Parameter D: A New Metric for Measuring Airflow Obstruction

A new study published in the Annals of the American Thoracic Society suggests that Parameter D may be a new metric for measuring airflow obstruction. Currently used spirometry measures of airflow obstruction are influenced by demographics, predominantly by age, complicating the selection of diagnostic thresholds for the presence of airflow obstruction.

A study was conducted to develop diagnostic thresholds for Parameter D, a new metric for detecting airflow obstruction, which quantifies the rate of rise of expiratory volume over time. Researchers 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 [FEV1], FEV1/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 R². A diagnostic threshold was developed for Parameter D using population-based percentiles. Based on concordance between the lower limit of normal (LLN) for FEV1/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)
• COPD (positive by both criteria)

Associations with structural lung disease, exacerbations, and mortality were tested using multivariable analyses.

Results

In contrast to FEV1 and FEV1/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 (Genetic Epidemiology of Chronic Obstructive Pulmonary Disease) (n = 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 FEV1/FVC < LLN but were missed by the Parameter D threshold.

Compared with subjects in the normal group, after adjustment for age, sex, race, body mass index, pack-years of smoking, and current smoking status, D+COPD was associated with:

• Worse structural lung disease (odds ratio [OR] for ⩾5% emphysema, 1.71; 95% confidence interval [CI], 1.37–2.12; OR for functional small airway disease ⩾ 15%, 2.1; 95% CI, 1.79–2.67)
• Significant symptoms (OR for modified Medical Research Council dyspnea score ⩾ 2, 1.25; 95% CI, 1.07–1.47; OR for St. George’s respiratory questionnaire ⩾ 25, 1.31; 95% CI, 1.13–1.53)
• A greater frequency of exacerbations (incidence rate ratio, 1.26; 95% CI, 1.10–1.46)
• Higher mortality (hazard ratio, 1.32; 95% CI, 1.10–1.57)

Over 5 years, 28% of the D+COPD group versus 8% of the normal group progressed to COPD by traditional criteria.

Parameter D is not affected by age, and a normal population-based diagnostic threshold results in the early identification of additional individuals with airflow obstruction with a substantial amount of structural lung disease and respiratory symptoms.

Reference

Eric Gartman, Matthew Jankowich. (2023) D for Destiny? Parameter D and Chronic Obstructive Pulmonary Disease. Annals of the American Thoracic Society 20:7, 953-954. Online publication date: 30 June 2023.

Keywords

Parameter D, new, metric, measuring, airflow, obstruction, Annals of the American Thoracic Society, Eric Gartman, Matthew Jankowich