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      Lobar analysis of collapsibility indices to assess functional lung volumes in COPD patients

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          Abstract

          Background

          We investigated correlations between lung volume collapsibility indices and pulmonary function test (PFT) results and assessed lobar differences in chronic obstructive pulmonary disease (COPD) patients, using paired inspiratory and expiratory three dimensional (3D) computed tomography (CT) images.

          Methods

          We retrospectively assessed 28 COPD patients who underwent paired inspiratory and expiratory CT and PFT exams on the same day. A computer-aided diagnostic system calculated total lobar volume and emphysematous lobar volume (ELV). Normal lobar volume (NLV) was determined by subtracting ELV from total lobar volume, both for inspiratory phase (NLV I) and for expiratory phase (NLV E). We also determined lobar collapsibility indices: NLV collapsibility ratio (NLV CR) (%) = (1 − NLV E/NLV I) × 100%. Associations between lobar volumes and PFT results, and collapsibility indices and PFT results were determined by Pearson correlation analysis.

          Results

          NLV CR values were significantly correlated with PFT results. Forced expiratory volume in 1 second, measured as percent of predicted results (FEV 1%P) was significantly correlated with NLV CR values for the lower lobes ( P<0.01), whereas this correlation was not significant for the upper lobes ( P=0.05). FEV 1%P results were also moderately correlated with inspiratory, expiratory ELV (ELV I,E) for the lower lobes ( P<0.05). In contrast, the ratio of the diffusion capacity for carbon monoxide to alveolar gas volume, measured as percent of predicted (DL CO/V A%P) results were strongly correlated with ELV I for the upper lobes ( P<0.001), whereas this correlation with NLV CR values was weaker for upper lobes ( P<0.01) and was not significant for the lower lobes ( P=0.26).

          Conclusion

          FEV 1%P results were correlated with NLV collapsibility indices for lower lobes, whereas DL CO/V A%P results were correlated with NLV collapsibility indices and ELV for upper lobes. Thus, evaluating lobar NLV collapsibility might be useful for estimating pulmonary function in COPD patients.

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          Most cited references 34

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          The prediction of small airway dimensions using computed tomography.

          Chronic obstructive pulmonary disease is characterized by destruction of the lung parenchyma and/or small airway narrowing. To determine whether the dimensions of relatively large airways assessed using computed tomography (CT) reflect small airway dimensions measured histologically, we assessed these variables in nonobstructed or mild to moderately obstructed patients having lobar resection for a peripheral tumor. For both CT and histology, the square root of the airway wall area (Aaw) was plotted versus lumen perimeter to estimate wall thickness. The wall area percentage was calculated as wall area/lumen area + wall area x 100. Although CT overestimated Aaw, the slopes of the relationships between the square root of Aaw and internal perimeter (Pi) measured with both techniques were related (CT slope = 0.2059 histology slope + 0.1701, R2 = 0.32, p < 0.01). The mean wall area percentage measured by CT for airways with a Pi of greater than 0.75 cm predicted the mean dimensions of the small airways with an internal diameter of 1.27 mm (R2 = 0.57, p < 0.01). We conclude that CT measurements of airways with a Pi of 0.75 cm or more could be used to estimate the dimensions of the small conducting airways, which are the site of airway obstruction in chronic obstructive pulmonary disease.
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            Computed tomography in pulmonary emphysema.

            Fifty-three patients with chronic obstructive airways disease and 19 age-matched controls were studied using computed tomography (CT). The study shows that CT can detect the presence and distribution of pulmonary emphysema. Pulmonary vascular changes detectable on chest radiography correlate well with lung density as measured by CT. Patients with marked CT changes of emphysema had significantly greater impairment of diffusion capacity and FEV1.0/VC than the patients with less severe changes.
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              Relationships between airflow obstruction and quantitative CT measurements of emphysema, air trapping, and airways in subjects with and without chronic obstructive pulmonary disease.

              This study evaluates the relationships between quantitative CT (QCT) and spirometric measurements of disease severity in cigarette smokers with and without chronic obstructive pulmonary disease (COPD). Inspiratory and expiratory CT scans of 4062 subjects in the Genetic Epidemiology of COPD (COPDGene) Study were evaluated. Measures examined included emphysema, defined as the percentage of low-attenuation areas≤-950 HU on inspiratory CT, which we refer to as "LAA-950I"; air trapping, defined as the percentage of low-attenuation areas≤-856 HU on expiratory CT, which we refer to as "LAA-856E"; and the inner diameter, inner and outer areas, wall area, airway wall thickness, and square root of the wall area of a hypothetical airway of 10-mm internal perimeter of segmental and subsegmental airways. Correlations were determined between spirometry and several QCT measures using statistics software (SAS, version 9.2). QCT measurements of low-attenuation areas correlate strongly and significantly (p<0.0001) with spirometry. The correlation between LAA-856E and forced expiratory volume in 1 second (FEV1) and the ratio of FEV1 to forced vital capacity (FVC) (r=-0.77 and -0.84, respectively) is stronger than the correlation between LAA-950I and FEV1 and FEV1/FVC (r=-0.67 and r=-0.76). Inspiratory and expiratory volume changes decreased with increasing disease severity, as measured by the Global Initiative for Chronic Obstructive Pulmonary Disease (GOLD) staging system (p<0.0001). When airway variables were included with low-attenuation area measures in a multiple regression model, the model accounted for a statistically greater proportion of variation in FEV1 and FEV1/FVC (R2=0.72 and 0.77, respectively). Airway measurements alone are less correlated with spirometric measures of FEV1 (r=0.15 to -0.44) and FEV1/FVC (r=0.19 to -0.34). QCT measurements are strongly associated with spirometric results showing impairment in smokers. LAA-856E strongly correlates with physiologic measurements of airway obstruction. Airway measurements can be used concurrently with QCT measures of low-attenuation areas to accurately predict lung function.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                International Journal of COPD
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove Medical Press
                1176-9106
                1178-2005
                2014
                09 December 2014
                : 9
                : 1347-1356
                Affiliations
                [1 ]Department of Radiology, Nagoya University, Nagoya, Aichi, Japan
                [2 ]Department of Respiratory Medicine, Graduate School of Medicine, Nagoya University, Nagoya, Aichi, Japan
                [3 ]Department of Radiology, Ichinomiya Municipal Hospital, Ichinomiya, Aichi, Japan
                Author notes
                Correspondence: Shingo Iwano, Department of Radiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Shouwa-ku, Nagoya 466-8550, Japan, Tel +81 52 744 2327, Fax +81 52 744 2335, Email iwano45@ 123456med.nagoya-u.ac.jp
                Article
                copd-9-1347
                10.2147/COPD.S72616
                4266257
                25525352
                © 2014 Kitano et al. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0) License

                The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                Categories
                Original Research

                Respiratory medicine

                segmentation, emphysema, computed tomography, pulmonary function

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