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Physics 1 > C8: Hemodynamics > Flashcards

C8: Hemodynamics Flashcards

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1
Q

define hemodynamics

A

the study of blood flow in the circulatory system, it refers to both blood and power

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2
Q

which muscles in the body are referred to as the venous heart

A

calf muscles

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3
Q

what are the 4 items that blood is composed of

A
  • plasma (55%) - made of water and protein
  • RBCs (45%)
  • WBCs (~1%)
  • platelets (~1%)
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4
Q

what does the term hematocrit refer to

A

the % of blood volume that is composed of cells

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5
Q

define density

A

the mass per unit volume or the resistance of an object to accelerate

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6
Q

define viscosity

A

resistance to flow

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7
Q

what vessels control vascular resistance of blood flow

A

arterioles

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8
Q

is the largest amount of blood located in which vessels in the body?

A

veins

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9
Q

how is the pressure difference that is need for blood to flow created in the body

A

by the heart or gravity

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10
Q

how are pressure and flow rate related

A

directly

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11
Q

formula for pressure gradient

A

P gradient = P1 - P2 / Length

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12
Q

basic formula for volume flow rate

A

V flow rate (Q) = delta Pressure / Resistance

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13
Q

what is Poiseuille’s resistance formula for a long straight tube

A

R = 8 x length x viscosity / pie x (r)^4

…w/ radius being the most dominant factor

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14
Q

formula for volume flow rate for a long straight tube only (when considering resistance)

A

Q = delta pressure x pie x (d)^4 / 128 x length x viscosity

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15
Q

if the size of a vessel is constant, will a thin or large vessel produce slow flow

A

thinner = slower

but if theres a stenosis, then thinner means faster velocity

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16
Q

describe plug flow, where is it seen?

A

flow pattern that has almost all RBCs travelling at the same velocity…. will have a thin envelope

-seen at the opening of larger vessels like the AO

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17
Q

describe laminar parabolic flow, where is it seen?

A

flow pattern where the RBCs move in concentric layers w/ the fastest velocity at the centre… will have fairly thin envelope and clear window

-most common flow pattern in normal arteries

18
Q

describe jet flow, where is it seen?

A

flow pattern seen at areas of significant reduction in vessel diameter… e.g. stenosis

19
Q

describe disturbed flow, where is it seen?

A

flow pattern that natural occurs at bifurcations, curves or tapering of vessels…. not all layers of blood move in laminar fashion

  • may see spectral broadening and/or reversal
  • eg carotid bulb
20
Q

describe turbulent flow, where is it seen?

A

flow pattern that is seen just past a stenosis

-flow velocities and direction vary greatly.

21
Q

what type of spectral waveform would you get w/ turbulent flow
is turbulent flow normal?

A
  1. filled in spectral tracing since there are many velocities
  2. not normal except near the heart
22
Q

what does a Reynolds number (RN) predict

A

can predict onset of turbulence in a vessel

23
Q

having an RN greater than what value indicates turbulence?

A

2000

24
Q

what is the continuity rule?

what does it explain

A

it says: in the presence of a stenosis, the volume of flow must remain constant proximal to, at, and distal to the stenosis

it explains why we get a ‘jet’ when we have a stenosis… the velocity of blood must increase in a stenosis in order to keep the volume flow constant

25
Q

if the diameter of a stenosis is 1/2 of the vessel, what happens to the velocity of blood flow in this area

A

the velocity will double to maintain volume flow rate

26
Q

whats the relationship b/w pressure and velocity

A

inversely related

27
Q

when is a stenosis considered hemodynamically significant

A

if it causes a reduction of 50% or > in diameter of the vessel

28
Q

total fluid energy is composed of what 2 factors

A 
potential energy (PE)
kinetic energy
29
Q

formula for PE

A

intravascular pressure plus gravitational potential energy

30
Q

how is intravascular pressure produced

A

by the contraction of the heart, hydrostatic pressure and static filing pressure

31
Q

describe the changes of pressure experienced at a stenosis

A

at a stenosis theres a pressure drop in order to accommodate the acceleration of blood through the stenosis… after the stenosis blood decelerates

32
Q

describe the changes of PE experienced at a stenosis

A

PE is converted to KE when it enters the stenosis and then is converted pack to PE after the stenosis

33
Q

what is the simplified Bernoulli’s equation

A

change in pressure = 4 (v2)^2

34
Q

what is tradus parvus

why does it occur

A

the drop in acceleration time and peak systolic velocity of arterial flow after a stenosis…..

…. the stenosis detracts from the pressure gradient that was created by the heart

35
Q

does tardus parvus indicate proximal or distal stenosis

A

proximal

36
Q

what type of spectral trace will you get if theres a stenosis distally

A

you’ll have a smaller peak velocity and you’ll lose diastole because blood cant get through the stenosis as easily

37
Q

what is the windkessel effect

why does it occur?

A

the continued forward flow in the AO during diastole… occurs as a result of the elasticity of the vessel walls contracting back to their original shape

38
Q

why isnt there any backwards flow in the AO during diastole

A

the AO valve has closed

39
Q

which phenomenon is responsible for creating the dicrotic notch

A

windkessel effect

40
Q

why does flow reversal in arteries happen

A

the pressure wave travels along the walls of the vessel faster than the blood flowing in the vessel…. the wave reaches the end of the arterial system and causes the wave to be reflected backwards….. this causes the vessel wall to expand and contract against the flow of blood causing reversal

reversal also occurs due to the increased pressure down stream and the heart relaxing

41
Q

what is a subclavian steal?

A

occurs when a stenosis is located at the origin of the vertebral artery… the stenosis causes a decrease in pressure which allows blood to instead flow retrogradely and into the subclavian artery rather than the vertebral…

… this ‘steal’ occurs in peak systole when the velocity is the highest and causes the other vertebral artery to have to work much harder and deliver the majority of the blood to the brain

Physics 1 (7 decks)

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