Effects of tiotropium or combined therapy with salmeterol on hyperinflation in COPD

Hyperinflation is widely accepted as an abnormal state affecting clinical symptoms, activities of daily living and exercise tolerance in chronic obstructive pulmonary disease (COPD). Reducing hyperinflation is an essential theme in COPD treatment. In this study, we let patients with COPD hyperventilate to evoke hyperinflation, and evaluated the effects of tiotropium alone or in combination with salmeterol on hyperventilation-evoked hyperinflation.

Thirty-eight patients with COPD received pulmonary function tests including hyperventilation-evoked hyperinflation testing and the St. George's Respiratory Questionnaire (SGRQ) before treatment, after tiotropium administration for 8 weeks, and after combined therapy with salmeterol for 8 weeks.

Before treatment, inspiratory capacity (IC) after hyperventilation decreased significantly in a breathing frequency-dependent manner. After tiotropium administration, forced expiratory volume in one second (FEV1) increased significantly. IC after hyperventilation decreased significantly in a breathing frequency-dependent manner; however, IC was significantly greater than that before treatment (at rest, p=0.001; after hyperventilation at twice the resting respiratory rate, p=0.0009; and after hyperventilation at three times the resting respiratory rate, p<0.0001). The SGRQ score also improved significantly. After combined therapy with salmeterol, FEV1 increased significantly compared with after tiotropium alone. However, there was no significant difference between the IC after tiotropium alone and that after combined therapy, at each stage. However, after combined therapy the SGRQ score significantly improved compared with that after tiotropium alone.

Tiotropium improved airflow obstruction and hyperventilation-evoked hyperinflation. In combination with salmeterol, the improvement in airflow obstruction was greater, but hyperventilation-evoked hyperinflation was not further improved.