Control of Cardiac Output

Question 1

Define afterload

Answer 1

the load the heart must eject against

Question 2

Outline preload

Answer 2

amount the ventricles are stretched (filled) in diastole = related to end diastolic volume or central venous pressure

Question 3

What is total peripheral resistance?

Answer 3

resistance to blood flow offered by all the system vasculature

Question 4

What happens to the pressure of fluid in a tube as it encounters resistance?

Answer 4

Restriction = less outflow to the next chamber = pressure lowers

Question 5

What will happen when constricting the arterioles?

Answer 5

arterioles offer the greatest resistance = constriction increases resistance = fall in pressure in capillaries and on venous side but rise in pressure on arterial side

Question 6

Outline what happens if total peripheral resistance fall and cardiac output is unchanged

Answer 6

= arterial pressure fall + venous pressure will increase (less pinching = more blood can get through lowing arterial and raising venous)

Question 7

What happens if total peripheral resistance increases and cardiac output is unchanged?

Answer 7

= arterial pressure will increase = venous pressure will fall (more pinching = even less can get through raising arterial and lowering venous)

Question 8

If cardiac output increase and total peripheral resistance is unchanged what happens?

Answer 8

= arterial pressure will increase + venous pressure will fall (more kicked out = raising arterial, lowering venous as taken from there)

Question 9

If cardiac output decreases and total peripheral resistance is unchanged what happens?

Answer 9

= arterial pressure will fall and venous pressure will rise (less kicked out = lowering arterial, raising venous as hasn’t been taken from there)

Question 10

What happens if the tissues need more blood?

Answer 10

arterioles and precapillary sphincters will dilate = fall in peripheral resistance = heart need to pump more to maintain arterial pressure high and venous pressure low

Question 11

What is the equation for cardiac output?

Answer 11

CO = SV X HR –> 70kg = 5L/min

Question 12

What is the equation for stroke volume?

Answer 12

SV = EDV (end-diastolic vol) – ESV (end-systolic vol) = typically 70ml

Question 13

What does the ventricular compliance curve show?

Answer 13

The higher the venous pressure the more the heart fills

Question 14

Outline the frank-starling law of the heart

Answer 14

The more the heart fills, the harder it contracts (up to a limit)

If you stretch the fibres of the heart before contracting it will contract harder

Question 15

Increased venous return leads to?

Answer 15

Increased left ventricular end-diastolic pressure and volume = increase in SV

Question 16

What does the length tension curve for cardiac muscle show?

Answer 16

If sarcomere length is too short filament overlap interferes with contraction.

In cardiac muscle, also get an increase in Ca sensitivity as muscle fibres are stretched

Question 17

Why does starlings law of the heart ensure both circulation loops are equal?

Answer 17

with increased fill there is increased stroke volume which is received by the other side of the heart and the same occurrence happens

Question 18

Define contractility

Answer 18

Force of contraction for a given fibre length

Question 19

What factors increase heart contractility?

Answer 19

Extrinsic such as sympathetic stim and circulating adrenaline

Question 20

What is aortic impedance?

Answer 20

Pressure in the aorta

Question 21

List the factors that determine cardiac output

Answer 21

How hard ventricle contracts (determined by EDV + contractility)

how hard it is to ejects blood (determined by aortic impedance)

Question 22

If metabolism increases what happens to total peripheral resistance, arterial and venous pressure?

Answer 22

TPR falls = more blood supply = lowers arterial pressure and raised venous pressure

Question 23

In what situation does both arterial and venous pressure change in the same direction?

Answer 23

Standing up and exercise

Question 24

Increase SV with increased filling is what type of control mechanism?

Answer 24

Intrinsic

Question 25

What is end diastolic vol?

Answer 25

Vol in venticles at end of filling in diastole

Question 26

What is the end systolic vol?

Answer 26

Vol in ventricle at the end of systolic contraction

Question 27

How hard the ventricle contracts is determined by?

Answer 27

EDV + contractility