Aim: To evaluate the factors affecting air trapping on expiratory
CT, its correlation with pulmonary function tests and its value for
discriminating pulmonary diseases.
Method: A total of seventy-five patients 28 chronic obstructive
pulmonary disease, 21 asthma, 17 interstitial lung disease, and 9
bronchiectasis patients were included in this study. All patients
underwent inspiratory HRCT, expiratory HRCT, and pulmonary
function tests. Expiratory scans were evaluated for the presence of
air trapping. The cross-sectional area and the ratio of air-trapping
was calculated. Smoking history, duration of illness were noted.
Statistically a correlation between the level and extent of air
trapping, its correlation with pulmonary function tests and factors
affecting air trapping were evaluated.
Result:Air trapping was detected in 59 patients. In ten of these
patients there was no mosaic pattern on inspiratory images. Air
trapping on expiratory images was mostly seen in asthma patients
(7 out of 10). The level of air-trapping showed a good correlation
with the extent of air trapping in general, but in asthma patients the
level of air-trapping did not correlate with the extent of trapping.
There was a good correlation between pulmonary function tests and
the level and extent of air trapping. The duration of illness affected
the extent of air-trapping.
Conclusion: Expiratory images are effective for discriminating
asthma from other obstructive lung disease. The level and extent
of air trapping detected on expiratory images which are mainly
affected by illness duration, are good predictors of pulmonary