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CVS > Session 2: Control of Cardiac Output > Flashcards

Session 2: Control of Cardiac Output Flashcards

1
Q

Define afterload.

A

The load the heart must eject blood against (roughly equivalent to aortic pressure)

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2
Q

Define preload.

A

Amount the ventricles are stretched (filled) in diastole - related to the end diastolic volume or central venous pressure.

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3
Q

Define total peripheral resistance.

A

Sometimes referred to as systemic vascular resistance - resistance to blood flow offered by all systemic vasculature.

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4
Q

Which vessels offer the greatest resistance?

A

The arterioles

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5
Q

What does constriction of the arterioles do in terms of resistance?

A

It increases resistance.

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6
Q

What is the consequence of this increased resistance?

A

The pressure in the capillaries and on the venous side will fall and the pressure on the arterial side will increase.

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7
Q

For the next couple of questions, if you need help go back and look at page 5 to 8. However try the questions first.

A

Yup

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8
Q

What happens if there is a decrease in TPR (total peripheral resistance) but CO (cardiac pressure) stays the same?

A

There will be an increase in venous pressure and a decrease in arterial pressure.

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9
Q

What happens if there is an increase in TPR but CO stays the same?

A

There will be an increase in arterial pressure and a decrease in venous pressure.

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10
Q

What happens if there is an increase in CO but TPR stays the same?

A

There is a decrease in venous pressure and increase in arterial pressure. This is because with each beat the heart takes more blood from the veins.

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11
Q

What happens if there is a decrease in CO but TPR stays the same?

A

An increase in venous pressure and a decrease in atrial pressure.

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12
Q

Explain what happens if tissues need more blood.

A

The arterioles and precmpillary sphincters will dilate. This causes TPR to decrease. Because of this there is an increase in venous pressure and decrease in atrial pressure. To combat this the heart will start pumping more so that the arterial pressure doesn’t fall and so that the venous pressure doesn’t rise. This is done by intrinsic and extrinsic mechanisms.

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13
Q

How is cardiac output calculated?

A

CO = stroke volume (SV) x heart rate (HR)

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14
Q

How is stroke volume calculated?

A

SV = end diastolic volume (EDV) - end systolic volume (ESV)

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15
Q

What is the typical stroke volume in an average man at rest?

A

Around 70 ml.

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16
Q

What is the typical volume of blood pumped from a heart in 1 minute in an average man at rest? (Say 70 bpm per second)

A

4.9 L

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17
Q

How can then stroke volume be manipulated?

A

By either a change in EDV or a change in ESV.

18
Q

When does ventricular filling happen?

A

During diastole

19
Q

The ventricle fills until the walls stretch enough to produce an intraventricular pressure equal to the venous pressure. What happens if the venous pressure increases?

A

The heart fills more.

20
Q

What happens if the heart fills more?

A

The ventricular pressure increases to equal the venous pressure.

21
Q

What is Frank-Starling Law of the heart?

A

If you stretch the fibres of the heart before contracting, it will contract harder.
The more the heart fills the harder it contracts due to the stretching of the fibres.
The harder the heart contracts the higher the stroke volume.

22
Q

What can cause the heart to fill up more?

A

An increased venous pressure. How much the ventricles fill depends on compliance.

23
Q

What is compliance?

A

It describes how easy a chamber of the heart or a blood vessel expands when it is filled with a volume of blood.

24
Q

What is the Starling curve? Describe it. What does it represent?

A

It says the as the left ventricular end diastolic pressure increases so does the stroke volume.
In more detail increasing venous return leads to increased left ventricular end-diastolic pressure (LVEDP) and volume (increased preload). This causes an increase in stroke volume, so that the extra blood is pumped out of the ventricle.

25
Q

What is the normal operating point at rest of the left ventricle at end of diastolic pressure? Pressure and stroke volume wise?

A

8 mm Hg and around 70ml

26
Q

How does the contractile force of the cardiac muscle relate to the resting length of the sarcomere?

A

The longer or more stretched the sarcomere is the higher the contractile force (up to a point).

27
Q

Why is the Starling’s Law of the Heart important?

A

As the heart fills more the stroke volume increases. This is important to ensure that both sides are balanced. If this wasn’t the case the right ventricle could end up with more blood and not pump out as much as is going in. This means that more blood comes into the right ventricle than the left atria/ventricle.
So it ensures that the output between the two pumps remain the same.

28
Q

Define contractility.

A

The force of contraction for a given fibre length.

29
Q

What happens to stroke volume as you manipulate contractility?

A

An increase in contractility increases stroke volume.

A decrease, decreases stroke volume.

30
Q

How can contractility be manipulated extrinsically?

A

The sympathetic stimulation and circulating adrenaline can increase contractility.
Reducing sympathetic stimulation will reduce contractility.

31
Q

What is afterload?

A

The pressure that the heart has to pump against (the pressure in the aorta). This is also called material pressure.

32
Q

What factors determine cardiac output?

A 
How much the ventricle empties (ESV)
How hard it is to eject blood (arterial pressure)
Stroke volume
Heart rate
Contractility
33
Q

What happens if the metabolism of the body increases?

A

Dilation occurs to get more nutrients to cells. This causes a decrease in TPR. An increase in venous pressure and a decrease in arterial pressure.

34
Q

What are the consequences of this?

A

The increase in venous pressure means that heart rate and stroke volume will increase to match the cardiac output needed. This increases arterial pressure back to normal and decreases venous pressure.

35
Q

Explain what happens when you are standing up regarding cardiac output.

A

The venous pressure goes down, cardiac output goes down and also the arterial pressure. Now both venous and arterial pressure have changed in the same direction which can not be fixed by intrinsic mechanisms.

36
Q

If this problem cannot be fixed by intrinsic mechanisms of the heart, how is it fixed?

A

By baroreceptor reflex and autonomic nervous system response to increase heart rate and TPR.

37
Q

What happens if these relfexes do not work properly?

A

You get postural hypotension.

38
Q

Explain what happens during exercise regarding cardiac output.

A

Initially muscle pumping and venocosntriction returns more blood to the heart.
Later on TPR decreases so venous pressure increases and so does venous return.
Very early response of increased heart rate.
There is an increase in contractility
All in all:
Increase in venous pressure, heart rate, contractility and cardiac output.

39
Q

Where would you examine right atrial pressure?

A

By palpating the right internal jugular vein by the jugular venous pulse. Estimate the highest visible pulsations (JVP height) above sternal angle +4 cm = JVP in cm H2O.

40
Q

What does a graph of JVP look like?

A

This is a graph of the pressure of the right atria.
The graph rises at ‘a’ which is a contraction of the atrium. There is then a drop in pressure due to the blood emptying the atrium and going into the ventricle. At ‘c’ there is a small increase in pressure again due to the tricuspid valves shutting and causing some influx which increases the pressure.
The pressure then further drops into x-descent where the ventricle contracts forcing some dilation of the atrium and decreases the pressure. Then there is some increase in pressure as the atrium passive fills again from the veins. And last there is a small decrease called y-descent due to the opening of the tricuspid valve once again.

41
Q

What will increase JVP?

A

If the right side of the heart doesn’t pump blood out properly
Volume overload with IV infusion
If something impairs filling of the heart.

CVS (18 decks)

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