Compliance - Decreased blood pressure Find out how compliance allows arteries to store elastic energy (and lower pressure). Rishi is a pediatric infectious disease physician and works at Khan Academy.
Compliance - Decreased blood pressure
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- Alright I'm going to compare two individuals.
- One individual with very compliant blood vessels and that person as a result of the fact that they are compliant is going to be very happy.
- And then one person with very non compliant vessels. And that person will be sad.
- And we also have 2 parts of the heart cycle. We have systole and diastole.
- We are going to do it both for systole and diastole.
- I'll write it out again because I want to make sure we see clearly the difference between someone with compliant blood vessels and someone with non compliant vessels.
- Remember non compliant means having stiff blood vessels.
- And the processes that cause this are things like arteriosclerosis for the large vessels or arteriolosclerosis for the small vessels.
- Lets divide it out with a large line.
- So lets imagine that we have now for our first person who has compliant blood vessels in systole. What will that look like.
- So lets say you have your heart here and I'm going to stretch out the aorta.
- It doesn't normally look this way but I'm going to try and show you what it would look like in a person that has the ability to have nice flexible arteries.
- It would look something like that.
- And the same region of the heart and blood vessels in someone with non-compliant arteries would look like this.
- So again this is right when the heart is squeezing blood out.
- So we know blood is flowing through here.
- And in fact just to highlight the fact that this person has very stiff vessels let me show you these atherosclerotic plaques sitting inside their arteries making them stiff.
- So really they are unable to be flexible. They are not ballooning out.
- Let me show you what the vessel kind of would look like just so you can see how ballooned out this persons blood vessels really are.
- So this is that inner dimension of the vessel; this is what it would look like if they didn't balloon out but in fact they did.
- So lets take a point, maybe there and there, and lets call that the spot where we are checking pressure energy.
- I'm going to talk in terms of energy.
- This is where we are actually detecting pressure energy.
- This bar represents actually how much energy we actually see.
- So this is a representation of how much pressure energy is at that spot.
- Lets assume that even though we know the vessels are different in these two people that their hearts are the same.
- They are working equally hard and putting a similar amount of energy into the blood vessels.
- We know that the pressure energy should be quite similar between the two from the hearts standpoint.
- We also know that blood is moving out so we can look at movement energy as well. I'm going to draw that as a bar also.
- We've got movement energy in yellow and pressure energy in purple.
- As you look at this you will see that the movement energy, I'm going to assume for the two cases is similar, so similar sized bar.
- Actually in people with atherosclerosis they have compensation so they actually start looking a little different.
- But just for right now lets imagine that we are taking a snapshot at the moment after these vessels became hard.
- So that is the movement energy and I will label it movement.
- In purple is the pressure energy.
- What I want you to notice is that I haven't addressed a very important point which is that this is ballooned out.
- So we know that just like in a balloon or rubber band if you stretch it out you are going to get some extra energy we call elastic energy.
- That elastic energy would be something like that. It would actually take up a chunk of that pressure energy.
- Its the pressure in the blood that is actually causing the vessels to balloon out.
- This is the elastic energy which just took a chunk of that pressure energy away.
- What is left is the leftover pressure energy.
- We have really no ballooning on this side so really it is all pressure energy.
- So if I was actually going to measure how much energy, obviously I don't measure movement energy or elastic energy, the only thing I really measure in the doctor's office is the pressure energy.
- They say "Hey, your pressure was so-and-so".
- Let's give numbers so we can keep all this straight.
- This person might have a blood pressure of 160 and the person who is happy with compliant vessels might have a blood pressure of 120.
- We can see exactly why: Because some of that pressure energy got taken away and stored as elastic energy.
- You can already see how elastic energy is really helpful because it helped you lower the pressure.
- Now what happens in diastole.
- Now the heart is resting. The heart is taking a quick breather to refill.
- The vessels are now a little bit less full of blood because a lot of that blood has already left and gone on to the foot and the face and the different parts of the body.
- This is what the inside of the vessel looks like again just to keep that straight in our heads.
- In this non compliant person's vessels they actually look basically the same. It is not going to look any different.
- You've got your atherosclerosis. That didn't go away. This is just looking at two different parts of the heartbeat, the resting and active part of the heart beat.
- So none of that goes away.
- Lets say I do the same experiment where I look at this purple X and I take a look at how much pressure energy there is.
- I know that there is going to be less than before because the heart is taking a break.
- So this is all residual, whatever is left over from systole.
- I've got a little bar of purple there and lets say the bar is about the same height here.
- I've got some pressure energy here as well.
- Already you can see that the lesson from the first part of this picture was that we have a little bit of elastic energy here and you can see that.
- Otherwise, the two vessels would look the same but you can see there are still some areas where it is a little stretched out.
- So lets draw that in here.
- There is a little bit of elastic energy left. Its not completely gone.
- Already you can see that that means in diastole my pressure is going to fall as well.
- I've got lower pressures in diastole just like we did in systole.
- This is my non compliant diastolic blood pressure.
- I would even throw up some numbers. Lets say this is 100 and maybe up here its 80. Its got to be a little bit lower.
- Notice this. This is really interesting. Notice this elastic energy here. Is it the same as the amount here?
- The answer is obviously no. Its not the same. There is less.
- The other cool feature about elastic energy is that not only does it lower your pressure which we have talked about, but it also can be used to convert it into movement energy.
- Isn't that interesting? You can use this stored elastic energy to move blood. You can use this for movement energy.
- You can see that this actually adds up. You can see that the elastic energy before is about the same as the elastic energy plus the movement energy afterwards.
- So there are 2 important points here.
- One is that the elastic energy helps lower the pressure. We saw that here are here.
- And two, is that it actually helps you generate movement of blood.
- You can actually now in diastole move some blood forward because the elastic energy is recoiling like a rubber band, and that energy has to go somewhere.
- It is going into moving some blood forward.
- It is taking a little bit of blood and saying okay, move forward a little bit.
- You actually don't have that phenomenon, that interesting cool property is not actually happening down here.
- You don't have any of that on the non compliant side.
- So these are the things I wanted to point out for you and show you why it is so important to have flexible arteries.
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