Comparison of airway reactivity induced by histamine, methacholine, and isocapnic hyperventilation in normal and asthmatic subjects.

Abstract

In an investigation of a rapid screening test for airway reactivity using isocapnic hyperventilation with room air and cold air the results of this test were compared with the airway response to histamine and methacholine challenge. Twelve nonatopic, nonsmoking normal [human] subjects and 11 subjects with stable asthma who had an FEV1 [1-s forced expiratory volume] above 74% of the predicted value were studied. In the normal subjects isocapnic hyperventilation with room air (75 l/min; 22.degree. C [SEM [standard error of the mean] 0.2.degree.]; 10 mg H2O/l air) and isocapnic hyperventilation with cold air (77 l/min; -10.degree. C [0.9.degree.]; 2.4 mg H2O/l air) produced no significant change in FEV1. In the asthmatic subjects, hyperventilation with room air (71 l/min; 22.degree. C [0.8.degree.]; 10 mg H2O/l air) caused a mean fall in FEV1 of 11.7%; cold air hyperventilation (70 l/min; -10.degree. C [0.9.degree.]; 2.4 mg H2O/l air) caused a mean fall in FEV1 of 20.4%. Cold air hyperventilation produced greater separation between normal and asthmatic subjects than room air. The provocative concentration of histamine required to reduce the FEV1 by 20% (PC20) correlated closely with PC20 for methacholine (r = 0.95; P < 0.001). Both tests separated normal from asthmatic subjects. PC20 for both histamine and methacholine correlated with the fall in FEV1 after cold air hyperventilation (r = 0.93, P < 0.001; r = 0.87, P < 0.001, respectively). Results of a rapid screening test based on hyperventilation with cold air correlate well with a standard pharmacological challenge.