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Biomedical subjects

D Vorwerk

Publications and source records attributed to D Vorwerk.

At least 109 records · Page 6Linked to original sources
PubMed1990

[Dynamic contrast medium-aided ultrasound cavography in patients with a caval filter].

In 35 patients during 42 examinations, vena-caval blood flow was visualized by application of a new ultrasonic contrast medium (Echovist) via a dorsopedal vein. A caval filter had previously been implanted in 32 patients. In 94 out of 99 cases, application of the contrast medium allowed a diagnostically relevant enhancement of the echogenicity of the caval blood flow. In addition, the caval filters allowed altered flow geometry to be depicted in detail.

Adult↗
PubMed1990

[Laser angioplasty and the removal of calcified plaques. An in vitro study].

The ablative potentials of five different lasers on normal and diseased vascular tissue were tested in vitro. Post-mortem aortic specimens of normal wall, lipomatous and calcified plaques were exposed to both continuous wave lasers (argon, neodymium-YAG 1064 nm) coupled to hot-tipped or sapphire tipped fibres and pulsed lasers (Excimer 193 nm, CO2, erbium-YAG). Histomorphological changes and penetration were evaluated microscopically. Pulsed lasers of all wavelengths used were able to ablate vascular tissue of all stages including heavily calcified plaques. Thermal lasers were able to penetrate the normal wall and lipomatous plaques, but did not reach any evident reaction on calcified plaques. Thermal lasers may have only limited potentials in angioplasty, since ablation of calcified plaques is not possible.

Angioplasty, Balloon↗
PubMed1990

[The technical requirements for percutaneous fine-caliber cholangioscopy. Experimental experiences with an animal model].

A total of 115 percutaneous fine-calibre cholangioscopies were performed in an animal model, using different types of fine-calibre cholangioscopes of 0.8 to 2.8 mm. diameter. Additional properties of single endoscopes included different flexibility, deflectability of the tip, occlusion balloon and working channel. Due to the low steerability of the instruments used, a coaxial guidance by an introducing sheath was mandatory for sufficient imaging quality. Besides flexibility and provision of a working channel, no other properties contributed to a successful endoscopic inspection of the biliary system.

Animals↗
PubMed1990

[Imaging of penile vascular anastomoses using color-coded Doppler ultrasound: comparison with CW Doppler ultrasound and clinical aspects].

In fourteen patients undergoing surgical revascularization (11 with Hauri's, three with Virag's anastomosis) because of erectile dysfunction, the patency of vascular anastomosis was evaluated and visualized by color-coded-Doppler sonography (CCDS). Results were compared with continuous-wave Doppler (CWD) and clinical data. CCDS proved to be superior to CWD with regard to assessment of flow in the penile vessels and to applicability. Strength and direction of flow can be judged visually. Therefore, the nature of the imaged vessel (artery or vein, deep or dorsal artery) can be differentiated. There is a good correlation of CCDS and CWD in their evaluation of the patency of the anastomosis. CCDS showed higher accuracy in detecting deep cavernosal arteries.

Adult↗
PubMed1990

Tissue response of the biliary and digestive system of rabbits after MTBE infusion into the gallbladder.

We evaluated the tissue response of the biliary and digestive system after Methyl-tert-Butyl-Ether (MTBE) gallbladder infusion in 32 rabbits. After laparotomy, MTBE (5-11 ml) was infused into the gallbladder for eight hours. Animals were sacrificed after eight hours or after two months. Control animals received saline solution infusion into the gallbladder. Afterwards the gallbladder, the common bile duct, the liver, the pancreas and the duodenum were examined histologically. All animals receiving MTBE had different degrees of gallbladder necrosis, common bile duct necrosis and necrosis of intrahepatic bile ducts. After two months, scar formation and a hyperplastic cholecystitis were observed. Control animals did not have comparable tissue reactions; only small areas of necrosis in the gallbladder and the common bile duct occurred after eight hours. The gallbladder, common bile duct and liver remained unchanged in those animals which survived two months. Although the results of this animal study cannot be directly transferred to humans, the data suggest that MTBE should be used in gallstone therapy with caution, and that if it is used, a well-controlled follow-up of these patients is necessary.

Animals↗
PubMed1990

Vascular tissue ablation by an erbium-YAG laser: a fiber-transmittable pulsed laser in the infrared range.

Vascular tissue ablation by an erbium:YAG laser of 2,940 nm was tested in-vitro with the application of increasing energies from 20 to 80 mJ per pulse. Effective ablation of normal vascular tissue, lipomatous atheromas and calcified plaques was achieved. Penetration depth was considerably diminished in the presence of calcifications. The lasered craters showed smooth surfaces and were regularly shaped. The solid state erbium:YAG, which is transmittable by fluoride fibers, offers theoretical advantages for laser angioplasty.

