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Vascular > Ch. 2 Physiology and Hemodynamics > Flashcards

Ch. 2 Physiology and Hemodynamics Flashcards

1
Q

What is the arterial system?

A

A multi-branched elastic conduit set into oscillation by each beat of the heart

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2
Q

How much blood does each beat pump?

A

About 70 milliliters of blood into the aorta causing a blood pressure pulse

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3
Q

Cardiac contraction begins:

A

Pressure in left ventricle rises rapidly
Left ventricle pressure exceeds that in the aorta
Aortic valve opens, blood is ejected, BP rise

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4
Q

What determines amount of blood entering arterial system?

What determines amount that leaves?

A

Cardiac output

Arterial pressure and total peripheral resistance

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5
Q

Movement of any fluid medium between two points requires what two things?

A
  1. A pathway along which the fluid can flow

2. A pressure differential ( higher pressure E moves to lower pressure E)

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6
Q

What does the amount of flow depend on?

A

Energy difference: includes losses resulting from fluid movement.

Any resistance which tends to oppose such movement

Hint:
Lower Resistance = Higher flow rate
Higher Resistance = Lower flow rate

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7
Q

What is total energy contain in moving fluid the sum of?

A

Pressure, kinetic and gravitational energies

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8
Q

What is Pressure (potential/stored) energy?

A

Stored energy (released when walls recoil)

Major form of E for circulation of blood

Expressed in mmHg

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9
Q

What is Kinetic energy (velocity)?

A

Small for circulating blood

Expressed in terms of fluid density and its velocity measurements.

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10
Q

What is Gravitational energy?

A

Hydrostatic pressure, is equivalent to the weight of the column of blood extending from the heart to level where pressure is measured.

Ex: Average sized supine pt

  • arteries and veins nearly same level as heart
  • There is 0 mmHg against the arteries and veins at the ankle
  • When standing, HP increases, adding about 100 mmHg against ankle vessels. ( Ankle P = plus 100mmHg)
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11
Q

What is needed to move blood from one point to another?

A

An energy gradient.

The larger the gradient the greater the flow.

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12
Q

What does inertia relate to?

A

The tendency of a fluid to resist changes in velocity (i.e. body at rest tends to stat at rest)

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13
Q

What happens as the blood moves farther out to a periphery?

A

Energy is dissipated largely in the form of heat.

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14
Q

How is energy in the body restored?

A

continually by pumping action of the heart

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15
Q

What is movement of a fluid (blood) dependent upon?

A

physical properties of the fluid and what it is moving through.

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16
Q

Resistance equation

A 
R= 8nL/pie r4
resistance = 8 x viscosity x length/ pie x radius to the 4th power
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17
Q

What is resistance directly and inversely proportional to?

A

Directly proportional to variables in numerator ( viscosity and length)

Inversely proportional to variable in denominator ( radius)

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18
Q

What change makes the most dramatic effect on resistance?

A

Vessel diameter

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19
Q

How is internal friction within a fluid measured?

A

By its viscosity

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20
Q

How does the hematocrit effect blood viscosity and velocity?

A

Elevated hematocrit increases viscosity and lowers velocity while severe anemia decreases blood viscosity and raises velocity.

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21
Q

What is Laminar flow?

A

Consists of evenly distributed frequencies during systole.

Higher frequency flow in center; stationary layer remains at the wall. Laminar flow is considered stable flow.

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22
Q

When is plug flow likely seen?

A

At vessel origin as well as during initial cardiac upstroke.

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23
Q

Where is parabolic flow usually seen?

A

Downstream once laminar flow is fully developed

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24
Q

What causes viscous energy loss?

What causes inertial loss and where does it occur?

A

Viscous energy loss is due to increased friction between molecules and layers which ultimately causes energy loss.

Inertial losses occur with deviations from laminar flow, due to direction and/or velocity changes.
- this type of energy loss occurs at the exit of a stenosis.

25
Q

Poiseuille’s Equation

Defines relationship between what three things?

A

Pressure, volume flow, and resistance

Helps define how much fluid volume moves through vessel

Q= P/R Q=Volume Flow P=Pressure R= Resistance

Q= (P1 - P2) pie x r4 / 8nL

26
Q

Radius (r4) of vessel is directily proportional to what?

A

volume flow

27
Q

How will small changes in the radius change the volume flow?

A

It will create large changes in volume flow

28
Q

What is the Law of Conservation of Mass?

A

It explains the relationship between velocity and area.

Q= AxV

29
Q

Bernoulli’s

A

Pressure/Velocity relationship (inversely related)

Total energy contain in moving fluid is the sum of pressure, kinetic and gravitational energies.

If one changes the others make up for the difference in order to maintain the original total fluid energy amount. (performing exam on supine pat, there is NO change in hydrostatic pressure)

Hint: velocity goes up - pressure goes down vice versa

30
Q

Why do flow separation (curves/ pressure gradients) occur and what do they result in?

A

They occur because of geometry change with or without intra-luminal disease; regions with reverse flow, stagnant flow or little movement.

Examples include: bypass graft anastamosis site; or valve cusp site.

31
Q

Reynolds Number (Re)

A

Pressure / Flow relationships

predicts when fluid becomes unstable/disturbed

> 2000 (unitless number) means laminar flow tends to become disturbed

32
Q

Where does steady flow originate from?

How is its behavior?

A

originates from steady driving pressure.

It is more predictable behavior

In a rigid tube, energy losses mainly viscous; can be described by Poiseuille’s equation.

33
Q

What does pulsatile flow change?

