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 uncertainty, 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 allergic asthma may have airflow limitation only after exposure to an asthma trigger or patients with nocturnal asthma only at night. (See "Allergen avoidance in the treatment of asthma and allergic rhinitis" and "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 .