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

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 non-atopic, non-smoking normal subjects and 11 subjects with stable asthma who had an FEV, above 74% of the predicted value were studied. In the normal subjects isocapnic hyperventilation with room air (75 I/min; 22°C (SEM 0.20); 10 mg H,O/l air) and isocapnic hyperventilation with cold air (77 1/min; - 10°C (0.90); 2.4 mg H O/1 air) produced no significant change in FEV. In the asthmatic subjects, hyperventilation with room air (71 1/min; 220C (0.80); 10 mg H O/l alr) caused a mean fall in FEV of 11 7%; cold air hyperventilation (70 1/min; - 10°C (0.90); 2.4 mg H,O/l air) caused a mean fali in FEVy of 20 4%. Cold air hyperventilation produced greater sep-aration between normal and asthmatic subjects than room air. The provocative concentration of histamine required to reduce the FEVy by 20% (PC20) correlated closely with the PC for methacholine (r = 0-95; p < 0.001).Both tests separated normal from asthmatic subjects. PC,0 for both histamine and methacholine correlated with the fall in FEV after cold air hyperventilation (r = 0.93, p < 0-001; r = 0-87, p < 0-001 respectively). We conclude that the results of a rapid screening test based on hyperventilation with cold air correlate well with a standard pharmacological challenge.