The validity and reliability of a novel isotope ratio infrared spectrometer to quantify 13C enrichment of expired breath samples in exercise

Abstract

Rationale: The traditional method to measure 13CO2 enrichment in breath involves isotope ratio mass spectrometry (IRMS) and has several limitations such as cost, extensive training and large space requirements. Here we present the validity and reliability data of an isotope ratio infrared spectrometer (IRIS) based method developed to combat these limitations. Methods: Eight healthy male runners performed 105 min of continuous running on a motorised treadmill while ingesting various carbohydrate beverages enriched with 13C and expired breath samples obtained every 15 min in triplicate. A total of 213 breath samples were analysed using both methods, while 212 samples were repeated using IRIS to determine test-retest reliability. Bland-Altman analysis was performed to determine systematic and proportional bias, and intraclass correlation coefficient (ICC) and coefficient of variation (CV) to assess level of agreement and magnitude of error. Results: The IRIS method demonstrated a small but significant systematic bias to overestimate δ13CO2 (0.18‰; p < 0.05) compared with IRMS, without any proportional bias or heteroscedasticity and a small CV% (0.5%). There was a small systematic bias during the test-retest of the IRIS method (-0.07‰; p < 0.05), no proportional bias, an excellent ICC (1.00) and small CV% (0.4%). Conclusions. The use of the Delta Ray IRIS to determine 13C enrichment in expired breath samples captured during exercise has excellent validity and reliability when compared with the gold standard IRMS.