DETECTION OF SMALL AIRWAY DYSFUNCTION USING SPECIFIC AIRWAY CONDUCTANCE

Study objective: To assess the potential utility of specific airway co nductance (sGaw) in detecting small airways dysfunction, the postlung- transplant bronchiolitis obliterans syndrome (BOS) was used as a model of small airways dysfunction. BOS is defined as an otherwise unexplai ned 20% reduction in FEV1. We hypothesized that if sGaw is sensitive t o small airways dysfunction, it should decrease before the decline in FEV1. Design/methods: The pulmonary function test and sGaw measurement s of patients who underwent heart-lung or bilateral lung transplantati on between May 1981 and January 1993 were reviewed. Patients with and without BOS were identified. A significant decrease in sGaw was define d as a 20% fall from baseline, Results: Twenty-six BOS and 15 non-BOS patients had at least three sGaw measurements such that trends could b e examined, Eleven of the 26 BOS patients (42%) had a significant decr ease in sGaw before a 20% decrease in FEV1, as compared to 2 of the 15 non-BOS patients (13%) (p = 0.08). In comparison, 12 of the 26 BOS pa tients (46%) and 1 of the 15 non-BOS patients (27%) had a significant decrease in forced expiratory flow at 23 to 75% of the forced lung vol ume (FEF25-75) (p = 0.32), an accepted test of small airways dysfuncti on. Conclusion: sGaw tended to decrease before FEV1 in BOS. The trend in sGaw was similar to the trend in FEF25-75. We conclude that (1) sma ll airways may contribute more to airway conductance than previously t hought, and (2) further prospective studies are warranted to better de fine the relative contribution of small and large airways to sGaw.