Experimental investigation of pulsatile flows in tubes

Haemodynamic analysis of vessel remodelling in STA-MCA bypass for Moyamoya disease and its impact on bypass patency

The purpose of this study is to estimate the remodelling characteristics of STA-MCA bypass and its influence on patency via the use of computational fluid dynamic (CFD) technology. The reconstructed three-dimensional geometries from MRA were segmented to create computational domains for CFD simulations. Eleven patients, who underwent regular MRA both immediately following surgery and at the six months follow-up, were studied. The flow velocities at STA were measured via the use of quantitative MRA (QMRA) to validate simulation results. STA-MCA bypass patency was confirmed for each patient immediately following surgery. The simulation indicated that the remodelling of the arterial pedicle in nine patients was associated with a reduction in the resistance to flow through the bypass. For these cases, the modelling of a driving pressure of 10mmHg through the bypass at 6 months post-surgery resulted in a 50% greater blood flow than those found immediately following surgery. However, two patients were found to exhibit contradictory patterns of remodelling, in which a highly curved bending at the bypass immediately post-surgery underwent progression, with increased resistance to flow through the bypass at 6 months follow-up, thereby resulting in a modelled flow rate reduction of 50% and 25%, respectively. This study revealed that STA-MCA bypass has a characteristic remodelling that usually reduces flow resistance. The initial morphology of the bypass may have had a significant effect on the outcome of vessel remodelling.

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.

Parameter fitting of digital models of pulsatile hemodynamics based on intravascular measurements in the rabbit aorta

The objective was to describe and evaluate methods of in vivo intravascular assessment of pressure and flow within the systemic arterial tree for further digital processing and individualized simulation. In rabbits intra-aortic pressure and flow were measured by insertion of microcatheters and/or a Doppler probe, which were moved to different angiographically documented sites. Various catheters and sheaths were evaluated prior to digitized processing of the obtained data, which was based on electrotechnical analoga for description of elastic vascular segments. Fourier transformation and filtering provided signal data for further identification of the investigated parameters. Catheters with an inner diameter > or = 0.9 mm produced reliable pressure signals. Simultaneous measurement of pressure and flow reduced the reliability of the absolute values by reduction of the cross-sectional diameter of the investigated vascular segments. Numerical optimization methods were used to identify parameters in the proposed models from the measured data sets. Characterization of hemodynamics by intravascular measurements of pressure and flow proved feasible. Pressure recordings should be judged critically if the cross-sectional area of the catheter covers a significant fraction of the vessel. Post-processing of such data sets may assist in future treatment planning and simulation of concomitant changes of intravascular pressure and flow.