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Physiological associations of computerized tomography lung density: a factor analysis

Authors Suzanne Marsh, Sarah Aldington, Mathew V Williams, Michael Nowitz, Andrew Kingzett-Taylor, et al

Published 15 June 2006 Volume 2006:1(2) Pages 181—187


Suzanne Marsh1, Sarah Aldington1, Mathew V Williams1, Michael Nowitz2, Andrew Kingzett-Taylor2, Mark Weatherall3, Phillipa Shirtcliffe1, Alison Pritchard1, Richard Beasley1,4

1Medical Research Institute of New Zealand, Wellington, New Zealand; 2Pacific Radiology Limited, Wellington, New Zealand; 3Wellington School of Medicine & Health Sciences, Wellington, New Zealand; 4University of Southampton, United Kingdom

Background: Objective quantification of emphysema using computerized tomography (CT) density measurements is rapidly gaining wide acceptance as an in vivo measurement tool. However, some studies have suggested that abnormal lung function in the absence of emphysema can affect lung density, and the role of such measurements in identifying and monitoring the progression of emphysema is not clear.

Objective: To clarify the relationship between lung density measurements and pulmonary function.

Methods: CT measurements of the proportion of lung occupied by low density tissue (as percentage of lung area below predetermined Hounsfield unit [HU] thresholds) were obtained in a large random population (n = 739) and the association with detailed pulmonary function tests studied using factor analysis.

Results: Density measurements showed a greater association with measures of hyperinflation and airflow obstruction than measures of gas transfer (correlation coefficient, high resolution scan, –950 HU threshold vs FEV1/FVC, RV, and DLCO/VA of –0.39, 0.22, and –0.15 respectively). The strongest lung density factor coefficients of 0.51 (standard resolution scan, –950 HU threshold) and 0.46 (high resolution scan, –910 HU threshold) were seen with factors

predominantly consisting of measures of airflow obstruction and hyperinflation. Most variation in lung density was not accounted for by lung function measurements (communality 0.21–0.34).

Conclusion: Lung density measurements associate most strongly with measures of airway disease that are not specific to emphysema.

 

Keywords: emphysema, CT lung density, COPD, lung function tests

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