you'll actually notice that it makes sounds.

ドキ、ドキという音がします。

And those sounds are usually described

英語ではラブ ダブ、ラブ ダブという風に聞こえます。

as lub dub, lub dub, lub dub.

文字に書くとLub Dub です。

And if you actually try to figure out

これの繰り返しです。

what that would spell out like, usually it's

この音は何でしょう。

something L- U- B, D- U- B. And it just repeats over and over

これを説明するため、心臓の弁を拡大しました。

and over.

この絵を使って心臓の音の正体を解明します。

And to sort of figure out where those sounds come from,

まず心臓の各部の名前ですが、

what I did is I took that diagram of the heart

血液が入ってくる右心房

that we've been using and actually exaggerated

これが右心室

the valves, made them really, really

血液はここから肺に送られます。

clear to see in this picture.

そして左心房に戻り

And we'll use those valves to kind of talk

左心室へ

through where those sounds are coming from.

これが心臓の構造です。

So let's start by labeling our heart.

血液が通過する弁に注目してみましょう。

So we've got at the top, blood is coming into the right atrium

右心房から右心室へ流れます。

and going to the right ventricle.

これと同時に血液は左心房から左心室へも流れます。

It goes off to the lungs, comes back

どうして同時にこのような動きができるのでしょう。

into the left atrium and then the left ventricle.

血液は常に心臓の中を流れているんでしたね。

So these are the chambers of our heart.

肺から来た血液は左心室に送られ、

Now, keep your eye on the valves.

体を巡ってきた血液は右心房から右心室へ。

And we'll actually talk about them

つまり心臓の左右の心室は常に血液で一杯です。

as the blood moves through.

心室に血液を送り込むためには

So let's start with blood going from the right atrium this way

弁が開かなければなりません。

into the right ventricle.

これが三尖弁

Now, at the same moment that blood is actually

こちらが肺動脈弁です。

going from the right atrium to the right ventricle,

これは僧帽弁

blood is actually also going from the left atrium

左心房と左心室を区切る弁です。

to the left ventricle.

そしてこれが大動脈弁。

Now, you might think, well, how's that possible?

このように心臓には4つの弁があります。

How can blood be in two places at one time?

心室に血液が送り込まれているときは

But now remember that blood is constantly

三尖弁と僧帽弁は開いています。

moving through the heart.

肺動脈弁も開いていますが、実際に開いているでしょうか。

So in a previous cycle, you actually

いいえ、実際は閉じています。

had some blood that was coming back from the lungs,

右心房から右心室へ血液が流れる場合を考えてみます。

and that's what's dumping into the left ventricle.

これから示す黒色の矢印は不適切な流れを表します。

And in a new cycle, you have a bit of blood

血液がこちらから流れるとします。

that's going from the right atrium to the right ventricle.

ほんとはこちらに流れてはいけません。

So you have simultaneously two chambers

そういうことが起きないように、この弁が閉じるのです。

that are full of blood-- the right and left ventricle.

こちらについても同じことです。

Now, to get the blood into those ventricles,

血液が逆流しようとすると

the valves had to open.

この弁が閉じてそれを防ぎます。

And specifically, let's label all the valves now.

このように血液は白の矢印の方向に流れ、

So here you have our tricuspid valve,

黒の矢印の方向には流れないようになっているのです。

and I'm going to label that as just a T.

つまり三尖弁と僧帽弁が開いているとき、

And then up here, you have the pulmonary valve,

肺動脈弁と大動脈弁は閉じているのです。

and this'll be just a P. And on the other side,

こうして両方の心室には血液が充満すると、

you've got the mitral valve, which separates the left atrium

心臓は収縮を始めます。

from the left ventricle.

そして血液が大動脈に送られるのです。

And you've got the aortic valve.

ですから、こちらの黒の矢印は消しましょう。

So these are the four valves of the heart.

正しくはこちらに流れます。

And as the blood is now in the ventricles,

弁もこのように開いて、

you can see that the tricuspid and the mitral valve are open.

血液を正しい方向に流すのです。

So far, so good.

この2つの弁を通過して血液が流れるのです。

Now, I've actually drawn the pulmonary valve as being open.

先程と同様、こちらも逆流する可能性があります。

But is that really the case?

血液がこちらの、間違った方に流れようとすると

And the answer is no, because what happens

この弁が閉じるのです。

is that as blood is moving down from the right atrium

両方の心室に同じ機能があります。

to the right ventricle, let's say that--

こうして弁が閉じることで

and I'm going to draw it in black.

血液が逆流しないようになっているのです。

Black arrows represent the bad or the wrong direction of flow.

さて、三尖弁や僧帽弁が閉じるときには音を出します。

So let's say some blood is actually

三尖弁と僧帽弁が閉じるとき出す音が

trying to go that way, which is not the way it should be going.

英語ではラブ(lub)と聞こえます。

What happens is that these two valves, they,

これが最初の音です。

based on their shape, are actually

S1と書きます。

not-- they're going to jam up.

ダブ(dub）は2つ目の音

They're going to basically just jam up like this,

これをS2と言います。

and they're not going to let the blood pass through.

三尖弁と僧帽弁が閉じるとき聞こえるのがS1です。

So this is what happens as that valve closes down.

三尖弁と僧帽弁が閉じるということは、

And the same thing happens on this side.

つまり肺動脈弁と大動脈弁が開くということですね。

Let's imagine you have some backwards flow of blood

しかし音の正体は三尖弁と僧帽弁です。

by accident, meaning that it's going in the wrong direction.

