Biomechanics of dog pulmonary vascular bed
The elastic behavior or ability of the vessels to deform under pressure affects both the pressure-flow and the pressure-volume relationships in the pulmonary vascular bed. In the normal lung, vasomotor tone is low. However, physiological vasoconstrictor stimuli, such as hypoxia and serotonin, can increase smooth muscle tone in the vessel wall and thereby cause changes in vessel mechanical properties. The hemodynamic consequences of altering the mechanical properties of pulmonary blood vessels can vary depending on the site of action of a particular vasoconstrictor stimulus. The general aim of this dissertation is to provide biomechanical data needed for hemodynamic modeling of the dog pulmonary vascular bed. The goal was two fold. The first was to determine the distensibility of small pulmonary arteries, veins, and capillaries in normal lung. The second was to determine the influence of vasoconstriction on the diameters of small arteries and veins. To obtain this information under conditions that are similar to those of the intact functioning lung, the isolated perfused lung and microfocal x-ray angiography were the methods of choice for this study. In the 0 to 30 Torr pressure range, arteries exhibited linear diameter versus pressure curves and size independent distensibility (2%/Torr) whereas veins exhibited curvilinear diameter versus pressure curves and a weak negative correlation (r = $-$0.32) between distensibility and size (average 1.9%/Torr in the 0 to 19 Torr pressure range). Serotonin and Norepinephrine caused constriction of arteries and veins, respectively, but caused no significant changes in their distensibilities. In the same pressure range (0 to 30 Torr), capillaries exhibited linear volume (as reflected from capillary mean transit time) versus pressure curve and 3.3%/Torr volume distensibility. Hypoxia and serotonin each produced a different pattern of responses in regard to vessel size or type even when the magnitude of the increase in perfusion pressure was the same. In the size range studied, hypoxia constricted the small arteries while the larger arteries were distended by the increase in pressure. On the other hand, serotonin constricted arteries of all sizes. Hypoxia cause little constriction in veins whereas serotonin had no influence on veins. The response of vessels to either stimulus exhibited parallel heterogeneity.
"Biomechanics of dog pulmonary vascular bed"
(January 1, 1994).
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