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\begin{document}

\title{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}



\author[1]{Marshall McCue}%
\affil[1]{Sable Systems International}%


\vspace{-1em}



  
  \date{May 22, 2024}


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\selectlanguage{english}
\begin{abstract}
\textsuperscript{13}C-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 \textsuperscript{13}C-breath testing in humans
and other animals and describe the impact that contamination that
ambient/background CO \textsubscript{2} in the air can have on the
accuracy of \textsuperscript{13}C-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 \selectlanguage{greek}δ \selectlanguage{english}\textsuperscript{13}C from breath samples mixed
with ambient CO \textsubscript{2}. Unfortunately, Keeling plots are not
suited for \textsuperscript{13}C breath testing in common situations
where 1) a subject's VCO \textsubscript{2} is dynamic 2) ambient {[}CO
\textsubscript{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 \textsubscript{2}{]} and
the \selectlanguage{greek}δ \selectlanguage{english}\textsuperscript{13}CO \textsubscript{2} of ambient air as well as
the diluted breath sample to back-calculate the \selectlanguage{greek}δ \selectlanguage{english}\textsuperscript{13}CO
\textsubscript{2} in the CO \textsubscript{2} exhaled by the animal. We
validate this approach by titrating a sample of
\textsuperscript{13}C-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 \selectlanguage{greek}δ
\selectlanguage{english}\textsuperscript{13}C of alveolar gas of humans or animals in real time
without having to scrub ambient CO \textsubscript{2} or rely on
estimated values.%
\end{abstract}%



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\textbf{Hosted file}

\verb`Atmospheric CO2 dilution Manuscript-bow.docx`  available at \url{https://authorea.com/users/621168/articles/644848-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}\selectlanguage{english}
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\end{figure}\selectlanguage{english}
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\end{figure}\selectlanguage{english}
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\includegraphics[width=0.70\columnwidth]{figures/Figure-3/Figure-3}

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\end{figure}\selectlanguage{english}
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\end{figure}

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