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FHB Exam 1 - Cardiovascular Physiology > Lecture 14 - Circulation/Hemodynamics > Flashcards

Lecture 14 - Circulation/Hemodynamics Flashcards

1
Q

What is Poiseulle’s Law Equation?

A
  • steady laminar flow of fluids through uniform cylindrical tubes
  • Cardiovascular system is composed of branching, elastic tubes of varying diameter non-newtonian fluid

Flow = change in pressure/ Resistance (R)

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2
Q

What is the equation for flow? What does it vary directly & inversely with?

A

Flow = [(P1-P2 * )Pi * r^4]/ 8L*n

Directly with:

  • pressure gradient
  • radius to the 4th

Inversely:

  • Length of vessel
  • viscosity

flow = CARDIAC OUTPUT

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3
Q

Why do small changes in radius cause large changes in blood flow?

A

blood flow is related to the fourth power of the radius

  • therefore, small changes in radius cause LARGE changes in blood flow (increase)
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4
Q

If you double the diameter, how does flow change?

A

Increases 16 times

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5
Q

If you vasoconstrict a vessel by 2, how does blood flow change?

A

DECREASES by 16

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6
Q

How does resistance relate to length, viscosity, and radius? Directly & Inversely with what?

A

R= 8Ln(viscosity) / Pi * r^4

Directly:

  • length
  • viscosity

Inversely:
- radius to the 4th

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7
Q

What are the most important determinants of blood flow in the cardiovascular system? Which of these is usually constant?

A
  1. Pressure Gradient
  2. Radius

PRESSURE is held constant, so changes in radius cause LARGE changes in blood flow to a tissue/organ

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8
Q

As length of a vessel increases, how does resistance change? Viscosity?

A

Resistance INCREASES

  • as viscosity increases, resistance INCREASES
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9
Q

If the Left & Right Ventricle generate the same cardiac output, why is the pressure generated by the LEFT Ventricle higher?

A

DUE TO RESISTANCE

  • increased after load in the L. Ventrile causes by arterial blood pressure
  • as pressure increases, resistance increases

P= Flow * Resistance

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10
Q

What is VISCOSITY?

A

Internal frictional resistance between adjacent layers of a fluid (lack of slipperiness)

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11
Q

What does viscosity depend on?

A

Shear Stress (pressure) / Shear rate (velocity)

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12
Q

Define:
1. Shear Stress

  1. Shear Rate
A
  1. Resistance to movement between Laminae (pressure)

2. Relative VELOCITY between laminae

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13
Q

How is shear rate distributed in blood vessels? How does low viscosity affect this?

A

PARABOLIC PROFILE

  • faster velocities in the middle - more axial
  • outermost = slowest & therefore highest pressure
  • LOWER viscosity = SHARPER parabolic profile
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14
Q

What are units of viscosity?

A

Poise

dyne sec/cm^2

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15
Q

What is the difference between a newtonian & non-newtonian fluid? How do they relate to viscosity?

A
  1. Newtonian = viscosity is CONSTANT & HOMOGENOUS
    - over range of shear stress/ shear rate
    (plasma, water)
  2. Non- newtonian:
    - velocity not constant
    - NOT homogenous

(whole blood)

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16
Q

How does hematocrit affect viscosity?

A
  • As hematocrit increases, viscosity increases
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17
Q

What are 2 examples of low and high hematocrit & their relation w/ viscosity?

A
  1. Anemia = low hematocrit = low viscosity (causes murmurs due to turbulent flow)
  2. Polycythemia = HIGH hematocrit
    - high viscosity
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18
Q

What is the normal range of hematocrit?

A

35% - 50%

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19
Q

Is the relationship between viscosity & hematocrit LINEAR?

A

No

  • at a certain hematocrit percentage (more than 50%), viscosity DRASTICALLY increases
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20
Q

Why is viscosity created in blood vessels?

A

each layer flowing against the other

  • viscosity created because layers have INTERNAL FRICTIONAL RESISTANCE against each other
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21
Q

If shear rate increases, and no significant change in pressure, how does this change viscosity?

A

this causes a DECREASE in viscosity!

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22
Q

What is blood doping?

A
  • injecting previously refrigerated blood to INCREASE oxygen carrying capacity
  • this also increases viscosity (which is only an issue for older people)
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23
Q

What is axial streaming? Does this cause more or less frictional resistance?

A

Tendency of RBCs to accumulate in AXIAL laminae (in the middle)
- line up one by one = LESS FRICTIONAL RESISTANCE

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24
Q

What is plasma skimming?

