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Biomedical subjects

F Schellhammer

Publications and source records attributed to F Schellhammer.

28 records · Page 2Linked to original sources
PubMed1999

Vein graft-coated stents for endovascular occlusion of canine experimental arteriovenous fistulae.

RATIONALE AND OBJECTIVES: To evaluate different vein graft-coated stent systems in the endovascular treatment of experimental arteriovenous fistulae (AVF) in a canine model. METHODS: Bilateral carotid-to-external jugular vein AVF were created. Two balloon-expandable tantalum stents (Strecker stent), two self-expanding nitinol stents (Strecker stent), and one stainless-steel stent (Wallstent) were coated with autologous vein grafts and placed using a transfemoral approach. Angiography was performed immediately after stent placement and at week 1 and 3, as well as at months 3, 6, and 9. All stents were removed and underwent histologic examination. RESULTS: Occlusion of the AVF succeeded with the Wallstent and both tantalum stents. The nitinol stents were misplaced, maintaining the AVF. One undersized tantalum stent and the Wallstent were occluded after 3 weeks. One nitinol stent was occluded at 3 months, whereas the two remaining stents were patent during the whole observation period. No inflammatory tissue response was seen, and no host-versus-graft reaction was present. CONCLUSIONS: Preparation and implantation of vein graft-coated stents, especially in the case of self-expanding stent systems, is cumbersome. This restricts the common use of such a coating, which shows an excellent biocompatibility. Vein graft-coated stents might be of use in infected endangered vessels.

Alloys↗
PubMed1999

Polyethylene terephthalate and polyurethane coatings for endovascular stents: preliminary results in canine experimental arteriovenous fistulas.

PURPOSE: To evaluate polyethylene terephthalate and polyurethane as coatings of vascular endoprostheses in the treatment of experimental arteriovenous fistulas (AVFs). MATERIALS AND METHODS: Nineteen bilateral carotid artery-to-external jugular vein AVFs were created in 10 adult dogs. Fourteen polyethylene terephthalate-coated and five polyurethane-coated self-expandable nitinol stents were placed with a transfemoral approach. Angiography was performed immediately after placement, after 1 and 3 weeks, and at months 3, 6, 9, and 12. All grafts were examined histopathologically. RESULTS: The AVF was successfully occluded with all but one of the polyethylene terephthalate-coated stents. Graft patency was seen with 12 polyethylene terephthalate-coated stents, while acute vessel occlusion was evident with two polyethylene terephthalate-coated stents following percutaneous transluminal angioplasty immediately after implantation. In the group with polyurethane-coated stents, three graft dislocations and two delayed vessel occlusions were observed. In both groups, histologic examination disclosed a mild foreign body reaction with a few macro-phages. No inflammatory reactions were seen. An unorganized fibrin layer was found adjacent to the polyurethane coating. CONCLUSION: Polyethylene terephthalate-coated nitinol stents showed good biocompatibility and a high rate of occlusion of experimental AVFs. The mechanical properties of the polyethylene terephthalate coating were similar to those of the nitinol stents, which facilitated handling. Polyurethane-coated stents showed frequent dislocation.

Alloys↗
PubMed1998

Somatosensory evoked potentials: a simple neurophysiological monitoring technique in supra-aortal balloon test occlusions.

The aim of this study was to evaluate somatosensory evoked potentials (SEP) as a simple neurophysiological monitoring method in supra-aortal balloon test occlusions (BTO). The 13 patients examined had carcinoma of the larynx (n = 6), nasopharyngeal malignancy (n = 3), sphenoid meningioma (n = 2), mycotic aneurysm (n = 1), and a tumor of the carotid body (n = 1). Transfemoral balloon occlusion of the internal carotid artery was maintained for 30 min and monitored both clinically and by SEP. None of the 13 patients showed neurological deficits or pathological changes in the SEP. No thromboembolic complications occurred during BTO. In 11 cases the cervical vessels could be spared or reconstructed during surgery. No neurological symptoms occurred during the clinical follow-up. One patient died the day after BTO due to cardiac arrest. Neurophysiological monitoring of preoperative BTO using SEP is a technically simple method. A similar method has been shown to have a high sensitivity and reliability in carotid surgery.

Adolescent↗
PubMed1998

Are superabsorbers useful for endovascular embolization of saccular aneurysms? An in vitro study.

