The relations between expiratory chest CT using helical CT and pulmonary function tests in emphysema

Chest computed tomography (CT) and pulmonary function tests are usually used for the evaluation of emphysema. We performed the present study to evaluate more accurately the relationship between the degree of morphological change and the functional abnormality in emphysema. We used a helical CT apparatus to obtain the CT images both at full inspiration and full expiration, We classed the degree of emphysema into 5 grades (0-4) by visual observation on CB image obtained at the two levels, upper and lower fields, on each side. We assigned each of these grades a visual score. We also calculated the average ratio of CT numbers of each of the lung fields at full expiration to :hat at full inspiration far each level. We designated this the Ell ratio. We then examined the relationship between the findings acquired by each of these two methods and pulmonary function test results. nle visual score showed correlations with FEV(1)(% predicted) (-0.592, p < 0.0001), RV/TLC(%)(0.425, p < 0.025), and DL(CO)/VA(% predicted)(-0.538, p < 0.0001). The VI ratio showed correlations with FEV(1)(% predicted) (-0.620, p < 0.0001), RV/TLC(%)(0.661, p < 0.0001), and DL(CO)/VA(% predicted) (-0.299, p < 0.05). Compared with the E/I ratio, the visual score showed much higher correlation with DL(CO)/VA(% predicted), but the E/I ratio showed stronger correlation with RV/TLC(%) than did the visual scare. The visual score may reflect the degree of emphysema, whereas the E/I ratio reflects the air trapping. These findings suggest that the helical CT is useful in the evaluation of emphysematous changes and that the E/I ratio reflects the air trapping.