Simulations / Anatomy & Physiology

Airway Flow Explorer

During an asthma attack the airway lining swells, muscles tighten, and mucus builds up. In an idealized model, airflow depends on the fourth power of the airway radius, so a small narrowing makes a big difference.

Controls

Percent reduction in airway radius.
Percent increase in the radius after narrowing.
100% is normal quiet breathing. Pushing harder moves more air but tires the muscles.
Model: Poiseuille flow, Q ∝ ΔP × r⁴, so resistance ∝ 1 / r⁴. Real lungs branch into many airways and air is not a perfect laminar fluid, but the steep dependence on radius is real. This tool is for learning and is not medical advice.
Radius
of normal
Resistance
times normal
Airflow
of normal
Effort to keep normal flow
times normal pressure

Try this

  • Narrow the airway by 20%. By what percent does airflow fall?
  • Narrow it by 50%, then raise breathing effort. Can you restore normal flow?
  • Apply the medicine slider and see how a small opening recovers a lot of flow.

What to notice

  • A 19% reduction in radius cuts flow roughly in half because 0.81⁴ ≈ 0.43.
  • The curve is steep at small radii, so the same percentage change matters more.

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