Adaptation of the NDIR technology to (CO2)-C-13 breath tests under increased inspiratory O-2 concentrations

作者：Vogt Josef A^*; Wachter Ulrich; Mehring Juergen; Radermacher Peter; Georgieff Michael; Fischer Heinz; Hoelscher Uvo; Moede Michael; Fabinski Walter

来源：Journal of Applied Physiology, 2009, 107(1): 302-307.

DOI：10.1152/japplphysiol.90913.2008

• breath test
• stable isotopes

Vogt JA, Wachter U, Mehring J, Radermacher P, Georgieff M, Fischer H, Holscher U, Moede M, Fabinski W. Adaptation of the NDIR technology to (CO2)-C-13 breath tests under increased inspiratory O-2 concentrations. J Appl Physiol 107: 302-307, 2009. First published May 14, 2009; doi:10.1152/japplphysiol.90913.2008.-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 support (CO2)-C-13 breath tests to assess bacterial growth in the stomach, gut, or liver function. CO2 NDIR 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 N-2 to lower the oxygen content down to the usual range of 15-20%. Accuracy and precision were tested using synthetic gas mixtures with increasing (CO2)-C-13-to-(CO2)-C-12 ratios ((CO2)-C-13/(CO2)-C-12), either based on synthetic air with similar to 20% volume O-2 or on pure O-2. For samples with delta C-13 values smaller than 300 (or (CO2)-C-13/(CO2)-C-12 smaller than 0.003), the dilution does not significantly increase the bias in the (CO2)-C-13/(CO2)-C-12 determination, and the within-run imprecision is smaller than 1 delta C-13. 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 N-2 dilution 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.

• 出版日期2009-7