functional residual capacity

Physiology

• volume remaining in the lungs after a normal, passive exhalation
• represents the point of the breathing cycle where the lung tissue elastic recoil & chest wall outward expansion are balanced & equal
• inward & outward lung compliances are balanced
  • work to inflate the lungs is the lowest
• total amount of air in a person's lungs at the lowest point of their tidal volume
• combination of the expiratory reserve volume & the residual volume
  • cannot be measured directly using spirometry; has to be calculated

Reference interval

• in a normal individual, this is ~ 3 liters
• it is position-dependent
  • greatest when upright, decreasing when supine or prone, even more so in Trendelenburg & head down positions
• functional residual capacity increases slightly with age

More general terms

• static lung volume