Respiratory mechanics after heart-lung and bilateral lung transplantation

The factors determining respiratory mechanics following heart-lung transplantation (HLT) and bilateral lung transplantation (BLT) are incompletely understood.

The dynamic and static lung volumes of 15 patients after HLT (n = 6) and BLT (n = 9) with no evidence of obliterative bronchiolitis were analysed to assess the factors which determine lung volumes following transplantation. Post-transplantation total lung capacity (TLCpost) was compared with the size of the recipient's lungs (TLCpre), the predicted capacity of the thorax of the recipient (TLCpred), and the predicted size of the donor's lungs (TLCdon). In addition, the post-transplantation respiratory mechanics were investigated by measuring the static pressure-volume (PV) curve of the lungs and the maximum respiratory pressures in a subgroup of nine patients (four HLT, five BLT).

TLCpost was closely related to TLCpred in both groups and showed no correlation with TLCpre. The mean (95% CI) TLCpost was 102.5 (90.2 to 115)% predicted for the recipient 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) and functional residual capacity (FRC) remained increased after transplantation 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.

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 FRC and RV might be due to a persistent change in the static pressure-volume curve of the chest wall.