5. Control Of Cardiac Output

Question 1

What does afterload mean?

Answer 1

The load the heart must eject blood against

Roughly equivalent to aortic pressure

Question 2

What is preload?

Answer 2

Amount the ventricles are stretched (filled) in diastole

Related to the end diastolic volume or central venous pressure

Question 3

What is total peripheral resistance?

Answer 3

Resistance to blood flow offered by all the systemic vasculature

Question 4

What happens if TPR falls and CO is unchanged?

Answer 4

Arterial pressure will fall

Venous pressure will increase

Question 5

What happens if TPR increases and CO is unchanged?

Answer 5

Arterial pressure will increase

Venous pressure will fall

Question 6

What happens if CO increases and TPR is unchanged?

Answer 6

Arterial pressure will increase

Venous pressure will fall

Question 7

What happens if CO decreases and TPR is unchanged?

Answer 7

Arterial pressure will fall

Venous pressure will rise

Question 8

What happens if there is a higher demand in the tissue for blood?

Answer 8

Arteriolar and precapillary sphincters dilate
Peripheral resistance falls
Heart needs to pump more so that arterial pressure does not fall
Heart responds to changes by intrinsic and extrinsic mechanisms

Question 9

What are intrinsic and extrinsic mechanisms?

Answer 9

Intrinsic - what heart does on its own

Extrinsic - neuronal/hormonal effects

Question 10

How do you work out stroke volume?

Answer 10

End diastolic volume - end systolic volume

Question 11

Describe the Ventricular Compliance Curve

Answer 11

The higher the venous pressure, the more the heart fills
The more the heart fills, the higher the left ventricular pressure
Compliance can be increased or decreased in diseased states

Question 12

What is the Frank-Starling Law of the heart?

Answer 12

If you stretch the fibres of the heart before contracting, it will contract harder
Therefore the more the heart fills, the harder it contracts, therefore the bigger the stroke volume

Question 13

Describe the lengthy tension curve for cardiac muscle

Answer 13

If sarcoma remains length is too short, filament overlap interferes with contraction
In cardiac muscle, also get an increase in calcium sensitivity as the muscle fibres are stretched

Question 14

What ensures that both sides of the heart pump maintain the same output?

Answer 14

Increased stroke volume with increased filling of heart - intrinsic control mechanism

Question 15

What is contractility?

Answer 15

Force of contraction for a given fibre length

Question 16

What can increase contractility?

Answer 16

Extrinsic factors such as sympathetic stimulation and circulating adrenaline

Question 17

What affects how much the ventricle empties?

Answer 17

How hard it contracts

How hard it is to eject blood

Question 18

What are contractility and heart rate controlled by?

Answer 18

Autonomic nervous system

Question 19

What will a decrease in arterial BP do?

Answer 19

Reduced parasympathetic NS activity and stimulate sympathetic NS increase heart rate and increase contractility

Question 20

What happens if metabolism of the body increases?

Answer 20

TPR will fall to supply more blood
Results in a fall in retrial pressure and an increase in venous pressure
Heart will respond by pumping more

Question 21

What conditions will increase jugular venous pulse?

Answer 21

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