Diagnosis and classification of asthma.

Ithough asthma is a disease that has been described for centuries, attempts at definition and criteria for diagnosis have only occurred within the last several decades. ‘There is, however, still not a universally agreed upon definition. A definition of asthma recently proposed by the expert panel on the management of asthma would probably be acceptable to most:’ “Asthma is a lung disease with the followi,sg characteristics: (1) airway obstruction that is reversible (but not completely so in some patients) either spontaneously or with treatment; (2) airway inflammation; and (3) increased airway responsiveness to a variety of stimuli.” The first element of the above definition, reversible airway obstruction, is common to most proposed definitions of asthma. The second element, airway inflammation, is the subject of another paper in the Symposium, and therefore, will not be discussed further here. The third element, increased airway responsiveness, deserves additional comment.6 Airway hyperresponsiveness, the exaggerated bronchoconstrictive response to various physical or pharmacologic agents, is almost always present in asthma, and the level of airway hyperreactivity correlates reasonably well with the severity of the clinical disease.’ A wide variety of physical agents, such as cold, dry air inhalation, exercise, hyperventilation, and nonisotonic aerosol challenge have been used; methacholine and histamine are the most common pharmacologic agents employed. The mechanism of airway hyperresponsiveness is unknown but may involve airway inflammation, neural control mechanisms, or abnormalities in bronchial epithelial cells. #{176}