A new functional method to choose the target lobe for lung volume reduction in emphysema – comparison with the conventional densitometric method

Abstract

Juergen Hetzel,1 Michael Boeckeler,1 Marius Horger,2 Ahmed Ehab,1 Christopher Kloth,2 Robert Wagner,3 Lutz Freitag,4 Dirk-Jan Slebos,5 Richard Alexander Lewis,6 Maik Haentschel1 1Division of Haematology, Oncology, Rheumatology, Immunology and Pulmonology, Department of Internal Medicine, 2Department of Diagnostic and Interventional Radiology, 3Division of Endocrinology, Diabetology, Angiology, Nephrology and Clinical Chemistry, Department of Internal Medicine, Eberhard Karls University Tuebingen, Tuebingen, Germany; 4Division of Pulmonology, University Hospital Zurich, Zurich, Switzerland; 5Department of Pulmonary Diseases, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands; 6National Pollen and Aerobiology Research Unit, Institute of Science and the Environment, University of Worcester, Worcester, UK Background: Lung volume reduction (LVR) improves breathing mechanics by reducing hyperinflation. Lobar selection usually focuses on choosing the most destroyed emphysematous lobes as seen on an inspiratory CT scan. However, it has never been shown to what extent these densitometric CT parameters predict the least deflation of an individual lobe during expiration. The addition of expiratory CT analysis allows measurement of the extent of lobar air trapping and could therefore provide additional functional information for choice of potential treatment targets. Objectives: To determine lobar vital capacity/lobar total capacity (LVC/LTC) as a functional parameter for lobar air trapping using on an inspiratory and expiratory CT scan. To compare lobar selection by LVC/LTC with the established morphological CT density parameters. Methods: 36 patients referred for endoscopic LVR were studied. LVC/LTC, defined as delta volume over maximum volume of a lobe, was calculated using inspiratory and expiratory CT scans. The CT morphological parameters of mean lung density (MLD), low attenuation volume (LAV), and 15th percentile of Hounsfield units (15%P) were determined on an inspiratory CT scan for each lobe. We compared and correlated LVC/LTC with MLD, LAV, and 15%P. Results: There was a weak correlation between the functional parameter LVC/LTC and all inspiratory densitometric parameters. Target lobe selection using lowest lobar deflation (lowest LVC/LTC) correlated with target lobe selection based on lowest MLD in 18 patients (50.0%), with the highest LAV in 13 patients (36.1%), and with the lowest 15%P in 12 patients (33.3%). Conclusion: CT-based measurement of deflation (LVC/LTC) as a functional parameter correlates weakly with all densitometric CT parameters on a lobar level. Therefore, morphological criteria based on inspiratory CT densitometry partially reflect the deflation of particular lung lobes, and may be of limited value as a sole predictor for target lobe selection in LVR. Keywords: emphysema, chronic obstructive pulmonary disease, high-resolution computed tomography, lung volume reduction

Keywords

• Emphysema - Chronic obstructive pulmonary disease – High-resolution computed tomography – Lung volume reduction