MEDIAL NECROSIS AND ACUTE ALTERATIONS IN AORTIC DISTENSIBILITY FOLLOWING REMOVAL OF THE VASA VASORUM OF CANINE ASCENDING AORTA

Objective: It is known that the outer layers of the thoracic aorta rec eive substantial blood flow through vasa vasorum. This study was under taken to test the hypothesis that removal of vasa vasorum flow will al ter the elastic properties of the ascending aorta. Methods: Distensibi lity of the ascending aorta was determined before and 30 min after car eful removal of the periaortic fat network which contains the vasa vas orum in 10 acutely instrumented dogs (experimental group) and the resu lts were compared with those obtained from six weight matched sham ope rated control dogs. Aortic distensibility was measured using the formu la: distensibility=2xpulsatile changes in aortic diameter divided-by ( diastolic aortic diameterXpulse pressure). Aortic pressures were measu red directly from the ascending aorta by a pressure gauge. Aortic diam eters were simultaneously determined by an elastic air filled ring con nected to a transducer. The efficacy of the technique for the interrup tion of vasa vasorum blood supply to the aortic wall was proved in six additional animals by histology of transverse blocks of aortic wall f rom the area of interest. Histology was performed before vasa vasorum removal in two animals, 30 min after vasa vasorum removal in another t wo, and 15 d after vasa vasorum removal in the remainder. Results: At baseline, there was no difference in the measured variables between th e two groups. Aortic distensibility decreased significantly in the exp erimental group after vasa vasorum removal by 0.90(SEM 0.17) 10(-6).cm 2-dyn-1 (p<0.001), while it remained unchanged in the control group du ring the experiment. Complete removal of vasa vasorum of the ascending aorta was found in experimental group animals which were killed 30 mi n after operation, while ischaemic medial necrosis was observed in tho se killed 15 d after operation. Conclusions: Vasa vasorum removal led to an acute decrease in the distensibility of the ascending aorta. Lac k of blood supply to the outer part of the aortic wall is most likely to have accounted for these findings.