Stroke volume

Question 1

Define preload, afterload & contractility

Answer 1

Preload – end diastolic volume, intrinsic regulation

Afterload – resistance to ventricular ejection

Contractility – end systolic volume, extrinsic regulation

Question 2

How is cardiac output regulated

Answer 2

Heart rate & stroke volume

Question 3

What is the Frank Starling mechanism

Answer 3

Relationship between preload & stroke volume

Ventricular muscle stretching leads to stronger contractile force

Question 4

How does contractility affect stroke volume

Answer 4

SNS activation –> increased contractility of heart –> increased strength of contraction at any given preload

Increased contractility allows heart to empty more, handle greater preload & increase stroke volume 

B1 adrenoreceptors increase contractility (sympathetic stimulation)

M2 muscarinic receptors decrease contractility (parasympathetic stimulation)

Question 5

How does preload affect stroke volume

Answer 5

Low = ventricular filling reduced = reduced stroke volume

High = ventricular filling increased = increased stroke volume

Preload is major component of intrinsic regulation of stroke volume

Question 6

Fill in the preload diagram

Answer 6

Question 7

How does afterload affect arterial tone

Answer 7

Creates resistance against ventricle pump

Increased stroke volume = increased afterload

Increased afterload = decreased stroke volume (heart has to work harder to maintain cardiac output)

Decreased afterload = increased stroke volume

Question 8

Define & describe relationship between blood pressure, cardiac output & total peripheral resistance

Answer 8

Peripheral resistance & cardiac output alter blood pressure

Peripheral resistance influenced by:
SNS in vasculature (alpha & beta adrenoreceptors)
Renin-angiotensin aldosterone system (RAAS)

Increased BP –> parasympathetic response –> slows HR & decreases CO
Decreased BP –> sympathetic response –> increases HR, increases vascular tone & increases CO

Blood pressure = cardiac output X total peripheral resistance

Question 9

What is pulse pressure & what is it influenced by

Answer 9

Systolic pressure – diastolic pressure

Influenced by:
Arterial compliance
Stroke volume
Ejection rate

Question 10

What is arterial compliance

Answer 10

Ability to accommodate increase in pulse pressure

Question 11

How is stroke volume measured

Answer 11

end diastolic volume - end systolic volume