There is controversy in discussions about this procedure because many physicians report that the complication rate is almost the same as without a filter. Fig. S10 (online supplementary file) demonstrates that particles captured in the filter can escape if the closing of the filter occurs during the diastolic phase. It has been demonstrated that it is crucial that the
filter is closed during the systolic phase to prevent this escape. From these experiments the following can be clearly seen: All three velocity components have to be measured. The flow rate ratio between the internal and external carotid artery is the most important and significantly influences the flow separation region. The experiments show that particles in flow separation regions sometimes PARP inhibitor rotate over several pulse cycles before they are washed away. They can, however, suddenly adhere to the wall and remain there. The Selleck NSC 683864 pulse wave is not strong enough to wash these small deposits away. The procedure of plaque formation starts. More particles are attracted to and adhere to this area and the flow rate ratio is altered because of the higher resistance caused by the deposits. This effect continues and the stenosis enlarges. The geometry only plays a significant role in these regions with larger bifurcation angles, >40°, where a backward flow is created. In 3D measurements, the calculated shear stresses are
up to 20% higher than those found when measuring only the axial velocity component. With an increasing flow rate, the separation region is slightly reduced but the shear stresses increase. 10–16 Pa are the highest shear Resveratrol stresses in a healthy carotid artery and are found just at the apex. Shear stresses higher than 180–250 Pa have been measured in models with 90% stenosis for 100–200 ms. Downstream of such stenoses, vortices are created where particles can remain over several pulse cycles. They can also adhere to the wall, creating a growing stenosis. Oscillation
causes shear stresses between 1–40 Pa in such recirculation zones. Biochemical reactions are released. It is very important that stents have to be placed precisely. End threads or wires should never reach into the vessel lumen. Filters have to be closed during the systolic phase, so that no particles escape during the diastolic phase, before they can be pulled out. Experimental studies including MRI, ultrasound measurements and new ultrasound imaging which can measure all three velocity components will be increasingly important in the future to aide in training and refinement of diagnostic and therapeutic procedures. “
“Wall shear stress (WSS), the friction force of flowing blood that acts on the endothelial wall, can vary considerably throughout the vascular beds and has shown to be altered at the outlet or at the inner curvature of arteries, respectively. In an animal model, Cheng et al.