FEV1 is used for the classification of disease severity and is a good predictor of COPD mortality. However, it is a poor predictor of clinical symptoms, exercise tolerance, and response to bronchodilators in COPD. Progressive reduction in inspiratory capacity (IC) during exercise reflects dynamic hyperinflation and is a good predictor of decreased exercise ability as well as increased exertional dyspnea. In animal models of COPD, N-acetylcysteine (NAC), an antioxidant/mucous modifier, has been shown to modify small airways, which mainly causes lung hyperinflation.
Our goal was to examine the effect of 1,200 mg/d of NAC on lung hyperinflation at rest and after exercise in patients with moderate-to-severe COPD.
This was a randomized, double-blind, cross-over study that included 24 eligible patients > 40 years of age with a diagnosis of COPD, a FEV1 < 70% of predicted, FEV1/FVC ratio < 0.70, and a functional residual capacity > 120% of predicted normal. Patients were randomized to placebo treatment or NAC treatment twice daily for 6 weeks. This was followed by a 2-week washout period, and then patients were crossed over to alternate therapy for an additional 6 weeks. Evaluation was performed after each 6 weeks of each treatment.
IC and FVC were higher especially after exercise after NAC treatment compared with placebo treatment. In addition, the relationship of residual volume to total lung capacity was reduced in a similar pattern. Furthermore, endurance time was longer after NAC treatment compared with placebo treatment.
NAC treatment of patients with stable, moderate-to-severe COPD has a beneficial effect on physical performance, probably due to a reduction in air trapping.
Clinicaltrials.gov Identifier: NCT00476736