Parameter D: New Measure of Airflow Obstruction

Currently used spirometry measures of airflow obstruction are influenced by demographics, predominantly by age, complicating selection of diagnostic thresholds for the presence of airflow obstruction. To develop diagnostic thresholds for Parameter D, a new metric for detection of airflow obstruction, which quantifies the rate of rise of expiratory volume over time. We analyzed spirometry data of normal subjects enrolled in the 2007-2008, 2009-2010, and 2011-2012 NHANES (National Health and Nutrition Examination Survey) cohorts and calculated Parameter D using the expiratory volume-time curve. Relationships between demographics and lung function (forced expiratory volume in 1 second [FEV ], FEV /forced vital capacity [FVC], and Parameter D) were tested using generalized linear models in NHANES and UK Biobank. The variation in lung function explained by demographics was estimated using . A diagnostic threshold was developed for Parameter D using population-based percentiles. Based on concordance between the lower limit of normal (LLN) for FEV /FVC and the Parameter D threshold, four groups were identified: normal (no airflow obstruction by either criterion), D chronic obstructive pulmonary disease (D COPD; positive by Parameter D only), D COPD (positive by LLN only), and COPD (positive by both criteria), and associations with structural lung disease, exacerbations, and mortality were tested using multivariable analyses. In contrast to FEV and FEV /FVC, demographics cumulatively explained only 9% of the variance in Parameter D in NHANES ( = 4,945) and 3% in UK BioBank ( = 109,623). In COPDGene (Genetic Epidemiology of Chronic Obstructive Pulmonary Disease) ( = 9,542), a diagnostic threshold of -3.15 resulted in the identification of an additional 10.8% of participants with airflow obstruction. A total of 3.7% had FEV /FVC