hi this is dr. cat fleece in video J we're going to focus on the mechanical phases of heart contraction collectively referred to as the cardiac cycle to be more specific the cardiac cycle includes all of the physical or mechanical events that occur in one heartbeat so all of the things the physical things that we can witness with our eyes during one heartbeat now considering that on average we have about 70 to 75 beats per minute it should make sense to you that one heartbeat is going to last just a tad bit less than a seconds so on average about 0.8 seconds we're going to be using some terminology over and over again when we talk about systole which can either refer to the atria or the ventricles we're referring to contraction so systole is a fancy way of referring to contraction notice that the contraction of the atria lasts a lot shorter than the contraction of the ventricles for obvious reasons they're much smaller diastole refers to the relaxation of the the chambers there's actually also a period when the heart is totally relaxed that is both the atria and the ventricles are completely relaxed as a matter of fact about half of the length of a heartbeat about 0.4 seconds is totally relaxed and we refer to that as the quiescent period as in being quiet the heart is not doing anything physically keep in mind not physically electrically there's all kinds of stuff happening I put down here the dicrotic notch we probably will not point that out right away it has something to do with the change in pressure that occurs in the aorta as during blood flow I'll explain that to you later in the event I forget be sure you do look up what we mean by the dicrotic notch please now as we dive into learning about the cardiac cycle and all the different phases one thing to never forget is that fluids and gases always follow their pressure gradients blood is a fluid air isn't a gas so here in the cardiovascular system we're going to focus on the blood flowing from areas of high pressure to areas of low pressure following it's pressure gradient once we get through the respiratory system we're going to talk about the flow of gases whether it's oxygen or carbon dioxide even others moving from areas of high concentration to or higher pressure I'm sorry to lower pressure areas they're going to follow their pressure gradients so here we see a figure out of your open Stax book that summarizes the cardiac cycle and it has a lot of information in it I'm going to very carefully tease it apart for you step by step and eventually I'm hoping that you will be able to literally mimic what I have done and possibly create your own diagram to better understand the cardiac cycle the first thing I'm going to do is point out to you the bigger portions of the picture notice that we have all of this portion of the picture that is green well that is the ventricular systole face and because it's a little hard to see that I'm going to write that over here in the green so this is ventricular systole all of that green on the other hand everything in the blue all of this represents as it shows here ventricular diastole so all of all of the light blue color represents ventricular diastole okay now we're going to look at the smaller circle and within this smaller circle we have a rather short systole for the atria so here are atria are contracting well everything in the purple on the other hand refers to atria relaxing so atria relaxing the purple atria contract in this beiges color what we should do next then is compare the ventricular phases which of course are on the outside and the blue and the green with the atrial phases which are the inside circle in the beige and in the purple and what you can see is that when the atria are contracting our ventricles are relaxed and when our atria are relaxed we're going to see that our ventricles are first contracting but then they're spending quite a bit of time relaxed as well this tells us as I mentioned earlier that there's actually a substantial time period when both atria and ventricles are relaxed so let's take a look at that so everything in the purple is atrial diastole and everything in the light blue is ventricular diastole and so what we see then maybe I should use a different color we'll use yellow notice that full diastole of the whole heart that is both atria and ventricles starts here where we see the beginning of this ventricular relaxation but by then the atria are already relaxed both atria and ventricles are relaxed throughout here throughout here and then here we see the beginning of atrial systole and notice that that indeed is about half of the cardiac cycle so about point four seconds not easy to see this yellow but we discussed this on the previous slide already now we're ready to discuss the more specific phases that make up the cardiac cycle where we are going to add some more terminology and I'm going to point out these new terms first before we explain when they occur and why we're all familiar already with diastole and systole but let's take a look at the terms ISO volumetric isovolumetric contraction versus ISO VAT volumetric relaxation when we use this term isovolumetric ISO always refers to the same so we're talking here about the same volume for a very brief moment we're going to see that the heart is going to not change the amount of blood that is present in it the volume within the heart is the same and this is right before a hard goes or the ventricles go into full-blown contraction full-blown