Mock Circulatory Loop Compliance Chamber Employing a Novel Real-Time Control Process

Abstract

The use of compliance chambers in mock circulatory loop construction is the predominant means of simulating arterial compliance. Utilizing mock circulatory loops as bench test methods for cardiac assist technologies necessitates that they must be capable of reproducing the circulatory conditions that would exist physiologically. Of particular interest is the ability to determine instantaneous compliance of the system, and the ability to change the compliance in real-time. This capability enables continuous battery testing of conditions without stopping the flow to change the compliance chamber settings, and the simulation of dynamic changes in arterial compliance. The method tested involves the use of a compliance chamber utilizing a circular natural latex rubber membrane separating the fluid and air portions of the device. Change in system compliance is affected by the airspace pressure, which creates more reaction force at the membrane to the fluid pressure. A pressure sensor in the fluid portion of the chamber and a displacement sensor monitoring membrane center deflection allow for real-time inputs to the control algorithm. A predefined numerical model correlates the displacement sensor data to the volume displacement of the membrane. The control algorithm involves a tuned p loop maintaining the volume distention of the membrane via regulation of the air space pressure. The proportional integral (PI) controller tuning was achieved by creating a computational model of the compliance chamber using Simulink TM Simscape V R toolboxes. These toolboxes were used to construct a model of the hydraulic, mechanical, and pneumatic elements in the physical design. Parameter Estimation TM tools and Design Optimization TM methods were employed to determine unknown physical parameters in the system, and tune the process controller used to maintain the compliance setting. It was found that the resulting control architecture was capable of maintaining compliance along a pressure-volume curve and allowed for changes to the compliance set point curve without stopping the pulsatile flow.

Realistic aortic phantom to study hemodynamics using MRI and cardiac catheterization in normal and aortic coarctation conditions

“…The compliance chamber allowed us to simulate the arterial compliance and to obtain physiologic diastolic pressures and pressure waveforms. The compliance chamber provides the capacitance of the circulatory system, which is crucial for maintaining the blood pressure during ventricular diastole and dampening pressure waves . The compliance chamber was placed in the DAo in order to avoid the damping of the inflow velocities and to simulate the arterial compliance downstream from the phantom …”

“…A compliance chamber (Fig. A) was installed in the circuit after the DAo in order to simulate arterial compliance, to obtain physiologic diastolic pressures and physiologic pressure waveforms. It was built using transparent acrylic of 4 mm thick with a total internal volume of 600 cm 3 .…”

Nonlinear Dynamics of Human Aortas for Material Characterization

“…Mock circulatory loops (MCL) were developed to test cardiovascular devices in vitro by recreating physiological pulsatile blood flow conditions [10][11][12]. The principal components of closed-loop MCL are as follows: (i) the pulsatile pump, (ii) the expansion chamber with an air cushion to replicate the Windkessel effect of the arterial tree, and (iii) pinch valves to reproduce the peripheral resistance.…”

Mock circulatory loops used for testing cardiac assist devices: A review of computational and experimental models

“…For future MCLs, it is imperative to address these limitations of current MCLs. Integrating fully automated compliance chambers 138 and resistance devices 139 allows the implementation of the necessary autoregulation of the CVS. Parts of the CVS that are too difficult to model hydraulically can be implemented into the MCL with a numerical model, obtaining a flexible and cost-effective H-MCL.…”