The Hering-Breuer inflation reflex limits tidal volume by:

• A Peripheral chemoreceptors detecting rising PaO2 and signalling apnoea
• B Slowly-adapting pulmonary stretch receptors activating vagal afferents that inhibit the inspiratory centre ✓
• C Central chemoreceptors detecting rising pH during lung inflation, inhibiting breathing
• D Rapidly-adapting irritant receptors triggering the deflation reflex

Explanation

Slowly-adapting pulmonary stretch receptors (SARs) in airway smooth muscle respond to lung inflation. As tidal volume increases, their firing rate rises; afferent impulses travel via the vagus nerve to the nucleus tractus solitarius and then to the Bötzinger complex, which inhibits the inspiratory (pre-Bötzinger) ramp neurons, terminating inspiration and initiating expiration. This Hering-Breuer reflex is prominent at tidal volumes >1 L in awake adults and is more physiologically important in anaesthetised subjects and infants. Rapidly-adapting receptors mediate cough and deep breaths, not inflation-termination.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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