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

Abstract

Background: Patients with chronic obstructive pulmonary disease have an increased inspiratory work, since they must overcome high loads due to increased airway resistance.

Aim: To determine if the reduction in the metabolic cost of exercise observed in patients with chronic obstructive pulmonary disease (COPD) after inspiratory muscle training, was due to a reduction in the 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 with COPD (FEV1 44 +/- 18%) not subjected to training, and 7 healthy controls (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 containing air and 5% CO2. Exercise VO2 was measured at submaximal exercise.

Results: Oxygen cost of breathing was increased in patients with COPD and it 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 the reduction in exercise VO2 or the increment in maximal inspiratory pressure.

Conclusions: The reduction in exercise VO2 after inspiratory muscle training is not due to a reduction in the oxygen cost of breathing.