The American Thoracic Society defines asthma as a disease characterized by increased responsiveness of the trachea and bronchi to various stimuli and manifested by widespread narrowing of the airways that changes in severity either spontaneously or as a result of therapy. In this context asthma is a physiologic diagnosis. It is most often recognized when a patient complains of episodic wheezing and dyspnea and most often confirmed by the demonstration of variable airways obstruction on spirometric testing
