hey everyone it's sarah thread sterner sorry and calm and in this video we're going to be talking about cardiac preload versus after lobe and when you get done watching this youtube video don't forget to access the free quiz that will test you on preload and afterload so let's get started what is preload and afterload well these two terms play an important role in influencing cardiac output and cardiac output is the amount of blood that this heart pumps throughout the body per minute and it plays a very important role in maintaining tissue perfusion so your heart takes the blood it's received it's nice and fresh and oxygen and it provides that to the cells that make up our tissues and organs and our cells are very specific about their oxygen and if they don't get a lot of it they start to die and the patient starts going through those stages of shock now cardiac output is calculated by taking the heart rate and multiplying it by the stroke volume now this is where preload and afterload come into play and stroke volume is the male a blood pumped by a ventricle with each beat because stroke volume is affected by three things one thing is affected by is contractility and contractility is the strength of cardiac cells to contract / shorten now we're not really going to concentrate on contractility main thing we're gonna concentrate on are the other two factors that affect stroke volume and that is preload and afterload so let's talk about preload first now preload is the mount the ventricles stretch at the end of diastole now what phase of the cardiac cycle is vastly what's going on during this faith this is that relaxation filling phase and we're talking about the filling phase of these ventricles are being filled with blood so blood is draining down from either the right or left atrium your AV valves your tricuspid mitral / bicuspid valves are nice and open and blood is flowing down and once the have filled that is the part that we are talking about the preload so you can also refer to the preload as the in diastolic volume it's that volume amount that isn't that ventricle once it is filled at that end of that diastolic phase so now let me illustrate preload for you and to do that let's use a balloon so let's pretend the end of this balloon is our ventricle and our vin Terkel is in the diastolic phase so it's filling with blood ok now we're at the end of dice Lea once it's filled with blood and preload is the amount that this ventricle stretched once it was filled at the end of - Lea so it's the end diastolic volume now let's talk about how we can increase preload and how we can decrease preload because if we increase preload we can play a role in increasing stroke volume and this will help increase cardiac output and some cases you might want to do that like with hypovolemic shock your patient doesn't have a lot of fluid in the body so we want to increase that preload to increase stroke going to increase cardiac output so one way we can increase preload is through the administration of IV fluids and how that's given is that you stick a patient's vein with a needle you leave a cannula inside of it and it will drip fluids into the venous system now what that's going to do is that's going to increase the blood return the venous blood return to the heart so for increasing blood volume that's returning to the heart the male of volume that is filling in these ventricles at the end of astley is going to be high so we're going to have an increase preload another way we can do that is through the sympathetic nervous system stimulating that and the body can do that naturally on its own or we can give drugs to do that like vasopressors and what happens in a nutshell is you have vasoconstriction where those vessels are gonna clamp down they're gonna narrow and this is going to increase venous return to the heart so it's the same concept we're going to have more blood returned to that heart so that's going to increase the amount of volume that's going to be in that ventricle at the end of its filling face so we're increasing our preload now how can we decrease this preload where these ventricles aren't going to stretch as much at the end of dice Leiby cuz sometimes we need to do that if a patient is in fluid overload like with heart failure we want to decrease their preload in one way we can do that is through the administration of diuretics and how diuretics work is that they will use the renal system and they will remove extra fluid from the blood line and the patient will urinate that out and a type a diuretic that comes to mind is like furosemide lasix so when we give that drug that's going to pull fluid out of that blood volume and it's gonna decrease the male a blood return coming to that heart so if you don't have a lot of blood volume coming to the heart that's gonna decrease how much these ventricles are gonna stretch once they're filled hence decreasing preload another way is through vasodilation so it'll have the opposite effect of what vasoconstriction have and a drug that can do that is like nitroglycerin and what happens is instead of having the narrowing of the vessels you're gonna have dilate and they're gonna wanna and when they widened that's gonna increase blood pulling and it's gonna decrease the male and venous return coming to that heart so you're gonna decrease the amount that these ventricles are going to stretch once they have filled now let's talk about cardiac afterload okay this is the pressure that the ventricles must work against in order to get the semilunar valves open so blood can leave the ventricle and go either to the lungs or to the body and cardiac afterload is really affected by vascular resistance so if you have a high vascular resistance that that ventricle is having to pump again that's going to increase its afterload and let me illustrate this for you and explain a little bit further okay so we have our right ventricle and our left ventricle and the goal of the right side of the heart is to get blood to the lungs and in order to do that this right ventricle is coming up against pulmonary vascular resistance this is that vascular resistance I was talking about that it's gonna affect our afterload so you have the right ventricle it has to open up this pulmonic valve which is a semilunar valve and once it's open blood is gonna be shot through the pulmonary artery go to the lungs where gas exchange is going to occur and very similar over here on the left side left side has to get this a Orting valve open once it's open it's going to go up through the aorta into systemic circulation but here we have systemic vascular resistance that this led ventricle must overcome in order to get this aortic valve open so let's pretend we have our ventricle again and this is our left ventricle and my fingers that are clamping this shut is the aortic valve it's closed and this part right here is the aorta and it has vascular resistance in it systemic vascular resistance and the pressure of this is really keeping this aortic valve closed and to this ventricle can overcome this systemic vascular resistance to open it up to pump blood out so this ventricle it must overcome that vascular resistance here that's our afterload so if we have high systemic vascular resistance increase this is going to increase our afterload it's going to increase the amount of pressure that this ventricle has to overcome in order to get this a or DIC valve open so blood can be shot out through the body so let's talk about things that can increase after load and decrease after load so increase after load when you have vaso striction going on again that's a narrowing of those arteries so if we have narrowing of the arteries that it's affecting our systemic vascular resistance or if we even have narrowly faced of constriction that's affecting our pulmonary vascular resistance that's going to increase the pressure that these ventricles must overcome to get these semilunar valves open so blood can go either to the lungs or throughout the body and one thing that can increase afterload is pulmonary hypertension and we talked about this with our congenital heart defects where they have increased blood flow that keeps going to those lungs it damages the arteries that feed the lungs they narrow and you get pulmonary hypertension so if we have pulmonary hypertension this is going to increase the pulmonary vascular resistance so that's going to increase really that workload on that rot ventricle it's gonna increase the afterload because you have such a high pressure here and it's keeping this pulmonic valve closed so it's going to increase the after load the amount of pressure that this ventricle must overcome to get that semilunar valve open so blood can go throughout this system if you have a really high pressure blood pressure going on with like vasoconstriction with systemic vascular resistance that's when it increase that workload on that left ventricle and increase it's after load the pressure it must overcome to get by or to valve open to get blood to systemic circulation so after low and vascular resistance really go hand in hand now another thing that can increase after load is a valve problem so let's say we have our aortic valve it's narrowed we have a or txt enosis narrowing of a valve so we have issues an obstruction of outflow of that blood that's leaving that left ventricle so it's really this left ventricle just having to work really hard to even get blood through this aortic valve because it's narrow so that's when it increased the pressure that this the left integral has to overcome due to that narrowing of aortic valve to get blood throughout the body so a or --tx enosis can ink our afterload now what's something that can decrease after load well a lot of times we need to give drugs to patients to decrease their after code because their ventricles are exhausted so we can give them like vaso dilators dilate that it's gonna dilate the vessels out it's going to decrease vascular resistance so we decrease vascular resistance due to why mean of those vessels it's gonna decrease pressure and it's going to decrease the after load because it's gonna decrease the pressure that that ventricle must work against the gift that semilunar valve open so blood can flow out of the heart okay so that wraps up this review over preload versus after load thank you so much for watching don't forget to take the free quiz and to subscribe to our channel for more videos