Modeling-based determination of physiological parameters of systemic   VOCs by breath gas analysis: a pilot study
  In this paper we develop a simple two compartment model which extends the Farhi equation to the case when the inhaled concentration of a volatile organic compound (VOC) is not zero. The model connects the exhaled breath concentration of systemic VOCs with physiological parameters such as endogenous production rates and metabolic rates. Its validity is tested with data obtained for isoprene and inhaled deuterated isoprene-D5. 
Karl Unterkofler, Julian King, Pawel Mochalski, Martin Jandacka, Helin   Koc, Susanne Teschl, Anton Amann, and Gerald Teschl
q-bio.QM