CVS 6.1 - Control of Cardiac Output

Question 1

What happens if there is a decrease in total peripheral resistance, at a given cardiac output?

Answer 1

• Arterial pressure DECREASES as less pressure is needed to overcome a lower resistance (increases heart rate)
• Venous pressure INCREASES due to an increase in the rate of entry which increases the volume (increases heart rate)

Question 2

What happens if there is an increase in total peripheral resistance, at a given cardiac output?

Answer 2

• Arterial pressure INCREASES due to needing to overcome more pressure
• Venous pressure DECREASES due to a decreased rate of entry which decreases volume

Question 3

What happens if there is an increase in cardiac output, at a given TPR?

Answer 3

• Arterial pressure INCREASES - increased volume = increased pressure to overcome resistance
• Venous pressure DECREASES as the volume in the veins decreases to account for increased cardiac output

Question 4

What happens if there is an decrease in cardiac output, at a given TPR?

Answer 4

• Arterial pressure DECREASES - decreased volume etc.

- Venous pressure INCREASES - blood retained in veins for longer = increased volume

Question 5

What is end diastolic volume?

Answer 5

The volume of blood left in the ventricles at the end of diastole

Question 6

What is end systolic volume?

Answer 6

The volume of blood left in the ventricles at the end of systole

Question 7

What is stroke volume?

Answer 7

The difference between end diastolic volume and end systolic volume

Question 8

What determines how much the ventricles fill during diastole?

Answer 8

• Venous pressure
• Ventricle fills until walls stretch and have enough blood to equal venous pressure
• Higher vp = more ventricles fill during diastole

Question 9

What is pre-load?

Answer 9

The end diastolic stretch of the myocardium, determined by venous pressure

Question 10

What is after-load?

Answer 10

The force necessary to expel blood in the arteries

Question 11

What is the effect of an increased venous pressure on stroke volume?

Answer 11

Increases stroke volume

Question 12

What is the effect of a decrease in arterial pressure on stroke volume?

Answer 12

Increases stroke volume

Question 13

What is contractility?

Answer 13

• The potential of the muscle fibres of shortening and therefore contracting (more stretch = increased force of contraction)
• Shows the relationship between end diastolic volume and stroke volume

Question 14

What increases contractility?

Answer 14

Sympathetic activity

So makes heart more susceptible to venous pressure

Question 15

What controls autonomic outflow to the heart?

Answer 15

• Signals sent by baroreceptors in the aortic arch and carotid sinus
• Sense arterial pressure and send messages to the medulla

Question 16

What are the effects of changes in venous pressure on cardiac output?

Answer 16

• Increased VP = Increased CO (increases pre-load)

- Decreased VP = Decreased CO (decreases pre-load)

Question 17

What are the effects of changes in arterial pressure on cardiac output?

Answer 17

• Increased AP = Decreased CO (increases after-load)

- Decreased AP = Increased CO (decreases after-load)