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Biomedical subjects

L Ruprecht

Publications and source records attributed to L Ruprecht.

At least 19 recordsLinked to original sources
PubMed1998

Laser catheter coagulation of normal and scarred ventricular myocardium in dogs.

BACKGROUND AND OBJECTIVE: Larger lesions would increase success rates of catheter ablation of ventricular arrhythmias. Therefore, improved radio frequency current application techniques, but also alternative energy sources, are being investigated. The purpose of this study was to determine morphology and dimensions of ventricular lesions induced by transcatheter application of laser energy. MATERIAL AND METHODS: A total of 244 lesions were produced by Nd:YAG laser pulses, 1,064 nm, 10-30 W, 15-60 s, percutaneously (endocardial approach, n = 124) and under visual control (epicardial approach, n = 120) in the left ventricular walls of 24 anesthetized dogs. RESULTS: Dimensions of lesions increased with the amount of energy applied. Maximal values were obtained at 20 W, 60 s: depth = 12.6 +/- 1.1 mm (transmural); width = 15.0 +/- 2.8 mm; volume = 1,582 +/- 777 mm3. Volumes of lesions did not change significantly when induced through previously scarred myocardium. Histologically, lesions were clear-cut, without crater or thrombus formation. Procedures and follow-up periods of up to 22 months were without complications. CONCLUSION: Nd:YAG laser pulses at 10-20 W and 15-60 s produce homogeneous myocardial lesions of coagulation necrosis of reproducible sizes, in a controllable manner, without unwanted effects on the ventricular walls, in normal and through scarred myocardium of dogs. The laser method is a promising alternative for ablation of ventricular arrhythmias including candidates with ischemic heart disease.

Animals↗
PubMed1998

Transcatheter endomyocardial laser revascularization: a feasibility test.

By means of a special catheter system, a total of 76 endomyocardial laser channels were percutaneously produced in a controllable manner at selected sites in 6 beating canine hearts. Acute patency of channels (length = 4-11 mm, diameter = 0.5-1.2 mm) was documented angioscopically and histologically. This minimally invasive method might be useful for revascularising certain patients with ischemic heart disease without resorting to open-chest surgery.

Angioscopy↗
PubMed1996

Mapping guided laser catheter ablation of the atrioventricular conduction in dogs.

Safety and efficacy of mapping guided laser catheter ablation of the AV junction was tested in a canine model. A total of 43 laser pulses (continuous wave, Nd:YAG, 1,064 nm, 30 W, irradiated spot diameter 2.0-2.5 mm) were delivered in 15 dogs (2-5 per dog) via a novel laser catheter system. Pulses were selectively aimed at: (1) the AV node; (2) the His bundle; and (3) the bundle branches. Laser pulses of 9.7 +/- 1.1 seconds (n = 31) produced reversible conduction disturbances in the targeted segment of the AV conduction system, while pulses of 28.6 +/- 7.9 seconds (n = 9) resulted in chronic block. The dogs survived the procedure without complications. Follow-up was 6.5-10.5 months. Histopathologically, lesions showed clear-cut oval-shaped areas of fibrosis of 0.5-18.0 mm in diameter and 0.5-3.5 mm (transmural) in depth, depending on the irradiation time. Pervenous mapping guided laser catheter irradiation of the AV junction can produce AV block consistently and selectively in the targeted segment of the right ventricular conduction system in dogs. The method is safe and can be performed in a controllable manner by using the catheter system presented.

Animals↗
PubMed1995

Tracheoesophageal anastomosis, continent gastrostomy and oesophagostomy--a new experimental model in minipiglets.

Tracheoesophageal fistulae endanger newborn children by aspiration pneumonia. An animal model of this dangerous malformation was thought to be impossible until now. By tracheoesophageal anastomosis, occlusion of the oesophagogastral junction, proximal cervical oesophagostomy and continent gastrostomy in 25 minipiglets a reliable model of tracheoesophageal fistula has been developed. After establishing the model in a pilot study the mortality following the establishment of this procedure was 5.6% and the minipiglets survived in excellent condition for 2-10 week periods under complete alimentary restriction and gastrostomy feeding. Therefore the method seems to be suitable for long-term investigations on major oesophagotracheal surgery.

Anastomosis, Surgical↗
PubMed1994

Electrocatalytic glucose sensor.

An electrocatalytic glucose sensor for in vivo application has been developed. The sensor is a flow-through cell with three electrodes and can be integrated into a blood vessel. The principle of measurement is based on the direct electrochemical oxidation of glucose at a membrane-covered noble-metal electrode. To test the potential long-term in vivo function of the sensor, it was implanted in the carotid artery of a sheep. Thus, the sensor performance was verified over a period of 71 days. During this time, a nearly constant blood flow through the cell was achieved, which indicates good blood compatibility of the materials used. It was possible to set up a calibration that was valid over 24 days (mean error 2.3 mmol l-1). The tested cross-sensitivity of the sensor towards cysteine, acetyl salicylic acid and other small molecules shows tolerable effects on this type of glucose measurement. Only high concentrations of lactate and ethanol require a special adaptation of the calibration to suppress their influence. Minor cross-sensitivity and promising long-term stability recommend this type of sensor for in vivo monitoring of blood sugar level. However, for intravasal application, it is necessary to modify the present sensor design to a catheter-type construction.

