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Four cases with unusual aortic dissection found unexpectantly at the time of operation, and their aortographic and anatomic findings and surgical treatment are described. One of the patients had a type I aortic dissection with intimo-intimal intussusception and another had a type I dissection with one portion of the intimal wall unidentifiable up to the origin of the innominate artery. One patient had a type III dissecting aneurysm with retrograde dissection into the aortic arch and ascending aorta, and the fourth patient had a dissecting aneurysm involving the ascending aorta and the innominate, right common carotid, and right vertebral arteries with a re-entry at the aortic arch.

The effects of cross-clamping the descending aorta for 90 minutes were studied in 45 dogs divided into four groups. In all animals the left atrial, central venous, carotid artery, and femoral artery pressures, urine output, and thermal dilution cardiac output were constantly recorded, and blood samples were drawn every 30 minutes for the determination of epinephrine, norepinephrine, and plasma renin activity. During aortic cross-clamping, Group I dogs (n = 15) were placed on femoral vein-femoral artery cardiopulmonary bypass and Group II dogs (n = 15) were given intravenous sodium nitroprusside; in Group III dogs (n = 5) an external shunt from the ascending aorta to femoral artery was used, and in Group IV dogs (n = 10) no adjunct was employed. During aortic cross-clamping, the following hemodynamic parameters significantly increased: in Groups II, III, and IV, carotid artery pressure; in Group III, cardiac index; and in Groups III and IV, cardiac stroke work. While the descending aorta was cross-clamped, mean femoral artery pressure decreased in all groups: 47.5% in Group I, 79% in Groups II and IV, and 44.8% in Group III. During aortic cross-clamping, plasma epinephrine and norepinephrine levels markedly increased in Group IV, and plasma renin significantly increased in all groups. The hemodynamic findings on the fifth and seventh postoperative days were similar to those before cross-clamping of the aorta in all groups. There was no paraplegia in Groups I and III dogs, but 60% of group IV and 40% of Group II dogs were paralyzed.