Compensation and decompensation in heart failure | NCLEX-RN | Khan Academy
Compensation and decompensation in heart failure | NCLEX-RN | Khan Academy
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Content
2.539 -> - [Voiceover] So what do we mean when
3.139 -> we say compensation?
5.1 -> Well, let's remember that heart failure,
6.484 -> you have this decreased ability
7.827 -> to meet your body's demands, right?
10.029 -> Well, your heart and body have this way
11.408 -> of trying to make up for
this decreased ability
13.278 -> and increase the blood you supply,
15.002 -> and that's called compensation.
16.936 -> Because you're compensating
for this decreased supply.
19.405 -> But in heart failure this can lead
20.922 -> to something called decompensation.
23.327 -> So eventually you can't compensate anymore
25.551 -> and your symptoms start to get worse
26.76 -> and heart failure gets worse.
29.728 -> So there are a couple main
ways we try to compensate.
31.675 -> And each of these ways either
increase your stroke volume
34.624 -> or increase your heart rate.
36.233 -> And remember that cardiac output
37.906 -> equals stroke volume times heart rate.
39.986 -> So if you increase either one of those
41.477 -> you're gonna increase your cardiac output.
44.674 -> The first thing we're gonna look at
45.587 -> is activating your
sympathetic nervous system.
48.695 -> And this is like your
fight or flight response.
51.118 -> So, for example, what
if you're hiking along
52.932 -> in the woods and you see this bear?
54.795 -> Your sympathetic nervous
system is gonna kick in.
57.079 -> And your heart rate's
definitely gonna go up
58.717 -> and your stroke volume is
definitely gonna go up.
61.258 -> And so your body is preparing you
62.971 -> to either fight or flight, or run away.
67.756 -> So when your cardiac output goes down
69.851 -> your sympathetic nervous system kicks in.
71.806 -> And it uses these receptors
73.097 -> on the heart that tell the heart to
74.932 -> one, beat or contract
harder with more force
78.248 -> which increases your stroke volume.
80.617 -> And two, to beat faster,
81.908 -> which increases your heart rate.
83.749 -> But if you use these too much
84.885 -> they start to down-regulate.
87.324 -> Or decrease in amount.
88.495 -> So you know, there's less of them.
90.616 -> And less receptors means your heart
92.084 -> won't respond as it did before.
95.135 -> So think of it like this.
96.226 -> What if you're moving?
97.71 -> And you call a bunch of your friends over
98.992 -> to try to help you move your stuff.
101.092 -> And you know, they're glad
to come over and help you.
103.371 -> And so you move your stuff
104.457 -> and then you decide next week,
105.901 -> oh, I want to move again.
106.977 -> So you call them up again
108.173 -> and say "hey, I need some more help".
109.849 -> And they're like okay, I
guess it's kinda weird,
111.209 -> but I'm gonna come help you.
112.691 -> And then they come.
113.469 -> But then the next week you're like,
114.387 -> oh, I'm gonna move again.
115.442 -> And then you keep doing
this week after week
117.712 -> and those friends are gonna start to
118.841 -> well one, question why
you're moving so much.
120.941 -> And two, they're gonna stop
121.976 -> maybe answering your phone calls.
124.227 -> It's sorta the same thing
125.172 -> with your sympathetic nervous system.
127.665 -> When you activate it too much
128.716 -> it's gonna start helping less and less.
133.043 -> So the next big way we
can compensate is by
135.001 -> increasing this thing called preload.
137.27 -> Now preload is defined as this
pressure in the ventricles.
139.759 -> So in this lower chamber,
141.446 -> after it's filled but before it contracts.
143.644 -> So during diastole.
145.907 -> When it's filled, the walls
and the heart muscle cells
148.656 -> are all stretched out
150.224 -> because it's like filling
up a water balloon.
152.025 -> So you put the water in
it and then the water
154.327 -> causes that balloon to expand, right?
157.508 -> So the more you fill in,
159.121 -> the higher this pressure or preload.
161.337 -> So as you keep filling, the
walls stretch more and more
163.448 -> and we get higher pressures or preload.
167.138 -> To do this, to fill more,
168.332 -> to get more blood in those ventricles
170.476 -> your body releases these specific hormones
172.442 -> like antidiuretic hormone,
or we call it ADH sometimes,
176.73 -> or aldosterone, to increase
this filling volume.
181.085 -> So if the ventricles used to
have about 100 milliliters
183.326 -> at the end of diastole,
185.105 -> now maybe they have a little more,
186.455 -> like 115 milliliters.
189.051 -> This extra little bit
might not seem like a lot,
191.742 -> it's like one tablespoon,
193.415 -> but it's enough to
stretch the heart chamber
194.878 -> and muscles just a little more.
197.785 -> So that's great, but why
does increasing the preload,
200.24 -> or filling pressure, increase
the force of contraction,
203.062 -> and so your stroke volume?
205.886 -> Well, think of it like
stretching a rubber band.
208.069 -> The more you stretch the rubber band
209.558 -> the more force it'll
snap back with, right?
213.974 -> Okay, so there's a lot
going on here, right?
215.637 -> So let's go one step at a time.
217.701 -> So as you fill the
ventricles with more blood
219.956 -> it stretches those muscles out, right?
222.314 -> And just like the rubber band did,
223.748 -> when you stretch it out it contracts,
225.698 -> or it snaps back with more force.
