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Cardiovascular Engineering

Cardiovascular Engineering - Poster Session A

Poster H13 - Design and Fabrication of a Pulse Duplicator Capable of Replicating the TAVR Procedure

Thursday, October 24, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Human heart valves ensure unidirectional movement of blood flow. Various diseases affecting heart valves are common, especially in older populations. The most effective treatment is often an artificial heart valve, inserted either by open-heart surgery or a catheter-based procedure. Since the invention of the artificial heart valve in the 1950s, the design has seen many improvements. These improvements and customizations continue today, addressing anatomical variation, material hypersensitivity, and unique pathology. Novel heart valve designs are still needed to address such issues. These new valve designs must undergo thorough in vitro testing before clinical trials, highlighting the need for novel testing platforms.

Pulse duplicators replicate the pressure and flow conditions within the cardiovascular system, including the cardiac cycle, resistance and compliance of the blood vessels, and body temperature, among others. Commercial pulse duplicators exist with a variety of features. However, market devices are often both cost-prohibitive and missing essential features, such as the ability to simulate valve placement procedures, or bio-reactor elements needed for cell-laden models. In this study, we designed and constructed a novel pulse duplicator as a testing platform for our three-dimensional (3D)-bioprinted heart valve models. We used ISO-5840 to comply with international standards for pulse duplicator design. Importantly, our testing platform has the capability of simulating the transcatheter aortic valve replacement (TAVR) in vitro.

Materials and

Methods:  We used Solidworks software to model the left atrium and ventricle of the heart, including pulmonary and aortic openings. The model was 3D-printed using flexible 80A resin (3DMaterials, Warren, NJ) and an Anycubic Photon Mono M5s Pro liquid-crystal display (LCD) 3D printer (AnyCubic, Shenzhen, China). 1-inch diameter polyvinyl chloride (PVC) tubing was attached to the 3D-printed heart structure model, representing blood vessels. Plastic connectors branched the tubing to model arteries, needed for the TAVR procedure. This circuit of tubing was filled with phosphate-buffered saline (PBS) as a blood substitute. A container was added to the tubing circuit and partially filled with PBS, simulating compliance of blood vessels under pressure. Pressure sensors (NXP USA Inc, Eindhoven, Netherlands) and flow rate sensors (DIGITEN, Shenzhen, China) were added to measure hydrodynamic parameters.

Sheets of thermoplastic polyurethane (TPU) were vacuum molded, creating inflatable plastic pockets. These pockets were held around the heart structure using a 3D-printed rigid casing. 0.125-inch diameter tubing attached these pockets to a source of pressurized air, through 3 solenoid valves (Clippard, Cincinnati, OH) (Figure 1). A Raspberry Pi (GeeekPi, Pencoed, Wales) controlled these valves (Figure 2), pneumatically pressurizing the heart structure using custom Python code. Pressure and flow rate sensors were wired to the same system. 25mm aortic and mitral artificial heart valves (Abbot, North Plymouth, MN) were inserted via a catheter (Abbot, North Plymouth, MN) and expanded once in anatomically correct positions. The cyclic contraction was adjusted to produce pressures, flow rate, and heart rate in accordance with ISO-5840.

Results, Conclusions, and Discussions: Results
In this work, we created a unique pulse duplicator compliant with ISO-5840 and capable of replicating the TAVR procedure. We employed commercial valves with known hydrodynamic properties to evaluate the accuracy of our pulse duplicator system. Using the Raspberry Pi, we controlled the pressure measured in the artery at systole and diastole. These numbers depend on the effectiveness of the artificial heart valves and the amount of pneumatic pressure applied to the heart structure. Based on ISO-5840, the diastole/systole pressure was adjusted as low as 60/40 mmHg, simulating hypotension, and as high as 210/120 mmHg, simulating severe hypertension. The Raspberry Pi controller also adjusted the heart rate between the required 30-200 bpm.

We measured the cardiac output via flow meters. When using the commercial heart valves, a cardiac output of 3-5 L.min-1 was observed. Measurements were taken 30 times per second to account for changes in flow rate over a cardiac cycle. The flow rate sensor measured heart valve regurgitation when placed between the ventricle and the artificial heart valve. Effective orifice area (EOA) was derived from flow and pressure data, and the blood substitute density. Our work consistently measured an EOA of over 1.45 cm^2 for effective heart valves. While providing all necessary features, the cost of constructing this testing platform was in the range of $1,000-1,200.

Conclusion
We presented the design and development of a cost-effective pulse duplicator system capable of testing the hydrodynamics of novel artificial heart valve designs, and replicating the TAVR procedure. We demonstrate that all relevant factors were measured accurately, and in compliance with ISO-5840.

Discussion
The design created in this work simulated heart contraction using pneumatics and inflatable pockets, similar to the work described by Goswami et al. (2023). However, our work concerned testing heart valve models by evaluating their performance in the TAVR procedure and quantifying the associated hydrodynamic parameters. Additionally, we replaced the fabric covering used by Goswami with a 3D-printed case, which significantly improved the robustness of our testing platform. We also positioned our endoscopic camera inside the ventricle structure, to avoid obstructing flow in modeled blood vessels.

Acknowledgements (Optional):