RATIONALE AND OBJECTIVES, Pulmonary edema frequently is treated with v
entilation but its effects on the distribution of edema, including gra
vity-dependent gradients as determined by computed tomography (CT) sca
nning, are unclear, METHODS. TO study this, 30 to 50 mL 5% albumin in
dextran were instilled in both caudal lobes of supine dogs, They were
ventilated only on the left side for 1 minute (n = 4), 30 minutes (n =
6), or 60 minutes (n = 6), and the lobes excised, frozen, and imaged
in a CT scanner, Regions of interest were outlined on regional CT slic
es and tissue from corresponding regions taken for measurements of ext
ravascular lung water (quantity of wet lung [Qwl]/dry quantity of lung
[dQl]) and for histology to grade interstitial and alveolar edema. RE
SULTS. After ventilation for 30 and 60 minutes, the CT density of the
left caudal lobes was significantly lower than the right caudal lobes
(P < 0.05), with no significant differences in their Qwl/dQl. Although
gravity-dependent gradients of Qwl/dQl were demonstrated, they were u
naffected by ventilation, Histology showed a trend for more interstiti
al edema in left caudal lobes ventilated for 60 minutes compared with
lobes ventilated for 1 minute (P = 0.054), CONCLUSIONS. Ventilation ap
pears to act primarily by maintaining lung aeration and may play a min
or role in alveolar fluid clearance.