cardiovascular: control of cardiac output

Question 1

3 things that directly influence CO

Answer 1

preload/afterload/ cardiac contractility

Question 2

whats preload

Answer 2

degree of stretch of heart right before contraction; EDV; CVP

Question 3

whats afterload; what is it influenced by

Answer 3

force against which LV pumps

TPR and aortic stiffness

Question 4

frank starling relationship crux; implications; shape of graph

Answer 4

the fuller the heart, the more it will pump
EDV/EDP and stroke volume are correlated;
stroke volume of LV=RV
upward sloping, plateauing

Question 5

mechanism behind frank starling relationship

Answer 5

cross bridge theory: maximum tension generated when cardiac sarcomeres are stretched to 2micrometres
cardiac cells are very sensitive to stretch

Question 6

CO vs stroke volume

Answer 6

CO: vol of blood pumped per minute

Stroke vol: vol of blood pumped per heartbeat

Question 7

how does heart failure change the frank starling curve? how does the compensated/decompensated heart failure curve look? explain compensatory mechanism

Answer 7

heart failure: lower amplitude
compensated: higher than HF, lower than normal
decompensated: lower than HF
pt has heart failure-> BP drops-> water + salt excretion drops/ SNS activated/ RAAS activated-> blood volume rises/ cardiac contractility increased/ HR increases/ venoconstriction -> EDP/EDV rises-> CVP rises-> Stroke volume increases
decompensated heart failure curve kicks in as heart failure continues

Question 8

how does afterload affect CO? does it affect it to a large extent?

Answer 8

afterload does not affect CO much within physiological range.
+ afterload-> stroke volume/ ejection fraction falls-> more blood remains in heart at end of systole-> EDV and EDP rises-> stoke volume restored by frank starling mechanism
ANREP response-> Ca release-> cardiac contractility rises
HOWEVER, increased BP-> baroreceptor reflex causes BP and CO to decrease

Question 9

what is CVP affected by; what does it affect

Answer 9

volume of blood and vein capacitance

affects preload

Question 10

how does increased SNS activation affect frank starling curve

Answer 10

increased contractility + venoconstriction-> upward and rightward shift