closing volume

The amount of air in the lungs at which the flow from the lower sections of the lungs becomes severely reduced or halts altogether during expiration.

The volume of gas in the lungs in excess of the residual volume (RV) at the time when small airways in the dependent portions of the lungs close during maximal exhalation; abbreviated CV. CV normally increases with age and is also increased in obstructive airways disease. It can be used to detect the disease in high-risk patients before clinical signs appear. The closing capacity (CC) is equal to CV plus RV.