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Airflow Obstruction - Simplified
Diagnosis threshold: ATS and GOLD guidelines say: if the FEV₁/FVC ratio (after using a bronchodilator) is less than 0.70, the patient has airflow obstruction (i.e., air is not flowing out freely).
What is FEV₁?
  • FEV₁ = the amount of air you can forcefully breathe out in 1 second
  • It reflects a balance between two forces:
    • Lung elastic recoil - the lungs' natural push to squeeze air out
    • Airway resistance - narrowed airways slowing air down
What happens during expiration (breathing out)?
  • As the lungs empty, they lose their elastic push (recoil)
  • Airways also get narrower as lung volume drops
  • Both effects together = less and less airflow as you exhale
In COPD:
  • Mild COPD: Flow problems only appear at low lung volumes (looks like a "scooped out" dip at the bottom of the flow-volume curve)
  • Advanced COPD: The entire flow-volume curve is reduced - all breathing phases are affected
FEV₁ in COPD:
  • FEV₁ drops in COPD largely because of small airway disease (narrowing of tiny airways deep in the lungs)
  • This is somewhat separate from emphysema (destruction of lung tissue), though both contribute
Bottom line: FEV₁/FVC < 0.70 = airflow obstruction. In COPD, the main culprit is damaged small airways reducing airflow, with the flow-volume curve showing progressive worsening as disease advances.
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