CVS Session 6 Flashcards Preview

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Flashcards in CVS Session 6 Deck (76):
0

What determines arterial pressure?

Cardiac output
TPR

1

What determines venous pressure?

Rate heart pumps blood out
Rate of blood entry

2

What do arterial pressure and venous return both affect?

Stroke volume
Heart rate

3

If the cardiac output is kept constant and the TPR decreases, what happens?

Body asks for more blood so pressure gradient across system has to decrease
Arterial pressure decreases
Venous pressure increases

4

If the cardiac output remains constant and the TPR increases, what happens?

Body needs less blood so more pressure dissipated
Arterial pressure increases
Venous pressure decreases

5

What does a constant TPR indicate?

No change in body demand for blood

6

If the TPR is kept constant and cardiac output increases, what happens?

Increased arterial pressure - extra blood must be pushed out
Decreased venous pressure - blood removed from veins

7

If TPR is constant and cardiac output decreases, what happens?

Arterial pressure decreases
Venous pressure increases
Less blood removed from veins

8

What blood pressure changes occur after consumption of a meal?

Metabolism changes --> local metabolites dilate arterioles --> TPR decreases --> arterial pressure decreases and venous pressure increases

9

How are TPR and the body's need for blood related?

They are inversely proportional

10

What is demand-led pumping?

When the heart pumps more blood to meet increased demand and restore arterial and venous pressures to normal

11

What is stroke volume?

Difference b/w end diastolic volume and end systolic volume

12

Why is the stroke volume only a portion of its maximum value?

Needs to be variable to match demand

13

How do you increase stroke volume?

Fill heart more in diastole
Leave less blood remaining at the end of systole

14

Which is the dominant variable acting on stroke volume?

Venous pressure - increase to increase stroke volume

15

What variable has a small effect on stroke volume?

Arterial pressure - decrease to increase stroke volume

16

How does increasing venous pressure increasing heart filling in diastole?

Ventricle fills until intra ventricular pressure = venous pressure

17

What is the ventricular compliance curve?

Pressure vs volume of the ventricle with the curve giving end diastolic volume

18

What is Starling's law of the heart?

More in = more out

19

By what mechanism does Starling's law of the heart works.

Fuller heart = more stretched ventricle therefore harder ventricle contracts thus increasing stroke volume

20

What automatically causes an increase in stroke volume?

Increase in venous pressure

21

What does the Starling curve relate?

Stroke volume to venous pressure

22

What does the slope of the Starling Curve indicate?

Contractility of ventricle

23

Does contractility quantify how much the heart can contract?

No, it is itself a variable

24

What causes the starling Curve to level off and subsequently decrease?

Overfilling of the heart

25

Why does the stroke volume fall off when the heart is overfilled?

Force of contraction of the heart is impeded by the pericardium

26

How is the Starling Curve described?

Monotonic - increase venous pressure --> increase stroke volume
Fairly linear until close to overfilling

27

Which two factors determine end systolic volume?

How hard ventricle contracts
How hard blood is ejected

28

What is the principal determinant of end systolic volume?

How hard the ventricle contracts

29

What determines how hard the ventricle contracts?

End diastolic volume (Starling's law)
Contractility

30

How is contractility increased?

Increase sympathetic activity by increasing NA action on cardiac myocytes

31

What determines how hard blood is ejected from the heart?

Aortic impedance
TPR (therefore indirectly effects end systolic volume)

32

What does harder ejection of blood mean for arterial pressure?

It will increase

33

Is the control of heart rate an intrinsic property of the heart?

No

34

What controls heart rate?

Autonomic outflow controlled by signals from baroreceptors

35

What affect does decreased arterial pressure have on parasympathetic and sympathetic activity?

Decreases parasympathetic activity - decreased vagal outflow and no ACh on pacemaker cells
Increases sympathetic activity - increase HR and contractility

36

Why is the amplified change of cardiac output caused by increased contractility limited?

Diastole time is limited so at >180 bpm diastole time is too short for sufficient ventricular filling for an increased cardiac output

37

What is the Bainbridge reflex?

Increased venous pressure sensed by R atrium --> decreased parasympathetic activity --> increased HR

38

How does increased venous pressure effect the heart?

Increases rate only

39

Is regulation of heart rate affected by the absence of the Bainbridge reflex?

Nope

40

What effect does increasing venous pressure have on the CVS?

Increase stroke volume
Increase HR
Therefore, increases cardiac output

41

What effect does decreasing arterial pressure have on the CVS?

