Am. J. Respir. Crit. Care Med., Vol 149, No. 5, May 1994, 1266-1275.
Effects of pulmonary fibrosis on the distribution of edema. Computed tomographic scanning and morphology
MP Zwikler, TM Peters and RP Michel
Department of Pathology, McGill University, Montreal, Quebec, Canada.
The pulmonary interstitium acts as an important safety factor against
alveolar flooding. To test the hypothesis that in advanced fibrosis, edema
is redistributed away from a less compliant interstitium to flood alveoli,
we induced severe left lung fibrosis in six dogs with radiation and
intratracheal bleomycin. Twenty-four months later, edema was induced by
infusing 20% body weight lactated Ringer's solution over 30 min, preceded
and followed by computed tomography (CT) scanning. Lower lobes were frozen,
and samples were taken for extravascular lung water measurements (Qwl/dQl),
regional blood volume, and light microscopic grading of interstitial and
alveolar edema. The total volumes of the control and fibrotic lungs were
800 +/- 63 and 45 +/- 10 ml (SE), respectively, indicative of severe
fibrosis. Before edema, the fibrotic carinal and basal slices had CT
densities 3.5 and 2.2 times greater than respective control slices. After
edema, the densities of all control lung slices rose 2.5 times and that of
fibrotic carinal and basal slices rose 1.5 times. Edema significantly
accentuated the small gravity-dependent gradient in CT density of control
lungs, but it had minimal effect on this gradient in fibrotic lungs. The
Qwl/dQl for control and fibrotic lower lobes were 8.7 +/- 0.8 and 6.8 +/-
0.7 g H2O/g dry lung, respectively, but the amounts of water per lung
volume were similar, and there was no gravity-dependent gradient in Qwl/dQl
or in regional blood contents. By light microscopy, we found significantly
less interstitial and more alveolar edema in the fibrotic lobes. We
conclude that in severe pulmonary fibrosis, similar amounts of water
accumulate per lung volume as in controls, and that there is predominant
alveolar flooding over interstitial edema. We also conclude that the
gravity-dependent gradients in CT densities postedema in the control lungs
are not accounted for by edema fluid or congestion, but probably by
atelectasis.
