Cardiac Function Flashcards

1
Q

How to calculate cardiac output (and units)

A

Cardiac output = Stroke volume (litres/beat) x heart rate (beat/min)

Litres/min

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2
Q

Cardiac output, stroke volume, heart rate at rest

A

5 L/min; 70ml; 70bpm

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3
Q

Effect of sympathetic nervous system on heart rate

A

Activation of B-adrenoceptors causes an increase in heart rate

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4
Q

Effect of parasympathetic nervous system on heart rate

A

Activation of muscarinic receptors causes a decrease in heart rate

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5
Q

Effect of hormones on heart rate

A

Adrenaline acting on beta-adrenoceptors causing an increase in heart rate

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6
Q

Effect of intra/extracellular ions on heart rate

A

Alterations in membrane potential - e.g. K+

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7
Q

Stroke Volume

A

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

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8
Q

End Diastolic Volume vs End Systolic Volume

A

The volume of blood in the heart during the respective phases of contraction

Stroke volume is 70ml; difference

**note that ESV is not 0

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9
Q

Factors affecting stroke volume

A

Pre-load (If more blood enters, more will leave)
Cardiac Contractility (ability of heart to contract)
After-load (pressure against which blood is pushed)

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10
Q

Pre-load and factors influencing it

A

Amount of blood is returned to the heart during a cardiac cycle

Primarily influenced by venous return

Also affected by filling time & atrial contractility

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11
Q

Why does an increase in LV volume cause an increase in stroke volume (mechanically)

A

If there is more stretch on cardiac muscle fibres, their contraction will have more force and can push out more blood (length-tension relationship)

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12
Q

Cardiac contractility

A

The amount of force generated by cardiac muscle fibers. It can vary independently from the degree of stretch i.e. ventricular contractility can vary at any given end-diastolic volume depending upon other influences

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13
Q

Factors cause increases in stroke volume by affecting cardiac contractility

A

Increased SNS activity
Calcium
Positive inotropic drugs
e.g. digoxin

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14
Q

Factors cause decreases in stroke volume by affecting cardiac contractility

A

Reduced SNS activity
Hypoxia
Acidosis
Heart failure!!

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15
Q

Afterload

A

Amount of pressure that the heart needs to exert to eject the blood during ventricular contraction

An increase in aortic pressure will increase afterload as more pressure needs to build up in the LV to allow valve opening

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16
Q

What does an increase in afterload correspond to in terms of stroke volume at constant pre-load

A

An increase in afterload would reduce stroke volume at constant preload

17
Q

Discuss the changes that occur on LV volume against LV pressure during a contraction

A
18
Q

Effect of increased afterload on stroke volume and ESV

A

Increased afterload decreases SV by increasing ESV

19
Q

Effect of increased preload on stroke volume and ESV

A

Increased SV but same ESV

20
Q

Effect of increased cardiac contractility on stroke volume and ESV

A

Increased SV and decreased ESV