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Radiologic and Clinical Features of COPD Patients With Discordant Pulmonary Physiology^*

Lessons From ₁-Antitrypsin Deficiency

^* From the University Hospital Birmingham, NHS Foundation Trust, Birmingham, UK.

Correspondence to: Robert A. Stockley, MD, DSc, Queen Elizabeth Hospital, Department of Respiratory Medicine, Nuffield House, Birmingham B15 2TH, UK; e-mail: rob.stockley{at}uhb.nhs.uk

Abstract

Introduction: Subjects with COPD display heterogeneity in clinical, physiologic, and radiologic characteristics, which are thought to result from different pathophysiologic mechanisms. It is important to identify and understand specific phenotypes for patient management. We investigated differences in emphysema distribution and health status in ₁-antitrypsin deficient subjects (PiZ) with discordant lung function.

Method: CT scan densitometry, arterial oxygen tension, and St. George respiratory questionnaire scores were compared for 15 subjects with normal FEV₁ and lung diffusion capacity corrected for alveolar ventilation (KCO), both defined as > 80% predicted (group 1), 10 subjects with abnormal FEV₁ and normal KCO (group 2), 15 subjects with normal FEV₁ and abnormal KCO (group 3), and 10 subjects with both an abnormal FEV₁ and KCO (group 4).

Results: Group 2 subjects had the greatest predominance of basal emphysema, and group 3 subjects had the least. Upper zone voxel index (ie, the percentage of voxels < –910 Hounsfield units) was greater in all groups with abnormal lung function (p = 0.003, 0.044, and < 0.001, respectively), indicating more upper zone emphysema than in subjects with normal lung function. Lower zone voxel index was increased in groups 2 and 4 compared to groups 1 and 3. Groups 2 and 4 had a lower PaO₂ (p < 0.001) than the other groups. All groups with abnormal lung function had a worse quality of life than those with normal lung function.

Conclusion: Abnormality of FEV₁ is associated with basal-predominant emphysema, and abnormality of KCO is associated with relatively more upper zone emphysema; but, an isolated defect in KCO has a significant effect on health status.

Key Words: ₁-antitrypsin deficiency • COPD • CT scanners • quality of life • respiratory function tests