Progressive TLC loss after unilateral lung transplantation in IPF: Functional respiratory imaging differentiates between transplanted and native lung

Abstract

Background: After unilateral lung transplantation (ULT) changes in lung function (LF) may be difficult to attribute to either the transplanted or native lung. Differentiation may be extremely important when LF suggests bronchiolitis obliterans syndrome (BOS) or restrictive airway syndrome (RAS). Previous work from our group demonstrated with functional respiratory imaging (FRI) that disease progression in IPF is characterized by an increase in fibrosis (lung tissues density), decrease in lung volumes and increased airway caliber. Aims and objectives: Here we aimed to find out whether FRI could help to find the cause of progressive decrease in TLC and VC after left ULT in IPF. Methods: Inspiratory CT scans were collected at Y6, Y8 and Y10 after ULT. We collected FRI data for both the transplanted and native lung for the relative lung volume, the specific airway volume and the average Hounsfield unit (HU) compensated for lung volume. Results: TLC was 4.98 (75%) and 3.93 (59%) at Y6 and Y10 after ULT, respectively. VC was 3.46 (82%) and 2.77 (68%) at Y6 and Y10 after ULT, respectively. FRI demonstrated that this reduction in lung volumes was attributed to a reduction in the native lung volume (41% and 34% of total at Y6 and Y10, respectively) caused bya significant increase in fibrotic tissue (+23%). Conclusions: Here we show that FRI enables to differentiate between characteristics of left and right lung, in contrast to measurements of TLC and VC, both parameters unable to distinguish between left and right lung. FRI helped us to conclude that the progressive decrease in TLC after ULT was mainly caused by progressive fibrosis in the native lung.