The Experts below are selected from a list of 57510 Experts worldwide ranked by ideXlab platform
Andrei V. Alexandrov - One of the best experts on this subject based on the ideXlab platform.
-
quantification of microspheres appearance in brain vessels implications for Residual Flow velocity measurements dose calculations and potential drug delivery
Stroke, 2008Co-Authors: Vijay K. Sharma, Annabelle Y. Lao, Georgios Tsivgoulis, Marc D. Malkoff, Anne W Alexandrov, Andrei V. AlexandrovAbstract:Background and Purpose— Characteristics of ultrasound-activated gaseous microspheres (μS) reflective of their size and quantities are needed for future dose-escalation and drug delivery trials. Methods— A double-blind, interobserver-validated analysis of multi-gate power-motion Doppler μS traces included large (>8μ) μS from agitated saline injections in the right-to-left shunt (RLS) positive stroke patients and small (<5μ) μS from acute patients without shunts receiving thrombolysis and perflutren-lipid μS. Results— In 101 μS traces from 50 RLS-positive and 10 thrombolysis+μS treated patients, a large μS passage had median maximum duration 30.8 ms (interquartile range [IQR] 22.0ms), multi-gate travel time (MGTT) 58.6±19.3 ms versus small μS: duration 8.3ms (IQR 4.3ms), MGTT 43.2±13.9ms, P<0.001. Small μS had higher embolus-to-blood ratio (EBR): 17.5 (IQR 9.3) versus 7.5 (IQR 4), P<0.001. Receiver-operating curve areas were: duration 0.989 (95% CI 0.968 to 1.000), MGTT 0.766 (0.672 to 0.859), and EBR (Embo...
-
a pilot randomized clinical safety study of sonothrombolysis augmentation with ultrasound activated perflutren lipid microspheres for acute ischemic stroke
Stroke, 2008Co-Authors: Andrei V. Alexandrov, Robert Mikulik, Marc Ribo, Vijay K. Sharma, Annabelle Y. Lao, Georgios Tsivgoulis, Rebecca M. Sugg, Andrew D BarretoAbstract:Background and Purpose— Ultrasound transiently expands perflutren-lipid microspheres (μS), transmitting energy momentum to surrounding fluids. We report a pilot safety/feasibility study of ultrasound-activated μS with systemic tissue plasminogen activator (tPA). Methods— Stroke subjects treated within 3 hours had abnormal Thrombolysis in Brain Ischemia (TIBI) Residual Flow grades 0 to 3 before tPA on transcranial Doppler (TCD). Randomization included Controls (tPA+TCD) or Target (tPA+TCD+2.8 mL μS). The primary safety end point was symptomatic intracranial hemorrhage (sICH) with worsening by ≥4 NIHSS points within 72 hours. Results— Fifteen subjects were randomized 3:1 to Target, n=12 or Control, n=3. After treatment, asymptomatic ICH occurred in 3 Target and 1 Control, and sICH was not seen in any study subject. μS reached MCA occlusions in all Target subjects at velocities higher than surrounding Residual red blood cell Flow: 39.8±11.3 vs 28.8±13.8 cm/s, P<0.001. In 75% of subjects, μS permeated to area...
-
heads down flat positioning improves blood Flow velocity in acute ischemic stroke
Neurology, 2005Co-Authors: Anne W Wojneralexander, Zsolt Garami, Oleg Y Chernyshev, Andrei V. AlexandrovAbstract:Background: Acute stroke patients are routinely positioned with the head of the bed (HOB) elevated at 30° despite lack of evidence for increased intracranial pressure. Objectives: To determine the effect of HOB positions in real time on Residual blood Flow velocity in acutely occluded arteries causing stroke and whether resistance to Residual Flow increased with lower HOB positions. Methods: In a repeated-measures quasi-experiment, the effect of 30, 15, and 0° HOB on middle cerebral artery (MCA) mean Flow velocity (MFV) in patients with acute ( Results: Twenty patients were evaluated (mean age 60 ± 15 years; median NIH Stroke Scale [NIHSS] score 14 points). MCA MFV increased in all patients with lowering head position (maximum absolute MFV value increase 27 cm/s, range 5 to 96% from baseline values at 30°). On average, MCA MFV increased 20% (12% from 30 to 15° and 8% from 15 to 0°; p ≤ 0.025). Mean arterial pressure and heart rate were unchanged throughout the intervention. PI remained unchanged (mean values 0.89 at 30° elevation, 0.91 at 15° elevation, and 0.83 at 0° elevation) at each HOB position, indicating no increase in resistance to blood Flow. Immediate neurologic improvement (average 3 NIHSS motor points) occurred in three patients (15%) after lowering head position. Conclusion: Acute ischemic stroke patients may benefit from lower head-of-the-bed positions to promote Residual blood Flow to ischemic brain tissue.
