Chapter 2 - Physiology and fluid dynamics Flashcards

1
Q

Total energy made up of 3 components

A

1) Potential
2) Kinetic
3) Gravitational

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2
Q

Source of potential energy (2)

A

1) heart pump

2) vessel distension (elastin)

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3
Q

Kinetic energy depends on (2)

A

1) Density of blood

2) velocity of blood (squared)

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4
Q

Types of laminar flow (2)

A

1) Parabolic flow (bullet shape)

2) Plug flow - all travel at same velocity

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5
Q

Relationship of resistance to length and radius

A

R = 8nL / pir^4

n = viscosity
L = length
r = radius
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6
Q

Define inertial loss (4)

A

1) change in direction
2) change in velocity
3) deviation from laminar flow
4) loss of energy

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7
Q

Poiseuille’s Law

A

Q = P/R

Q = flow

Q = (P1 - P2) pi r^4 / 8nL

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8
Q

Law of conservation of mass on velocity and volume and cross-section relationship

A

V = Q/A

V = velocity
Q = flow
A = cross sectional area
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9
Q

Define eddy currents

A

small circular currents when streamline flow breaks

occurs with vortices

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10
Q

Reynolds number (Re)

A

Re = Vp2r / n

V = velocity
p = density (constant)
n = viscosity (constant)
r = radius
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11
Q

Reynolds number limit before turbulent

A

2000

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12
Q

Bernoulli principle

A

velocity and pressure are inversely related

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13
Q

Define flow separation and where it occurs

A

Defn: pressure gradients in a vessel

1) intraluminal disease
2) bifurcation
3) turn point

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14
Q

Flow separation in systole and diastole

A

Systole: flow reversal
Diastole: stagnant, no movement/flow

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15
Q

Define steady flow

A

1) steady driving pressure

2) energy losses described by Poiseuille’s equation

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16
Q

Stages of pulsatile flow

A

1) Forward flow through periphery
2) Temporary flow reversal due to phase shifted negative pressure gradient and peripheral resistance
3) flow moves forward again
4) vessel recoil converting potential energy to kinetic energy

17
Q

Flow reversal decreases in:

A

1) vasodilation (exercise, heat)

2) stenosis

18
Q

Flow reversal increases in:

A

1) vasoconstriction

19
Q

Low resistance flow vascular beds (6)

A

1) ICA
2) vertebral
3) renal
4) celiac
5) splenic
6) hepatic

20
Q

High resistance flow vascular beds (6)

A

1) aorta
2) ECA
3) subclavian
4) iliac
5) extremity
6) fasting SMA

21
Q

Response to vasoconsctriction and vasodilation in medium, small and minute/capillaries arteries

A

Vasoconstriction:

  • medium and small = increase flow
  • minute/capillaries = decrease flow

Vasodilatation

  • medium and small = decrease flow
  • minute/capillaries = increase flow
22
Q

Effect of cardiac arrhythmia in assessing velocity

A

Difficult to accurately measure PSV

  • take averages of few cycles (10)
  • use velocity ratio instead
23
Q

Effect of aortic stenosis in assessing velocity

A
  • delay in systolic upstroke

- decreased PSV (underestimate stenosis)

24
Q

Effect of aortic regurg/insufficiency in velocity waveform

A

1) pulsus bisferiens (double systolic peak)
2) diminished diastolic flow
3) reversed diastolic flow

25
Other factors that increase peak systolic velocity
1) high cardiac output 2) young physically fit adults 3) anemia
26
Low cardiac output on PSV waveform
1) lower velocity | 2) rounded waveform
27
Effect of intra-aortic balloon pump on PSV waveform
1) double peak | 2) underestimate PSV
28
Causes of increased systemic pulsatility in veins
1) upper extremilty and neck is normal 2) elevated right heart pressure (CVI, HF, tricuspid regurg/insufficiency, COPD, PH, CKD) 3) fluid overload (overhydration)
29
Effect of obstruction on flow proximal and distal
``` Proximal = high resistance signal Distal = low resistance monophasic pattern ```
30
Hemodynamic significant stenosis requires this much diameter or lumen reduction
75% cross-sectional reduction | 50% diameter reduction
31
Effect of lesion in series
``` Worse than if single long lesion Disturbed flow pattern at exit of lesion - jet effect - turbulence - eddy formation ```
32
Effect of lesions in parallel
overall resistance less than resistance in individual stenosis
33
Non-narrowing factors that cause spectral broadening
1) Too large Doppler sample volume (sampling midstream and vessel wall together) 2) inappropriate doppler angle 3) doppler sample volume too close to wall