Measurement of "closing volume" as a simple and sensitive test for early detection of small airway disease.

Abstract A single-breath Argon bolus method for measuring the lung volume at which the dependent lung zones cease to ventilate presumably as a result of airway closure (i.e., the "closing volume") was used on a group of sixty-six nonsmokers and on a group of forty-six smokers, whose ages ranged between eighteen and eighty-two years. "Closing volumes" were measured with the subjects in the sitting and supine positions together with the subdivisions of lung volume, one second forced expired volume (FEV 1 ), maximum expiratory flow rate (MEFR), airway resistance (Raw) and specific airway conductance (SGa). In both seated and supine nonsmokers the percentage ratio of "closing volume" to vital capacity increased linearly with age. In thirty-three seated smokers (72 per cent of all smokers studied) either the percentage ratio of "closing volume" to vital capacity was above the normal limits (+2 SD) for nonsmokers or there was a profound abnormality of the expired alveolar plateau, indicating disease of the small airways. Similar results were found with the subjects in the supine position. In only fourteen smokers (30 per cent of all smokers studied) results of one or more of the conventional lung function tests were outside the normal limits. It is concluded that measurement of the "closing volume" provides a test which detects small airway abnormalities much earlier than the conventional lung function tests. Furthermore, the test is so simple and rapid that it is suitable for routine or wide-scale studies.