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.