Bio 201 -006 WindKessel Project

Group members:

Cody Bukowski

Steve DiBianca

Erica Henn

1) Explain the Windkessel effect using Arterial Flow, Pressure and Volume.

Both stiff and compliant experience arterial flow. Stiff aorta have a higher pressure while compliant aorta have a higher volume. When the aorta is stiff it does not have properties of high elasticity and flexibility, meaning the volume will remain the same. A compliant aorta will exhibit properties of elasticity and flexibility meaning the volume can increase. This allows the ventricle to more easily pump blood through a relaxed aorta and pooling will be seen. and are very important when speaking about the pressure and volume in the aorta and ventricle. Diastole is a gradual decrease in pressure, however although the pressure of the ventricle decreases the pressure of the aorta does not due to the pooling of the compliant aorta. The effects systole and diastole due to varied changes in resistance, compliance and stiffness are known as the Windkessel effects.

When looking at the patterns of a lead pipe, it is analogous to the flow of a stiff aorta. As the piston starts and stops pushing blood, the pressure inside the ventricle drops, resulting in the cease of aortic flow. After systole, the flow from the aorta to the distal vessels is almost completely terminated due to the stiffness causing a drop in aortic pressure, volume and flow.

When looking at the patterns of a water balloon they are comparable to the flow in the compliant aorta because there is more compliance due to aortal distension. Compared to the lead pipe, the water balloon has a greater aortic volume and flow rate. With the ability to expand a more compliant aorta can hold more volume, thus gradually decreasing in pressure, flow, and volume.

Through Matlab we are able to study the simulations and clearly see that the aorta is more compliant than it is stiff. The reason for this is to accommodate to the pooling of blood that could be used as a reserve during any type of increased cardio activity.

Figure 1. Pressure flow and aortic volume vs. time

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Figure 2. Pressure, flow and volume vs. time

2.) Define Rsistance and Compliance. What are the primary and secondary parameters that are affected by the changes in both Resistance and Compliance? Explain how these combination of changes have an effect on the arterial parameters and Why? . In a blood vessel resistance is defined the opposition to the direct flow of blood. Blood flow is determined by its viscosity and obstacles that can obstruct the flow. Compliance is a measure of a blood vessel’s flexibility and elasticity. Blood vessels expand and contract in response to factors of flow and. Smooth muscle is responsible for the contraction and expansion, which account for the flexibility and elasticity. Stiffness is the reciprocal value of this. This experiment shows the effects when resistance and compliance are varied in the aorta.

Plots were constructed to see how the changes in resistance, compliance, and stiffness effects blood flow. As seen in Figure 2.1, resistance was decreased by a factor of 10 while holding stiffness constant cause the aortic pressure to parallel the ventricular pressure. Blood varies form systolic (max pressure) and diastolic (min pressure). When aortic pressure and ventricular pressure are parallel the transition for systolic to diastolic is abrupt. Since there is less resistance pooling of blood is not seen during diastole making the inflow and outflow of the aorta almost equal. Also the aortic volume reaches its max and begins to fall during systole, before diastole. These results make sense because with less resistance the aorta cannot oppose the blood flow from the ventricle. Figure 2.1 also shows when stiffness if decreased by 10 and resistance is held constant. There is a significant amount of aortic pooling because the aortic outflow is much smaller than the inflow and aortic volume increases very quickly during systole but only gradually decreases during diastole, creating a high .

Figure 2.2 represents an increasing aortic resistance by a factor of ten while keeping the stiffness constant. This plot is similar to that of Figure 2.1 which keeps resistance constant while decreasing stiffness by a factor of ten. This makes sense because in general increasing the resistance increases opposition to blood flow, resulting in a decrease in the magnitude of the change in aortic pressure from systole to diastole, and a gradually decrease in the pressure in the aorta from systole to diastole. Increased stiffness of the vessel causes little blood pooling in the aorta.

Figure 2.3 represents both the increase in stiffness and resistance by a factor of ten, and the decrease in the stiffness and resistance by ten. In Figure 2.3 there is a plot that looks somewhat similar to the normal output plot of Figure 2. The reason for this is because the two effects of increasing and decreasing stiffness and resistance are essentially opposite due to the factor number. In general, a greater resistance leads to a plot closer to that of the water balloon model, while on the other hand a greater stiffness causes the plot to look closer to the lead pipe model. These representations are revered, meaning that when the stiffness is less, it will look more like the water balloon model, while less resistance will closely mimic the lead pipe model.

Figure 2.1. Decreased resistance, keeping stiffness constant (left) and decreased stiffness, keeping resistance constant (right)

Figure 2.2. Increased resistance with stiffness constant (left) and increased stiffness with resistance constant (right).

Figure 2.3. Decreased resistance and stiffness (left) and increased resistance and stiffness (right) by a factor of 10 compared to standard values.

Figure 2.4. Increased resistance with decreased stiffness (left) and decreased resistance with increased stiffness (right) by a factor of 10 compared to standard values.

3) What physiological conditions cause such a change in resistance and compliance?

The physiological conditions that could cause a change in resistance and compliance are those related to the smooth muscle contractions of the arteries. Because arterial blood vessels have smooth muscle running along their outsides, contractions of the smooth muscle would cause constriction in the blood vessels, changing their resistance and compliance. With constriction occurring, there is less room to stretch, so the compliance would decrease. Because the diameter of the blood vessel would become smaller with the constriction occurring, the resistance would increase.

4) Of the quantities that vary in time (i.e., variables - as opposed to those that are fixed (called parameters), which quantities do we need to know to give a complete description of the state of the systems? Use results from SimpWind.mdl

We would need to know the change in volume of blood in the artery. Once we know that we can calculate other variables, such as pressure and flow. This is seen in the figures above