The PV (Pressure-Volume) loop is a graphical representation of left ventricular function, plotting volume on the x-axis and pressure on the y-axis, showing the cardiac cycle's phases: filling (mitral valve open), isovolumetric contraction, ejection (aortic valve open), and isovolumetric relaxation; the end-systolic pressure-volume relationship (ESPVR) line reflects cardiac contractility, with steeper slopes indicating higher contractility, and various valvular pathologies alter this curve—increased afterload (aortic stenosis) shifts the curve rightward with concentric hypertrophy and S4 sound, while volume overload conditions (aortic regurgitation, mitral regurgitation) shift it upward with eccentric hypertrophy and S3 sound, whereas mitral stenosis reduces filling without significant ventricular changes.
PV Loops Explained: Cardiac Physiology & Pathology
Added:hi guys this is meg tutor berry and welcome to my channel in today's video we're going to be talking about pv loops we'll start by looking at a normal pv loop and then talk about some pathology so let's look at a normal pp loop the first thing you want to do is look at your axis so on your x axis you have left ventricular volume on your y axis you have left ventricle pressure okay um so i like to start from point a point a is my end systolic volume so let's say it's about 50 ml esv remember that esv is whatever little volume that's left behind from the previous cycle okay so that's esv so that's what we start with and once we have our esv we can start our filling phase remember with the for the filling phase i need my mitral valve to be open so blood can come down and fill the ventricles so point a is also where the mitral valve opens and then we go from point a through c increasing in volume without any change in pressure so this is my diastole or my filling phase once i'm done filling the mitral valve will close and at point c let's say it's about 120 ml this is my end diastolic volume it's the final volume of the ventricle at the end of diastole so about 120 ml okay and this is where the mitral valve will be closed remember that the spinal volume is also called the preload in the heart so once the mitral valve is closed um the left ventricle needs to push the blood out into the aorta right but that doesn't happen instantaneously there's a there's a brief period when both the aortic valves and the mitral valve is closed and our ventricle goes through this period of isovolumetric contraction what happens during this period is that the ventricle is constantly increasing is is contracting and increasing left ventricular pressure and as soon as left ventricular pressure equals or exceeds the pressure of the aorta so aortic pressure that's when the aortic valve opens okay so we go through a period of iso-volumetric contraction and you can see that here because the volume doesn't change because the blood can't leave and but the pressure in the left ventricle increases at point d left ventricular pressure exceeds aortic pressure and this is where the aortic valve opens this work that the left ventricle does in order to open that aortic valve that's called our afterload okay so once the aortic valve is open we can start our systolic phase or the ejection phase so this is my systole this is where the left ventricle is actively pushing the blood out of the aorta so the left ventricle volume if you can see um decreases we go from about 120 ml to about 50 ml the point of highest pressure is also called our systolic blood pressure okay and then once we're done with the ejection phase the aortic valve will close and the blood that we're left behind will be our end systolic volume and just like we had an isovolumetric contraction phase there will also be an isovolumetric relaxation phase so iso volumetric relaxation phase and then we'll start the cycle all over again so stroke volume is the difference between our end diastolic volume minus and a systolic volume so in this case it would be 120 minus 50 ml and remember that the area under this curve so all of this area here let's make this blue is our stroke work okay so um this is what a normal pv uh loop looks like one thing i want to talk about is this espvr line this espvr line is dependent on contractility or it's representative of the contractility of the heart remember that when contractility increases the slope of the espvr will be higher so you'll have a greater slope if the contract energy decreases the slope of espvr the line would decrease with it what are some things that can increase or decrease contractility so let's write that here so things that can have a positive effect on contractility one thing remember is a greater preload because remember if you fill the ventricle more the ventricle stretches more and the inotropy or the contractility will be higher okay it's the starling's law so more preload more contractility but also remember your sympathetic system can come in and increase your contractility what are some things that have a negative effect on contractility so a lower preload so if you feel the heart less the muscles will stretch less and your contractility will be uh lower and you'll have a decreased slope of espvr and also your parasympathetic system um can have a negative effect on your contractility and just to show you um if this is our normal espvr line if the curve is like that this is the higher slope versus if the curve ever changes to something like this this would be a lower slope which would represent lower contractility okay so that's what a normal uh pb loop looks like and um we should move on to the pathology so let's start with aortic stenosis remember in aortic stenosis your aortic valve is to nose and it's harder for the left ventricle to push out blood so less blood goes through the aorta and my left ventricle has to work harder to push the blood out okay so what we see is the afterload increases right you can see that the amount of work that the left reticle has to do is much more right so the after load would significantly increase in aortic stenosis and like we said the left ventricle is pushing out less blood so we only are able to push out let's say half of the blood that we that we of the end diastolic volume so the end diastolic volume is about 120 we're only pushing out about six um let's say 80 instead of a normal 50 milliliters okay so your end systolic volume increases because you're left with more blood and because you're pushing out less adv is almost same just slightly increased and the stroke volume remembers the difference and the stroke volume decreases what are some heart changes we see with aortic stenosis remember when um the left ventricle has to work harder we have we see this thing called