シャドーイング練習: SVINutes: Basics of Subclavian Steal - 動画で英語スピーキングを学ぶ
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Hello, I'm Dr. Sashir Manava. In today's SVINutes, we will be discussing the basics of subclavian steel syndrome, an important diagnosis and cause of vertebral basler insufficiency that
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can be difficult to recognize. We will cover the primary risk factors, approach to diagnosis and common medical and surgical therapies available. Subclavian steel refers to a syndrome caused by
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occlusive disease in the proximal subclavian artery resulting in a reversal of flow in the ipssolateral vertebral artery. This results in blood being stolen from the cerebral circulation to supply the arm leading commonly to symptoms of vertebral basler insufficiency. In rare cases
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this steel phenomenon can even affect the heart resulting in anga due to coronary circulation supply via an internal memory graft. Regarding vascular pathophysiology, the concern is related
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distal profusion pressure in the vertebral artery which can decrease as the degree of ipssol subclavian artery stenosis increases. Eventually the profusion pressure will fall below that offered by the unaffected vertebral artery or collateral anterior circulation and
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result in flow reversal in the affected vertebral artery. More commonly the left vertebral artery is affected possibly due to a more acute angle of origin. Let's talk about risk factors.
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Aththeroscerosis is the most common cause of subclavian artery stenosis. Therefore, patients with vascular risk factors such as uncontrolled hypertension, hyper lipidmia, hypoglycemia, and smoking are at higher risk of developing this disease. However, less common causes should also
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be considered such as large vessel granulomitis vasculitis as seen in Takiasu's arteritis, thoracic outlet syndrome as seen in those patients with the presence of a cervical rib and stenosis
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related to postsurgical repair of the aorta. Think repair of aortic dissection or corctation of the aorta. Importantly, younger patient populations may have subclavian steel related to congenital
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abnormalities such as right-sided aortic arch with an isolated left subclavian artery or other variations of aortic arch and branch anatomy. Regarding the epidemiology of subclavian steel,
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exact incidence is unknown. The joint study of extranial arterial occlusion by fields at all showed a 2.5% incidence in over 6,000 patients studied with only 5.3% of these
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patients experiencing neurological symptoms. Let's talk about symptoms. If symptoms are present, arm claudication is the most common complaint. Occasionally coolness or paristhesas in the arm can also be noted. Upper extremity exercise by reducing arterial resistance increases blood flow
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to the arm and can precipitate lateralizing symptoms of vertebral basler insufficiency among persons without sufficient collateral flow. Vertebrasler insufficiency presents classically as drop attacks but can also manifest as dizziness, disequilibrium, atexia, dipopia, vision change,
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nestagmus, tinidis or even hearing loss which highlights the importance of a detailed and thorough neurological exam. Remember chest pain or anga can also be seen in rare causes of coronary subclavian steal phenomenon. Physical examination findings suggestive of a significant
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subclavian stenosis includes a discrepancy of at least greater than 15 mm mercury in blood pressure readings taken in both upper arms, delayed or decreased amplitude pulses in the affected arm andor a brewy in the supercloavicular fossa. Rarely skin changes or nail blood changes
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can be seen in the affected arm. In regards to imaging diagnosis, duplex ultrasonography and transcranal Doppler are excellent first-line tests that have the advantage of showing real-time physiology while being portable and non-invasive. Duplex ultraography can help to
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quantify subclavian stenosis and visualize some extraanial segments of the vertebral artery but can be limited by operator dependency, anatomical issues and limited visualization. However,
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duplex ultrasound can inform on the directionality of extranial vertebral artery segments visualized and certain waveform patterns can indicate a pre-steal or steal phenomenon. Transcranial Doppler cuff testing can help to assess vertebral artery flow reversal either spontaneous or induced
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to identify those patients at risk of induced flow reversal. A blood pressure cuff is placed on the symptomatic arm inflated to a pressure significantly above the systolic blood pressure for a few minutes and during cuff inflation and deflation the TCD monitors the blood flow
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velocity in the ipsateral vertebral artery looking for a change in the direction from antiggrade to retrograde flow. Commonly the severity of subclavian steal is classified into three grades. grade one presupplavian steal, grade two intermittent partial
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steal as well as grade three which is total steal. When ultrasound studies are abnormal, the addition of magnetic resonance angography and/or CT andography are important non-invasive
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tools that can assist in further grading the degree of subclavian artery stenosis as well as provide more detailed information regarding aortic arch branching patterns and presence of aththeroscerosis in other vessels. Regarding medical management of subclavian steal syndrome,
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if the stenosis is caused by athoscorotic disease, patients would benefit from secondary preventive measures to control vascular risk factors including blood pressure control, smoking sessation, glycemic control, and lifestyle changes. Anti-platlet therapy may be warranted in
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athoscorotic causes of subclavian artery stenosis as well. Most cases of subclavian stenosis are asymptomatic, but severe symptomatic cases may require surgical intervention. Conventionally
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open bypass surgery had been pursued with the main approach being prosthetic extraanatomic bypass grafting from the ipsal corateed to the subclavian artery. Additional methods of bypass are also shown here on the slide. With the advent of newer minimally invasive techniques allowing
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for endovascular angioplasty and stenting. However, endovascular treatment of subclavian stenosis may be preferred in some patients. Some limitations include total subclavian artery occlusion precluding canulation longer extensive lesions, stent obstruction of vertebral artery
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origin flow and bleeding risk with longer term dual anti-platlet therapy. No randomized trials have compared endovascular versus surgical methods for treatment of subclavian stenosis. Therefore, an individualized patient care approach is best. In conclusion, subclavian still syndrome can be
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a difficult to recognize condition. But with improved recognition and diagnosis, we may be able to prevent more serious complications. Thank you for watching this SVINute video on the basics of subclavian steal and stay tuned for more helpful content.
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「SVINutes: Basics of Subclavian Steal」を使って、シャドーイングで英語を練習しましょう。
毎日15〜30分の練習で、IELTSスピーキングへの自信と実践的な英会話力が身につきます。
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。