Heart as a Pump Flashcards
what is cardiac ouptut
volume of blood pump per min (5 L/min at rest)
equation for cardiac output
CO = HR x SV
what is stroke volume
amount of blood pump per beat
what controls heart rate
set by SA node
affected by autonomic NS
what affects stroke volume (3 things)
1) preload (venous return)
2) afterload (resistance to flow - aortic pressure)
3) strength of contraction
For LV what is preload ~ to?
end diastolic volume
factors that affect preload
1) blood volume
2) filling pressure and time (HR)
3) resistance to filling
- RA pressure
- AV stensosis
- ventricular compliance
Graph of EDPVR
what does graph mean
incr LV volume, incr LV pressure
Graph of EDPVR
what does slope mean
inverse of ventricular compliance
steeper slope = decr compliance b/c harder for ventricle to fill (hypertrophy)
how does hypertrophy affect EDPVR?
how does dilation affect EDPVR?
hypertrophy = steep slope = decr compliant
dilation = shallow slope = very compliant
for LV what is afterload ~ to?
aortic pressure
factors affecting afterload
1) aortic pressure
2) wall stress so wall thickness and radius (T= dP * R / u(thickness))
3) aortic stenosis
what is inotropy
contractility - force of contraction independent of fiber length
describes systolic fxn of heart
what is the biggest factor affecting inotropy
sympathetic tone
what is shown on EDPVR
P-V relationship during filling of heart BEFORE CONTRACTION
what does EDPVR slope mean
passive elastic properties of heart
slope = inverse of compliance steeper = less complaint
EDPVR represents the ___ on the left ventricle
PRELOAD
what is shown on systolic pressure-volume relationship
P-V relationship at PEAK OF ISOMETRIC CONTRACTION
compare slopes of EDPVR vs. systolic PV relationship
Systolic P-V relationship is steeper (pressure incr a lot for small change in volume
what properties are included in systolic PV relationship
ACTIVE + PASSIVE
how do you create the Starling (ventricular function) curve
subtract SPVR from EDPVR
what does starling curve represent?
active tension
what are all the possible y axes for Starling curve
ventricular fxn on y-axis = tension, CO, stroke volume
what are all the possible x axes for Starling curve
preload on x-axis = length, pressure, or EDV
what does frank-starling law of heart describe (3 things)
1) heart ALWAYS ON ASCENDING LIMB OF STARLING CURVE
2) heart responds to incr in EDV with incr in force
3) what goes in heart must come out
what does a violation of frank starling law lead to?
HEART FAILURE
HOW DOES incr preload affect PV loop?
shift EDV to the right
more EDV, so heart contract with more force to ensure same end systolic volume
–> INCR STROKE VOLUME
How does incr afterload affect PV loop?
shift end systolic volume to the right and shift top pressure line up
incr aortic pressure = heart work harder to eject, less time
incr end systolic volume (can’t empty)
–> DECR STROKE VOLUME
How does incr inotropy affect PV loop?
new Starling curve
shift top line up and shift end systolic volume to the left
peak pressure higher
–> INCR STROKE VOLUME (until return to original)
