Airway bypass procedure: Quantitative low dose multi-detector computed tomography and pulmonary function tests in patients with severe emphysema
Background:Airway bypass (ABP), a new bronchoscopic procedure for lung volume reduction (LVR), can improve the functional status of patients with severe emphysema. Analysis of lung volumes and severity of pulmonary emphysema was performed by quantitative low-dose multi-detector CT (QLDCT) before and after LVR by ABP and was correlated to the functional status of the patients. Methods:In a prospective study six patients were followed after ABP. Pulmonary function test (PFT) and QLDCT measurements were obtained before and after ABP (one week, one month, six months). All four CT data sets were analysed to give the following parameters: total lung volume derived from CT (TLV-CT), functional lung volume (FLV), emphysema index (EI), and ratio of the air space volume (ASV) to the tissue space volume (TSV). These results were correlated with TLC, RV, FEV1, six minute walk test, IGTV, and RV/TLC derived from PFT results. Results:TLV-CT correlated with TLC (r=0,89), RV (r=0,93), and IGTV (r=0,91). The mean FLV (volume of the lung greater than -950 Hounsfield units) increased by 10% after ABP (p<0,05), slightly worsened over time but sustained up to six months after ABP (6%, p<0,05). The mean ratio of the air space volume to the tissue space volume (ASV/TSV) decreased by 12% after the procedure (p<0,05), and remained significantly decreased. Postprocedural FLV correlated with FEV1 (r=0,49). Conclusion: Reexpansion of the normal lung and reduced hyperinflation seems to be induced by collateral ventilation. Reexpansion of the normal lung, reduced hyperinflation, and correlation between QLDCT and PFT values indicate a potential role of ABP in the therapy of emphysema.