Control Of Cardiac Output

Question 1

After load

Answer 1

Load the heart must eject blood against (aortic pressure)

Question 2

Pre load

Answer 2

Amount the ventricles are stretched (filled) in diastole (end diastolic volume/central venous pressure)

Question 3

Central venous pressure

Answer 3

Pressure in large veins draining to heart

Question 4

Total peripheral resistance

Answer 4

Systemic vascular resistance - resistance to blood flow offered by systemic vasculature

Question 5

What happens to pressure as it encounters resistance on the other side

Answer 5

Drops

Question 6

How do arterioles increase resistance

Answer 6

Constriction - pressure in capillaries and venous side will fall
Arterial pressure will rise

Question 7

What happens if total peripheral resistance decreases (CO unchanged)

Answer 7

Lower resistance =
arterial pressure fall (easier to flow)
Venous pressure increase (builds up venous side)

Question 8

What happens if total peripheral resistance increases (CO unchanged)

Answer 8

Arterial pressure increases

Venous pressure fall

Question 9

What happens if cardiac output increases

Answer 9

Increase arterial pressure (more blood pumping out)

Decrease venous pressure (easier for blood to flow into empty heart)

Question 10

What happens if CO decreases?

Answer 10

Arterial pressure decreases (less blood out)

Venous pressure increases (heart isn’t as empty so less easy to flow in)

Question 11

What happens when tissues need more blood?

Answer 11

Arterioles and precapillary sphincters dilate
Less resistance
Arterial pressure falls - heart needs to pump more to maintain pressure
Venous pressure raises - heart pumps more to ensure doesn’t rise

Question 12

2 ways which heart responds to changes in CVS and aBP

Answer 12

Intrinsic and extrinsic

Question 13

Cardiac output

Answer 13

Stroke volume x heart rate

Question 14

Stroke volume

Answer 14

End diastolic volume (finished filling) - end systolic volume (finished emptying)

EDV - ESV

Question 15

Typical cardiac output

Answer 15

5L per minute

Question 16

Typical stoke volume

Answer 16

70ml

67% of EDV

Question 17

How can you increase stroke volume

Answer 17

Increase end diastolic volume (fill blood more)

Decrease end systolic volume (pump more blood out)

Question 18

When does ventricular filling occur?

Answer 18

Diastole
AV valves open
Aortic and pulmonary closed

Question 19

When do the ventricles stop filling?

Answer 19

Until the intraventicular pressure is equal to venous pressure
Higher venous pressure = more filling of heart = higher ventricular pressure

Question 20

What is the ventricular compliance curve?

Answer 20

Higher venous pressure = more filling of heart = higher ventricular pressure

Question 21

Frank starling law of the heart

Answer 21

If you stretch fibres of heart before contracting it will contract harder

More the heart fills = harder contraction

Harder contraction = bigger stroke volume

Question 22

What is how much the ventricles fill dependent on?

Answer 22

Compliance -

Increased compliance - dilated walls, thinner (less pressure exerted)

Decreased compliance - hypertrophy (stiff and high pressure)

Question 23

Starling curve

Answer 23

Increase venous return = Left ventricular end diastolic pressure increase = increase in stroke volume = increase preload

Question 24

Length tension curve cardiac muscle

Answer 24

If sarcomere length too short - filament overlap interferes with contraction (decreases force)

Question 25

What happens to cardiac muscle fibres when stretched?

Answer 25

Increase calcium sensitivity

Question 26

What does starlings law of the heart ensure?

Answer 26

Both sides of the heart are balanced

Increased stroke volume from increased filling = intrinsic

Maintain same output both sides of heart