Boaz Nishri

Hemodynamic Evaluation of Embolic Trajectory in an Arterial Bifurcation. An In-Vitro Experimental Model

Background and Purpose— Despite the importance of embolism as a major cause of brain infarction, little is known about the hemodynamic factors governing the path large emboli tend to follow. Our aim was to test in vitro, whether hemodynamic parameters other than flow ratios between bifurcation branches may affect the distribution of embolic particles in a Y-shaped bifurcation model, used as an analogue to an arterial bifurcation. Methods— In vitro experiments were conducted using suspensions of sphere-shaped particles (0.6, 1.6, and 3.2 mm) in water-glycerin mixture, using steady and pulsatile laminar flow regimes in a Y-shaped bifurcation model (identical branching angles [&thgr;1=&thgr;2=45o] with one daughter branch diameter wider than the other [D1=6 mm, D2=4 mm]; average Reynolds number 500). Results— Experiments using naturally buoyant particles under steady flow conditions and four outlet-flow ratios revealed that small (0.6 mm) and mid-sized (1.6 mm) particles entered into either the narrower or wider bifurcation daughter branch nonpreferentially, proportionally to the flow ratios. Large particles (3.2 mm), however, preferentially entered the wider daughter branch. Moreover, as the flow ratio increases this phenomenon was augmented. Further experiments revealed that the preference of the wider daughter branch for high particle-to-branch diameter-ratios further increases under pulsatile flow and by the density ratio between particles and fluid. Conclusion— Particles’ distribution in a bifurcation is affected, beyond its outlets-flow-ratios, by the particle-to-branch diameter-ratio. The tendency of large particles to preferentially enter the wider bifurcation branch, beyond the flow ratio, is augmented under pulsatile flow conditions and is affected by particle-to-fluid density-ratio. These findings may have important implications for understanding the hemodynamic mechanisms underlying the trajectory of large emboli.

A Novel Endovascular Device for Emboli Rerouting Part I: Evaluation in a Swine Model

Background and Purpose— The feasibility and safety of a novel endovascularly delivered tubular mesh designed to reroute emboli away from a critical artery as a means of ischemic stroke prevention was tested in vitro and in vivo. Methods— Emboli rerouting efficacy was assessed in vitro. Perfusion through the external femoral artery that was jailed by the device, cellular proliferation rate over the jailing mesh, and the resulting tissue coverage of the orifice were assessed in the swine iliofemoral bifurcation. Device-induced embolization was assessed in a swine kidney model. Results— In vitro experiments demonstrated that particles as small as 60% of the pore dimension can be rerouted by the device, although at low efficacy, and rerouting efficacy approached 100% as the particle size approached the pore dimension. Repeat assessment of flow preimplantation and at various follow-up times by Doppler ultrasound showed no significant changes in the perfusion ratio of the jailed branch to the parent artery or the jailed branch to the naive contralateral artery either as a result of device implantation or at the follow-up times. Tissue coverage over the jailed ostium was limited to approximately 12% after stabilization. Cellular proliferation rate gradually decreased to diminishing level approximately 22 weeks postimplantation. The devices implanted across the renal arteries did not demonstrate any device-induced embolization after 1 month. Conclusions— It is proposed that this device could be used to reroute emboli away from important intracranial vessels as a means of stroke prevention.

Similarity of the Swine Vasculature to the Human Carotid Bifurcation: Analysis of Arterial Diameters

PURPOSE We assessed the similarities of the iliac bifurcation in two breeds of swine to the known human carotid bifurcation, in order to assess its applicability as a preclinical model of the human carotid bifurcation. MATERIALS AND METHODS Mixed-Landrace crossbreed (domestic; n = 66) and Yucatan miniswine (Yucatan; n = 13) were studied. The diameters of the iliac bifurcation arteries were measured from angiographic pictures, the relations between the arterial diameters and the animals weight assessed, and diametrical ratios calculated. Findings were compared with the known human carotid bifurcation. RESULTS The external iliac diameter (approximately 6-7mm) in the lower weight swine was similar to the known human common carotid artery. The best similarity was found between the diametrical ratios of the human internal to common carotid artery (mean 0.63) to the swine profunda to external iliac (means 0.68 and 0.65 for the domestic and Yucatan, respectively). The arterial diameters of the domestic swine were highly correlated with their weight that increased considerably with time, while in the Yucatan group, arterial diameters did not change with increasing weight and the average weight increase rate was low. Thus, the estimated arterial diameter increase rate over time was high in the domestic while minor in the Yucatan group. CONCLUSIONS Similarities were found between the swine iliac bifurcation arteries to the human carotid bifurcation in terms of diameters, diametrical ratios and angle. The swine iliac bifurcation may be used for preclinical endovascular research of devices intended to the human carotid bifurcation, with miniswine strains a preferable model for long-term studies.

EFFICACY OF A NEW PERMANENT ARTERIAL FILTRATION DEVICE

The Diverter is a new permanent arterial diversion device designed to divert emboli away from the internal into the external carotid artery to prevent embolic stroke. The purpose of this study was to assess experimentally the hemodynamic performance and diverting capacity of the Diverter to be implanted at the carotid bifurcation.