Airways resistance in bronchial challenge testing

Introduction: Measurement of airways resistance is an alternative to spirometry to assess airflow obstruction. This can be measured by the interrupter technique (RInt) using a handheld device. We wished to know how RInt compared to forced expiratory volume in 1 s (FEV1) during a histamine challenge test.

Methods: Twenty-nine (13 male) patients, aged 48.9 (SD 15.3) years, referred for a histamine challenge test, were enrolled. Patients had measurement of RInt then FEV1 after administration of saline and following doubling concentrations of histamine from 0.06 to 8 mg/ml. Extrapolation of the log dose-response curve was undertaken to calculate the concentration (provocation concentration, PC) causing an increase airways resistance of 20, 40, 60, 80, 100, 120, 140 and 160% (RInt PC1.2 to RInt PC2.6) and a reduction in FEV1 by 20% (FEV1 PC20). The number of patients with a negative challenge (i.e. PC>8 mg/ml histamine) was calculated for FEV1 and each change in airway resistance. Patients assessed their procedure-provoked symptoms of breathlessness, dizziness and tiredness on a visual analogue scale.

Results: Geometric (SD) PC20 for FEV1 was 1.87 (0.5) mg/ml with 11 patients having a negative challenge. A RInt PC20 had the best agreement with FEV1 PC20 [Kappa 0.39 (p=0.024)]. There is a significant negative correlation between RInt and FEV1 (r=-0.94). The respective mean (SD) breathlessness, dizziness and tiredness scores for RInt were 26 (4) mm, 18 (3) mm, 22 (4) mm and for spirometry were 40 (4) mm, 27 (5) mm, 31 (5) mm. There was a significant (p<0.05) difference for breathlessness.

Conclusion: RInt was tolerated better than spirometry. A doubling of airways resistance had the best agreement with PC20 FEV1.