Inflation inhibits further inspiration; deflation stimulates it
Expansion
- Inflation (Hering-Breuer) reflex - lung distension stimulates slowly adapting stretch receptors in airway smooth muscle; vagal afferents inhibit inspiration and prolong expiration, preventing overinflation
- Deflation reflex - collapse stimulates increased ventilatory effort
Both are carried by the vagus, and both are abolished by bilateral vagotomy.
In adults the inflation reflex is weak and is only triggered above a tidal volume of about 1 litre, so it acts as a protective mechanism during exercise or mechanical ventilation rather than a regulator of quiet breathing.
In neonates it is much more active and contributes to setting the normal breathing pattern.
Other pulmonary reflexes worth grouping with it: rapidly adapting (irritant) receptors, which trigger cough, bronchoconstriction and hyperpnoea in response to dust, smoke and histamine; and juxtacapillary (J) receptors, stimulated by interstitial oedema, producing the rapid shallow breathing of pulmonary oedema.