Although the operative mortality rate decreased over time for patients with aortic dissection, the risk for those with acute aortic dissection during the last 10 years (1983 to 1992) is probably more realistic than that observed in the preceding 5-year interval (1978 to 1982). The operative mortality rates for patients with chronic aortic dissection have remained relatively static. Earlier diagnosis of acute aortic dissection before development of cardiac tamponade and renal impairment is critical to improve the operative salvage rate. Long-term outcome still is not optimal, which emphasizes the need for better serial postoperative aortic imaging surveillance and medical follow-up and blood pressure control.
The incidence of peripheral vascular complications in 272 patients with aortic dissection during a 25-year span was determined, as was outcome after a uniform, aggressive surgical approach directed at repair of the thoracic aorta. One hundred twenty-eight patients (47%) presented with acute type A dissection, 70 (26%) with chronic type A, 40 (15%) with acute type B, and 34 (12%) with chronic type B dissections. Eighty-five patients (31%) sustained one or more peripheral vascular complications: Seven (3%) had a stroke, nine (3%) had paraplegia, 66 (24%) sustained loss of a peripheral pulse, 22 (8%) had impaired renal perfusion, and 14 patients (5%) had compromised visceral perfusion. Following repair of the thoracic aorta, local peripheral vascular procedures were unnecessary in 92% of patients who presented with absence of a peripheral pulse. The operative mortality rate for all patients was 25% +/- 3% (68 of 272 patients). For the subsets of individuals with paraplegia, loss of renal perfusion, and compromised visceral perfusion, the operative mortality rates (+/- 70% confidence limits) were high: 44% +/- 17% (4 of 9 patients), 50% +/- 11% (11 of 22 patients), and 43% +/- 14% (6 of 14 patients), respectively. The mortality rates were lower for patients presenting with stroke (14% +/- 14% [1 of 7 patients]) or loss of peripheral pulse (27% +/- 6% [18 of 66 patients]). Multivariate analysis revealed that impaired renal perfusion was the only peripheral vascular complication that was a significant independent predictor of increased operative mortality risk (p = 0.024); earlier surgical referral (replacement of the appropriate section of the thoracic aorta) or more expeditious diagnosis followed by surgical renal artery revascularization after a thoracic procedure may represent the only way to improve outcome in this high-risk patient subset. Early, aggressive thoracic aortic repair (followed by aortic fenestration and/or abdominal exploration with or without direct visceral or renal vascular reconstruction when necessary) can save some patients with compromised visceral perfusion; however, once visceral infarction develops the prognosis is also poor. Increased awareness of these devastating complications of aortic dissection and the availability of better diagnostic tools today may improve the survival rate for these patients in the future. The initial surgical procedure should include repair of the thoracic aorta in most patients.
Because of the occurrence of two polypeptide chains in the insulin molecule, it has been proposed by several investigators, most recently by Givol et al.,I that it may be synthesized in vivo as a single large polypeptide chainwhich is converted byproteolysis to insulin after the native conformation has been established. This mechanism would undoubtedly ensure correct and efficient assembly in vivo. However, high yields of insulin have been obtained in vitro by recombination of separated or synthetic chains, especially when directing groups are employed.2 The results of Humbel3 also are consistent with a separate parallel synthesis of the two chains of angler fish insulin. Furthermore, Wang and Carpenter4 have looked for a "proinsulin" in pancreatic extracts but have concluded that if such exists, it comprises less than 10 per cent of the total insulin in the pancreas.The preponderant acinar tissue in the mammalian pancreas and its proteolytic enzymes has restricted most studies of insulin biosynthesis to a few species of teleost fish in which the islet tissue is separate from the pancreas.5' 6 Insulinproducing tumors of the islets of Langerhans, which occasionally occur in humans, are uniquely suited for the study of insulin biosynthesis since they are composed mainly of fB cells and are well separated from the surrounding acinar tissue. We recently obtained part of an islet cell adenoma that was removed from the pancreas of a patient with severe hypoglycemic episodes. When slices from this tumor were incubated with tritiated leucine or phenylalanine, the amiho acids were incorporated into insulin. A second labeled protein was separated from the acid-alcohol soluble fraction which could be shown to be related immunologically and chemically to insulin. Treatment of the second fraction with trypsin resulted in its conversion to a form that could not be distinguished from insulin. The results suggest that there is a precursor in the synthesis of insulin and that the precursor is a larger protein than insulin. Materials and Me)hods.-DL-phenylalanine-1H (675 mc/mmole) and LIleucine 4,5-H3 (5.0 c/mmole) were obtained from the New England Nuclear Corporation. Crystalline trypsin (Trypure) was obtained from Novo Terapeutisk, Copenhagen.Incubation procedure: Approximately 200 pg of slices were prepared from the fresh tumor and placed in two small beakers, each of which contained 5.0 ml of cold incubation medium. The medium was Hank's salt solutions containing 320 mg/100 ml of glucose and 20 mg/liter of each of the 18 naturally occurring amino acids. In one beaker approximately 1.5 mc of tritiated phenylalanine was substituted for phenylalariine, while in the other beaker 0.3 mc of tritiated leucine was substituted for leucine. The beakers were incubated 4.5 hr at 370C in a Dubnoff shaking metabolic incubator under an atmosphere of l95% 02/5% CO2.Extraction procedure: The contents of each beaker were extracted with cold acid-alcohol solution and the extracts partially purified by the method of Davoren.8 Gel filtration proc...
TxCAD incidence appears to be lower in patients treated with ganciclovir who are not treated with calcium blockers. Given the limitations imposed by post hoc analysis, a randomized clinical trial is required to address this issue.
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