Cardiac Output

Question 1

Define Cardiac Output, units

Answer 1

CO = SV x HR

The volume of blood pumped by each ventricle per minute (L/min)

Question 2

Define Preload

Answer 2

The amount of blood that hits the ventricle in each beat (defined at end of diastole)

Question 3

Define Afterload

Answer 3

The pressure against which the ventricle is ejecting blood

Question 4

Define Stroke Volume

Answer 4

SV = EDV - ESV

The volume of blood ejected from each ventricle during each ventricular contraction

Question 5

Neural control of CO?

Answer 5

ANS - carotid body baroreceptors send afferents along CN IX

aortic arch baroreceptors send afferents along CN X

Question 6

What’s the main way CO is affected and how is this influenced?

Answer 6

Total venous return, affected by metabolism and local blood flow of each organ/tissue
Total venous return affects preload which affects EDV to alter SV and therefore CO

Question 7

Link Starlings law to preload

Answer 7

Starlings law: more muscle there is to be stretched, the greater power it will contract with
Greater the preload, the greater the cardiac contractility

Question 8

What would affect ESV?

Answer 8

Ventricular hypertrophy as thickened walls mean increased stress and afterload (pressure) so ESV will increase and then SV/CO will be reduced

Question 9

What’s the relationship between SV, contractility and ESV?

Answer 9

Greater contractility will reduce ESV (more blood ejected) and therefore SV will be increased (and CO)

Question 10

What’s the equation for ejection fraction?

Answer 10

EF = SV / EDV x 100

Question 11

What factors affect CO?

Answer 11

Anything influencing HR: ANS innervation or hormones

Anything influencing SV: Preload affects EDV, contractility (hormones/ANS) and afterload (vasodilation/vasoconstrction) influences ESV