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Heart FIlure > Cardiac Function > Flashcards

Cardiac Function Flashcards

1
Q

Cardiac output

A 
Litres/min
Stroke volume (l/beat) x heart rate (beat/min)
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2
Q

Healthy cardiac output at rest

A

5 litres/min

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3
Q

Healthy stroke volume at rest

A

70 ml

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4
Q

Healthy heart rate at rest

A

70bpm

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5
Q

Factors affecting heart rate

A

Intrinsic - SA node (pacemaker) and AV node (conduction)

  1. SNS - activation of beta-adrenoceptors causes increase
  2. PNS - activation of muscarinic receptors causes decrease
  3. Hormones
  4. Extra/intracellular ions
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6
Q

What is stroke volume?

A

Volume of blood ejected by each ventricle in a single heart beat
Represents the difference between end diastolic volume and end systolic volume

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7
Q

What affects stroke volume

A

Pre-load
Cardiac contractility
After-load

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8
Q

Pre-load

A

Filling pressure of the heart at the end of diastole

End diastolic volume dependent upon end-diastolic pressure

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9
Q

What is pre-load influenced by?

A

Venous return (venous tone, blood volume, posture, intrathoracic pressure)
Atrial contractility
Filling time - increased heart rate reduced filling time and can limit EDV

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10
Q

Describe the length-tension relationship using a curve

A

Frank-Starling curve - stroke volume y, EDV x
Blood returning to the heart will be pumped out

Force of contraction of cardiac muscle fibres is proportional to degree of stretch
Increased stretch (EDV), increased force of contraction and therefore increased contractility (stroke volume increases)
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11
Q

Cardiac contractility

A

Innate ability for heart to contract

Amount of force generated by cardiac muscle fibres can vary independently from degree of stretch

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12
Q

End diastolic volume

A

Amount of blood in ventricle at the end of diastole

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13
Q

How can muscle fibres of the heart be made more effective as a contractile pump?

A

Increased SNS activity
Increased calcium
Positive inotropic drugs eg. Digoxin, changes F-S relationship

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14
Q

How can muscle fibres of the heart be made less effective as a contractile pump?

A

Decreased SNS activity
Hypoxia
Acidosis (associated with hypoxia)
Heart failure - hypertrophy

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15
Q

After load

A

Aortic pressure is a force the heart is pushing against

Increased aortic pressure increases after load which reduces stroke volume at a constant pre-load

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16
Q

When is velocity of contraction greatest?

A

At fixed length

Low loads

17
Q

Describe LV pressure-volume changes in a single cardiac cycle

A
  1. Starting volume (preload) = EDV
  2. Isovolumic phase of systole - increase in pressure, no change in volume
  3. When force (left ventricular pressure) exceeds load (aortic pressure) aortic valve opens
  4. Ejection phase of systole - further slight increase in pressure, reduction in volume

Extent of reduction in volume = stroke volume

18
Q

Pressure and volume at preload

A

140ml, 0mmHg

19
Q

P and V at isovolumic phase of systole

A

Rise in LVP no change in volume

20
Q

Isovolumic phase of diastole

A

Fall in LVP with no change in volume

21
Q

Ejection phase

A

Decreases volume, slowing increase of pressure

22
Q

Ventricular filling

A

Increased volume

No change in pressure

23
Q

How does an increased pre-load affect pressure and volume relationship

A

More forceful ejection - increased pressure

More volume to remove - increased stroke volume

24
Q

How does increased aortic pressure (afterload) affect pressure-volume relationship?

A

Same EDV
Have to generate higher pressure in ventricle to exceed aortic
Less time for ejection to take place, smaller ejection of blood
Therefore stroke volume decreases

25
Q

What would happen in the next heartbeat after a beat with high afterload?

A

EDV increased, cardiac muscle fibres will contract more to increase stroke volume and return to normal afterload

26
Q

LT effect of high afterload

A

Heart failure as heart has to work harder chronically

27
Q

What is the affect on pressure-volume relationship when cardiac contractility is increased?

A

Increased stroke volume due to increase contraction
Higher pressure
Less blood at the end of systole (decreased EDV)

28
Q

Affect on next heartbeat after higher cardiac contractility?

A

Less contraction needed

Heart FIlure (9 decks)

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