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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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