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Biomedical subjects

D Vorwerk

Publications and source records attributed to D Vorwerk.

At least 73 records · Page 4Linked to original sources
PubMed1995

[Color-coded duplex ultrasonography in the diagnosis of renal artery stenosis].

PURPOSE: Colour-coded duplex sonography was performed for diagnosis of renal artery stenosis to define standards and criteria for stenosis. MATERIAL AND METHODS: In 20 normotensive volunteers and 123 patients with arterial hypertension, bilateral intrarenal Doppler spectra were examined and the following parameters including side ratios were calculated: pulsatility index (PI), resistance index (RI), acceleration time index (AT) and acceleration index (AI). RESULTS: In 29 of the 123 patients, angiography showed unilateral renal artery stenosis. Acceleration index (AI) was found as the most reliable parameter with a sensitivity of 100% and a specificity of about 94% for stenoses grading at least 70%. CONCLUSIONS: Colour-coded duplex sonography can depict relevant stenoses reliably, but anatomical variations may limit its value as a single screening method. Colour-coded duplex sonography can be, therefore, recommended as an adjunct to angiography for assessment of haemodynamic relevance.

Adolescent↗
PubMed1995

[Intrarenal duplex sonography in detecting flow changes after renal PTA].

PURPOSE: Changes of the intrarenal Doppler signal were analysed before and after renal balloon dilatation to assess the technical success of PTRA. MATERIALS AND METHOD: In 33 patients, intrarenal Doppler signal was depicted before and after renal PTA. Doppler flow curve was analysed by using the acceleration index (AI), acceleration time index (AT) and resistance index (RI); for all indices side ratios (AI-R, AT-R and RI-R) were calculated. Balloon dilatation was angiographically successful in all cases. Average stenosis graded 71% before and 21% after PTA. RESULTS: By definition of limits for all indices used, a single patient was graded as non-stenotic before balloon dilatation by application of AI/AI-R and no patient was graded nonstenotic by AI/RI-R. After renal PTA, all indices significantly changed towards normal findings and by application of both AI/AI-R and AI/RI-R, only a single patient was graded stenotic after PTA. CONCLUSION: Intrarenal Doppler signal analysis reliably allows to detect flow changes following renal PTA in patients with renal artery stenosis. It may therefore be used as a noninvasive method to monitor flow improvement after renal PTA and during follow-up.

Adolescent↗
PubMed1995

[The rheolytic thrombectomy of an iliac vein].

As an alternative to thrombolysis, a patient with recent rethrombosis of the right iliac vein was successfully recanalized by using a 5 F rheolytic catheter system. The patient had undergone bilateral stent recanalisation of the pelvic veins after iliocaval thrombosis due to retroperitoneal fibrosis three months earlier.

Aged↗
PubMed1995

Experimental arterial stent placement. Comparison of a new Nitinol stent and Wallstent.

RATIONALE AND OBJECTIVES: To compare technical aspects and neointima formation of a new Nitinol stent and a Wallstent. METHODS: A Nitinol sten and a Wallstent were placed into the iliac arteries of 14 sheep (total of 28 stents) and followed angiographically. Seven sheep were killed after 1 month and 7 after 4.5 months. Examination of histologic specimen by light microscopy was performed to determine neointimal and medial thickness inside the stents. Measurements were analyzed statistically. RESULTS: Neointima was thicker in Nitinol stents (N) than in Wallstents (W) (P < 0.004), both adjacent to (W = 0.265 mm, N = 0.596 mm) and between the stent wires (W = 0.177 mm, N = 0.361 mm). Because of poor radiopacity and the Crochê releasing technique, delivery was more difficult with Nitinol stents. High-grade stenosis was found in two Nitinol stents at 1 and 4.5 months of follow-up, respectively. One Wallstent was insufficiently incorporated into the vessel wall. CONCLUSIONS: The observed difference in neointima formation that may be caused by differences in design, mechanical properties or the metal alloy of the stents probably is too insignificant to be relevant to patency of large arteries. However, it may be relevant in small vessels such as coronary arteries.

Alloys↗
PubMed1995

Primary stent placement for chronic iliac artery occlusions: follow-up results in 103 patients.

PURPOSE: To report results of primary stent placement for treatment of chronic iliac artery occlusions. MATERIALS AND METHODS: The authors placed 154 primary stents in 103 patients with iliac artery occlusions of at least 3 months duration. Mean length of the occluded segments was 5.1 cm. All patients had symptoms, with claudication or trophic changes. Mean ankle-arm index at rest was 0.48. Follow-up included angiography, Doppler ultrasound, and clinical examination. RESULTS: Ninety-nine patients demonstrated clinical improvement, with relief or improvement of claudication. Complications that required percutaneous or surgical intervention occurred in six patients; minor complications occurred in another six. Embolization occurred in five patients. Primary patency was 87% after 1 year, 83% after 2 years, and 78% after 4 years; secondary patency was 94%, 90%, and 88% at 1 year, 2 years, and 4 years, respectively. CONCLUSION: Primary stent placement should be the treatment of choice in unilateral chronic iliac artery occlusion.