systole to where they can literally eject the blood so we go from isovolumetric contraction to ventricular contraction ventricular ejection then we're going to once again see an ISO volumetric phase called the isovolumetric relaxation and once again for a fraction of a moment we do not see any change of volume in the chuckles this occurs right before the heart especially the ventricles fully relaxed and that will allow for blood to start filling the ventricles again now another observation to make with these isovolumetric phases both of them is that all of the valves are going to be closed during an ISO volumetric phase all four valves are going to be closed in the isovolumetric contraction phase and in the isovolumetric relaxation phase so that's a really very important thing for you to remember all valves are closed here and all valves are closed here okay great let's now start in the period where the heart is completely relaxed meaning during that quiescent period which I marked in the yellow and more specifically we're going to start therefore here so both the ventricles and the atria are relaxed and consequently the pressure within the heart is very low there's nothing squeezing the heart so the pressure is low and that allows for blood to start trickling in through the superior and inferior vena cava through the pulmonary veins even the coronary sinus so blood is trickling first into these atria and as the blood starts to trickle into the atria they can push against it can push against the valves here somewhat which are rather relaxed anyway because we don't see much contraction at this point or any contraction and so from the atria the blood trickles via the atrioventricular valves slowly but surely into the ventricles now while this is happening pretty soon the atria start to contract and they do that of course because they have become depolarized with the help of the intrinsic conduction system which in turn is manipulated by the extrinsic conduction system and I would have liked to have seen that there is already a little bit of blood in these ventricles here that seems to be to make much more sense to me so by the way as the blood is beginning to trickle into the fully relaxed heart and even at the time when the atria begin to contract as we see here the semilunar valves these valves here are closed so the semilunar valves are closed those are the valves at the base of the pulmonary trunk and the aorta and you'll see why that is in just a moment so our pulmonary semilunar valve is closed as well as our aorta k-- semilunar valve is closed okay so our aorta I'm sorry our atria begin to squeeze and more and more blood collects into the ventricles and as that blood begins to collect in the ventricles the blood begins to push up against our atrioventricular valves and that pushes the atrioventricular valves closed so that is why we see that now all the valves are closed our semi Lunars were already closed and now with the pressure of the blood building up in the ventricles the atrioventricular valves closed as well and we see for a very brief moment that all valves are closed and this is called the isovolumetric contraction because all valves are closed the blood is not going anywhere and the volume in the heart remains the same in the in the ventricles in particular now during all of these mechanical activities and the blood flowing the intrinsic conduction system has been doing it's job and so we were beginning to see that depolarization is reaching those Purkinje fibers and that leads them eventually to the systole of the ventricles the ventricles slowly starts to start to build up pressure and eventually the pressure of the blood is going to be such that they that the blood can push open the semilunar valves the AV valves remain shut this is what we refer to as the ventricular ejection phase the blood is literally ejected from the ventricles into the pulmonary trunk or into the aorta now let's stop here for just a moment because we need to ask ourselves how much pressure must that blood in the ventricles build up to push open little semilunar valves well the pressure in the ventricles must exceed output the V pressure which is the ventricles the ventricles pressure is going to have to exceed the pressure in the aorta and the pressure in the pulmonary trunk if not the blood will stay within the ventricles it's not going to be able to go anywhere so once again we need to create a pressure gradient we need to create a high pressure environment in these ventricles which they do by squeezing squeezing contracting contracting and ultimately the pressure inside of the ventricles exceeds that of the pulmonary trunk and the aorta and the blood automatically will follow it's pressure gradients from the ventricles into these vessels because the semilunar czar forced open great so the blood is being ejected it goes into these arteries and very quickly our ventricle are beginning to repolarize and also therefore relax and consequently the pressure in our ventricles starts to drop so now we're going to see that the pressure within the ventricles is going to turn to a pressure that is lower that the pressure is now lower than the pressure in the blood vessels in the aorta and the pulmonary trunk in which direction is the blood going to want to go now well it's going to want to go backwards in the aorta and the pulmonary trunk and that's going to literally close our semilunar valve so it's the brief backflow of the blood in the pulmonary