airflow obstruction happens first in distal airways


  • distal, smaller airways are impacted first when there's airflow obstruction
  • this manifests as reduced airflow at lower volumes (end of expiration)
  • this is why obstructive PFTs have characteristic appearance
  • end of expiration tapers much slower while the first part (FEV1) is less affected
  • FEF2575%FEF_{25-75\%} are sometimes used to describe this decrease in small airway flow between 25% and 75% of exhaled FVC (flow volume loops normal definition). However the measurements are widely variable and thus not used.1

Footnotes

  1. ERS ATS technical standard on interpretive strategies for routine lung function tests