The present invention relates to an assay for evaluating alveolar exchange of
oxygen. A 13C-labeled substrate, such as 13C-sodium bicarbonate
is administered to a subject by oral or iv intake, and exhaled 13CO2
is measured. The 13CO2 in expired breath can be collected
at various time points following administration of the substrate and measured in
per mil with a mass analyzer or photometer, such as an IR spectrometer.
This process can be used as a diagnostic test for the indication of, treatment
and/or evaluation of the severity of respiratory tract diseases or infections.
