Abstract

A method for the collection and measurement of low-molecular-weight volatile hydrocarbons exhaled in human breath as a result of lipid peroxidation in vivo is described. Subjects breathed in a closed-circuit rebreathe system and samples were taken over a 2-h period, extracted, and analyzed by gas-liquid chromatography isothermally on a 3-m column of n-octane/Porasil-C. Immediately, prior to rebreathing subjects were equilibrated with scrubbed air containing very low ambient levels of hydrocarbons to eliminate the effects of previous exposure to hydrocarbon-contaminated environments. Only under these conditions could hydrocarbon exhalation be measured. In the rebreathe system C3-C5 hydrocarbon concentrations increased linearly initially but reached a steady state after 1.5 h while ethane did not approach equilibrium even after 2 h. The steady-state equilibrium was demonstrated to be due to tissue uptake and metabolism of the hydrocarbon gases. Ethane metabolism was slow, allowing calculation of the endogenous production from the initial rate of change in concentration and an experimentally determined total body solubility coefficient. Similar calculations for pentane were not valid as metabolism was rapid; therefore production was estimated from the equilibrium value reached after 2 h. Ethane production in six healthy subjects was calculated to be 95.1 +/- 19.0 pmol/kg/h while equilibrium values for pentane were 120 +/- 50 pmol/liter. This method now allows the quantitation in man of lipid peroxidation in vivo.