Airflow limitation and inspiratory capacity at rest to total lung capacity ratio (IC/TLC) as a measure of resting hyperinflation were measured in 59 patients with COPD (GOLD I-IV). Mean daily physical activity was assessed with a tri-axial accelerometer. Measurements of dynamic hyperinflation during ADL (¦¤IC and inspiratory reserve volume at end ADL) were performed at patients' home using a portable breath-by-breath system.
Multiple regression analysis showed that resting as well as ADL-induced dynamic hyperinflation independently contributed to decreased daily physical activity, together explaining 45.8 % of the variance in physical activity. In contrast to hyperinflation, the severity of airflow limitation (FEV1) appeared to have no unique part in explaining how physically (in-) active patients were.
The presence of resting hyperinflation and occurrence of dynamic hyperinflation during ADL contribute to reduced physical activity levels in patients with COPD, independently of the degree of airflow limitation.