A framework for the modeling of suspended multicomponent particulate systems with applications to atmospheric aerosols

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1995.Includes bibliographical references (p. 408-415).by Timothy J. Resch.Ph.D

Changes in aneurysm morphology and stent-graft configuration after endovascular repair of aneurysms of the descending thoracic aorta

AbstractObjective: We sought to study changes in morphology and stent-graft configuration of descending thoracic aortic aneurysms after endovascular repair. Methods: Twenty-three patients treated with custom-made stent-grafts were studied. The stent-graft consisted of continuous, stainless-steel Z stents mounted within a polyester graft. In the last 11 cases the stents were interconnected with 3 longitudinal wires. Contrast-enhanced spiral computed tomography was performed preoperatively and at 1, 3, and every 6 months postoperatively. Angiography was used preoperatively and at 1-year follow-up. Proximal and distal necks were assessed for diameter and length. Aneurysm diameter, endoleaks, stent-graft migration, and changes in stent-graft configuration were evaluated. Results: During follow-up (median, 18 months; range, 1-48 months), excluded aneurysms decreased in diameter by 4 mm (0.5-10 mm, P =.0018). Endoleaks prevented size decrease. Five patients displayed neck dilatation, 4 at both the proximal and distal fixation sites and 1 only distally. In 7 (30%) patients there was proximal migration of the distal end of the stent-graft. Three (13%) patients displayed both distal migration of the proximal end of the stent-graft and proximal migration of the distal end of the stent-graft. There was a significant correlation between stent-graft kinking and appearance of proximal or distal stent-graft migration (P =.05 and P =.0007, respectively). In no case did the migration lead to appearance of an endoleak before intervention was performed. Conclusion: Excluded descending thoracic aortic aneurysms decrease in size on midterm follow-up. A subgroup of patients prone to neck dilatation might exist. A combination of neck dilatation and vector forces acting on stent-grafts in the tortuous thoracic aorta might lead to stent-graft migration.J Thorac Cardiovasc Surg 2001;122:47-5

In situ bending of thoracic stent grafts: Clinical application of a novel technique to improve conformance to the aortic arch

PurposeA straight thoracic stent graft often complies poorly with the curvature of the aortic arch. We have previously reported an in vitro model of a modified stent graft that can be bent in situ after deployment to improve conformance to the aortic arch. We now report the first clinical experience with this technique in three consecutive patients.MethodsBetween September 2007 and August 2008, three patients were treated for different pathologies of the aortic arch with a modified thoracic stent graft that was fitted with a sliding self-locking knot and a detachable Bowden cable. Transfemoral traction on the Bowden cable enables controlled shortening of the proximal part of the stent graft at the inner curve after deployment. The stent graft is thereby directed to allow for better apposition to the aortic wall.ResultsThe modified thoracic stent grafts were correctly orientated and deployed in all patients. Transfemoral traction on the Bowden cable successfully bent all stent grafts and improved vessel wall apposition without a residual gap on the inner curve. The Bowden cable was successfully released and withdrawn in all patients.ConclusionIn situ bending of thoracic stent grafts with a sliding self-locking knot is feasible and improves proximal apposition of the device at the inner curve of the aortic arch. More data and longer follow-up are required to confirm the applicability of this technique

Intra-aneurysm sac pressure measurements after endovascular aneurysm repair: differences between shrinking, unchanged, and expanding aneurysms with and without endoleaks

