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FRC: definition

Functional Residual Capacity. The amount of volume remaining in the lung after a normal exhalation.

Lung Volumes:

  • TLC = Total Lung Capacity
  • VC = Vital Capacity
  • IC = Inspiratory Capacity
  • FRC = Functional Residual Capacity
  • Vt = Tidal Volume
  • RV = Residual Volume
  • ERV = Expiratory Reserve Volume
  • IRV = Inspiratory Reserve Volume

Dependent on the balance of the inward force of the lung and the outward force of the chest wall determines the volume. The inward force of the lung, or “elastic recoil,” consists of the elastic fibers of the lung tissue, as well as the contractile forces of airway smooth muscles and the surface tension of alveoli. The outward force of the chest wall is exerted by the ribs, joints, and muscles.

Variables: Age, Sex, Height, Weight (Increases with Height and Age, Decreases with weight. Smaller in females).