mechanics

Question 1

define preload

Answer 1

weight that stretches muscle before stimulated to contract

Question 2

define afterload

Answer 2

weight not apparent to muscle in resting state, only encountered after starting to contract

Question 3

isometric-preload relationship

Answer 3

greater preload leads to greater force because it stretches before contraction

Question 4

isotonic-afterload relationship

Answer 4

greater afterload leads to reduced shortening and velocity (heavier weight = reduced shortening but same force)

Question 5

preload-afterload relationship

Answer 5

greater preload leads to greater shortening for given afterload

Question 6

in vivo correlates of preload

Answer 6

blood filling in diastole stretches resting ventricular walls, and stretch determines the preload before ejection (dependent on venous return); mre blood leads to greater contraction

Question 7

how is preload measured in vivo

Answer 7

wall stress at end of diastole so end-diastolic volume, end-diastolic pressure, right atrial pressure

Question 8

in vivo correlates of afterload

Answer 8

load against which left ventricle ejects blood after opening of aortic valve (pressure of blood in arteries); any increase decreases isotonic shortening and velocity

Question 9

how is afterload measured in vivo

Answer 9

wall stress during systole so diastolic blood pressure

Question 10

effect of hypertension on ventricular work

Answer 10

higher diastolic blood pressure (afterload) means ventricle has to work harder to expel blood as shortening reduced; must reduce otherwise blood flows backwards

Question 11

what does a pressure-volume loop show

Answer 11

how left ventricular pressure and volume change in cardiac cycle

Question 12

what signifies preload

Answer 12

A - end-diastolic volume; blood stretching muscle fibres

Question 13

what signifies afterload

Answer 13

B - diastolic blood pressure; blood pressure in aorta

Question 14

in a pressure-volume loop, what valves open and close at A, B, C and D

Answer 14

A: mitral valve closes, B: aortic valve opens, C: aortic valve closes, D: mitral valve opens

Question 15

what happens during diastole (D → A)

Answer 15

atrial pressure > ventricular pressure, so blood enters ventricles, increasing volume

Question 16

why does the pressure increase slightly during diastole

Answer 16

because end-diastole volume is increasing, so preload is also

Question 17

what happens at A

Answer 17

mitral valve closes because ventricular pressure > atrial pressure

Question 18

what happens between A and B

Answer 18

isovolumetric contraction (where walls contract but volume remains constant)

Question 19

what happens at B

Answer 19

aortic valve opens because ventricular pressure > aortic pressure

Question 20

what happens during systole (B → C)

Answer 20

blood ejected so volume falls, but pressure increases as fibres shorten

Question 21

what happens at C

Answer 21

aortic valve closes

Question 22

what happens between C and D

Answer 22

isovolumetric relaxation

Question 23

diagram of pressure-volume loop

Answer 23

benjis

Question 24

effect on pressure-volume loop of increasing preload (left ventricular filling)

Answer 24

larger volume of blood (A and B shift right), causing ventricle fibres to contract more strongly and quicker to produce a larger stroke volume

Question 25

effect on pressure-volume loop of decreasing preload (left ventricular filling)

Answer 25

smaller volume of blood (A and B shift left)

Question 26

effect on pressure-volume loop of increasing afterload

Answer 26

smaller stroke volume (C and D shift right) as ventricle walls won't shorten as much, reducing force and velocity at which blood ejected against higher diastolic pressure (C and B shift up)

Question 27

effect on pressure-volume loop of decreasing afterload

Answer 27

larger stroke volume (C and D shift left) as ventricle walls will rapidly shorten, producing a larger force and velocity at which blood ejected against lower diastolic pressure (C and B shift down)

Question 28

diagram of how preload and afterload affect pressure-volume loop

Answer 28

benjis

Question 29

define contractility

Answer 29

force of contraction of myocardium

Question 30

what measures contractility

Answer 30

ejection fraction

Question 31

what stimulation increases contractility

Answer 31

sympathetic

Question 32

effect of increasing contractility on pressure-volume loop

Answer 32

greater gradient of tangent to C

Question 33

effect of decreasing contractility on pressure-volume loop

Answer 33

reduced gradient of tangent to C

Question 34

diagram of contractility in pressure-volume loop

Answer 34

benjis