Early bronchiolitis obliterans syndrome shows an abnormality of perfusion not ventilation in lung transplant recipients

• The physiological changes of Chronic Allograft Dysfunction (CLAD) post lung transplantation are poorly understood.
• In very early BOS, stage 0p, there is significant heterogeneity of perfusion compared to no BOS (BOS stage 0).
• BOS-0p is different in nature from other BOS stages, presenting with an increased heterogeneity in perfusion, but not ventilation.

Long-term survival of lung transplant patients is limited, principally because of Bronchiolitis Obliterans Syndrome (BOS). BOS is primarily classified based on airflow obstruction however there is recent data to suggest that the rejection process can lead to a restrictive ventilatory defect with involvement of the pulmonary vasculature. This study evaluates perfusion heterogeneity in different BOS stages by measuring the relative dispersion (RD) of an arterial spin labelling MRI blood flow image. Acinar ventilation heterogeneity (Sacin) was determined using the Multiple Breath Nitrogen Washout technique. In 24 post transplant patients with a range of severity in BOS status, Sacin increased as BOS level rose from stage 0 to stage 3. In contrast, RD-perfusion was not elevated at BOS 1 and 2 combined compared to BOS 0 and becoming elevated only at BOS-3. However, RD-perfusion in BOS-0p was elevated compared to BOS-0, without an increase in Sacin. These results suggest that BOS-0p is different in nature from other BOS stages.