Journal of Applied Physiology, Vol 65, Issue 3 1180-1190, Copyright © 1988 by American Physiological Society
Distribution of pulmonary vascular resistance in experimental fibrosis
R. P. Michel, T. S. Hakim and C. R. Freeman
Department of Pathology, Royal Victoria Hospital, Montreal, Quebec, Canada.
To elucidate mechanisms of pulmonary hypertension in interstitial fibrosis,
we compared the left lower lobes (LLL) of six dogs in which fibrosis was
induced by radiation and bleomycin with the normal right lower lobes (RLL)
for 1) slope and intercept of the vascular pressure-flow (P-Q) curves, 2)
segmental resistances with arterial and venous occlusion under base-line
conditions, after serotonin and vasodilators, and 3) light-microscopic
morphology and morphometry. We found that 1) the total volume and vascular
compliance of the fibrotic LLL were five and four times less, respectively,
than controls, 2) the slope and intercept of the P-Q curves in the LLL were
154.0 +/- 65.8 (SE) mmHg.l-1.min-1 and 8.2 +/- 1.5 mmHg, respectively,
compared with 18.3 +/- 2.3 and 3.2 +/- 0.9 for the RLL, 3) the resistance
of the arterial, middle, and venous segments in the LLL were higher than in
the RLL, but middle segment resistance rose disproportionately, and 4)
constriction of the arterial segment with serotonin was similar in LLL and
RLL, and vasodilators were ineffective. Histologically, fibrosis involved
36% of the lung, and the capillary bed was severely obliterated. Arteries
showed an increased percentage of medial and intimal thickening and
peripheral muscularization; venous abnormalities were less marked. We
conclude that pulmonary fibrosis increases vascular resistance mainly in
the middle segment, largely by loss of tissue and obliteration of the
microvasculature.
