A modified rebreathing technique using an infrared gas analyzer

To lower the cost and improve accessibility of the rebreathing technique for measuring cardiopulmonary function during exercise, we implemented a fast-response infrared (IR) gas-analyzer system to simultaneously measure lung diffusing capacity, cardiac output, lung tissue volume, and lung volume by a rebreathing technique in five healthy subjects at rest and during steady-state exercise. Interferences by water vapor and CO₂ on the analyzer were determined and corrected for. During rebreathing, a gas mixture of 0.4% C₂H₂-0.3% CH₄-9%. He-30% O₂, and either 0.3% C¹⁸O or 0.3% C¹⁶O in a balance of N₂ was simultaneously 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 technique using the IR analyzer is accurate for the measurement of cardiopulmonary function at rest and during exercise.