hi everybody this is the video for chapter 17 part d um we're going to review cardiac output and the regulation of cardiac output but before we get into exactly what cardiac output is um let's review the three volumes the three terms that we discussed in um part c of chapter 17 in both the video and the outline so the three volumes that we discussed were end diastolic volume stroke volume and end systolic volume i'm abbreviating these terms here on the whiteboard but i want to make sure that when you're studying this and you're practicing you're writing out the all of the words because for exams i don't want you to abbreviate anything besides like oxygen carbon dioxide and water everything else has to be written out so let's review end diastolic volume is the amount of blood that's in each ventricle after ventricular diastole so that normal amount is about 120 milliliters um for end diastolic volume i always think that it's like the maximum amount that the ventricle can hold right so it's it's almost like a hundred percent it's the total amount of blood that's in the ventricles even after the ventricles are like topped off with blood now after ventricular diastole right remember the ventricles are filling in diastole then comes ventricular systole so the ventricles contract and they contract forcefully and cause the blood to be ejected out so how much blood leaves the ventricle is called stroke volume stroke volume um yeah is just the um normal amount of stroke volume is 70 milliliters and it's the amount of blood that is ejected so we can say this is like maximum volume you can come up with your own own ways to remember it i always think it's just maximum amount that the ventricle can hold stroke volume is the um amount of blood that is ejected or the amount that leaves sorry and then we always have some that remains right we always have some that remains the ventricles don't fully empty and then fully fill that that's not efficient so um there's always some blood that remains and the blood that remains is called the end systolic volume esv it's the amount of blood that remains in the ventricle after ventricular systole so after those ventricles contract how much blood is remaining and the normal amount for that is 50 milliliters and i usually say like this is the amount left over or the amount that remains however you want to think of it doesn't matter to me i also want you to be able to recognize these normal values appreciate that they may change a little bit but when we are doing calculations it's really important for you to remember what looks normal and what would be like grossly wrong so if you're doing a calculation and you calculate for stroke volume and you get 80 milliliters that's okay that makes sense that should make sense to you right it's not 70 that's not but maybe maybe they were like exercising or something there's more blood um leaving the the heart that's okay if you calculated for stroke volume and you got seven liters um that's grossly wrong like the the heart can't hold seven liters so it most certainly can't eject um seven liters per beat so um so i want you to make sure that you're recognizing these numbers and when you're doing your equations for cardiac output that you can tell when something is is wrong and it's usually just a conversion issue or the math is incorrect a little bit of math in this part of chapter 17 not a lot we're not talking calculus here we're just talking fairly simple linear equations so let's go to our first equation let me clear this the first equation is simply an equation four stroke volume so stroke volume equals end diastolic volume minus sorry my mouth talks fast my fingers write slow and systolic volume stroke volume equals and diastolic volume minus and systolic volume okay if we were given normal 120 milliliters that's maximum minus 50 milliliters that's what's left over equals stroke volume is 70 milliliters now that's the way you do the math but i want you to think about think about it think about these terms think about what they mean end diastolic means the maximum amount of blood in the ventricle okay maximum amount of blood in the ventricle minus 50 milliliters okay so i would take away what remains right and systolic volume is what's left over so if i have the value for the maximum and i have the value for the what's left over i can calculate how much left how much left is stroke volume and that calculation gives me 70 milliliters so always be thinking think about what these terms mean don't just plug and chug and do the math and try to rush through the math the math is easy these are linear equations it's just you know fairly simple math um but i want you to think about what's going on next um we have ejection fraction ejection fraction is usually how stroke volume is reported it's reported in uh like a percent so ejection fraction because it's a fraction we'll just write e f here for ejection fraction equals part out of the hole so it's the stroke volume out of end diastolic volume and we multiply by 100 to get a person stroke volume the amount that leaves and diastolic volume the whole the the total amount that we started with right so for a fraction we do part out of whole part out of pole this is the maximum amount this is the amount that left so ejection fraction is the percent equivalent to stroke volume right we want to know what's the percent of the blood that leaves the heart for every b that's our ejection fraction usually you'll see that um more often than just a volume right so instead of reporting in milliliters they would report ejection fraction which is a percent they being doctors cardiac nurses whomever is talking about cardiac physiology i don't really i don't know who they are but you know what i'm saying okay next up we have cardiac output which is the sort of title of this section cardiac output it's the amount of blood that's pumped into both the pulmonary right to the lungs and to the systemic circuit per minute in one minute it's an indication of how well the heart is functioning and how efficient the left ventricle is we need our left ventricle to be efficient why and i might ask you something like this on your test why do we care if the left ventricle is efficient first of all the left ventricle pumps oxygenated blood to the system what's in the system active tissues why do we need act why do we need oxygenated blood to go to active tissues because tissues are made of cells and our cells need oxygen right to make atp the mitochondria need that oxygen to keep making atp what's atp cellular energy if an active if cells very active it needs more oxygen to make more atp more energy more activity more energy more activity the cell is not getting oxygen cannot be active right if it's really