Pulmonary Veins and Bronchial Vessels Undergo Remodeling in Sustained Pulmonary Hypertension Induced by Continuous Air Embolization Into Sheep

Abstract

While it is well known that chronic pulmonary hypertension is accompanied by characteristic structural changes in the pulmonary arteries, it is becoming increasingly apparent that the remodeling process also involves the venous side of the circulation. The present paper utilizes a sheep model of sustained pulmonary hypertension induced by continuous air embolization (CAE) into the pulmonary arterial circulation to examine the structure of the pulmonary veins and bronchial vasculature. Morphometric techniques were applied to the pulmonary veins and bronchial vessels following distension of the venous circulation with a barium—sulfate gelatin mixture; this route of filling also resulted in distension of the bronchial vessels. Four and 12 days of CAE resulted in a significant increase in the proportion of muscular pulmonary veins (e.g., percent muscular veins < 75 μm following 12 days CAE = 17.7 ± 6.9; controls = 0), an approximate doubling in percent venous medial thickness, and a 50% reduction in number of barium-filled peripheral vessels. Examination of the bronchial circulation revealed a striking increase in volume due both to a 50% increase in vessel diameter and a threefold increase in number of small vessels (p < . 05). The authors conclude that CAE-induced chronic pulmonary hypertension is associated with remodeling of both the pulmonary veins and bronchial circulation as well as the pulmonary arteries. The mechanisms for these structural alterations are not certain, but may include local release of vasoactive and inflammatory mediators and an increase in bronchopulmonary anastomoses.

Key Words:

• adventitial thickening
• bronchial hypertrophy and dilatation
• chronic pulmonary hypertension
• intimal thickening
• structural remodeling