Thorax 1999;54:384-389 ( May )

Comparison of low attenuation areas on computed tomographic scans between inner and outer segments of the lung in patients with chronic obstructive pulmonary disease: incidence and contribution to lung function

Y Nakano,^a H Sakai,^a S Muro,^c T Hirai,^d Y Oku,^b K Nishimura,^c M Mishima^e

^a Department of Experimental Pathology, ^b Department of Medical Systems Control, ^c Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan, ^d Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada, ^e Department of Physical Therapeutics, Kyoto University Hospital, Kyoto, Japan

Correspondence to: Dr Y Nakano, Department of Experimental Pathology, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8397, Japan.

Received 3 June 1998; Returned to authors 28 July 1998; Revised version received 19 October 1998; Accepted for publication 11 November 1998

BACKGROUNDThe low attenuation areas on computed tomographic (CT) scans have been reported to represent emphysematous changes of the lung. However, the regional distribution of emphysema between the inner and outer segments of the lung has not been adequately studied. In this study the regional distribution of low attenuation areas has been compared by quantitative CT analysis and the contribution of the regional distribution to pulmonary function tests evaluated in patients with chronic obstructive pulmonary disease (COPD).
METHODSChest CT images and the results of pulmonary function tests were obtained from 73 patients with COPD. The lung images were divided into inner and outer segments in the upper (cranial), middle, and lower (caudal) sections. The percentage ratio of low attenuation area to corresponding lung area (LAA%) was then calculated. The LAA% of each segment was also compared with the results of pulmonary function tests.
RESULTSThe mean (SD) LAA% of the inner segment was 39.1 (18.5) compared with 28.1 (13.2) for the outer segment (p<0.0001). Linear and multiple regression analyses revealed that airflow limitation is closely correlated with the inner segment LAA% of the lower lung. In contrast, the carbon monoxide transfer factor is closely correlated with the inner segment LAA% of the upper lung.
CONCLUSIONLow attenuation areas on CT scans are more often found in the inner segment of the lung than in the outer segment, and the contribution of the inner segment to pulmonary function tests may be greater than the outer segment.


Keywords: emphysema; regional distribution; computed tomography

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