Airway response to mannitol among healthy subjects

Little is known how subject characteristics affect the airway responsiveness to mannitol, what is the upper limit of a normal response, and what is the reproducibility of the response among healthy subjects.

Mannitol testing was performed in 125 healthy, nonsmoking subjects with an age range of 18-82 years and an almost equal male-to-female ratio. 25 of them repeated the test. The airway response to mannitol was expressed as the final percentage fall in forced expiratory volume in 1 s (FEV₁) after the final cumulative dose of mannitol (FFALL) and as response-to-dose ratio (RDR), calculated as FFALL divided by the final cumulative dose of mannitol. The upper limits of the normal response were calculated as mean+1.65×sd.

Neither age, gender, height, body mass index, atopy, nor baseline FEV₁ affected the responses statistically significantly. The mean±sd FFALL was 5.29±4.90% with an upper limit of 13.4%. The mean±sd RDR was 0.78±0.71% per 100 mg with an upper limit of 1.96% per 100 mg. In the repeated tests, the intraclass correlation coefficients were 0.46 and 0.35, respectively.

The subject characteristics do not have a significant effect on the airway responsiveness to mannitol. Therefore, the same upper limits of a normal response can be used in all adult nonsmoking subjects. Among healthy subjects with very mild airway responsiveness to mannitol, FFALL and RDR are poorly reproducible.