We read with considerable interest the letter from M Carone and FG Salerno, in which they commented on our article demonstrating that forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) negatively predicts survival in idiopathic pulmonary fibrosis (IPF).1
As M Carone and FG Salerno described, it is true that lung elastic recoil increases with progression of lung fibrosis in IPF. The idea that high lung elastic recoil makes it difficult to blow expiration fast and consequently makes FEV1/FVC high might be possible. Evaluating real lung compliance by measuring transpulmonary pressure of patients with IPF and assessing an association with FEV1/FVC would be helpful to understand the mechanism, as M Carone and FG Salerno suggested.
Cortes-Telles et al. demonstrated a negative relationship between disease severity assessed with total lung capacity and FEV1/FVC, although they excluded patients with FEV1/FVC < 70% and with evident emphysema on chest CT from their analysis.2 Furthermore, a few studies demonstrated a negative relationship between FEV1/FVC and survival the same as in our study.3,4 Therefore, it is likely that lower FEV1/FVC has a favorable impact on both severity and survival in IPF, considering the consistent results of previous reports including ours.
Several reasons might explain the favorable impact of low FEV1/FVC in IPF. The somewhat good effect of smoking, simply negative mirror image of FVC, and increased lung elastic recoil which was proposed in the letter would be candidates. In our data, FEV1/FVC showed a significant negative relationship with survival1; however, interestingly, the significant relationship disappeared when evaluated among only never smokers, although the number of patients who were included in the analysis decreased from 114 to 57 (data not shown). Further studies among more patients exclusively with never smokers and/or among patients whose detailed smoking history, such as pack-year, are available may provide some insights. Anyways, we definitely concur with the opinion of M Carone and FG Salerno that further studies are needed to understand the role of airway obstruction which is involved in IPF.
References
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