What is oscillatory shear stress?
Oscillatory shear stress (OSS), derived from disturbances in blood flow in these arterial regions, induces pro-atherogenic phenotypes in endothelial cells and makes them more susceptible to the development of plaques [2,3].
Does low and oscillatory wall shear stress correlate spatially with early atherosclerosis?
Abstract. Low and oscillatory wall shear stress is widely assumed to play a key role in the initiation and development of atherosclerosis.
What is the oscillatory shear index?
The oscillatory shear index (OSI) represents the change of. direction of the WSS vector from a predominant blood flow. direction during the cardiac cycle, and is defined by. OSI = 0.5× 1.0 − t.
What is high shear stress?
High shear stress, as found in laminar flow, promotes endothelial cell survival and quiescence, alignment in the direction of flow, and secretion of substances that promote vasodilation and anticoagulation.
Is shear stress good or bad?
Maintenance of a physiologic, laminar shear stress is known to be crucial for normal vascular functioning, which includes the regulation of vascular caliber as well as inhibition of proliferation, thrombosis and inflammation of the vessel wall. Thus, shear stress is atheroprotective.
What is relative residence time?
Background: Relative residence time (RRT) is a marker of disturbed blood flow, marked by low magnitude and high oscillatory wall shear stress (WSS). The relation between solute residence time in proximity to the vascular endothelium and the atherosclerotic process is well appreciated in the literature.
What causes shear stress to increase?
The strength of the shear stress depends on the flow rate and the geometry of the channel; the narrower the channel or the higher the flow velocity, the higher is the shear stress.
Why does a wall shear stress?
In arterial blood flow, the wall shear stress expresses the force per unit area exerted by the wall on the fluid in a direction on the local tangent plane. There is substantial evidence that the wall shear stress induced by the pulsatile blood flow in the arterial system affects the atherogenic process.
What is the difference between space time and residence time?
space time is the time required to process the one reactor volume of feed and the residence time is the amount of time spent by a particle until it exits the reactor.
How are flux and residence time related?
Residence time is the total amount in the reservoir divided by the total flux in or out. As input increases residence time decreases and when input decreases residence time increases.
What does high wall shear stress mean?
High wall shear stress (WSS) has recently been proposed as one possible causative factor, promoting the development of high-risk plaques. High WSS has been shown to induce specific changes in endothelial cell behavior, exacerbating inflammation and stimulating progression of the atherosclerotic lipid core.
How can I increase my shear strength?
For example, in reinforced concrete beams, reinforcement in the form of stirrups is used to increase the member’s shear strength. The shear strength of a material is heavily dependent on its cross-sectional area. The wider and thicker a section is, the higher the shear strength of the component.
What is residence time equation?
residence time: Tr = V/I [T], a measure of the average time a molecule of water spends in a reservoir. The residence time defined for steady-state systems is equal to the reservoir volume divided by the inflow or outflow rate.
What does negative wall shear stress mean?
Negative shear stress at some points along a surface generally indicate reversed flow. This happens most often in a region where the boundary layer has separated off of a surface.
Is concrete strong in shear?
In addition to that, concrete is especially weak in handling shear stress (the force that tends to cause deformation in a material) and has poor elasticity.
Why is shear stress important?
shear stress, force tending to cause deformation of a material by slippage along a plane or planes parallel to the imposed stress. The resultant shear is of great importance in nature, being intimately related to the downslope movement of earth materials and to earthquakes.
What is the fundamental difference between CSTR & PFR?
Like the CSTRs, a constant flow of reactants and products and exit the reactor. In PFRs, however, the reactor contents are not continuously stirred. Instead, chemical species are flowed along a tube as a plug, as shown in Figure 25.2.
When do you use PFR?
Plug flow reactors are used for some of the following applications:
- Large-scale production.
- Fast reactions.
- Homogeneous or heterogeneous reactions.
- Continuous production.
- High-temperature reactions.
Does low and oscillatory wall shear stress play a role in atherosclerosis?
Low and oscillatory wall shear stress is widely assumed to play a key role in the initiation and development of atherosclerosis. Indeed, some studies have relied on the low shear theory when developing diagnostic and treatment strategies for cardiovascular disease. We wished to ascertain if this consensus is justified by published data.
What is wall shear stress (WSS)?
The wall shear stress (WSS) generated by the blood flow at the vascular wall plays an important role in the pathophysiology of atherosclerosis (Slager et al., 2005 ).
Is the low/oscillatory shear theory true?
Indeed, the relation between intimal thickness and OSI was much stronger than that between intimal thickness and mean shear. Today the low/oscillatory shear theory is widely regarded as established, and it is contrary views that are regarded as heterodox. The present systematic review considers whether the evidence justifies that consensus.
What is oscillatory shear index (OSI)?
In the 1980s, flow reversal was identified as another key factor, and an oscillatory shear index (OSI) was introduced by Ku et al. 5 to quantify it. This index has the time-averaged magnitude of WSS in the denominator, so high OSI tends to be associated with low mean shear; the low and oscillatory shear theories have become fused to some extent.