Use of over-sized mature pulmonary lower lobe grafts results in superior pulmonary function

Background. Mature lobar transplantation will increase the pediatric donor organ pool; however, issues regarding size discrepancy between donor grafts and recipient lungs remain unresolved. We hypothesized that an over- sized mature pulmonary lobar allograft implanted into an immature recipient would provide adequate long-term pulmonary function versus a size-matched mature lobar graft or an immature whole lung. Methods. We investigated our hypothesis in a porcine orthotopic left lung transplant model in which 19 immature animals made up one control and three recipient groups. Group I underwent sham left thoracotomy (control, n = 4). Group II received age- and size-matched immature whole left lung transplant (n = 6). Group III received mature size-matched left upper lobe transplants (n = 4). Group IV received mature over-sized left lower lobe transplants (n = 5). Twelve weeks after implantation, data were collected after the native fight lung was excluded. Results. Graft weight was significantly elevated in group IV as compared with the explanted lung (72.4 ± 6.8 versus 38.3 ± 4.5 g; p = 0.003). Pulmonary artery pressure and pulmonary vascular resistance were significantly elevated in group III as compared with the over-sized mature lower lobe transplants (51.8 ± 2.2 versus 40.4 ± 2.5 mm Hg [p < 0.0001] and 1,605.9 ± 117.5 versus 857.6 ± 133.6 dynes·s·cm^-5 [p < 0.0005], respectively). A trend toward decreased oxygenation was identified in group II. Conclusions. Over-sized mature lobar grafts provide improved hemodynamics as compared with size-matched grafts. Mature left lower lobe grafts are superior to size-matched upper lobe grafts in this model, probably as a result of an augmented vascular bed.