A system including a first sampling portion configured to sample inhalation gas made up of a first gaseous mixture, a second sampling portion configured to sample exhalation gas made up of a second gaseous mixture, a gas analyzer configured to measure gas concentrations, a switching valve that controls flow of the sampled inhalation gas and the sampled exhalation gas to the gas analyzer so as to alternately measure concentration of gaseous components within the first and second gaseous mixtures, a humidity control system that maintains humidity within the first and second gaseous mixtures to a predetermined humidity level, and a calculation section configured to calculate concentration differences of the gaseous components between the first and second gaseous mixtures.
