Design and Development of a Systemic Mock Circulation Loop with a Novel Beating Left Ventricular Simulator



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Mock Circulation Loops (MCLs) are used as a mechanical representation of the human cardiovascular system for in vitro testing of most cardiovascular devices. Thus, MCLs are essential to most of the cardiac device designs as a testbed. Cardiac device design procedures generally adopt mock circulatory systems before advancing to animal or clinical trials, which are much more troublesome and expensive. Therefore, various physiological cardiac failure or operating scenarios, need to be replicated in the MCL towards the testing of cardiovascular devices. Replicating these different scenarios requires not only a fully-automated MCL that can reproduce the necessary conditions precisely and switch between them without trouble, but also a beating LV simulator that mimics an actual human LV’s parameters, such as geometry, LV wall movement trajectories and elastance of the LV wall. A fully automated MCL design is proposed in this study and the beating LV simulator concept is analyzed, designed, prototyped and tested in the scope of this study. The novel and challenging part of this study was the development of the beating LV simulator. Due to the fact that designing a beating LV simulator which replicates geometry, wall motions, and muscle fiber orientations of an actual human LV chamber is a complex problem; a design analysis method known as Interpretive Structural Modeling (ISM) method, was applied to selected design approaches of the beating LV simulator’s actuation. Pneumatic muscles, flexible bands or strings, and artificial muscle materials were considered as candidates for different design approaches to replicate the wall motion and function of an actual human LV. ISM analysis showed that pneumatic muscle approach has proven to be the most promising. As a result, the pneumatic muscle approach was adopted to achieve realistic LV wall motions of various operating conditions. The beating LV simulator was prototyped by using Pneumatic Artificial Muscles (PAMs) and latex based elastic tissue material. Four PAMs were placed on the LV inner mold in the helical orientation and latex tissue material was applied on them. The fiber orientation of the cardiac muscles plays an essential role on the pumping performance of the actual LV chamber. Therefore, a thermally loaded FEA model was developed to investigate different fiber orientations in the future. The FEA model was validated by using experimental results of the beating LV simulator. Moreover, polymer based artificial heart valves (AHVs) were designed and prototyped for use in the MCL system, however, mechanical check valves were used in the experiments due to the short lifecycle of the prototyped AHVs. A state-space based numerical model with a time varying LV compliance was adopted and implemented. The numerical model draws an analogy to the systemic cardiovascular system, as an electrical circuit for MCL parameter estimation, and consistency investigation of the developed beating LV simulator’s experimental results. The numerical results were obtained for two cases. These were, healthy human resting operating cardiovascular conditions and the parameters of the numerical model were adjusted for the beating LV simulator’s experimental setup. The results of the prototyped beating LV simulator experiments showed that the goal of achieving realistic LV cardiac mechanics is possible. 50, 60, and 70 beats per minute cardiac cycles were generated in the experiment and an average flow rate of 2 liters per minute was obtained. The stroke volume of the beating LV simulator was 33.3 ml with an ejection fraction of 28.2% and the twist angle of the apex was measured as 21 degrees in cyclic loading. Additionally, the static loading experiment results were compared with the FEA model results and the comparison showed that the results are correlated.



Mock circulation loops (MCL), Mock circulatory systems (MCS), Interpretive structural modeling (ISM), Pneumatic artificial muscles (PAM), Artificial muscles, Left ventricular simulator