Low attenuation area on computed tomography in asthma. Comparison between smoking and nonsmoking subjects.

The percentage of attenuation area < -950HU (% LAA) on high resolution computed tomography (HRCT) was compared between 17 smoking and 24 nonsmoking patients with asthma. 1. FEV1/FVC value was lower in smoking patients (56.4%) than in nonsmoking patients (66.0%), however, the difference was not significant. 2. The percentage of LAA of the lung was larger in smoking patients compared with that in nonsmoking patients in all the three anatomic levels: the % LAA was 14.4% in nonsmoking and 20.3% in smoking patients at lower lung level (3cm above the top of the diaphragm). However, this was not significant. The maximal % LAA among the three lung levels on HRCT was 21.6±12.5% in smoking, and 15.7±11.9% in nonsmoking patients. This suggested that the maximal % LAA was larger in smoking patients, however, this was not significant. 3. The mean CT number of the lung on HRCT was smaller in smoking patients (-897.3HU) than in nonsmoking patients (-884.7HU). 4. Three of 4 nonsmoking patients whose % LAA was more than 30% had severe intractable asthma with long-term glucocorticoid therapy. The results suggest the possibility that smoking influences the % LAA of the lung on HRCT in asthma. It could be also speculated that % LAA is influenced by severity of asthma.

HRCT (high resolution computed tomography)による-950HU以下の肺野のlow attenuation area(LAA)について,17例の喫煙喘息症例と24例の非喫煙喘息症例で比較検討した｡1.FEV1.0%値は,喫煙症例(56.4%)で非喫煙症例(66.0%)に比べ低い値が示されたが,両群間に有意の差は見られなかった｡2.% LAAは,肺野のいずれの高さにおいても,非喫煙症例に比べ喫煙症例で高い傾向が見られたが,有意の差ではなかった｡Maximal % LAAは,喫煙症例で21.6%,非喫煙症例15.7%であり,同様に喫煙症例で高い傾向が見られたが,有意の差は見られなかった｡3.平均CT値は,非喫煙症例(-884.7HU)に比べ,喫煙症例(-897.3HU)で低い値であった｡4.% LAAが30%以上を示 す4例の非喫煙症例のうち,3例がステロイド依存性の重症難治性喘息であった｡これらの結果より,喫煙が肺野の% LAAに影響をあたえる可能性もあるものの,疾患の重症度がより影響が強い可能性が示唆された｡