Resting and ADL-induced dynamic hyperinflation explain physical inactivity in COPD better than FEV1.
BACKGROUND
Physical activity and health status deteriorate early in the course of chronic obstructive pulmonary disease (COPD). This can only partially be explained by the degree of airflow limitation. Changes in (resting and dynamic) lung volumes are known to be associated with functional impairments and thus might influence physical activity level. The aim of the present cross-sectional study was to explore the contribution of dynamic hyperinflation during daily life activities (ADL) in the decline in physical activity.


METHODS
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 (ΔIC and inspiratory reserve volume at end ADL) were performed at patients' home using a portable breath-by-breath system.


RESULTS
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.


CONCLUSIONS
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.