Epidemiological limitations of the nitrogen closing volume test.

Closing volume was measured in 216 men aged 46-68 years. They were divided in 5 age groups and classified as either symptomatic or asymptomatic according to answer to standardized interviews. In 3 of 5 age groups mean value for closing volume percent (CV%) for symptomatic persons was lower than the mean value for asymptomatic persons. CV% is not considered useful as the dependent variable in a multiple regression analysis. In all 5 age groups the mean value of slope of alveolar plateau was higher for symptomatic than for asymptomatic persons. Slope af alveolar plateau is considered useful as dependent variable in a multiple regression analysis. One of the reasons for the false negative CV%-values is believed to be influence of increased uneven and sequential ventilation of the lungs, expressed in the slope of alveolar plateau.