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This study examined a pulsatile flow simulator for the purpose of evaluating two measurement devices, an extracorporeal flow probe with an electromagnetic flow meter and several thermodilution catheters. We measured the performance of these devices in a range of low to high flows. Using either saline or blood as a perfusate, we obtained different results with these fluids (p less than 0.001). Each catheter behaved in a linear manner, although variation occurred among the catheters with both saline (minimum slope 1.090, maximum slope 1.190) and blood (minimum slope 1.107, maximum slope 1.154). An increase in rate and stroke volumes of the simulator did not demonstrate an identifiable trend in error. The thermodilution catheters were most accurate at 5.0 L/min irrespective of rate, stroke volume, or perfusate used. In contrast, the electromagnetic flow meter accurately represented flows across the wide range of outputs examined (2.4 to 10.7 L/min). (Slope with saline 1.091, slope with blood 1.080) Throughout the range of flow, the flow meter gave a calibration line 5% higher with blood than with saline. The results indicate that accurate measurement of pulsatile blood flow can be achieved in vitro with an electromagnetic flow meter using saline as a perfusate, provided a correction factor is determined and applied to convert values for saline to accurate values for blood.

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The rate of aneurysm formation in umbilical vein grafts has been reported to lie between 1% and 8%. However, in these reported series the number of grafts with aneurysms was related to the number of grafts inserted. When the denominator is changed to patent grafts at a given time period, the incidence changes drastically. In this study, duplex scanning was used to detect aneurysms in patent grafts. Four types of aneurysms--localized fusiform, localized eccentric, diffuse, and anastomotic--were recognized. Excluding anastomotic aneurysms, 33% of the grafts patent at 3 years were aneurysmal; in those patent at 4 years, 45% were aneurysmal; and in those patent at 5 or more years, 65% were aneurysmal. On grounds of theoretical considerations, it is believed that duplex scanning is more reliable than either clinical examination or arteriographic study for detecting these aneurysms. There is now evidence that the supporting Dacron mesh is too weak and must be strengthened. Despite aneurysm formation, the patency rate in our series has remained second only to saphenous vein grafts, as previously reported.

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