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<h5 class="section-title" id="d4972857e205">Rationale and Objectives</h5>
<p id="P2">Many COPD patients have marked discordance between FEV
<sub>1</sub> and degree of emphysema on CT. Biomechanical differences between these
patients have
not been studied. We aimed to identify reasons for the discordance between CT and
spirometry in some patients with COPD.
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<h5 class="section-title" id="d4972857e213">Materials and Methods</h5>
<p id="P3">Subjects with GOLD stage I–IV from a large multicenter study (COPDGene)
were arranged
by percentiles of %predicted FEV
<sub>1</sub> and emphysema on CT. Three categories were created using differences
in percentiles:
Cat
<sub>spir</sub> with predominant airflow obstruction/minimal emphysema, Cat
<sub>CT</sub> with predominant emphysema/minimal airflow obstruction, and Cat
<sub>matched</sub> with matched FEV
<sub>1</sub> and emphysema. Image registration was used to derive Jacobian determinants,
a measure
of lung elasticity, anisotropy and strain tensors, to assess biomechanical differences
between groups. Regression models were created with the above categories as outcome
variable, adjusting for demographics, scanner type, quantitative CT-derived emphysema,
gas trapping, and airway thickness (Model 1), and after adding biomechanical CT metrics
(Model 2).
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<h5 class="section-title" id="d4972857e233">Results</h5>
<p id="P4">Jacobian determinants, anisotropy and strain tensors were strongly associated
with
FEV
<sub>1</sub>. With Cat
<sub>matched</sub> as control, Model 2 predicted Cat
<sub>spir</sub> and Cat
<sub>CT</sub> better than Model 1 (Akaike Information Criterion, AIC 255.8 vs. 320.8).
In addition
to demographics, the strongest independent predictors of FEV
<sub>1</sub> were Jacobian mean (β= 1.60,95%CI = 1.16 to 1.98; p<0.001), coefficient
of variation
(CV) of Jacobian (β= 1.45,95%CI = 0.86 to 2.03; p<0.001) and CV strain (β= 1.82,95%CI
= 0.68 to 2.95; p = 0.001). CVs of Jacobian and strain are both potential markers
of biomechanical lung heterogeneity.
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<h5 class="section-title" id="d4972857e253">Conclusions</h5>
<p id="P5">CT-derived measures of lung mechanics improve the link between quantitative
CT and
spirometry, offering the potential for new insights into the linkage between regional
parenchymal destruction and global decrement in lung function in COPD patients.
</p>
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