Increase stroke volume - sympathetic and direct effect
Increase heart rate - principal effect of baroreceptors
Therefore increases cardiac output

42

What effect does decreased arterial pressure have on veins and flow in the skin and gut?

Causes venoconstriction
Temporarily increases flow resistance in skin and gut tissues

43

How does eating a meal or carrying out light exercise affect venous and arterial pressures?

Increases venous pressure
Decreases arterial pressure

44

What causes the pressure changes seen in eating a meal/taking light exercise?

Release of local metabolites decreasing TPR

45

How does significant exercise threaten bloodflow to the brain?

Very large and rapid decrease in TPR decreases arterial pressure

46

How can significant exercise cause pulmonary oedema?

Large and rapid decreases in TPR increases venous pressure --> heart overfills --> L and R heart outputs not matched due to easier perfusion of lungs --> transient excess blood in lungs pushes fluid into tissues

47

How is overfilling of the heart in significant exercise prevented?

Pre-emptive increase in heart rate driven by the brain

48

How does the pre-emotive increase in heart rate seen in significant exercise vary between well-trained and untrained individuals?

Well-trained: occurs before exercise starts to maximise cardiac output
Untrained: rapid increase on starting exercise

49

If the heart rate increases w/no other change, what happens initially?

Cardiac output increases

50

What happens after the immediate rise in cardiac output seen when heart rate increases w/ no other changes?

TPR remains constant therefore venous pressure reduced --> decreased filling of heart in diastole --> stroke volume reduced to exactly same extent HR increased

51

Why is the heart driven by the circulation?

Increased cardiac output and HR would cause the heart to stop therefore proportions of stroke volume and HR must be altered

52

How are the R and L ventricles matched?

Share common pacemaker so only match by stroke volume
If RH pumps more, LH fills more --> LH pumps more

53

In what circumstance will blood accumulate in the lungs?

If heart is at the top of the Starling Curve - LH cannot respond to RH so ventricles are no longer matched

54

What must the arterial and venous pressure changes do in order to allow the cardiac control system to function without problem?

Move in different directions, irrespective of magnitude

55

Why does blood pool in the superficial veins of the legs upon standing?

Transmural pressure is high as these veins are surrounded by air not water which is less affected by gravity

56

Why does arterial pressure fall upon standing?

Central venous pressure decreases --> transient decrease in venous return so cardiac output falls

57

Why can the decrease in arterial pressure upon standing not be corrected by increased contraction of the heart?

Decreased venous return

58

How is arterial pressure restored upon standing?

Decrease is detected by baroreceptors --> stimulate increase HR but venous pressure still low --> TPR increases to defend arterial pressure

59

How is TPR increased to defend arterial pressure?

Briefly shut down bloodflow to skin and gut

60

What effect muscle-pumping have when standing up?

Increases venous return

61

What causes postural hypotension?

ANS vasoconstriction doesn't work
Circulatory volume is reduced

62

Who is postural hypotension commonly seen in?

Elderly

63

What is the net effect of heamorrhage?

Blood loss from veins causing decrease in venous volume

64

Describe what changes take place in heamorrhage.

Decrease blood volume decreases venous pressure --> decreased cardiac output --> decreased arterial pressure --> detected by baroreceptors which increase HR and TPR

65

What effect does increasing the HR caused by the baroreceptors in response to decreased arterial pressure in haemorrhage have on venous pressure?

Decreases it further - makes it worse

66

Which pressure change does increasing the TPR in response to heamorrhage help?

Arterial

67

What causes the risk of loss of perfusion to vital organs in haemorrhage?

Decreased arterial pressure

68

What must occur for a haemorrhage to be overcome?

Increase in venous pressure
Replacement of blood volume cost

69

How does the body cope with losing 1 l of blood without outside help?

Venoconstriction to increase venous return
Autotransfusion to move ECF into blood

70

In what circumstance will both arterial and venous pressure increase?

When circulating volume is higher than it should be e.g. long term high sodium levels

71

Why does long term hypernatraemia cause vasoconstriction?

Increases venous pressure --> increases cardiac output and therefore arterial pressure --> over-perfusion of tissues washes away metabolites

72

Why does over-perfusion of tissues increase and maintain arterial pressure?

Causes increase in TPR

73

Why should hypertension be treated as soon as it is detected?

Avoid arterial pressure being too high for too long as this causes resistance vessels to become bigger and fatter allowing them to constrict harder, worsening hypertension

74

What leads to hypertension?

More blood causing high arterial pressure for as long as blood is maintained

75

How is modification of resistance vessels prevented?

Reduction of circulating volume