Does lung growth occur when mature lobes are transplanted into children?

Lung volume increases after living donor lobar lung transplantation (LD) in children. The mechanism responsible for this increase may be alveolarization (lung growth) or alveolar dilation. The diffusing capacity of the lung for carbon monoxide adjusted for lung volume (DLco/VA) should decrease if alveolar dilation occurs, but not if lung growth occurs. Pulmonary function tests were measured 1-12 months after transplant in 20 children receiving LD transplants and in 11 children receiving cadaveric whole lung transplantation (CL). One month after transplant there were no differences between LD and CL recipients in age, gender, or height. Compared to the first month after transplant, height increased at 6-12 months after LD (p < 0.05), and only at 12 months after CL (p = 0.02). Total lung capacity (TLC) showed an 11-22% increase at 3-12 months after LD, and an 11-14% increase at 6-12 months after CL. DLco/VA showed an 11-17% decrease at 3-12 months after LD. However, in recipients of CL, DLco/VA showed a transient decrease of 10% at 3-6 months post-transplant, but was not significantly lower at 9-12 months. LD recipients had lower DLco/VA values than CL recipients at 6-12 months after transplant (p < 0.05). We conclude that following LD, lung volume increases, but DLco/VA decreases. We speculate that alveolar dilation, rather than alveolarization, is the primary mechanism of increased lung volume in children following LD.