Concepts of preload and afterload of the ventricles. Stroke volume output and cardiac output

Question 1

preload definition

Answer 1

initial stretching of cardiomyocytes before ventricular contraction

Question 2

preload - factor 1

Answer 2

venous return

the volume of the blood returning back to the heart from systemtic + pulmonic circulation

higher venous return = higher preload

Question 3

preload - factor 2

Answer 3

ventricular compliance

= ability of ventricle to change shape when blood pressure + blood volume increases

higher compliance = higher preload

Question 4

preload - factor 3

Answer 4

atrial contraction

= ability of atria to contract filling ventricles with blood causing them to stretch more

more atrial contraction = more preload

Question 5

preload - factor 4

Answer 5

body position

lying down = more venous return = more preload
upside down = less venous return = less preload

Question 6

preload - factor 5

Answer 6

venous tone

more SNS activity = more vasoconstriction = more bloodlflow to the heart = more preload

Question 7

preload - factor 6

Answer 7

length

there is an optimal length for the cardiomyocytes to be stretched
if too much stretching = too much blood = bad contraction = bad CO

Question 8

preload - factor 7

Answer 8

frank starlings law
= relationship between SV + EDV

• more blood flow
• more force of contraction
• cardiomyocytes stretched to optimal length
• actin-myosin interact more

Question 9

preload - factor 8

Answer 9

blood volume

more blood volume = more venous return = more preload

Question 10

afterload - definition

Answer 10

• the resistance the heart’s left ventricle must overcome
• in order to be able to eject blood into aorta
• during contraction phase

Question 11

afterload - factor 1

Answer 11

blood pressure

= pressure exerted on the vessel walls by fluid inside when passing through vascular system

more BP = more afterload

Question 12

afterload - factor 2

Answer 12

viscosity

thicker blood = more hematocrit = more vascular resistance = more afterload

Question 13

afterload - factor 3

Answer 13

aortic compliance

if aorta can stretch without difficulty then its easier for the ventricles to fill with blood
= less afterload

Question 14

afterload - factor 4

Answer 14

valves

bad valves (stents) = more pressure needed to open them = higher afterload

Question 15

afterload - factor 5

Answer 15

systemic vascular resistance

= resistance in systemic circulation when left ventricle tries to eject blood

Question 16

afterload - factor 6

Answer 16

pulmonic vascular resistance

= resistance in pulmonic circulation when right ventricles tries to eject blood

Question 17

stroke volume

Answer 17

= volume of blood pumped by the left ventricle
in 1 cardiac cycle

depends on
- preload
- afterload
- contractility

SV= EDV - ESV
= 70ml/min

Question 18

cardiac output

Answer 18

= volume in blood pumped by the whole heart in 1 cardiac cycle

depends on
- stroke volume
- heart rate

CO = SV x HR
= 500ml