Transient flow reversal combined with sustained 
embolic prevention in transcervical revascularization 
of symptomatic and highly-emboligenic carotid stenosis for optimized endovascular lumen reconstruction 
and improved peri- and post-procedural outcomes

Introduction : Approximately 20% of all acute ischemic strokes occur in the vertebrobasilar (VB) circulation. Similar to carotid stenosis, symptomatic vertebral artery (VA) stenosis is associated with a high risk of stroke recurrence. The use of embolic protection devices for recanalization in the setting of carotid stenosis in order to improve clinical outcomes is well established. Recent randomised trials have failed to demonstrate improvement of clinical outcomes in VB stroke patients treated with stenting. To our knowledge, these studies did not require the use of embolic protection devices or techniques. This may be due to several factors. Firstly, since the caliber of the stenotic segment of VA is not large enough to safely allow the protection device delivery system to pass through, initial angioplasty without protection is needed. Secondly, the most common segment of VA to become stenotic is its origin, and usually after stenting of this segment, the edge of the stent is protruding into the SCA. When the angle of the VA relative to the SCA is acute, passing the filter capture catheter through this protruded stent is very difficult and dangerous. Methods : We are introducing a VA reversal blood flow technique for prevention of emboli through the VB system in the setting of symptomatic extracranial VA stenosis. In this technique, we used a balloon tip guide catheter in order to transiently occlude the proximal segment of the SCA, causing flow arrest. We then evaluated the presence of blood flow reversal in the VA. Theoretically, this induction of blood flow reversal in the VA can be considered protective because it washes the embolic particles into the distal SCA. Results : Of the 11 cases of VA origin symptomatic stenosis, 4 had desirable VA blood flow reversal after balloon occlusion trial. These patients had successful angioplasty‐stenting of the VA origin using balloon mounted stent without major complications such as ischemic stroke in the posterior circulation territory. Conclusions : This study demonstrates the feasibility of proximal SCA balloon occlusion to cause transient flow reversal in the VA during angioplasty +/‐ stenting of the proximal VA. Future studies are required to determine the effectiveness of this approach in the setting of extracranial VA stenosis due to atherosclerosis, especially at its proximal segment.

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PREDICTION OF FLOW REVERSAL IN TWO-PHASE TRANSIENT FLOW

Proceeding of International Heat Transfer Conference 6 ◽

10.1615/ihtc6.740 ◽

1978 ◽

Author(s):

H. A. Khater ◽

W. B. Nicoll

Keyword(s):

Transient Flow ◽

Flow Reversal ◽

Two Phase

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Shock Tube Simulation of the Transient Surge Phase Inside an Axial Compressor

Volume 2A: Turbomachinery ◽

10.1115/gt2018-75052 ◽

2018 ◽

Author(s):

Paul Xiubao Huang ◽

Robert S. Mazzawy

Keyword(s):

Shock Wave ◽

Shock Tube ◽

High Speed ◽

Transient Flow ◽

Pressure Ratio ◽

Axial Compressor ◽

Dynamic Effect ◽

Initiation Site ◽

Flow Reversal ◽

Expansion Waves

This paper is a continuing work from one author on the same topic of the transient aerodynamics during compressor stall/surge using a shock tube analogy by Huang [1, 2]. As observed by Mazzawy [3] for the high-speed high-pressure (HSHP) ratio compressors of the modern aero-engines, surge is an event characterized with the stoppage and reversal of engine flow within a matter of milliseconds. This large flow transient is accomplished through a pair of internally generated shock waves and expansion waves of high strength. The final results are often dramatic with a loud bang followed by the spewing out of flames from both the engine intake and exhaust, potentially damaging to the engine structure [3]. It has been demonstrated in the previous investigations by Marshall [4] and Huang [2] that the transient flow reversal phase of a surge cycle can be approximated by the shock tube analogy in understanding its generation mechanism and correlating the shock wave strength as a function of the pre-surge compressor pressure ratio. Kurkov [5] and Evans [8] used a guillotine analogy to estimate the inlet overpressure associated with the sudden flow stoppage associated with surge. This paper will expand the progressive surge model established by the shock tube analogy in [2] by including the dynamic effect of airflow stoppage using an “integrated-flow” sequential guillotine/shock tube model. It further investigates the surge formation (characterized by flow reversal) and propagation patterns (characterized by surge shock and expansion waves) after its generation at different locations inside a compressor. Calculations are conducted for a 12-stage compressor using this model under various surge onset stages and compared with previous experimental data [3]. The results demonstrate that the “integrated-flow” model closely replicates the fast moving surge shock wave overpressure from the stall initiation site to the compressor inlet.

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