## 3 Design and Simulation of Mock Circulatory Platform
### Design of Mock Circulatory Platform  
The mock circulatory platform of this study mimics the cardiovascular components to simulate the physiology of the human cardiovascular system. The platform is designed as a one atrium and one ventricle structure, to study how each component of arteries contributes to pulse wave generation. In this study, the effects of respiration were not considered, so the right atrium and right ventricle were integrated into the reservoir. The right atrium and the right ventricle have a major role in supplying blood to the lungs for respiration, and changes in blood pressure due to breathing are as small as several mmHg and do not contribute to changes in the blood pressure waveform [22]. It consists of components such as the ventricle, atrium, valves, arteries, and peripheral resistances. In terms of mechanical components, it consists of a pump that acts as a heart, tubes that simulate aorta and arteries, and a reservoir that acts as a vein and peripheral resistance.  
Figure 4a shows the layout of the mock circulatory platform, which consists of 4 modules. The heart module has a chamber acting as left atrium and a piston acting as left ventricle. There are valves between each component: a pulmonary valve between the reservoir and atrium, and a mitral valve between the atrium and ventricle. The fluid is pressurized in the ventricle and goes through the aortic valve to the aorta simulation module. The pulmonary valve and mitral valve are membrane valves, and the aortic valve is a check valve designed to streamline to suppress turbulence. The artery module consists of ascending, descending, and abdominal aorta, and implements a femoral artery that splits into two tubes at the branch. The reservoir module is intended to realize venous and peripheral resistance. It consists of a resistance valve mounted at the ends of tubes, including a femoral artery, and a reservoir that stores fluid. The arm phantom module and the renal artery branching to the kidney are also implemented for further detailed physiological studies. Figure 4b shows the fabricated new mock circulatory platform. The aortic components, except the ascending aorta, are made of rigid acrylic to suppress compliance. This is to perform a more precise parametric study by allowing adjustment of compliance only in the ascending aorta to which the compliance chamber is applied.  
Figure 3: Simulation of the 4-element windkessel model: (**a**) implemented electric circuit of the 4-element windkessel model; (**b**) simulated pressure waveforms at the ventricle and aorta; (**c**) normalized aortic pressure according to various peripheral resistance; (**d**) normalized aortic pressure according to various aortic compliance.  
Pressure measurements are made at two points: ventricle and ascending aorta. This is to measure the input pressure waveform to which the fluid is pressurized and the aortic pressure waveform transmitted through the aortic valve. Pressure waveforms at the ventricular pump and ascending aorta are measured with the PST164 pressure sensor from EFE (Ivry-la-Bataille, France) and sampled with 1 kHz sampling rate by the USB-6003 data acquisition device from NI (Austin, TX, USA). A linear motor was used as the ventricular pump, and it was controlled by the SPiiPlusCMnt motor controller from ACS motion control (Israel). The control cycle is 100 Hz, and acceleration up to 5 g is possible. Throughout this study, the fluid inside the system was assumed as pure water, with density \(\rho=1000\) kg/m\({}^{3}\) and \(\rho=1000\) kg/m\({}^{3}\). The pressure waveform is assumed to be a constant constant, and the pressure waveform is assumed to be constant. The pressure waveform is assumed to be  
and viscosity \(\mu=1.0016\times 10^{-3}\) Pa-s. A low-frequency filter was applied to the measured pressure waveform, since impulsive noise is generated when the aortic valve closes. However, the dicrotic notch was also suppressed along with valve closing noise.