CHRONIC OBSTRUCTIVE PULMONARY DISEASE

Prediction of the rate of decline in FEV₁ in smokers using quantitative computed tomography

R Yuan^1,2, J C Hogg^1,3, P D Paré^1,4, D D Sin^1,4, J C Wong¹, Y Nakano⁵, A M McWilliams^4,6,6, S Lam^4,6,6, H O Coxson^1,2

¹ University of British Columbia James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research and the Providence Heart + Lung Institute, St Paul’s Hospital, Vancouver, British Columbia, Canada
² Department of Radiology, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
³ Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada
⁴ Division of Respiratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada
⁵ Department of Respiratory Medicine, Shiga University of Medical Science, Otsu, Shiga, Japan
⁶ Cancer Imaging Department, British Columbia Cancer Agency, University of British Columbia, Vancouver, British Columbia, Canada

^{Correspondence to} Dr H O Coxson, Department of Radiology, Vancouver General Hospital, 855 West 12th Ave, Room 3350 JPN, Vancouver, British Columbia, V5Z 1M9, Canada; harvey.coxson{at}vch.ca

Background: A study was undertaken to determine if quantitative CT estimates of lung parenchymal overinflation and airway dimensions in smokers with a normal forced expiratory volume in 1 s (FEV₁) can predict the rapid decline in FEV₁ that leads to chronic obstructive pulmonary disease (COPD).

Methods: Study participants (n = 143; age 45–72 years; 54% male) were part of a lung cancer screening trial, had a smoking history of >30 pack years and a normal FEV₁ and FEV₁/forced vital capacity (FVC) at baseline (mean (SD) FEV₁ 99.4 (12.8)%, range 80.2–140.7%; mean (SD) FEV₁/FVC 77.9 (4.4), range 70.0–88.0%). An inspiratory multislice CT scan was acquired for each subject at baseline. Custom software was used to measure airway lumen and wall dimensions; the percentage of the lung inflated beyond a predicted maximal lung inflation, the low attenuation lung area with an x ray attenuation lower than –950 HU and the size distribution of the overinflated lung areas and the low attenuation area were described using a cluster analysis. Multiple regression analysis was used to test the hypothesis that these CT measurements combined with other baseline characteristics might identify those who would develop an excessive annual decline in FEV₁.

Results: The mean (SD) annual change in FEV₁ was –2.3 (4.7)% predicted (range –23.0% to +8.3%). Multiple regression analysis revealed that the annual change in FEV₁%predicted was significantly associated with baseline percentage overinflated lung area measured on quantitative CT, FEV₁%predicted, FEV₁/FVC and gender.

Conclusion: Quantitative CT scan evidence of overinflation of the lung predicts a rapid annual decline in FEV₁ in smokers with normal FEV₁.

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