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

1

## What is the flow equation?

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Q = ΔP/R

Q = Flow

P = Pressure

R = Resistance

2

## Describe the flow equation

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- 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?

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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)?

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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?

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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

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- 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

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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

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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?

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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

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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?

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T = (ΔP ⋅ r)/μ

T = wall stress/tension

ΔP = *transmural* pressure

r = radius

μ = wall thickness

15

## Describe LaPlace's Law

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- 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?

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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?

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- 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?

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- 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?

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- 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