Supernormal Maximal Mid-Expiratory Flow Rates in Diffuse Interstitial Lung Disease

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Abstract
The frequency of changes in maximal mid-expiratory flow rate (MMF) were studied in 32 nonsmokers and 22 smokers with diffuse interstitial lung disease (DILD) and in 36 healthy nonsmoking control subjects. Supernormal MMF to total lung capacity (TLC) and MMF to forced vital capacity (FVC) ratios (> 120% of predicted) were significantly more common in nonsmokers with DILD than in healthy nonsmokers but the prevalence of supernormal forced expired volume in 1 s (FEV1) to FVC ratios was similar. In nonsmokers with DILD, a supernormal MMF/TLC ratio was associated with a significantly greater static lung recoil pressure (Pst) and a tendency toward a higher maximal expiratory flow to Pst ratio than in normals, suggesting that the increased MMF is due to the combined effects of increased driving pressure for flow and reduced resistance in peripheral airways.