CV FUN 101 Flashcards
Increases to cardiac output are resisted by:
1) increased afterload
2) decreased preload - due to less time for filling
3) decreased preload - transfer of blood from venous side to arterial side
3 fold increase in HR causes X increase in CO
64%
Decrease in HR causes:
1) decreased afterload
2) increased preload - due to venous filling and arterial emptying
3) SV increased due to greater preload via Frank-Starling mechanism
Mean Systemic Vascular Filling Pressure
when venous pressure equals arterial pressure: this is a very bad thing
Increased contractility causes
1) increased afterload (arterial pressure)
2) decreased preload (venous pressure - EDV)
3) however, ESV is also decreased
Increasing contractility is limited by
the fact that we are already at 65% of maximum contractility normally, so there is limited ability to increase it
Decrease in contractility
lower afterload
higher preload
but resisted by Frank-Starling
Increased SVR
increased afterload causes a drop in CO
venous pressure remains the same
body shifts by increasing HR and contractility
Decreasing SVR
due to vasodilation (beta-2)
decreased afterload
increased preload - increased contraction (F-Starling mechanism)
SVR and CO up
dangers of decreased SVR
brain does not vasodilate, therefore too much blood going elsewhere is bad for the brain
increased blood volume, increased venous tone, lying down
importantly these all increase CO;
increasing blood volume raises arterial and venous pressures, which by Frank-Starling increases CO
lying down and increased venous tone both cause a shift in venous circulation, whereby capacitive veins are drained and the blood goes to the central venous system
threshold for brain consciousness loss
25% decrease in blood flow to brain
maximizing cardiac output
increased contractility, decreased SVR (not too far!), increased venous resistance, increased HR
Bernoulli’s principle in CV system
across valves and in aneurism; anywhere where there is great velocity change over short distance
