Impact of tidal volume, GAP index and anti-fibrotic treatment on disease progression and mortality in IPF patients

Background: Despite novel treatment options, idiopathic pulmonary fibrosis (IPF) still shows a progressive and fatal course. In search for further parameters of disease progression, we studied the role of Tidal Volume (VT), alongside with established risk factors such as FVC or GAP index. Aim and Methods: We analyzed 266 IPF patients recruited in Giessen und Paris into the eurIPFreg for baseline data, change in VT or other lung function values, and intake of antifibrotics (AF) for a follow up period of up to ten years. The estimated effects of VT on the hazard ratio (HR) were adjusted by sex, age at t0, smoking status, AF, ideal body weight and GAP score at t0. Results: The cohort showed the following demographics: 80.6% males, mean age at t0 67.8 years, FVC 64.7% pred., 77.4% active or previous smokers. VT correlated significantly with VC % pred., FVC % pred., pH and pCO2. A survival analysis revealed a highly significant impact of GAP score on survival, higher in the group under AF. VT also exerted significant effects on survival; every 100ml increase in the baseline VT was associated with a predicted decrease of the HR by a factor of 0.84 and a correspondingly improved survival. There was no clear evidence for a protective effect of very low TV. Conclusions: In IPF subjects, multiple factors affect outcome, among these are GAP index, smoking, antifibrotic treatment, and also VT. Against our anticipation, very low VTs were not associated with improved outcome, most likely because baseline VT is impacted by FVC and, hence, the extent of fibrotic disease.