Bronchoprovocation

Bronchoprovocation testing refers to a group of procedures used to provoke narrowing of the airways in susceptible individuals in order to assess airway hyperresponsiveness and to support the diagnosis of asthma or evaluate treatment effects. It is also used in research settings to quantify airway reactivity.

Tests are broadly categorized as direct and indirect. Direct challenges use agonists that act directly on airway smooth muscle, most commonly methacholine or histamine, causing bronchoconstriction. Indirect challenges trigger mediator release from inflammatory cells or involve physical triggers; examples include mannitol inhalation, hypertonic saline inhalation, cold air exposure, and exercise-induced bronchoconstriction. Exercise testing is widely used to assess exercise-induced bronchial symptoms.

The procedure typically involves baseline spirometry, followed by administration of the provoking agent in increasing doses or by having the patient perform a controlled exercise protocol. Spirometry is repeated after each step to detect a fall in forced expiratory volume in one second (FEV1). A common positive threshold is a 20% decline in FEV1 from baseline, although the exact criteria can vary by protocol and population; some tests report the provocative concentration or dose that produces a 20% drop (PC20 or PD20).

Interpretation requires clinical context. A positive test indicates airway hyperresponsiveness but is not disease-specific; asthma is the most frequent cause, but heightened reactivity can occur in other conditions such as chronic obstructive pulmonary disease or allergic inflammation.

Safety and supervision are essential. Tests are conducted in clinical or research labs with trained personnel, continuous monitoring, and access to rescue medications and emergency equipment. Contraindications include acute bronchospasm, recent myocardial infarction or stroke, and other conditions where inducing bronchoconstriction would be dangerous.