Hemodynamics & Vasculature (complete)

Question 1

What is the flow equation?

Answer 1

Q = ΔP/R

Q = Flow
P = Pressure
R = Resistance

Question 2

Describe the flow equation

Answer 2

• Pressure differences drive flow
• Vascular resistance opposes flow

Flow-in MUST EQUAL flow-out

Question 3

What are some limitations of the flow equation as it relates to the CV system?

Answer 3

Assumptions are made that aren’t always true:

• Constant pressure
• Constant resistance
• Straight rigid tube
• Laminar flow
• Non-pulsatile flow

Question 4

What is the difference between flow (Q) and velocity (v)?

Answer 4

Q: volume/time

• Constant throughout the system
• CO = total flow

v: distance/time
- v = Q/A
- v is highest in aorta (small cross-sectional area)
- lowest in capillaries

Question 5

What is Poiseulle’s Law?

Answer 5

Q = ΔP ⋅ (πr^4)/(8ηl)

r = radius
η = viscosity
l = length

All the above relate to R

• r is disproportional
• η and l are proportional

Question 6

Describe Poiseulle’s Law

Answer 6

• Flow is proportional to 4th power of radius

- Therefore vessel radius is the BIGGEST determinant of flow

Question 7

For resting muscles, which equation should you use?

Answer 7

Q = ΔP/R

Question 8

From blood flow to the muscle during exercise and the radius changes, which equation do you use?

Answer 8

Q = ΔP ⋅ (πr^4)/(8ηl)

Question 9

Describe parallel resistance in blood vessels

Answer 9

1/R(t) = 1/R(1) + 1/R(2) + 1/R(3)

Total resistance of network of vessels is lower than the single lowest resistant vessel

Ex: capillaries total resistance is low even though individual capillaries have high resistance

Question 10

Describe series resistance in blood vessels

Answer 10

R(t) = R(1) + R(2) + R(3) — additive

Total resistance > individual resistance

Q is constant through series, so pressure drops

Occurs in arteries, arterioles, capillaries => together

Question 11

How does turbulent flow occur?

Answer 11

In areas with:

• Large diameter
• High velocity
• Low viscosity
• Change in diameter
• Irregularities on walls (eg plaque)

Sounds like an aorta!

Turbulent flow produces shearing forces that can damage vasculature endothelium

Question 12

How is the pulsatile flow of blood produced by heart converted to steady flow in the capillary beds?

Answer 12

• Pulse pressure is dampened by arterial system

Question 13

Define vascular compliance

Answer 13

C = ΔV/ΔP

C = compliance
V = volume
P = pressure

• Represents elastic properties of vessels/chambers
• Veins more compliant than arteries

Vessels lose compliance with age!! (arteriosclerosis) => older people have higher systolic pressure and pulse than younger

Question 14

What is LaPlace’s Law?

Answer 14

T = (ΔP ⋅ r)/μ

T = wall stress/tension
ΔP = *transmural* pressure
r = radius
μ = wall thickness

Question 15

Describe LaPlace’s Law

Answer 15

• Describes relationship btwn tension in a vessel wall and the transmural pressure
• For example, hypertension increases stress on vessel walls
• in an aneurysm => wall bulges & ^ radius => ^ cell tension in order to prevent splitting

Question 16

What is Fick’s Principle?

Answer 16

X = Q • [x]

X(used) = Q([x]in - [x]out)

mV(O2) = CO([O2]a - [O2]v)

a = arterial
v = venous

Question 17

How can Fick’s Principle be used to determine transcapillary efflux?

Answer 17

• ask how much of the oxygen was used in the caps

- so use the equation: X(used) = Q([x]in - [x]out)

Question 18

What is hydrostatic pressure?

Answer 18

• fluid pressure
• aka blood pressure in the capillary
• at beginning of capillary
• favors FILTRATION b/c P(c) > P(i)

Question 19

What is oncotic pressure?

Answer 19

• Osmotic force exerted by solutes, primarily in blood
• at the end of capillary
• favors REABSORPTION b/c of more protein in blood than interstitial fluid

Question 20

What is Starling’s Equation?

Answer 20

Flux = k {[P(c) - P(i)] - [π(c) - π(i)]}

Flux = net flux across capillary wall
k = constant
P(c) = capillary hydrostatic pressure
P(i) = interstitial
π(c) = capillary oncotic pressure
π(i) = interstitial