シャドーイング練習: Ischemic Stroke - causes, symptoms, diagnosis, treatment, pathology - 動画で英語スピーキングを学ぶ

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There are two main types of stroke.

An ischemic stroke, which is when there is a blocked artery that reduces blood flow to the brain,

and a hemorrhagic stroke, which is when there is an artery in the brain that breaks, creating a pool of blood that damages the brain.

Of the two, ischemic strokes are much more common, and the amount of damage they cause is related to the parts of the brain

that are affected and how long the brain suffers from reduced blood flow.

Now, if symptoms self -resolve within 24 hours, it's called a transient ischemic attack, and there are usually minimal long -term problems.

Okay, let's start with some basic brain anatomy.

The brain has a few regions.

The most obvious is the cerebrum, which is divided into two cerebral hemispheres, each of which has a cortex,

an outer region divided into four lobes including the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe.

There are also a number of additional structures including the cerebellum

which is down below as well as the brainstem which connects to the spinal cord.

The right cerebrum controls muscles on the left side of your body and vice versa.

The frontal lobe controls movement and executive function which is our ability to make decisions.

The parietal lobe processes sensory information which lets us locate exactly where we are physically

and guides movement in a three -dimensional space.

The temporal lobe plays a role in hearing, smell, memory, as well as visual recognition of faces and language.

Finally, there's the occipital lobe, which is primarily responsible for vision.

The cerebellum helps with muscle coordination and balance.

And finally, there's the brain stem, which plays a vital role in functions like heart rate, blood pressure, breathing, gastrointestinal function and consciousness.

The brain receives blood from the left and right internal carotid arteries, as well as the left and right vertebral arteries,

which come together to form the basilar artery.

The internal carotid arteries turn into the left and right middle cerebral arteries, which serve the lateral portions of the frontal,

parietal, and temporal lobes of the brain.

Each of the internal carotid arteries also gives off branches called the anterior cerebral arteries

which serve the medial portion of the frontal and parietal lobes

and connect with one another with a short little connecting blood vessel called the anterior communicating artery.

Meanwhile, the vertebral arteries and basilar arteries give off branches to supply the cerebellum and the brain stem.

In addition, the basilar artery divides to become the right and left posterior cerebral artery,

which mainly serves the occipital lobe and some of the temporal lobe as well as the thalamus.

Finally, the internal carotid arteries each give off a branch called the posterior communicating artery, which attaches to the posterior arteries on each side.

So together, the main arteries and the communicating arteries complete what is called the circle of willis,

a ring where blood can circulate from one side to the other in case of a blockage.

The Circle of Willis offers alternative ways for blood to get around an obstructed vessel.

In general, the brain can get by on diminished blood flow, especially when it happens gradually, because that allows enough time for collateral circulation to develop,

which is where a nearby blood vessel starts sending out branches of blood vessels to serve an area that's in need.

But once the supply of blood flow is reduced to below the need of the tissue, it causes tissue damage, which we call an ischemic stroke.

There are two main ways an ischemic stroke happens.

One mechanism is endothelial cell dysfunction, which is when something irritates or inflames the slippery inner lining of the artery, the tunica intima.

One classic irritant is the toxin found in tobacco, which floats around in the blood damaging the endothelium.

That damage becomes a site for atherosclerosis, which is where a plaque forms.

This is when a buildup of fat, cholesterol, proteins, calcium, and immune cells form and start to obstruct arterial blood flow.

This plaque has two parts to it, the soft, cheesy, textured interior and the hard outer shell which is called the fibrous cap.

Branch points in arteries and particularly the internal carotid and middle cerebral arteries are the most common spots for atherosclerosis.

Usually though, it takes years for plaque to build up and this slow blockage only partially blocks the arteries.

And so even though less blood makes it to the brain tissue, there's still some blood.

So strokes happen when there is a sudden and complete or nearly complete blockage of the artery.

So let's see how that can happen.

Since plaques sit in the lumen of the blood vessel, they're constantly being stressed by mechanical forces from blood flow,

and interestingly, it's often the smaller plaques that are more dangerous.

Their fibrous caps are softer than the large ones, and are prone to getting ripped off.

Once that happens, the inner cheesy filling is exposed to the blood and is thrombogenic, which means that they tend to form clots very quickly.

Platelets adhere to the exposed cheesy material and they release chemicals that enhance the clotting process.

Within a minute, that artery can be fully blocked.

Another mechanism for ischemic stroke formation is an embolism.

An embolic stroke typically happens when a blood clot breaks off from one location, travels through the blood, and gets lodged in an artery downstream,

typically an artery, arterial, or capillary with a small diameter.

These blood clots typically emerge from atherosclerosis but they can also form in the heart.

For example stagnant blood flow can form a clot and blood can stagnate due to atrial fibrillation or after a heart attack.

