Temporal Patterns of Body Composition After Heart and Lung Transplantation Assessed by Bioelectrical Impedance Analysis

Background/Objectives: Body composition may influence functional capacity and long-term outcomes after thoracic organ transplantation. However, direct comparisons of body composition patterns between heart transplant (HTx) and lung transplant (LTx) recipients remain limited. This study compared body composition parameters and their relationship with time since transplantation in HTx and LTx recipients using bioelectrical impedance analysis (BIA). Methods: This cross-sectional study included 79 clinically stable transplant recipients (38 HTx and 41 LTx) with a median time of 9 months after transplantation (range, 1 month–9 years). Body composition was assessed using the SECA mBCA 515 analyzer. Absolute fat mass (AFM), relative fat mass (RFM), fat-free mass (FFM), skeletal muscle mass (SMM), phase angle (PA), and extracellular water-to-total body water ratio (ECW/TBW) were measured. Associations between body composition parameters and time since transplantation were modelled using adjusted generalized additive models with separate smooth functions for HTx and LTx recipients. Results: Positive cross-sectional associations between AFM and time since transplantation were observed during the 3–9-month post-transplant interval in both groups (HTx: 0.72 kg/month, p = 0.042; LTx: 0.83 kg/month, p = 0.021). In contrast, significant positive associations between SMM and time since transplantation were observed exclusively among LTx recipients during the 1–3-month (0.59 kg/month, p = 0.039) and 3–9-month (0.49 kg/month, p = 0.003) intervals, whereas no significant associations were observed after HTx. In LTx recipients, ECW/TBW was negatively associated and PA positively associated with time since transplantation during the 3–9-month interval. Conclusions: HTx and LTx recipients exhibited different cross-sectional patterns of body composition according to time since transplantation. HTx recipients were characterized by greater adiposity without a significant association between SMM and time since transplantation, whereas LTx recipients showed positive associations between SMM and time since transplantation during the early post-transplant intervals.