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.Comment: 16 page
