| 1. |
- Roos, Håkan, et al.
(författare)
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Air bubble release and flow-induced forces in stent grafts
- 2017
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Ingår i: Engineering Health.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Background: Stent grafts are used to treat aortic aneurysms, as a minimal invasive alternative to open surgery. The aorta is accessed via percutaneous punctures in the groins and insertion of guide wires. A stent graft is advanced over the guide wire and deployed in the desired position, using x-ray fluoroscopic guidance. The procedure significantly reduces short-term morbidity and mortality compared to open repair, but has a higher rate of late complications and re-interventions. Two possible complications are: release of air bubbles during thoracic stent graft deployment may lead to cerebral embolization and immediate stroke, and long-term migration due to flow-induced forces may lead to leakage into the aneurysm sack and remaining risk of aortic rupture. Objectives: Stent grafts are compressed in a long, soft and thin delivery catheter. Once the stent graft is in position, the surgeon withdraws the catheter, allowing the self-expanding stent graft to expand radially to the artery wall, or to a previously inserted stent graft. The stent graft is kept in place by the expansion force of the over-sized stent, and in some cases by anchoring hooks. Despite a strict preparation procedure, there is a risk that air is trapped in the compressed stent graft and released into the aorta during deployment. The present work describes two of our studies. In the first experimental study we measure the total amount of air released by two different brands of thoracic stent grafts and investigate the size and origin of the air bubbles. In the second experimental and numerical study angulated iliac limbs stent grafts are mounted in a pulsatile flow model to determine the flow-induced displacement forces under a variety of conditions.Methods: The air release measurements and visualizations are performed by inserting and deploying stent grafts in a closed water-filled container. A high-resolution and high-speed camera is used to capture the air release process, and the total amount of air collected in the container is measured. An experimental pulsatile flow model, with conditions similar to aortic in vivo conditions, is used to measure the proximal and distal displacement forces of iliac stent grafts under different angulations, pulsation frequencies, pressures, and configurations (tapered, tubular, bellbottom). Fluid-structure interaction simulations are used to determine the forces numerically.Results: We found that air is released during deployment of thoracic stent grafts and that the largest bubbles come from the proximal end. There is a significant difference between the two brands of stent grafts that have been investigated. The flow-induced forces are under some conditions comparable to the forces required to extract the iliac limb stent grafts. Both the forces and the graft movements increase with angulation and with perfusion pressure, but not with stroke rate. The distal displacement forces are particularly large for the bellbottom configuration. The origin of the forces is mainly the pressure, while the contributions of shear force and flow redirection are insignificant. The flexibility of the stent graft material reduces the forces (by 15% under the conditions in the numerical simulations in the present work).Conclusions: New packing and/or preparation procedures should be developed to reduce the amount of air released during deployment of thoracic stent grafts. Improved anchoring of the distal ends of stent grafts should be considered.References[1] Displacement Forces in Iliac Landing Zones and Stent Graft Interconnections in Endovascular Aortic Repair: An Experimental Study. Roos H, Ghaffari M, Falkenberg M, Chernoray V, Jeppsson A, Nilsson H.European Journal of Vascular and Endovascular Surgery 2014:47(3):262-267.
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| 2. |
- Roos, Håkan, 1967, et al.
(författare)
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Displacement Forces in Iliac Landing Zones and Stent Graft Interconnections in Endovascular Aortic Repair: An Experimental Study
- 2014
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 47:3, s. 262-267
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Stent graft migration influences the long-term durability of endovascular aortic repair. Flow-induced displacement forces acting on the attachment zones may contribute to migration. Proximal fixation of aortic stent grafts has been improved by using hooks, while distal fixation and stent graft interconnections depend on self-expansion forces only. We hypothesized that flow-induced displacement forces would be significant at the distal end, and would correlate with graft movements. Methods: As part of an experimental study, an iliac limb stent graft was inserted in a pulsatile flow model similar to aortic invivo conditions, and fixed-mounted at its proximal and distal ends to strain gauge load cells. Peak displacement forces at both ends and pulsatile graft movement were recorded at different graft angulations (0-90°), perfusion pressures (145/80, 170/90, or 195/100mmHg), and stroke frequencies (60-100b.p.m.). Results: Flow-induced forces were of the same magnitude at the proximal and distal end of the stent graft (peak 1.8N). Both the forces and graft movement increased with angulation and perfusion pressure, but not with stroke rate. Graft movement reached a maximum of 0.29±0.01mm per stroke despite fixed ends. There were strong correlations between proximal and distal displacement forces (r=0.97, p<.001), and between displacement forces and graft movement (r=0.98, p<.001). Conclusions: Pulsatile flow through a tubular untapered stent graft causes forces of similar magnitude at both ends and induces pulsatile graft movements in its unsupported mid-section. Peak forces are close to those previously reported to be required to extract a stent graft. The forces and movements increase with increasing graft angulation and perfusion pressure. Improved anchoring of the distal end of stent grafts may be considered. © 2013 European Society for Vascular Surgery.
