Asthma has defied a precise definition acceptable to all, even though clinicians recognize that asthma will present with a constellation of signs and symptoms of intermittent dyspnea, cough, chest tightness, and wheezing. Part of the problem relates to the lack of specificity of these "classic" symptoms of asthma. Despite this variability, the following typical pathophysiologic features both characterize and assist in the diagnostic evaluation of the patient with asthma:
- Reversibility of airflow limitation. This is not always clinically demonstrable, as patients with mild disease often do not have airflow limitation at the time they are tested.
- Variable airflow limitation. As an example, patients with nocturnal asthma may have airflow limitation only after exposure to an asthma trigger or at night. (See "Nocturnal asthma".)
- Hyperresponsiveness to external triggers. "Twitchy airways" or airway hyperresponsiveness (AHR) is defined as an excessive response to an aerosolized provocation that elicits little or no response in a normal person.
- Inflammation of the airways is associated with and may underlie airway hyperresponsiveness .
Several types of bronchoprovocation testing are available to assess airway responsiveness in specific patient situations, including pharmacologic challenge, exercise challenge, eucapnic voluntary hyperpnea, food additive challenge, and antigen challenge.
The appropriate use of bronchoprovocation testing in patients with asthma or suspected of having asthma will be reviewed here. The pathogenesis and diagnosis of asthma and the role of bronchoprovocation testing in the diagnosis of occupational asthma are discussed separately. (See "Pathogenesis of asthma" and "Diagnosis of asthma in adolescents and adults" and "Use of pulmonary function testing in the diagnosis of asthma" and "Occupational asthma: Clinical features and diagnosis".)
Measurement of airway responsiveness by bronchoprovocation testing is potentially useful for several reasons: