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Excerpt
Biopsies were obtained from the costal DIA of 5 patients (age 56 ± 2 years, FEV1 19 ± 1 % predicted normal; RV 270 ± 18% predicted normal) and 4 age matched subjects (AMS) with essentially normal pulmonary function in an effort to examine fiber type specific adaptations to COPD. Specimens were analyzed for the type, cross-sectional area (CSA), and succinate dehydrogenase (SDH, μmol fumerate/l/minute) activity of individual fibers using standard histochemical and microdensitiometric techniques. We noted that: (a) COPD had a higher % of type I (65 ± 7 vs 42 ± 3 %, p = 0.002) and a lower % of type II (b+x) fibers (10 ± 3 vs 32 ± 3%, p = 0.002); (b) fibers, irrespective of type, were smaller in COPD than in AMS (mean CSA 2233 ± 108 vs 3587 ± 284 μm2, p = 0.000); (c) the relative CSA of the DIA occupied by type I fibers was greater in COPD (66 ± 7 vs 45 ± 6 %, p = 0.005), whereas the opposite was true for relative CSA occupied by type II(b+x) fibers (9 ± 2 vs 31 ± 6 %, p = 0.001); and (d) fiber type specific values of SDH tended to be higher in COPD than in AMS, but these differences were not statistically significant. In addition, type I fibers in COPD made a greater relative contribution to the SDH activity of the DIA (73 ± 5 vs 54 ± 7 %, p = 0.009), while the opposite was the case for their II(b+x) fibers (6 ± 2 vs 26 ± 6%, p = 0.009). We hypothesize that the high % of slow fibers, their large contribution to aerobic oxidative activity and the small fiber size of the DIA in COPD represent adaptations to chronic overuse.