Aortic Diseases↗
PubMed1990

Aspiration catheter for percutaneous thrombectomy: clinical results.

The clinical application of an aspiration thrombectomy system is presented. The system consists of a 7-F Teflon catheter with a rotating coaxial propeller-tipped wire. Thrombectomy was successful in treating occlusion of two femoropopliteal arteries and one hemodialysis implant but was not completely successful in a draining shunt vein. Preliminary results are encouraging; mechanical thrombectomy may offer an alternative to local lysis therapy.

Aged↗
PubMed1990

Mechanical revascularization of occluded iliac arteries with use of self-expandable endoprostheses.

Self-expandable endoprostheses were used to restore the vascular lumen following mechanical recanalization of iliac occlusions without preceding thrombolytic therapy. During a 24-month period 48 of 68 occlusions were successfully recanalized. The vessel lumen was restored with the combined use of dilation with an "undersized" balloon and subsequent stent insertion. Early reocclusion occurred in two patients; the patency rate at 6 months was 93.3% (28 of 30 patients). Restenosis prompted repeat intervention in two patients. Percutaneous transluminal angioplasty combined with the use of self-expandable stents is a promising alternative to vascular surgery, although techniques for safely crossing the occluded segment require further improvement.

Adult↗
PubMed1990

Color-coded image-directed Doppler sonography compared with digital subtraction angiography in the follow-up of percutaneous vascular endoprostheses.

Color-coded image-directed Doppler sonography (CCIDS) was used in the follow-up of self-expandable vascular endoprostheses and was compared with the results of digital subtraction angiography and Doppler pressure indices. The stents were implanted in iliac and femoral arteries or hemodialysis fistulae of 26 patients. The aim of the study was to evaluate the potential of the new imaging method to identify local flow patterns inside of vascular endoprostheses. The stents were identified by sonography in all cases; laminar flow was represented in CCIDS by homogeneous Doppler signals. In case of a distinctly reduced lumen, intravenous digital subtraction angiography (DSA) and CCIDS were both able to identify the stenotic process; however, CCIDS was superior in the demonstration of minute flow irregularities. No different flow patterns were detected in comparing recent with older vascular implants.

Angiography, Digital Subtraction↗
PubMed1990

Fine caliber cholangioscopy.

The miniaturized diameters of endoscopes (miniendoscopes) allow percutaneous access for endoscopic visualization of the extrahepatic and intrahepatic biliary system. Practical aspects of different miniendoscopes in an experimental model are described. Clinically, fine caliber cholangioscopy is helpful in detection of retained biliary stones. Nevertheless, discrimination of benign and malignant stenosis remains difficult, and simultaneous intervention under endoscopic guidance is compromised by the low steerability of the instruments.

Animals↗
PubMed1989

[Percutaneous implantation of vascular endoprostheses (stents) in the iliac and femoral arteries].

Flexible, self-expanding metallic mesh stents were implanted via a percutaneous catheter delivery system, immediately after balloon dilatation, in 68 patients (59 males and 9 females; mean age 56.6 [40-73] years). All had stenoses or occlusion of the iliac or femoral arteries. The bridged vessel segments were 3.5-27 cm long; the stent lumen ranged from 6 to 12 mm diameter. Good blood flow was restored in all 68 patients. The Doppler sonographic index increased on average by 0.33 to a mean of 0.9 (0.4-1.2). An early stent occlusion occurred in three patients (one femoral artery with a stented length of 27 cm thrombosed after 24 hours, two iliac stents were found to be occluded four and eight weeks, respectively, after insertion). Transitory peripheral emboli occurred in two patients with femoral stents. In five patients (four with femoral stents, one with an iliac stent) marked intimal hyperplasia with stenosis developed after 4-10 months; in four of them they were successfully treated by the percutaneous technique. The described percutaneous stent placement method is suitable for treating arterial stenoses or occlusions which cannot be satisfactorily dilated by balloon, as well as restenoses and local complications after angioplasty. It is particularly effective in iliac arteries.

Adult↗
PubMed1989

[Laser ablation of the nucleus pulposus: optical properties of degenerated intervertebral disk tissue in the wavelength range 200 to 2200 nm].

Percutaneous ablation of degenerative disk material by laser has been introduced recently as an alternative to enzymatic or mechanical discectomy. The optical properties of degenerative disk material were evaluated in the range from 200 to 2200 nm, which includes most of the laser wavelengths used for medical purposes. Remittance rate was determined in 16 post-mortem disks using a spectrophotometric unit and rate of absorption and scatter were calculated. High rates of diffuse remittance were found for classical laser wavelengths such as the argon or the Nd:YAG II laser indicating only low rates of absorption. In contrast, much higher rates of absorption were determined for excimer or mid-infrared lasers as well as for the Nd:YAG I (1320 nm), which appear more appropriate for laser discectomy than the Nd:YAG (1064 nm) laser.

