Study objectives: To establish a novel method allowing
detection of regional abnormalities in gas distribution at the acinar
level by high-resolution CT (HRCT).
Nonsmoking control subjects (n = 28) and patients with
smoking-induced COPD (n = 47).
results: Changes in lung CT densities were examined by HRCT while
the subjects inhaled a gas mixture consisting of 21% O2 in
SF6 or 21% O2 in He. HRCT images of the
right upper and lower lung fields were obtained at the end of
inspiration and expiration of the second and 60th breaths after the
start of each gas. Introducing mean lung density (MLD) and relative
area with low CT attenuation (%LAA), we analyzed the differences in
acinar SF6 and He distribution in the early phase (second
breath) and in the equilibrium state (60th breath). We found that the
differences in inspiratory MLD between the SF6 and He
images at the 60th breath were qualitatively consistent with the
differences predicted from the physical properties of these gases.
However, the differences in inspiratory MLD between the SF6
and He images taken at the second breath were smaller than those at the
60th breath, especially in the smoking group with COPD. These
differences in second-breath inspiratory MLD in the smoking group were
smaller in the upper lung field than in the lower lung field. The
differences in MLD between the two gases were not detected at
end-expiration at the time of either the second or 60th breaths. The
%LAA values did not differ between the SF6 and He images
in either the nonsmoking group or the smoking group.
Conclusions: SF6/He-associated HRCT images
obtained at end-inspiration, but not at end-expiration, in the early
breathing phase are useful for predicting acinar gas distribution
abnormalities in patients with COPD.