sGAW = 0.205 (P = 0.014); Raw = - 0.169 (P = 0.043). Correlation ratios between the variations in phlethysmographic parameters and those in the exercise capacity measured by 6MWT in COPD patients after follow-up periods of 6 months are: FEV1 = 0.371 (P = 0.001); FEF 25 - 75% = 0.207 (P = 0.083).