deprived of oxygen that's not good it might die right so we we definitely need our left ventricle to be as efficient as possible do we need our left ventricle to work a little bit harder if our tissues are more active yeah yeah what happens when you exercise does your heart rate go up you think you're pumping more blood to your active muscles you are because your tissues need that oxygen to continue to be active because they got to make atp they have to continue to have that energy okay so cardiac output very important equation pretty easy equation the cardiac output is heart rate times stroke volume so heart rate times stroke volume linear equation cardiac output equals heart rate times stroke volume heart rate is in beats per minute okay so volume is in milliliters per beat please whenever you're giving me a value don't forget units if i'm asking a value for um and diastolic volume any volume you have to report it in either milliliters or liters depending on on what we're talking about heart rate you don't just say 70 70 what 70 beats per minute right so here we have the the um units for heart rate and for stroke volume yes the beats cancel out and what we're left with is milliliters per minute and that's the that's the units for cardiac output so cardiac output is milliliters per minute and remember um you can always convert that milliliters to liters if it's easier to report that way in any any um any calculation so if you're reporting thousands of milliliters we don't really do that we we would move the decimal and report it in liters okay so if cardiac output equals heart rate times stroke volume what are the two factors that would affect cardiac output well the two factors would be heart rate or stroke volume that's it so if we want cardiac output to increase if we want cardiac output to increase the two things that can happen would be an increase in heart rate and or an increase in stroke volume it's a linear equation one side of the equal sign goes up something on the other side of the equal sign also has to go up if cardiac output were decreased what would be causing it we'd either have a decrease in heart rate and or a decrease in stroke volume linear equation what happens on one side of the equal side has to happen on the other side of the equal sign so in your outline we have factors that affect cardiac output heart rate and stroke volume you see this here um let's think here okay one thing that affects stroke volume so let me just write this again cardiac output equals let's just write it stroke volume times heart rate because we're talking about stroke volume first um the first thing that is in your outline is preload um preload um is the degree to which sarcomeres stretch okay so um preload when we think of of preload and we think of the stretching of the ventricle the stretching of the muscle a really great way to think of that is um filling a water balloon right so if you put water in a balloon what happens to the balloon right it stretches more water that goes in causes more stretching same thing that occurs in our heart more blood goes into that ventricle we get more stretching that stretching is preload okay so um i think here the amount of preload is determined largely by that end diastolic volume right so again think of the the water balloon example if we have more volume inside that balloon we have more stretch so we have more end diastolic volume more blood in the ventricle we have more stretch two variables that affect edv the length of time the ventricle is in diastole think about it if that ventricle is in diastole there's more time for it to fill with blood so end diastolic volume would increase if it's in diastole a long time it has more time to fill more blood more stretch higher preload also venous return so if we are pumping and squeezing more blood back to the heart right and more blood is coming back that's called venous return more blood coming back also increases our end diastolic volume if we have more more coming back to the atria then it's the only way it's gonna the only place it's gonna go if it more comes back to the atria more has to fill into the ventricles so we would have an increased edv um there is a uh law it's called the frank starling law and um it essentially let me read what the book says frank starling law states that the more ventric ventricular muscle cells are stretched the more forcefully they contract so just the way to remember it i think um is just more and more out if there's more blood that comes in and there's a higher preload a higher stretch because of more blood that causes a more forceful contraction so the more we get in the more we can we can squeeze out the more we get in the more we can squeeze out that's frank starling so i have here for um under preload i have um blank edv so i want increased edv more blood right a higher volume that's like that maximum capacity higher volume of edv causes an increase in preload does that make sense more blood more stretch frank starling says that if i have a higher stretch i get a more contraction so a bigger push a bigger contraction causes an increase in stroke volume right if we squeeze harder we can eject more blood so going back to this equation if we have an increase in stroke volume how would that affect cardiac output it would also increase it so when we do this and we go through all of these equations we always have to go back to this equation right we always want to see how all of these things are affecting cardiac output so when when i you know i'm going to ask you this on your test and your quizzes i mean let's be honest so when i ask this on your quiz and your test and i say you know tell me one thing that's affected or whatever i've i don't know how i'll ask it i i mean i do but i'm not going to tell you if you just tell me preload that doesn't mean anything right with cardiodynamics things are moving they're going up or they're going down they're going up or they're going down so you have to tell me an increase in preload causes this a decrease in preload causes this an increase in heart rate causes a increase in cardiac output you have to tell me increase or decrease with cardiodynamics you can't just say a term heart rate well do heart rate doing what right so you have to make sure that you're you're on um you're thinking about this dynamically this is cardiodynamics okay contractility is another thing that affects um stroke volume let me clear this because it's a mess when i studied this in college and then in grad school [Music] it doesn't matter what term you use first heart rate or stroke volume when i studied this i would every time i would um write out you know an another factor i would always start my notes with the equation so i can i can see how the