A

Tendency of smaller vessels to contain relatively MORE plasma and less RBC’s due to axial streaming

(line up in middle in smaller vessels & much less RBC’s)

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25
Q

What is the hematocrit in smaller vessels as compared to larger vessels? What is the term for this?

A

HIGHER in LARGER vessels

  • lower in smaller due to PLASMA SKIMMING
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26
Q

As tube diameter increases, what else increases?1

A
  1. Viscosity

2. Hematocrit Ratio

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27
Q

If you decrease shear rate, how is viscosity affected?

A

INCREASES

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28
Q

If there is a decrease in velocity, and a decrease in DIAMETER, what is the net affect?

A

DECREASE IN VISCOSITY

  • due to AXIAL STREAMING
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29
Q

What is the term for the following:

less RBC’s go off into smaller vessels because of axial streaming

A

PLASMA SKIMMING

  • as tube diameter decreases, hematocrit DECREASES because there is more PLASMA here instead
30
Q

What two reasons account for why is there a 45% hematocrit in Great Veins & 40% hematocrit in capillaries?

A
  1. Axial Streaming
  2. Plasma Skimming
  • hematocrit in smaller vessel is less than the hematocrit of a larger vessel
31
Q

What is laminar flow? Turbulent flow?

A
  1. Fluid moves in parallel concentric layers (parabolic profile)
  2. Disorderly pattern of fluid movement
32
Q

What can turbulent flow cause (4)

A
  1. Murmurs
  2. damage to Endothelial Lining
  3. Thrombi
  4. Kortkoff sounds
33
Q

The longer the tube, the more or less internal frictional resistance?

A

MORE internal frictional resistance

  • pressure will INCREASE
34
Q

What are Kortkoff sounds?

A

when we inflate the cuff & create the stenosis

  • it created TURBULENT flow through the stenosis
    created a CLICK due to the turbulent flow (artifically induced KOROTKOFF SOUNDS)
  • caused by increase in VELOCITY due to decrease in diameter
35
Q

What is the term for stenosis of carotid artery causing a sound when you place the stethoscope over the carotid? Why does this occur?

A

BRUIT!

  • stenosis causes TURBULENT flow
36
Q

How do blood clots occur from turbulent flow?

A

damage to endothelial lining

  • lead to blood clots
  • break off
  • rupture & cause embolisms
37
Q

What is platelet aggregation?

A

THROMBI

38
Q

What does Reynold’s number determine?

A

TURBULENT FLOW

  • higher than 3000 = greater chance of turbulent flow
39
Q

What is the equation for Reynold’s Number? What does it depend on?

A

RN = pDv / n (viscosity)

directly:

  • density
  • diameter
  • velocity

Indirect:
- viscosity

40
Q

What occurs at a critical velocity?

A

blood flow changes from LAMINAR to TURBULENT

41
Q

higher velocity, density, and diameter = greater what?

A

REYNOLD’s number!

42
Q

Why does a person with anemia develop murmurs?

A
  • lower viscosity = higher chance of turbulent flow

- develop murmur at a stenosis

43
Q

Where are you most likely to find a high reynolds number in the body, if viscosity was kept constant?

A

AORTA

  • largest diameter
44
Q

What causes turbulence in Kortkoff sounds?

A

VELOCITY

  • by lowering diameter you increase the velocity
45
Q

How does velocity change in an increase in cross-sectional area?

A

DECREASES!

  • vary inversely
    ex: putting thumb over a hose –> increases velocity by decreasing area
46
Q

How are individual vessels affected vs. Capillaries by a change in area?

A
  1. Individual Vessels :
    clot in carotid
    - blood will squirt & you will hear a bruit
  2. Capillary: blood will not squirt through the blocked capillary because it will find another place to go!
47
Q

In a constant flow system, what happens to total energy?

A

stays CONSTANT

PE + KE = total energy

48
Q

In a decrease in cross-sectional area (stenosis), PE is converted to what? How does pressure change & velocity?

A
  1. kinetic energy!
  2. Pressure DECREASED
    because
  3. VELOCITY INCREASED
49
Q

The following are applications of what principle:

  1. Aortic Stenosis
  2. Atrial Stenosis
  3. Aneurysms
  4. Lateral Vs End Pressure
A

TOTAL ENERGY STAYES CONSTANT

  • so in aneurysm as area increases (radius), velocity decreases, and pressure INCREASES
  • as KE decreases, PE increases (change relative to one another to keep total energy CONSTANT)
50
Q

Explain why blood from L. Ventricle can flow into the Aorta even though this is going AGAINST the pressure gradient (low to high)

A

Left. ventricle has decreases area upon contraction, resulting in INCREASED velocity (decreased pressure)

  • the increase in velocity shows that blood flows from HIGH to LOW kinetic energy areas
51
Q

Is total energy greater or less in a stenotic region as compared to regular vessel as it flows DOWN?

