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Semester 2 > CVS Session 6 > Flashcards

CVS Session 6 Flashcards

0
Q

What determines venous pressure?

A

Rate heart pumps blood out

Rate of blood entry

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1
Q

What determines arterial pressure?

A

Cardiac output

TPR

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2
Q

What do arterial pressure and venous return both affect?

A

Stroke volume

Heart rate

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

What does a constant TPR indicate?

A

No change in body demand for blood

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6
Q

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

A

Increased arterial pressure - extra blood must be pushed out

Decreased venous pressure - blood removed from veins

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7
Q

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

A

Arterial pressure decreases
Venous pressure increases
Less blood removed from veins

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8
Q

What blood pressure changes occur after consumption of a meal?

A

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

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9
Q

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

A

They are inversely proportional

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10
Q

What is demand-led pumping?

A

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

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11
Q

What is stroke volume?

A

Difference b/w end diastolic volume and end systolic volume

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12
Q

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

A

Needs to be variable to match demand

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13
Q

How do you increase stroke volume?

A

Fill heart more in diastole

Leave less blood remaining at the end of systole

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14
Q

Which is the dominant variable acting on stroke volume?

A

Venous pressure - increase to increase stroke volume

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15
Q

What variable has a small effect on stroke volume?

A

Arterial pressure - decrease to increase stroke volume

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16
Q

How does increasing venous pressure increasing heart filling in diastole?

A

Ventricle fills until intra ventricular pressure = venous pressure

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17
Q

What is the ventricular compliance curve?

A

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

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18
Q

What is Starling’s law of the heart?

A

More in = more out

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19
Q

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

A

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

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20
Q

What automatically causes an increase in stroke volume?

A

Increase in venous pressure

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21
Q

What does the Starling curve relate?

A

Stroke volume to venous pressure

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22
Q

What does the slope of the Starling Curve indicate?

A

Contractility of ventricle

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23
Q

Does contractility quantify how much the heart can contract?

A

No, it is itself a variable

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24
Q

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

A

Overfilling of the heart

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25
Q

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

A

Force of contraction of the heart is impeded by the pericardium

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26
Q

How is the Starling Curve described?

A

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

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27
Q

Which two factors determine end systolic volume?

A

How hard ventricle contracts

How hard blood is ejected

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28
Q

What is the principal determinant of end systolic volume?

A

How hard the ventricle contracts

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29
Q

What determines how hard the ventricle contracts?

A

End diastolic volume (Starling’s law)

Contractility

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30
Q

How is contractility increased?

A

Increase sympathetic activity by increasing NA action on cardiac myocytes

31
Q

What determines how hard blood is ejected from the heart?

A

Aortic impedance

TPR (therefore indirectly effects end systolic volume)

32
Q

What does harder ejection of blood mean for arterial pressure?

A

It will increase

33
Q

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

A

No

34
Q

What controls heart rate?

A

Autonomic outflow controlled by signals from baroreceptors

35
Q

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

A

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

36
Q

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

A

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

37
Q

What is the Bainbridge reflex?

A

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

38
Q

How does increased venous pressure effect the heart?

A

Increases rate only

39
Q

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

A

Nope

40
Q

What effect does increasing venous pressure have on the CVS?

A

Increase stroke volume
Increase HR
Therefore, increases cardiac output

41
Q

What effect does decreasing arterial pressure have on the CVS?

A

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

42
Q

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

A

Causes venoconstriction

Temporarily increases flow resistance in skin and gut tissues

43
Q

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

A

Increases venous pressure

Decreases arterial pressure

44
Q

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

A

Release of local metabolites decreasing TPR

45
Q

How does significant exercise threaten bloodflow to the brain?

A

Very large and rapid decrease in TPR decreases arterial pressure

46
Q

How can significant exercise cause pulmonary oedema?

A

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
Q

How is overfilling of the heart in significant exercise prevented?

A

Pre-emptive increase in heart rate driven by the brain

48
Q

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

A

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

49
Q

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

A

Cardiac output increases

50
Q

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

A

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

51
Q

Why is the heart driven by the circulation?

A

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

52
Q

How are the R and L ventricles matched?

A

Share common pacemaker so only match by stroke volume

If RH pumps more, LH fills more –> LH pumps more

53
Q

In what circumstance will blood accumulate in the lungs?

A

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

54
Q

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

A

Move in different directions, irrespective of magnitude

55
Q

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

A

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

56
Q

Why does arterial pressure fall upon standing?

A

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

57
Q

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

A

Decreased venous return

58
Q

How is arterial pressure restored upon standing?

A

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

59
Q

How is TPR increased to defend arterial pressure?

A

Briefly shut down bloodflow to skin and gut

60
Q

What effect muscle-pumping have when standing up?

A

Increases venous return

61
Q

What causes postural hypotension?

A

ANS vasoconstriction doesn’t work

Circulatory volume is reduced

62
Q

Who is postural hypotension commonly seen in?

A

Elderly

63
Q

What is the net effect of heamorrhage?

A

Blood loss from veins causing decrease in venous volume

64
Q

Describe what changes take place in heamorrhage.

A

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

65
Q

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

A

Decreases it further - makes it worse

66
Q

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

A

Arterial

67
Q

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

A

Decreased arterial pressure

68
Q

What must occur for a haemorrhage to be overcome?

A

Increase in venous pressure

Replacement of blood volume cost

69
Q

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

A

Venoconstriction to increase venous return

Autotransfusion to move ECF into blood

70
Q

In what circumstance will both arterial and venous pressure increase?

A

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

71
Q

Why does long term hypernatraemia cause vasoconstriction?

A

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

72
Q

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

A

Causes increase in TPR

73
Q

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

A

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
Q

What leads to hypertension?

A

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

75
Q

How is modification of resistance vessels prevented?

A

Reduction of circulating volume

Semester 2 (45 decks)

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