C47-30 Parametric Response Mapping Patterns in Chronic Lung Allograft Dysfunction-Free Lung Transplant Recipients

Abstract Rationale Parametric Response Mapping (PRM) is a computed tomography (CT) voxel-based method applied to paired inspiratory and expiratory CT that identifies normal lung, functional small airways disease (fSAD), or parenchymal disease (PD). Prior studies have shown that elevated fSAD is associated with chronic lung allograft dysfunction (CLAD). PRM patterns in CLAD-free patients remain incompletely characterized. Methods We conducted a cross-sectional analysis of a multicenter prospective cohort study evaluating the utility of PRM as a noninvasive biomarker for chronic lung allograft dysfunction (CLAD) prediction. Bilateral lung transplant recipients (LTR) with a forced expiratory volume in 1 second (FEV1) greater than 90% of their baseline FEV1 were enrolled. Whole lung CT scans taken at study enrollment were analyzed with PRM to quantify the percentage of normal lung, fSAD, PD, and emphysema. Baseline lung allograft dysfunction (BLAD), a term describing abnormally low lung function, was defined as an FEV1 Z-score -1.645 at the time of enrollment. Group differences were assessed using Wilcoxon rank-sum test. This study was approved by the University of Michigan, IRB HUM00177002. Results After exclusions, 247 patients were analyzed. There were 103 (41.7%) females, and the median age was 61.0 years (interquartile range (IQR): 53.0-67.0). The median time from transplant to enrollment was 15.0 months (IQR: 7.0-35.0), and 116 (47.0%) patients were less than 1 year from transplant. The median PRM percentages were: normal lung 69.4% (IQR: 56.3-77.7), PD 12.7% (IQR: 8.3-23.0), fSAD 0.6% (IQR: 0.1-4.2), emphysema 0.1% (IQR: 0.0-0.1). The number of patients with fSAD 10% was 210 (85.0%) and fSAD 5% was 191 (77.3%). The mean raw FEV1 was 2.63 (standard deviation (SD): 0.7). BLAD was present in 52 (21.1%) patients. The median percentage of PD was higher in patients with BLAD (26.0%, IQR: 15.0-37.8%) compared with BLAD-free patients (11.2%, IQR: 8.0-19.0%, p 0.001). Patients that were less than 1 year post-transplant had higher PD percentage (14.9, IQR: 10.5-26.0) than patients greater than 1 year post-transplant (10.6, IQR: 6.6-19.7, p 0.0001). Conclusions In a population of CLAD-free bilateral lung transplant recipients, most had a low percentage of functional small airway disease by Parametric Response Mapping CT analysis. The percentage of PRM-identified parenchymal disease was higher in patients with BLAD and in patients less than 12 months post-transplant. This abstract is funded by: CF Foundation #LAMA23AB0