Lecture 5- Control Of Cardiac Output

Question 1

What mechanical factor determines preload?

Answer 1

Venous pressure

Question 2

What mechanical factor determines what happens during systole?

Answer 2

Afterload

Question 3

What is starlings law?

Answer 3

Increase in venous pressure and end diastolic volume will lead to increase in stroke volume “more in more out”

Question 4

What does a fall in peripheral resistance lead to?

Answer 4

Increased stroke volume as it is easier to eject blood. However blood pressure will be lowered whereas with a higher afterload stroke volume will decrease but pressure will be higher

Question 5

Chemical effect of noradrenaline and adrenaline on the heart?

Answer 5

Provide a positive inotropic effect

Question 6

Effect of total peripheral resistance on heart rate?

Answer 6

Low resistance will cause a decrease in blood pressure and so the heart will beat faster in order to compensate

Question 7

What is afterload?

Answer 7

The load the heart must eject blood against, usually roughly equal to aortic pressure

Question 8

What is preload?

Answer 8

Amount the ventricles are stretched in diastole and is released to the end diastolic volume or central venous pressure

Question 9

What is total peripheral resistance?

Answer 9

Sometimes called systemic vascular resistance it is the resistance to blood flow offered by all the systemic vasculature

Question 10

What happens if arterial resistance is increased?

Answer 10

Arterial pressure and total peripheral resistance will fall but venous pressure will increase

Question 11

What happens if TPR increases and CO is unchanged

Answer 11

Arterial pressure increase and venous pressure fall

Question 12

What happens if CO increases and TPR is unchanged

Answer 12

Arterial pressure increase venous pressure fall

Question 13

What happens if CO decrease and TPR is unchanged?

Answer 13

Arterial pressure will fall and venous pressure will increase

Question 14

What a problem associated with increased venous pressure?

Answer 14

Oedema

Question 15

What causes total peripheral resistance to fall?

Answer 15

Dilation of arterioles and pre capillary sphincters

Question 16

What causes increased heart rate in exercise?

Answer 16

Decrease in TPR to allow oxygen to tissues. This decrease arterial pressure and increases venous pressure so the heart combats this by increasing heart rate

Increased venous return through muscle pumps also

Question 17

What is stroke volume?

Answer 17

SV=EDV-ESV average is 70ml

Question 18

How can stroke volume be increased?

Answer 18

By increasing EDV eg mitral valve regurgitation or decreasing ESV

Question 19

What is the ventricular compliance curve?

Answer 19

Describes the relationship between venous pressure and end diastolic pressure.

Increased compliance means that an increase in volume results in less pressure than in a normal heart while decreased compliance is the opposite

Question 20

What factors determine how much the ventricles will fill?

Answer 20

Venous pressure and compliance

Question 21

What is Frank-starling’s law of the heart?

Answer 21

The more the heart fills the harder it contracts (up to a point)

Question 22

Intrinsic example of stroke volume control?

Answer 22

Increased stroke volume caused by increased filling of the heart ensures that both sides of the heart have the same output.

Question 23

Effect of contractility?

Answer 23

Increased contractility will increase starling curve (higher stroke volume at a given end diastolic pressure) and decreased contractility will lower the starling curve

Question 24

Effect of increased afterload?

Answer 24

Occurs when total peripheral resistance is increased. Results in lowered venous pressure which lowers the venous return to the heart

Question 25

What factors determine CO?

Answer 25

How hard it contracts- determined by end diastolic volume and contractility (increased sympathetically)

How hard it is to eject blood (afterload)

Question 26

Effect of standing up?

Answer 26

Blood pool at feet, reduces venous pressure which reduces cardiac output which reduces arterial pressure.

Baroreceptor reflex and autonomic nervous system increase resistance and heart rate.

If these mechanism fail you get postural hypotension

Question 27

How does exercise increase cardiac output?

Answer 27

Increase heart rate, venous pressure and contractility

Question 28

How do you measure jugular venous pulse?

Answer 28

See lecture

Question 29

What can increase jugular venous pressure?

Answer 29

Right side of heart doesnt fill properly because its impaired

Volume overload with IV infusion

Right side of heart doesnt pump blood it properly