bronchospasm

Picture a garden hose with a muscular sleeve around it. When that sleeve suddenly squeezes, the hose's bore shrinks and water trickles instead of flows. Bronchospasm is the airway version: the bands of smooth muscle wrapping the bronchi and bronchioles contract abruptly, narrowing the tubes and making air harder to push in and especially out.

Mechanistically, bronchospasm is sudden constriction of bronchial smooth muscle, often triggered by inflammatory mediators, allergens, irritants, cold air, exercise, or certain drugs. It raises airway resistance and produces wheeze, chest tightness, cough, and breathlessness. In asthma it is a central event during attacks; it can also occur in COPD and in reactions to inhaled irritants.

Because the muscle constriction itself is reversible, fast-acting bronchodilators — short-acting beta-agonists, sometimes with antimuscarinics — relax the muscle and relieve it quickly. However, bronchospasm is only one component of an asthma attack; mucosal swelling and mucus also narrow the airway and respond more slowly, mainly to anti-inflammatory treatment.