Theoretically emboli, both gaseous and solid, would be expected to appear in the Doppler spectrum as short duration high intensity signals. Experimental studies have confirmed the sensitivity of the technique. Embolic signals have been detected in patients with a variety of embolic sources including prosthetic cardiac valves and carotid stenosis. In the latter group they appear to be clinically relevant correlating with time since symptoms, the degree of stenosis and plaque ulceration, and being reduced or abolished after carotid endarterectomy. However early studies have given very different frequencies of embolic signals. This may partly reflect different patient populations but also emphasizes the importance of technical factors. These are discussed in this review. A number of automated systems have been developed to detect embolic signals but none yet developed have sufficient sensitivity and specificity for routine use.

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Background: The embolic signal obtained by TCD varies in sound, pitch and duration according to the size of the embolus and the materials of which it is composed. We tried to differentiate the micro-embolic signal from various embolic sources by wave analysis and also to clarify its clinical significance.
Methods and Results: We recorded micro-embolic signals using TCD in 10 patients with various embolic conditions; 3 patients on a left ventricular assistance system (LVAS), 3 patients after replacement of the mitral valve with a prosthesis (MV), 2 patients with non-valvular atrial fibrillation (NVAF), and 2 patients with high-grade carotid stenosis (CS) . Acoustic power (AP), frequency, duration and background blood velocity (Vbg) were measured by a microcomputer system. The average duration of the embolic signal was longer in patients with LVAS and MV than in those with NVAF and CS. All patients who showed a correlation between Vbg and all parameters (AP, frequency, duration) were asymptomatic.
Conclusion: The duration of micro-embolic signals, which reflects the size and components of the embolus, differs largely according to the embolic source. The correlation of background velocity with three parameters of micro-embolic signals (AP, duration, frequency) which appear to reflect the homogeneity of micro-emboli, may be a parameter indicating stroke risk.

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prospective studyの結果, 内頚動脈狭窄症では無症候性であっても60%以上の狭窄例では内科的治療例より血栓内膜剥離術 (CEA) の方がを脳梗塞発生の予防効果があることが報告されている.Carotid duplex ultrasound (CDUS) は無侵襲であり, 頻回な検査が可能であり, 狭窄度のスクリーニングには有効性が報告されている.著者らの施設ではCDUSとMRAの組み合わせにより, 血管撮影を行なわずにCEAの適応を決定している.今回の研究は術前CDUSで測定した内頚動脈狭窄部のpeak systolic flow verocity (PSV) およびend-diastolic flow velocity (EDV) 値, carotid index (peak carotid artery velocity/common carotid artery velocity) を測定して手術所見での実際の残存血管内腔との相関を検討した.対象は91例の内頚動脈狭窄症の患者で, 8例は両側の狭窄を認めるためtotal99血管について検討している.37血管は無症状, 62血管は症候性であった.CDUSは4-7また5-10MHz linear transducer (ATL UItra-mark9HDI scanner) を使用した.結果として, 手術所見での残存血管内腔は0.21-2.72mmで平均1.08mmであった.77%の血管では残存血管内腔が1.5mm以下であった.PSVが440cm/s以上, EDVが155cm/s以上, またcarotid indexが10以上の症例は実際の内腔は1.5mm以下であった (specificity100%, sensitivityはそれぞれ58%, 63%, 30%) .またこの三つの指標がすべて当てはまる症例ではsensitivityは72%に達した.またPSVが200cm/s以上であり, EDVが140cm/sec以上かcarotid indexが4.5以上である例ではsensitivityは96%, specificityは61%であった.著者らがresidual lumenが1.5mm以下をcutoff pointとした理由は, 残存血管内腔が1.5mmであればNASCET criteriaでは60-75%の狭窄に相当すると考えている.また著者らの過去の研究ではCDUSでresidual lumenが1.5mm以下になると内頚動脈の血流のhemodynamic changeがおこるという結果からである.以上の結果から, 内頚動脈狭窄症ではCDUSによるPSV, EDV, carotid indexはresidual lumenがCEAの適応を決定に非常に有用であると結論づけている.

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High intensity transient signals (HITS) were detected in patients with a high risk of stroke. The signals were detected in the middle cerebral artery for 15-30 min by a TC2020 or Multi-Dop DX4. HITS were never detected in young healthy volunteers (n=20) . The HITS count in patients with cerebral infarction (16-20/30 min, n-42) was significantly higher than that in patients without cerebrovascular disease (0.5±0.7/30 min, n17) (p<0.01) . In the cerebral infarction group, the HITS count in patients without antiplatelet (20±29/30 min, n=20) was significantly higher than that in patients with antiplatelet (9±6/30 min, n=22) (p<0.01) . HITS were frequently detected in patients fitted with mechanical valves (St. Jude Medical valve) (14.3±34.5/15 min, n=51), and the count was significantly higher than that in open heart surgery patients without mechanical valves (0.05+0.08/15 min, n=11) (p<0.01) . In the mechanical valve replacement group, the HITS count in patients with cerebral infarction after surgery (88±66/30 min, n=43) was significantly higher than that in patients without a historyof stroke (7±7, n-8) (p<0.01) . The HITS intensity in the mechanical valve replacement group (15.1+4.3 dB, n=31) was significantly greater than that in the cerebral infarction group (10.8+1.1dB, n-32) (p<0.05) . In the mechanical valve replacement group, the HITS intensity in patients with post-surgical cerebral infarction (18±3.5 dB, n8) was significantly greater than that in patients without a history of stroke (14.5±5.6 dB, n=23) (p<0.0001) . During veno-arterial extracorporeal membrane oxygenation (V-A ECMO), HITS were frequently detected (124±60/15 min, n=6), and the HITS count was negatively correlated with activated coagulation time (ACT) . HITS may therefore reflect the presence of microemboli and indicate the risk of stroke or the state of blood coagulation.

