Prognostic significance of a reduced FEV3/FVC ratio.

An FEV3/FVC ratio below the lower 95% confidence limit of normal with otherwise normal spirometry has been shown to be a more reliable measure of midflow or mild airways osbtruction and is associated with a past smoking history. When compared to normal controls, as a group, they have a higher total lung capacity (TLC), more airtrapping, lower diffusion and sGaw. There is no longitudinal data regarding whether subjects with an initial reduction in FEV3/FVC develop more definitve evidence of airways obstruction. Methods: A large pulmonary lab database spanning 13 years was analyzed. Subjects were identified who had simultaneous spirometry, plethysmography, and diffusing capacity on more than one occasion, at least 1 year apart. In order to screen out subjects with progressive restrictive disease, only subjects with a normal first and last TLC were studied. The control group had initial normal spirometry (n=829 at 1 year, n=500 at 3 years, n=256 at 5 years). The study group had only a reduced FEV3/FVC (n=99 at 1 year, n=60 at 3 years, n=38 at 5 years). Results: In subjects that had an initial normal spirogram, 9.2% after 1 year, 9.8% after 3 years (