AbstractObjectiveOur objective was to study intra-aneurysm pressure after endovascular aneurysm repair (EVAR) in shrinking, unchanged, and expanding abdominal aortic aneurysms (AAAs) with and without endoleaks.MethodsDirect intra-aneurysm sac pressure measurement (DISP) by percutaneous translumbar puncture of the AAA under fluoroscopic guidance was performed 46 times during the follow-up of 37 patients (30 men; median age, 73 years [range, 58-82 years]; AAA diameter: median, 60 mm [range, 48-84 mm]). Three patients were included in two different groups because DISP was performed more than once with different indications. Tip-pressure sensors mounted on 0.014-inch guidewires were used for simultaneous measurement of systemic and AAA sac pressures. Mean pressure index (MPI) was calculated as the percentage of mean intra-aneurysm pressure relative to the simultaneous mean intra-aortic pressure.ResultsMedian MPI was 19% in shrinking (11 patients), 30% in unchanged (10 patients), and 59% in expanding (9 patients) aneurysms without endoleaks. Pulse pressure was also higher in expanding (10 mm Hg) compared with shrinking (2 mm Hg; P < .0001) AAAs. Four of the nine patients with expanding AAAs underwent five repeated DISPs later in the follow-up, and MPIs were consistently elevated. Seven of the 10 patients with unchanged AAAs without endoleaks underwent further computed tomography follow-up after DISP; 2 expanded (MPI, 47%-63%), 4 shrank (MPI, 21%-30%), and 1 remained unchanged (MPI, 14%). Type II endoleaks (6 patients, 7 DISPs) were associated with wide range of MPI (22%-92%). Successful endoleak embolization (n = 4) resulted in pressure reduction.ConclusionsIntra-aneurysm sac pressure measurement is an important adjunctive for EVAR evaluation, possibly allowing early detection of failures. High pressure is associated with AAA expansion and low pressure with shrinkage. Type II endoleaks can be responsible for AAA pressurization, and successful embolization appears to result in pressure reduction

Persistent collateral perfusion of abdominal aortic aneurysm after endovascular repair does not lead to progressive change in aneurysm diameter

AbstractPurpose: To differentiate between the phenomenon of collateral perfusion from a side branch versus graft-related endoleaks after endovascular repair of abdominal aortic aneurysms (AAA), with respect to aneurysm size and prognosis. Methods: We successfully treated 64 AAA patients with endovascular grafting. We followed all the patients postoperatively with spiral computed tomography at one, three, six and 12 months, and biannually thereafter. We measured aneurysm diameters preoperatively and postoperatively. We calculated preoperatively the relation of maximum aortic diameter (D) to the thrombus-free lumen diameter (L) expressed as an L/D ratio. Median follow-up was 15 months. Results: Sixteen patients had collateral perfusion during follow-up. We successfully treated two patients with embolization. One patient showed resolution of collateral perfusion after we stopped warfarin treatment. Two patients died of unrelated causes during follow-up. One patient was converted to surgical treatment, and two patients showed spontaneous resolution of their collateral perfusion. The group of patients with perfusion showed no statistically significant change of their aortic diameter on follow-up. The group of patients without perfusion showed a median decrease in aortic diameter of 8mm (p < 0.0001) at 18 months postoperatively. The group of patients with perfusion had significantly less thrombus in their aneurysm sac preoperatively than the group without perfusion, as expressed by the L/D ratio (mean L/D 0,61 versus 0,78, respectively; p = 0.0021.) Conclusion: There was no significant increase in aortic diameter on an average 18 months postoperatively despite persistent collateral perfusion. This may indicate a halted disease progression in the short term. Embolization of collateral vessels is associated with risk of paraplegia. We recommend a conservative approach with close observation if aneurysm diameter is stable. (J Vasc Surg 1998;28:242-9.

Endovascular repair of descending thoracic aortic aneurysms: an early experience with intermediate-term follow-up

AbstractPurpose: The purpose of this study was to report an initial experience with the endovascular repair of descending thoracic aortic aneurysm. Complications and intermediate-term morphologic changes were identified with the intent of altering patient selection and device design. Methods: Endografts were placed into 25 patients at high-risk for conventional surgical repair over a 3 ½–year period. Devices were customized on the basis of preoperative imaging information. Follow-up computed tomography scans were obtained at 1, 3, 6, and 12 months and yearly thereafter. Additional interventions occurred in the setting of endoleaks, migration, and aneurysm growth. Results: The overall 30-day mortality rate was 20% (12.5% for elective cases; 33% for emergent cases). There were 3 conversions to open repair. Neurologic deficits developed in 3 patients; 1 insult resulted in permanent paraplegia. Neurologic deficits were associated with longer endografts (P = .019). Three endoleaks required treatment, and 1 fatal rupture of the thoracic aneurysm treated occurred 6 months after the initial repair. Migrations were detected in 4 patients. The maximal aneurysm size decreased yearly by 9.15% (P = .01) or by 13.5% (P = .0005) if patients with endoleaks (n = 3 patients) were excluded. Both the proximal and distal neck dilated slightly over the course of follow-up (P = .019 and P = .001, respectively). The length of the proximal neck was a significant predictor of the risk for endoleakage (P = .02). Conclusion: The treatment of descending thoracic aortic aneurysms with an endovascular approach is feasible and may, in some patients, offer the best means of therapy. Early complications were primarily related to device design and patient selection. All aneurysms without endoleaks decreased in size after treatment. Late complications were associated with changing aneurysm morphologic features and device migration. The morphologic changes remain somewhat unpredictable; however, alterations in device design may result in improved fixation and more durable aneurysm exclusion. (J Vasc Surg 2000;31:147-56.