If a clot forms in the left atrium it moves into the left ventricle

and from there it has direct route to the brain.

On the other hand

And if a clot forms in the low pressure veins or right atrium,

then it goes to the right ventricle and gets lodged in the pulmonary capillaries, with no way of getting to the brain.

An important exception is if a person has a heart defect, like an atrial septal defect, that allows blood

and potentially a blood clot to wander from the right side of the heart over to the left side of the heart.

In that situation, a venous or right atrial blood clot will have bypassed the pulmonary circulation and established a route to the brain.

One specific type of ischemic stroke is called a lacunar stroke,

and they typically involve the deep branches of the middle cerebral artery that feed the basal ganglia.

Lacunar refers to lake, and is called that since after a lacunar stroke,

the damaged brain tissue develops fluid -filled pockets called cysts that look like little lakes under a microscope.

Lacuna strokes classically develop as a result of highline arteriolosclerosis, which is when the arteriole wall gets filled with protein.

This can happen as a result of hypertension or diabetes, and can make the artery wall quite thick, reducing the size of the lumen.

In addition to problems specific to an artery, something like shock can lead to reduction in blood flow throughout the entire body.

In these cases, the tissues that are the furthest downstream are affected the most.

This is because healthy tissue continues to extract what it needs from the blood flowing by,

leaving little to no oxygen and nutrients for the tissue furthest away.

The furthest downstream tissues in the brain are at the border of two different blood supplies.

When the blood flow throughout the body is diminished for any reason, they get damaged, and this pattern of injury is called a watershed infarct.

Regardless of the mechanism of an ischemic stroke, it's helpful to remember that there is an ischemic core,

which is the brain tissue that will likely die from ischemia, and then there is the tissue around the core,

called the ischemic penumbra, which is preserved for a period of time by collateral circulation

and has a chance to survive if blood flow is restored quickly enough.

Regardless of the type of ischemic stroke, without a steady supply of glucose and oxygen, cells run out of energy within minutes,

and you get a high buildup of sodium and calcium levels in the cells.

High sodium levels draw water into the cell, making it swell, and this is called cytotoxic edema.

And high calcium leads up to the buildup of reactive oxygen radicals

that react with lipids in the membranes of mitochondria and lysosomes.

Damage to these organelles allow apoptosis inducing factors and degradative enzymes to seep out of the cell.

Over a period of 4 -6 hours, immune cells begin to haul away damaged cells, and the resulting inflammation damages the blood -brain barrier,

allowing fluids and proteins to get into the brain tissue, causing swelling or vasogenic edema.

Because the skull creates a fixed volume,

the swelling leads to a mass effect where the swollen brain tissue pushes into the unaffected side of the brain, called cingulate, or uncal herniation,

or slips down and out of the base of the skull,

called cerebellar tonsil herniation, which is particularly dangerous because it can push onto the brainstem and affect breathing and consciousness.

Stroke symptoms depend on the exact part of the brain that is affected.

For example, an interior or middle cerebral artery stroke can cause numbness and sudden muscle weakness.

If a stroke affects the BRCA area, which is usually the left frontal lobe, or the Wernicke's area, which is usually the left temporal lobe,

then it can cause slurred speech or difficulty understanding speech, respectively.

100

If there's a posterior cerebral artery stroke, then it can affect vision.

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An acronym to remember some common stroke symptoms is FAST.

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Facial drooping, arm weakness, speech difficulties, and time.

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Time is obviously not a symptom,

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but just a reminder to help as quickly as possible to minimize cell injury and maximize the chance of a full recovery.

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To diagnose and confirm the location and size of an ischemic stroke, medical imaging with a CT or MRI can be used.

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Also, angiography, which uses a contrast injected into the blood, can help to visualize the exact location where blood flow is blocked within an artery.

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In addition, using flare -sequenced MRIs, it's possible to distinguish a new stroke injury from an old one.

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In an ischemic stroke, the ultimate treatment is to re -establish blood flow as quickly as possible to prevent further cell injury, particularly in the penumbra.

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Every minute counts.

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So thrombolytic enzymes like tissue plasminogen activator or TPA are used to activate the blood's natural clot -busting mechanism,

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but TPA does have a time limit of when it can be used.

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Aspirin is also used to prevent platelets from forming additional clots.

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If TPA is unsuccessful, surgical procedures can be used that push a wire through the artery and physically remove the clot.

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In mechanical embolus removal in cerebral ischemia, called MERCY for short, the wire grabs onto the clot and draws it out of the artery.

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In suction removal, the wire is used to physically break down the clot and the clot fragments are removed with suction.

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After a stroke has occurred, there is an elevated risk of having additional strokes, so it's important to minimize risk factors,

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the main one being quitting smoking, but others include having a healthy blood pressure, normal LDL cholesterol levels, and controlling other diseases like diabetes.

