sem 2: preload and afterload

Question 1

what is cardiac output

Answer 1

volume of blood ejected per minute
CO= SV x HR
CO= BP/TPR

Question 2

what 4 factors control stroke volume

Answer 2

heart rate
contractility
preload
afterload

Question 3

what is preload

Answer 3

strecthing of the heart at rest

linked to starlings law

Question 4

what is afterload

Answer 4

stressing of the heart wall

linked to laplaces law

Question 5

what is HR controlled by

Answer 5

autonomic nerves

Question 6

what is contractility controlled by

Answer 6

sympathetics

Question 7

what is energy of contraction

Answer 7

the amount of energy required to generate stroke volume

Question 8

what is starlings law

Answer 8

the enrgy of contraction of cardiac muscle is proportional to the muscle fibre length at rest

Question 9

what is good measure of preload

Answer 9

CVP (Pressure in great veins)

Question 10

in a stretched muscle what is the less interferance of

Answer 10

mechanical interference - more crossbridge formation - increased sensitivity to Ca2+ ions

Question 11

what does after load oppose

Answer 11

ejection

Question 12

what is afterload determined by

Answer 12

wall stress

energy of contraction needed to overcome it

Question 13

what is laplaces law

Answer 13

P = 2T/r

Question 14

in a larger heart is there more or less wall stress

Answer 14

more

Question 15

what is wall tension composed of

Answer 15

T= wall stress(s) x wall thickness(w)

Question 16

in a smaller radius heart:

Answer 16

greater wall curvature
more wall stress directed to the center
less afterload
better ejection

Question 17

what does laplaces law say about arterial blood pressure

Answer 17

increased arterial blood pressure will lead to increased wall stress and increased afterload

Question 18

two causes of heart failure

Answer 18

volume overloaded( e.g. MI, cardiomyopathies, mitral valve regurgitation) 
pressure overloaded- e.g. hypertension, aortic stenosis

Question 19

what does heat failure lead to

Answer 19

increased wall stress because of equation

Question 20

how does the heart compensate with increased wall stress

Answer 20

hypertrophy

greater myocyte side- so wall stress disappated over larger area

Question 21

what is the bad thing about hyptertrophy

Answer 21

greater O2 demand, ultimately decreases contractility