Precision measurement of carbon isotope ratio in exhaled breath for the detection of helicobacter pylori
University of Southampton, School of Electronics and Computer Science,
The utility of breath trace compounds as bio-markers for various physiological conditions has long been exploited for the diagnosis of various diseases. Urea breath tests have been adopted as the gold standard for the detection of Helicobacter pylori which is a primary cause for acute gastritis and peptic ulcers. In these tests, small changes in the ratio of stable CO2 isotopomers, 13CO2 and 12CO2, present in exhaled breath
are measured precisely and this is conventionally done by using an Isotope Ratio Mass Spectrometer. However, the huge cost and complexity involved in operating these instruments has restricted their widespread use. A viable and low cost alternative is offered by instruments employing non-dispersive infrared absorption techniques. The feasibility of such an instrument has been explored in this work.
The instrument presented here is a two channel isotope ratiometer that performs whole band integrated absorption measurements. Detection is based on a novel feedback mech-
anism whereby an imbalance in the channel absorptions causes the pathlength along one of the channels to be altered in order to bring the system back to balance. This change in ratio of pathlengths is directly related to the change in the 13CO2/12CO2 concentration. Signffcant amount of work has already been done to investigate the effects of interferences from coincident absorption bands and other spectral effects that can lead to spurious results.
A comprehensive description of the overall system design, development and performance evaluation of the first prototype instrument has been presented here. This involved significant computer modeling and simulations and the results were verified experimentally. These results provided sufficient evidence to suggest the feasibility of such an instrument
as a diagnostic tool. It was also concluded that some design improvements were required to circumvent issues related to pathlength variation and a list of recommendations has
been provided for this purpose. On the basis of the results obtained as part of this research endeavour, it was concluded that the non-dispersive instrument design presented here can form the basis for a low cost commercial alternative for performing carbon isotope ratio breath tests.
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