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Current time:0:00Total duration:7:51

Compensation and decompensation in heart failure

Video transcript

so what do we mean when we say compensation well let's remember that heart failure you have this decreased ability to meet your body's demands right well your heart and body have this way of trying to make up for this decreased ability and increase the blood you supply and that's called compensation because you're compensating for this decreased supply but in heart failure this can lead to something called d compensation so eventually you can't compensate anymore and your symptoms start to get worse and heart failure gets worse so there are a couple main ways we try to compensate in each of these ways either increase your stroke volume or increase your heart rate and remember that cardiac output equals stroke volume times heart rate so if you increase either one of those you're going to increase your cardiac output the first thing we're going to look at is activating your sympathetic nervous system and this is like your fight-or-flight response so for example what if you're hiking along in the woods and you see this bear your sympathetic nervous system is going to kick in your heart rates definitely going to go up your stroke volume is definitely going to go up and so your body's like preparing you to either fight or flight or run away so when your cardiac output goes down your sympathetic nervous system kicks in and it uses these receptors on the heart that tell the heart to one beat or contract harder with more force which increases your stroke volume and two to beat faster which increases your heart rate but if you use these too much they start to down-regulate or decrease in amount so you know there's less of them unless receptors means your heart won't respond as it did before so think of it like this what if you're like moving you call a bunch of your friends over to try to help you move your stuff and you know they're glad to come over and help you and so you move your stuff and then you side next week oh I want to move again so you call them up again and say I need some more help and they're like okay I guess it's kind of weird but I'm going to come help you and then they come but then the next week you're like oh I'm going to move again and then you keep doing this week after week and those friends are going to start - well one question while you're moving so much and - they're going to stop maybe answering your phone calls it's sort of the same thing with your sympathetic nervous system when you activate it too much it's going to start helping less and less so the next big way we can compensate is by increasing this thing called preload now preload is defined as this pressure in the ventricles so in this lower chamber after it's filled but before it contracts so during diastole when it's filled the walls and the heart muscle cells are all stretched out because it's like filling up a water balloon so you put the water in it and then the water causes that balloon to expand right so the more you fill in the higher this pressure or preload so as you keep feeling the wall stretch more and more and we get higher pressures or preload to do this to fill more to get more blood in those ventricles your body releases these specific hormones like antidiuretic hormone or we call ADH sometimes or aldosterone to increase this filling volume so if the ventricle is used to have about 100 milliliters at the end of diastole now maybe they have a little more like a hundred and fifteen milliliters this extra little bit might not seem like a lot it's like one tablespoon but it's enough to stretch the heart chamber and muscles just a little more so that's great but why does increasing the preload or filling increase the force of contraction and so your stroke volume will think of it like stretching a rubber band the more you stretch the rubber band the more forest it'll snap back with right okay so there's a lot going on here right so let's go one step at a time so as you fill the ventricles with more blood it stretches those muscles out right and just like the rubberband did when you stretch it out it contracts or it snaps back with more force and when it contracts with more force you get more stroke volume and get more blood ejected until this guy named frank starling saw this and kind of decided to cut corners and create this law that says as you increase your pressure or your preload you also increase your stroke volume and that's the frank-starling law suite so increasing preload increases stroke volume in therefore your cardiac output and is one way we can compensate but again like over activation of the sympathetic nervous system this is a real delicate balance so these muscles now contract with more force right but that means that they use up more energy to do that and therefore they need more blood and if there's no additional blood flow coming to the heart muscle cells that can begin to die off so let's get back to that first analogy where that guy's moving all the time but this time maybe he decides to oh I'm gonna pay my friends to help and so all of a sudden they all come running back and then they help him move and they kind of support his weekly moves but then all of a sudden he starts moving every other day and he's not increasing their pay well they start to get overworked and without more money they're going to leave right it's kind of same thing with our muscle cells they're contracting harder and they're working harder so they need more oxygen and more blood but they're not getting that so they start to die off so we just saw that when you contract harder you eject more blood well besides increasing preload there's one more way we can do that and that's gaining muscle that's bulking up this is also called myocardial hypertrophy where your heart gains muscle mass and when it gains muscle it contracts harder because it's stronger so to try to make up for this decrease in stroke volume or this death of cardio myocyte sore heart muscle cells these surviving cardiomyocytes become elongated and they grow this causes the heart muscle as a whole to get larger so you get this enlarged heart muscle so it's like the ones that don't die are like whoa I got to start bulking up so I can take over for these guys that are contracting anymore he's booked up muscle cells contract harder they eject more blood and they increase cardiac output perfect but as we know this usually comes at a cost right well more work means more oxygen and more blood supply but with heart failure we know that that's not an option and so without an increased supply these bulked up cells get overworked and then they start to die off not only that if the heart muscle gets too big the Chamber's start to get smaller and so there's less blood that can fill in the Chamber's those were the three modes of compensation you can activate your sympathetic nervous system you can increase your preload or you can gain muscle which is called myocardial hypertrophy and so for each of these our goal is to increase cardiac output by either heart rate or stroke volume but like we saw when you use any of these too much it leads to unintended consequences and eventually heart failure gets worse and this is what we call D compensation so when you overuse the sympathetic nervous system your receptors start to go away and you end up with a lowered response when you increase preload your muscle cells stretch and then contract harder but this costs more oxygen and then eventually leads to cell death similarly with hypertrophy these bigger muscles also use more oxygen and without that the cells die so not only that these three can often feed back on each other like the death of muscle cells from an increased preload might result in hypertrophy because of those remaining cells start to bulk up and this increases cell death even more and then as the heart weekends from this it might stimulate the sympathetic nervous system to try beat harder and faster which further progresses heart failure most of the time it's really difficult to pinpoint which one was the initial culprit but the major takeaway should be that compensation regardless of its intentions is often a major contributor to worsening heart failure and eventually decompensation