132 research outputs found
Graphene Oxide–Antimony Nanocomposite Sensor for Analysis of Platinum Group Metals in Roadside Soil Samples
The present study introduced a very sensitive and low-cost analytical procedure based on voltammetry to study platinum group metals in road dust and roadside soil matrices. Cathodic stripping voltammetry in conjunction with a reduced graphene oxide-antimony nanocomposite sensor and ICP-MS analysis were used to analyse roadside soil and dust samples. The results were processed to evaluate possible pollution in order to map the distribution of the PGMs along specific roads in the Stellenbosch area, outside Cape Town. The results revealed that within each site under investigation, Pd was more abundant than Pt and Rh using both voltammetric and spectroscopic methods. The AdDPCSV results obtained showed concentrations for Pd(II) ranging between 0.92 – 4.0 ng kg–1. For Pt (II), the concentrations ranged between 0.84 – 0.99 ng kg–1. For Rh(III), concentrations ranged between 0.42 – 1.21 ng kg–1. The ICP-MS results showed Pd concentrations ranging between 0.01 – 0.34 µg kg–1. For Pt the concentrations ranged between 0.004 – 0.07 µg kg–1. For Rh, concentrations ranged between 0.002 – 0.26 µg kg–1. The analysis showed significant levels of all PGMs in soil and dust samples analysed. Metal concentration in dust and soil followed the trend Pd > Pt > Rh using both voltammetric and spectroscopic technique
Voltammetric Analysis of Platinum Group Metals Using a Bismuth-Silver Bimetallic Nanoparticles Sensor
This study dealt with the development of a bismuth-silver bimetallic nanosensor for differential pulse adsorptive stripping voltammetry of platinum group metals (PGMs) in environmental samples. The nanosensor was fabricated by drop coating a thin bismuth-silver bimetallic film onto the active area of the screen-printed carbon electrodes. Optimization parameters such as pH, dimethylglyoxime (DMG) concentration, deposition potential and deposition time, stability test and interferences were also studied. In 0.2 M acetate buffer (pH = 4.7) solution and DMG as the chelating agent, the reduction signal for PGMs ranged from 0.2 to 1.0 ng L−1. In the study of possible interferences, the results have shown that Ni(II), Co(II), Fe(III), Na+, SO42−, and PO43− do not interfere with Pd(II), Pt(II), and Rh(III) in the presence of DMG with sodium acetate buffer as the supporting electrolyte solution. The limit of detection for Pd(II), Pt(II), and Rh(III) was found to be 0.07, 0.06 and 0.2 ng L−1, respectively. Good precision for the sensor application was obtained with a reproducibility of 7.58% for Pd(II), 6.31% for Pt(II), and 5.37% for Rh(III) (n = 10)
Optimisation of Parameters for Spectroscopic Analysis of Rare Earth Elements in Sediment Samples
The rapid demand for rare earth elements (REEs) in recent years due to increased use in various technological applications, agriculture, etc. has led to increased pollution and prevalence of REEs in the environment. Therefore, monitoring for REEs in the aquatic environment has become essential including the risk assessment to aquatic organisms. Since direct determination of REEs in sediment samples prove difficult at times, due to low concentrations available and complex matric effects, separation and enrichment steps are sometimes used. In this work, various REEs were determined employing wet acid digestion and lithium metaborate fusion in our optimised analytical technique. A comparison of the two analytical techniques was also made. The results obtained from the optimised ICP-OES radial view technique were in 5% agreement with the ICP-MS results from the same samples. The accuracy of the method was checked with the geological reference material GRE-03 and found to be in reasonable agreement. We demonstrated that there is a consistent relationship between the signals of the REEs and nebuliser gas flow rates, plasma power and pump speed. The detection limits for all the REEs ranged from 0.06 mg L-1 Yb to 2.5 mg L-1 Sm using the ICP-OES fusion technique
Renal Artery Stenosis and Obstructive Uropathy: To Resect or to Stent?
