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CVS > Control Of Cardiac Output > Flashcards

Control Of Cardiac Output Flashcards

1
Q

What is afterload?

A

The pressure the heart must pump/eject blood against

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2
Q

What is preload?

A

The amount the ventricles stretch in diastole

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3
Q

What determines preload?

A

End diastolic volume
Central venous pressure

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4
Q

What is Central venous pressure?

A

Pressure in the large veins draining into the heart

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5
Q

What is arterial pressure and where is it normally measured?

A

Pressure in the large arteries
Measured at Brachial arteries

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6
Q

What is Total peripheral resistance? (TPR)

A

Resistance to blood flow offered by all the systemic vasculature

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7
Q

Which blood vessels offer the greatest resistance?

A

Arterioles

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8
Q

How/why do arterioles have the greatest resistance?

A

Narrow lumen
Lumen can constrict narrowing it increasing resistance

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9
Q

What is the affect of constricting arterioles on arterial pressure and venous pressure?

A

LOWERS VENOUS PRESSURE
INCREASES ARTERIAL PRESSURE

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10
Q

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) is reduced (Arterioles dilate) but Cardiac output remains the same?

A

Blood flows easier so arterial pressure decrease
Central venous pressure increases

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11
Q

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) is increased (arterioles constrict) but Cardiac output remains the same?

A

Arterial pressure INCREASED
Central venous pressure DECREASED

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12
Q

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) stays the same but Cardiac output increases?

A

Arterial pressure INCREASES
(So heart fills easier with blood since it is emptied more)
Central venous pressure DECREASES

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13
Q

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) stays the same but Cardiac output decreases?

A

Arterial pressure DECREASES (Heart doesn’t empty as much)
Heart doesn’t as readily fill with blood
Central venous pressure must INCREASE

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14
Q

What feature is usually changed to allow for increased demands of blood to be met?

A

Reduce peripheral resistance
(Arterioles dilate)

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15
Q

When arterioles dilate what affect does this have on arterial pressure and venous pressure?

A

Decreases arterial pressure
Increases venous pressure

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16
Q

How does the heart ensure that arterial pressure and venous pressure dont change when there’s an increased demand for blood?

A

Pumps more

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17
Q

What is cardiac output?

A

Volume of blood ejected from the left ventricle per min (or per unit time)

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18
Q

What is the equation for cardiac output

A

Cardiac output = Stroke vol x Heart rate

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19
Q

What is the equation for Stroke volume?

A

SV = End diastolic volume - end systolic volume

SV = EDV - ESV

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20
Q

What is the average Cardiac output for the average man?

A

5L/min

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21
Q

What is the average stroke volume for the 70kg man at rest?

A

70ml

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22
Q

How can stroke volume be increased? (Think about the equation)

A

Increase EDV (End Diastolic Volume)
Decrease ESV (End systolic volume)

23
Q

During diastole what valves are open and closed?

A

Tricuspid and Mitral valve is open
Pulmonary and aortic valve are closed

24
Q

How does venous pressure affect end diastolic volume?

A

Higher the venous pressure the larger the end diastolic volume (the more the heart fills)

25
Q

What is Frank-Starling law?

A

The more the heart fills (the more the fibres of the heart stretch) the harder it contracts up to a limit

26
Q

How does strength of contraction affect stroke volume?

A

Harder contraction = higher stroke volume

27
Q

What is the type of relationship between left ventricular end-diastolic pressure and stroke volume?

A

Linear relationship (up until a point)

28
Q

How does an increased amount of stretching of the heart fibres increase contraction strength?

A

More stretch = Inc Ca2+ sensitivity = more contraction
ALSO
More cross bridges can occur

29
Q

How are both sides of the heart balanced?

A

If 1 side of the heart has to pump more blood, the other side must match it

30
Q

What is an example of an intrinsic mechanism which ensures both sides of the heart are balanced?

A

Increasing stroke volume as heart fills up with more blood

31
Q

What is meant by contractility?

A

Force of contraction for a given fibre length

32
Q

What EXTRINSIC factors affect contractility?

A

Sympathetic stimulation
Circulating adrenaline

33
Q

What is afterload? (Aortic impedance)

A

The pressure the heart has to pump against

34
Q

How does increased TPR affect venous pressure and therefore the filling of the heart?

A

Reduces venous pressure
Reduces filling of the heart

35
Q

What is the effect of hyper tension (increased arterial pressure) on the heart?

A

Heart works harder due to a larger afterload
Hypertrophy likely to follow

36
Q

What receptors are important in controlling cardiac output?

A

Baroreceptors

37
Q

What do baroreceptors detect and where are they found?

A

Stretch receptors found in the aorta and carotid arteries

38
Q

How does the nervous system act when arterial blood pressure drops?

A

Stimulate sympathetic nervous system
Reduce parasympathetic nervous system

39
Q

How is cardiac output determined?

A

Strength of contraction (EDV and contractility)
How hard it is to eject blood (aortic impedance)

40
Q

How does TPR change when theres an increased demand for blood?

A

Decreases

41
Q

How does the heart need to respond when TPR has decreased to increase blood supply?

A

When TPR decreases venous pressure INCREASES

This means heart fills more
Frank-starling law states heart will contract harder

42
Q

How does increased cardiac output affect arterial and venous pressure?

A

Inc arterial
Dec venous

43
Q

How is venous pressure and arterial pressure affected pooling of blood in the feet when you’re sitting down then you stand up?

A

Venous and arterial pressure both drop since pressure is higher at the feet due to gravity

44
Q

What is the baroreceptor reflex?

A

Detecting drop in arterial pressure, ANS increases sympathetic activity and decreases parasympathetic activity
INCREASED HR AND CONTRACTILITY

45
Q

What happens if the baroreceptor reflex fails when you stand up?

A

Postural hypotension

46
Q

What happens in response to exercise?

A

Decreased TPR (Inc venous pressure)
Inc HR
Inc contractility

47
Q

Where is the jugular vein generally located?

A

Neck

48
Q

What muscle is the internal jugular vein posterior to?

A

Sternocleidomastoid muscle

49
Q

What other blood vessel is the internal jugular vein directly in contact with?

A

Superior vena cava

50
Q

What can the internal jugular be used to estimate?

A

Central venous pressure

51
Q

How can the internal jugular vein be used to estimate the central venous pressure?

A

Patient lies at 45º
Head turned to left
Height of pulsations estimated against sternal angle

52
Q

What is the estimated normal highest visible pulsation of the Jugular vein?

A

5 to 8cm

53
Q

How does ESV affect venous pressure?

A

More blood that remains in heart the harder it is to fill with blood
This means venous pressure must increase

CVS (21 decks)

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