Abstract
The clinical application of maximum expiratory flow-volume (MEFV) curves in making an early diagnosis of emphysema and disease of small airways is reviewed. Previous analysis of the physiologic basis of the forced expiratory spirogram indicates that the MEFV curve contains the same information as the volume-time plot. However, the MEFV curve more readily allows quantitative analysis of flow at both high and low lung volumes during forced exhalation. In early obstructive airway diseases pathology may be limited to peripheral airways. Analysis of flow at low lung volume is therefore diagnostically important, because the peripheral airways make their greatest contribution to total airway resistance at low lung volumes, and flow is related to the geometry of the noncompressed small airway units. In early emphysema physiologic abnormalities should be most apparent at low lung volumes because of the shape of the pressure-volume curve. The diffusing capacity is reduced in the presence of parenchymal destruction, as in emphysema, but is not decreased in diseases limited to airways.
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