INTRODUCTION: Atherosclerotic renal artery stenosis causes hypertension that is resistant to medical management and may eventually lead to loss of kidney function. The treatment options for uncontrolled hypertension include best medical therapy (BMT), renal artery stenting (RAS), or surgical intervention; however, the optimal modality remains uncertain. This is the case of a patient with renal artery stenosis complicated by concurrent obstructive uropathy.
CASE DESCRIPTION: Our patient is a 66-year-old male with a long-standing history of hypertension uncontrolled with BMT (beta blocker, angiotensin II receptor blocker (ARB) and a thiazide diuretic) and progressive renal insufficiency which was presumed to be due to prostatic obstructive uropathy. Despite undergoing a transurethral prostatectomy, his renal function continued to decline. A pelvic magnetic resonance angiogram (MRA) was performed which showed bilateral renal artery stenosis with the left being worse than the right. Computed tomography angiogram (CTA) was then performed which confirmed significant bilateral renal artery stenosis of 80 percent and 60 percent of the left and right renal artery respectively. The patient then underwent balloon angioplasty followed by stenting of both vessels without complication. Post-stenting angiography showed less than 30 percent stenosis of either vessel. During hospitalization, he had some improvement in his blood pressure, and his renal function was improved from baseline. One month follow up showed no significant change in blood pressure from initial visit prior to stenting.
DISCUSSION: In healthy subjects, reduced renal perfusion lowers the glomerular filtration rate (GFR), causing a response by the renin-angiotensin-aldosterone system (RAAS) which leads to a compensatory increase in blood pressure. Although the GFR is reduced, renal parenchyma is able to adapt to reduced blood flow if perfusion pressure is reduced by 40 percent. There are a number of ways to manage renal artery stenosis, including RAS versus BMT. Currently, the effects of stenting are controversial and not fully understood. Multiple randomized trails have shown confounding results. Some trails have shown benefit in RAS, while others have demonstrated increase adverse outcomes due to renal reperfusion. In this case, we decided to to proceed with RAS given the significant stenosis on imaging, the patient's clinical presentation of worsening renal function despite BMT, and having ruled out other causes of progressive renal failure. The decision to intervene in these patients is usually determined on a case-by-case basis after discussion between surgeon, nephrologist and patient and after educating the patient on the risks and benefits.N
Thoracic Endovascular Repair of Descending Thoracic Aortic Thrombus
INTRODUCTION: Penetrating atherosclerotic ulcers (PAU) develop in the internal elastic lamina and indicate severe aortic atherosclerosis. PAU can have an associated intraluminal aortic thrombus, with associated risk of thromboembolism with subsequent mesenteric infarct and limb loss. We present a case of persistent descending thoracic aortic thrombus, with embolic renal infarcts, necessitating repair.
CASE DESCRIPTION: A 80-year-old woman with history of bilateral renal infarcts on Eliquis and uncontrolled hypertension was referred to our department for extensive aortic atherosclerosis and 6mm ulceration proximal to the celiac artery, demonstrated on a CT. A follow up Computed Tomography Angiogram (CTA) demonstrated a persistent descending thoracic aortic thrombus and thoracic endovascular repair (TEVAR) was indicated. Preoperative imaging demonstrated >50% stenosis of the distal left common femoral artery (CFA).
We accessed the proximal left CFA and subsequently placed stent grafts in the descending thoracic aorta, distally to proximally. Completion aortogram revealed complete occlusion in left external iliac artery. Doppler signals to the left foot were diminished on prompt exam.
Current intraoperative imaging showed thromboembolism vs. flow-limiting dissection in the left CFA and external iliac arteries. Given these findings, an open endarterectomy of the iliac arteries was indicated, along with stent graft deployment in the left external iliac artery and bilateral stents in the common iliac arteries.
A complete angiogram revealed a flow-limiting thromboembolism in the left superficial femoral artery (SFA). This was treated with covered stent placement, excluding the thrombus. Subsequent imaging demonstrated brisk flow into the left foot. On exam, pulses were palpable in the feet bilaterally and she moved all extremities. This patient had an uneventful hospital course and was discharge on postoperative day three.
