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Kun Qing

Kun Qing

University of Virginia

Title: A New COPD Phenotype Characterized by Hyperpolarized Xenon-129 MRI

Biography

Biography: Kun Qing

Abstract

Purpose: Airway-predominant chronic bronchitis (CB) and alveolar-predominant emphysema (EM) were regarded as major phenotypes of smoke-induced COPD.  Routine clinical tools, including pulmonary function tests (PFTs) and computed tomography (CT), have their limitations to characterize COPD. This study will characterize COPD phenotypes using a new imaging tool - hyperpolarized xenon-129 (Xe129) MRI [1].

Methods: Thirteen healthy and thirty-three COPD subjects were recruited and underwent PFT, CT. COPD patients were phenotyped into three groups by PFT percent diffusion capacity (%DLCO) and CT percent of EM lung tissue (%EM): 1) EM: low %DLCO and high %EM; 2) CB: high %DLCO and low %EM; and 3) mixed indeterminate (IND) phenotype: low %DLCO but low %EM. Xe129 MRI was subsequently administered to determine airflow limitation by measuring percent of ventilation dead space (%VD) and alveolar gas uptake by measuring Xe129 diffused into interstitial tissue [tissue/gas ratio, reflecting lung tissue integrity] or into red blood cells (RBCs) [RBC/tissue ratio, reflecting gas exchange and pulmonary perfusion].

Results and Discussion: Using the criteria described above, 18% of patients (6/33) were EM predominant; 21% (7/33) were CB phenotype; and surprisingly, 61% (20/33) were IND phenotype. The IND group had %FEV1 substantially overlapped the CB group (p>0.05, Figure 1a), and did not show significantly higher %VD than the control group (p>0.05, Figure 1b). Also, no statistical differences were found in Xe129 tissue/gas ratios among the control, CB and the IND groups (p>0.05). However, the RBC/tissue ratios, measuring gas transfer from the interstitium further to the blood stream, were much lower in the mixed group as compared to all other groups (p<0.05) (Figure 1d). 

Conclusion: There seemed to be a new mixed phenotype of COPD identified in a majority of COPD patients, which had minimal emphysematous tissue destruction, but impaired gas exchange to the blood as indicated by Xe129 MRI.