Development and characterisation of a hybrid mock circulatory loop with baroreceptor response

Abstract

In the UK alone, as of April 2020, 340 patients awaited a heart transplant, but only 172 transplants were available. Ventricular Assist Devices (VADs), which support the heart’s pumping function and serve as a bridge-to-transplant or permanent support for heart failure patients, offer a solution. The Mock Circulatory Loop (MCL) facilitates the design, development, and evaluation of VADs by simulating the native cardiovascular system (CVS). However, current MCLs often lack the capability to simulate critical pressure regulatory mechanisms, specifically the baroreflex response, which adjusts cardiac output and systemic resistance to maintain CVS pressure. This thesis seeks to enhance MCL design by incorporating the baroreflex response. A control system, based on the velocity and acceleration of a linear motor, was designed to regulate heart rate in the left ventricle simulator, achieving a range of 0 − 120𝑏𝑝𝑚. A physical automated resistor, capable of adjusting resistance within the physiological range of 9 − 20.0𝑚𝑚𝐻𝑔𝑚𝑖𝑛/𝐿, was introduced. Following this, a numerical model of the baroreflex response was integrated with the hydraulic setup. Testing of the enhanced MCL under three dynamic scenarios - clamping, volume addition, and volume reduction - revealed promising outcomes. During the clamping test, the MCL sustained pressure for the initial 15𝑠 post-clamping. In the volume reduction experiment, removing 2𝐿 of water led to a mere 6𝑚𝑚𝐻𝑔 drop in pressure, while adding 2𝐿 resulted in just a 3𝑚𝑚𝐻𝑔 increase. The developed MCL offers an enhanced platform to test VADs, from resistance shifts and pressure fluctuations to the baroreflex mechanisms. Research following from this thesis should focus on improving the left ventricle simulator to control cardiac contractility, further integrating it into the MCL.