Hemodynamics

Question 1

Relationship between velocity and flow

Answer 1

V=Q/A

Q = flow (cm^2/s)

A = cross-sectional area

Question 2

If no branching…

And the cross sectional area increases…

The flow will

Answer 2

Stay the same

(Velocity decreases)

**if branching…flow can change

Question 3

Cross-sectional area is largest in the ?

Answer 3

Capillaries…

So velocity is much lower in capillaries compared to the aorta and bigger arteries

Question 4

Turbulent flow

Answer 4

Disordered, inefficient flow

Not ideal

Can do damage to the endothelium

Occurs at branch points and points with vessel narrowing

Question 5

Laminar flow

Answer 5

Most efficient type of flow

Concentric layers of flow

Layers closer to the walls = slower due to friction

Question 6

Reynolds number

Answer 6

Re = pDv/n

P = density
D = diameter
V = velocity
N = viscosity

Greater than 200 = turbulent

Question 7

Factors that would increase reynolds number and turbulency

Answer 7

Increased blood density, velocity, and vessel diameter

Question 8

Factors that decrease reynolds number and turbulency

Answer 8

Increased blood viscosity

Question 9

Anemia effecy on Re

Answer 9

Decreases viscosity —> increases Re

Question 10

Increased CO —> Re?

Answer 10

Increases velocity —> increases Re

Question 11

Decreased vessel diamter —> Re?

Answer 11

Increases velocity —> increases Re

Question 12

Dramatic increase in systolic pressure in the external or internal carotid in comparison to the common and other carotid = sign of what

Answer 12

Stenosis of one of the carotid branches…thus directing much of the blood flow to the other…instead of splitting the flow between the two after bifurcation

Question 13

Pulse pressure =

Answer 13

Difference between systolic and diastolic pressures

Question 14

Mean arterial pressure

Answer 14

Diastolic pressure + 1/3*pulse pressure

Is the area under the graph of arterial pressure over the period of one cardiac cycle

Question 15

Distensibility

Answer 15

Ability to change dimension in response to force

Ensure steady flow

Reduces the amount of work the heart has to do

Rigid vessels over time can lead to heart failure

Question 16

Compliance

Answer 16

Change in volume for a given change in pressure (deltaV/deltaP)

Measure of how distensible vessels are

Question 17

Elasticity

Answer 17

Ability to return to normal size after being distended

Lost over time/age

Which causes an increase in systolic pressure, and since diastolic pressure remains the same…pulse pressure increases with age

Question 18

Ohm’s law for blood flow

Answer 18

Q = delta P/R

Q = flow. (Was current)

P = pressure (was voltage)

Question 19

Poiseuille’s law

Answer 19

Replaces R with an equation in Ohm’s

R = 8(viscosity)(length)/pi*radius^4

Sub into Ohm’s law

Question 20

Effect of the following on flow

1. Decrease viscosity
2. Increase viscosity
3. Decreased radius
4. Increased radius
5. Decreased length
6. Increased length

Answer 20

1. Up (anemia)
2. Down (polycythemia)
3. Down (vasoconstriction)
4. Up (vasodilation)
5. Up (rare)
6. Down (rare)

Question 21

Total resistance for vessels in a series =

Answer 21

Resistances added up

Benefit = allows laminar flow

But otherwise cannot just have series because of increasing resistance…blood wouldn’t get back to the heart

Question 22

Total resistance with vessels in parallel

Answer 22

Inverse of total = inverse of each individual

Overall resistance is lowered

Benefit = can shunt blood from one vessel to another depending on the resistance

Question 23

Does viscosity of blood constant?

Answer 23

No

Not a Newtonian fluid…

Why?

1. Blood viscosity increases with increasing hemacrit
2. Fahraeus-Lingqvist effect = small diameter vessels, red blood cells move toward the center of … so outer part being more fluid…becomes less viscous and less friction
3. Blood viscosity decreases with increased flow

Question 24

Compare primary functions of arteries, veins, and capillaries

Relate those differences in structure

Answer 24

1. Arteries:
   - lots of smooth muscle to handle force of blood pumping through it
   -adventitia secures arteries in place
   -ENDOTHELIAL LAYER
   —> separates blood from smooth muscle…receives signals and sends messenges that cause smooth to constrict or dilate

1A. Arterioles

• responsible for regulating total peripheral resistance
• vasoconstriction = increased pressure upstream and decreased downstream…

