A MODIFIED REBREATHING TECHNIQUE USING AN INFRARED GAS ANALYZER

To lower the cost and improve accessibility of the rebreathing techniq ue for measuring cardiopulmonary function during exercise, we implemen ted a fast-response infrared (IR) gas-analyzer system to simultaneousl y measure lung diffusing capacity, cardiac output, lung tissue volume, and lung volume by a rebreathing technique in five healthy subjects a t rest and during steady-state exercise. Interferences by water vapor and CO2 on the analyzer were determined and corrected for. During rebr eathing, a gas mixture of 0.4% C2H2-0.3% CH4-9% He-30% O-2, and either 0.3% (CO)-O-18 or 0.3% (CO)-O-16 in a balance of N-2 was simultaneous ly sampled by both a mass spectrometer and the IR analyzer, permitting paired comparisons. Measurements obtained by the two devices were not significantly different. We conclude that this modified rebreathing t echnique using the IR analyzer is accurate for the measurement of card iopulmonary function at rest and during exercise.