okay so we're going to start talking about the cardiac cycle and we're going to be discussing this diagram here um i don't want you to get intimidated by this diagram i know there's a lot going on here but hopefully we'll be able to break it down into its separate components and it will be much more easy to to grasp so this diagram is called wiggers diagram and it was named after the cardiologist and physiologist who first drew it and that was dr carl wigger so before we start breaking wieger's diagram let's start talking about the cardiac cycle using just a different approach and so if we look at this figure here this diagram and we start right here sorry and we start right here looking at the picture what you will notice is that all four chambers of the heart are open and they are relaxed so what will then happen is that blood will be rushing from the atria into the ventricles um and this is before any kind of contraction happens there's no contraction happening in the atria and there's no contraction happening in the ventricles so as soon as the av valves open the mitral valve on the left and the tricuspid valve on the right most of the blood is just simply going to move from the atria into the ventricle just by the effect of gravity as a matter of fact about 80 percent of blood is going to move in this manner that is then going to be followed by atrial systole or atrial contraction the atria are going to contract and they're going to continue ejecting blood into the ventricle this is what we would call the atrial kick and surprisingly this atrial kick is only responsible for 20 percent of ventricular filling so the majority of ventricular filling happens passively um and 20 percent would happen um actively by the atria by atrial contraction okay so now we now blood has moved from the atria into the ventricles now what's going to happen is ventricular systole now the ventricles are going to contract but if you pay close attention and you look here the ventricles are contracting but blood is not being ejected because what happens is as your ventricles start filling with blood right we start off at maybe 5 to seven millimeters of mercury then we go into ventricular filling right and we end at about 12 millimeters of mercury but if you recall our normal blood pressure is going to vary somewhere between 120 and 80 millimeters of mercury so in order for the ventricles to be successful in ejecting blood and pushing blood through the aortic valve we need to increase ventricular pressure to a value that is at least greater than the diastolic pressure and so if we're starting off at 12 millimeters of mercury the ventricles need to contract and start building up pressure that can exceed the pressure of um that's present in the aorta which is going to be the diastolic pressure so this brief period of time in which you are going to have ventricular contraction but no ejection is actually called the period of isovolumetric contraction or isovolumic contraction this is going to be very brief but nonetheless it is present what is eventually going to happen is that your ventricles are going to generate enough pressure to open the aortic valve or the pulmonic valve as we're talking about the right heart we're going to open up the aortic valve and as a result blood is going to rush out of the ventricle and into the aorta and systemic circulation this is ventricular on the second phase of ventricular systole and this is what we would call ventricular ejection now after systole is over after your ventricles contract and expel blood your va what's going to happen is that they're going to start relaxation so diastole just like systole is made up of different components the early phase of diastole your ventricles are going to start relaxing and pressure is going to drop now as now at first pressure though is if we draw a heart maybe something like this right and so this is your aortic valve and this was the mitral valve you're only concerned right here now about ejecting blood so blood is go is being ejected but then as your ventricles relax what's gonna happen is blood will now be moving in the opposite direction now as blood attempts to move in the opposite direction the aortic valves are going to close shut you're going to close shut not allowing blood to come back into the ventricle but your ventricle still has high pressure and this high pressure is going to prevent blood moving from the atria back into the ventricle and so just like we had a period of isovolumetric contraction we're going to have a period of isovolumetric relaxation in which the ventricles relax but the av valves are closed shut and the semilunar valves are also closed shut there's going to be a brief period of time until the pressure in the ventricle is low enough actually lower than the pressure in the atria only then only then will the mitral and tricuspid valves open to allow blood to flow back into the ventricle and start ventricular filling and the cardiac cycle continues and so this cycle just goes on and on and this is what we refer to as the cardiac cycle so a complete diastole and systole together compose the cardiac cycle so again we start by blood rushing into the ventricles passively that is followed by the atrial systole or the atrial kick to get that last 20 of blood into the ventricles this is followed by a period of ventricular contraction but no ejection what we would call isovolumetric contraction and this is going to last until the ventricles generate enough pressure that exceeds the pressure in the arteries after that you're going to get ventricular ejection blood is actually going to rush out of the ventricle then the ventricles are going to start relaxation and blood is going to flow back and close the aortic valves this is followed by the period of iso volumetric relaxation all the way until the pressure in the left ventricle becomes lower than the pressure in the left atrium then when it becomes lower then the mitral valves are going to open allowing blood again to enter back into the heart and the cycle continues this figure shows exactly the same thing and the reason why i just wanted to include it is because it has it shows the electrocardiogram or the ecg tracings that coincide with the different phases of the cardiac cycle so the p wave that you see here represents atrial depolarization or rachel contraction as you see there the qrs complex represents a ventricular contraction and the t wave represents the ventricular repolarization okay so now we can go back to wigger's diagram and start dissecting this a little bit i want you to notice here that we have pressure we have volume and everything that's happening down here on the x-axis this is then going to be considered time right okay i want to start talking about wiggers diagram by or actually let's continue talking about the different curves so this dashed line here is your aortic pressure we're going to discuss this later i have a separate slide for this um in red here is your ventricular pressure left