Hemodynamics Flashcards

1
Q

What are the constraints of Poiseulle’s Law?

A

It only applies to the laminar flow of Newtonian fluids.

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2
Q

What is Poiseulle’s Law?

A

F = [(Pi-Po)π(r^4)]/[8Ln]

Flow is proportional to the pressure gradient and the radius to the 4th power. It is inversely proportional to the viscosity.

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3
Q

What is the equation for resistance to flow?

A

R = [8Ln]/ [π(r^4)]

Resistance is proportional to the viscosity length and is inversely proportional to the radius to the 4th power.

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4
Q

What is viscosity?

A

Viscosity is the internal frictional resistance and it increases as the length and the hematocrit increases.

It is equal to: Shear Stress/Shear Rate (Pressure/Velocity)

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5
Q

What is the shear stress?

A

Resistance to movement between laminae (pressure)

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6
Q

What is the shear rate?

A

Relative velocities between laminae (velocity of blood flow)

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7
Q

What is laminar flow?

A

Fluid moves in parallel concentric layers.

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8
Q

What is turbulent flow?

A

Disorderly flow in the vessels.

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9
Q

What is Reynold’s number equal to?

A

Rn = pDv/n

p = density
D = diameter
v = velocity
n = viscosity
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10
Q

At what value of the Reynold’s number does turbulent flow occur?

A

> 3000

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11
Q

What can turbulent blood flow cause?

A

It can cause:

a) murmurs
b) damage to endothelial lining
c) thrombi
d) Korotkoff sounds

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12
Q

What is the Bernoulli Principle?

A

In a constant flow system, the total energy of summing the kinetic and potential energies, is constant.

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13
Q

What is the Bernoulli Principle important in?

A

It is important in stenosis as a decrease in the cross sectional area will result in an increase in the kinetic energy.

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14
Q

What is the Laplace relationship?

A

Tension = (Pressure x Radius)/Wall Thickness

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15
Q

How does the Laplace relationship apply to capillaries?

A

Capillaries have: small radius = low wall tension, so they can withstand very large transmural pressures.

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16
Q

How does the Laplace relationship apply to arteriolar vasoconstriction?

A

They have relatively large wall thickness/lumen diameter ratio = low wall tension; so it provides greater control of vessel diameter and blood flow.

17
Q

How does the Laplace relationship apply to aneurysms?

A

Aneurysms have a large radius = high wall tension; so it cannot withstand transmural pressures and therefore will eventually rupture.

18
Q

How does the Laplace relationship apply to dilated hearts?

A

Dilated hearts have large radius = high wall tension = higher afterload, results in more systolic work, and higher oxygen consumption to overcome higher wall tension.

19
Q

What happens to velocity as cross sectional area increases?

A

It decreases.

20
Q

Why does velocity decrease from the aorta to capillaries if the cross sectional area is decreasing?

A

The overall cross-sectional area of all of the capillaries is increasing much more than the arteries that it is coming from and so the velocity will decrease.

21
Q

How is series resistance calculated?

A

R1 + R2 + R3 …

22
Q

How is parallel resistance calculated?

A

1/R1 + 1/R2 + 1/R3 …