An Insensitive Measure of Impairment in Patients with Asbestosis and Chronic Obstructive Pulmonary Disease?

interstitial fibrosis (asbestosis) and COPD in causing impairment is difficult to ascertain because both will tend to similarly affect commonly used physiologic parameters of impairment; forced vital capacity (FVC); forced expiratory volume in one second (FEy,), diffusing capacity (D), and alveolar-arterial oxygen gradient (P[A-a]O,); however, the total lung capacity (TLC) is affected in opposite directions by asbestosis (decreases TLC) and COPD (increases TLC).56 Despite the confounding effect of COPD, the TLC is frequently used as both a diagnostic criterion for asbestosis, as well as an indication of the degree of restrictive impairment attributable to asbestosis. Because of the opposing effects of COPD and