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CO 2 -scrubbing, zero gases, Keeling plots, and a new mathematical approach to ameliorate the deleterious effects of ambient CO 2 during 13 C-breath testing in humans and animals
  • Marshall McCue
Marshall McCue
Sable Systems International

Corresponding Author:[email protected]

Author Profile


13C-Breath testing is increasingly used in physiology and ecology research because of what it reveals about the different fuels that animals oxidize to meet their energetic demands. Here we review the practice of 13C-breath testing in humans and other animals and describe the impact that contamination that ambient/background CO 2 in the air can have on the accuracy of 13C-breath measurements. We briefly discuss physical methods to avoid sample contamination as well as the Keeling plot approach that researchers have been using for the past two decades to estimate δ 13C from breath samples mixed with ambient CO 2. Unfortunately, Keeling plots are not suited for 13C breath testing in common situations where 1) a subject’s VCO 2 is dynamic 2) ambient [CO 2] may change, 3) a subject is sensitive to hypercapnia, or 4) in any flow-through indirect calorimetry system. As such, we present a mathematical solution that addresses these issues by using information about the instantaneous [CO 2] and the δ 13CO 2 of ambient air as well as the diluted breath sample to back-calculate the δ 13CO 2 in the CO 2 exhaled by the animal. We validate this approach by titrating a sample of 13C-enriched gas into an air stream and demonstrate its ability to provide accurate values across a wide range of breath and air mixtures. Researchers can now instantaneously calculate the δ 13C of alveolar gas of humans or animals in real time without having to scrub ambient CO 2 or rely on estimated values.
22 May 2023Submitted to Rapid Communications in Mass Spectrometry
22 May 2023Submission Checks Completed
22 May 2023Assigned to Editor
22 May 2023Review(s) Completed, Editorial Evaluation Pending
24 May 2023Reviewer(s) Assigned
12 Jul 2023Editorial Decision: Revise Major
17 Jul 20231st Revision Received
18 Jul 2023Submission Checks Completed
18 Jul 2023Assigned to Editor
18 Jul 2023Review(s) Completed, Editorial Evaluation Pending
26 Jul 2023Reviewer(s) Assigned
26 Aug 2023Editorial Decision: Accept