RESPIRATORY MECHANICS AFTER HEART-LUNG AND BILATERAL LUNG TRANSPLANTATION

Background - The factors determining respiratory mechanics following h eart-lung transplantation (HLT) and bilateral lung transplantation (BL T) are incompletely understood. Methods - The dynamic and static lung volumes of 15 patients after HLT (n = 6) and BLT (n = 9) with no evide nce of obliterative bronchiolitis were analysed to assess the factors which determine lung volumes following transplantation. Posttransplant ation total lung capacity (TLCpost) was compared with the size of the recipient's lungs (TLCpre), the predicted capacity of the thorax of th e recipient (TLCpred), and the predicted size of the donor's lungs (TL Cdon). In addition, the post-transplantation respiratory mechanics wer e investigated by measuring the static pressure-volume (PV) curve of t he lungs and the maximum respiratory pressures in a subgroup of nine p atients (four HLT, five BLT). Results - TLC post was closely related t o TLCpred in both groups and showed no correlation with TLCpre. The me an (95% CI) TLCpost was 102.5 (90.2 to 115)% predicted for the recipie nt in the HLT group and 109 (97.6 to 120)% predicted for the recipient in the BLT group. Despite the near normal TLC, residual volume (RV) a nd functional residual capacity (FRC) remained increased after transpl antation in both groups. These abnormalities were not attributable to either airflow obstruction or expiratory muscle weakness. On average, lung compliance expressed in terms of the shape constant of the static pressure-volume curve of the lungs was mildly reduced in both groups compared with values predicted for the recipient. Conclusions - These results suggest that at high lung volumes the chest wall adapts to the size of transplanted lungs, while at lower volumes the increase in FR C and RV might be due to a persistent change in the static pressure-vo lume curve of the chest wall.