Theoretical And Experimental Study Of The Variation Of Cmrr Due To Variations Of Patient Cables In Electrocardiographs  

Abstract Category: Engineering
Course / Degree: Bachelor's degree
Institution / University: Campus Bio-Medico di Roma, Italy
Published in: 2008

Thesis Abstract / Summary:

The electrocardiogram is undoubtedly the most popular examination for its high content of pathophysiological information, simplicity, bloodlessly, safety and for economical reasons. This analysis has a great diagnostic importance, so very close constraints are imposed to the quality of the electronic signal. Among the electronic features of an electrocardiographs (ECG) an important aspect is the amplifier CMRR. The first stage of the signal amplifier in an ECG should give a high value of CMRR, to enhance the amplification of a differential mode, which contains the biological information, compared to the signal of common mode, that conveys interferences. Through the development of the mathematical model that expresses the relationship between the CMRR and the resistive variations of patient cable, was demonstrated the influence of the imbalance of input resistances on the preamplifier stage. The circuit architecture used for validation in the real, of the results obtained by the mathematical model, is made of the variable resistances that produces patient cable imbalance, a cabled amplifier, and filters. Such a circuit has been built both in the breadboard and on the matrix and tested in both cases. The behavior of the circuit, in the frequency range of interest, was tested in simulation with an electronic circuit simulator.
From the results of the study became evident that the CMRR is a function of the unbalance of input resistances, so of the patient cable, and is a function of frequency. The study of the mathematical model has led to detect the peak values of CMRR higher than the CMRR owned by the amplifier stage, so the performance of the model improves on a set of values of imbalance resistors. The definition of these values of interest is defined by the following parameters: variation of resistance, variation of CMRR, value of frequency. The circuit testing will produce charts from which it emerges that the change in resistance produces an increase of CMRR over a frequency range that decreases with the growing of imbalance. This reduction encroacheds on the higher frequencies in the analysis range, while preserving the low frequencies. There is also a value of imbalance that has a maximum value of CMRR. Increasing imbalance in excess of the said value get a reduction of CMRR is obtained up to a value less than what is obtained from the circuit without imbalance. Finally, here is the comparison between the differential and common mode amplifier measured both in the study simulation and in the experimental study.

Thesis Keywords/Search Tags:
electrocardiograph, CMRR; ECG, patient cable, variation of resistance

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Submission Details: Thesis Abstract submitted by Cristina Zappullo from United Kingdom on 09-Jan-2015 00:23.
Abstract has been viewed 2061 times (since 7 Mar 2010).

Cristina Zappullo Contact Details: Email: cristina.zap@libero.it Phone: +393381929546

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