Lec 17 Venous Return Flashcards
How does CO change in right atrial pressure?
decreased CO with increased right atrial pressure
Where is steady state CO on frank-starling curve?
- steady state CO is where frank-starling curve intersects venous return curve
What 3 variables can change venous return curve
- arterial resistance
- venous compliance
- blood volume
What does the starling curve represent?
- the function of the heart in isolation
- CO increased with increased preload
What is difference between venous return curve and starling curve significance?
starling = heart in isolation
venous return curve = function of entire circulation
What is the venous return curve [axes]? what does it show?
- function of entire circulation
- y intercept = max flow at zero atrial pressure
- x intercept = mean systemic pressure = pressure present if no flow
What is relationship between blood flow into atrium and atrial pressure?
when atrial pressure lower –> easier for blood to flow into atrium
What is true of relationship between cardiac output and venous return in steady state?
- cardiac output = venous return in stead state
- steady state occurs at the intersection point of venous return and starling curves
What does the flat portion on left of venous return curve represent?
negative pressure in the atrium
What happens to starling curve when you alter contractility?
- new curve intersects venous return curve in different location = alter steady state
- decreased contractility = smaller slope [less SV for same LVEDP]
- increased contractility = bigger slope
How does positive inotropic effect alter steady state?
- increases CO of steady state
- decreases right atrial pressure
How does negative inotropic effect alter steady state?
- decreases CO of steady state
- increases right atrial pressure
What happens to venous return curve when you alter contractility?
nothing
what happens to starling and venous curves when you alter contractility?
increased contractility –> bigger slope of frank starling [decreased contractility –> smaller slope]
contractility does not change venous return
what happens to starling and venous curves when you alter blood volume?
frank starling: no change
venous return: parallel shift [shift right with increased volume, shift left with decrease volume]
– changes both x and y intercepts
what happens to starling and venous curves when you increase TPR [arteriolar constriction]?
increased TPR
- decreased slope of frank starling [shift right]
- decreased slope of venous return [same x intercept, smaller y intercept]
decreased TPR
- increased slope of frank starling [shift left]
- increased slope of venous return [same x intercept, bigger y intercept]
How does increased blood volume effect alter steady state?
- increased CO
- increased right atrial pressure
How does decreased blood volume effect alter steady state?
- decreased CO
- decreased right atrial pressure
How does increased TPR alter steady state?
- decreased CO
- unchanged right atrial pressure
How does decreased TPR alter steady state?
- increased CO
- unchanged right atrial pressure
What does increased TPR signify?
increased afterload
What does increased afterload do to SV and starling?
- decreased SV/CO
- shifts starling curve to the right
What do venoconstriction/decreased venous compliance do to venous return curve? to starling curve?
nothing to starling curve
to venous return:
shift right [shallower slope, same Y intercept, bigger x intercept]
-
What do venoconstriction/decreased venous compliance do to steady state?
- increase in CO due to increased preload
- higher right atrial pressure
General rules of 3 ways to alter venous return
change in blood volume
- parallel shift of venous return curve
constriction/dilation arterioles
- rotation of venous return curve, no change x intercept
constriction/dilation veins
- rotation venous return curve, no change y intercept
What is y intercept of venous return graph?
maximal flow with no atrial pressure
What is x intercept of venous return graph?
venous pressure with no flow
How does increased blood volume change the intercepts of venous return? what does this mean?
- increased x intercept: increase no-flow pressure
- increased y intercept: increase maximal flow
How does arteriolar dilation change the intercepts of venous return? what does this mean?
- same x intercept: no change in no-flow pressure because most blood in the veins
- increased y intercept: resistance decreases –> max flow increases
How does constriction of veins change the intercepts of venous return? what does this mean?
- bigger x intercept: alters no-flow pressure because most blood in veins
- same y intercept: no change in max flow because this is determined by arterioles
What changes occur in heart failure?
- decrease in contractility due to damaged myocardium
- retain fluids to increase preload
- chronic sympathetic stimulation to improve myocardial performance
How does chronic sympathetic stimulation in heart failure alter CO/venous pressure?
- increase CO
- decrease venous pressure [from just MI state bust still higher than original]
What happens to steady state immediately after MI?
- no change in venous return curve, right shift in frank starling [= decreased contractility]
- steady state: increased venous pressure, decreased CO
What happens to steady state after MI + fluid retention [with just MI as baseline]?
- get no change in frank starling from MI state
- get parallel right shift in venous return
- steady state: increased venous pressure, increased CO from immediately after MI but still lower than normal
What happens to steady state after MI + fluid retention + sympathetic stimulation [with MI + fluid as baseline]?
- get no change in venous return curve
- get left-shift in frank starling from MI + fluid state [but still to the right of the original healthy]
- steady state: decreased venous pressure compared to MI + fluid, increased CO compared to MI + fluid [but doesn’t return fully to normal]
Why is increased atrial pressure a problem?
increased atrial pressure –> iincreased pressure in plumonary system, this is why heart failure is congestive
What 4 relationships to represent circulation
- output vs right atrial pressure [frank-starling]
- blood flow vs arterial pressure
- arterial volume vs arterial pressure
- venous volume vs venous pressure
What 3 constraints of circulation relationships
- cardiac output = venous return
- venous pressure about = to right atrial pressure
- arterial volume + venous volume = constant
