A patient with severe emphysema has a lung compliance of 0.6 L/cmH2O (normal ~0.2 L/cmH2O). Which structural change best explains this?
- A Destruction of elastin in alveolar walls reducing lung elastic recoil ✓
- B Excess mucus deposition in airways increasing elastic recoil
- C Fibrosis replacing air spaces with stiff collagen, reducing compliance
- D Hyperinflation stretching the diaphragm, increasing total respiratory system compliance
Explanation
Compliance is the inverse of elastance (C = 1/E). Normal lung elastic recoil depends on intact elastin and collagen fibres in alveolar walls plus surface tension. In emphysema, protease-mediated (principally elastase from neutrophils/macrophages) destruction of alveolar wall elastin reduces lung elastic recoil, making the lungs abnormally easy to inflate — increased compliance. This contrasts with pulmonary fibrosis, where collagen deposition increases stiffness, reducing compliance. High compliance in emphysema means the lung hyperinflates but cannot generate adequate recoil pressure to drive air out, causing air trapping and increased RV/TLC.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.