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DMS 223- Intro to Vascular Ultrasound > Venous Hemodynamics > Flashcards

Venous Hemodynamics Flashcards

1
Q

What is the major function of veins?

A
  • to act as a conduit for the flow of blood back to the heart
  • participates in regulation of the circulation
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2
Q

Describe the walls of veins

A

thin walled and collapsible

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3
Q

Describe veins during normal function

A
  • low pressure

- partially filled w/ blood and only partially expanded

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4
Q

*How much blood is found in the venous system”?

A

-80% of the blood in the body is found in the venous system

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5
Q

How can veins change size?

A
  • veins can constrict or enlarge to change peripheral resistance and alter flow
  • increase in pressure of a vein can contain 6-10X the volume of blood as an artery of comparable size.
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6
Q

When is venous pressure the lowest?

A

-when patient is lying flat (supine or prone)

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7
Q

When is venous pressure the highest?

A

when patient is standing

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8
Q

How can veins vary their resistance to blood flow?

A

by changing the cross-sectional area

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9
Q

What happens when veins are partially empty? (shape-wise and function)

A

-they assume an elliptical cross-sectional shape, which offers a great deal of resistance to blood flow as they take on a more circular shape

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10
Q

What happens when veins are distended?

A

-they offer almost no resistance to blood flow as they take on a more circular shape

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11
Q

What is the importance of the radius to the resistance?

A

-their ability to change shape permits veins to accommodate increases in blood flow w/o causing increases in the pressure gradient to the heart

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12
Q

*What is transmural pressure?

A
  • *the pressure on the walls of a vessel
  • *the difference between the pressure exerted on the venous walls from within the vein (intraluminal pressure) and from outside the veins (interstitial pressure) and is related to the amount or volume of blood in the vein
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13
Q

What is the normally the pressure within the veins?

A

low and pushing outward

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14
Q

What does a large circular shape in veins do?

A

can carry more blood w/o an increase in pressure and offer less resistance to flow

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15
Q

What do flattened veins do?

A

with low volume they offer more resistance to flow

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16
Q

*Where is the greatest portion of circulating blood located? and how much?

A
  • *in the venous system

- *veins carry about 2/3rds of the blood in the body

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17
Q

What happens to veins in the supine position?

A

-they take on an elliptical shape due to low transmural pressure

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18
Q

What happens to veins in the standing position?

A

they take on a circular shape due to high transmural pressure

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19
Q

What happens when intraluminal pressure is higher than pressure in surrounding tissue?

A

transmural pressure increases, distending the vessel

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20
Q

What happens when intraluminal pressure is lower than surrounding tissue pressure?

A

-transmural pressure is low, and the vessel collapses

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21
Q

What is the transmural pressure normally in the venous system?

A

-very low, which allows for a flexible shape and increased compressibility

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22
Q

What happens when the pressure in the venous system increases to an abnormal level?

A

the veins become engorged w/ blood and demonstrate diminished flexibility/compressibility

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23
Q

What is a major force affecting the venous system?

A

hydrostatic pressure

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24
Q

What is the reference point of the human body for hydrostatic pressure?

A

the right atrium

25
*What is hydrostatic pressure?
* -equivalent to the weight of a column of blood pressing against the vessels measured at a height above or below heart level - reported in mmHg and directly proportional to height
26
What is caused by weight of a fluid as measured compared to a reference point?
hydrostatic pressure
27
What is the pressure within a blood vessel?
-equal to the dynamic pressure supplied by the contraction of the heart plus the hydrostatic pressure
28
*How does hydrostatic affect arteries and veins?
*it affects both equally
29
What plays the greater role in determining overall venous pressure?
-the hydrostatic pressure plays a greater role b/c the dynamic pressure is so low in the veins
30
What happens to the hydrostatic pressure in supine?
-it is negligible b/c all arteries and veins are roughly at the same level as the right atrium
31
What is hydrostatic pressure related to?
position
32
What is the hydrostatic pressure at the heart level?
zero
33
What is the hydrostatic pressure in supine?
HP = 0 mmHg
34
What is hydrostatic pressure above the heart?
negative
35
What is hydrostatic pressure at the ankle when standing and why?
-100 mmHg at ankle b/c HP increases when standing
36
When is hydrostatic pressure the highest?
-in a standing patient, in the feet
37
What has a profound effect on the venous return to the heart?
-changes in intrathoracic and intraabdominal pressure
38
What happens during inspiration?
- the diaphragm descends, which decreases the pressure in the chest cavity; this causes blood to pool into the pulmonary vascular bed and also pulls air into the lungs - descending movement of diaphragm results in an increase in intraabdominal pressure; this partially collapses the IVC, which impedes venous return from the legs
39
What happens during expiration?
the diaphragm moves upward, which decreases the intraabdominal pressure, resulting in an increase in blood flow from the legs and a decrease in blood flow into the thorax
40
What do calf veins act as?
reservoirs for blood
41
What is the effect of The Calf Muscle Pump Mechanism?
- calf veins act as reservoirs for the blood | - this aids in venous return
42
What does The Calf Muscle Pump Mechanism consist of?
- deep and superficial veins of the lower legs - contracting leg muscles - venous sinusoids - venous valves: preventing retrograde flow
43
What is known as the venous heart?
calf muscles
44
What happens when the calf muscles contract?
-it squeezes the veins and propels the blood against the force of gravity (hydrostatic pressure) cephalad toward the heart
45
How much pressure can the contraction of the calf muscles generate?
-greater than 200 mmHg
46
What is the effect of the closure of valves in the deep veins?
it decreases the length of the column of blood, which helps reduce the venous pressure
47
What happens when the calf muscle relaxes?
b/c veins in calf are empty, blood is drawn into the area from the superficial veins via perforators
48
What happens in competent venous valves?
-the blood will travel in only one direction toward the heart and from superficial to deep system
49
What happens upon relaxation in the more proximal segments of the leg?
the valves close to prevent reflux of blood from these segments
50
What happens in the normal pattern of venous flow?
it decreases venous pressure and pooling and increases venous return to the heart and cardiac output
51
What happens with incompetent valves?
the opposite occurs, venous pressure and venous pooling increases, decreasing venous return to the heart and cardiac output
52
What is spontaneous flow?
flow is detected in the vein w/o flow augmentation
53
*Do calf veins and saphenous veins of the lower extremity and the radial and ulnar veins of the upper extremity have spontaneous Doppler signals
- Normally NO | - *but all other veins should demonstrate spontaneity
54
What is it called when velocity of flow changes in response to respiration?
Phasicity/respiratory pattern
55
What happens when phasic pattern is absent?
-flow is described as continuous and it can be seen when there is a proximal obstruction or when stop breathing for brief moments
56
What does continuous flow imply?
intrinsic or extrinsic obstruction between the sampled vessel and the heart
57
What is the respiratory response to deep veins in the lower extremities and upper extremities during inspiration?
-flow in LE will decrease as diaphragm moves inferiorly and flow in UE will increase toward the heart
58
What is the response to deep veins in lower extremities and upper extremities during expiration?
-diaphragm moves superiorly; LE flow increases, and UE flow decreases

DMS 223- Intro to Vascular Ultrasound (2 decks)

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