Simplified Diagnosis of Small-Airway Obstruction

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Abstract
Two simple, noninvasive single-breath tests, the maximum expiratory flow volume curve and "closing volume," were used to detect obstruction of the small airways in nine patients with respiratory problems but with normal results on routine pulmonary-function studies. These nine patients, however, did have an abnormal alveolar-arterial oxygen gradient at rest (22 to 40 mm Hg) and exhibited frequency dependence of dynamic lung compliance, suggesting small-airway obstruction. "Closing volume" was abnormally high in seven of the nine patients (18 to 40 per cent of vital capacity), and the curves for maximum expiratory flow volume were abnormal in all, especially at low lung volumes.