A<unk>  can be performed with a single<unk>  breath, or multiple ones. Both tests use similar tools, both can estimate functional residual capacity and the degree of nonuniformity of gas distribution in the lungs, but the multiple-breath test more accurately measures absolute lung volumes. The following describes a single-breath<unk>  test: A subject takes a breath of 100% oxygen and exhales through a one-way valve measuring<unk>  content and volume. A plot of the<unk>  concentration (as a % of total gas) vs. expired volume is obtained by increasing the<unk>  concentration from zero to the percentage of<unk>  in the alveoli. The<unk>  concentration is initially zero because the subject is exhaling the dead space oxygen they just breathed in (does not participate in alveolar exchange), and climbs as alveolar air mixes with the dead space air. The dead space can be determined from this curve by drawing a vertical line down the curve such that the areas below the curve (left of the line) and above the curve (right of the line) are equal. Most people with a normal distribution of airways resistances will reduce their expired end-tidal<unk>  concentrations to less than 2.5% within seven minutes. Individuals with high resistance in their airways can take longer than seven minutes to remove all the<unk> .
Nitrogen washout
Alveolar gas equation
Multiple inert gas elimination technique
Oxygen enhancement ratio
Post bronchodilator test
PAH clearance
Surfactant–albumin ratio
Gas exchange