-
thrombolysis in brain ischemia tibi transcranial doppler Flow grades predict clinical severity early recovery and mortality in patients treated with intravenous tissue plasminogen activator
Stroke, 2001Co-Authors: Andrew M Demchuk, Scott W Burgin, Ioannis Christou, Robert A Felberg, Philip A Barber, Michael D Hill, Andrei V. AlexandrovAbstract:Background and Purpose—TIMI angiographic classification measures coronary Residual Flow and recanalization. We developed a Thrombolysis in Brain Ischemia (TIBI) classification by using transcranial Doppler (TCD) to noninvasively monitor intracranial vessel Residual Flow signals. We examined whether the emergent TCD TIBI classification correlated with stroke severity and outcome in patients treated with intravenously administered tPA (IV-tPA). Methods—TCD examination occurred acutely and on day 2. TIBI Flows were determined at distal MCA and basilar artery depths, depending on occlusion site. TIBI waveforms were graded as follows: 0, absent; 1, minimal; 2, blunted; 3, dampened; 4, stenotic; and 5, normal. National Institutes of Health Stroke Scale (NIHSS) scores were obtained at baseline and 24 hours after administration of tPA. Results—One hundred nine IV tPA patients were studied. Mean±SD age was 68±16 years; median NIHSS score before administration of tPA (pre-tPA) was 17.5. The tPA bolus was administer...
G Iglesias - One of the best experts on this subject based on the ideXlab platform.
-
tidal stream energy impacts on estuarine circulation
Energy Conversion and Management, 2014Co-Authors: V Ramos, M Sanchez, R Carballo, M Veigas, G IglesiasAbstract:Abstract Among the impacts on the marine environment associated with the operation of a tidal farm, the alteration of the transient and Residual Flow velocities must be assessed in detail, for they constitute the driving force of important environmental processes such as sediment and pollutant transport, and nutrient dispersion. The objective of this study is to assess the impacts caused by the operation of a tidal farm on the transient and Residual Flow by means of a case study: a tidal stream farm in Ria de Ribadeo, an estuary in NW Spain. For this purpose a 3D numerical model of the estuary is implemented and successfully validated based on field data of tidal levels and Flow velocities. The energy extracted by the tidal stream farm from the Flow is accounted for by adding a momentum sink term in the equations of the model. Two scenarios representative of typical winter and summer conditions are considered. The results show that the disturbances to the transient Flow patterns are concentrated in the proximity of the farm, with a weakening of the Flow upstream and, especially, downstream of the farm (up to 0.25 ms −1 ) and an intensification on both sides (up to 0.10 ms −1 ). As for the Residual Flow, we find that the operation of the tidal farm does not disrupt the complex 3D Residual circulation of the ria, but it does lead to modifications of the Residual Flow of up to 0.025 ms −1 , or approximately 10% of the baseline Residual Flow, which affect a much larger area than in the case of the transient Flow (up to approximately 2 km from the farm). The repercussions of these alterations of the transient and Residual Flow patterns of the estuary for its sedimentary and biological processes warrant further research. Overall, these results confirm the importance of assessing the impacts of a tidal stream farm on the Flow.
-
tidal stream energy impact on the transient and Residual Flow in an estuary a 3d analysis
Applied Energy, 2014Co-Authors: M Sanchez, R Carballo, V Ramos, G IglesiasAbstract:The interest in the exploitation of the tidal stream energy has increased significantly over the last years and several tidal farms have been proposed. In spite of this, only a few studies dealt with the potential impacts on the environment resulting from the extraction of this energy, most of them by using 2D numerical models. However, some of the areas of interest for tidal stream exploitation, such as the Galician Rias, present complex transient and Residual circulation patterns which in turn result in one of the largest oceanic productivities in the world and whose potential changes cannot be properly studied by means of 2D models. In this work, a 3D numerical model was implemented in Ria de Ortigueira, a promising region for tidal stream energy exploitation, to study the potential Flow changes due to the operation of a power plant, including the assessment of the potential impacts on the 3D Residual Flow in a real estuary. First, the model was validated on the basis of current velocity measurements, then, it was used to describe the potential effects resulting from the operation of a previously proposed tidal stream farm during typical winter and summer conditions. For this purpose, the momentum sink approach was used. Overall, it was found that the resulting transient Flow modifications were concentrated in the area occupied by and next to the farm, with nearly negligible effects outside the inner ria. Furthermore, important asymmetry effects were also observed; although the inner part of the estuary is flood dominated, the most important effects occur during the ebb as a result of the complex geometry of this area. Finally, the effects on the Residual Flow are of the same order, in terms of percentage of velocity variation, as in the case of the transient Flow; however, they extend over a wider region, affecting the middle ria, where a complex 3D circulation pattern (a positive estuarine circulation) develops. Nevertheless, the operation of the tidal plant is not capable of modifying the general 3D Flow structure in this area.