ventricular pressure all of this is looking at the left ventricle the dashed line here that that's happening right here this is your atrial pressure curve looking at the blue line this is your left ventricular volume and finally here is your ecg and then your phonocardiogram the most important of these are going to be the ventricular pressure curve and the ventricular volume curve although these two are also very important and we will be talking about them so let's start talking and let's start the cardiac cycle here right at this time point what happens your your valves open your mitral valve is open allowing blood to rush from the ventricle uh sorry from the atria and all the way into the ventricle then you can see the volume increasing that makes that makes sense now after that blood is going to continue rushing into the left ventricle but at a slower pace and so keep that in mind the first period is kind of rapid and we would call it the rap period of rapid inflow or rapid ventricular filling the second period um we're still getting ventricular filling but it's slower and we'll call this diastasis now all of a sudden you should notice that there is this slight increase in ventricular filling this is due to the atrial kick or atrial systole providing that 20 percent so we can break down diastole into three main phases one would be the phase of rapid inflow two would be diastasis and three would be atrial systole the first two amount for eighty percent of ventricular filling and this last phase amounts to about 20 percent of ventricular filling what i also want you to notice is on the ecg you see the p wave here this is the electrical activity representing atrial depolarization and is followed by atrial systole and always remember that electrical activity precedes mechanical activity so you're going to see the changes in the ecg first then you're going to see the mechanical activity happening later okay so great so now the atria contracted and they started pushing in blood and that is going to end here now the ventricles are going to start contracting but remember your end diastolic pressure or the pressure at the end of diastole was somewhere around 12 millimeters of mercury this is not high enough to match what's happening in your systemic circulation your stomach circulation has higher pressures so the ventricles are trying to open the door but there is resistance so what's gonna happen is that they're gonna push push push build up resistance build up pressure until that pressure is great enough to actually exceed the pressure in the systemic circulation and you can see that by this brief period between these two lines i drew these two black lines here in which there is no change in ventricular volume however if you pay close attention you see a significant rise in ventricular pressure but look here at this dashed curve that represents aortic pressure only when the red curve surpasses the dashed line right which is aortic pressure is when you actually open up the aortic valve and you actually get blood ejecting out of the left ventricle and into the aorta this is also represented by the sharp decrease that we see in ventricular volume due to ejection of blood right so there you go you have your ejection but then ventricular volume starts reducing until it's actually lower at right here it's actually lower um pressure starts reducing that volume pressure starts reducing until it's lower than the pressure in the systemic circulation right because if you extend this dashed line let's use a different color maybe green if you extend this dash line like that right once pressure is lower then your aortic valves are going to close shut but yet your pressure is higher than the pressure the pressure in the left ventricle is still higher than the pressure in the atria and so you're going to get this period of isovolumetric relaxation in which you're going to get a decrease in pressure in the ventricles but no change in ventricular volume because the mitral valve has not opened yet why has it not opened yet because the pressure in the left ventricle is still greater than the pressure in the left atrium this is going to remain the case until your pressure in the ventricle is lower than the pressure in the atrium and i zoomed in here because i want you to see this the same thing that we saw up top so here we saw that you only get ejection if the left ventricular pressure or the red curve surpasses the dashed line which is aortic pressure same thing here you will not get filling unless the red curve which is left ventricular pressure is lower than the dashed curve which is your atrial pressure so the same thing happens once pressure is lower and then that your mitral valves will open and we can start this whole process once again so the aortic valve [Music] aortic valve opens you get ejection followed by isovolumic relaxation then diastole rapid inflow diastasis and atrial systole when we look at the phonocardiogram your heart sounds your love and dub right your heart sounds only happen when or they happen due to the closure of the valves so if you're listening to the heart when the valves close they make a sound and then you can listen to that sound using a stethoscope so where are the valves closing well the valves close at a bunch of different time points they close here your mitral valve is going to close right this will represent what we would call s1 but also you're going to have a closure here where the aortic valve closes and we would call this s2 so s1 is your lub and s2 is your dub lub dub lub dub lub dub that is closure of these two valves and so it's important to note that the period between s1 and s2 represents systole and the period between s2 and the next s1 represents diastole you should also note that the time period between s1 and s2 or the time period for systole is a little bit shorter than the time period for diastole so the cardiac cycle is actually one-third in systole and two-thirds in diastole okay um you sometimes you see this third heart sound right this is s3 or what's known as a ventricular gallop it's a third heart sound and it would happen if you have a compliant heart patients with heart failure one type of heart failure in which they have the the the heart chambers are dilated and they're compliant and then you can hear actually the sound of blood flowing in against that compliant heart and that is what's going to cause s3 and finally we want to go over the atrial pressure curve which you see right here and this is the dashed line right over here so if you take a closer look you will see that we have three waves we'll have the a wave we'll have the c wave and then we will have the v wave that you see right here so what are these waves and what do they represent so looking at the a wave right here the a wave actually just represents atrial systole so when the atria contract to get rid of that 20 percent of ventricular volume or that extra amount of blood that's remaining in the atria at the end of ventricular systole the atria