Biomedical Engineering Reference
In-Depth Information
to a lower fluid shear stress and shear strain rate. It is noted that high shear stress
is necessary for preventing platelet-dependent thrombosis (Sukavaneshvar et al.
2000b). Moreover, reduced blood into the aneurysm also means flow stagnation and
the induction of thrombosis increases. These undesirable conditions all contribute
towards aneurysm rupture (Liou and Liou 2004b). Therefore, the type of stents
deployed must have sufficient porosity to minimise aneurysmal rupture but prevent
platelet aggregation (Kim et al. 2010a). The results shown can enable medical ex-
perts to evaluate the effectiveness of stent designs and their corresponding porosi-
ties in prevention of aneurysm dilation leading to rupture.
1.3.8
Assessment of Medical Devices
Congestive heart failure at its end stage leaves limited therapeutic options for car-
diac patients. In such situations, mechanical assist therapy such as the ventricular
assist device can be used to assist the cardiovascular system via means of artificial
heart pump. Since its first implantation by Rose et al. (1954) and its first clinical ap-
plication by Hall et al. (1964), research on improving its safety and mechanical reli-
ability has been pursued. Clinical trial by Randomized Evaluation of Mechanical
Assistance for the Treatment of Congestive Heart Failure (REMATCH) is a large-
scale assessment of ventricular assist device efficacy in recent years. The purpose
of REMATCH is to conduct a series of randomized clinical trials and evaluate the
ventricular assist device with reference to optimal medical management in the case
of congestive heart failure patients who are ineligible for transplant. The study dem-
onstrated that ventricular assist device is a superior surgical remedy when compared
to drug therapy (Rose et al. 1999). It has the capability to restore haemodynamics
and the nutritional status of the blood circulatory system and reverses the abnor-
malities of the heart caused by heart failure syndrome (Jessup 2001; Kherani et al.
2004). However, one of the primary concerns by most patients is the associated fi-
nancial costs with this therapy (Bieniarz and Delgado 2007; Hernandez et al. 2008).
A Spiral Vortex Ventricular Assist Device (SV-VAD) supports cardiac patients
with refractory heart failure. Unfortunately, thrombus formation and risk of stroke
due to flow complications may lead to aggravated conditions. The haemodynam-
ics of a continuous flow in the ventricular chamber of a SV-VAD can be analyzed
using CHD. Particle image velocimetry and laser Doppler anemometry can mea-
sure cross-sectional averaged axial and tangential velocities; which are used for
validating the simulated spiral flow in a transparent acrylic SV-VAD replica. The
relationship between swirling flow and blood cell damage can be established by
evaluating flow effect on thrombosis due to high shear stress (Fig. 1.16 ). Flow stag-
nation within the SV-VAD should be insignificant and its low shear stress should
minimize hemolysis (Wong et al. 2010a).
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