Assessing small airways disease.

A simple method of assessing smaller airways obstruction is easily available and could be used retrospectively. In contrast to the mean forced expiratory flow between 25 and 75% of forced vital capacity (FVC; FEF25–75%), which measures the mid-portion of exhalation ending at nearly the same time as the forced expiratory volume in one second (FEV1) in these subjects, the FEV3/FVC% or (1-FEV3/FVC)% are excellent measures of small airways function. They measure the fraction of volume exhaled near the end of a forced exhalation, i.e. from airspaces and airways with the longest time constants [3, 4]. However, because they are ratios (as are FEV1/FVC and FEF25– 75%) they are not ideal measurements of airway responsiveness to bronchodilators. Rather, preand post-absolute volumes, such as FEV1, FEV3 and FEV6, should be compared to assess bronchodilator effect. Presumably, if there is a small airways bronchodilator effect in the ciclesonide-treated group, the increase from preto post FEV3 (DFEV3) or FEV6 (DFEV6) should exceed that of preto post-FEV1 (DFEV1). For example, if the DFEV1 was 150 mL and the DFEV3 and DFEV6 were also 150 mL, the dominant change was in the larger airways. If the DFEV1 was 150 mL and the DFEV3 and DFEV6 were 200– 250 mL, there was also an important change in the smaller airways. These simple measurements would objectively disclose whether the smaller airways were directly affected by the ciclesonide.