Poiseuille's Law

• Poiseuille's Law:

  • Flow of gas through an airway is:
  • directly proportional the fourth power of its internal radius i.e. r^4
  • inversely proportional to its length
  • inversely proportional to viscosity of gas
• Poiseuille's Law - Clinical Relevance:

  • Length of airways remains constant
  • Therefore a change in radius (airway calibre) is most important factor
  • A small change in radius leads to big change in airway resistance
  • Increased airway resistance leads to decreased airflow
  • Clinically this is called airflow limitation or obstruction
• Poiseuille's Law - Clinical Relevance Pt2:

  • Therefore any pathology which reduces the calibre of airway will lead to increased airways resistance, decrease airflow and airflow limitation