Locke E, Thielke S, Diehr P, Wilsdon AG, R Barr G, Hansel N, Kapur VK, Krishnan J, Enright P, Heckbert SR, et al. Effects of respiratory and non-respiratory factors on disability among older adults with airway obstruction: the Cardiovascular Health Study. COPD. 2013  ;10(5):588-96.