Cardiac Function Flashcards
What is the Heart’s job
Pump blood
How much blood in one beat gets ejected?
1 stroke volume
How do you measure cardiac output?
SV*HR=CO
What is a normal cardiac output?
5.7L/min
What are two ways you can regulate cardiac output?
Heart rate
Stroke volume
What’s the easiest way to change or regulate CO
Heart rate
How do you alter the heart rate in order to regulate CO?
With a chronotrope (any substance that affects HR)
How can you change the stroke volume so that you can change CO?
- Altering preload (frank starling) (volume at end of diastole)
- Altering afterload (force-velocity) (systemic BP)
- Contractility (Ca2+ sensitivity)
When preload is changed, how will the heart pump different?
It still pumps exactly what it is given, so more force is generated in order to eject extra load.
When changing preload, what changes?
EDV
When changing preload, what stays the same?
ESV
CO between left and right side of heart
They match
Changing preload is changing what law
Frank starling
What relationship do you change when you change afterload?
Force velocity relationship
Increased work the heart has to do
What stays the same in changing the afterload?
EDV
What changes in changing the afterload?
ESV
If the afterload is increased
Heart will spend more time generating force and less time ejecting volume
What does changing contractility do
Changes muscle performance at any preload or afterload
What also means how efficient the heart is
Contractility
How does changing contractility work
Alters calcium handling sensitivity of TnC
What are substances that affect contractility?
Inotropes
What do positive inotropes do
Increase contractility
- increases SV by decreasing ESV
- heart more efficient
What do negative inotropes do
Decrease contractility
- decrease SV by increasing ESV
- heart less efficient
What kind of inotrope causes the heart to generate more force and eject more blood?
Positive inotrope
On the loop graph, what do we look at to determine changes in contractility?
Look at change of the slope from end of systole to 0. This indicates contractility if its slanted
If the ESV is 50mls and the EDV is 150mls, what is the stroke volume?
150-50=100
If the ESV is 50mls and the EDV is 150mls and heart rate is 100bpm, what is the cardiac output?
150-50=100
100*100=10,000ml/min (10L/min)
Predict the effect of a negative chronotrope of diastolic filling time
Increased
Series of curves relating preload to cardiac output
Cardiac function curve (frank starling curve)
Altering preload (venous return) on cardiac function curve does what
Moves along the same curve
Altering contractility or afterload on a cardiac function curve does what
Makes a new curve
What two types of graphs does afterload show on
Frank starling, and vascular function
On a cardiac function curve, what happens if you increase contractility?
A new curve will appear higher up on the graph
On the cardiac function curve, if you decrease contractility, what will you see?
A curve below the normal curve on the graph
If you add a beta agonist, what will this do to the cardiac function curve?
It will increase contractility so it will give us a curve higher up on the graph above the normal line
What will sympathetic stimulation do to a cardiac function curve
Increases contractility so the curve will be higher above the normal curve
If you add Ca2+, what will this do to the cardiac function curve
It will increase contractility, causing the curve to be higher up on the graph than the normal line
If the preload is the same, but cardiac output is increased what does this mean
Increased contractility
If you add a positive inotrope, how does that change the cardiac function graph?
Causes the curve to be up higher than the normal curve because of increased contractility
If you give someone a negative inotrope, what will this do to the cardiac function graph?
Cause the curve to be lower than the normal one due to decreased contractility
What will a B-blocker do to the cardiac function curve?
Cause the curve to be lower than the normal curve due to decreased contractility
How do you get a change on the same curve on the cardiac function graph?
Change preload or stroke volume
Series of curves relating to venous blood pressure to venous return
Vascular function curve
What does the vascular function curve show
Shows that as RA pressure increases, venous retune decreases
-CO would also fall because no blood flow
Changing what things would cause the curve to be shifted in vascular function curve
- blood volume
- vascular compliance/resistance (SVR)
What will decreasing the resistance do to pressure
Increase it
On the vascular function curve, what does decreased resistance look like?
It will be a curve that is higher up on the graph above the normal curve.
Harder to pump blood
What does increased resistance look like on a vascular function curve?
A curve below the normal curve
If you increase blood volume, what will this look like on a vascular function curve?
A curve above the normal curve
If you increase the blood volume, what will this look like on the vascular function curve?
A curve lower than the normal one
As pressure in RA increases, what happens to venous retune as well as cardiac output?
Both decrease
What does combining the cardiac function (frank starling) curve and the vascular function curve do
Allows for comparisons of venous retune and CO and physiological changes can be visualized
On the combined function curve, where is the steady state?
Where the two lines meat
Changes to inputs on the combined functions curve does what
Shifts lines, new intersection is the new steady state
PNS does not cause increased contractility directly, but how can if decrease contractility indirectly?
Because PNS will increase preload, which then causes increases contractility
What does a B blocker do to contractility and afterload
Decrease contractility, increase afterload