DISCUSSION: PAUs are a collective part of Acute Aortic Syndrome (AAS), seen in 2-8% of patients with AAS. PAUs develop from aortic mural thrombi, located most frequently in the abdominal aorta. A PAU > 4mm thick with ulceration is categorized as a complex plaque and warrants surgical repair. Anticoagulation is not sufficient for complex plaques. Endovascular repair (EVAR) is preferred to open since operating time is shorter, involves smaller incisions, and decreased hospital stay, with improved perioperative morbidity and all-cause mortality. Employing quality vascular access and wire manipulation can reduce endoleaks, access complications, and peripheral embolization. If complications arise, prompt imaging to access the stenotic vessels is necessary. This case demonstrates the potential morbidity of aortic thrombus embolization and the attention to detail required for successful treatment.N
An Interesting Case Highlighting Management of Pelvic Congestion Syndrome
INTRODUCTION: The development of valvular incompetence and/or obstruction in the pelvic and gonadal veins causing disabling symptoms comprises Pelvic Congestion Syndrome (PCS). It is a less known pathologic condition commonly occurring in women of child bearing age, and diagnosis can be challenging due to a variety of clinical presentations. Nutcracker syndrome (NCS) is a potential cause of PCS and involves compression of the left renal vein between the superior mesenteric artery and the aorta. We report one such case of a woman who presented with chronic pelvic pain.
CASE DESCRIPTION: Our patient is a 31-year-old woman evaluated in our clinic with 6 years of unbearable back and suprapubic pain associated with dyspareunia and dysuria. She underwent evaluation by her gynecologist, and a transvaginal ultrasound demonstrated vaginal varicosities. Computed tomography angiogram (CTA) showed dilated left ovarian vein contiguous with left greater than right pelvic varicosities. We then performed a diagnostic venogram that demonstrated left pelvic venous plexus consistent with pelvic varicosities in the left ovarian vein and NCS anatomy. We decided to treat the PCS first. The patient underwent foam sclerotherapy of the pelvic venous plexus using 3cc of foam sclerosing agent (polidocanol) followed by coil embolization of the left ovarian vein. Post embolization venogram demonstrated radiographically successful treatment with no flow in the ovarian vein and preserved flow in the left renal vein.
DISCUSSION: Chronic pelvic pain due to pelvic congestion is often associated with a constellation of symptoms including pelvic pain, dyspareunia, dysmenorrhea, and dysuria causing negative cognitive, behavioral, sexual and emotional consequences. There are three types of chronic pelvic pain, categorized by etiology. Type I is secondary to valvular incompetence of pelvic or ovarian veins, Type II is secondary to obstruction of outflow, and Type III is due to local compression. Venography is the gold standard for diagnosis. Treatment is directed at providing symptomatic relief with medical therapy, and treating the underlying cause by either endovascular (sclerotherapy and embolization, left renal venous stent placement) or open surgical techniques (including gonadal vein transposition, left renal vein transposition, or saphenous vein bypass).N
Management of Endoleak After Abdominal Aortic Aneurysm Repair
INTRODUCTION: Abdominal aortic aneurysm (AAA) represents a potentially life-threatening condition that requires proper surveillance and treatment. While AAA was historically treated by open surgical repair, technologic advances have resulted in Endovascular Aortic Aneurysm repair (EVAR) becoming the primary repair technique for AAA. Persistent endoleaks are a known complication of EVAR that often require additional intervention. We present a case highlighting the management of a Type 1B endoleak post-EVAR.
CASE DESCRIPTION: Our patient is a 66-year-old male with history of EVAR at outside facility, and was evaluated in clinic with an enlarging iliac artery aneurysm. Computed tomography angiogram (CTA) demonstrated a 5cm aneurysmal degeneration of the right common iliac artery, most likely due to an endoleak in the distal portion of the stent (Type 1B). Due to the existing aortic endograft with a high flow divider, this required a combined axillary and femoral artery approach. The patient underwent placement of iliac branch endoprosthesis (IBE) at the right common iliac artery bifurcation with limb extension into both the external iliac and hypogastric arteries. Completion angiogram demonstrated successful extension of the endograft with exclusion of both the AAA and iliac aneurysm, preserved patency of the right hypogastric artery, and no endoleak.
