We enrolled stable outpatients with chronic obstructive pulmonary disease who had a forced expiratory volume in 1 s ( FEV1 ) of less than 50 % predicted , significant hyperinflation ( total lung capacity > 100 % and residual volume > 150 % ) , a restricted exercise capacity ( 6 min walking distance < 450 m ) , and substantial breathlessness ( MRC dyspnoea score 3 ) .