Angiography, Digital Subtraction↗
PubMed1995

Venous stenosis and occlusion in hemodialysis shunts: follow-up results of stent placement in 65 patients.

PURPOSE: To provide follow-up data on the use of self-expanding stents in hemodialysis fistulas to improve the technical success of balloon angioplasty. MATERIALS AND METHODS: Ninety-two self-expanding vascular stents were placed in 65 patients (29 men and 36 women 25-79 years of age; mean, 57.6 years) with failing hemodialysis fistulas or shunts. RESULTS: Stent placement was successful in all patients, but rethrombosis of the shunt occurred in six patients (10%) within 1 week. There were 96 episodes of reobstruction. In 87 cases, percutaneous or combined surgical and percutaneous repeat intervention was performed. The cumulative shunt function rate was 88% after 6 months, 86% after 1 year, and 77% after 2 years. CONCLUSION: Stent placement in hemodialysis fistulas helps treat lesions that cannot be adequately treated with percutaneous transluminal angioplasty (PTA) alone but has a follow-up patency rate similar to that of PTA. Standard central venous stents have a better patency rate than after PTA.

Adult↗
PubMed1995

Percutaneous balloon embolectomy with a self-expanding tulip sheath: in vivo experiments.

PURPOSE: To test a self-expanding tulip-shaped sheath designed for percutaneous embolectomy in an in vivo animal experiment. MATERIALS AND METHODS: In nine sheep, a total of 23 percutaneous balloon embolectomies were performed with use of a self-expanding tulip sheath device with an outer diameter of 9- or 10-F when collapsed. A 10-F instrument was used in 11 cases, and a 9-F instrument was used in 12. Radiopaque emboli were pushed into the aorta via the left carotid or contralateral femoral artery with a 16-F introducer sheath. RESULTS: The embolus was captured in the tulip cage in all 23 cases. Retrieval of the embolus into the sheath was complete in 21 of 23 cases. In two cases, minor parts of the embolus dislodged from the sheath. Major embolism did not occur. In nine cases, the outer sheath had to be cleared of remaining clot particles with aspiration. CONCLUSION: The noncovered self-expanding tulip sheath is an effective and safe instrument for percutaneous embolectomy under in vivo conditions.

Animals↗
PubMed1995

Late reobstruction in iliac arterial stents: percutaneous treatment.

PURPOSE: To retrospectively analyze in a nonrandomized fashion the efficacy of percutaneous reintervention in obstructed iliac stents. MATERIALS AND METHODS: In 21 symptomatic patients with iliac lesions, 26 reinterventions (16 for stent occlusion and 10 for stent stenosis) were performed. Restenoses were treated with balloon dilation and either atherectomy or stent placement. Reocclusions were treated with atherectomy or aspiration thrombectomy and then recanalization with balloon dilation and selective stent placement. RESULTS: Balloon angioplasty for stent stenosis was effective in all but one patient. Recanalization was successful in 14 of 16 patients with stent occlusion. The mean period of patency after reintervention was 18 months +/- 15. Cumulative stent stenosis patency after reintervention was 87% after 1 year. Stent occlusion patency was 57%. Recurrent stent obstruction occurred in eight of 24 (33%) patients with successful primary interventions. CONCLUSION: Percutaneous reintervention for both stent stenosis and occlusion is feasible with a moderate complication rate and may be attempted before surgery.

Angioplasty, Balloon↗
PubMed1995

[Color-coded duplex ultrasound in chronic dissecting abdominal aortic aneurysm. Differentiation between true and false aortic lumen with reference to the blood supply to larger abdominal arteries].

PURPOSE: This study was carried out to evaluate the ability of color-coded duplex sonography (CCDS) to differentiate between true and false aortic lumen with regard to the blood supply to the major aortic branches in cases of chronic dissecting abdominal aortic aneurysm. METHODS: In eight patients with aortic dissection, the Doppler spectrum was analyzed for maximum systolic velocity (Vmax), pulsatility index (PI), acceleration time (AT), acceleration index (HAN-DA index, AI), and, in renal arteries, for the side ratio of AT and AI (AT-R, AI-R). Computerized tomography and angiography were used to define blood supply to the aortic branches by true and false aortic lumen. RESULTS: Four of five iliac arteries with continued dissection showed differences between true and false lumen in all Doppler parameters; one showed no difference. In the remaining iliac arteries and the viseral branches, blood supply by true or false aortic lumen could not be differentiated by CCDS. CONCLUSION: In cases of chronic dissecting abdominal aortic aneurysm, CCDS is not able to differentiate between true and false aortic lumen with regard to the blood supply to the major aortic branches.