DISCUSSION: Endoleaks are a known complication of EVAR and frequently require intervention. There are multiple type of endoleak. Type 1 endoleaks denote leaks due to inadequate seal, and are divided further into 1A (proximal seal zone) and 1B (distal seal zone). Type II are due to branch vessel, type III endoleak are due to graft connection, and type IV due to graft porosity. The identification of location and type is frequently challenging and requires an angiogram. The management is based on the type of leak. Our patient had a type IB, due to leakage around the distal right common iliac limb. Relining the endograft with placement of an IBE device and extension of the stents into the external iliac and hypogastric arteries ensured development of adequate seal while preserving blood flow distally. With extensive pre-operative case planning and an intricate knowledge of the vascular anatomy, the modern vascular surgeon is equipped to provide advanced endovascular treatment options for complex vascular conditions.N
Challenging Endovascular Retrieval of Multiple Well Incorporated Inferior Vena Cava Filters
INTRODUCTION: Inferior Vena Cava (IVC) filters are placed in patients to prevent pulmonary embolism in patients with recurrent deep venous thromboembolism or in high risk patients who cannot tolerate anticoagulation at their initial event. IVC filters are designed as either optional (retrievable) or permanent, and filter selection is based on the indication for placement. We present a case of complex retrieval of two IVC filters from the same patient with a history of chronic venous thromboembolism and post thrombotic syndrome.
CASE DESCRIPTION: Our patient is a 63 year-old male with a remote history of trauma that resulted in chronic venous thromboembolism and post thrombotic syndrome of left lower extremity. He presents a rare case where he had two separate IVC filters placed during his treatment; initially, a permanent filter was placed, with an additional retrievable filter placed due to recurrent pulmonary emboli. He eventually tolerated anticoagulation, and wanted these filters removed due to their possible contribution to his chronic leg swelling and pain.
From a right internal jugular vein approach, the retrievable superior filter was removed with the conventional snaring technique. We were unable to remove the second filter using conventional snare technique, as well as a through and through “flossing” approach from both jugular and femoral vein access points. We then proceeded with using a 16Fr laser extractor sheath with multiple laser treatments, followed by large aortic balloon expansion from the femoral access site, in an attempt to loosen the filter from the IVC sidewall. This combination of approaches did free the filter from the IVC wall, but the filter remained outside the sheath. Under fluoroscopic visualization, we brought the dislodged filter into the internal jugular vein and, after surgically exposing the vein, successfully removed the filter. Completion venogram confirmed removal of both filters without venous extravasation.
DISCUSSION: This case illustrates the complexity in removing permanent IVC filters in select patients wherein the legs of the filter have embedded into the IVC wall. In patients with higher complexity of IVC filter removal, various methods have been described. Two advanced modes of extraction which are popular are the Endobronchial Forceps Extractions and the Laser-Assist Snare Extraction. Different devices have their unique characteristics and different failure modes. In patients with filter legs embedded in the vessel wall, a more robust approach with laser-assist, balloon endotraction, and external traction to free it from the IVC sidewall may be required for successful retrieval, as in this patient.N
Instances and connectors : issues for a second generation process language
This work is supported by UK EPSRC grants GR/L34433 and GR/L32699Over the past decade a variety of process languages have been defined, used and evaluated. It is now possible to consider second generation languages based on this experience. Rather than develop a second generation wish list this position paper explores two issues: instances and connectors. Instances relate to the relationship between a process model as a description and the, possibly multiple, enacting instances which are created from it. Connectors refers to the issue of concurrency control and achieving a higher level of abstraction in how parts of a model interact. We believe that these issues are key to developing systems which can effectively support business processes, and that they have not received sufficient attention within the process modelling community. Through exploring these issues we also illustrate our approach to designing a second generation process language.Postprin
A schumpeterian model of growth in the world economy: Some notes on a new paradigm in international economics
- …