A 62-year-old woman is evaluated in follow-up after her first hospitalization for an acute exacerbation of COPD. She is currently completing a 5-day course of oral glucocorticoids. She has not had fever, and her cough and sputum production have improved. Although she feels much better, she notes that her exercise capacity has not returned to its preadmission baseline. Medical history is otherwise unremarkable. She has a 30-pack-year history of smoking but stopped smoking 3 years ago. Her medications are tiotropium, mometasone/formoterol, and as-needed albuterol.

On physical examination, vital signs are normal. Oxygen saturation breathing ambient air is 92%. Lung examination shows mildly diminished airflow but is otherwise clear. The remainder of the examination is unremarkable.

Pulmonary function testing performed 5 months ago showed an FEV1 of 55% of predicted.

Which of the following is the most appropriate treatment?