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Elevated FRC DDx


= residual volume + expiratory reserve volume

= volume of gas in the lungs after normal expiration

= lung volume where elastic recoil of chest and lung are in equilibrium (but in opposite directions)

Increased FRC (in general) results from:

  • Decreased inward lung recoil
  • Increased outward chest recoil
  • Bronchoconstriction/airway obstruction
  • Lung hyperinflation

Differential diagnosis for increased FRC:

Obstructive lung disease (higher end-expiratory volumes -> hyperinflation -> ↑FRC)

  • Emphysema
  • Asthma
  • Bronchiectasis
  • Exercise (↑RR/Tidal volume may not allow for sufficient lung emptying -> hyperinflation)
  • Age (associated with a gradual loss of elastic lung tissue)