Lec 17 Venous Return

Question 1

How does CO change in right atrial pressure?

Answer 1

decreased CO with increased right atrial pressure

Question 2

Where is steady state CO on frank-starling curve?

Answer 2

• steady state CO is where frank-starling curve intersects venous return curve

Question 3

What 3 variables can change venous return curve

Answer 3

1. arterial resistance
2. venous compliance
3. blood volume

Question 4

What does the starling curve represent?

Answer 4

• the function of the heart in isolation

- CO increased with increased preload

Question 5

What is difference between venous return curve and starling curve significance?

Answer 5

starling = heart in isolation

venous return curve = function of entire circulation

Question 6

What is the venous return curve [axes]? what does it show?

Answer 6

• function of entire circulation
• y intercept = max flow at zero atrial pressure
• x intercept = mean systemic pressure = pressure present if no flow

Question 7

What is relationship between blood flow into atrium and atrial pressure?

Answer 7

when atrial pressure lower –> easier for blood to flow into atrium

Question 8

What is true of relationship between cardiac output and venous return in steady state?

Answer 8

• cardiac output = venous return in stead state

- steady state occurs at the intersection point of venous return and starling curves

Question 9

What does the flat portion on left of venous return curve represent?

Answer 9

negative pressure in the atrium

Question 10

What happens to starling curve when you alter contractility?

Answer 10

• new curve intersects venous return curve in different location = alter steady state
• decreased contractility = smaller slope [less SV for same LVEDP]
• increased contractility = bigger slope

Question 11

How does positive inotropic effect alter steady state?

Answer 11

• increases CO of steady state

- decreases right atrial pressure

Question 12

How does negative inotropic effect alter steady state?

Answer 12

• decreases CO of steady state

- increases right atrial pressure

Question 13

What happens to venous return curve when you alter contractility?

Answer 13

nothing

Question 14

what happens to starling and venous curves when you alter contractility?

Answer 14

increased contractility –> bigger slope of frank starling [decreased contractility –> smaller slope]

contractility does not change venous return

Question 15

what happens to starling and venous curves when you alter blood volume?

Answer 15

frank starling: no change

venous return: parallel shift [shift right with increased volume, shift left with decrease volume]
– changes both x and y intercepts

Question 16

what happens to starling and venous curves when you increase TPR [arteriolar constriction]?

Answer 16

increased TPR

• decreased slope of frank starling [shift right]
• decreased slope of venous return [same x intercept, smaller y intercept]

decreased TPR

• increased slope of frank starling [shift left]
• increased slope of venous return [same x intercept, bigger y intercept]

Question 17

How does increased blood volume effect alter steady state?

Answer 17

• increased CO

- increased right atrial pressure

Question 18

How does decreased blood volume effect alter steady state?

Answer 18

• decreased CO

- decreased right atrial pressure

Question 19

How does increased TPR alter steady state?

Answer 19

• decreased CO

- unchanged right atrial pressure

Question 20

How does decreased TPR alter steady state?

Answer 20

• increased CO

- unchanged right atrial pressure

Question 21

What does increased TPR signify?

Answer 21

increased afterload

Question 22

What does increased afterload do to SV and starling?

Answer 22

• decreased SV/CO

- shifts starling curve to the right

Question 23

What do venoconstriction/decreased venous compliance do to venous return curve? to starling curve?

Answer 23

nothing to starling curve

to venous return:
shift right [shallower slope, same Y intercept, bigger x intercept]
-

Question 24

What do venoconstriction/decreased venous compliance do to steady state?

Answer 24

• increase in CO due to increased preload

- higher right atrial pressure

Question 25

General rules of 3 ways to alter venous return

Answer 25

change in blood volume
- parallel shift of venous return curve

constriction/dilation arterioles
- rotation of venous return curve, no change x intercept

constriction/dilation veins
- rotation venous return curve, no change y intercept

Question 26

What is y intercept of venous return graph?

Answer 26

maximal flow with no atrial pressure

Question 27

What is x intercept of venous return graph?

Answer 27

venous pressure with no flow

Question 28

How does increased blood volume change the intercepts of venous return? what does this mean?

Answer 28

• increased x intercept: increase no-flow pressure

- increased y intercept: increase maximal flow

Question 29

How does arteriolar dilation change the intercepts of venous return? what does this mean?

Answer 29

• same x intercept: no change in no-flow pressure because most blood in the veins
• increased y intercept: resistance decreases –> max flow increases

Question 30

How does constriction of veins change the intercepts of venous return? what does this mean?

Answer 30

• bigger x intercept: alters no-flow pressure because most blood in veins
• same y intercept: no change in max flow because this is determined by arterioles

Question 31

What changes occur in heart failure?

Answer 31

1. decrease in contractility due to damaged myocardium
2. retain fluids to increase preload
3. chronic sympathetic stimulation to improve myocardial performance

Question 32

How does chronic sympathetic stimulation in heart failure alter CO/venous pressure?

Answer 32

• increase CO

- decrease venous pressure [from just MI state bust still higher than original]

Question 33

What happens to steady state immediately after MI?

Answer 33

• no change in venous return curve, right shift in frank starling [= decreased contractility]
• steady state: increased venous pressure, decreased CO

Question 34

What happens to steady state after MI + fluid retention [with just MI as baseline]?

Answer 34

• get no change in frank starling from MI state
• get parallel right shift in venous return
• steady state: increased venous pressure, increased CO from immediately after MI but still lower than normal

Question 35

What happens to steady state after MI + fluid retention + sympathetic stimulation [with MI + fluid as baseline]?

Answer 35

• get no change in venous return curve
• get left-shift in frank starling from MI + fluid state [but still to the right of the original healthy]
• steady state: decreased venous pressure compared to MI + fluid, increased CO compared to MI + fluid [but doesn’t return fully to normal]

Question 36

Why is increased atrial pressure a problem?

Answer 36

increased atrial pressure –> iincreased pressure in plumonary system, this is why heart failure is congestive

Question 37

What 4 relationships to represent circulation

Answer 37

1. output vs right atrial pressure [frank-starling]
2. blood flow vs arterial pressure
3. arterial volume vs arterial pressure
4. venous volume vs venous pressure

Question 38

What 3 constraints of circulation relationships

Answer 38

1. cardiac output = venous return
2. venous pressure about = to right atrial pressure
3. arterial volume + venous volume = constant