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- So your heart pumps blood essentially to two places and the first place is your body. So you have your oxygenatedblood on the left side and we gotta remember that the lefts and the rights are switched because we’re looking at theanatomical view of the heart. So it pumps it out to your body and your body gets that oxygen. Your body uses it upand then circulates it back into the right side where this time it’spumped out to the lungs and gets re-oxygenatedand gets that oxygen back and then it’s circulatedback into the left side. And the amount of blood at any time pumped to your body is sortof based on this demand that your body has for blood. You can kind of think ofit like you have this gage that says, “Hey, I need this much blood “to sustain this much activity.” And this can change, so if you start working out or something, your demands might go up and your heart can accommodate for that and start pumping more blood to that body to meet those new demands. Heart failure describes this condition where the heart can’t meetthe demands of the body. So at any given time, the heart’s not able to pump enough blood tomeet the body’s demands. And there are essentiallytwo types of heart failure. The first one we callsystolic heart failure and systolic refers to systoli, which is the phase of the cardiac cycle where blood is pumped out of the heart and so systolic heart failure is when those heart musclesaren’t pumping blood with enough force. So this often means thatthose muscles are weakened and smaller than with a healthy heart and this typically makes itlook quite a bit different. And when these smaller muscles contract, they don’t squeeze as hard as they used to and this causes less blood to be ejected with each contraction.
- Now, I say contraction because the heart’s this muscle, right? So, when it contracts, it squeezes. You can kind of think of it like you have this water bottle thatyou’re holding with your hand and you squeeze the water bottle and it shoots the water out. It’s the same concept with your heart. When those muscles contract, they squeeze the blood and that’s how you eject blood to bothyour body and your lungs. With systolic heart failure, since your heart muscles are smaller, think about squeezingthat water bottle again, but just pinching it. It’s gonna be a lot harder tosqueeze the water out, right? Well, it’s the same thing for the heart with smaller and weaker muscles. It’s gonna be way harder for it to squeeze and pump that blood out to the body. You probably noticed that this heart has these sort of enlargedlooking lower chambers and at the same time, it hasthis really thin muscle wall and these are really characteristic traits of a heart with systolic failure. And these small musclesmake it really hard for it to pump blood to the body. So that was the firsttype of heart failure. The second type is calleddiastolic heart failure and instead of being a pumping problem with the muscles being too small, diastolic failure is a filling problem which is why we call it diastolic failure, because it refers to diastoli which is that phase in the cardiac cycle where the heart fills with blood. So with this type of failure, your body’s not receiving enough blood because your heart’s notfilling with enough blood to pump out in the first place. So if we jump back tothat water bottle analogy, this time you’re holding it with one hand, just like we were for the healthy heart, but instead the bottle’sfilled with less water, so even if you squeezeit with the same force as a healthy heart, lesswater is gonna be ejected simply because there’sless water in the bottle. And this is essentially what’s happening with diastolic failure. Since there’s less bloodfilling in the ventricles, even if it’s pumping with the same force, less blood’s gonna be ejected to the body.
- But why is there less bloodfilling in the chambers? Well, it’s because those muscles are actually larger in this case and they take up more space and this leaves less space for that blood to fill in to the ventricles. Okay, so far we’ve shownboth types of heart failure and each time we’ve shownit happening on both sides. Well, this isn’t always the case. It’s definitely possible tohave isolated heart failure. So maybe you only have the left side or maybe you might only haveit isolated to the right side. One important thing to not though is that usually a left-sidedcase happens first and then that ends up leadingto a right side failure. I know I’m only showingsystolic failure here, but I should not thatthis isolated failure can happen with eithersystolic or diastolic. So, depending on whichside this is happening on, the left or the right, the symptoms are gonnabe a little different. Let’s just go ahead and startwith the left side first. So since the left sidepumps blood out to the body, that means it’s coming in from the lungs and if it’s not pumping itvery efficiently to the body, that blood starts to getbacked up into the lungs. Think of it like a traffic jam. What happens when they close a lane and then they only letone car through at a time? All those other cars get backed up. It’s kind of the same thing. This blood gets backed up into the lungs because it’s only pumping alittle bit out at a time now. So a really common symptomof left-sided heart failure is fluid build up in the lungs. This is called congestion and it’s also sometimes why wesay congestive heart failure. Alright, so that was left-sided failure. Let’s take a look at right-sided failure. Again, I’m just gonnashow systolic failure, but let’s just note thatthis can either happen with systolic or diastolic.
- This time, since weknow that the right side pumps blood to your lungs, we also know that it comes from the body. And since it doesn’t pumpblood as well to the lungs, we have that traffic jam situation again, but this time it getsbacked up into the body. So patients with right-sidedfailure might start getting fluid build up intheir feet, legs and abdomen. And again, just like the left side, you have congestion or fluid build up, but this time it’s in yourbody instead of your lungs. So as a quick recap, you couldjust have systolic failure on the right side or you could just have systolic failure on the left side and it’s possible to have both. In the same way, you can have diastolic on the right side only or you could have itonly on the left side. Or you might have both. It’s even possible to have a combination of systolic and diastolic failure. So now that we’ve kindof nailed those down, let’s talk about this really important way that we measure the heart’s ability to meet the demands of the body and that’s called cardiac output. Cardiac output representsthe total amount of blood that the heart’s ableto pump every minute, usually given in litersof blood per minute. And the normal cardiac output is around five liters per minute. Now, cardiac output can be broken down into two other components and the first is stroke volume which is the amount ofblood pumped out every beat which is different than cardiac output because it’s every beat, not every minute and so we take this stroke volume and we multiply it by your heart rate, which is measured in beats per minute and those two multiplied together equals your cardiac output. So if you were to change eitherstroke volume or heart rate, for example, let’s sayI lowered stroke volume, since cardiac output’s dependenton these two variables, cardiac output’s also gonna go down and that’s what happenswith heart failure. Cardiac output is lowerbecause the heart’s not pumping as much blood per minute. This is usually becausethere’s a lowered stroke volume or a lowered amount of blood pumped out with each contraction. So usually heart failure isconsidered a secondary disease, meaning that it’s caused bysome kind of pre-existing or underlying disease thatalready affects cardiac output.
- Specifically, we’re gonnathink about diseases that cause the deathof cardiac muscle cells which are also called cardiomyoctes. And when those muscle cells die, the heart gets weaker and getsway worse at pumping blood. This lowers stroke volume and then it also lowersyour cardiac output. And when the cardiac output goes down, the heart has two optionsto increase it again. Based on our equation, that’sstroke volume and heart rate. And your heart actually does that and this is called compensation. So your heart compensatesby either squeezing harder and increasing stroke volume, or beating faster andincreasing heart rate. In the early stages of heart failure these methods canactually help quite a bit in compensating for decreased supply, but over time those surviving muscle cells become overworked becausethey’re constantly trying to either beat faster or squeeze harder. But to do either of those things, those cells need more oxygen. This is the whole issue with heart failure in the first place, adecreased supply of oxygen, those muscle cellswon’t receive the oxygen and more muscle cells tend to die off. And when more die off, strokevolume goes down even more and this causes this whole cycle to repeat which causes heart failure to get worse.
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