Control of Cardiac Output

Question 1

What is the equation for cardiac out put?

Answer 1

CO= SV x HR

Question 2

If you increase TPR what happens to arterial and venous pressure if CO does not compensate?

Answer 2

Arterial pressure rises

Venous pressure reduces

Question 3

If TPR decreases and venous pressure thus increases what happens to venous return?

Answer 3

It increases.

Question 4

What is pre-load?

Answer 4

Amount the ventricles stretch or fill in diastole. A function of EDV or central venous pressure.

Question 5

What is total peripheral resistance?

Answer 5

Resistance to blood flow offered by all systemic vasculature.

Question 6

The load the heart must eject blood against is known as?

Answer 6

The after load

Its related to aortic pressure

Question 7

If CO increases but TPR is unchanged what happens to arterial and venous pressure?

Answer 7

Arterial pressure increases

Venous pressure decreases

Question 8

Cardiac out put responds to changes in arterial blood pressure and central venous pressure by what mechanism types?

Answer 8

Intrinsic and extrinsic

Question 9

If you start to exercise pre capillary sphincters to skeletal muscle will open and thus TPR will fall. If TPR fell and CO didn’t change the arterila pressure would drop and the venous pressure would rise, so how does the heart stop this?

Answer 9

Heart increases CO by increasing rate and contractility. This gives a higher SV and HR to maintain arterial pressure and avoid venous hypertension.

Question 10

Whats a normal ejection fraction?

Answer 10

67%

Question 11

How are venous pressure and EDV related?

Answer 11

The ventricles passively fill and stretch until the pressure in the ventricle equals that of the venous system

Question 12

What is compliance?

Answer 12

Compliance is the left ventricle filling a bit without increasing the pressure. Disease can increase or decrease compliance.

Question 13

What happens in ventricular filling in increased compliance?

Answer 13

Pressure doesn’t rise as it should

Question 14

What is Frank Starlings law?

Answer 14

If you stretch a heart more it will contract harder giving a larger stroke volume

The higher the EDV the bigger the contraction, to a limit.

Question 15

High preload means what for Stroke volume?

Answer 15

Increased CVP means increase preload which means higher EDV and so a greater SV.

Question 16

What do length tension curved for cardiac muscle show?

Answer 16

If sarcomere are two short at the begining of contraction the levels of contraction is lower.

Question 17

When cardiac muscle cells are streched they contract more- by which two mechanisms is this change brought about?

Answer 17

More stretch means more contraction by Frank Starlings law. (intrinsic mechanism)
Increase stretch means increased calcium sensitivity in cardiac muscle cells.

Question 18

If the slope of a Frank Starling curve is altered what has changed?

Answer 18

Contractility

Question 19

What are extrinsic factors affecting cardiac output?

Answer 19

Sympathetic stimulation from circulating adrenaline acting on Beta 1 receptors

Question 20

Increase sympathetic innervation of the heart does what?

Answer 20

Positive inortopy

Positive chronotropy

Question 21

What happens to stroke volume in increased TPR?

Answer 21

High TPR means high arterial pressure- so greater after load.
The venous pressure decreases so heart filling is lowered.

Question 22

What effects how much the ventricles empty?

Answer 22

The contractility and the EDV

The after load

Question 23

The parasympathetic nervous system innervates the heart by what nerve?

Answer 23

The Vagus nerve

Question 24

Describe demand led pumping

Answer 24

Metabolism increases so tissue demand increases.
TPR falls to supply tissues.
Arterial pressure decreases and venous pressure increases.
Heart beats harder and faster to maintain arterial pressure. This happens by intrinsic and extrinsic mechanisms.

Question 25

How does cardiac out put respond to TPR changes

Answer 25

The changes in cardiac out put act to oppose the TPR changes in terms of arterial and venous pressure effects

Question 26

What happens when we stand up to arterial and venous pressure? (if we had no reflexes or compensatory mechanisms)

Answer 26

They both decrease. Venous pooling leads to reduced CO and thus lower arterial pressure.

Question 27

What stops postural hypotension?

Answer 27

baroreceptor reflexes, autonimic nervous system and increase TPR

Question 28

In exercise how is venous return increased?

Answer 28

Muscle pump activity

Lower TPR

Question 29

Who’s law states higher EDV gives higher SV

Answer 29

Starlings