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Abstract
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.
Acknowledgments
The authors thank Joan Soriano and Harvey Coxson for their helpful comments in the design of the study and interpretation of the results. We thank Denise Fabian for her help with the Wellington Respiratory Health Survey and in producing the manuscript. We would also like to thank Avrille Holt, Patricia Heuser, and Eleanore Chambers for their help in conducting the questionnaires and Dylan Taylor-Edwards and Finau Fala for data entry. With thanks to the radiography and administrative staff of Pacific Radiology, Wellington, New Zealand.