Changing cardiac output

Question 1

What is preload?

Answer 1

Amount that ventricles are filled and stretched in diastole

Question 2

What are the factors of preload?

Answer 2

Central venous pressure (CVP)
LV-EDV
Left ventricular end diastolic pressure (LV-EDP)

Ventricular compliance

Question 3

What is afterload?

Answer 3

The load that the LV must eject blood against

Question 4

What is afterload aprroximately equivalent to?

Answer 4

Aortic pressure

Question 5

What effect does resistance have on blood pressure?

Answer 5

Causes blood pressure to decrease

Question 6

How does blood pressure change in the arteries? Why?

Answer 6

Increases and decreases

due to systole and diastole

Question 7

How does blood pressure change in the arterioles? Why?

Answer 7

Decrease in blood pressure

due to arterioles offering resistance

Question 8

What is the relative blood pressure in capillaries, venules, veins etc.? Why?

Answer 8

Low blood pressure

because come after arterioles, after drop in blood pressure

Question 9

How does blood pressure change in capillaries, venules, veins etc.?

Answer 9

Slowly decreases

Question 10

If cardiac output remains the same, and TPR drops, what happens to arterial pressure? Why?

Answer 10

Pressure in arteries decreases

more blood flow through arterioles, less blood in arteries

Question 11

If cardiac output remains the same, and TPR drops, what happens to venous pressure? Why?

Answer 11

Pressure in veins increases

more blood flow through arterioles, more blood entering veins

Question 12

If cardiac output remains the same and TPR increases, what happens to arterial pressure? Why?

Answer 12

Pressure in arteries increases

less blood flow through arterioles, backs up in arteries

Question 13

If cardiac output remains the same and TPR increases, what happens to venous pressure? Why?

Answer 13

Pressure in veins decreases

less blood flow through arterioles, less blood in veins

Question 14

If TPR remains the same and cardiac output increases, what happens to arterial pressure? Why?

Answer 14

Arterial pressure increases

heart pumps more blood into arteries

Question 15

If TPR remains the same and cardiac output increases, what happens to venous pressure? Why?

Answer 15

Venous pressure decreases

blood removed from veins by heart and pumped into arteries

Question 16

If TPR remains the same and cardiac output decreases, what happens to arterial pressure? Why?

Answer 16

Arterial pressure decreases

less blood entering arteries

Question 17

If TPR remains the same and cardiac output decreases, what happens to venous pressure? Why?

Answer 17

Venous pressure increases

blood backs up in veins

Question 18

How does the heart prevent changes in arterial and venous blood pressure due to changes in TPR?

Answer 18

Changes its cardiac output

Question 19

What is the equation for cardiac output?

Answer 19

Cardiac output = heart rate x stroke volume

Question 20

What are the factors of cardiac output?

Answer 20

Heart rate

Stroke volume

Afterload

Question 21

What is stroke volume?

Answer 21

The volume of blood ejected from the LV per heartbeat

Question 22

What is the equation for stroke volume?

Answer 22

Stroke volume = EDV - ESV

Question 23

What is the average stroke volume?

What percentage is this of the average EDV?

Answer 23

70ml

67%

Question 24

What are the factors of stroke volume?

Answer 24

Preload

Contractility

Question 25

What are the types of mechanisms by which the heart changes its cardiac output? What do they each mean?

Answer 25

Intrinsic mechanisms - within the heart itself Extrinsic mechanisms - outside of the heart

Question 26

What is the intrinsic mechanism of changing the heart's cardiac output?

Answer 26

Frank-starling mechanism

Question 27

What is the Frank-Starling mechanism?

Answer 27

Increased preload increased force of contraction increased stroke volume up to a point

Question 28

How is preload increased?

Answer 28

Increase CVP bigger difference in pressure between veins and LV, more blood flow from veins to LV increased LV-EDV, LV-EDP Increase ventricular compliance

Question 29

How are CVP and LV-EDP related to each other? Why?

Answer 29

They are approximately equal | because then there is no pressure difference between the veins and LV, so no blood flow from veins to LV

Question 30

What is ventricular compliance?

Answer 30

The ability of the ventricle to distend to hold a higher volume of blood without significant increase in pressure

Question 31

What are the axes of the ventricular compliance curve? And their units?

Answer 31

x axis = LV blood volume (ml) y axis = LV pressure (mmHg)

Question 32

What is normal LV pressure with LV blood volume of 120ml?

Answer 32

8mmHg

Question 33

What is decreased ventricular compliance?

Answer 33

Higher pressure with same blood volume

Question 34

What is an example of a cause of decreased ventricular compliance?

Answer 34

LV hypertrophy

Question 35

How does decreased ventricular compliance affect the gradient of the ventricular compliance curve?

Answer 35

Steeper gradient

Question 36

What is an example of a cause of increased ventricular compliance?

Answer 36

Dilation of LV

Question 37

What is increased ventricular compliance?

Answer 37

Higher blood volume with same pressure

Question 37

How does increased ventricular compliance affect the gradient of the ventricular compliance curve?

Answer 37

Flatter gradient

Question 39

What are the axes of the Frank-Starling curve?

Answer 39

x axis = CVP/LV-EDV/LV-EDP y axis = stroke volume

Question 40

Why does the Frank-starling mechanism work?

Answer 40

Sarcomeres in cardiac muscle are stretched decreased actin-myosin overlap increased sensitivity to calcium ions increased force of contraction

Question 41

What are the axes of the length tension curve for cardiac muscle?

Answer 41

x axis is sarcomere length y axis is force of contraction

Question 42

What is the extrinsic mechanism of changing the heart's cardiac output?

Answer 42

Autonomic nervous system affecting - heart rate - contractility

Question 43

What is heart rate?

Answer 43

Number of heart beats per minute

Question 44

What is contractility?

Answer 44

Force of contraction for a given fibre length

Question 45

How can contractility be increased?

Answer 45

Sympathetic nervous system innervating the LV is activated more

Question 46

How does an increase in contractility affect the cardiac output?

Answer 46

Increased force of contraction increases stroke volume increased cardiac output

Question 47

How does an increase in contractility affect the Frank-Starling curve?

Answer 47

Larger stroke volume for same CVP/LV-EDV/LV-EDP Steeper gradient

Question 48

How does a decrease in contracility affect the Frank-Starling curve?

Answer 48

Smaller stroke volume for same CVP/LV-EDV/LV-EDP Flatter gradient

Question 49

How does the Frank-starling mechanism affect the cardiac output of the right side of the heart compared to the left side?

Answer 49

Ensures their cardiac outputs are equal e.g. if one side of the heart has a higher cardiac output, then the other side of the heart has a higher preload, has a higher stroke volume, giving a higher cardiac output

Question 50

How does standing up affect blood in the legs? Why?

Answer 50

Causes pooling of blood in the legs | due to effect of gravity

Question 51

How does blood pooling in the leg affect arterial and venous pressure?

Answer 51

Both decrease | as blood collects in the veins of the leg

Question 52

Which mechanism is responsible for changing the heart's cardiac output when both arterial and venous pressure decrease? Why?

Answer 52

Extrinsic mechanism Not intrinsic because venous pressure has decreased, smaller pressure difference between veins and LV, less blood flow from veins to LV, decreased preload