Reduced transplant lung volumes after single lung transplantation for chronic obstructive pulmonary disease

Single lung transplantation is now an extremely successful option for the treatment of end-stage chronic obstructive pulmonary disease (COPD). This procedure involves placing a normal sized lung in a hyperinflated hemithorax. Preliminary observations of these patients suggest that the transplanted lung volume is smaller than expected and often the native (COPD) lung increases in volume. The purpose of this investigation was to quantify the volume contributions of the transplant and native lung to the total lung capacity. In seven patients who underwent single lung transplant for end-stage COPD the transplant and native lung volumes were measured by computer-analyzed planimetry immediately after transplant and the following 6 mo post-transplant. The transplant lung volume was smaller than predicted immediately after transplant at only 33 +/- 5% (mean +/- SD) of predicted TLC. This did not change significantly over the next 6 mo. Native lung volume increased following transplant to 74 +/- 19% predicted TLC at 1 mo and 80 +/- 16% at 6 mo. Five of the seven patients subsequently underwent measurement of pleural pressures at TLC. The mean static pleural pressure at TLC was low at -16 +/- 5.1 cm H2O. In summary, following single lung transplantation for COPD the transplanted lung is significantly restricted. We conclude that the likely mechanism of this restriction is due to low transpulmonary pressure generation.