Functional Residual Capacity (FRC) is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration. At FRC, the elastic recoil forces of the lungs and chest wall are equal but opposite and there is no exertion by the diaphragm or other respiratory muscles.
FRC is the sum of Expiratory Reserve Volume (ERV) and Residual Volume (RV) and measures approximately 2400 ml in a 70 kg, average-sized male. It can not be estimated through spirometry, since it includes the residual volume. In order to measure RV precisely, one would need to perform a test such as nitrogen washout, helium dilution or body plethysmography.
A lowered or elevated FRC is often an indication of some form of respiratory disease. For instance, in emphysema, the lungs are more compliant and therefore are more susceptible to the outward recoil forces of the chest wall. Emphysema patients often have noticeably broader chests because they are breathing at larger volumes.
The helium dilution technique is a common way of measuring the functional residual capacity of the lungs.
Famous quotes containing the words functional, residual and/or capacity:
“In short, the building becomes a theatrical demonstration of its functional ideal. In this romanticism, High-Tech architecture is, of course, no different in spirit—if totally different in form—from all the romantic architecture of the past.”
—Dan Cruickshank (b. 1949)
“The volatile truth of our words should continually betray the inadequacy of the residual statement. Their truth is instantly translated; its literal monument alone remains.”
—Henry David Thoreau (1817–1862)
“Has the art of politics no apparent utility? Does it appear to be unqualifiedly ratty, raffish, sordid, obscene, and low down, and its salient virtuosi a gang of unmitigated scoundrels? Then let us not forget its high capacity to soothe and tickle the midriff, its incomparable services as a maker of entertainment.”
—H.L. (Henry Lewis)