Thoracic electrical impedance model: Investigation into the contribution of ventricular blood volume to the impedance cardiogram.

Mohammad Akhand (2011). Thoracic electrical impedance model: Investigation into the contribution of ventricular blood volume to the impedance cardiogram. MPhil Thesis, School of Information Technol and Elec Engineering, The University of Queensland.

       
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Author Mohammad Akhand
Thesis Title Thoracic electrical impedance model: Investigation into the contribution of ventricular blood volume to the impedance cardiogram.
School, Centre or Institute School of Information Technol and Elec Engineering
Institution The University of Queensland
Publication date 2011-06
Thesis type MPhil Thesis
Supervisor Prof Stuart Crozier
A/P Stephen Wilson
Dr Feng Liu
Total pages 110
Total black and white pages 110
Language eng
Subjects 08 Information and Computing Sciences
Abstract/Summary Quantification of cardiac output (CO) is an important measure in the assessment and management of heart failure. This measure, derived from ventricular Stroke Volume (SV) can be achieved through modern imaging technologies or invasive catheter studies, but neither approach is suitable for safe, long-term monitoring or repeated observations. The non-invasive technique based on Thoracic Electrical Bioimpedance (TEB) provides long-term beat-to-beat measurement of SV through measurement of the electrical impedance changes across the torso when a minute alternating current is applied. Despite its relative safety and benign nature, it is still considered inaccurate and thereby not generally accepted as a clinical tool. This overall project intends to improve the accuracy and reliability of the TEB method. A key part of this study produced an expedited construction method for an electrically accurate thorax model. The dominant contributors and their contributions to the pulsatile thoracic impedance were also investigated. The thorax models were constructed with different subsets of thoracic tissue types. The TEB forward problem was solved in each model to identify the subset of tissue types that produced the minimum error in voltage potential calculation. The contributions of ventricular blood volume change (VBVC) and flow induced blood conductivity change (FIBCC) to the pulsatile thoracic impedance were calculated. Short axis cardiac MR images were used to construct the ventricular heart models. Thus, for each case 20 different models were constructed at 20 epochs over a cardiac cycle. Time-harmonic voltage simulations were performed to calculate the voltage potential difference due to FIBCC, VBVC and FIBCC-VBVC . The voltage difference at each epoch was expressed as a percentage of that at the first epoch. The Electrical accuracy of the virtual thorax model can be preserved by constructing the model only from a subset of thoracic tissue types of blood, fat, liver, lung, muscle, skin and internal air. This introduces about 5-8% error in the voltage potential calculation, but significantly speeds calculations. The VBVC and the FIBCC contribute to the measured voltage potential change between the electrodes by a maximum of about 2.4% and 0.28% respectively. When considered simultaneously, they contribute to the measured voltage potential change between the electrodes by a maximum of about 0.6%. The FIBCC negates about 75% of contribution from the VBVC measured at the end systole of a cardiac cycle. Thus, the FIBCC cast significant influence on the pulsatile thoracic impedance resulting from the VBVC. The expedited construction method of a thorax model will facilitate the investigation of the TEB method accuracy with a large number of individuals. It will reveal the population variability of the TEB derived SV estimate. The investigation into the contributions of ventricular blood volume change and flow induced blood conductivity change will help understand the biological origin of the pulsatile thoracic impedance in a greater detail. It will also contribute to the correction of the thoracic impedance wave form. Thus, it is hoped that the study will contribute towards the improvement of the accuracy and reliability of the TEB method.
Keyword thoracic model
teb
pulsatile thoracic impedance
stroke volume

 
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Created: Fri, 09 Dec 2011, 10:43:25 EST by Mr Mohammad Akhand on behalf of Library - Information Access Service