Respiratory oscillometry in monitoring lung transplant allograft function: a systematic scoping review

Acute and chronic lung rejection are major barriers to the long-term survival of lung transplant recipients. Current spirometry-based monitoring of allograft function is limited by the low sensitivity in detecting distal airway abnormalities where allograft rejection evolves. Emerging evidence from haematopoietic stem cell transplant patients with chronic pulmonary graft-versus-host disease suggests that respiratory oscillometry may offer improved sensitivity in identifying small airway obstruction at earlier stages. In this scoping review, we explore the utility of oscillometry in monitoring lung transplant allograft function. We identify eight studies reporting the analysis of 1282 bilateral and 36 single lung transplant (SLT) recipients conducted between 2016 and 2024. While the limited number of studies precludes definitive conclusions, the review findings highlight some compelling and promising data. Oscillometry may be more sensitive in detecting acute rejection, tracking graft injury and monitoring rejection treatment than spirometry. Additionally, oscillometry demonstrated the potential to independently identify and distinguish different chronic lung allograft dysfunction (CLAD) phenotypes at onset, providing a risk assessment for subsequent CLAD development. Oscillometry parameters also correlated well with spirometry in both healthy lung allografts and advanced CLAD cases, suggesting that oscillometry may complement or even substitute for spirometry in situations where spirometry is not feasible. This review underscores the potential of respiratory oscillometry as a valuable tool in post-lung transplant monitoring. Future large-scale, multicentre, prospective studies are needed to further validate its clinical utility, especially in combination with spirometry and other noninvasive modalities, to enhance the early detection and management of allograft rejection.