Hemodynamics & Vasculature (complete) Flashcards Preview

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Flashcards in Hemodynamics & Vasculature (complete) Deck (20):
1

What is the flow equation?

Q = ΔP/R

Q = Flow
P = Pressure
R = Resistance

2

Describe the flow equation

- Pressure differences drive flow
- Vascular resistance opposes flow

Flow-in MUST EQUAL flow-out

3

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

Assumptions are made that aren't always true:

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

4

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

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

5

What is Poiseulle's Law?

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

6

Describe Poiseulle's Law

- Flow is proportional to 4th power of radius
- Therefore vessel radius is the BIGGEST determinant of flow

7

For resting muscles, which equation should you use?

Q = ΔP/R

8

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

Q = ΔP ⋅ (πr^4)/(8ηl)

9

Describe parallel resistance in blood vessels

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

10

Describe series resistance in blood vessels

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

11

How does turbulent flow occur?

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

12

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

- Pulse pressure is dampened by arterial system

13

Define vascular compliance

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

14

What is LaPlace's Law?

T = (ΔP ⋅ r)/μ

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

15

Describe LaPlace's Law

- 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

16

What is Fick's Principle?

X = Q • [x]

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

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

a = arterial
v = venous

17

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

- ask how much of the oxygen was used in the caps
- so use the equation: X(used) = Q([x]in - [x]out)

18

What is hydrostatic pressure?

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

19

What is oncotic pressure?

- 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

20

What is Starling's Equation?

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