Georgios Tsivgoulis - One of the best experts on this subject based on the ideXlab platform.
-
quantification of microspheres appearance in brain vessels implications for Residual Flow velocity measurements dose calculations and potential drug delivery
Stroke, 2008Co-Authors: Vijay K. Sharma, Annabelle Y. Lao, Georgios Tsivgoulis, Marc D. Malkoff, Anne W Alexandrov, Andrei V. AlexandrovAbstract:Background and Purpose— Characteristics of ultrasound-activated gaseous microspheres (μS) reflective of their size and quantities are needed for future dose-escalation and drug delivery trials. Methods— A double-blind, interobserver-validated analysis of multi-gate power-motion Doppler μS traces included large (>8μ) μS from agitated saline injections in the right-to-left shunt (RLS) positive stroke patients and small (<5μ) μS from acute patients without shunts receiving thrombolysis and perflutren-lipid μS. Results— In 101 μS traces from 50 RLS-positive and 10 thrombolysis+μS treated patients, a large μS passage had median maximum duration 30.8 ms (interquartile range [IQR] 22.0ms), multi-gate travel time (MGTT) 58.6±19.3 ms versus small μS: duration 8.3ms (IQR 4.3ms), MGTT 43.2±13.9ms, P<0.001. Small μS had higher embolus-to-blood ratio (EBR): 17.5 (IQR 9.3) versus 7.5 (IQR 4), P<0.001. Receiver-operating curve areas were: duration 0.989 (95% CI 0.968 to 1.000), MGTT 0.766 (0.672 to 0.859), and EBR (Embo...
-
a pilot randomized clinical safety study of sonothrombolysis augmentation with ultrasound activated perflutren lipid microspheres for acute ischemic stroke
Stroke, 2008Co-Authors: Andrei V. Alexandrov, Robert Mikulik, Marc Ribo, Vijay K. Sharma, Annabelle Y. Lao, Georgios Tsivgoulis, Rebecca M. Sugg, Andrew D BarretoAbstract:Background and Purpose— Ultrasound transiently expands perflutren-lipid microspheres (μS), transmitting energy momentum to surrounding fluids. We report a pilot safety/feasibility study of ultrasound-activated μS with systemic tissue plasminogen activator (tPA). Methods— Stroke subjects treated within 3 hours had abnormal Thrombolysis in Brain Ischemia (TIBI) Residual Flow grades 0 to 3 before tPA on transcranial Doppler (TCD). Randomization included Controls (tPA+TCD) or Target (tPA+TCD+2.8 mL μS). The primary safety end point was symptomatic intracranial hemorrhage (sICH) with worsening by ≥4 NIHSS points within 72 hours. Results— Fifteen subjects were randomized 3:1 to Target, n=12 or Control, n=3. After treatment, asymptomatic ICH occurred in 3 Target and 1 Control, and sICH was not seen in any study subject. μS reached MCA occlusions in all Target subjects at velocities higher than surrounding Residual red blood cell Flow: 39.8±11.3 vs 28.8±13.8 cm/s, P<0.001. In 75% of subjects, μS permeated to area...
John P Cheatham - One of the best experts on this subject based on the ideXlab platform.
-
evaluation of the amplatzer vascular plug for embolization of peripheral vascular malformations associated with congenital heart disease
Catheterization and Cardiovascular Interventions, 2006Co-Authors: Sharon L Hill, William E. Hellenbrand, Ziyad M Hijazi, John P CheathamAbstract:Objective: The purpose of this study is to evaluate the recently FDA-approved AMPLATZER® Vascular Plug in the embolization of vascular lesions associated with congenital heart disease (CHD). Background: Fistulas and arteriovenous malformations have been occluded using various devices. The AMPLATZER Vascular Plug is a self-expandable, cylindrical device, used for embolization in the peripheral vasculature. Methods: A total of 84 vessels in 52 patients with CHD from 11 centers were occluded with 89 AMPLATZER Vascular Plugs, delivered through a coronary guide catheter in various vascular sites, including collaterals, pulmonary arterio-venous and coronary artery fistulas, transhepatic tracts, central shunts, patent ductus arteriosus (PDA), and excluded hepatic vein. Complete vessel occlusion was demonstrated within 10 min in 94% of patients. Results: There was no device embolization, vascular disruption, or procedure-related complication. One vascular plug implanted in a large type C PDA required surgical removal followed by PDA ligation, after 5 weeks from successful implant because of significant Residual Flow through the device. Conclusions: The AMPLATZER Vascular Plug is an effective transcatheter occlusion device in the embolization of a wide variety of vascular lesions associated with CHD. Based on our early experience, caution should be used when considering the Vascular Plug as a closure device for large PDA. © 2005 Wiley-Liss, Inc.
