We will analyze post hoc, data that was previously published: Gelb AF et al.Chest 2006;131:690-695. We have shown that tiotropium increases resting inspiratory capacity thereby providing lung volume protection against metronome paced hyperventilation induced dynamic hyperinflation. End point will be to correlate increase in tiotropium induced FEV 1(L) and inspiratory capacity with extent of underlying emphysema as scored by lung CT ( Gelb AF et al:Chest 1996; 109: 353-359)in 29 patients with COPD. We will also correlate the decrease in inspiratory capacity following metronome paced hyperventilation induced dynamic hyperinflation with extent of lung CT scored emphysema.