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Original Research: COPD |

Heterogeneity of Specific Gas Volume ChangesSpecific Gas Volume Changes in COPD: A New Tool to Plan Lung Volume Reduction in COPD

Caterina Salito, PhD; Livia Barazzetti, MSc; Jason C. Woods, PhD; Andrea Aliverti, PhD
Author and Funding Information

From the TBMLab (Drs Salito and Aliverti and Ms Barazzetti), Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan, Italy; the Center for Pulmonary Imaging Research (Dr Woods), Cincinnati Children’s Hospital Medical Center, Cincinnati, OH; and the Department of Physics (Dr Woods), Washington University, St. Louis, MO.

CORRESPONDENCE TO: Caterina Salito, PhD, Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, P.zza L. da Vinci, 32, 20133 Milano, Italy; e-mail: caterina.salito@polimi.it


FUNDING/SUPPORT: This work was supported by the National Institutes of Health [Grant R01-HL090806].

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2014;146(6):1554-1565. doi:10.1378/chest.13-2855
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OBJECTIVE:  The aim of this work was to investigate if regional differences of specific gas volume (SVg) in the different regions (lobes and bronchopulmonary segments) in healthy volunteers and patients with severe emphysema can be used as a tool for planning lung volume reduction (LVR) in emphysema.

METHODS:  CT scans of 10 healthy subjects and 10 subjects with severe COPD were obtained at end-inspiration (total lung capacity [TLC]) and end-expiration (residual volume [RV]). For each subject, ΔSVg (ΔSVg = SVg,TLC − SVg,RV, where SVg,TLC and SVg,RV are specific gas volume at TLC and RV, respectively) vs ΔV (ΔV = V,TLC−V,RV, where V,TLC and V,RV are lung volume at TLC and RV, respectively) was plotted for the entire lung, each lobe, and all bronchopulmonary segments. For each subject, a heterogeneity index (HI) was defined to quantify the range of variability of ΔSVg/ΔV in all bronchopulmonary regions.

RESULTS:  In patients with COPD, SVg,TLC and SVg,RV were significantly higher and ΔSVg variations lower than in healthy subjects (P < .001). In COPD, ΔSVg/ΔV slopes were lower in upper lobes than in lower lobes. In healthy subjects, the entire lung, lobes, and bronchopulmonary segments all showed similar ΔSVg/ΔV slopes, whereas in COPD a high variance was found. As a consequence, HI was significantly higher in subjects with COPD than in healthy subjects (0.80 ± 0.34 vs 0.15 ± 0.10, respectively; P < .001).

CONCLUSIONS:  SVg variations within the lung are highly homogeneous in healthy subjects. Regions with low ΔSVg/ΔV (ie, more pronounced gas trapping) should be considered as target areas for LVR. Regions with negative values of ΔSVg/ΔV identify where collateral ventilation is present. HI is helpful to assess the patient in the different stages of disease and the effect of different LVR treatments.

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