trunk and the aorta due to the fact that the pressure in the ventricles is dropping so much compared to what the pressure is in these blood vessels that now are semi Lunars closed and once again we're back to an ISO volumetric face but this time the heart is relaxed so we call it isovolumetric relaxation phase these phases of isovolumetric time periods are very brief by the way and so very soon as the heart's pressure especially the ventricular pressure continues to decrease we're going to see that then blood starts to fill the heart again as a matter of fact more than likely blood already has begun to be able to fill the atria somewhat during this isovolumetric relaxation phase of the ventricles and we start the whole cycle all over again so what is so crucial for you to understand in this diagram is the fact that blood always flows from an area of high pressure to low pressure and the pressure is manipulated by the heart when the atria contract the pressure in the atria Rises such that the blood literally is moved from the atria into the ventricles when the when the ventricles contract they can contract hard enough to where the pressure inside of them overcomes the pressures in the arteries that leave the heart and consequently the blood will be able to leave and be ejected by opening valves in this case the semilunar valves analogously the ventricles can create a very low pressure area to where the blood begins to flow backwards in the vessels this is a brief moment because immediately our semilunar valves closed preventing further backflow and ultimately the pressure within the heart is low enough to where the blood from the low-pressure superior inferior vena cava will trickle in so your veins have very little pressure left in them and you will see will learn:about blood vessels and their pressure in our next chapter but for now accept the fact that the pressure of the blood in the superior and inferior vena cava is very very low but still slightly above zero when the heart is fully relaxed the pressure inside of the heart is zero so that is enough of a pressure gradient to where blood starts to trickle in now that was a very long discussion of the cardiac cycle and that explains or shows to you how important it is for you to understand the cardiac cycle we can now relate the cardiac cycle to the EKG remember that the EKG is a graphical representation of the electrical events but if we know when the electrical events occur we can then deduce when the mechanical events occur so for instance right here is the P wave during which time the atria depolarize so through ordering the p-wave we're going to see in response to depolarization of the atria will see that the atria contract and they do this for a little while until we see that the ventricles have become depolarized and then they can start to contract so throughout the depolarization of the ventricles which occurs during the QRS complex we're going to see ventricular systole systole so we first have atrial systole the squeezing of the atria then they begin to relax and then the ventricles begin to squeeze and they continue to squeeze into the t wave because we need to have repolarization of the ventricles occurring first before we can see ventricular diastole so near the end of the T wave definitely we should see that the ventricles start to relax and of course we already have our atria atria relaxed so this time period here that I'm showing you now would literally be when the heart is fully relaxed that quiescent period so from the beginning of the contraction of the atria to the very end of the relaxation of the ventricles is literally one heartbeat those are all the mechanical events that occur during one cardiac cycle and that takes approximately more or less about 0.8 seconds I'm hoping that I'm making it very clear that the EKGs are the electrical events but if we know when depolarization and repolarization occurs we can therefore deduce when contraction and relaxation of our different chambers occur be sure you can distinguish that we're going to add to this presentation a quick discussion of the sounds that are created when our heart contracts after that we're going to put a lot of information together on one complex graph that we need to discuss then when the heart contracts with we we can actually distinguish between the closing of the AV valves and the semilunar valves they both create slightly different sounds and at different times in layman's terms we refer to them as the love and the dub sound the first sound the lub is the closing of the AV valves while the DUP is the closing of the semilunar valves now down the road you're going to learn how to exactly position your status cope because of course that's the instrument that you use to listen to a person's heart sounds and when you learn to more specifically position your status cope you will be able to distinguish the sounds between all four valves but if we just listen to our heart whether you know whether bear ears we hear a love and a duck and that represents the closing of AV vs. semilunar valves often people say that heart murmurs are created due to problems with valves actually there's some truth to that it's not inaccurate but most heart murmurs are actually created due to the sloshing around of the blood inside of the heart and the the anatomy on the inside of the heart tends to change somewhat as we get older it's somewhat different in young children and that might lead to some of these heart murmurs