ではダブ(dub)の方はどうでしょう。

Well, then these valves are going to close down.

今のと正反対です。

So the white arrows represent the correct flow of blood,

あとで話しましょう。

and the black arrows represent the incorrect flow of blood.

心室が収縮すると弁が開いて

So these valves shut down like that.

逆流が起こるかも知れませんから、

So now you can see how the valves,

この弁が閉じます。

the aortic and pulmonary valve, are actually

弁が閉じた時に音がするのです。

closed when the mitral and tricuspid valve are open.

ダブ（dub）の正体は

So what happens after this?

肺動脈弁と大動脈弁が閉じる音なのです。

So now our ventricles are full of blood, right?

一方で三尖弁と僧帽弁が開きます。

They're full of blood.

絵のほうにもこの状態を描き入れましょう。

And let's say they squeeze down, and they jettison all the blood

この2つの弁が開きます。

into those arteries.

そして血液が再び心室に流れこむのです。

Well, now you're going to have-- this is actually

こんな風にリズミカルに心臓は動いていて

going to close down.

弁が閉じる度にドキドキという音がするのです。

Let's say this arrow flips around.

これで心臓の中の血液が一巡しました。

These arrows become white, because the direction of flow

このサイクルが繰り返されるのです。

is going to be in the direction we want it.

さて、心臓は一定の間隔を空けて拍動します。

It's going to go this way and this way

時系列で表すと、これがS1、そしてS2

And to allow that, of course, I need

そして再びS1とS2という具合です。

to show you that these open up.

この短い時間に心臓が収縮して

And they allow the blood to go the way that we want it to go,

肺動脈弁と大動脈弁が開き

so now blood is going to flow through those two valves.

血液を体中に送り出します。

But similar to before, you could have some backflow here.

この時期を収縮期といいます。

You could have backflow here.

次の拍動までのこの時間に

And you can have backflow here.

血液は心房から心室に流れます。

So you can imagine now, let's say

この時期を拡張期といいます。

you have a little bit of backflow that

ですから心臓のドキドキ、

wants to go this way, which is the wrong direction.

あるいはラブダブというのは

Right?

心臓が収縮したり拡張したりするときに

Well, then these valves are going to close up.

弁が閉じる音なのです。

They're going to say, no, you can't go that way.

They're going to close right up, and they're

going to not allow blood to go that way.

So this is going to happen on both sides, both ventricles.

And the valves shut.

And so basically the backflow of blood

is not allowed, because the valves keep shutting.

And when the valves snap shut-- so for example, right now

the tricuspid valve and the mitral valve snapped shut.

Well, that makes a noise.

So when T and M snap shut, that makes a noise that we call lub.

That's that first noise, that first heart sound.

In fact, sometimes people don't even call it lub dub.

They say, well, it's the first heart sound.

And to make that even shorter, sometimes people call that S1.

So if you hear S1, you know they're

talking about that same exact thing.

And this dub is called the second heart sound.

And, no surprise, just as before, if that's S1,

this is S2.

So you'll hear S1 when the tricuspid and mitral valve

snap shut.

So far, so good.

But you also know that if that's what's making noise,

you can kind of guess-- and it's a very smart guess-- that

at the same time, the pulmonic valve and the aortic valve

just opened.

So if the other valves snap shut, these just opened.

Right?

You can kind of assume that, although the noise

you're hearing is actually from here.

So what's happening with dub?

Well, the opposite.

And what I mean by that is-- let me now

show you what happens a moment later.

Well, after the ventricles are done squeezing,

then we get to a point where you might

have a little bit of flow that way and that way,

just as I drew before.

And these valves snap shut as well.

So now these snap shut.

And as these snap shut-- because they

don't want to allow backflow, right?

They're going to snap shut like that.

They make noise.

And so when you have dub, you actually

have noise coming from the pulmonic and aortic valve

snapping shut.

And that must mean that then the other two valves just opened

up-- the tricuspid and mitral just opened.

You can assume that, right?

And I didn't draw that in the picture.

Let me update my picture now to show that.

So now these two have opened up, and blood

is coming into the ventricles again.

So it's actually a nice little rhythm that you get going.

And every time these valves go open and shut, you hear noise.

So you can kind of figure out what's happening based on--

and these actually-- let me erase that.

And now you have white arrows going this way.

And we've returned to where we started from.

So you basically have a full cycle,

and between these two-- so let's say from lub to dub,

because there's a little bit of space there.

If you were to follow it over time, over time,

this is what it might look like if this is a little timeline.

You might hear lub here, or the first heart sound.

I'll just call it S1.

And you might hear S2 here, the second heart sound.

And then you'll hear S1 again over here and S2.

And what's happening between the two-- so between these two,

this time lag here-- is that blood is actually

squeezing out, because the pulmonary and aortic valves

just opened.

It is squeezing out and going out to the whole body.

So this is when blood is going to the body,

and sometimes we call that systole.

And between dub and the next lub-- so

in this area right here-- well, at that point,

blood is kind of refilling from the atriums

into the ventricles, and we call that diastole.

So now you can actually listen to your heart.

And you can actually figure out, well,

if you're listening to the sound between lub and dub

or the space in time between lub and dub,

that's when you're having systole.

And if you're listening to or waiting for the sound

to start up again-- so you just heard dub,

and you're waiting for lub again-- then that space in time

is diastole.