Raymond J Gibbons - One of the best experts on this subject based on the ideXlab platform.
-
noninvasive prediction of Residual blood Flow within the risk area during acute myocardial infarction a multicenter validation study of patients undergoing direct coronary angioplasty
American Heart Journal, 1997Co-Authors: Panithaya Chareonthaitawee, Timothy F Christian, Stuart T Higano, James H Okeefe, Peter B Berger, Michael K Oconnor, Michael Spain, Cindy L Grines, Raymond J GibbonsAbstract:Abstract Background In a previous study from a single center, radionuclide measures of collateral Flow with technetium 99m sestamibi have been shown to be significantly associated with angiographic Residual (antegrade and collateral) Flow and independent predictors of final infarct size in acute myocardial infarction. This study examined whether the previously described radionuclide measures of blood Flow to the infarct zone were reproducible with different laboratories and imaging systems. Methods and Results Residual Flow to the infarct zone was assessed by both invasive and noninvasive methods in 77 patients with first-time myocardial infarction (32 anterior, 45 nonanterior). All patients underwent acute coronary angiography before any intervention within 8 hours of the onset of chest pain (4.0 ± 1.5 hours; range 1.2 to 7.9 hours). 99m Tc sestamibi was injected intravenously before reperfusion therapy, and tomographic imaging was performed 1 to 6 hours after injection. A central core laboratory processed the acquired images from three centers, each with a unique camera and computer system. Three previously published methods based on the severity of the acute perfusion defect were used to measure Residual Flow to the infarct zone (nadir, severity index, area). Antegrade (Thrombolysis in Myocardial Infarction Flow) and collateral Flow before direct angioplasty were blindly graded on a four-point scale (0 to 3) from the acute angiogram. The simple sum of the two grades was defined as the angiographic Flow index, representing Residual Flow to the jeopardized zone. All three noninvasive measures of Residual Flow were highly associated with the angiographic Flow index in a linear fashion: severity index ( p = 0.0006), area ( p = 0.003), and nadir (minimum/maximum counts; p = 0.004). This association was independent of the laboratory where the data were acquired. Conclusions Despite different laboratories and camera systems, radionuclide measures of Residual Flow were highly associated with the angiographic Flow index before reperfusion therapy. These results suggest that these measures are applicable on a broader scale for the noninvasive determination of collateral and antegrade Flow in acute myocardial infarction. (Am Heart J 1997;134:639-46.)
-
Residual Flow to the infarct zone as a determinant of infarct size after direct angioplasty
Circulation, 1993Co-Authors: Ian P Clements, Timothy F Christian, Stuart T Higano, Raymond J Gibbons, Bernard J GershAbstract:BACKGROUND In acute myocardial infarction, Residual Flow to the infarct zone either through antegrade Flow in the infarct-related coronary artery or collateral Flow from the non-infarct-related arteries is often present before reperfusion therapy. The purpose of this study was to assess the influence of antegrade Flow in the infarct-related artery and/or collateral Flow to the infarct zone before successful direct angioplasty on infarct size and myocardial salvage in patients with acute evolving myocardial infarction. METHODS AND RESULTS Sixty patients with acute evolving myocardial infarction underwent direct successful angioplasty without prior thrombolytic therapy. The myocardium at risk of infarction, the final infarct size, and myocardial salvage were measured by tomographic perfusion imaging with 99mTc sestamibi. Antegrade Flow in the infarct-related artery before intervention was graded according to the Thrombolysis in Myocardial Infarction (TIMI) study group classification. Collateral Flow to the infarct zone before angioplasty was also graded (0 through 3, 0 being no collateral Flow). The presence of even minimal antegrade Flow before angioplasty (TIMI grade 1) in the infarct-related artery compared with absent Flow was associated with a significant reduction in final infarct size (9 +/- 17% versus 23 +/- 19% of left ventricle, P = .02) and a significant increase in myocardial salvage (23 +/- 16% versus 14 +/- 13% of left ventricle, P = .05) after angioplasty. When antegrade Flow in the infarct-related artery was absent before angioplasty, the presence of collateral Flow before angioplasty resulted in a significantly smaller final infarct size (P = .01) and more myocardial salvage (P = .05) after angioplasty. Both antegrade infarct-related artery Flow and collateral Flow to the infarct zone had significant independent ability to predict infarct size after angioplasty. When collateral grade and TIMI grade were added to provide an estimate of Residual Flow, a model including Residual Flow, myocardium at risk, and the interaction of Residual Flow and infarct site explained 83% of the variability in infarct size after angioplasty. CONCLUSIONS The presence of antegrade Flow in the infarct-related artery and/or collateral Flow to the infarct zone before direct angioplasty in acute evolving infarction results in a smaller infarct size after direct successful angioplasty.