Medial necrosis and acute alterations in aortic distensibility following removal of the vasa vasorum of canine ascending aorta

Abstract

It is known that the outer layers of the thoracic aorta receive substantial blood flow through vasa vasorum. This study was undertaken to test the hypothesis that removal of vasa vasorum flow will alter the elastic properties of the ascending aorta. Distensibility of the ascending aorta was determined before and 30 min after careful removal of the periaortic fat network which contains the vasa vasorum in 10 acutely instrumented dogs (experimental group) and the results were compared with those obtained from six weight matched sham operated control dogs. Aortic distensibility was measured using the formula: distensibility = 2 x pulsatile changes in aortic diameter divided by (diastolic aortic diameter x pulse pressure). Aortic pressures were measured directly from the ascending aorta by a pressure gauge. Aortic diameters were simultaneously determined by an elastic air filled ring connected to a transducer. The efficacy of the technique for the interruption of vasa vasorum blood supply to the aortic wall was proved in six additional animals by histology of transverse blocks of aortic wall from the area of interest. Histology was performed before vasa vasorum removal in two animals, 30 min after vasa vasorum removal in another two, and 15 d after vasa vasorum removal in the remainder. At baseline, there was no difference in the measured variables between the two groups. Aortic distensibility decreased significantly in the experimental group after vasa vasorum removal by 0.90(SEM 0.17) 10(-6).cm2.dyn-1 (p < 0.001), while it remained unchanged in the control group during the experiment. Complete removal of vasa vasorum of the ascending aorta was found in experimental group animals which were killed 30 min after operation, while ischaemic medial necrosis was observed in those killed 15 d after operation. Vasa vasorum removal led to an acute decrease in the distensibility of the ascending aorta. Lack of blood supply to the outer part of the aortic wall is most likely to have accounted for these findings.