Bronchoconstriction

Bronchoconstriction is narrowing of the bronchi caused by contraction of the smooth muscle surrounding them. It increases resistance to airflow and can make breathing difficult.

Airway smooth muscle: Contractile muscle surrounding the airways that regulates their diameter. Its contraction directly produces bronchial narrowing.
Asthma: A chronic disease involving variable respiratory symptoms and fluctuating limitation of expiratory airflow. Bronchoconstriction contributes to asthma's episodic airflow limitation.
Allergen-induced bronchoconstriction: Airway narrowing caused by exposure to an allergen in a sensitized person. It illustrates an immune-triggered route to bronchoconstriction.
Bronchus: A large airway branch that carries air from the trachea into a lung. Bronchi are the airways whose smooth muscle contracts.
Bronchial hyperresponsiveness: An exaggerated tendency of the airways to narrow in response to stimuli. It makes bronchoconstriction occur more readily or intensely.
Exercise-induced bronchoconstriction: Transient airway narrowing that occurs during or after physical exercise. It is a recognizable form of bronchoconstriction associated with exertion.
Cold air-induced bronchoconstriction: Airway narrowing triggered by inhaling cold, often dry, air. It shows that environmental conditions can provoke airway narrowing.
Bronchiole: A small branching airway in the lungs that lacks cartilage in its walls. Narrowing in these smaller airways can strongly impede airflow.
Parasympathetic nervous system: The branch of the autonomic nervous system that supports functions such as digestion and regulates involuntary organs. Vagal parasympathetic signals can trigger airway smooth-muscle contraction.
Methacholine challenge test: A pulmonary function test that measures airway responsiveness to inhaled methacholine. The test deliberately provokes bronchoconstriction to assess airway responsiveness.

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