1. Preparation: The subject is seated comfortably and fitted with a nose clip and a mouthpiece connected to a spirometer. 2. Inhalation: The subject inhales a known concentration of an inert gas. 3. Equilibration: The gas is allowed to mix thoroughly within the lungs. 4. Measurement: The final concentration of the gas is measured after equilibration. 5. Calculation: The initial and final concentrations of the gas are used to calculate the lung volumes.
