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Abstract
An implantable rotary blood pump (IRBP) is a. heart assist device used to support end-stage heart failure patients, either as a bridge to transplant or permanent support. The aim of this dissertation is to investigate the interaction between an IRBP and the cardiovascular system (CVS) using carefully designed in vivo animal experiments and a mathematical model.
Using data obtained from a steady flow mock loop under a wide range of pump operating points and fluid viscosities, flow and differential pressure estimate models were obtained using dimensional analysis. Linear correlations between estimated and measured pump flow over a flow range of 0.5 to 8.0 L/min resulted in a slope of 0.98 (R2 = 0.985) and an average error of 0.20±0.14 L/min (mean±standard deviation). Similarly, linear correlations between estimated and measured pump differential pressure resulted in a slope of 1.03 (R2 = 0.997) over a pressure range of 60 to 180 mmHg, with an average error of l.84±1.54 mmHg. The pump model was then modified and validated under a pulsatile flow environment. The model was shown to be able to predict the time course of the simulated haemodynamic variables with reasonable accuracy.
Based on in vivo experimental data recorded in healthy pigs and dogs under a wide range of operating conditions, a lumped parameter model of heart-pump interaction was developed. Fitting of model parameters to the experimental measurements was performed to evaluate the robustness and validity of the mathematical model under the various operating conditions. It was shown from the simulation results that the model was able to reproduce the experimental data in terms of both mean values and steady state waveforms. The individual effect of key model parameters on the efficiency of rotary pump assistance was studied using variations in parameter values. Detailed discussion regarding the applicability of some of the control parameters proposed in the literature was also presented based on the experimental results and model simulations.
A deadbeat controller for the control of pulsatile pump flow in the IRBP was proposed, using noninvasive measurements of pump speed and current as inputs to a dynamical model of pulsatile flow estimation. The performance of the controller was evaluated using the mathematical model. The controller was shown to be able to respond quickly to sudden perturbations in the CVS and adjust pump flow accordingly to avoid dangerous or undesirable situations.