Cardiac Pressure Volume Loop Flashcards
what is the cardiac equation for work?
work=pressure x volume change
what are the two types of contractions in the heart?
isovolumic and isotonic contractions
when do valves open and close in the heart?
open when pressure on the initial side is greater than the pressure of the opposite side
closes when the pressure on the opposite side is greater than the initial side
what is it called when the cardiac muscle contracts without changing volume?
isovolumetric contraction
what occurs in the MVO->MVC phase of the cardiac cycle?
the ventricle fills with blood, slight passive increase in pressure with muscle stretching. the mitral valve closes
what is another name for the end diastolic volume?
preload
what occurs in the MVC->AVO phase of the cardiac cycle?
both valves are closed and the ventricular muscle is contracting. during this time there is isovolumetric pressure increase and it ends when the aortic valve opens.
what occurs in the AVO->AVC phase of the cardiac cycle?
the aortic valve is open when the ventricular pressure is greater than that in the aorta. ventricular pressure continues to increase and then decreases near the end of contraction. aortic valve closes when pressure is equilibrated
what is the afterload? what is it equal to?
the pressure that is applied backwards by the aorta during systole
it is equal to the pressur eat the end of systole when the aortic valve closes
what occurs in the AVC->MVO phase of the cardiac cycle?
ventricle relaxes isovolumetrically. mitral valve opens when pressure is lower than the pressure in the atrium
what is the end systolic pressure volume relationship? what does it represent?
a curve that describes the maximal pressure that can be developed by the ventricle at any given left ventricular volume
represents the end systolic elastance
what is compliance? what is the equation?
how easy it is to fill the ventricle
compliance=change in volume/change in pressure
what is the compliance of a healthy ventricle?
very compliant during diastole and not very compliant during systole
what does high compliance mean?
that a small change in pressure would cause a large change in volume
what is the relationship of elastance to compliance? what does a low elastance mean?
it is the inverse of compliance
a low elastance is easy to fill
what does ESPVR provide an index of?
myocardial contractility
why is ESPVR an improved index of systolic function over hemodynamic parameters?
because it is insensitive to changes in preload, afterload and heart rate
what does the end diastolic pressure volume relationship describe?
the passive filling curve for the ventricle
describes the actual and hypothetical pressure change with increased filling of the ventrical
what happens to the ESPVR as contractility increases?
it becomes steeper and shifts to the left
what is inotropy?
contractility
what occurs to the EDPVR when compliance decreases?
there is a higher ventricular end diastolic pressure at any given end diastolic volume
what would happen to the end diastolic volume for a ventricle with decreased compliance?
it would be less than if it had more compliance
how is the amount of work expended during a contraction calculated?
afterload x preload
what is the temporal relativity of different portions of the cardiac cycle?
isovolumetric phases are relatively short compared to the phases in which valves are open
what is stroke volume?
the amount of blood ejected by the ventricle in a contraction
the difference between the end diastolic volume and the end systolic volume
what affects the stroke volume?
changes in preload, afterload and inotropy
when is the stroke volume most impacted by afterload?
when the heart is failing
what is the ejection fraction?
the fraction of end diastolic volume that is ejected out of the ventricle during each contraction
what is the equation for ejection fraction?
EF=SV/EDV (stroke volume/ end diastolic volume)
what is the typical ejection fraction of a healthy ventricle?
0.55-0.6
what does the ejection fraction dependent upon?
preloading and afterloading
what does a low ejection fraction usually reflect?
systolic dysfunction and severe heart failure
what is EF used as a clinical indicator of?
inotropy
what are the units of measurement for preload and afterload?
L
mmHg
what two conditions increase the amount of work the heart does?
pumping more blood (increased preload)
increased systemic resistance (increased afterload)
what happens to the volume pressure curve when there is an increase in diastolic end volume?
slight increase in end diastolic pressure and higher peak pressure during systole (frank-sterling law)
what occurs to the volume pressure curve when there is an increased aortic pressure?
lower stroke volume due to an increase in end systolic volume, higher aortic valve opening pressure and higher peak pressure during systole
what effect does the increase of sympathetic stimulation have on the volume pressure curve?
increased stroke volume due to a decrease in end systolic volume and increased peak pressure during systole
how much does can the ejection fraction increase by with increased sympathetic stimulation?
15%
what is the main effect that parasympathetics have on the heart?
negative chronotropic effect
decrease the heart rate
what are the two main cardiac sympathetic consequences?
positive chronotropic effect and positive inotropic effect (increased heart rate and contractility)
what effects do increased afterload and preload have on stroke volume?
afterload decreases and preload increases
what regulates cardiac output mainly?
oxygen demand by the cells of the body