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| 3. |
- Roos, Håkan, 1967, et al.
(författare)
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Displacement Forces in Stent Grafts: Influence of Diameter Variation and Curvature Asymmetry
- 2016
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 52:2, s. 150-156
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Long-term durability after endovascular aortic repair is influenced by stent graft migration causing types I and III endoleaks. Flow induced displacement forces have been shown to have the potential to cause migration. In this study, the influence of the distal diameter of iliac limb stent grafts and the shape of graft curvature on flow induced displacement forces, were investigated. Methods: In an experimental pulsatile flow model mimicking aortic conditions in vivo, flow induced displacement forces at the proximal and distal ends of iliac limb stent grafts were studied at different angles (0-90 degrees) and perfusion pressures (145/80, 170/90, 195/100 mmHg). Bell-bottomed, tapered, and non-tapered stent grafts and also asymmetric stent graft curvatures at 90 bend were studied. Measurements of graft movement were performed at all studied angulations and graft shapes. Results: For all stent graft diameters, flow induced displacement forces increased with higher pressure and increased stent graft angulation. Forces in the bell-bottom graft were considerably higher than in tapered and non-tapered grafts, with a markedly elevated peak force at the distal end (proximal end, 2.3 +/- 0.06 N and distal end, 6.9 +/- 0.05 N compared with 1.7 +/- 0.08 N and 1.6 +/- 0.08 N in non-tapered grafts; p <.001 both). Peak forces in tapered and non-tapered grafts were not significantly different between the proximal and distal end. In asymmetric stent graft curvatures, a significant increase in displacement forces was observed in the attachment zone that was closest to the stent graft bend. Graft movement increased with greater displacement forces. Conclusion: Flow induced displacement forces in iliac limb stent grafts are significant and are influenced by distal stent graft diameter and the shape of the graft curvature. The displacement forces are particularly high at the large distal end of bell-bottom grafts. Wide iliac arteries treated with bell-bottom stent grafts may require more vigilant surveillance and improved stent graft fixation.
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| 4. |
- Roos, Håkan, et al.
(författare)
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Fluid Pressure Derived Force is the Main Contributor to Iliac Limb Displacement Forces – Shear Force and Redirection of Flow are Negligible
- 2019
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 58:6 (supplement 1), s. e18-e19
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Tidskriftsartikel (refereegranskat)abstract
- Introduction - Complications after EVAR, including aortic rupture, continue to be a problem also in long term follow-up1. There is still a need for life-long surveillance and late re-interventions raises the question about long term EVAR-durability. Additional iliac stent grafts due to distal endoleak type I are among the more frequent among these late re-interventions2,3,4. There are indications that graft migration at iliac landing zones and graft interconnections are among the most common causes and that wide iliac arteries predispose for these complications5. Flow induced displacement forces have, in an experimental model, been shown to be significant also at distal landing zones in EVAR stent grafts6 and particularly high in grafts with large distal diameters7. These findings indicate that late EVAR failures are linked to flow induced displacement forces and subsequent graft migration. We have therefore conducted a study of fluid structure interaction with the aim to differentiate the magnitude of the different force components and numerically evaluate the forces acting on iliac limb stent grafts in different graft configurations. Methods - The displacement forces in iliac limb stent grafts were numerically evaluated using a finite volume approach for fluid-structure interaction (FSI) with the open source tool FOAM-extend-3.1. The grafts were modelled with homogeneous properties in three configurations; tapered (16 mm proximal diameter, 12 mm distal diameter), non tapered (16-16 mm) and bellbottom (16-27 mm), all at 90° angulation (see 16-27 in figure). Experimentally determined pulsatile conditions were applied for different pressures; 145/80, 170/90, 195/100 mmHg. Results - Stent graft displacement forces increased with higher fluid pressure in all graft configurations. Maximum forces in bellbottom grafts (proximal end 2.3 N, distal end 8.1 N) were particularly high compared to tapered (proximal end 2.5 N, distal end 1.2 N) and non tapered grafts (proximal end 2.5 N, distal end 2.5 N). The effects of shear stress and redirection of flow were together less than 2.8 % of the total forces in all graft configurations, whereas pressure derived forces were the main contributor to the forces acting on the stent graft. The flexibility of the stent graft absorbed up to 15 % of the forces. Conclusion - The forces acting on stent grafts during pulsatile flow are significant and particularly high in the distal end of grafts with large distal diameter. The main contributor to these displacement forces is pressure while the contribution of shear and redirection of flow are negligible. The flexibility of the stent graft tends to absorb a significant part of the forces.