Scandinavian trial of uncomplicated aortic dissection therapy : study protocol for a randomized controlled trial

Peer reviewe

Three-Dimensional Geometric Analysis of Balloon-Expandable Covered Stents Improves Classification of Complications after Fenestrated Endovascular Aneurysm Repair

In balloon-expandable covered stent (BECS) associated complications after fenestrated endovascular aneurysm repair (FEVAR), geometric analysis may determine the cause of failure and influence reintervention strategies. This study retrospectively classifies BECS-associated complications based on computed tomographic angiography (CTA) applied geometric analysis. BECS-associated complications of FEVAR-patients treated in two large vascular centers between 2012 and 2021 were included. The post-FEVAR CTA scans of complicated Advanta V12 BECSs were analyzed geometrically and complications were classified according to its location in the BECS. BECS fractures were classified according to an existing classification system. In 279 FEVAR-patients, 34 out of the 683 included Advanta V12 BECS (5%) presented with a complication. Two Advanta V12 complications occurred during the FEVAR procedure and 32 occurred during follow-up of which five post-FEVAR CTA scans were missing or not suitable for analysis. In the remaining 27 BECSs complications were classified as (endoleaks (n = 8), stenoses (n = 4), occlusions (n = 6), fractures (n = 3), and a combination of complications (n = 6)). All BECSs associated complications after FEVAR with available follow up CTA scans could be classified. Geometric analysis of BECS failure post-FEVAR can help to plan the reintervention strategy

A systematic review of how homeopathy is represented in conventional and CAM peer reviewed journals

BACKGROUND: Growing popularity of complementary and alternative medicine (CAM) in the public sector is reflected in the scientific community by an increased number of research articles assessing its therapeutic effects. Some suggest that publication biases occur in mainstream medicine, and may also occur in CAM. Homeopathy is one of the most widespread and most controversial forms of CAM. The purpose of this study was to compare the representation of homeopathic clinical trials published in traditional science and CAM journals. METHODS: Literature searches were performed using Medline (PubMed), AMED and Embase computer databases. Search terms included "homeo-pathy, -path, and -pathic" and "clinical" and "trial". All articles published in English over the past 10 years were included. Our search yielded 251 articles overall, of which 46 systematically examined the efficacy of homeopathic treatment. We categorized the overall results of each paper as having either "positive" or "negative" outcomes depending upon the reported effects of homeopathy. We also examined and compared 15 meta-analyses and review articles on homeopathy to ensure our collection of clinical trials was reasonably comprehensive. These articles were found by inserting the term "review" instead of "clinical" and "trial". RESULTS: Forty-six peer-reviewed articles published in a total of 23 different journals were compared (26 in CAM journals and 20 in conventional journals). Of those in conventional journals, 69% reported negative findings compared to only 30% in CAM journals. Very few articles were found to be presented in a "negative" tone, and most were presented using "neutral" or unbiased language. CONCLUSION: A considerable difference exists between the number of clinical trials showing positive results published in CAM journals compared with traditional journals. We found only 30% of those articles published in CAM journals presented negative findings, whereas over twice that amount were published in traditional journals. These results suggest a publication bias against homeopathy exists in mainstream journals. Conversely, the same type of publication bias does not appear to exist between review and meta-analysis articles published in the two types of journals

Financing essential HIV services: a new economic agenda.

Anna Vassall and colleagues discuss the need for, and challenges facing, innovative and sustainable financing of the HIV response. Please see later in the article for the Editors' Summary