2. Control Of Cardiac Output

Question 1

What is afterload?

Answer 1

The load the heart must eject blood against

Question 2

What is afterload roughly equivalent to?

Answer 2

Aortic pressure

Question 3

What is preload?

Answer 3

The amount the ventricles are stretched (filled) in diastole.
Related to EDV and CVP.

Question 4

What is stroke volume?

Answer 4

The difference between EDV and ESV.

Question 5

What is cardiac output the product of?

Answer 5

HR x SV

Question 6

What is end diastolic volume determined by?

Answer 6

The filling of the LV.
The ventricles fill in diastole as the venous pressure drives blood into them.
Fills until intraventricular pressure matches venous pressure.

The higher the venous pressure, the more the ventricle will fill in diastole.

Question 7

What is stroke volume determined by?

Answer 7

How much the ventricle contracts during systole.

Mechanical and chemical factors will influence this.

Question 8

Which 2 mechanical factors influence stroke volume?

Answer 8

Preload - determined by venous pressure

Afterload - pressure in arteries which heart has to overcome

Question 9

Increased venous pressure will lead to increased stroke volume. True or false?

Answer 9

True

Question 10

Why does a decrease in TPR result in increased stroke volume?

Answer 10

Reduction of afterload (pressure in arteries), so it’s easier for the heart to expel the blood into the aorta.

Question 11

If TPR is high, what is the effect on stroke volume?

Answer 11

Decrease stroke volume because it is much harder to eject the blood.
Lower stroke volume but higher pressure will be generated.

Question 12

Which 2 mechanical mechanisms will increase stroke volume?

Answer 12

Increasing venous pressure or decreasing total peripheral resistance.

Question 13

What factors may affect the contractility of the heart and the force of contraction?

Answer 13

Neurotransmitters
Hormones
Drugs

Question 14

How does increasing sympathetic activity increase stroke volume?

Answer 14

Noradrenaline and adrenaline have a positive inotropic effect, so will increase contractility.

Question 15

Rises in ________ pressure increase ______________ and therefore increase ___________.

Answer 15

venous
Stroke volume
Cardiac output

Question 16

Falls in arterial pressure _________ stroke volume therefore __________ cardiac output.

Answer 16

Increase

Increase

Question 17

If TPR falls, what will happen to arterial and venous pressure?

Answer 17

Arterial pressure will decrease

Venous pressure will rise

Question 18

How does the heart response to a decrease in arterial pressure?

Answer 18

Increases heart rate and stroke volume (SNS) and therefore cardiac output.
This will increase arterial pressure and reduce venous pressure to restore status quo.

Question 19

What is total peripheral resistance?

Answer 19

Resistance to blood flow offered by all the systemic vasculature

Question 20

Which blood vessels offer the greatest resistance?

Answer 20

Arterioles

Question 21

What happens to the pressure of blood as it flows through resistance?

Answer 21

Pressure decreases

Question 22

How do arterioles increase resistance?

Answer 22

By contracting

Question 23

How does contraction of an arteriole affect the pressure of the arterial and capillaries/venous side?

Answer 23

Pressure in the capillary/venous side will fall

Pressure in the arterial side will rise.

Question 24

What will happen to the arterial and venous pressure if TPR falls and CO is unchanged?

Answer 24

Decrease arterial pressure

Increased venous pressure

Question 25

What will happen if TPR increases and CO is unchanged?

Answer 25

Increased arterial pressure | Decreased venous pressure

Question 26

What will happen if CO increases and TPR is unchanged?

Answer 26

Increased arterial pressure | Decreased venous pressure

Question 27

What will happen if CO decreases and TPR is unchanged?

Answer 27

Decreased arterial pressure | Increased venous pressure

Question 28

How does the heart increase blood flow to a particular area?

Answer 28

Precapillary sphincters will dilate, decreasing peripheral resistance.

Question 29

How does the heart 'see' changes in demand?

Answer 29

Arterial blood pressure Central venous pressure It response to changes in these by intrinsic and extrinsic mechanisms.

Question 30

How can you calculate CO?

Answer 30

CO = SV x HR

Question 31

How can you calculate SV?

Answer 31

SV = EDV - ESV Increase SV by increase in EDV or decreasing ESV

Question 32

What is the typical stroke volume?

Answer 32

70 ml 67% of normal EDV

Question 33

What relationship does the ventricular compliance curve illustrate?

Answer 33

The higher the venous pressure, the more the heart fills.

Question 34

What is the Frank-Starling law of the heart?

Answer 34

If you stretch the fibres of the heart before contracting, it will contract harder. (Increasing preload increases CO)

Question 35

How does compliance effect the extent of ventricle filling?

Answer 35

Rescued compliance will reduce filling. | Increased compliance will increase filling.

Question 36

What ensures that both sides of the heart remain balanced?

Answer 36

Starlings law Increased SV with increased filling is an INTRINSIC control mechanism. Ensures same output in both sides.

Question 37

Why is it important that the heart is balanced ?

Answer 37

The same volume of blood that is pumped to the body must also be pumped to the lungs.

Question 38

What extrinsic factors alter contractility?

Answer 38

Sympathetic stimulation- NA and adrenaline

Question 39

How does increasing arteriolar resistance decrease CO?

Answer 39

Increased arterial resistance which will increase aortic pressure (after load) Also decreases venous pressure which reduces filling of the heart.

Question 40

Whwr are the 2 main factors which determine how hard the ventricle contracts?

Answer 40

- EDV | CONTRACTILITY

Question 41

How does the heart respond to a decrease in arterial BP?

Answer 41

Reduce parasympathetic NS activity and stimulate sympathetic NS to imcrease HR and contractility.