Schoeller D A, Klein P D, Watkins J B, Heim T, MacLean W C
Am J Clin Nutr. 1980 Nov;33(11):2375-85. doi: 10.1093/ajcn/33.11.2375.
Unlike 14CO2 breath tests, 13CO2 breath tests are performed in the presence of a large background of naturally occurring isotope. Because the exact abundance of 13CO2 in breath can be changed by variations in diet, a study of the 13C abundance of dietary constituents and their effects on breath 13CO2 has been undertaken. Dietary constituents have been combusted to CO2 and the relative abundance of 13C analyzed by mass spectrometry. Breath CO2 was collected and isotopically analyzed after the ingestion of several dietary constituents and test meals. The 13CO2 abundance of breath CO2 was shown to change in response to the 13C abundance of the substrate being oxidized. Conversely, a test meal that closely approximates the 13C abundance of fasting breath CO2 from North Americans was shown not to alter the 13CO2 abundance in breath. Investigation of the breath 13CO2 response to individual 13C-labeled dietary constituents demonstrated that amino acids produced the earliest 13CO2 response followed in order by medium chain triglycerides, carbohydrates, and long chain triglycerides. Because of the variation in 13C abundances in nature, the 13C abundance of any unlabeled substrate ingested during a 13CO2 breath test must be considered in order to eliminate artifacts that may reduce the sensitivity of the breath test or produce erroneous results. Methods for correcting breath tests for changes in background 13CO2 abundance are also discussed.
与¹⁴CO₂呼气试验不同，¹³CO₂呼气试验是在大量天然存在的同位素背景下进行的。由于饮食变化会改变呼出气体中¹³CO₂的确切丰度，因此开展了一项关于饮食成分的¹³C丰度及其对呼出气体¹³CO₂影响的研究。将饮食成分燃烧生成CO₂，并通过质谱分析¹³C的相对丰度。在摄入几种饮食成分和测试餐之后，收集呼出气体中的CO₂并进行同位素分析。结果表明，呼出气体中¹³CO₂的丰度会随着被氧化底物的¹³C丰度变化而改变。相反，一种与北美人群空腹呼出气体CO₂的¹³C丰度非常接近的测试餐，并未改变呼出气体中¹³CO₂的丰度。对呼出气体¹³CO₂对单个¹³C标记饮食成分的反应进行研究表明，氨基酸产生的¹³CO₂反应最早，其次依次是中链甘油三酯、碳水化合物和长链甘油三酯。由于自然界中¹³C丰度存在差异，因此在¹³CO₂呼气试验期间，必须考虑摄入的任何未标记底物的¹³C丰度，以消除可能降低呼气试验灵敏度或产生错误结果的假象。本文还讨论了针对背景¹³CO₂丰度变化校正呼气试验的方法。
