, using a new method for the calculation of peripheral impedance. Simulations of the human arterial system under normal and stenotic arterial conditions were compared with other published simulations, as well as measured clinical data and known clinical quantitative and qualitative characteristics: the harmonic arterial input impedance spectrum demonstrated a mean error of 0.07-0.1 mmHg.s.cm(-1), compared with equivalent simulation and physiological data, respectively; qualitative and quantitative variation of blood pressure and flow waveforms along the arterial tree followed clinical trends; arterial pulse wave velocities compared favourably with physiological data close to the aortic root (-50-20 cm s(-1) difference), but there were larger differences in the periphery (149-1192 cm s(-1) difference); qualitative as well as quantitative variation of blood flow waveforms with progressive stenotic arterial disease, as measured by the pulsatility index, demonstrated an error between 2 and 16% in comparison with mean clinical data for critical stenosis. Under the given test conditions, the forward model was found closely to represent clinically observed haemodynamic characteristics of the human arterial system.