Evidence suggests rigid aortic grafts increase systolic blood pressure: Results of a preliminary study

Abdominal aortic aneurysm (AAA) is a serious complication of the aorta and is treated using vascular bypass grafts. Two main classes of graft are available to treat AAA; grafts implanted by open surgery and stent-grafts implanted using minimally invasive endovascular techniques. Both classes of graft consist of an aortic section which bifurcates into two iliac sections. It has been hypothesized that implantation of aortic grafts and stent-grafts serve to significantly increase abdominal aortic pressures. In this study, an open-loop computer-controlled pumping system was built to produce physiologically realistic pressure and flow-rates. Models of a compliant abdominal aortic aneurysm, a compliant walled graft and a tapered graft were manufactured using an injection moulding technique and fused deposition modelling was used to create a rigid walled graft. A specific transient flow-rate waveform was then applied at the inlet of each model and the resulting pressure waveforms 30 mm upstream from the bifurcation was recorded. Peak pressure measurements were recorded over the course of the pulse for each model. The compliant aneurysm model was found to have a systolic pressure of 107 mmHg while the complaint graft model was 153 mmHg. The rigid graft model had a peak systolic pressure of 199 mmHg. In the tapered graft, the peak pressure dropped to 142 mmHg. The data suggests that implanting a graft model in place of an aneurysm model in an in vitro flow circuit can increase the pressures recorded upstream from the iliac bifurcation and that tapered grafts may alleviate this problem.