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Occasionally, a surgery may be necessary to help clean arteries obstructed by severe atherosclerosis.

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For example, in a carotid endarterectomy, the internal carotid artery is opened up and atherosclerotic plaque is removed.

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Alternatively, a stent might be placed to keep the artery opened up.

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Okay, as a quick recap, an ischemic stroke occurs when there is an acute decrease in the arterial blood supply.

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It can be due to atherosclerosis, a thrombus, or an embolus, or a global reduction in blood flow.

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The goal is to identify symptoms and re -establish blood flow to prevent long -term damage.

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To remember this, a common acronym is FAST, facial drooping, arm weakness, speech difficulties, and time.

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このレッスンの語彙とスピーキングのポイント

このスピーキングレッスンは、動画「Ischemic Stroke - causes, symptoms, diagnosis, treatment, pathology」を教材にしています。繰り返し出てくる語は次のとおりです：blood, stroke, artery, brain, arteries。この動画には、シャドーイング用の文が83文、単語が2020語あります。音声の長さは13:06です。話す速さは1分あたり約154語で、日常会話に近い自然なペースです。英語の頻出3,000語に含まれる単語は70%だけなので、語彙は難しめです。

この動画の重要語彙

動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。

単語	発音	意味
artery 名詞	/ˈɑɹ.təɹ.i/	動脈
tissue 名詞	/ˈtɪʃ.(j)u/	織物
vessel 名詞	/ˈvɛsəl/	船舶
mechanism 名詞	/ˈmɛk.ə.nɪ.zəm/	仕組み, 機構
symptom 名詞	/ˈsɪm(p)təm/	症状, 症候
muscle 名詞	/ˈmʌs.əl/	筋肉, 筋
wire 名詞	/ˈwaɪɚ/	針金, 線
connect 動詞	/kəˈnɛkt/	繋げる
difficulty 名詞	/ˈdɪfɪkəlti/	難しさ
oxygen 名詞	/ˈɑksɪd͡ʒən/	酸素
communicate 動詞	/kəˈmjuːnɪkeɪt/	伝える
weakness 名詞	/ˈwik.nɪs/	弱さ, 弱小
calcium 名詞	/ˈkælsi.əm/	カルシウム, 石灰素
downstream 形容詞	/ˌdaʊnˈstɹiːm/	下流
cheesy 形容詞	/ˈt͡ʃiːzi/	安っぽい, 見掛け倒しの

動画に出てくる句動詞

単語	意味
rip off 動詞	ぼったくる, 法外な額を請求する

この動画の文法

話し手がよく使っている文型を、動画の実際の表現とともに紹介します。

文型	動画での表現
受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる	are affected · is divided · is called
関係詞節 who / which + 節 — 人や物について情報を加える	stroke, which is · cerebrum, which is · function which is
現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している	have bypassed · has occurred

注意したい発音

「th」の音: breathe /bɹiːð/, thick /θɪk/, atherosclerosis /ˌæθɚoʊskləˈɹoʊsəs/, furthest /ˈfɜː(ɹ)ðɪst/
「sh」と「zh」の音: tissue /ˈtɪʃ.(j)u/, circulation /ˌsɝkjʊˈleɪʃən/, reduction /ɹɪˈdʌk.ʃən/, consciousness /ˈkɑnʃəsnəs/, recognition /ˌɹɛkəɡˈnɪʃ(ə)n/
長い単語（アクセントの位置に注意）: mechanism /ˈmɛk.ə.nɪ.zəm/, difficulty /ˈdɪfɪkəlti/, communicate /kəˈmjuːnɪkeɪt/, circulation /ˌsɝkjʊˈleɪʃən/, anterior /ænˈtɪɹ.i.ɚ/

日本語話者が苦手な音：

/r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: cerebral /səˈɹi.bɹəl/, temporal /ˈtɛm.pə.ɹəl/, regardless /ɹɪˈɡɑɹd.lɪs/, removal /ɹɪˈmuː.vəl/, cholesterol /kəˈlɛstəɹɒl/
/v/ — /b/ にならないように、上の歯を下唇に当てる: vessel /ˈvɛsəl/, removal /ɹɪˈmuː.vəl/, divide /dɪˈvaɪd/, respectively /ɹɪˈspɛktɪvli/, vital /ˈvaɪtəl/
/f/ — 「フ」ではなく、上の歯と下唇で出す: difficulty /ˈdɪfɪkəlti/, physically /ˈfɪz.ɪ.kli/, fluid /ˈflu.ɪd/, defect /ˈdiːfɛkt/, refer /ɹɪˈfɜː/

この動画での練習方法

まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
自分の声を録音して元の音声と比べます。artery, tissue, vesselなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →

シャドーイング練習: Ischemic Stroke - causes, symptoms, diagnosis, treatment, pathology - 動画で英語スピーキングを学ぶ

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