The vascular endothelium has been shown to secrete vasodilatory and vasoconstrictor substances. In the setting of experimental endothelial stripping or carotid endarterectomy, the vascular endothelium has been shown to regenerate, forming a coherent layer in seven to ten days. However, morphologic and functional alterations in the neoendothelium have been shown to exist as late as four weeks postoperatively. It is possible, therefore, that the neoendothelium in the operated-on segments in patients with thromboembolic pulmonary hypertension may create an abnormally low resistance segment in endarterectomized lung zones by its effect on vascular smooth muscle, thus shunting flow toward zones that were endarterectomized. Additional biopsy specimens, arterio-graphic, and physiologic observations should clarify the relative contributions of the various mechanisms postulated. canadian family pharmacy
Whatever its bases, however, the most important clinically relevant observations regarding steal are that it occurs rather commonly and that, if it is encountered after a successful thromboendarterectomy in which the involved vessels were not entered, rethrombosis or embolism is an unlikely cause.
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