Humans↗
PubMed1989

Thermal laser-induced stenosis of the common bile duct. An alternative model for experimental research.

An experimental model of bile duct stenosis and occlusion in dogs is presented. After percutaneous cholecystostomy of the gallbladder, which had been affixed to the abdominal wall during laparotomy four weeks earlier, a standard 2 mm laser heat probe adapted to an Nd:YAG laser (1,064 nm) was advanced inside the proximal common bile duct in 12 animals, using 6 or 7 F sheaths. The proximal part of the common bile duct was exposed to laser pulses of 6 to 10 Watts for one second. Within 3 to 15 days, total occlusion or severe stenosis of the common bile duct consistently occurred and was verified by follow-up percutaneous cholecystocholangiography. No perforations occurred. Compared with other models, laser thermal damage is an easy and reliable method of producing bile duct stenoses for experimental purposes.

Alanine Transaminase↗
PubMed1989

Venous stenoses in dialysis shunts: treatment with self-expanding metallic stents.

A flexible, self-expanding metallic endoprosthesis was employed for the treatment of venous outflow stenoses in four patients with a polytetrafluoroethylene shunt and two patients with a Brescia-Cimino shunt. The stenoses had led to shunt occlusion in five patients and to flow impairment in one. In the occluded shunts, thrombectomy and subsequent balloon angioplasty were performed in four patients, and percutaneous recanalization with angioplasty was performed in one. One shunt with decreasing flow was percutaneously dilated. Since the underlying stenoses recurred in four patients after 24 hours and did not respond sufficiently to angioplasty in two patients, up to four stents were placed in the venous segments. Thrombosis of the stents occurred in two patients after 24 hours and in one after 6 weeks and was successfully recanalized with thrombectomy in two. At 2-6 months follow-up, the stents and the shunts were patent in five patients. In three of these patients, intima hyperplasia, associated with narrowing of the stent lumen in two, was noted within 4 months after stent placement.

Adult↗
PubMed1989

Iliac and femoral artery stenoses and occlusions: treatment with intravascular stents.

Forty-five patients with atherosclerotic stenoses and occlusions of the iliac and superficial femoral arteries were treated with a flexible, self-expanding, metallic intravascular stent. Of these patients, 37 were treated immediately after inadequate angioplasty. At a follow-up period of 2-12 months, intravenous digital subtraction angiograms demonstrated patency of the vessels with stents in 40 of 45 patients. The mean Doppler ankle/arm index increased from 0.60 to 0.92 immediately after treatment and was 0.89 at follow-up. Early thrombotic stent occlusion occurred in two patients. Intimal hyperplasia was a late effect and led to stent stenoses in three patients after 5-9 months and stent occlusion in one patient after 6 months. In three patients, percutaneous recanalization with balloon and Simpson catheters was successful. Intravascular stents proved particularly useful for maintenance of patency after angioplasty in occlusions of the iliac and femoral arteries and in treatment of stenoses due to eccentric and severely ulcerated plaques. The stents also helped manage complications after angioplasty. Long-term results will depend on the degree, frequency, and progression of intimal hyperplasia narrowing the vascular lumen.

Adult↗
PubMed1989

Elimination of the nonionic contrast medium iopromide in end-stage renal failure by hemodialysis.

The increasing life-expectancy of patients with end-stage renal failure has led to a significant increase of diagnostic and interventional radiologic measures. The contrast media used in these procedures, however, are excreted only very slowly, due to the renal failure. We have therefore studied the elimination of the nonionic x-ray contrast medium iopromide (Ultravist) during dialysis in nine anuric patients with end-stage renal failure. All of the patients received 100 ml iopromide (30 g iodine) for the visualization of their Cimino-Brescia shunt. They were then dialyzed 30 minutes after the injection. The plasma iodine concentration declined from 1.7 to 0.7 mg I/ml plasma during the 3-hour dialysis treatment. The iopromide clearance was a constant 80 ml/min. This is the equivalent of a relative dialysance of 65% of the creatinine clearance. There were no incidences of side effects requiring therapy in this high-risk group of patients. The quality of the image was good in all cases. Iopromide proved itself to be an x-ray contrast medium with a low rate of side effects, which can be effectively eliminated from the body by means of conventional dialysis.

Adult↗
PubMed1988

Combined treatment of stone-obstructed hepatico-jejunostomy with interventional techniques and ESWL.

In a 37-year-old woman with recurrent stenosis of a biliary digestive tract anastomosis and subsequent formation of bile stones, current methods of percutaneous management were useful in dilating the stenotic areas but could not remove a single bile stone within the left hepatic duct. It was successfully treated by using extracorporeal shock wave lithotripsy (ESWL) without major side effects.

Adult↗