A new flexible automated system for the study of exhaled gases

Expired gas analysis has been largely relegated to the measurement of VO2 and VCO2 by a variety of methods. We designed and built a new flexible automated expired gas analysis instrument, the Volume Accumulating Metabolic Monitor (VAMM), capable of simultaneous and continuous quantitative expired gas analysis for a multiplicity of gas species. All expired gas is collected into one of two twin reservoirs. This approach allows analysis of one reservoir while collection occurs into the other. The instrument mixes the expired gas and determines the volume of the desired gas species using a combination of indicator gas dilution and mass spectrometry. We tested the VAMM's ability to measure the 13CO2 2-hr collection after intravenous 13C-aminopyrine. Aminopyrine is metabolized to CO2. Ten healthy volunteers underwent expired gas collection and analysis for 140 min. All studies were performed in the recumbent posture after an 8 hr fast. The initial 20 min were used to establish a baseline 13CO2 production. Following the injection of 2 mg/kg 13C-aminopyrine, expired gas was collected for an additional 120 min. The mean 2-hr 13CO2 enrichment was 7.1 ?2.9 ml (range 3.5 ml to 13.2 ml). This represented a percent collection of 26.8 ?9.1 (range 16.5 to 48.6). Peak excretion occurred at 84.9 ?17.5 min (range 50 min to 108 min). The VAMM provided significantly better 13CO2 excretion profiles than previously described. This technology can easily be customized to study not only other similar metabolic processes but also other gas excretions.