Tests that measure FRC include alung plethysmographor a helium dilution method.
Even though you exhale, air is still left in the lungs.
The volume of remaining air after a normal breath is called the FRC.
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As you breathe, youralveoli(tiny air sacs) always stay open.
This is due to a number of factors.
Surfactant, a sticky substance that lines the inside of your alveoli, helps keep them open.
The elasticity of the lungs also keeps your alveoli partially inflated.
Because your lungs remain partially open between breaths, it is easier for you to inhale.
Less elasticity means more trouble breathing.
Results can also help in the diagnosis of lung diseasespecifically when differentiating betweenrestrictive and obstructive lung disease.
As you breathe in and out, the air pressure inside the chamber is measured.
When you have a helium dilution test, you use a spirometer that contains helium.
Interpreting Your FRC Results
Normally, FRC values range between approximately 1800 ml to 2500 ml.
Major alterations in your FRC can indicate the presence or progression of lung disease.
Hopkins E, Sharma S.Physiology, Functional Residual Capacity.
In: StatPearls [Internet].
2005;26(3):511-522. doi:10.1183/09031936.05.00035005
Delgado BJ, Bajaj T.Physiology, Lung Capacity.
2019 Aug 1;117(4):230-236. doi:10.5546/aap.2019.eng.230.
J Phys Ther Sci.
2019 Jan;31(1):29-32. doi:10.1589/jpts.31.29.
Epub 2019 Jan 10.
