Cardiovascular - Cardiac Output

Question 1

What is cardiac output?

Answer 1

How much blood is pumped in one minute

Question 2

How much blood is pumped in one minute?

Answer 2

5L/min

Question 3

What is stroke volume?

Answer 3

Amount of blood pumped out of left ventricle per beat

Question 4

Average amount of blood pumped out by left ventricle per beat?

Answer 4

70 mL/beat

Question 5

What is end systolic volume (ESV)? And what is end of diastole volume (EDV)?

Answer 5

Amount of blood left in left ventricle at the end of systole (or contraction)

Amount of blood filled in left ventricle at the end of diastole (relaxation)

Question 6

What is ejection fraction (EF)?

Answer 6

Expressed as a %

How much blood left ventricle pumps out per contraction

Indicator of cardiac health

Question 7

How do you calculate cardiac output?

Answer 7

CO = SV x HR
= 70 mL/min x 75 beats/min
= 5250 mL/min (5.25 L/min)

Question 8

How do you calculate stroke volume?

Answer 8

SV = EDV - ESV

OR

EF X EDV

Question 9

What three factors effect EF?

Answer 9

1. Contractility
2. Preload
3. Afterload

Question 10

Example equation for EF, ESV, SV and CO

Answer 10

EF = If left ventricle fills up to 100 mL (EDV) and pumps out only 60 mL (ESV) then EF is 60/100 = 60 %

EDV = 100 mL

ESV = If 60 mL is pumped out then 100-60 = 40 mL left in left ventricle

SV = EDV - ESV
= 100 mL - 40 mL
= 60 mL/beat

OR

EF x EDV
= 0.60 x 100
= 60 mL/beat

CO = 60 mL/min x 75 beats/min
= 4,500 mL/min

Question 11

What is contractility?

Answer 11

Force of contraction of the heart muscle (the more forceful, the more blood it ejects)

Increase in contractility = increase in SV

Question 12

Starling’s law of heart - how does it relate to contractility?

Answer 12

The more blood in the ventricle, the more can be pumped out

Question 13

What is the inotropic effect?

Answer 13

How strong the heart muscle contracts without stretching heart fibres

Question 14

How can ions affect contractility and heart rate? (Ca and K)

Answer 14

Reduced Ca+ = depresses hr and contractility
Elevated Ca+ = prolongs contractions - heart failure
Reduced and elevated K+ = heart will be poorly and irregularly

Question 15

What is preload? (EDV)

Answer 15

Amount of blood in ventricles at the end of diastole - amount that can fit in left ventricle has to do with how much cardiac myocytes can stretch

Increase in preload stretch = increased force of contraction
Decrease in preload stretch = decrease force of contraction

Question 16

What is afterload?

Answer 16

Refers to resistance the ventricle must overcome to eject blood

Question 17

What happens if aorta is stiff or filled with blood? (Hypertension)

Answer 17

Left ventricle will need to work harder to overcome resistance

Same thing for right ventricle

Question 18

Can body adjust cardiac output to meet needs?

Answer 18

Yes