RATIONALE AND OBJECTIVES: The authors conducted in vitro evaluation of superabsorber for endovascular embolization of saccular aneurysms. METHODS: The swelling properties of the superabsorber Sanwet IM-7000 were investigated in various solvents. The material used was granulate (group A: particle size approximately 459 microm; group B: particle size approximately 20 microm) as well as cubes with an edge length of 1 mm prepared from a block. With ascending concentrations of Sanwet IM-7000 held in suspensions made of Lipiodol and 96% ethanol, the injectability was determined using microcatheters (2.1 F/3 F). The behavior of Sanwet IM-7000 as occlusion material for aneurysms was examined in a sacciform glass-model aneurysm. RESULTS: The granule showed no significant increase in size in Lipiodol and in 96% ethanol, so that they were chosen for catheter measurement. In Lipiodol suspension the maximum fraction of the granulate suitable for injection through a 3 F catheter was 3.2%. In 96% ethanol suspension the maximum fraction of granulate suitable for injection through a 3 F catheter was 0.8%. Suspended in Lipiodol Sanwet IM-7000 showed a moderate swelling in the aneurysm model, whereas the use of 96% ethanol resulted in a pronounced swelling of the granulate (100 vol%) after the 96% ethanol was washed off. Irrespective of the granulate size used, a rinse-off process of the granulate occurred in the model aneurysm at a flow rate above 200 mL x min(-1). Cubes prepared from a block of the base polymerisate of Sanwet IM-7000 showed a delayed increase in size. The final size in 0.9% NaCl solution was reached in the cubes after 220 min, in the granulate already after 20 mins. The cubes displayed a high form stability. CONCLUSIONS: Due to the substance-related absence of intercorporeal cross-linking and the unpredictable increase in size, embolization of aneurysms using Sanwet IM-7000 granulate is inadvisable at present. In spite of a longer swelling time and because of its form consistency, the use of prepared cubes could provide a reasonable alternative.

Aneurysm↗
PubMed1997

Poly-lactic-acid coating for endovascular stents. Preliminary results in canine experimental arteriovenous fistulae.

RATIONALE AND OBJECTIVES: The authors evaluate polylactic-acid (PLA) as a coating of vascular endoprostheses in the treatment of experimental arteriovenous fistulae (AVF) in a canine model. METHODS: Bilateral carotid external jugular AVF were created in five adult dogs. Seven PLA-coated nitinol stents were placed using a transfemoral approach to cover five AVF. Contralateral controls remained untreated. Angiography was performed immediately after stent placement and at weeks 1 and 3, as well as at months 3, 6, and 9. All grafts were removed and underwent histologic examination. RESULTS: In two cases, the occlusion of the AVF was successful, but misplacement of stents occurred in three cases, which showed occlusion of the parent vessel between week 1 and month 3. One thrombembolic stent occlusion was evident during angiographic control. One vessel occlusion was disclosed distal to the stented arterial segment. Histologic examination revealed a mild inflammatory reaction with the presence of macrophages. However, there was no foreign-body reaction of fragmentation of the vessel wall. CONCLUSIONS: Histologic examination revealed good biocompatibility of PLA, which is a well-known biodegradable material. Elastic mismatch of the nonelastic coating and the self-expandable nitinol stent led to misplacement, whereas vessel occlusion was probably due to PLA filaments fraying into the vessel lumen. Using a different textile structure, PLA might be a material suitable for coated stents.

Alloys↗
PubMed1997

Pseudocoarctation of the abdominal aorta.

The case of an asymptomatic pseudocoarctation of the abdominal aorta is reported. Pronounced kinking of the abdominal aorta was seen on angiograms, without stenosis or collateral circulation. Angiography revealed normal renal arteries originating from the malformated aortal segment. The possible etiology and the need for the therapeutical intervention are discussed.

Aged↗
PubMed1995

Self-expanding nitinol stents in canine vertebral arteries: hemodynamics and tissue response.

