Functional residual capacity (FRC) should be:
|A||Less than closing capacity (CC)|
|B||More than CC|
|D||More in inspiration and less in expiration|
More than CC
Closing capacity is the volume at which airway closes functional residual capacity should be 1 liter more than losing capacity. If it falls below closing capacity premature airway closure will take place which can lead significant hypoventilation.