Causes of allograft dysfunction after single lung transplantation for emphysema: Extrinsic restriction versus intrinsic obstruction

Background: A subset of patients with emphysema who have undergone single lung transplantation (SLT) may subsequently present with dyspnea, worsening airways obstruction, hypoxemia, and progressive chronic native lung hyperinflation. The leading cause of late allograft dysfunction is bronchiolitis obliterans syndrome (BOS). However, extrinsic restriction manifests with a similar clinical presentation and is an additional mechanism to consider. We describe the use of the inspiratory lung resistance (R-Li) to distinguish a decline in respiratory status due predominantly to either extrinsic restriction or BOS. Methods: We studied five patients who underwent SLT for emphysema between 1992 and 1995, in whom the diagnoses of BOS and extrinsic restriction were subsequently entertained. Forced expiratory volume in 1 second (FEV1), R-Li, Static lung compliance, elastic recoil pressure at total lung capacity (TLC), and the slope of the maximum flow static recoil (MFSR) plot were measured. Results: All patients had seven ah-how obstruction, with mean FEV1 0.98 +/- 0.24 liter (26 +/- 5% predicted), elevated static lung compliance, reduced elastic recoil pressure at TLC, and reduced slope of the MFSR plot. Three patients had "low" R-Li (9.3-12.8 cm H2O/L/sec). Obstruction was attributed predominantly to extrinsic restriction, These patients underwent lung volume reduction surgery (LVRS) on the native lung; improvements in pulmonary mechanics were observed at 6 months. In contrast, two patients had markedly elevated R-Li (17.3 and 17.4 cm H2O/L/sec). Obstruction was attributed predominantly to intrinsic airway disease from BOS that was subsequently documented at autopsy. Conclusions: The R-Li appears to be a useful adjunct to the clinical history in distinguishing a decline in respiratory status due predominantly to either BOS or extrinsic restriction in patients who have undergone SLT for emphysema. Determination of the mechanism of allograft dysfunction may allow the selection of an appropriate subset of patients who would benefit from LVRS.