Methacholine and Histamine Inhalation Challenges in Asthma: Relationships to Age of Onset, Length of Illness, and Pulmonary Functions

Levels of airway's hyperreactivity, as indexed by methacholine and histamine thresholds, were determined for hospitalized asthmatic patients using the serial concentration, constant‐breath method. Airways hyperreactivity was categorized into tow and high based on a split of the sample of subjects tested. These categories were unrelated to pulmonary function measurements obtained throughout hospitalization. Patients having high airways hyperreactivity to histamine or methacholine were admitted for intensive inpatient care at a younger age, had an earlier age of onset, and had asthma of longer duration than patients having low airways hyperreactivity. These latter results suggested that relatively greater airways hyperreactivity is more likely to be associated with early onset of the illness.