Closing capacity is the lung volume at which small airways in the lower lung begin to collapse during exhalation — a phenomenon that becomes more relevant with age, anesthesia, or lying flat.
Closing capacity is the closing volume added on top of residual volume.
General anesthesia and supine positioning both reduce FRC, while closing capacity stays roughly the same or rises with age — increasing the chance that closing capacity overtakes FRC during surgery and airways collapse mid-breath.
Small airways in the lower lung close during normal tidal breathing, contributing to atelectasis and V/Q mismatch. This becomes more common with age, obesity, and lying flat.
The closing volume — the volume at which dependent airways start to close — plus the residual volume beneath it.
Yes — conditions that reduce lung elastic recoil, like emphysema, raise closing capacity independent of age.