<原著>吸入肺シンチグラフィーによる下気道粘液線毛輸送の検討 : 総合的評価システムの開発

Abstract

It is widely accepted that the impairment of tracheobronchial clearance (TBC) are closely related to the development and the progression of chronic bronchial infections. We investigated TBC in patients with chronic bronchal infections (bronchiectasis; 11 cases, diffuse panbronchiolitis; 9 cases and primary ciliary dyskinesia; 3 cases) and also in 6 healthy subjects by a radioactive aerosol (^<99m>Tc-human serum albumin, 4.4 ± 1.4μm in diameter) inhalation scintigraphy with cough control in order to elucidate the relationships between impaired TBC and chronic bronchial infections. All subjects were not current smokers. After 4-minutes inhalation of radioactive aerosols (tidal volume : 500ml×20/min.), radioactivities in whole right lung were measured every 20 seconds for 2 hours serially and then measured at the time of 6 and 24 hours after inhalation. Immediately after the serial recording for 2 hours, single photon emission computed tomography (SPECT) was performed to assess the deposition pattern of radioactive aerosols. During the first 2 hours, all the subjects were instructed to avoid coughing as much as possible to evaluate the mucociliary clearance without cough effect. And then the subjects were allowed to cough between 2 and 24 hours after inhalation. All radiation counts were corrected for background radiation and physical decay of ^<99m>Tc. Because it is considered that the deposited aerosols are eliminated much more slowly in alveoli (biological half life : several months) than in airways (biological half life : several hours), the radioactivity remaining at the time of 24 hours was defined as alveolar deposition (ALV). Initial bronchial deposition (Br0) was defined as initial whole lung deposition (L0) minus ALV. We evaluated the TBC with following parameters; 1) Br0/L0 (%) : ratio of initial bronchial deposition to initial lung (bronchial and alveolar) deposition 2) Br2/Br0 (%), Br6/Br0 (%) : bronchial retention ratio; the ratio of bronchial deposition at the time of 2 and 6 hours after inhalation to initial bronchial deposition, respectively. 3) TMV (mm/min.) : tracheal mucus velocity (rate of shift of radioactive bolus on tracheal mucosa), which was measured during the period of first 2 hours under prohibition of cough. The patients (23 cases) were divided into two groups with regards to cough control for the first two hours of the scintigraphy : cough-controlled group (19 cases) and cough-uncontrolled group (4 cases). The cough-controlled group was subdivided into two subgroups (group A and group B) according to Br0/L0 : group A<47.9% (mean+SD of Br0/L0 in healthy control) ≦ group B. More proximal aerosol deposition was demonstrated in group B and cough-uncontrolled group by SPECT. Br2/Br0 was significantly elevated in group A (p<0.05) and group B (p<0.05) despite more proximal aerosol deposition, and also seemed to be elevated in cough-uncon-trolled group, compared to healthy control. Br6/Br0 was, however, almost equal among all disease groups and healthy control, which suggested that cough played an important role in eliminating airway fluid in chronic bronchial infections and that the impaired mucociliary clearance might be partially compensated by the cough effect. TMV was significantly slower in disease groups (14 patients) than in healthy control. In the rest (9 patients) of the patients, any boli for the measurement of TMV were not detected on tracheal mucosa during the serial imaging for the first 2 hours, which also suggested the remarkable impairment of the mucociliary clearance. We concluded that mucociliary clearance was impaired in patients with chronic bronchial infections and cough played very important roles in compensation of the impaired mucociliary clearance. We also concluded that our integrated system was very useful for evaluating the mucociliary clearance and the cough effect separately.