Hemodynamics

Question 1

What are the constraints of Poiseulle’s Law?

Answer 1

It only applies to the laminar flow of Newtonian fluids.

Question 2

What is Poiseulle’s Law?

Answer 2

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.

Question 3

What is the equation for resistance to flow?

Answer 3

R = [8Ln]/ [π(r^4)]

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

Question 4

What is viscosity?

Answer 4

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)

Question 5

What is the shear stress?

Answer 5

Resistance to movement between laminae (pressure)

Question 6

What is the shear rate?

Answer 6

Relative velocities between laminae (velocity of blood flow)

Question 7

What is laminar flow?

Answer 7

Fluid moves in parallel concentric layers.

Question 8

What is turbulent flow?

Answer 8

Disorderly flow in the vessels.

Question 9

What is Reynold’s number equal to?

Answer 9

Rn = pDv/n

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

Question 10

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

Answer 10

> 3000

Question 11

What can turbulent blood flow cause?

Answer 11

It can cause:

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

Question 12

What is the Bernoulli Principle?

Answer 12

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

Question 13

What is the Bernoulli Principle important in?

Answer 13

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

Question 14

What is the Laplace relationship?

Answer 14

Tension = (Pressure x Radius)/Wall Thickness

Question 15

How does the Laplace relationship apply to capillaries?

Answer 15

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

Question 16

How does the Laplace relationship apply to arteriolar vasoconstriction?

Answer 16

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

Question 17

How does the Laplace relationship apply to aneurysms?

Answer 17

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

Question 18

How does the Laplace relationship apply to dilated hearts?

Answer 18

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

Question 19

What happens to velocity as cross sectional area increases?

Answer 19

It decreases.

Question 20

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

Answer 20

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.

Question 21

How is series resistance calculated?

Answer 21

R1 + R2 + R3 …

Question 22

How is parallel resistance calculated?

Answer 22

1/R1 + 1/R2 + 1/R3 …