1B. Metaarterioles

• connects arterioles to venules
• bypasses flow directly from arteriole to venule
• allows completely shunt blood away from capillaries or just some

2. Veins
   - just enough of SmM for constriction and dilation
   Valves allow for unidirectional flow and compartmentalization
   - highly distensible - allows them to hold high volume for reservoir purposes
3. Capillaries
   - single layer of endothelial cells
   - sites for exchange with surrounding tissue

Question 25

Why the drastic drop in pressure moving from muscular arteries to capillaries

Answer 25

Compensates for the increase in resistance in the capillaries

Question 26

Law of LaPlace

Answer 26

T = P * r ``` T = wall tension P = transmural pressure R = radius ``` **capillaries can withstand a elevated “P” due to a small radius Aneurysms —> arteries remodel themselves to cope with an increasing wall tension - bulging to make a sphere shape

Question 27

In order for diffusion to happen...the substance must be what is nature?

Answer 27

Hydrophobic

Question 28

Fick’s Law

Answer 28

Diffusion in the capillary follows this law J = -PS (Co - Ci) ``` J = movement of solute over time P = each substance diffusing across has a different eas of diffusion S = surface area, as you increase S...easier to get inside C = concentrations inside/out (gradient...most important factor) ```

Question 29

Edema affect on diffusion across capillary

Answer 29

You have liquid that is pushing on the tissue ...adding distance between the capillary and tissue Once this happens...diffusion becomes diffusion limited...you have to wait for material to make its way to the tissue

Question 30

Filtration

Answer 30

Capillary —> interstitial fluid Capillaries have a higher pressure, fluids push into fluid Driven by hydrostatic pressure...but it decreases as you approach the venule

Question 31

Absorption

Answer 31

As you get to the venules...hydrostatic pressure diminishes and now the dominant pressure is oncotic pressure Which is formed by plasma proteins in the plasma (mostly albumin) in the capillary...these proteins will start to pull water into capillary

Question 32

Sterling equation

Answer 32

Summarizes the flow of fluid is equal to the difference in hydrostatic pressure minus the difference in oncotic pressure The drop is pressure from arteriole to venule serves as a change from filtration —> absorption If difference in HSP > difference OP = filtration (positive #)

Question 33

Goal of vasodilation? Vasoconstriction?

Answer 33

Vasoconstriction: Causes pressure to decrease DOWNSTREAM in the capillaries Leads to a DECREASE in filtration and INCREASE in absorption —> leads to restoration of blood volume Vasodilation: Causes pressure to increase DOWNSTREAM in the capillaries Leads to INCREASE filtration and DECREASE absorption —> leads to edema

Question 34

Pinocytosis

Answer 34

Method by which you get large lipid insoluble molecules into the cell

Question 35

Effects of vasodilation of arterioles on filtration and absorption Vasoconstriction of arterioles

Answer 35

Increased pressure on arterilar side... Increased filtration and decreased absorption —> more fluid entering into the interstitial space. Constriction = opposite

Question 36

Function of lymphatic system...

Answer 36

Vessels intercalated by capillary bed Pressure within bed is lower than pressure within the capillaries...so fluid can flow into them Main importance = helps resotre blood to its normal volume Prevents edema

Question 37

Deep vein thrombosis (DVT)

Answer 37

Caused by clot forming in the venous side...restricting blood flow Messing up the flow —> increase in venous pressure —> similar effect as if you vasodilated the arterioles Increase filtration and decrease absorption

Question 38

Decrease pressure on arteriolar side Effect?

Answer 38

Enhanced reabsorption Cause = vasoconstriction

Question 39

Increased pressure on the arteriolar side Effect?

Answer 39

Enhanced filtration/edema Cause = vasodilation

Question 40

Increased pressure on venous side

Answer 40

Effect = enhanced filtration/edema (same as increasing arteriolar pressure) Cause = heart failure, venous clots

Question 41

Decreased pressure on venous side Effect =?

Answer 41

Effect = enhanced reabsorption (same as decreased pressure on arteriolar side) Cause = hemorrhage Need to restore blood volume

Question 42

Why does tension remain low in capillaries? Veins?

Answer 42

Capillaries have a small radius Veins have little pressure Refer to Law of LaPlace: T = P x R

Question 43

What characteristic of veins allow them to make good ‘reservoirs’ of blood?

Answer 43

They have high compliance Takes a small change in pressure to instill a large change in volume