What are the characteristics of a gas used in a diffusion capacity test?

In a diffusion capacity test, the gas utilized must be inert and insoluble to accurately assess the ability of the alveoli in the lungs to transfer gases between the air and blood. An inert gas does not chemically react with other substances, ensuring that the measurement reflects only the diffusion process, rather than any potential chemical interactions that could interfere with results.

Additionally, low solubility is crucial because it allows the gas to remain in the alveolar space and not be absorbed into the blood. This characteristic ensures that the test effectively measures the rate at which gas diffuses across the alveolar-capillary membrane without being affected by changes in solubility or reactivity, which could distort the evaluation of lung function.

In contrast, gases that are reactive or soluble could alter the outcome of the diffusion test by participating in chemical reactions or being absorbed into the bloodstream, thus not providing a true representation of the diffusion capacity of the lungs.