System of automated gas-exchange analysis for the investigation of metabolic processes

Abstract

Conventional gas-exchange instruments are confined to the measurement of O2 consumption (V˙o 2) and CO2 production (V˙co 2) and are subject to a variety of errors. This handicaps the performance of these devices at inspired O2 fraction (Fi O2 ) > 0.40 and limits their applicability to indirect calorimetry only. We describe a device based on the automation of the Douglas bag technique that is capable of making continuous gas-exchange measurements of multiple species over a broad range of experimental conditions. This system is validated by using a quantitative methanol-burning lung model modified to provide reproducible 13CO2production. The average error for V˙o 2 andV˙co 2 over the Fi O2 range of 0.21–0.8. is 2.4 and 0.8%, respectively. The instrument is capable of determining the differential atom% volume of known references of13CO2 to within 3.4%. This device reduces the sources of error that thwart other instruments at Fi O2 > 0.40 and demonstrates the capacity to explore other expressions of metabolic activity in exhaled gases related to the excretion of 13CO2.