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Vascular > Hemodynamics > Flashcards

Hemodynamics Flashcards

1
Q

What is the main function of the heart?

A

~ Return blood from the capillaries back to the heart

~ Act as a reservoir to maintain homeostasis

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2
Q

At any given time what is the percent of blood volume moving through the veins?

A

80%

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3
Q

How large is the resistance of flow against veins? Why?

A

Little resistance to flow because of their large diameters

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4
Q

What is needed for blood to flow from 1 point to another?

A

A pressure gradient

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5
Q

What is another name for pressure gradient?

A

Energy gradient

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6
Q

Veins rely on a variety of mechanisms to do what?

A
  1. Prevent bidirectional flow

2. Aid in the return of blood against gravity

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7
Q

What mechanisms do veins rely on to prevent bidirectional flow and aid in the return of blood against gravity? (6)

A 
~ cardiac function
~ respiratory function
~ skeletal muscles
~ pressure gradients
~ venous valves 
~ compliance
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8
Q

What is capacitance?

A

The ability to collapse and expand and adapt to changes in the blood volume

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9
Q

What type of blood does the LV send through the arteries when it contracts?

A

High pressure pulsatile stream

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10
Q

What happens to the blood as it flows through the high resistance arterials and capillaries?

A

Looses pressure

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11
Q

By the time the arterial blood enters the venules what has the pressure been reduced to?

A

15mmHg

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12
Q

What is hydrostatic pressure?

A

The weight of a column of blood

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13
Q

Describe hydrostatic pressure

A

It is the pressure exerted by a fluid in a closed system and is equivalent to the weight of a column of blood extending from the heart to the level where the pressure is being measured

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14
Q

What causes hydrostatic pressure?

A

Gravity

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15
Q

What varies hydrostatic pressure?

A

Patient position
Standing = more pressure
Height

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16
Q

What must be overcome for blood to flow into the lower extremity veins?

A

Venous pressure

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17
Q

What type of person has more hydrostatic pressure?

A

Tall

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18
Q

What is hydrostatic pressure also know as?

A

Gravitational pressure

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19
Q

What is the primary factor in determining intravascular pressure within the venous system?

A

Hydrostatic pressure

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20
Q

What is the hydrostatic pressure in a supine person? Why?

A

15mmHg - negligible because all parts are at the same level as the RA

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21
Q

What happens to the leg veins when standing?

A

Dilate to accept the blood draining into them

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22
Q

When standing what is the venous pressure?

A

Rises to 110mmHg

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23
Q

What happens to the veins when standing?

A

Stiffen

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24
Q

What is needed for blood to flow?

A

Pressure gradient

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25
Q

What is the hydrostatic pressure in the capillaries?

A

15mmHg

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26
Q

What part of the body has the highest hydrostatic pressure?

A

Lower portion of the body

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27
Q

What happens to the force of gravity when you get further from the RA?

A

The force of gravity is greater

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28
Q

What happens to the capillary pressure in a raised arm?

A

Capillary pressure increases so the veins don’t collapse

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29
Q

Why is the pressure in the raised arm negative?

A

Due to the raised arm being above the RA pressure of 0

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30
Q

How does hydrostatic pressure affect the LE when stationary? (7)

A 
~ increase transmural venous pressure distally
~ increase venous distension 
~ increase venous pooling 
~ decrease capillary perfusion 
~ decrease venous return
~ decrease cardiac output 
~ hypotension
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31
Q

What is the hydrostatic pressure when standing for an average person?

A

Roughly 80 mmHg

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32
Q

What is the hydrostatic pressure of the average person when walking?

A

Roughly 25 mmHg

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33
Q

What does venous wall shape depend on? (3)

A

Pressure
Volume
Flow

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34
Q

What is compliance?

A

The veins ability to permit a large increase in venous flow without significant an increase in the venous pressure

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35
Q

What effects the veins compliance? (2)

A

Intramural or interstitial pressure

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36
Q

What is intramural pressure?

A

Internal pressure

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37
Q

What is interstitial pressure?

A

External pressure

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38
Q

What does blood capacitance vary and depend on? (4)

A
  1. Limb position
  2. Muscle pump activity
  3. Venous valve function
  4. Blood volume
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39
Q

What happens to the vein in the event of surplus fluid?

A

The vein will expand and increase in pressure

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40
Q

What does compliance allow to happen?

A

Allows for a range of venous volume changes without affecting the central venous pressure

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41
Q

What causes compliance to decrease?

A

Higher pressures and volumes

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42
Q

What is the difference between elasticity and compliance?

A

Elasticity is the ability to expand and recoil

Compliance is the ability to with stand a large amount of volume without affecting pressure

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43
Q

How do veins compare to arteries in reference to their elasticity/compliance?

A

Veins are less elastic then arteries but more compliant

Arteries have greater elasticity therefore having the ability to expand and snap back/recoil to original shape
Veins are more expandable and don’t have an original shape

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44
Q

What determines the cross sectional shape of a vein?

