Fundamental reason
Currently used spirometry measures for airflow obstruction are influenced by demographics, predominantly age, which complicates the selection of diagnostic thresholds for the presence of airflow obstruction.
Goals
To develop diagnostic thresholds for the D parameter , a new metric for the detection of airflow obstruction, which quantifies the rate of increase in expiratory volume over time.
Methods
We analyzed spirometry data from normal subjects enrolled in the 2007-2008, 2009-2010, and 2011-2012 NHANES (National Health and Nutrition Examination Survey) cohorts and calculated the D parameter using the expiratory volume-time curve.
Relationships between demographics and lung function (forced expiratory volume in 1 second [FEV 1 ], FEV 1 /forced vital capacity [FVC] and D parameter) were tested using generalized linear models in NHANES and UK Biobank. Variation in lung function explained by demographics was estimated using R 2. A diagnostic threshold for parameter D was developed using population-based percentiles.
According to the agreement between the lower limit of normal (LIN) for FEV 1 /FVC and the threshold of the D parameter, four groups were identified: normal (no airflow obstruction according to any of the criteria), D + chronic obstructive pulmonary disease ( D + COPD; positive only by the D parameter), D − COPD (positive only by LIN), and COPD (positive by both criteria), and associations with structural lung disease, exacerbations, and mortality were tested by multivariable analyses.
Results
Unlike FEV 1 and FEV 1 /FVC, demographics cumulatively explained only 9% of the variance in parameter D in NHANES (n = 4,945) and 3% in UK BioBank (n = 109,623). In COPDGene (Chronic Obstructive Pulmonary Disease Genetic Epidemiology) (n = 9542), 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 1 /FVC
Over 5 years, 28% of the COPD D+ group versus 8% of the normal group progressed to COPD by traditional criteria.
Conclusions The D parameter is not affected by age, and a normal population-based diagnostic threshold results in early identification of additional individuals with airflow obstruction with a substantial amount of structural lung disease and respiratory symptoms. |