contract you see an extra amount of blood increasing in the ventricles this is going to generate some pressure in the atria and that's going to be your a wave this is then right at this point right here this is when the atria will stop contracting and the ventricles will actually start contracting now when the ventricles contract you can imagine that some blood is going to push on the aortic valve which is still shut but also some blood is going to make its way back into the atria this is a very small amount of blood but nonetheless a small amount is actually going to enter the atria and then the pressure from the ventricles is going to cause the mitral valve to close shut when the mitral valve closes the leaflets of the valve kind of encroach a little bit and protrude into the atrial chamber this encroachment or protrudement or protrusion of the leaflets into the atrial chamber is what is going to generate the c wave and then as the pressure as the ventricles get rid of um of the blood you're at the same time the atria relaxes or is nature is already relaxed since here but the atria will start filling up again with blood as it receives blood coming in [Music] from the right side from the pulmonary circulation so the v wave actually just represents atrial filling so this is going to be atrial filling the a wave will be atrial contraction atrial systole and that c wave is going to represent the pressure increase in the atria due to ventricular contraction so moving on looking at the aortic pressure curve and in the aortic pressure curve um very similar to what's have what we would what we talked about and then the colors here represent what's happening here and so the red curve is where you start having the isovolumetric contraction of the left ventricle right but then as pressure in the left ventricle exceeds pressure in the um in the aorta that's when you're going to actually start getting ejection um the already valve opens and blood starts ejecting out into the aorta this reaches a top pressure this top pressure we refer to as your systolic blood pressure so the systolic blood pressure is simply that highest pressure that will be achieved during the cardiac cycle then pressure will start decreasing when pressure decreases blood is going to flow backwards and that backward flow of blood hits the leaflets of the aortic valve and closes it shut and that's why you get a little bit of rebound a rebound effect so you get decreased decreasing you get that slight rebound effect this is called your dicortic notch and this rebound is the insurance that's that happens due to that rebound of blood against the aortic valve and then pressure starts decreasing again until it reaches the lowest pressure in the systemic circulation or in the aorta before the next ejection occurs the lowest pressure is what we would call the diastolic blood pressure okay and the process happens again so if we go back here then this is your um let's use uh the purple this is your aortic curve you see it happens you see the diacortic notch and the insurance and then the decrease in pressure until it happens and occurs once again and it follows through with every cardiac cycle all right so what are the effects of the autonomic nervous system stimulation and cardiac output so here um you're going to see this curve a lot so the cardiac output is graphed on the y-axis and we're going to use right atrial pressure so we're looking at cardiac output as a function of right atrial pressure normally this is what your curve would look like and so you would see that in a higher right atrial pressure will usually lead to a higher cardiac output until a certain degree it's going to flatten out when you have a strong sympathetic stimulation that's going to push this curve upward and slightly to the left if you have a strong parasympathetic stimulation it's pushing the curve downward and to your right what are the main components of cardiac output cardiac output is your stroke volume multiplied by your heart rate and you can see that relationship down in this curve stroke volume in red and heart rate in green what i want you to notice is that we increase our stroke volume only to a certain extent after which we kind of reach this plateau and once we reach this plateau any further increases in cardiac output is going to be mediated by increases in heart rate not by increases in stroke volume so we kind of have an upper limit and a plateau for stroke volume that we don't have for heart rate for heart rate we do have an upper limit for heart rate but you can see that the relationship is linear all the way until you hit that limit while for stroke volume you're going to hit that limit quite early and then it just remains flat after that atrial arterial pressure also has an effect on cardiac output so our bodies so arterial pressure actually if you think about it we talked that the ventricles are not going to open until the pressure in the ventricle exceeds the pressure in the systemic circulation so what if someone has high blood pressure has hypertension and the pressure in the systemic circulation is just too great in order for them to actually get blood out of the heart the heart needs to work so much harder that's why we refer to this arterial pressure as afterload right it's not really pressure but that's what we're going to refer to it as because just easier to think of it and it works and we will explain these um or the concept of afterload and preload later um but if you think about it the greater the arterial pressure the greater the heart has to work our hearts can normally match that and it shouldn't be much of a problem when physiology is working normal but we do reach a limit around maybe i don't know 100 here it shows 150 um 170. after that what you see is that your cardiac output will will drop as arterial pressure increases at 250 cardiac output will drop all the way down to zero and so it's important to realize that and this is one reason why maintaining proper arterial blood pressures is actually very important and how a patient who has chronic elevated blood pressures how that is going to affect their heart and that's why a lot of these patients can end up with heart failure because just the heart can't keep up with the high demand in order to maintain cardiac output but for the most for the majority of the time um and especially when this is not a chronic problem your heart can maintain cardiac output constant at about 5 liters per minute throughout the wide range of blood pressures right this is your the normal physiological range this is where your blood pressure is normally going to be and you can see that the heart does a good job in maintaining cardiac output quite constant regardless of these fluctuations but if the fluctuations are chronic or if they exceed these these numbers you may your heart will not be able to regulate so this figures just shows you the efficiency of cardiac output autoregulation across a wide range of blood pressures all right thank you so much