hysteresis
Summary
A property where a system's output depends on its history; in pulmonary physiology, the lung's inflation and deflation pressure-volume curves differ due to surface tension and surfactant effects. Clinically relevant in ARDS and mechanical ventilation.
Detail
Hysteresis in pulmonary mechanics refers to the difference between the pressure-volume curve during inspiration versus expiration—the deflation curve lies above the inflation curve. This discrepancy arises from surface tension forces at the air-liquid interface in alveoli and surfactant behavior, which reduces surface tension more effectively during deflation. This has profound clinical implications: in ARDS, surfactant depletion increases hysteresis significantly. In mechanically ventilated patients, PEEP counteracts hysteresis by preventing alveolar derecruitment, improving gas exchange. Understanding hysteresis guides lung-protective ventilation strategies.
Sources
- First Aid for the USMLE Step 1
- Pathoma
- West's Respiratory Physiology
- Harrison's Principles of Internal Medicine
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