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Heart Failure RCM:5 > Cardiac function > Flashcards

Cardiac function Flashcards

1
Q

Formula for cardiac output

A

Stroke volume (L/beat) x heart rate (beat/min)

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2
Q

Units for cardiac output

A

litres/min

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3
Q

What is the normal stroke volume at rest

A

70ml

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4
Q

What is the normal heart rate at rest

A

70 beats per minute

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5
Q

What is the normal cardiac output at rest

A

5L/min

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6
Q

What does control of cardiac output depend on

A
  • Factors affecting heart rate

- Factors affecting stroke volume

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7
Q

What are the factors influencing heart rate

A
  • Sympathetic nervous system
  • Pasasympathetic nervous system
  • Hormones
  • EXtra/intracellular ions
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8
Q

How does the sympathetic nervous system inleucne heart rate

A

Activation of Beta adrenoceptors causes an increase in heart rate

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9
Q

How does the parasympathetic nervous system incuelce heart rate

A

Activation of muscarinig receptors causes a decrease in heart rate

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10
Q

How do hormones affect heart rate

A

Adrenaline acts on Beta adrenoceptors which causes an increase in heart rate

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11
Q

How do extra/intracellular ions affect heart rate

A

alterations in membrane potential (eg potassium)

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12
Q

What is stroke volume

A

Volume of blood ejected by each ventricle in a single heart beat

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13
Q

What does stroke volume represent

A

Difference between the end diastolic volume (EDV) and the end systolic volume (ESV)

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14
Q

Whats the EDV

A

End diastolic volume =

Amount of blood contained within ventricle when ventricle is fully relaxed

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15
Q

Whats the ESV

A

ESV= Amount of blood that remains in ventricle after ventricular contraction

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16
Q

What is stroke volume determined by the interaction of

A
  • pre-load
  • cardiac contractility
  • after-load
17
Q

Normal value of EDV

A

140ml

18
Q

Normal value of ESV

A

70ml

19
Q

What is pre-load

A

how much blood is coming back into the heart from venous system

20
Q

What is the after-load

A

How hard it is to pump the blood

21
Q

What is end diastolic volume dependent on

A

End diastolic pressure (pre-load)

22
Q

What is stroke volume primarily influenced by

A

Venous return (ie venous tone, blood volume, posture, intrathoracic pressure)

23
Q

What is venous tone

A

Contraction of veins

24
Q

What can filling time influence

A

Stroke volume

25
Q

What is filling time

A

Increasing heart rate reduces filling time and hence can limit EDV

26
Q

What else can influence stroke volume

A

Atrial contractility

27
Q

What happens if you increase the blood given to the heart

A

The more blood is pumped by the heart because of the length-tension relationship

28
Q

What is the length tension relationship

A

Increasing more blood to heart stretches the cardiac muscle fibres more so muscle fibres contract more forcefully which means the heart expels the extra blood added to It

29
Q

What factors increase stroke volume

A
  • INcrease SNS activity
  • CAlcium
  • Positive inotropic drugs
30
Q

What factors decrease stroke volume

A
  • Reduced SNS activity
  • HYpoxia
  • Acidosi
  • HEart failure
31
Q

How doe an increase in aortic pressure affect stroke volume

A

Will increase after load which will reduce stroke volume at a constant pre-load

32
Q

What causes an increase in aortic pressure

A

Increased peripheral resistance

Altered aortic stiffness

33
Q

What does an increase EDV (pre-load) lead to

A

An increase in stroke volume

34
Q

What does an increased aortic pressure (after-load) lead to

A

A decrease in stroke volume

35
Q

What does an increased cardiac contractility do

A

Increase stroke volume

36
Q

Why does increased cardiac contractility because of activated sympathetic nervous system lead to an increased EDV

A

because more blood is pushed out so stroke volume is increased. Increased EDV because more blood is pushed out

Heart Failure RCM:5 (10 decks)

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