concentric hypertrophy in the walls of the left ventricle this is when the walls of the left ventricle get really thick okay they get really bulky and thick and this is what we call concentric hypertrophy with concentric hypertrophy the sound associated is an s4 okay it's a late diastole sound and i like to think of it as um you know when you already have lots of water in a bucket and you like try to throw more water onto an already full bucket that's the sound of an s4 okay so what happens when you get um concentric hypertrophy is that the chamber of the heart becomes smaller so your bucket is smaller it holds less water to begin with right and if you're trying to squeeze uh push more blood onto it you're going to hear that s4 the murmur associated with aortic stenosis and i think we all know this mnemonic so it's aortic stenosis systolic murmur okay it will be a crescendo decrescendo type murmur i actually have a really nice uh video um that i'll be sharing a link to in the description of this video this i it's great to understand the different heart sounds and the different murmurs okay let's look at aortic vigors remember aortic regert is when your aortic valve is floppy and leaky so a lot of the blood regurgitate back regurgitates back into the ventricle okay so what happens when you get regurgitation your end diastolic volume would always be higher right because all that blood comes back and plops back into the ventricle so your end diastolic volume is very high your end systolic volume is also higher than normal and you can see that here but the systolic volume in this case it increases quite a bit because the increase in end diastolic volume is much greater than the slight increase in our end systolic volume um the changes that we see with aortic vigors remember when all the blood plops back into the heart here we have a type of volume overload right it's not that the heart has to pump harder it's just that it's filling up more than it needs to so when when we see a volume overload problem the type of hypertrophy we c is an eccentric or dilated hypertrophy and the heart sound with an eccentric hypertrophy is an s3 and i just like to think of it like that so if we have like a giant bucket and water like plops into the bucket because this is an early diastole sound s3 is an early diastole so think of filling the bucket in the early phases and that water is going to make a splush sound at the base of this uh you know big empty bucket and that's your s3 okay and the murmur uh for aortic regurge will be the opposite of um aortic stenosis so this would be a diastolic murmur okay one of the really important things we see with aortic records is that because all the blood a lot of the blood falls back into the ventricle um the diastolic blood pressure actually which is the the blood pressure out in the arteries um it decreases quite a bit okay because our cardiac output in a sense decreases the systolic blood pressure remains about the same so our pulse pressure which is the difference between the systolic minus diastolic um this difference would increase right so because let's say this stays about 120 but our diastolic you know falls down to instead of 80 it falls down to 60 so the difference would increase right so that's one thing we see with aortic regurg okay moving on to mitral regurge so mitral regurge is when the mitral valve rigger is floppy and leaky so when this heart when this left ventricle is in the systole and trying to push out blood through the aorta now the blood is actually going two directions it's going back into the atrium and it's also going into the aorta okay so one of the things that's really interesting with mitral weak urge is that the total stroke volume right increases because more blood ends up leaving the heart but the apparent stroke volume is actually low because yes more blood is leaving the left ventricle but only a part of it is getting into the aorta a lot of it is actually going back into the atrium so the apparent stroke volume of how much actually goes into the aorta is less than it would normally be um and in this you can see your end diastolic volume again is quite increased because um this is a regurgitation and the the blood will fall back and essentially come back to the ventricle and but the end systolic volume is much lower because we said the ventricle is pushing more blood out right so like we said the total stroke volume has increased the ventricles pushing more blood out and again this is because of starling's law so when more blood is filling the ventricle it's pushing more blood out but not all of it is going into the aorta and that's why the apparent stroke volume is lower so in this case esb also decreases and the stroke volume again would be quite increased and remember the murmur you remember misses this is the acronym so this is a systolic murmur because it's during this the the pathology is during this the pushing phase of the systole the sound again because it's a volume overload in the left ventricle every time you see a volume overload you always see s3 which is early diastole and the heart changes again because there's volume overload would be an eccentric or dilated um hypertrophy okay and the last one is mitral stenosis mitral stenosis is pretty interesting because it doesn't really affect the left ventricle at all the mitral valve when it becomes denotes is actually the left atria that gets enlarged because it starts to hold on to more blood okay so the the problem really what we see is a left atrial enlargement um for mitral stenosis and um in terms of our edv esp remember that it's it's getting harder to push the blood down into the ventricle so our end diastolic volume will be low and systolic volume will be low stroke volume would be low um and afterward also because of startling spores we're not filling enough so we won't be pushing hard enough so it looks like it mitosinosis looks very much like a normal pv loop because like we said pv loop represents left ventricular volumes and pressures so in terms of the shape it looks very normal it's just that everything has been shifted um to the left to lower volumes that's the only thing we see with mitral stenosis and because it's not any kind of hypertrophy in the ventricle there is no sound associated there's not an s3 not an s-port associated with mitral stenosis but there is a murmur though and mitral stenosis remember is a diastole murmur so it's a diastolic murmur it's the opposite of mitral veg and it should make sense because it this would be a problem in the filling phase when we're trying to fill the left ventricle so that is everything hopefully this helps thank you for your time
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