CVS S6 - Control of the CVS Flashcards Preview

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Flashcards in CVS S6 - Control of the CVS Deck (36):
1

Describe the effect on the CVS if metabolic demand of the body changes and cardiac output remains the same

If metabolic demand falls:
- TPR rises
- Arterial pressure rises
- Venous pressure falls

If metabolic demand rises:
- TPR falls
- Arterial pressure falls
- Venous pressure rises

2

Describe the effect on pressure in the veins and arteries if cardiac output is changed and TPR remains the same

If CO rises:
- Arterial pressure will rise
- Venous pressure will fall

If CO falls:
- Arterial pressure will fall
- Venous pressure will rise

3

How does the heart supply enough blood to the body at all times if cardiac output can fall or rise?

System is demand led

TPR changes in response to metabolic demand altering arterial and venous pressures and hence cardiac output

Cardiac output is therefore dependent on metabolic demand

4

How do changes in arterial and venous pressures form 'signals' to the heart?

Heart responds to increased venous and decrease arterial pressure by increasing cardiac output

Heart responds to decreased venous and increased arterial pressure by lowering cardiac output

In this way, changes in pressure lead to the heart being 'signalled' to meet demand

5

What is cardiac output the product of?

Stroke volume and heart rate

6

What is end diastolic volume?

The volume of blood in the ventricle at the end of diastole

7

What is end systolic volume?

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

8

What is stroke volume?

The difference between end diastolic and end systolic volume?

9

Describe the connections to the ventricle during diastole

What does this mean for ventricular filling?

During diastole the ventricle is connected to the veins and isolated from the arteries

Therefore the ventricle will fill until the walls stretch to the point that ventricular pressure matches venous pressure

10

Describe the relationship between venous pressure and ventricular filling

Higher the venous pressure the more the heart fills in diastole

11

What is the ventricular compliance curve?

Can you draw it?

Curve showing how end diastolic volume (x) is related to venous pressure (y)

Drawn as a shallow curve showing a positive relationship

12

Define the terms:

Pre-load

After-load

Pre-load is the end diastolic stretch in the myocardium, determined by venous pressure

After-load is the force needed to expel blood in the ventricles into the arteries

13

What is end systolic volume dependent on?

How hard the heart contracts

How hard it is to eject blood

14

Describe how end diastolic volume and stroke volume are related

The more the heart fills (the greater the end diastolic volume) the harder the ventricle will contract (up to a limit) and the bigger the stroke volume

This is Starlings' law of the heart and can be summarised simply as:
- More in = more out

15

Can you draw the Starling curve?

What does it show us?

X = Venous pressure
Y = Stroke volume
Gradient = Contractility

Curve is a steep rise followed by a short fall after the apex

This shows us that the more the heart fills, the harder it contracts (greater stroke volume)

There is however a limit where the heart becomes over-filled and the myocardium is overstretched, resulting in a fall in stroke volume after a certain venous pressure

16

Define the term 'contractility'

How is it determined?

The intrinsic ability of the myocardium to contract (ionotropic state)

The gradient of the Starling curve shows contractility

Delta stroke volume / Delta venous pressure

17

What effect does the sympathetic nervous system have on contractility?

Sympathetic activity makes the heart more susceptible to venous pressure, raising the gradient of the Starling curve

18

What effect does increased arterial pressure have on contractility and contractile force?

Raises contractility and hence contractile force by increasing sympathetic stimulation to the heart (via baroreceptors)

19

What is aortic impedance?

What effect does this have on arterial pressure?

The difficulty of ejecting blood from the ventricle, this mainly depends on TPR (rise in TPR raises aortic impedance)

This means the harder it is to eject blood the higher the pressure will rise in the arteries

20

What is the effect of a drop/rise in arterial pressure on the stroke volume?

If arterial pressure drops:
- End systolic volume will fall as there is decreased after-load, therefore stroke volume has risen

If arterial pressure rises:
- End systolic volume will rise as there is increased after-load, therefore stroke volume has fallen

21

What is the effect of a drop/rise in venous pressure on the stroke volume?

Drops:
- End diastolic volume will fall and stroke volume will fall due to decreased pre-load

Rises:
- End diastolic volume will fall and stroke volume will rise due to increased pre-load

22

Describe how falls and rises in arterial pressure affect the signals sent by the ANS to the heart and the changes this leads to

Baroreceptors sense the arterial pressure

Rise leads to:
- Heart rate falls by decreasing sympathetic and increasing parasympathetic activity
- Contractility falls due to reduced sympathetic activity

Fall leads to:
- Heart rate rises by increasing sympathetic and decreasing parasympathetic activity
- Contractility rises due to increased sympathetic activty

23

What is the Bainbridge reflex?

