Distribution of fluid in bronchovascular bundles with permeability lung edema induced by alpha-naphthylthiourea in dogs. A morphometric study.

We utilized light microscopic morphometry to examine the distribution of fluid in bronchovascular bundles of different sizes. Permeability edema was induced in 10 anesthetized dogs with 27 mg/kg of alpha-naphthylthiourea. Eight dogs served as controls. After moderately severe edema, diagnosed on chest radiographs and with decreasing arterial pO2, lobes were fixed with glutaraldehyde and formaldehyde or by freeze substitution. Postmortem wet weight to dry weight ratios were 7.82 +/- 0.62 (mean +/- SE) in the edematous lungs and 4.38 +/- 0.25 in the controls. Bronchovascular bundles were photographed and grouped as follows: bundles composed of separated arteries and bronchioles, bundles with connected arteries and bronchioles, and bundles with connected arteries and bronchi. The transparencies were projected on a tablet interfaced to a computer and the following areas were determined: T, the total bundle area; V, the vessel (artery) area; B, the airway (bronchiole or bronchus) area; A1, the tight periarterial adventitial sheath area; A2, the loose periarterial interstitial area; and A3, the bronchiolar/bronchial interstitial area. In addition, edema ratios for arteries (A2/V) and airways (A3/B) were calculated. We found that (a) A1 was very small and did not change with edema; (b) A2 in all bundles increased 10-fold with edema (p less than 0.01), whereas A3 increased 2- to 3-fold; (c) A2/V increased 9- to 15-fold in the edematous bundles (p less than 0.01) and (d) A3/B did not change in separated bundles (p greater than 0.05) but was approximately double after edema in the connected bundles with bronchioles and bronchi (p less than 0.01). We conclude that edema in bronchovascular bundles accumulates preferentially in the loose periarterial interstitium and does not appear to accumulate around smaller bronchioles. These data may be explained by anatomical factors and by gradients of interstitial pressure.