Date on Master's Thesis/Doctoral Dissertation

7-2013

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Bioengineering

Committee Chair

Koenig, Steven Christopher

Author's Keywords

Ex vivo perfusion; Vessel perfusion; Physiologic perfusion; Mock circulation; Pulsatile flow; Carotid artery

Subject

Heart valve prosthesis; Heart valves

Abstract

Introduction: Over time, continuous flow ventricular assist devices (VADs) have become the primary form of implanted mechanical circulatory support (MCS) due to their smaller size, higher energy efficiency, longer durability, and fewer LVAD-related complications when compared to pulsatile flow VADs. However, continuous and pulsatile flows may elicit different cellular and tissue response, particularly in the arterial vasculature, which could have a profound impact on the future operation of MCS devices. Therefore, a unique ex vivo perfusion system integrated with a mock adult circulatory system was design to study the impact of VAD-generated flow patterns on vascular function. Methods: The benefits of a mock circulatory loop and an ex vivo perfusion system were combined by designing and integrating a vessel perfusion chamber to an adult-sized mock circulatory loop as a parallel flow branch distal to VAD outflow. Testing was conducted using a mock over several physiologic conditions (normal, heart failure, and hypertension) and at various levels of VAD flow. The system was integrated into an incubator to allow for control of pH and temperature in future studies and fitted with a vessel for feasibility testing. Data was collected using a custom Labview program and analyzed using the HEART program, an automated beat-to-beat cardiovascular analysis program based in Matlab. Results: The chamber was successfully fabricated and installed in the mock circulatory system, allowing for perfusion and longitudinal stretching of bovine carotid arteries. The waveforms and values for pressures and flows created in the mock loop were similar to physiologic values under each tested condition. Under normal hemodynamic conditions (CO = 4.5 L/min, MAP = 91 mmHg) perfusion chamber flow was 0.51 L/min, while under HF conditions (CO = 3.3 L/min, MAP = 81 mmHg) it was reduced to 0.18 L/min, which are representative of in vivo carotid artery hemodynamics. Due to physiologic preloads and afterloads, VAD performance was as would be expected in clinical application. The system was found to be sufficient for future testing with bovine carotid arteries and extended perfusion times (>24 hours). Conclusions: This study resulted in an ex vivo vessel perfusion system that can successfully expose bovine carotid arteries to physiologic and VAD-specific hemodynamic waveforms. The ability to combine the mock ventricle with clinically implanted VADs makes this system both unique and clinically relevant for studying the effects of continuous versus pulsatile flow on the peripheral vasculature.

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