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Physics > Hemodynamics > Flashcards

Hemodynamics Flashcards

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1
Q

systole

A

blood into atria

contraction

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2
Q

diastole

A

blood into ventricles

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3
Q

arteries - flow, pump, compressibility

A

pulsatile flow
heart is pump
non-compressible

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4
Q

veins- flow, pump, compressibility

A

less pulsatile, phasic
leg contractions is pump
compressible

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5
Q

where are there valves

A

heart and veins

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6
Q

regurgitation

A

when the valves dont close enough

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7
Q

venous hemodynamic factors (2)

A

hydrostatic pressure

respiration

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8
Q

hydrostatic pressure - how does it change?

pressure supine vs standing

A

increases with increasing distance below heart
supine- 0 mmHg
standing- 100 mmHg

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9
Q

Describe how thoracic and abdominal volume (and pressure) changes with inspiration. What happens to venous return?

A

inspiration
increased thoracic volume, decreased pressure
decreased abdo volume, increased pressure
STOPS venous return

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10
Q

Describe how thoracic and abdominal volume (and pressure) changes with expiration. What happens to venous return?

A

expiration
decreased thoracic volume, increased pressure
increased abdo volume, decreased pressure
venous blood RETURNS from legs

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11
Q

what is valsalva and what does it do?

A

breath hold

increases abdo pressure, STOPS venous return

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12
Q

fluid

A

liquid or gas

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13
Q

driving force behind fluid flow

A

pressure, low to high

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14
Q

pressure formula

A

P = force/area

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15
Q

volumetric flow rate - what is it and whats the unit

A

volume of blood passing a point per unit time
applies to LONG STRAIGHT TUBE
mL/s

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16
Q

volumetric flow rate (Q) basic formula

A

Q = pressure/resistance (in vessel)

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17
Q

Resistance of a long straight tube depends on

A

tube length
viscosity
radius

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18
Q

poise

A

viscosity and resistance

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19
Q

If tube LENGTH increases what happens to flow RESISTANCE

A

length and resistance proportionate related

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20
Q

if tube RADIUS increases what happens to flow RESISTANCE

A

radius and resistance inversely related (to the power of 4!)

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21
Q

if VISCOSITY increases what happens to flow RESISTANCE

A

viscosity and resistance proportionately related

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22
Q

poise is what units

A

1 gram per cm^4-s

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23
Q

how much more viscious is plasma than water

A

50%

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24
Q

viscosity normal blood is what times that of water

A

5 times

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25
Q

what happens to flow rate if you increase resistance

A

Q and R are inversely related so decreases

26
Q

How does resistance depend on radius? If radius doubles, what happens to resistance?

A

Resistance depends on radius to the 4th power

radius doubles, resistance decreases X16 (2^4)

27
Q

how does vasodilation and vasoconstriction change flow resistance

A

vasodilation- decreases resistance

vasoconstriction- increases resistance

28
Q

When do you use the poiseuille equation?

A

when resistance is not known

29
Q

what happens to flow rate if you decrease diameter (according to poiseuille’s law)

A

flow rate decreases

30
Q

what happens to flow rate if you increase length

A

flow rate decreases (because resistance increases)

31
Q

volumetric flow rate in a tube depends on

A

pressure difference
length of tube
diameter of tube
viscoscity of fluid

32
Q

what are the two types of flow

A

laminar and turbulent

33
Q

what is laminar flow

A

flow in which layers of fluid slide over eachother in straight lines

34
Q

types of laminar flow (3)

A

plug flow
parabolic flow
disturbed flow

35
Q

Flow is seen at a stenosis or bifurcation

A

Disturbed flow

36
Q

Plug flow

A

Flow seen at the entrance to tubes where the same speed is seen across the vessel

37
Q

The fastest speed seen in parabolic flow? the slowest? what is the average flow speed?

A

fastest= centre
slowest= tube walls
average flow speed is 1/2 the fastest speed

38
Q

Type of flow seen after significant stenosis

A

Turbulent flow

39
Q

Flow where you’ll hear bruit

A

Turbulent

40
Q

Characterizing factor for turbulent flow

A

critical reynolds number, 2000 for blood

41
Q

Factors affecting reynolds number

A 
density (p)
velocity 
diameter
-------------
viscosity
42
Q

stenosis vs occulsion

A

partial vs complete blockage

43
Q

what is pulsatile flow

A

non-steady, acceleration and deceleration over cardiac cycle

44
Q

true or false - venous circulation is such that pressures, flow speed and patterns do not change over time

A

true

45
Q

with pulsatile flow, blood flow speed/pressure changes. this depends on (3)

A

impedence
intertia
compliance

46
Q

what are two things observed in compliant vessels with pulsatile flow

A

windkessel effect

flow reversal

47
Q

what is the windkessel effect

A

observed in compliant vessels where
systole = vessel expands and volume increases
distole = pressure decreases, compliant vessel contracts producing extended flow without driving pressure from the heart

48
Q

true or false - blood stops flowing during diastole

A

false

49
Q

what causes flow reversal and where is it seen

A

reversal of flow because decreased pressure and vessel contraction without valves to prevent back flow.
Not seen in the aorta because of valves

50
Q

what is the continuity rule

A

the volumetric flow rate is constant

51
Q

the continuity rule only applies under what conditions

A

a short segment, usually a stenosis or narrowing of lumen

52
Q

FORMULA for volumetric flow rate (continuity rule)

A

Q= velocity X area

53
Q

what happens if you decrease the area x2

A

speed increases X2 to maintain constant flow

54
Q

how does poiseuilles law contradict the continuity rule

A
  • poiseuille’s law suggests that flow speed decreases with smaller diameters
  • continuity rule suggests flow speed increases with smaller diameters

two situations are different because poiseuilles law = entire vessel, continuity rule is the diameter of a short portion (stenosis)

55
Q

If the AREA of a stenosis is 1/2 the distal vessel what happens to flow speed?

A

flow speed doubles

56
Q

if the DIAMETER of a stenosis is 1/2 the distal vessel what happens to flow speed?

A

flow speed quadrouples

57
Q

When does flow rate and distal pressure drop significantly with a stenosis?

A

beyond a diameter reduction of 50% (area reduction 75%)

58
Q

if you hear a bruit sound what has likely happened?

A

stenosis due to turbulence distal to stenosis

59
Q

velocity at a stenosis can tell us what

A

how much it’s stenosed

60
Q

what is the Bernoulli effect

A

a decrease in pressure in regions of high flow speed (velocity and pressure are inversely related)
therefore low pressure at the stenosis because high velocity

61
Q

what are the conditions of an aneurysm?

A

there is a decrease in speed at the widening, causing increased pressure

Physics (9 decks)

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