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The embolic signals detected by transcranial Doppler ultrasonography (TCD) are characterized as high-intensity transient signals (HITS) . Two types of TCD devices, conventional and embolus-oriented, are currently used. HITS demonstrated by an embolus-oriented TCD device correspond almost specifically to embolic signals. However, the characteristics of HITS in conventional TCD and their specificity to embolic signals remain to be studied. In this study, 10 ischemic patients were examined using a conventional TCD device. Six of these patients showed HITS. In all cases, these were partly unidirectional and partly bidirectional with a unilateral tendency, and the HITS were accompanied by chirping sounds. Since the chirping sounds had the typical characteristics of embolus origin which we had revealed experimentally, the HITS were interpreted to originate from moving emboli. We conclude that HITS with chirping sounds can be regarded as embolic signals in conventional TCD, irrespective of whether they are unidirectional or bidirectional with a unilateral tendency.

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To evaluate intracranial pressure by transcranial Doppler ultrasound (TCD), the mean flow velocity (MFV) and Gosling's pulsatility index (PI) of the middle cerebral artery (MCA) and basilar artery (BA) were measured before and after glycerol administration, and also regional cerebral blood flow (rCBF) was investigated simultaneously. Ten patients with brain tumors and 5 normal volunteers were selected. After glycerol administration in the patient group, MFV and rCBF showed a significant increase of more than 27% and 16% respectively, in the hemispheres ipsilateral and contralateral to the tumor (p<0.05), compared with the corresponding values in the control group. Inversely, the mean PI decreased to 16% on both sides. Moreover, changes in MFV and PI in addition to those induced by glycerol were closely correlated with those of rCBF in all patients. In conclusion, these results suggest that changes in MFV and PI revealed by TCD under glycerol administration might predict intracranial pressure, especially in patients with intracranial hypertension.

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mental activities, motor task, somatosensory stimulationなどによる脳局所の血流, 代謝の変化はPETやMEGなどではとらえることができる.しかしこれらの検査は検査時間が長く, 患者も搬送が必要である場合が多く, しかも非常に高価である.また急激で一過性の血流の変化がとらえられないことがある.一方TCDの有用性は簡便に繰り返し検査が可能であり, 急激で一過性の変化をとらえることができることであるが, 血流速度の変化がCBFの変化を反映しているかに疑問がある.今回の研究は視覚刺激を与えた時にPCA, BA, MCAの血流速度 (BFV) が変化を健常人を使い測定し, 過去に同様な刺激によるCBFの変化を検討したPET studyなどと比較してTCDの有効性を検討した.対象は男性7例女性7例で, 年齢は21-41歳であった.全例右利きであり, 現在投薬をうけておらずmental, neurological, vascular diseaseの既往はない.検査は明るさを一定にした静かな部屋を用いた.検査中は呼吸数, 脈拍, 血圧を連続的にモニターし, 検査前後のETCO2を測定した. TCD systemは二つの血管を同時に連続的に測定できるMulti-DOPX/TCD 7, Firma DWL, Electronische Systeme GmbHを使用した.刺激は1) 安静閉眼状態で10秒ごとにbeep toneのみを聞かせる.2) Room light下で, beep toneに従い開眼, 閉眼を繰り返す.開眼時の視線は前方においたwhite screenの中央に固定するように指導した.3) Room light下で開眼と閉眼を繰り返すが, 視線は部屋の中を見渡すように指導した.4) Goggleから両眼に光刺激を与える.10秒刺激, 10秒中止を14サイクル与える被検者は閉眼状態とした.5) Goggleからの光刺激で被検者は開眼状態とした.結果としては, 検査中に血圧, 脈拍などに変動は認あなかった.開眼のみ, また光刺激によりPCA, BAのBFVは著明に上昇したがMCAのBFVは変化を示さなかった.PCAとBAのBFVの変化ではPCAのほうが有為に上昇した (p<.0.0001) .両眼同時の刺激であったが, 右のPCAのBFVのほうが有為に上昇する傾向であった.これらの結果はすべて複数回検査したが再現性を認めた.著者らの考察としては, 過去にも各種刺激による特定の血管領域のBFVが上昇することは報告されている.しかしこれらの報告は反応が一定でなくvariationが多い.著者らは各種刺激による脳局所の血流代謝の変化を測定する場合にはtaskの選択が最も重要であり, これはPETの結果を参考にするのが有用であると述べている.今回の結果では右のPCAのBFVのほうが有為に上昇する傾向が認あられ, また開眼では注視時より視線を動かしている時のほうが変化が大きいとう結果であった.これは過去のPETでの報告と一致している.したがって両側PCAのBFVの連続測定は, 視覚刺激時によるPCAの血流増加を示していると結論づけている.

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