肺気腫における放射性エロソル吸入肺シンチグラムの異常集積像

Abnormal pulmonary deposition of radioactive aerosol in patients with pulmonary emphysema

　肺局所の換気をみるうえで，エロソル吸入シンチグラフィーは簡便な方法であり，とくに肺血流シンチグラムに示される肺血流減少の原因が，気道系にあるか否かを診断するうえ周で有用である^1）。また，本法はエロソルとしての特性のため，気道の軽微な閉塞性変化をも敏感に反映し，周辺肺野への分布減少や分布の不均等を示す^2,3）ことが知られる。井沢ら^4）は，慢性閉塞性肺疾患（CO—PD）にみられる異常集積像と病型^5）の関係をしらべ，肺門部を中心とした太い気道への沈着を呈す"中心型"が肺気腫型に，肺野にまだらな沈着を呈す"末梢型"が気管支炎型に対応することを指摘している。

　しかし，現在のところ，COPDに対する吸入シンチグラフィーの診断的意義が確立しているとはいいがたい。1つの問題点として，異常集積像を詳細な肺機能や形態学的所見とつきあわせて発生機序を検討した資料に乏しく，従って臨床的意義付けが明らかでないことがあげられよう。

Aerosolized ^99mTC was inhaled by patients with pulmonary emphysema to study patterns of ab-normal deposition and underlying mechanisms. Twenty-three patients with pulmonary emphysema confirmed by alveolobronchograms underwent aerosol inhalation and pulmonary function tests including airway resitance (R_aw), functional residual capacity by body plethysmograph (FRC-_box) and He dilution (FRC_He), pulmonary compliance, and arterial blood gases. The ab-normal depositions were classified into central and peripheral types by two observers and each pattern was divided into three grades.

Central type deposition was seen in all patients and 11 patients disclosed peripheral types deposition also. Scores of central and peripheral deposition were positively correlated to R_aw. FRC_box minuts FRC_He (air trapping) and FRC_box related pos-itively to scores of central deposition. PaCO₂ related positively to score of peripheral deposition. Frequency dependence of compliance did not relate to central and peripheral type depositions.

These results indicate that the main underlying mechanism for central deposition is increased airway resistance closely related to pulmonary emphysema. Airway abnormalities were thought to be an additional mechanism for combined central and peripheral depositions.