PULMONARY INFECTION WITH MYCOBACTERIUM-AVIUM-INTRACELLULARE LEADS TO AIR TRAPPING DISTAL TO THE SMALL AIRWAYS

To clarify the structure and function of the airways in Mycobacterium avium-intracellulare (MAI) infection, we performed pulmonary function tests and high-resolution computed tomography (HRCT) of the thorax in female patients 61 +/- 9 yr of age (n = 12) with pulmonary MAI infecti on without predisposing lung disease and compared their data with thos e of normal female volunteers 54 +/- 8 yr of age (n = 9). We calculate d the E/I ratio, i.e., the average ratio of HRCT number at full expira tion to that at full inspiration, as an index for the evaluation of ai r trapping distal to the small airways. Patients showed significant in creases in residual volume and slope of phase III (Delta N-2) of the s ingle-breath nitrogen test, and significant decreases in flow at 50 an d 25% of FVC, suggesting hyperinflation and obstruction of the small a irways. HRCT of patients revealed the small nodules and ectasis of bro nchioles and small bronchi located mainly in segments (S) S2, S3, S4, and S5. The E/I ratio was significantly elevated in patients, and espe cially higher in the upper lung field than in the lower lung field, su ggesting air trapping distal to the small airways. The difference of E /I ratio between the upper and lower field is probably related to the segmental distribution of CT abnormalities. These findings suggest tha t MAI infection can lead to air trapping distal to the small airways.