Spirometric correlates of improvement in exercise performance after anticholinergic therapy in chronic obstructive pulmonary disease

We wished to determine which resting spirometric parameters best reflect im provements in exercise tolerance and exertional dyspnea in response to acut e high-dose anticholinergic therapy in advanced COPD. We studied 29 patient s with stable COPD (FEV1 = 40 +/- 2% predicted [%pred]; mean +/- SEM) and m oderate to severe chronic dyspnea. In a double-blind placebo-controlled cro ss-over study, patients performed spirometry and symptom-limited constant-l oad cycle exercise before and 1 h after receiving 500 mu g of nebulized ipr atropium bromide (IB) or saline placebo. There were no significant changes in spirometry, exercise endurance, or exertional dyspnea after receiving pl acebo. In response to IB (n = 58): FEV1, FVC, and inspiratory capacity (IC) increased by 7 +/- 1%pred, 10 +/- 1%pred, and 14 +/- 2%pred, respectively (p < 0.001), with no change in the FEV1/FVC ratio. After receiving IB, exer cise endurance time (Tlim) increased by 32 +/- 9% (p < 0.001) and slopes of Borg dyspnea ratings over time decreased by 11 +/- 6% (p < 0.05). Percent change (%Delta) in Tlim correlated best with Delta IC%pred (p = 0.020) and change in inspiratory reserve volume (Delta TLC%pred) (p = 0.014), but not with Delta FVC%pred, Delta PEFR%pred, or Delta FEV1%pred. Change in Borg dy spnea ratings at isotime near end exercise also correlated with Delta IC%pr ed (p = 0.04), but not with any other resting parameter. Changes in spirome tric measurements are generally poor predictors of clinical improvement in response to bronchodilators in COPD. Of the available parameters, increased IC, which is an index of reduced resting lung hyperinflation, best reflect ed the improvements in exercise endurance and dyspnea after IB. IC should b e used in conjunction with FEV1 when evaluating therapeutic responses in CO PD.