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Cardiovascular System > Changing cardiac output > Flashcards

Changing cardiac output Flashcards

1
Q

What is preload?

A

Amount that ventricles are filled and stretched in diastole

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2
Q

What are the factors of preload?

A

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

Ventricular compliance

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3
Q

What is afterload?

A

The load that the LV must eject blood against

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4
Q

What is afterload aprroximately equivalent to?

A

Aortic pressure

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5
Q

What effect does resistance have on blood pressure?

A

Causes blood pressure to decrease

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6
Q

How does blood pressure change in the arteries? Why?

A

Increases and decreases

due to systole and diastole

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7
Q

How does blood pressure change in the arterioles? Why?

A

Decrease in blood pressure

due to arterioles offering resistance

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8
Q

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

A

Low blood pressure

because come after arterioles, after drop in blood pressure

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9
Q

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

A

Slowly decreases

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10
Q

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

A

Pressure in arteries decreases

more blood flow through arterioles, less blood in arteries

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11
Q

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

A

Pressure in veins increases

more blood flow through arterioles, more blood entering veins

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12
Q

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

A

Pressure in arteries increases

less blood flow through arterioles, backs up in arteries

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13
Q

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

A

Pressure in veins decreases

less blood flow through arterioles, less blood in veins

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14
Q

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

A

Arterial pressure increases

heart pumps more blood into arteries

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15
Q

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

A

Venous pressure decreases

blood removed from veins by heart and pumped into arteries

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16
Q

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

A

Arterial pressure decreases

less blood entering arteries

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17
Q

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

A

Venous pressure increases

blood backs up in veins

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18
Q

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

A

Changes its cardiac output

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19
Q

What is the equation for cardiac output?

A

Cardiac output = heart rate x stroke volume

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20
Q

What are the factors of cardiac output?

A

Heart rate

Stroke volume

Afterload

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21
Q

What is stroke volume?

A

The volume of blood ejected from the LV per heartbeat

22
Q

What is the equation for stroke volume?

A

Stroke volume = EDV - ESV

23
Q

What is the average stroke volume?

What percentage is this of the average EDV?

A

70ml

67%

24
Q

What are the factors of stroke volume?

A

Preload

Contractility

25
Q

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

A

Intrinsic mechanisms - within the heart itself

Extrinsic mechanisms - outside of the heart

26
Q

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

A

Frank-starling mechanism

27
Q

What is the Frank-Starling mechanism?

A

Increased preload
increased force of contraction
increased stroke volume

up to a point

28
Q

How is preload increased?

A

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

29
Q

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

A

They are approximately equal

because then there is no pressure difference between the veins and LV, so no blood flow from veins to LV

30
Q

What is ventricular compliance?

A

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

31
Q

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

A

x axis = LV blood volume (ml)

y axis = LV pressure (mmHg)

32
Q

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

A

8mmHg

33
Q

What is decreased ventricular compliance?

A

Higher pressure with same blood volume

34
Q

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

A

LV hypertrophy

35
Q

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

A

Steeper gradient

36
Q

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

A

Dilation of LV

37
Q

What is increased ventricular compliance?

A

Higher blood volume with same pressure

37
Q

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

A

Flatter gradient

39
Q

What are the axes of the Frank-Starling curve?

A

x axis = CVP/LV-EDV/LV-EDP

y axis = stroke volume

40
Q

Why does the Frank-starling mechanism work?

A

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

41
Q

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

A

x axis is sarcomere length

y axis is force of contraction

42
Q

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

A

Autonomic nervous system affecting

  • heart rate
  • contractility
43
Q

What is heart rate?

A

Number of heart beats per minute

44
Q

What is contractility?

A

Force of contraction for a given fibre length

45
Q

How can contractility be increased?

A

Sympathetic nervous system innervating the LV is activated more

46
Q

How does an increase in contractility affect the cardiac output?

A

Increased force of contraction
increases stroke volume
increased cardiac output

47
Q

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

A

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

Steeper gradient

48
Q

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

A

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

Flatter gradient

49
Q

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

A

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

50
Q

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

A

Causes pooling of blood in the legs

due to effect of gravity

51
Q

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

A

Both decrease

as blood collects in the veins of the leg

52
Q

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

A

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

Cardiovascular System (22 decks)

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