Medicinal cardio-pulmonary test gases (also called medicinal lung function test gases) are used for in-vivo diagnostic testing to measure either alveolar diffusion capacity in the lung (pulmonary function with CO as the investigative compound) or lung blood flow to give cardiac output (cardiopulmonary function with C2H2 or CO2 as the investigative compound).
The medicinal lung function test gases, which are inhaled, consist of gas mixtures containing a tracer gas. The exhaled gas is analyzed and differences in the concentration of the tracer gas can be used to diagnose different lung diseases.