numbers would shift if they would go up or they would go down so that's this is what i do this is how i teach it this is how i learned it contractility um this is uh the intrinsic pumping ability of the heart the ability to generate tension so if we have an increased contractility right if we squeeze more how would that affect stroke volume what do you think it would if you're squeezing more it would eject more right so contractility causes i would say an increase in stroke volume right we squeeze more more blood is ejected how would that affect end systolic volume that would cause end systolic volume to decrease take a second think about it yes contractility anything that causes an increase in contractility anything that causes an increase in contractility is called ionotropic agent so anything that causes an increase in contractility more force more force more blood ejected if more blood is ejected out then what's left has to be less right because you're only starting with a fixed amount you're only starting with your edv whatever that number is right if you're starting with an edv of 120 and you eject out instead of 70 maybe 80 right you checked out 80 then what do you have left not 50 you only have 40 left because you only started with 120. think about it but i love this you will love it too i promise okay afterload last thing afterload think of afterload as negative afterload is a force that that um pushes back it's a force that pushes back so the blood wants to leave the wants to leave the heart afterload is the force that's pushing back it's causing less blood to leave the heart it's a force the right and left ventricles must overcome in order to eject blood from the arteries largely determined guys by blood pressure people have um artery disease even if the arteries are not near the heart if they have an artery disease and they have um like a vascular issue they would have a higher afterload afterload is not a good thing we want afterload to be a normal if after load is high it's it's not very good for cardiac output so cardiac output equals heart rate time stroke volume we're still just looking at factors that affect stroke volume um so if we have an increase in afterload right this is like a not good thing not good an increase in after lube not good so it's a force that's pushing back the blood wants to be ejected after load is pushing back so if we have afterload an increase in afterload that would cause a decrease in stroke volume because more push back the blood can't be ejected as easily so if it can't be as ejected easily less less leaves the heart so we have a decrease in stroke volume how would that effect end systolic volume and systolic volume would be increased take a second increase after after think about after load is not good after load is the pushback right it's caused by blood pressure um people of a high afterload tend to have a decreased stroke volume not getting enough blood out right if you're not getting enough blood out the amount that's remaining is higher always take it back to here right if we have a high afterload a high afterload would cause a decrease in stroke volume you have to remember don't just say it changes stroke volume i don't care that it changes stroke volume you tell me how it changes it that's the only way you're going to get the points on the exam if i have an increase in afterload you would tell me that you have a decrease in stroke volume then i would ask you how would that affect cardiac output you would tell me the cardiac output would also be decreased because of stroke volume is decreased so is cardiac output you guys so cool okay um next we have factors that affect heart rate this is um fairly easy these are called chronotropic agents anything that affects a heart rate so cardiac output equals heart rate times stroke volume anything that increases heart rate would also increase cardiac output anything that decreases heart rate would decrease cardiac output fairly straightforward positive chronotropic agents include sympathetic nervous system hormones like epinephrine um thyroid hormones glucagon they actually used to use glucagon to increase heart rate and like stimulate the sympathetic nervous system before we had like other pharmaceuticals glucagon is just a naturally made hormone um so that's what they used to do and they that that's how they would increase cardiac output negative chronotropic agents would be like parasympathetic activation remember that's the rest and digest so if we had if we were like chilling and we weren't stressed about you know anatomy and physiology and um you know or the pandemic or anything like that you would be under parasympathetic which i don't know um if anyone has experienced parasympathetic in a while but if that were the case your cardiac output wouldn't have to be so high so we would have like a you know a decrease in it not not a bad decrease just we don't we don't have a lot of active um active tissues uh and we can decrease that cardiac output body temperature also affects um heart rate which also affects cardiac output high higher body temperature higher heart rate lower body temperature lower heart rate let me share these um hi let me share my screen and the worst okay and let me show you these okay these um last three slides so these slides are in your textbook 660 uh page 663 this one's on i just love it because it kind of shows you if we increase preload or increase contractility or decrease afterload how does that affect edv how does that affect esv how does that affect stroke volume the the piece that's not here but i want you to add would be how would then this affect cardiac output so if we increase stroke volume we increase cardiac output and the flip it just um shows you the opposite so if we decrease preload decrease contractility increase after load this is how we would affect stroke volume again decreased stroke volume um decreased cardiac output and then this is awesome this over this is an overview of everything we just talked about so this is regulation of cardiac output these are things that would all decrease cardiac output these are things that would increase cardiac output i would um spend time thinking about each one of these and i would essentially just try to recreate this in my notes either in full sentences in a flow chart like this however your brain works is fine but if you know these um all of all of these factors that are decreasing or increasing cardiac output you're good to go for part d of chapter 17. and really that's that's all i have for you today thanks hopefully um this makes sense and you can now study this and then you can do your cardiac function homework this the cardiac function homework covers all of this so chapter 17 part d bye everybody