[Airway responsiveness to isocapnic hyperventilation with room temperature air]

Isocapnic hyperventilation (IHV) with room temperature dry gas was evaluated in 63 asthmatics and 33 normal subjects, in order to asses the clinical relevance of the technique as a simplified test of airways hyperreactivity. The results between IHV and methacholine challenge (MCH) were compared in 32 asthmatics. Mostly asthmatics revealed obvious bronchoconstriction and average 21.4 +/- 14.8% decrease in FEV1 (delta FEV1) after hyperventilation. Among the normal subjects delta FEV1 was average 3.8 +/- 2.0%. Obvious difference was show between the normal and the asthmatics in reaction following IHV (P less than 0.001). When the criterion for a positive reaction to IHV was a decrease in FEV1 of 10 percent or greater, the sensitivity and specificity of the test were 85% and 100% separately. Three of the asthmatics demonstrated bronchodilative reaction and FEV1 increased notably than the base after hyperventilation. The positive percentages of IHV and MCH were similar (P greater than 0.05). The results suggest the IHV with room air determine bronchial reactivity is a simple and secure method.