A

Transmural pressure

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45
Q

What is transmural pressure?

A

The difference between intraluminal and interstitial pressures

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46
Q

What is intraluminal pressure?

A

Pressure within the vein, the force occurring within the walls of the vessel

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47
Q

How does an increase in intraluminal pressure affect transmural pressure and the shape of the vein?

A

Increases transmural and makes the vein rounder

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48
Q

What is interstitial pressure?

A

Pressure exerted against the vein by surrounding tissue and fluid, the force from outside the vein

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49
Q

How does low transmural pressure affect the vein?

A

As the volume and pressure decrease the vein wall collapses and becomes elliptical in shape

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50
Q

How does high interstitial pressure with low intraluminal pressure affect the vein?

A

It flattens the vein (low transmural)

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51
Q

What type of pressure is transmural pressure directly related to?

A

Intraluminal

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52
Q

What creates the pressure gradient in the IVC?

A

On inspiration the intrathoracic pressure is less then the abdominal pressure

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53
Q

Describe how the blood moves from the abdomen to the chest

A

Inspiration- intrathoracic pressure decreases and the intraabdominal pressure increases causing blood to flow into the chest

54
Q

What happens to the outflow from the peripheral veins upon inspiration?

A

Blood flow stops

55
Q

When is inflow allowed from the upper extremities?

A

During inspiration

56
Q

What is the result of CHF and why?

A

It increases venous pressure as the blood backs up

57
Q

What is the effect of the valsalva maneuver? (4)

A
  1. Increases both intrathoracic and intraabdominal pressure
  2. Respiratory changes are increased
  3. Pressure in the upper and lower extremities increase
  4. Flow stops/diminishes in both UE and LE
58
Q

What happens when a breath is released following valsalva?

A

Flow volume is increased and augmentation shown

59
Q

What’s an abnormal response to the valsalva maneuver?

A

Reversal of flow

60
Q

What type of pt should not be asked to preform the valsalva maneuver?

A

Pts with cardiac disease

61
Q

What is dynamic pressure?

A

Muscular contraction of the heart

62
Q

What causes a suction effect on venous blood flow?

A

Cardiac contraction and relaxation

63
Q

What are the components of the venous wave? (4)

A

A - atrial systolic wave
S - systolic wave
V - atrial diastolic wave
D - diastolic wave

64
Q

Draw and label the venous wave

A

…pg 6

65
Q

What are the 2 periods of increased venous flow during the cardiac cycle?

A
  1. Ventricular systole

2. When the AV valves open

66
Q

What events take place during ventricular systole?

A

~ atrial volume increases causes atrial pressure to decrease
~ increased flow from the veins into RA
~ venous pressure decreases

67
Q

What events take place when the AV open?

A

Venous blood enters the ventricles and atrial pressure decreases allowing venous flow into the heart

68
Q

What allows back flow happen during atrial contraction?

A

No valves in the IVC or atrial junction

69
Q

Where are changes in pressure and flow more evident? Large central veins or peripheral veins?

A

Large central veins and upper extremity

70
Q

Does cardiac contraction affect the blood flow from the lower extremities? Why?

A

No, because the strong respiratory variation in the leg (lower extremities are further away from the heart therefore have physics flow not pulsatile)

71
Q

How do cardiac conditions such as CHF or tricuspid insufficiency effect?

A

Increase central venous pressure creating pulsatile waveforms in the lower extremities due to the heart backing up and not effectively emptying

72
Q

What creates large changes in the intrathoracic and intraabdominal pressures?

A

Respiration

73
Q

What is phasicity?

A

Refers to the ebb and flow that occurs in the veins in response to respiration

74
Q

What is a major indicator of normal flow in the deep veins?

A

Phasicity

75
Q

Venous blood flow is affected by the movement of what structure?

A

Diaphragm

76
Q

How does inspiration stop/decrease venous flow from the lower extremities?

A

Intraabdominal pressure increases by lowering of the diaphragm causing the IVC to collapse

77
Q

How does inspiration result in increased flow (return) from the upper extremity veins?

A

Intrathoracic pressure decreases

78
Q

How does expiration affect the venous flow in the lower extremities?

A

Intraabdominal pressure decreases as the diaphragm rises and the IVC opens, venous flow resumes its phasic pattern

79
Q

How does expiration affect the venous flow in the upper extremity veins?

A

Intrathoracic pressure increases and results in decreased return flow

80
Q

Does respiratory function have greater affect on the lower or upper extremity veins?

A

Lower extremity veins

81
Q

Is the upper or lower extremity more pulsatile and why?

A

The upper extremity flow is more pulsatile due to the close proximity of the heart

82
Q

When does respiration have a small effect on venous flow?

