In contrast to the decline in FEV₁, the behavior of dynamic hyperinflation (DH) over time is unknown in patients with COPD. Metronome-paced hyperventilation (MPH) is a simple applicable surrogate for exercise to detect DH.

To evaluate changes in MPH-induced DH during two years follow-up in mild-to-severe COPD patients. Additionally, influence of smoking status on DH and the relation between DH and other lung function parameters were assessed.

Patients were recruited from a randomized controlled trial conducted in general practice. Measurements of lung function and DH were performed at baseline and after 12 and 24 months. DH was assessed by MPH with breathing frequency set at twice the baseline rate. Change in inspiratory capacity after MPH was used to reflect change in end-expiratory lung volume and therefore DH, presuming constant total lung capacity.

During follow-up, 68 patients completed all measurements. DH increased by 0.23±0.06L (p≤0.001). No significant changes in FEV₁ %pred were seen. Smokers had lower FEV₁ and a more rapid decline than non-smokers. DH in smokers increased more over time compared to non-smokers. The amount of DH correlated positively with resting inspiratory capacity.

After two years, a significant increase in MPH-induced DH in COPD patients was demonstrated, which was not accompanied by a decline in FEV₁. It might be that DH is a sensitive measure to track consequences of changes in airflow obstruction.