Background
Lung volume change in idiopathic pulmonary fibrosis (IPF) or chronic obstructive pulmonary disease (COPD) may impact upon fissures and diaphragm. CT measures designed to capture displacement of these structures may play a role in prognostication.

Methods
The cohorts studied were: baseline IPF with 273 patients (205 males, median age 67), serial IPF with 81 patients (66 males, median age 67) and baseline COPD with 150 patients (76 males, median age 64). Selected HRCT signs included oblique fissure retraction distance (OFRD), anterior junctional distance (AJD), sagittal lung height (SLH) and superior mediastinal level (SML). The disease extent on HRCT in IPF was scored by two observers. In COPD cohort, an automated application (Syngovia) was used for disease quantification. The CT measurements were validated against PFTs and mortality using linear regression and proportional hazards analyses.

Results
There were 203 baseline and 58 serial deaths in IPF cohorts with median survival 26 and 17 months respectively. In baseline IPF and COPD, SLH was the strongest determinant of TLC% and RV/TLC% respectively (R2 =0.28, P<0.005 and R2 =0.1 respectively, P<0.0005). In baseline IPF data, a combination of SLH, AJD and OFRD improved correlation with TLC% (R2=0.42, P<0.0005), predicting mortality independent of visual scores (HR=97, CI 0.96,0.99, P<0.0005). In serial IPF, annual AJD change predicted mortality (HR 0.97, 95% CI 0.95, 0.98; P<0.0005) better than annual FVC change (HR 0.98, 95% CI 0.96, 0.99; p<0.0005). In COPD, there was significant difference in patients with or without upper-zone predominant disease for OFRD and SML (P=0.04 and P<0.0005 respectively).

Conclusion
The CT signs of lung volume change correlate moderately with PFTs in COPD and IPF; being independent predictors of mortality when adjusted for visual scores in IPF and providing signal on zonal distribution of disease in COPD. In IPF, AJD proved to be a better predictor of outcome compared to FVC sequentially.