Helium Dilution Method
From WikiLectures
It allows the determination of the functional residual capacity of the lungs (the volume of air that the lungs contain after normal expiration).
Procedure[edit | edit source]
After normal exhalation, the examinee begins to breathe in a closed circuit with a mixture of oxygen and a known amount of helium. We measure the concentration of helium that remains in the device after the helium expands into the gas mixture in the lungs and a new equilibrium is established.
Mathematical relationships[edit | edit source]
Since the system is isolated from the environment, it is possible to calculate the functional residual capacity of the lungs according to the relationships:
- V2 = total gas volume in the system (FRC + gas volume in the device)
- V1 = volume of gas in the device
- C1 = initial (known) concentration of helium in the device
- C2 = final concentration of helium in the device after use by the subject