In this issue of Anesthesiology, Shi et al. report on the reproducibility of expiratory muscle thickness measured with ultrasound imaging in 30 patients ventilated in the intensive care unit (ICU). They also assess changes in expiratory muscle thickness during the first week of mechanical ventilation in 77 ICU patients. They conclude that ultrasound thickness measurements are reproducible, and that thickness decreases in 2 of 10 patients and increases in 1 of 10 patients during the first week of mechanical ventilation.

Should we concern ourselves with expiratory muscle thickness? Yes, for several reasons. Forceful contractions of the expiratory muscles are necessary to achieve dynamic airway compression, an essential element in effective cough. Expiratory muscle recruitment improves diaphragmatic neuromechanical coupling during loaded breathing, including during a failed weaning trial. Indirect measurements of expiratory...

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