Aged↗
PubMed1995

Transbrachial fine-needle arteriography with special focus on haemodialysis shunt imaging.

Retrospective analysis of the complication rate of transbrachial fine-needle arteriography was made to determine whether the advantages of arterial angiograms over venous fistulograms outweigh the possible complications. We included 236 patients who had undergone 454 arterial fine-needle punctures with a 22-gauge cannula in the cubital fossa. Spasm as the only reliably detectable early complication of this retrospective study occurred with a frequency of 1.9% in dialysis patients. The only late and severe complication we found in reviewing 217 arterial follow-up angiograms was one aneurysm. We consider arterial angiogram, using the fine-needle puncture technique, as a safe method for angiographic control of haemodialysis shunts. We attribute the low complication rate of less than 0.5% to the introduction of this technique.

Angiography↗
PubMed1995

Chronic venous occlusions in haemodialysis shunts: efficacy of percutaneous treatment.

PURPOSE: The efficacy of percutaneous treatment of chronic venous occlusions in haemodialysis fistulae was retrospectively analysed. MATERIALS AND METHOD: In 33 cases, percutaneous treatment of chronic venous occlusions was attempted. The type of shunt was an autologous arteriovenous fistula in 23 cases and a PTFE implant graft in 10 cases. The lesion involved forearm veins in six cases, an upper arm vein in 15 cases, and a central vein in 12 cases. The mean length of the occlusion was 7.4 +/- 5 cm with a range from 2 to 25 cm. Fresh thrombus material in addition to the chronic occlusion was present in five cases. The patients were referred for chronic shunt dysfunction in 29 cases and with acute shunt thrombosis with an underlying chronic venous occlusion in four cases. RESULTS: Mechanical recanalization succeeded in 27 of 33 occlusions (82%). In one further patient, direct recanalization failed but an alternative improved drainage was created by detouring the main venous outflow tract by the use of a stent. Immediate clinical success was therefore 85%. Simple balloon dilatation was used in 11 of 27 cases (41%). Additional stent implantation became necessary in 16 of 27 cases (59%). In 15 patients an event of reobstruction occurred during follow-up. Mean primary cumulative patency was 85% after treatment, 41% after 6 months, and 24% after 2 years. By use of reintervention shunt function was maintained at 74% up to 2 years. CONCLUSIONS: Percutaneous treatment of chronic venous occlusions is technically feasible with a success similar to treatment of stenotic lesions. Follow-up results do not show impaired follow-up data for that type of obstruction.

Aged↗
PubMed1994

[Laser thermal venous obliteration: experimental results in the rat model].

In an animal study, thermal laser application was tested for inducing venous thrombosis. In 54 rats, metal-tipped laser catheters ("hot tip") were trans-jugularly inserted into the distal inferior caval vein which was thermally damaged by laser pulses of 4-7 W. Suitable energy levels were defined in an acute experiment in 25 rats. Chronic experiment with 29 rats included survival time of two weeks after laser application, autopsy and histological work-up of the caval vein. In 27 rats, laser application was successfully performed and induced thrombosis in 17 animals. Perforation of the caval vein occurred in 10 rats. Thermal laser application is capable of inducing venous thrombosis. The power ranges inducing thrombosis or thermal perforation are, however, too narrow to allow safe clinical application of this technique.

Animals↗
PubMed1994

Doppler enhancement with SH U 508A in multiple vascular regions.

PURPOSE: To determine the magnitude and duration of peripheral vascular and cardiac Doppler signal enhancement after intravenous administration of contrast agent SH U 508A. MATERIALS AND METHODS: Suboptimal cardiac or peripheral vascular Doppler examinations were evaluated. A total of 75 intravenous bolus injections were made in 30 patients. Spectral audio Doppler intensity was measured throughout the duration of contrast effect. RESULTS: No clinically relevant adverse effects were noted, and Doppler enhancement was apparent in all cases. The diagnostic confidence of the investigators when scored before and after Doppler enhancement improved from 35% to 91% (P < .05). Doppler intensity increased more than 16 dB in all vascular regions investigated (P < .05). The contrast effect lasted for more than 120 seconds in the peripheral vascular and cardiac groups at equivalent doses. CONCLUSION: Intravenously administered SH U 508A is effective in markedly increasing cardiac, femoral arterial, and transcranial (cerebral arterial) Doppler signal intensity. The effect improves the clinical diagnostic confidence in cases of suboptimal unenhanced Doppler examinations.

Cerebral Arterial Diseases↗