Hyperventilation or exercise to induce asthma?

Bronchoconstriction was induced in asthmatic patients by means of isocapnic hyperventilation with dry air. Responses both within a day and between days did not differ significantly and corresponded closely with those observed after exercise. The mean fall in forced expiratory volume in one second (FEV1) observed with both techniques was equivalent to 36%. Isocapnic hyperventilation with dry air, as used in this study, was a potent stimulus and provoked a reproducible response. The method was physically less demanding than exercise and was more acceptable to patients.