 My name is Dr. Kamal and I'd like to welcome you on behalf of MedSmarter to our cardiac cycle video. So cardiac is a very high yield subject just because the number one killer in the US is cardiovascular disease. So definitely expect to see plenty of questions when it comes to cardio and especially cardiophysiology. So to help you guys with the cardiac physiology and the cardiac cycle, I want to do this video to break it down and help you understand what exactly is going on in the heart. So this is how your heart is functioning. So basically the mitral closes indicating, you know, the end of filling and then we need to get all of that now the left ventricle is nice and big. So we need to contract, get that blood out into the aorta because the body needs all of that freshly oxygenated blood. So this is how your heart is functioning when it comes to that. So that's how your heart should be functioning normally. So that's indicated by this black square. So the black square is how your heart should be functioning in a normal scenario, you know, not exercising, not with non-hypertensive patients and not fluid overloaded patients. But the step one exam definitely wants you to know also what happens in these other scenarios. So what happens if we have a scenario where we have a lot of contractility. So say you're exercising and your heart is contracting with additional force or what happens with increased afterload. So we have a lot of pressure in the aorta that the heart has to overcome or what happens if your fluid overloaded like those pregnant patients or say that there's just a lot of edema. So there's a lot of fluid retention. So what will happen in these patients? So we'll talk about these scenarios in detail. So what happens with high preload is something that we have to take into account called stroke volume. So stroke volume is basically this line right here. So this horizontal line. So the stroke volume basically looks into how much blood we had at the filling point and then how much blood after ejection is left over. So the difference between the two. So the wider this graph, the more the stroke volume, the smaller the graph when it comes to horizontally is the less the stroke volume. So in preload we have more filling. So preload you always want to think of the load of the heart of basically coming in from the SVC and IVC into the right atrium. So the more sort of fluid we have coming into the heart, the more preload we have. So that's basically designated in this graph by you see the elongation of the filling phase. So if you can reason that out, if we have more blood coming into the right ventricle and left ventricle now we're going to increase our stroke volume. So you can see that demonstrated here in the graph via the pink lines. So the pink lines are showing you if you had a lot of fluid overload then this is basically what would happen to the graph. So you would have more diastolic filling and that would correspond to the high preload. So then we have a scenario with increased afterload. So increased afterload you want to think of scenarios with hypertension, maybe some aortic calcification, aortic thickening. So anything that doesn't allow the normal expansion of the aorta and anything that's causing increased back pressure to the heart via the aorta. So with this increased afterload scenario now we're going to have high aortic pressures. So with high aortic pressures now this is going to decrease the stroke volume. So this is demonstrated in the graph here via the green lines. So if you can see this green line, when we talked about in a normal heart that the heart has to overcome the pressure in the aorta. Now you can see here the heart has to go through a lot more contraction for it to overcome this pressure in the aorta. And so this isovalometric contraction phase is elongated. And the problem with this is because we're spending all this time contracting to overcome the pressure in the aorta. Now we've wasted that time and the ejection phase gets drastically reduced. So if you can see here we're decreasing the stroke volume because now we don't have enough time to get the blood out. So this is in turn the contraction, the ejection phase is shortened. And now we're not getting all the blood out. So you can see increased end systolic volume. So now at the end of systole, we still have all this blood remaining. So if you can picture an overworked heart, which is very common in these hypertensive patients, basically they have very high heart rate. So they have very high resting heart rates. And this is a big factor in that the heart to overcome all that back pressure and afterload, it needs to basically pump very, very quickly in order to get whatever little time it has in the ejection phase. So if you can see the ejection phase is shortened and then it comes back to relaxation, and then again even filling time is shortened as well. So if you can picture, you see the horizontal is greatly reduced in a patient with high afterload. So in the horizontal line, this is again showing you the stroke volume. So you see in normal patient, we have end diastolic volume minus end systolic volume. So you see end diastolic volume versus end systolic volume. So normally we have a nice wide graph. So we're filling up the heart nicely, and we're also contracting and getting all of that blood out nicely. But in increased afterload, you can see why that would be reduced, visually represented here. So the last scenario I want to talk about is a scenario in which we'll have high contractility. So this could be a scenario where we have some sort of beta agonist on board or we're exercising, so we're sending an endogenous signal to the heart for it to contract more thoroughly. Or we could have a medication like digoxin, which also increases contractility. So this scenario is depicted by the blue line. So this blue line here shows you what happens when the heart is basically contracting to get that extra bit of blood out of the heart. So if you can see here, the graph is again going more wide. So this is depicted by an increased stroke volume. So an increased stroke volume here means that we're getting more blood out of the heart. So at the end of systole, if you can see here, we're getting more blood out. So you can see the left ventricular volume depicted at the bottom of the graph. Now this is decreasing. So we're basically in times of need of cardiac output, now we're getting more blood out of the heart. So the heart is doing an even better job at contracting and getting every little drop out of the left ventricle. So that's why we're going to have decreased end systolic volume. So that's a summary of the entire cardiac cycle. Very, very high yield. You definitely want to have a good understanding. Don't go through just simple memorization when it comes to the cardiac cycle. You want to visualize what exactly is going on in the heart. So visualize the different scenarios in which we would have high afterload, we would have high contractility, or in which we would have high preload. And it helps to sort of think about what measures the heart can go through to sort of deal with these scenarios. Okay? We would definitely like you to share this video. Also like it, subscribe to the channel. We're regularly adding additional medical questions, content, and then you can also use a special promo code right below and that will give you a discount as well.