Hemodynamics & Vasculature (complete) Flashcards Preview

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Flashcards in Hemodynamics & Vasculature (complete) Deck (20)
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What is the flow equation?

Q = ΔP/R

Q = Flow
P = Pressure
R = Resistance


Describe the flow equation

- Pressure differences drive flow
- Vascular resistance opposes flow

Flow-in MUST EQUAL flow-out


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


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


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


Describe Poiseulle's Law

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


For resting muscles, which equation should you use?

Q = ΔP/R


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

Q = ΔP ⋅ (πr^4)/(8ηl)


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


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


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


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


Define vascular compliance


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


What is LaPlace's Law?

T = (ΔP ⋅ r)/μ

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


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


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


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)


What is hydrostatic pressure?

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


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


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