228.118 -> And when it contracts with more force,
229.424 -> you get more stroke volume,
230.91 -> you get more blood ejected.
232.97 -> And so this guy named
Frank-Starling saw this
234.986 -> and kind of decided to cut corners
236.733 -> and create this law that says,
238.637 -> as you increase your
pressure or your preload,
241.076 -> you also increase your stroke volume.
243.4 -> And that's the Frank-Starling law.
248.41 -> Sweet, so increasing preload
increases stroke volume
251.099 -> and therefore, your cardiac output,
253.077 -> and is one way we can compensate.
255.403 -> But again, like over activation
257.108 -> of the sympathetic nervous system,
258.992 -> this is a real delicate balance.
261.528 -> So these muscles now contract
with more force, right?
263.996 -> But that means that they use
up more energy to do that.
266.98 -> And therefore, they need more blood.
269.491 -> And if there's no additional blood flow
271.01 -> coming to the heart muscle cells,
272.45 -> they can begin to die off.
276.262 -> So let's get back to that first analogy
277.599 -> where that guy's moving all the time.
279.346 -> But this time maybe he decides,
280.663 -> oh, I'm gonna pay my friends to help.
282.881 -> And so all the sudden
they all come running back
284.243 -> and then they help him move in
285.997 -> and they kinda support his weekly moves.
288.276 -> But then all of a sudden he starts
289.66 -> moving every other day,
290.9 -> and he's not increasing their pay.
293.055 -> Well, they start to get overworked,
294.407 -> and without more money,
they're gonna leave, right?
298.1 -> It's kinda the same thing
with our muscles cells.
299.612 -> They're contracting harder
and they're working harder.
302.248 -> So they need more oxygen and more blood,
303.829 -> but they're not getting that
so they start to die off.
307.991 -> So we just saw that
when you contract harder
309.438 -> you eject more blood.
311.414 -> Well, besides increasing preload,
312.695 -> there's one more way we can do that.
314.593 -> And that's gaining
muscle, that's bulking up.
317.553 -> This is also called
myocardial hypertrophy,
319.382 -> where your heart gains muscle mass.
322.387 -> And when it gains muscle
it contracts harder
324.657 -> because it's stronger.
327.15 -> So to try to make up for this
decrease in stroke volume
329.48 -> or this death of cardiomyocytes,
or heart muscle cells,
333.221 -> these surviving cardiomyocytes
335.459 -> become elongated and they grow.
337.774 -> And this causes the heart
muscle as a whole to get larger.
340.778 -> So you get this enlarged heart muscle.
344.616 -> So it's like the ones that don't die
345.58 -> are like whoa, I gotta start bulking up
347.235 -> so I can take over for these guys
348.92 -> that aren't contracting anymore.
351.752 -> And these bulked up muscle
cells contract harder,
353.858 -> they eject more blood and
they increase cardiac output.
356.909 -> Perfect.
358.382 -> But as we know, this usually
comes at a cost, right?
361.5 -> Well, more work means more oxygen
363.748 -> and more blood supply.
365.628 -> But with heart failure we know
that that's not an option.
368.51 -> And so without an increased supply
370.062 -> these bulked up cells get overworked
371.917 -> and then they start to die off.
373.986 -> Not only that, if the
heart muscle gets too big
376.69 -> the chambers start to get smaller
378.345 -> and so there's less blood
that can fill in the chambers.
384.083 -> So those were the three
modes of compensation.
386.567 -> You can activate your
sympathetic nervous system.
389.396 -> You can increase your preload.
391.233 -> Or you can gain muscle,
392.295 -> which is called myocardial hypertrophy.
395.111 -> And so for each of these,
396.268 -> our goal is to increase cardiac output.
398.639 -> By either heart rate or stroke volume.
400.888 -> But like we saw, when you use
401.909 -> any of these too much
403.42 -> it leads to unintended consequences.
405.625 -> And eventually heart failure gets worse.
407.356 -> And this is what we call decompensation.
410.606 -> So when you overuse the
sympathetic nervous system
412.473 -> your receptors start to go away.
414.561 -> And you end up with a lowered response.
417.17 -> When you increase preload,
418.802 -> you muscle cells stretch
and then contract harder,
421.122 -> but this costs more oxygen
422.819 -> and then eventually leads to cell death.
425.507 -> Similarly with hypertrophy,
426.969 -> these bigger muscles also use more oxygen.
429.839 -> And without that the cells die.
433.042 -> So not only that,
434.263 -> these three can often
feed back on each other.
436.42 -> Like the death of muscle cells
from an increased preload
438.903 -> might result in hypertrophy,
440.379 -> because those remaining
cells start to bulk up.
443.207 -> And this increases cell death even more.
445.676 -> And then as the heart weakens from this
447.359 -> it might stimulate the
sympathetic nervous system
449.221 -> to try and beat harder and faster,
451.49 -> which further progresses heart failure.
454.62 -> Most of the time it's
really difficult to pinpoint
456.548 -> which one was the initial culprit.
458.155 -> But the major takeaway
should be that compensation,
460.774 -> regardless of its intentions,
462.032 -> is often a major contributor
to worsening heart failure
464.932 -> and eventually decompensation.
Source: https://www.youtube.com/watch?v=x8aBKMYqGPY