A

driving pressure conditions &

the response of the system

34
Q

Explain the pulsatile flow change process

A

A. Systole - AO valve opens ; forward flow throughout periphery. (Fluid acceleration)

B. Late systole/ Early diastole- temporary flow reversal, due to a phase shifted negative pressure gradient and peripheral resistance, causing reflection of the wave proximally
** dicrotic notch is related to the closure of the ao valve and the influence of peripheral resistance

C. Late diastole - flow is forward again, as reflective wave hits the proximal resistance of the next oncoming wave, and reverses.

35
Q

What is Low resistance flow?

Examples?

A

it is steady in nature feeding a dilated vascular bed (i.e. there is more flow in diastole). Diastole reflects where the blood is going to.

Ex arteries: ICA, vertebral, renal, celiac, splenic, hepatic

36
Q

High resistance flow?

Examples

A

Pulsatile in nature (i.e. little to no flow in diastole). Reflections travel back up the vessel from the periphery producing flow reversals in the vessel flow.

Ex arteries: ECA, Subclavian, AO, Iliac, Exremity arteries, fasting SMA

37
Q

When might the reversal component of a high resistant signal disappear?

A

Distal to a stenosis due to decreased peripheral resistance, secondary to ischemia

38
Q

What is the Doppler flow like distal to a significant stenosis?

A

it is lower resistant. In addition it’s more rounded in appearance and is weaker in strength. Systole reflects where the blood came from.

39
Q

How would a normally high resistant (bi or triphasic) signal change as it approaches a significant stenosis or obstruction?

A

It may become monophasic

40
Q

Vasoconstrcition

A

Pulsatile changes in medium/small sized arteries of the limbs are increased. When this occurs, pulsatility changes are usually decreased in minute arteries. (more pulsatile in less time frame

41
Q

Vasodilatation

A

Pulsatile changes in medium/small sized arteries of the limbs are decrease (lower resistant). When this occurs, pulsatility changes are increased in minute areteries.

42
Q

What is the response in periphery when inflow pressure falls due to stenosis?

A

the usual response in periphery is to maintain flow by vasodilatation.

43
Q

How could total blood flow be fairly normal even in the presence of stenosis or complete occlusion of main artery?

A

Development of a collateral network, and a compensatory decrease in peripheral resistance.

44
Q

Arterial obstruction may alter flow in collateral channels nearby or further away from site of obstruction. Examples of changes may include:

A

Elevated velocity,
increase in volume flow,
pulsatility changes

45
Q

Could collateral location help determine tentative location of stenosis/obstruction?

A

Yes

46
Q

Exercises usually causes peripheral vasodilatation. What does this do to distal peripheral resistance and blood flow?

A

lowers distal peripheral resistance, enhancing BF

47
Q

Vasoconstriciton and vasodilatation of blood vessels within skeletal muscles also influenced by sympathetic nervous system for regulation of body temp

True or false

A

True

48
Q

What is a key vasodilator of resistance vessels within skeletal muscle?

A

Exercise

49
Q

What is autoregulation?

A

Ability of most vascular beds to maintain constant level of blood flow over a wide range of perfusion pressures.

Not present: perfusion pressure drops below a critical level.

BP rise= constriction of resistance vessels

BP fall= dilatation of resistance vessels.

50
Q

Exercise decreases resistance in the working muscle. What does this mean for the flow reversal component

A

there’s a decrease in the reversal component of the Doppler waveform.

A low resistant, monophasic flow signal is normally present in extremity arteries after vigorous exercise due to vasodilatation.

The same pattern also is also seen with disease. Peripheral dilation occurs in response to proximal obstruction.

51
Q

What might higher resistant signals result from?

A

Normal vasoconstriction at arteriolar level
OR
From distal arterial obstruction

52
Q

Flow to a cool extremity (vasocontriction) = ?

Flow to a warm extremity (vasodilatation) = ?

A

Cool extremity = pulsatile signals

Warm = continuous signals.

53
Q

True false

Pulsatility changes don’t differentiate well between occlusion and severe stenosis.

Waveforms may not be altered with good collateralization

Distal effects of obstructive disease may only be detectable following stress (i.e. excercise)

A

True

True

True

54
Q

A hemodynamically significant stenosis causes a notable reduction of what?

A

volume flow and pressure

Cross sectional area reduction of 75% = diameter reduction reduction of 50%

55
Q

Effects of flow abnormality produced by stenosis depends on factors such as

A

a. Length, diameter, shape, of narrowing
b. Multiple obstructions in the same vessel: resistance to flow is additive; it results in a higher resistance than in each individual narrowing.
c. Obstructions in different vessels that are parallel : resistance to flow is less than the resistance in each individual narrowing because less volume of blood blow is going through each narrowing.
d. Pressure gradient; peripheral resistance beyond stenosis.

56
Q

Proximal to a stenosis flow frequencies are usually…?

A

dampened, with or without disturbance

57
Q

Entrance into stenosis produces increased Doppler shift frequencies (DSF), resulting in…?

A

Spectral broadening and elevated velocities.

Flow disturbance occurs with high velocities and eddy currents.

Abnormal “jet” (elevated velocities) may be isolated to area of stenosis, but also approaching and/ or leaving it.

58
Q

Post- stenotic turbulence. At stenosis ext, flow does what?

A

Flow reversals, flow separations, vortices/eddy currents occur near edge of flow pattern.

Flow quality has multiple changes in direction and spectral broadening

Energy expended as “heat”

59
Q

What is the progression of flow pre at and post stenosis?

A

Pre= dampened

At = high velocities and eddy currents

Post= reversals, spectral broadening, changing in directions, energy expended as “heat”

Vascular (3 decks)

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