PURPOSE: To evaluate the hemodynamics and tissue response associated with stent placement in low-flow-velocity arteries. METHODS: Six self-expanding nitinol stents (5.5 mm caliber) were implanted transfemorally within the proximal segments of vertebral arteries (2.5 mm diameter) in six adult dogs during anticoagulative protection. RESULTS: Control angiograms demonstrated patency and 20% dilatation of all stented arteries. One artery was partially thrombosed 1 week later and subsequently showed a 50% stenosis. Throughout the observation period (4 to 9 months after stenting), the other five arteries remained patent without significant narrowing (< or = 15%). Small cervical muscle branches originating from the vertebral arteries within the stented segments remained patent. No major branch occlusions of the vertebrobasilar system were detected. Stent migration or kinking did not occur. MR studies of the brain 4 months after implantation revealed no infarcted areas. These findings were confirmed with brain sections. Stented artery specimens showed delayed stent dilatation. A comparison of the total mean thickness of intima covering the five 30- to 40-mm stents removed at 4, 6, and 9 months showed no significant difference (338, 332, and 389 microns, respectively). Histologic findings verified the macroscopic impression of a thicker intima at the inner curve of the stented artery segments and at the junctions of the stent filaments. The shortest (10 mm) stent had the thinnest neointimal growth (155 microns). Stented vessels showed compression of the media with atrophy, but without necrosis or perforation. Scanning electron photomicrographs revealed intact endothelial cell linings with typical elongated cells. CONCLUSIONS: No significant risk of thromboembolic events exists after implanting these nitinol stents in nonatherosclerotic vertebral arteries in dogs. Thicker neointimal growth after stenting may result from either low wall shear stress with possible flow separation or from changes in the shape and size of the stent, or both.

Alloys↗
PubMed1994

Self-expanding and balloon-expandable stents in the treatment of carotid aneurysms: an experimental study in a canine model.

PURPOSE: To assess the efficacy of metal stents for the treatment of different forms and sizes of carotid aneurysms. METHODS: A total of 14 experimentally constructed aneurysms in dogs were treated with transfemorally placed balloon-expandable tantalum and self-expanding nitinol stents. RESULTS: In 10 cases, stenting produced either immediate complete occlusion of the aneurysm (n = 7) or complete delayed thrombosis after 7 to 10 days (n = 3). In two cases treated with balloon-expandable tantalum endoprostheses, repeated angiography showed a persistent aneurysmal neck with a diameter of 1 mm. No incompletely occluded aneurysms were visible after implantation of nitinol stents. Nine-month angiographic follow-up revealed maximal stenosis of the stented vessel segment of up to 40% after placement of tantalum endoprostheses. However, no more than 15% stenosis followed the deployment of nitinol stents. Histologic examination confirmed these findings. Significantly greater intimal fibrocellular tissue growth surrounded tantalum filaments than nitinol filaments, which were covered with a smooth, thin neointimal layer. In two carotid arteries a subtotal and total occlusion of the parent vessel occurred after the insertion of a tantalum and nitinol stent, respectively. No recanalization of completely occluded aneurysms or delayed migration of a stent was observed. CONCLUSIONS: Porous, tubular self-expanding nitinol stents may become the treatment of choice for broad-based and fusiform aneurysms of the internal carotid artery. However, blood flow dynamics of the aneurysms must be studied carefully in order to select an appropriate mesh size for complete occlusion while preserving the parent vessel. Improvements in the introducing system, stent material, and stent shape are required for simple implantation and reduction of intimal hyperplasia.

Aneurysm↗
PubMedDate not supplied

Vein graft-coated vascular stents: a feasibility study in a canine model.

PURPOSE: To evaluate different vein grafts for luminal coating of endovascular stents in normal canine arteries. METHODS: Twenty-four tantalum Strecker stents were coated with either autologous (n = 10), denatured heterologous (n = 11), or denatured homologous vein grafts (n = 3). The carotid artery (n = 11) and the iliac artery (n = 13) were stented using a transfemoral approach. Angiograms were performed at days 0, 7, and 21, and months 3, 6, and 9. All grafts underwent histological examination. RESULTS: Eight of 10 autologous vein grafts showed patency during the whole observation period of 9 months, without histological signs of inflammation. Denatured heterologous vein grafts revealed acute (n = 3), subacute (n = 5), or delayed (n = 3) vessel occlusion. Hyaloid transformation of the vein graft and lympho-plasmacellular formations were seen. Denatured homologous vein grafts showed acute vessel occlusion. Although significant inflammatory tissue response was seen, no host-versus-graft reaction was present. CONCLUSION: Autologous vein graft-coated stents showed good biocompatibility in canine arteries. Preparation was cumbersome and required surgical venae-sectio. Denatured vein grafts, however, were limited by inflammatory reactions.

Animals↗