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Development of an implantable blood flow and pressure monitor for pulmonary hypertension : new finite element modelling based conductance catheter techniques for measuring blood flow

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Locke, Simon Ellis (2007) Development of an implantable blood flow and pressure monitor for pulmonary hypertension : new finite element modelling based conductance catheter techniques for measuring blood flow. PhD thesis, University of Tasmania.

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Abstract

Pulmonary hypertension patients could greatly benefit from use of an implantable
blood flow and pressure monitor that can be used to derive pulmonary resistance.
This thesis concentrates on the development of a suitable implantable sensor for
measuring flow. Various methods for measuring flow are assessed. Conductance
catheter techniques are proposed as some of the most promising, but suffer from
limited accuracy. The main chapters of the thesis concentrate on the development of
more accurate conductance catheter techniques. Realistic three-dimensional dynamic
models of the heart, developed from MRI and tagged MRI scans, were used with
finite element analysis to simulate the electric field arising from the conductance
catheter in the heart. Results show that catheter movement and tissue impedance
changes give non-negligible error using existing methods for calculating volume
from impedance measurements. A new method for calculating volume from
impedance measurements was developed that corrects for these and other errors. The
new method finds the inverse mapping of a parameterised numerical model. It also
allows use of additional data available from the conductance catheter technique,
including data from different current source configurations and frequencies. The new
technique was tested in a simplified model of the heart. Derivatives of the catheter
measurements with respect to the model parameters were determined at one
parameter configuration and formed into vectors. Derivative angles were then found
between the vectors, providing a method for assessing the separability of the
different model parameters. In addition they did not require creation of the inverse
mapping. Two different types of techniques for creating the inverse mapping were
tested. These were a new technique based on a distance metric and optimisation, and
traditional artificial intelligence techniques. Even in the presence of no measurement
error, limitations of traditional artificial intelligence techniques prevented successful
application. The new technique performed to the order of accuracy of the numerical
model on the same amount of data the traditional artificial intelligence techniques
were trained on. The new technique was further developed to compensate for
measurement error, and resulted in a further increase in accuracy. This thesis has
developed and tested new conductance catheter methods, and has moved us a step
closer to enabling practical development of an implantable blood flow and pressure
monitor.

Item Type: Thesis (PhD)
Keywords: Blood flow, Blood pressure, Pulmonary hypertension
Copyright Holders: The Author
Copyright Information:

Copyright 2007 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2007. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:58
Last Modified: 17 Jul 2017 06:13
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