Pattern of fluid accumulation in NO2-induced pulmonary edema in dogs. A morphometric study.

To ascertain whether the pattern of fluid accumulation could be altered by an agent introduced through the airways, the authors studied the physiology and morphology of 11 dogs exposed to 150-494 ppm.hr NO2 and compared them with 3 new and 5 previously reported control dogs. NO2 caused a partly reversible decrease in systemic arterial pressure and cardiac output, a fall in arterial PO2, and rapid shallow breathing, while pulmonary arterial and wedge pressures remained normal. Post mortem, lower (LL) and middle (ML) lobes were frozen, sections fixed for light microscopy by freeze-substitution, and wet weight/dry weight (W/D) ratios were measured. Alveolar edema was graded, and the distribution of interstitial edema around arteries and veins and within bronchovascular bundles was studied with morphometry: edema ratios (ER) were calculated as area of interstitium/area of vessel or airway. We found that NO2 produced an exposure-dependent increase in lung water (r = 0.73), and that both LL and ML had similar W/D ratios (7.77 and 8.39, respectively) and percent alveolar edema (30% and 34%). Morphometry of interstitial edema showed that the ER for vessels and airways of edematous LL were essentially similar to controls, while those of the ML were markedly increased. It is concluded that NO2 produces exposure-related lung edema and preferential alveolar flooding with probable secondary interstitial accumulation. The discrepancies in interstitial edema between middle and lower lobes may be due to differences in lung volume or in ventilation.