Airway anatomy and the mechanics of breathing: compliance, resistance and work of breathing
How the airway tree is built, why most airway resistance sits in medium bronchi, what sets compliance and FRC, how dynamic compression limits expiratory flow, and how to read ventilator pressures and flow-volume loops from first principles.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- The airway tree has about 23 generations. Generations 0 to 16 (trachea to terminal bronchioles) are the conducting zone and make up anatomical dead space of about 150 mL. Generations 17 to 23 (respiratory bronchioles, alveolar ducts, about 300 to 500 million alveoli, 50 to 100 m²) exchange gas.
- Compliance (ΔV/ΔP) describes stretchiness. Resistance (ΔP/flow) describes the pressure cost of moving gas. Work of breathing is the sum of elastic and resistive work.
- Most resistance is in medium bronchi, not small airways, because total cross-sectional area expands enormously in the periphery.
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Sources
- West's Respiratory Physiology: The Essentials (11th ed.)Wolters Kluwer (West and Luks, 2021), 2021
- Murray and Nadel's Textbook of Respiratory Medicine (7th ed.)Elsevier (Broaddus et al., 2022), 2022
- ERS/ATS technical standard on interpretive strategies for routine lung function testsEuropean Respiratory Journal (Stanojevic et al.), 2022
- Last updated
- 14 November 2026
What changed
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