Low physical activity is associated with mortality in COPD, but until now, only on the basis of self-reported activity levels. Waschki et al prospectively followed 170 people (~75% men, ~65 years old) with stable COPD for 48 months. Besides spirometry (mean FEV1 56% predicted), the investigators also collected other data expected to be predictive, including ankle-brachial index, inflammatory biomarkers, all the parameters of established prognostic indices (like BODE), BNP, echocardiography, etc.
They also followed physical activity level with actigraphy / pedometry. Guess what? Physical activity level predicted survival independently and more robustly than any other variable:
- The most active in the cohort had 0% mortality at 4 years.
- The sedentary had 9% mortality, 91% survival. Not bad.
- The "very inactive" had 31% mortality at 4 years. (I didn't know there was a category of inactivity below sedentary.)
The survivors walked about 1,600 steps more each day than the nonsurvivors.
Other variables also predicted survival (BODE index, ABI, etc), but not as well as activity level. Combining activity level with ankle-brachial index and adiponectin level had the best area-under-the-curve in predicting survival. CHEST 2011;140:331-342.
I recognize that this was not an intervention study. Nevertheless, how on earth do we get people with COPD to move more?