Alterations In Flow Dynamics Research Articles

Bubbles and Troubles: A Case of Azygous ACA with Bilateral ICA Aneurysm, Besides the Usual Distal ACA Aneurysm

Azygous ACA is one of the rare anatomic variants of anterior cerebral artery. Predisposition to aneurysm development is attributed to the alteration in flow dynamics. Such hemodynamic alteration is most commonly seen in the anterior circulation, causing distal ACA aneurysm to be the most commonly associated vascular pathology. Although neurosurgical literature is replete with anatomical reports of such cases, there has been no case reports where bilateral ICA aneurysms are also present with the distal ACA aneurysm. In this case, the presence of hypoplastic left A1 segment might predispose the other segments of Circle of Willis to hemodynamic alterations. Thus, whenever one comes across an azygous ACA in association with an additional anomaly he should be vigilant enough to look for other pathologies beyond the commonly encountered distal ACA aneurysm. The presence of azygous ACA also poses a technical challenge due to the risk of ischemic insult to anterior regions of bilateral hemispheres during temporary clipping of the single A2 trunk. In addition to it, the presence of a hypoplastic A1 segment also makes the approach to the giant aneurysm in ICA segment more technically demanding as cross flow is not adequate. So, the presence of multiple anatomic anomalies not just increases the number of vascular pathologies but also enhances the challenges that the surgeon has to face in planning the strategic approach to tackle all the lesions.

Examining the utility of river restoration approaches for flood mitigation and channel stability enhancement: a recent review

Increased anthropogenic activities, especially within the river corridor, have progressively disrupted natural flow regimes and segmented channel–floodplain connectivity. Consequent alterations in flow dynamics have caused geomorphic and hydrological changes in channel morphology and behaviour, decreasing their natural replenishment capacity, thereby causing their degradation. The simultaneous disconnection of the channel from its natural floodplain due to intensive cultivation and surface paving has also reduced possible floodwater outlets or seepage zones, which would have otherwise functioned as storm run-off storage buffers that reduced the flood peak downstream. Such occurrences of flow disruption, especially in low-relief topographic regions buffeted by high intensity monsoonal storms, accentuate flood-like situations, since natural channel capacities to transport excess storm-water are diminished, with this further enhancing ongoing or inducing riverbank erosion. Such events have accounted for much loss of life, livelihood and property worldwide and to mitigate their intensity, river restoration techniques have been promoted. These place greater emphasis on ecological management measures that attempt to restore and rehabilitate the geomorphic and hydrological functionality of the stream to a prior, more pristine state to achieve channel stability and regulate flows. Thus, frameworks based on river corridor management, riparian buffer creation and the River Styles Framework instituted guidelines, aided by geospatial analysis techniques, have yielded significant management strategies for such flood- and erosion-affected degraded channel corridors. This paper presents a recent review of such ecological techniques of flood and channel management, especially in monsoonal environments, while highlighting the issues concerning their implementation in developing nations.

Slip-driven electroosmotic transport through porous media.

We investigate the slip-driven transport of a Newtonian fluid through porous media under electrical double layer effect. We employ a semianalytical framework to obtain the underlying electrohydrodynamics for different configurations of porous media. We bring out an alteration in flow dynamics, stemming from interplay among the geometrical feature of the models and the interfacial slip as modulated by the electrical forcing. Further, we show the consequent effects of the underlying flow dynamics on the volumetric transport rate through different models. Also, we show the inception of reverse flow in the region close to the wall, resulting from the induced pressure gradient due to the convection of co-ions in the opposite direction to flow and pinpoint its effect of the flow rate variation under the influence of interfacial slip. We believe that the inferences obtained from the present analysis may improve the design of bio-MEMS (microelectromechanical systems) and microfluidic devices, which are used for in-situ bioremediation.

Validation of flow convergence region method in the assessment of carotid artery stenoses during color-flow duplex studies

Purpose: The flow convergence region (FCR) method (also known as the proximal isovelocity surface area method) is currently used in echocardiography to evaluate the flow through cardiac valves and septal defects. The FCR method is based on the characteristic alterations in flow dynamics that occur proximal to a stenotic orifice. Blood converges uniformly and radially towards an orifice that is small relative to the section of the vessel and forms concentric isovelocity hemispheric shells where velocity progressively increases and flow remains laminar. The purpose of the article is to validate the use of this principle in the detection and assessment of carotid stenoses in the course of color-flow duplex studies.Methods: It In this prospective study, 80 patients affected by unilateral or bilateral carotid artery stenoses were evaluated for the presence of the FCR from February 1997 to March 1999. The results were compared with digital subtraction angiography.Results: Color-flow duplex diagnosis of carotid artery stenoses of 70% or more was confirmed in 100% of the carotid artery stenoses (40/40 patients) with angiography. The FCR was detected in 72.2% (13/18) of carotid arteries affected by stenoses greater than 80%, in 54.4% (12/22) of carotid arteries affected by stenoses 70% to 80%, and in 13.6% (6/44) of carotid arteries affected by stenoses 50% to 69% (P <.001). In 5% of cases (2/40 of stenoses) the FCR was the only detectable sign of carotid stenosis.Conclusion: Our data suggest that a routine search for FCR in the course of color-flow duplex study of carotid arteries may further improve the reliability of this examination in the detection of carotid artery stenoses, particularly in the presence of heavily calcified lesions.

