1-second forced expiratory volume and density dependence in early airflow limitation

Density dependence variables (helium-to-air difference in forced expiratory flows at 50 and 25% vital capacity and volume of isoflow) were compared with spirographic performance (vital capacity, FEV 1.0) in 76 men aged 33-56 years. The group included nonsmokers, asymptomatic smokers, subjects with chronic expectoration, but normal ventilatory function and subjects with chronic expectoration and minimal obstructive ventilatory impairment. Low-level correlations were found (coefficients of less than 0.3) between delta He25% or volume of isoflow on one side and FEV1.0 or FEV1.0/VC. Some possibly confounding factors for these correlations are discussed. We conclude that density dependence variables are not consistently related to the FEV1.0 in subjects 'at risk' or with minimal airflow limitation.