A

GREATER

  • since velocity increased, energy is higher which allows it to flow down an ENERGY gradient (high to low)
52
Q

What is the equation for wall tension?

A

Wall tension = Pressure * Radius/Wall Thickness

53
Q

Define the wall tension for the following:

  1. Capillaries
  2. Arteriolar vasoconstriction
  3. Aneurysm
  4. Dilated Hearts
A
  1. Low WT due to SMALL RADIUS
    - can withstand large pressure
  2. low WT due to large WALL thickness/diameter ratio
  3. HIGH WT due to INCREASED RADIUS
    = cannot withstand high transmural pressures = RUPTURE
  4. HIGH WT - LARGE RADIUS - higher after load & more systolic work & higher oxygen consumption to overcome high wall tension
54
Q

What do dilated hearts increase?

A
  • systolic work
  • (work to overcome after load)
  • OXYGEN consumption
55
Q

Wall tension is the force that does what?

A

RIPS something apart

  • force pulling the heart or vessel apart (ex aneurysm or dilated heart)
56
Q

The large diameter of a dilated heart causes an increase in what that impedes shortening?

A

AFTERLOAD

  • Wall tension opposes shortening & generates enormous amount of systolic work & O2 consumption
57
Q

In an aneurysm, how are the following changed:

  1. Flow
  2. Pressure
  3. Wall thickness
A
  1. decreased flow - due to increased radius
  2. Increased pressure (KE converted to PE - velocity has decreased)
  3. Wall thickness decreases - stretching a balloon (it is the denominator)
58
Q

What is the major difference in resistance for systems in series and in parallel?

A

Series: total resistance is always higher than any resistance in a system

Parallel: total resistance is always LESS than any resistance in system (1/R total)

59
Q

What is the primary site of arterial resistance? (largest resistance site?)

A

ARTERIOLES

60
Q

What ar some vessels in series? Parallel?

A

Series: aorta, large arteries, small arteries, arterioles, capillaries, veins, venues, vena cava

Parallel: capillaries

61
Q

Where is the largest CHANGE (drop) in arterial pressure?

A

ARTERIOLES!

  • largest resistance (lowest pressure)
62
Q

DO capillaries have low or high total resistance? Is the drop in pressure across the capillaries significant?

A

LOW total resistance since has LARGEST cross-sectional area (even though they have the smallest diameter)

  • low drop in pressure because of this
63
Q

What are two reasons that veins hold 60% of total blood volume (majority of our blood is in venous system)?

A
  1. HIGH COMPLIANCE

2. Larger cross-sectional area than arteries ***

64
Q

Describe the following for Capillaries:

  1. Velocity
  2. Area
  3. Pressure
A
  1. SLOWEST velocity (largest area - varies inversely)
  2. LARGEST area
  3. smallest pressure drop/change

P=F/A

65
Q

What are two reasons that Arteries hold only 18% of total blood volume?

A
  1. Small total area

2. LOW COMPLIANCE

66
Q

What occurs during exercise to decrease overall peripheral resistance?

A

OPEN additional capillaries in parallel

– therefore total resistance DECREASES

67
Q

What occurs during hemorrhage to INCREASE Total Peripheral Resistance?

A
  • blood flow to many organ systems in parallel is SHUT DOWN
  • so under sympathetic stimulation, blood is shunted to brain,heart, lungs

= INCREASE total resistance
- raising blood pressure

68
Q

Why do the capillaries have a small amount of blood in them, even though they have the largest cross-sectional area? Why do they have the slowest velocity?

A
  1. SHORTEST LENGTH

2. Slow - so they can effectively exchange O2/CO2

69
Q

Administering whole blood/saline during hemorrhage does what to the venous curve?

A

shifts venous curve UP

  • increases CVP
  • increases preload
  • increases cardiac output
  • INCREASE BP!
70
Q

What is the reason that the viscosity of capillaries does not rise, since it has the slowest velocity (shear rate)?

A

Because of the small diameter - RBC’s line up in a line, more AXIAL streaming & PLASMA SKIMMING

so net viscosity is DECREASED

71
Q

Where is the largest pressure drop? Why is this not the capillaries?

A

ARTERIOLES

  • largest internal resistance since viscosity is increasing (lamina flowing against each other increasing the internal friction)
    = DECREASE IN PRESSURE because of increase in frictional resistance

Flow = P/R

  • because there is a large amount of capillaries, the pressure is distributed amongst them
72
Q

Where is there NO pulse pressure?

A

CAPILLARIES

FHB Exam 1 - Cardiovascular Physiology (26 decks)

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