Effects of inspiratory muscle training on the oxygen cost of breathing in patients with chronic obstructive pulmonary disease

Background: Patients with chronic obstructive pulmonary disease have an inc reased inspiratory work, since they must overcome high loads due to increas ed airway resistance. Aim: To determine if the reduction in the metabolic c ost of exercise observed in patients with chronic obstructive pulmonary dis ease (COPD) after inspiratory muscle training, was due to a reduction in th e oxygen cost of breathing. Patients and methods: Nine patients with COPD ( FEV1 39 +/- 13%) subjected to inspiratory muscle training, using a training load of 30% of maximal inspiratory pressure, during 10 weeks; 5 patients w ith COPD (FEV1 44 +/- 18%) not subjected to training, and 7 healthy control s (FEV1 110 +/- 10%) were studied. The cost of breathing was calculated as the difference in VO2 measured at rest and after breathing a gas mixture co ntaining air and 5% CO2. Exercise VO2 was measured at submaximal exercise. Results: Oxygen cost of breathing was increased in patients with COPD and i t was inversely correlated with FEV1 (r= -0.86 p<0.001). Inspiratory muscle training increased maximal inspiratory pressure and decreased exercise VO2 . Oxygen cost of breathing increased in six and decreased in three trained patients. Changes in this parameter after training did not correlate with t he reduction in exercise VO2 or the increment in maximal inspiratory pressu re. Conclusions: The reduction in exercise VO2 after inspiratory muscle tra ining is not due to a reduction in the oxygen cost of breathing.