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| 5. |
- Tokarev, Mikhail, 1982, et al.
(författare)
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DIC for Surface Motion Analysis Applied to Displacement of a Stent Graft for Abdominal Aortic Repair in a Pulsating Flow
- 2015
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Ingår i: PIV15; 11th International Symposium on Particle Image Velocimetry, Santa Barbara, California, USA, September 14-16, 2015. ; , s. 1-12
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Stent graft migration has been recognized to influence the long-term durability of endovascular aortic repair. Flow-induced displacement forces acting on the attachment zones may contribute to this migration. An experimental perfusion model consisting of the flow loop described by Roos et al. 2014 was used for further characterization of the pulsating flow induced stent graft movements with monocular and stereoscopic configurations of an optical imaging system. This paper adds new information on displacement measurement accuracy and 3D deformation analysis of the stent graft, which is used for abdominal aortic aneurysm treatment. The work describes used modification of Soloff’s Stereo PIV reconstruction algorithm for surface motion analysis. It was found that the oscillation of the stent graft’s body in the perpendicular direction to the front plane was 5 times less than side movements of the bent stent graft. These results can be used for further studies on different stent graft geometrical configurations and CFD simulations using fluid-structure interaction approach.
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| 6. |
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| 7. |
- Alm, Håkan, et al.
(författare)
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ChatGPT a powerful assistant, when using Double-Loop Co-Design
- 2024
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Konferensbidrag (refereegranskat)abstract
- Computers can now carry out tasks, by first learning from being given examples, rather than just doing exactly what they are told, this is often referred to as Machine Learning or AI. This has given almost endless possibilities what these machines can ultimately do. At the same time, it also gives us many threats and things to worry about from a safety, security and ethical point of view and voices are raised that we should control what AI is allowed to do by laws and regulations. By applying a Double loop Co-design approach to science this paper focusses on ChatGPT and researchers experience with effectiveness and ethics related to use o this tool. 3 workshops were conducted with totally 14 participants from 5 continents. Most of the respondents are positive and excited about what Chat GPT and AI can do for us, but they are also worried. The main concerns are that AI will do the creative and fun parts of our work and that it produces false facts. In conclusion, if applying a perspective conscious view of knowledge, AI can inspire human controlled creativity and informed decision making with multi-perspective views of reality.
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| 8. |
- Andersson, Mattias, et al.
