Flashcards in Hemodynamics Deck (22)

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1

## What are the constraints of Poiseulle's Law?

### It only applies to the laminar flow of Newtonian fluids.

2

## What is Poiseulle's Law?

###
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.

3

## What is the equation for resistance to flow?

###
R = [8Ln]/ [π(r^4)]

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

4

## What is viscosity?

###
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)

5

## What is the shear stress?

### Resistance to movement between laminae (pressure)

6

## What is the shear rate?

### Relative velocities between laminae (velocity of blood flow)

7

## What is laminar flow?

### Fluid moves in parallel concentric layers.

8

## What is turbulent flow?

### Disorderly flow in the vessels.

9

## What is Reynold's number equal to?

###
Rn = pDv/n

p = density

D = diameter

v = velocity

n = viscosity

10

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

### >3000

11

## What can turbulent blood flow cause?

###
It can cause:

a) murmurs

b) damage to endothelial lining

c) thrombi

d) Korotkoff sounds

12

## What is the Bernoulli Principle?

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

13

## What is the Bernoulli Principle important in?

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

14

## What is the Laplace relationship?

### Tension = (Pressure x Radius)/Wall Thickness

15

## How does the Laplace relationship apply to capillaries?

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

16

## How does the Laplace relationship apply to arteriolar vasoconstriction?

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

17

## How does the Laplace relationship apply to aneurysms?

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

18

## How does the Laplace relationship apply to dilated hearts?

### 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

## What happens to velocity as cross sectional area increases?

### It decreases.

20

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

### 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

## How is series resistance calculated?

### R1 + R2 + R3 ...

22