Validation of flow convergence region method in the assessment of carotid artery stenoses during color-flow duplex studies

The flow convergence region (FCR) method (also known as the proximal isovelocity surface area method) is currently used in echocardiography to evaluate the flow through cardiac valves and septal defects. The FCR method is based on the characteristic alterations in flow dynamics that occur proximal to a stenotic orifice. Blood converges uniformly and radially towards an orifice that is small relative to the section of the vessel and forms concentric isovelocity hemispheric shells where velocity progressively increases and flow remains laminar. The purpose of the article is to validate the use of this principle in the detection and assessment of carotid stenoses in the course of color-flow duplex studies. In this prospective study, 80 patients affected by unilateral or bilateral carotid artery stenoses were evaluated for the presence of the FCR from February 1997 to March 1999. The results were compared with digital subtraction angiography. Color-flow duplex diagnosis of carotid artery stenoses of 70% or more was confirmed in 100% of the carotid artery stenoses (40/40 patients) with angiography. The FCR was detected in 72.2% (13/18) of carotid arteries affected by stenoses greater than 80%, in 54.4% (12/22) of carotid arteries affected by stenoses 70% to 80%, and in 13.6% (6/44) of carotid arteries affected by stenoses 50% to 69% (P <.001). In 5% of cases (2/40 of stenoses) the FCR was the only detectable sign of carotid stenosis. Our data suggest that a routine search for FCR in the course of color-flow duplex study of carotid arteries may further improve the reliability of this examination in the detection of carotid artery stenoses, particularly in the presence of heavily calcified lesions.

Interferometric SAR observations of ice topography and velocity changes related to the 1996, Gjalp subglacial eruption, Iceland

A major volcanic eruption beneath the Vatnajokull ice cap from 30 September to 13 October 1996 melted up to 500m of overlying ice and produced 3.5km3 of water that was later released catastrophically onto the Skeidararsandur outwash plain. Here, we present pre- and post-event topography and velocity field maps of the ice cap surface derived from ERS-1/2 synthetic aperture radar (SAR) interferometry. Within the errors of this method our results reveal local topographic and ice flow variations near the eruption site and incision of a 140m meltwater trench. A 24-hour, 50cm subsidence of the frozen surface of the Grimsvotn caldera lake was also detected. However, despite the large increases in geothermal heat flux and basal meltwater availability associated with this event, there appears to be no regional-scale ice subsidence and little to no alteration in flow dynamics of the Vatnajokull ice cap.

Kinked catheters: radiographic appearance of functionally significant bends.

Several nonangiographic catheters commonly used in children were bent and kinked, radiographed, and perfused at different rates to identify appearances that corresponded to significant alterations in flow dynamics. Radiographic signs of catheter kinking (i.e., focal buckling) depended on the severity of bending and the angle of the radiographic beam relative to the plane of the bend. One or more straight lines appeared at the site of buckling; catheters that were not kinked did not demonstrate straight lines. Other signs were distortion of the round catheter lumen and bulging of the catheter material. Distortions short of sharp kinking did not compromise flow except in very small catheters.

Alteration of flow dynamics in the carotid artery system of "stroke" patients. Clinical and arteriographic study.

Percutaneous retrograde arch aortography was performed in a series of 94 patients with symptoms suggesting cerebrovascular insufficiency. In 26 of these a major stenosis (greater than 50% reduction of measured luminal diameter) was present in the cervical carotid artery(s). In 75% of this subgroup an arleriographic flow pattern was seen which correlated closely with the lateralization of cerebral ischemic manifestations. This pattern consists of a 0.5 sec or greater delay in linear flow of contrast material through the stenosed carotid artery as compared with the contralateral one. Evidence is presented to support the assumption that such a finding reflects an actual diminution of volume blood flow and is the result of the stenosis demonstrated. Two control groups of 19 neurologically normal and 60 neurologically symptomatic patients without significant stenosis of larger cerebral vessels were studied by arteriography in an identical manner. No patient in either control group manifested a unilateral delay in linear flow. Provided artefact can be excluded, this sign is believed to be a valuable index of the clinical significance of cervical carotid artery stenosis.