If venous pressure as sensed by baroceptors in the right atrium rises this will lead to reduced parasympathetic activity and a rise in heart rate

24

Give a detailed list of effects of an increase or decrease in arterial pressure on the heart

Hint: This summarises all the smaller cards in this deck related to the effects of arterial pressure on the heart

Increase:
- Increased end systolic volume and after-load
- Increased contractility
- Decreased heart rate and stroke volume
- Decreased cardiac output

Decrease:
- Decreased end systolic volume and after-load
- Decreased contractility
- Increased heart rate and stroke volume
- Increased cardiac output

25

Give a detailed list of effects of an increase or decrease in venous pressure on the heart

Hint: This summarises all the smaller cards in this deck related to the effects of venous pressure on the heart

Increase:
- Increased venous return
- Increased end diastolic volume and pre-load
- Increased contractile force (up to a limit)
- Increased heart rate and stroke volume
- Increased cardiac output

Decrease:
- Decreased venous return
- Decreased end systolic volume and pre-load
- Decreased contractile force
- Decreased heart rate and stroke volume
- Decreased cardiac output

26

Describe in detail the response of the CVS to eating a meal

Increased gut activity leads to a fall in TPR and subsequent fall in arterial pressure and rise in venous pressure

Rise in venous pressure triggers rise in cardiac output

Fall in arterial pressure triggers baroreceptors which signal the brain to increase sympathetic stimulation to the heart, raising heart rate and contractility and hence cardiac output rises

Extra pumping of the heart reduces venous pressure and raises arterial pressure

Demand met, system stable

27

Describe what would happen if heart rate were to increase with no other change

What does this tell us?

Initially cardiac output would rise, total peripheral resistance would however remain the same

The rise in cardiac output decreases venous pressure so stroke volume will fall

The cardiac output is back to its original value

This tells us the heart is driven by the circulation, not the other way around

28

What is the major effect of movement during exercise on the CVS?

Muscle pumping, which forces extra blood back to the heart

29

If muscle pumping was the only change during exercise (no response from the CVS) what would be the effect?

Venous pressure would rise greatly
Arterial pressure would fall greatly

These changes may be too big to cope with

30

What is the main problem the CVS must deal with during exercise?

This leads to the risk of?

The great increase in venous pressure that will lead to overfilling of the heart and push the heart towards the peak of the Starling curve

At the top of the Starling curve the left ventricular output cannot be further increased if the right ventricular output increases

Therefore there is a risk of blood accumulating in the lungs and pulmonary oedema may result

31

How does the CVS respond during exercise?

Why is this necessary?

An increase in heart rate, driven by the brain at the start of exercise

This means when venous pressure starts to rise heart rate is already high and stroke volume is kept down so the left and right cardiac outputs can be matched

32

What happens in the CVS when we stand up?

Blood pools in the superficial veins of the legs (great/short saphenous veins) due to gravity

Central venous pressure falls

Cardiac output falls as a result

Arterial pressure falls

Baroreceptors detect fall in arterial pressure

Increased sympathetic activity raises heart rate to raise arterial pressure

Venous pressure still low so TPR increases (skin/gut) to both defend arterial pressure and lower venous pressure

33

What is postural hypotension?

Sometimes the baroreceptor reflex which raises heart rate when arterial pressure falls as we stand up doesn't work

Arterial pressure remains low, this is postural hypotension

34

What is the response of the CVS to haemorrhage?

Reduced blood volume lowers venous pressure

Cardiac output falls

Arterial pressure falls

Baroreceptors detect fall in arterial pressure and increase in heart rate results (this can become very high)

TPR is increased

Rise in heart rate lowers venous pressure further

Problem is now worse, not better

35

What is needed to restore the CVS to normal function following haemorrhage?

Veno-constriction to raise the venous pressure

Blood transfusion to replace lost volume

36

What is the response of the CVS to a long term increase in total blood volume?

Blood volume controlled by kidney

Increase for days = an increase in venous pressure

Cardiac output rises

Arterial pressure rises

More blood is forced through tissues, which auto-regulates and raises TPR

Arterial pressure rises further and stays up