![]() ![]() Dr Emma Chung) is investigating the feasibility of using an ultrasound acoustic radiation force to deflect emboli away from vital organs, such as the brain, during surgery. This Engineering and Physical Sciences Research Council (EPSRC) study (P.I. Detection and deflection of emboli in the bloodstream We are also investigating the potential for using an acoustic radiation force to deflect emboli away from the brain and to distinguish solid emboli from bubbles. Recent advances include the development of software to estimate the sizes of air bubbles entering the cerebral circulation during cardiac surgery, use of 'virtual patient' simulations to estimate the impact of bubbles on cerebral blood flow, and development of digital MR subtraction software to assist Radiologists in identifying new embolic lesions. Our research group has extensive expertise in the detection and characterisation of cerebral emboli using transcranial Doppler ultrasound. Among the last 40 patients who were treated according to this regimen, reversible DID's were observed in only three patients (7.5%) and postoperative angiography to detect vasospasm was not necessary.A major cause of stroke comes from embolic debris (thrombus, bubbles and pieces of plaque) that travel through the cerebral circulation and become lodged in arteries supplying the brain. ![]() Based on the information provided by Doppler measurement of the individual blood flow velocity changes due to vasospasm, preventive hypertensive treatment was introduced to improve the perfusion pressure while patients were still in an asymptomatic stage. One patient (2%) died as a result of decompensated vasospasm. Seven patients (14%) developed delayed ischemic deficits (DID's), which were all functionally reversible. A comparison between the angiographically proven diameter of spastic arteries and the Doppler-measured blood flow velocity showed an inverse relationship in flow of the middle cerebral artery and the internal carotid artery that was statistically highly significant (p less than 0.001) while this correlation was only slightly significant in the A1 segment of the anterior cerebral artery (p = 0.054). ![]() The changes showed a significant relationship to the source of SAH, the side of the operative approach, and the method of nimodipine administration. The Doppler frequency changes that relate to blood flow accelerated between Days 3 and 10, and maximum blood flow velocities were recorded between Days 11 and 20, with normalization occurring within the following 4 weeks. Within the first 72 hours after SAH, the velocity was normal in the large branches of the circle of Willis and angiography revealed no signs of vasospasm. At short intervals (at least every 3rd day) the blood flow velocity in the different segments of the circle of Willis was measured with a noninvasive transcranial Doppler ultrasonography method. To prevent symptomatic vasospasm, the patients were given the calcium channel blocker, nimodipine, intravenously (2 mg/hr) for 14 days and orally (60 mg four times daily) for another 7 days. ![]() Fifty patients with ruptured aneurysms were operated on within 72 hours after the first subarachnoid hemorrhage (SAH). ![]()
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