A

When standing

83
Q

What happens to pressure and flow with inspiration? (4)

A
  1. Intrathoracic pressure decreases
  2. Diaphragm moves up
  3. Increased intraabdominal pressure increased abdominal venous outflow
  4. Flow from the peripheral veins decrease
84
Q

What happens to pressure and flow on expiration? (4)

A
  1. Intrathoracic pressure increases
  2. Diaphragm moves up
  3. Decreases intraabdominal pressure decreases abdominal pressure outflow
  4. Outflow from the peripheral veins increases
85
Q

Does the UE increase or decrease with respiration?

A

Increase

86
Q

Does the LE increase or decrease with respiration?

A

Decrease

87
Q

What 2 things does the venous system rely on for the movement of blood?

A
  1. Action of the muscle

2. Competence of valves

88
Q

How will the blood flow in normal functioning valves?

A

In one direction- towards the heart

89
Q

What is the effect of contracting voluntary muscles?

A

Propels blood towards the heart

90
Q

What is the effect of skeletal muscle activity on the venous pressure? Why?

A

Decreases because it interrupts the hydrostatic column of blood

91
Q

What occurs when there is a decreased hydrostatic pressure? (3)

A
  1. Decreased venous pooling
  2. Decreased capillary pressure
  3. Increased blood flow
92
Q

What occurs to the veins when the body is at rest and there is no muscle activity?

A

Veins act as reservoirs for blood collection

93
Q

What direction does blood flow in the deep and superficial veins with muscle contraction?

A

Flow moves towards the heart

94
Q

What occurs in the veins with muscle relaxation?

A

Small amounts of blood flow occurs in the perforators from the superficial system

95
Q

What is the most efficient pump in the body? (Besides heart)

A

Contraction of the gastrocnemius and soleus muscles

96
Q

What is the capacitance in the calf muscle during contraction?

A

200mmHg per contraction

97
Q

What percent of blood volume is ejected from the calf in a single contraction?

A

40-60% of venous blood volume

98
Q

What is another name for the calf muscles?

A

Venous heart

99
Q

What does the calf muscle dependent on? (3)

A
  1. Ability of calf muscles to contract
  2. Competency of the venous valves
  3. Patency of the outflow valves
100
Q

What venous pressure aids in the return of blood to the heart?

A

Lower venous pressure which reduces venous volume aid in the return

101
Q

How does chronic venous insufficiency occur?

A

Venous hypertension or failure to decrease venous pressure during exercise

102
Q

What is ambulatory venous hypertension?

A

Abnormally high venous pressure when standing

103
Q

What happens to the blood flow with ambulatory venous pressure when the calf muscle pumps?

A

Since the valves are dysfunctional blood is expelled in all directions on contraction, therefore pressures do not decrease normally

104
Q

What other conditions can occur as a result of ambulatory venous hypertension?

A

Edema and varicose veins

105
Q

What is the main function of the venous valves?

A

Direct blood flow towards the heart

Prevent retrograde flow (reflux)

106
Q

What layer of the vein do the valves arise from?

A

Intimal layer

107
Q

How many cusps does a valve have? What is this called?

A

2 cusps

Bicuspid

108
Q

What is the function of perforating veins?

A

Direct blood flow from superficial to deep veins

109
Q

Why are there more valves in the calf veins?

A

Due to the high hydrostatic pressure in the distal limb

110
Q

Why does the UE have less valves then the LE?

A

Gravity has less effect on the UE flow due to the shorter column of blood and closer proximity to the heart

111
Q

What is the venous valve sinus?

A

Normal dilation of the vein at the site of the valve and is wider then the valve segment

112
Q

What occurs to the venous valve segment during increased pressure?

A

The vein segment will expand

113
Q

Where is the most frequent site of thrombi? Why?

A

At the venous valve sinus due to stagnant flow

114
Q

How many valves are in the greater saphenous?

A

10-12

115
Q

How many valves are in the soleal sinus?

A

0

116
Q

How many valves are in the calf veins?

A

9-12 each

117
Q

How many valves are in the SFV?

A

1-3

118
Q

How many valves are in the EIV?

A

1 or none

119
Q

How many valves are in the IVC?

A

0

120
Q

How many valves are in the lesser saphenous?

A

6-12

121
Q

How many valves are in the perforators?

A

1 each

122
Q

How many valves are in the popliteal?

A

1-3

123
Q

How many valves are in the CFV?

A

1

124
Q

How many veins are in the common/internal iliac?

A

0

125
Q

How many valves are in the jugular?

A

1

126
Q

What phases of the cardiac cycle cause an increase in venous return?

A

When the AV open or during ventricular contraction during early systole

127
Q

In a supine pt, what is the typical hydrostatic pressure at the ankles?

A

10-15mmHg

128
Q

What is phasicity?

A

Ebb and flow in the blood as a response to respiration

129
Q

How can you correct for aliasing on a spectral waveform?

A

Decrease the baseline

Increase scale

130
Q

What effect does CHF have on venous pressure?

A

Increases the venous pressure

Vascular (5 decks)

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