Lecture Topic 12: Cardiac output

What is cardiac output?

Volume of blood ejected by each ventricles per minute

What is stroke volume?

Volume of blood ejected by each ventricle per beat

What is the equation for cardiac output?

Cardiac output = heart rate x stroke volume

What is the shortened / symbol version of the equation for cardiac output?

CO = HR X SV

What is the unit for HR?

bpm

What is the units for cardiac output?

L/min

What is the units for stroke volume?

ml

What can affect cardiac output?

Factors affecting HR and/or SV

What is the term to describe the factors affecting HR?

Chronotropic effects

What are the factors effecting HR?

Autonomic innervation / hormone

What neurotransmitter is released in parasympathetic?

Acetylcholine

What neurotransmitter is released in sympathetic?

Noradrenaline

What does the vagus nerve do?

Send impulse from cardioinhibitory centre to SA node

Which nerve is responsible for sending impulses from the cardioinhibitory centre to the SA node?

The vagus nerve

What does the cardioaccelerator centre make the adrenal medulla secrete?

Catecholamines

What is the chronotropic effect of the parasympathetic nervous system?

Negative

What is the chronotropic effect of the sympathetic nervous system?

Positive

What does the parasympathetic NS do to HR?

Decrease HR

What does the sympathetic NS do to HR?

Increases HR

What is the inherent rate of the SA node?

>100bpm

Why is the resting HR much lower than the inherent rate of the SA node?

Because theres little / no sympathetic activity during rest AND due to vagal tone

What does the vagal tone do to HR?

Reduces HR

Is vagal tone greater or lower in athletes? and what does that infer?

Greater, so reduced resting HR even more

Which factor has DIRECT affect on HR?

Venous return

How would you work out SV?

End diastolic vol - end systolic vol / EDV-ESV

What is the impact on SV when EDV increases?

Increased SV

What is the impact on SV when ESV decreases?

Increased SV

What is preload?

The degree to which ventricular muscle cells are stretched at the end of diastole

Which factor affects both EDV and ESV?

Preload

What component does preload affect?

EDV and ESV

What are ALL the determinants of EDV & ESV?

Preload / contractility / afterload

What is contractility?

The force produced by ventricular muscle cells during systole at a given preload

What is afterload?

The force the ventricle needs to overcome to open the semilunar valve and eject blood

How is preload proportional to EDV?

Directly proportional

What is preload directly proportional to?

EDV

What is preload dependent on?

Rate of venous return / Available ventricular filling time

What are all the factors effecting venous return? (just state)

Posture / skeletal muscle pump / respiratory pump / venous capacitance

What happens to the blood in the body whilst standing position?

Blood pools in leg veins, due to gravity