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Lung Function Tests

Functional Residual Capacity



The functional residual capacity (FRC) is the volume left in the lungs after passive expiration, i.e. without use of accessory muscles.
  • Significance

  • A marker of compliance of the lungs and chest wall.

Increased FRC

Increased functional residual capacity indicates increased lung compliance.
  • Causes of Increased FRC

  • Erect posture
  • Advanced age
  • Emphysema
  • Asthma

Reduced FRC

Reduced functional residual capacity indicates decreased lung compliance.
  • Causes of Reduced FRC

  • Supine position
  • Pulmonary fibrosis
  • Obesity
  • Abdominal swelling
  • Muscle relaxants
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