Adaptation of the NDIR technology to¹³CO₂breath tests under increased inspiratory O₂concentrations

Abstract

Nondispersive infrared spectroscopy (NDIR) allows the continuous analysis of respiratory gases. Due to its high selectivity, simple and robust setup, and small footprint, it is also used to support13CO2breath tests to assess bacterial growth in the stomach, gut, or liver function. CO2NDIR signals, however, are biased by oxygen in the gas matrix. This complicates NDIR-based breath tests, if the inspired oxygen concentration has to be adjusted to the subject's requirements, or hyperoxia-induced effects were studied. To avoid the oxygen-induced bias, a “dilution” approach was developed: expired gas is mixed with N2to lower the oxygen content down to the usual range of 15–20%. Accuracy and precision were tested using synthetic gas mixtures with increasing13CO2-to-12CO2ratios (13CO2/12CO2), either based on synthetic air with ∼20% volume O2or on pure O2. For samples with δ13C values smaller than 300 (or13CO2/12CO2smaller than 0.003), the dilution does not significantly increase the bias in the13CO2/12CO2determination, and the within-run imprecision is smaller than 1 δ13C. The practical use of this approach was validated in a pig study using a sepsis model reflecting a clinical situation that requires an increased oxygen concentration for respiration. The N2dilution eliminated the high bias in NDIR measurement, thus allowing the determination of the impact of oxygenation on glucose oxidation in patients ventilated with increased oxygen.

Breath Analysis with Broadly Tunable Quantum Cascade Lasers

“…This requirement limits applicability in intensive care scenarios, as patients are frequently hyperoxic due to ventilation. 26 Another alternative method in lieu of GC-MS measurements is laser-assisted ratio analysis (LARA), 27−29 which provides detection limits in the ppm range for isotope ratios; however, this method is also not suitable for online measurements.…”

“…While revealing sufficient sensitivity and accuracy for most applications, NDIRS usually requires large sample volumes (500–1000 mL) and low oxygen content resulting in collisional line broadening. This requirement limits applicability in intensive care scenarios, as patients are frequently hyperoxic due to ventilation …”

Measurement of CO2 Isotopologue Ratios Using a Hollow Waveguide-Based Mid-Infrared Dispersion Spectrometer

“…C arbon and oxygen isotope analysis of carbon dioxide (CO 2 ) is widely used in geochemistry, atmospheric chemistry, and medical diagnostics. 1−4 In geochemistry, quantification of 13 C/ 12 C isotope ratios in volcanic CO 2 gas is helpful for understanding changes in source regions and volcanic activity monitoring. Measurement accuracy of δ 13 C with 0.5‰ or better is important for a deeper understanding of volcanic system formation.…”

“…Measurement accuracy of δ 13 C with 0.5‰ or better is important for a deeper understanding of volcanic system formation. 5 In atmospheric chemistry, 13 C and 18 O serve as tracers that can accurately track and predict changes in CO 2 concentrations to determine the distribution of carbon sources and sinks in nature. 6 Precision in the range of 0.01 to 0.3‰ is of interest in atmospheric chemistry.…”

“…In the medical field, as established molecular biomarkers, changes in the contents of 13 CO 2 , 18 O 12 C 16 O, and 12 CO 2 in exhaled breath can be used to monitor multiple disease patterns, such as the diagnosis of Helicobacter pylori infections and noninvasive monitoring of glucose metabolism. 7,8 In the 13 C-urea breath test, the delta over baseline value relative to standards can be used to demonstrate the enrichment of 13 C. 9 18 O isotope analysis in breath gas can also be used to assist in the diagnosis of Helicobacter pylori pathogenesis. 10 A short-term precision of 0.5−1‰ for δ 13 C and δ 18 O determination is usually required for practical clinical applications.…”