Closed volume
The closed volume (CV) refers to the volume of air that can be exhaled when the small airways in the lower lungs begin to close during calm exhalation. The closed volume + residual gas volume is the closed volume (CC). Usually used closed volume / vital capacity% (CV / CC%) or closed volume / total lung% (CC / TLC%) as the evaluation index. Small airway lesions cause the small airway to close prematurely during exhalation, increasing the closed volume.
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