(författare)
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A population-based study of post-endovascular aortic repair rupture during 15 years
- 2021
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Ingår i: Journal of Vascular Surgery. - : Elsevier BV. - 0741-5214 .- 1097-6809. ; 74:3
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The devastating event of a ruptured abdominal aortic aneurysm (rAAA) in patients who have survived a previous AAA repair, either elective or urgent, is a feared and quite uncommon event. It has been suggested to partly explain the loss of the early survival benefit for endovascular aortic repair (EVAR) vs open surgical repair (OSR). The main objective of this study was to report the national incidence rate, risk factors and outcome of post-EVAR ruptures. Secondarily, the national incidence rate of ruptures after OSR (post-OSR ruptures) was investigated. Methods: We conducted a nationwide, population-based, retrospective cohort study using the inpatient and outpatient entries for all patients >40 years of age, receiving their first (index) surgical procedure for AAA, from 2001 to 2015. Only patients surviving their index procedure were included. The primary outcome was rAAA, registered after discharge from the index procedure (EVAR or OSR), identified in the Swedish National Patient Registry and the Cause of Death Registry. Results: In total, 14,859 patients survived their primary (index) AAA procedure. There were 6470 EVAR procedures, 5893 for intact AAA (iAAA) and 577 for rAAA. Of the 6470 EVAR patients, 86 cases of post-EVAR rupture were identified, corresponding with a cumulative incidence of 1.3% over a mean follow-up time of 3.9 years. The incidence rate was 3.4 (95% confidence interval [CI], 2.7-4.2)/1000 person-years. The independent risk factors identified for post-EVAR rupture were rAAA at index surgery HR 2.4 (95% CI, 1.4-4.1, p 0.002) and age (hazard ratio, 1.1; 95% CI, 1.0-1.1; P <.001). Freedom from post-EVAR rupture was 99%, 98%, and 96% at 3, 5, and 10 years, respectively. Total and postoperative mortality after post-EVAR rupture were 42% and 17% (30 days), 45% and 22% (90 days), and 53% and 33% (1 year). The incidence rate of post-OSR rupture was 0.9/1000 person-years (95% CI, 0.7-1.2). Conclusions: Post-EVAR rupture is a rare complication that can occur at any time after the index EVAR procedure. This finding may have implications for the discussion of limited follow-up programs and for the choice of procedure in patients with an AAA with a long life expectancy. An rAAA as the indication for the index surgery and age were identified as risk factors for post-EVAR rupture. The mortality associated with post-EVAR rupture is high, but lower than that of primary rAAA. The much lower risk of post-OSR rupture was confirmed, but must not be neglected as a possible late complication. © 2021 The Authors
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| 9. |
- Andersson, Mattias, et al.
(författare)
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Editor's Choice – Structured Computed Tomography Analysis can Identify the Majority of Patients at Risk of Post-Endovascular Aortic Repair Rupture
- 2022
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 64, s. 166-174
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The main objective was to report mechanisms and precursors for post-endovascular aneurysm repair (EVAR) rupture. The second was to apply a structured protocol to explore whether these factors were identifiable on follow up computed tomography (CT) prior to rupture. The third objective was to study the incidence, treatment, and outcome of post-EVAR rupture. Methods: This was a multicentre, retrospective study of patients treated with standard EVAR at five Swedish hospitals from 2008 to 2018. Patients were identified from the Swedvasc registry. Medical records were reviewed up to 2020. Index EVAR and follow up data were recorded. The primary endpoint was post-EVAR rupture. CT at follow up and at post-EVAR rupture were studied, using a structured protocol, to determine rupture mechanisms and identifiable precursors. Results: In 1 805 patients treated by EVAR, 45 post-EVAR ruptures occurred in 43 patients. The cumulative incidence was 2.5% over a mean follow up of 5.2 years. The incidence rate was 4.5/1 000 person years. Median time to post-EVAR rupture was 4.1 years. A further six cases of post-EVAR rupture in five patients found outside the main cohort were included in the analysis of rupture mechanisms only. The rupture mechanism was type IA in 20 of 51 cases (39%), IB in 20 of 51 (39%) and IIIA/B in 11 of 51 (22%). One of these had type IA + IB combined. One patient had an aortoduodenal fistula without another mechanism being identified. Precursors had been noted on CT follow up prior to post-EVAR rupture in 16 of 51 (31%). Retrospectively, using the structured protocol, precursors could be identified in 43 of 51 (84%). In 17 of 27 (63%) cases missed on follow up but retrospectively identifiable, the mechanisms were type IB/III. Overall, the 30 day mortality rate after post-EVAR rupture was 47% (n = 24/51) and the post-operative mortality rate was 21% (n = 7/33). Conclusions: Most precursors of post-EVAR rupture are underdiagnosed but identifiable before rupture using a structured follow up CT protocol. Precursors of type IB and III failures caused the majority of post-EVAR ruptures.
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| 10. |
- Arheden, Håkan, et al.
(författare)
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Blood flow measurements
- 2006
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Ingår i: MRI and CT of the Cardiovascular System. - 0781762715 ; , s. 71-90
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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