Impact of thoracic muscle volume on survival after lung transplantation

<bold>Background:</bold> Conflicting evidence exists regarding the association between body mass index (BMI) and survival after lung transplantation. BMI does not provide information on muscle, bone and fat distribution and is limited in assessing the overall body composition (BC). More specific measures of BC may help overcome this limitation. <bold>Aims:</bold> To evaluate the impact of thoracic muscle volume on 1-year survival after lung transplantation. <bold>Methods:</bold> A retrospective, automated BC analysis was conducted using a trained deep-learning network on chest CT scans obtained during lung transplantation evaluation at our center. Muscle volume was quantified and divided by bone volume to obtain a body size-adjusted muscle ratio. Cox models were used to analyze the influence of muscle ratio on 1-year mortality, controlling for donor and recipient factors. <bold>Results:</bold> Pre-transplant chest CT scans were available from 330 patients undergoing lung transplantation between 2010 and 2022. The cohort had a mean age of 51.87 years with 137 (42%) being female. COPD (n=117, 35%) and ILDs (n=132, 40%) were the most prevalent diseases. BMI and muscle ratio showed weak correlation (r=0.293, p<0.001). Smoothing spline regression revealed a continuous association between muscle ratio and 1-year mortality (linearity, p=0.003). For application of cox models, patients were grouped according to muscle ratio quartiles. Patients in the lowest quartile showed increased 1-year mortality (adjusted HR 2.28, 95%CI:1.22-4.25). In contrast, patients in the highest quartile did not exhibit a reduced 1-year mortality (HR 0.75, 95%CI: 0.34-1.66). <bold>Conclusions:</bold> Low muscle volume, as assessed with automated BC analysis, is associated with increased 1-year mortality.