Animals↗
PubMed1994

Morphologic effects of a sulfur(IV) aerosol on the nasal cavity of beagle dogs.

Morphologic changes were observed in nasal cavities of beagle dogs after long-term exposure to a respirable sulfur(IV) aerosol at a concentration equivalent to a sulfur dioxide (SO2) concentration of 0.6 mg/m3. The changes were characterized by a thickened epithelial layer resulting from epithelial proliferation, by a loss of secretory material, and by moderate mononuclear cell infiltration.

Administration, Inhalation↗
PubMed1994

Implantable electrocatalytic glucose sensor.

An electrocatalytic glucose sensor for in vivo application has been developed to determine the glucose level in blood and further to control the insulin dosage in a closed loop system for diabetes therapy. The principle of the electrocatalytic glucose sensor is based on the direct electrochemical oxidation of glucose at a membrane-covered platinum electrode. For a possible clinical application the sensor was built as a catheter. A set of implantations in the vena cava of sheep demonstrated the potential feasibility of the sensor. The sensor values were simultaneously checked by the enzymatic analysis of glucose in blood samples drawn separately from a femoral vein. It was possible to determine the glucose concentration in sheep for more than 130 days with tolerable deviations from glucose reference measurements. The mean error was 2.5 mmol/l. One of the catheters was explanted after 211 days and the histological examination revealed a good biocompatibility of all materials used. In additional experiments, the differences of the glucose concentration in vena cava as well as in the anterior and posterior femoral veins of a sheep were examined during glucose tolerance tests. These experiments verified our method of in vivo calibration of the long-term implantable glucose sensor.

Animals↗
PubMed1994

Catheter-directed laser coagulation of atrial myocardium in dogs.

The feasibility of transcatheter laser coagulation of atrial myocardium was tested in a canine model by using a combined electrode-laser catheter. In 17 anaesthetized beagles a total of 264 lesions, 12-19 per dog, and 3-5 in each area were produced in: (1) the lateral walls, (2) the posterior right atrial walls, (3) the inter-atrial septum, and (4) the atrial appendage. The power source was a continuous wave Nd:YAG laser. Irradiance was 1 kW.cm-2, at a wave length of 1064 nm, the irradiated spot diameter was 2.0-2.5 mm, and the pulse duration 5-60 s. Local intra-cardiac atrial potentials recorded from the targeted areas during laser irradiation dwindled after onset of the laser pulse, and their amplitude was reduced persistently by pulses of 15 s or longer. Histopathologically, the acute lesions showed intramural haemorrhage and coagulation necrosis, but there was no tissue vaporization or crater formation. Chronic lesions showed clear-cut oval-shaped areas of transmural fibrosis. Diameters of lesions, dependent on the amount of laser energy applied, measured from 4.6 +/- 0.5 mm (450 J) to 7.8 +/- 1.4 mm (1800 J). Follow-up lasted 6-25 months (average 10.5). All the animals survived the procedure without complications. Transcatheter laser coagulation of atrial myocardium is safe and can be performed in a controllable manner by using the catheter system presented.

Action Potentials↗
PubMed1994

Electrocatalytic glucose sensor for long-term in vivo use.

A catheter shaped electrocatalytic glucose sensor for in vivo application has been developed to determine the glucose level in blood and control the insulin dosage in a closed loop system for diabetes therapy. The principle of measurement is based on the electrochemical oxidation of glucose at a membrane-covered platium electrode. For various potential steps, the impedance obtained at two different frequencies is a function of the glucose concentration. A series of implantations in the vena cava of sheep demonstrated the potential feasibility of the sensor. It was possible to determine the glucose concentration in sheep for more than 130 days with tolerable deviations from glucose reference measurements. The mean error was 2.5 mmol/l. The catheter was explanted after 211 days and histological examination revealed a good biocompatibility of all materials used.

Animals↗
PubMed1993

In vivo experiment with the electrocatalytic glucose sensor in sheep.

In order to control the insulin dosage in diabetes therapy, an electrocatalytic glucose sensor for long-term implantation has been developed. To test the sensor function over a longer period, it was implanted as a flow-through cell in a sheep. The sensor was inserted into the carotid artery and driven by a portable electronic unit worn by the animal. The blood flow characteristics were nearly constant over the whole period of measurement. We were able to verify the sensor performance in one experiment lasting over 71 days. Stable calibrations of the sensor were achieved over longer periods of time, so that only a few calibrations are necessary in monitoring the blood glucose level during the whole period of implantation. It was thus possible to set up a calibration which was valid over 33 days (mean error 2.5 mM). These calibrations were not adversely affected by host reactions. The cross-sensitivity of the sensor was also verified, and it was found that the tested molecules did not significantly affect the sensor function. Only high concentrations of lactate and ethanol require a special adaptation of the calibration to suppress their influence. The sensor will be further improved to obtain a still longer calibration stability, and adapted for animal implantation, thus making it useful for clinical application.

Animals↗
PubMed1993

[Development and evaluation of an electrocatalytic glucose sensor for diabetes therapy].

For the continuous measurement of glucose levels in vivo, an electrocatalytic glucose sensor has been developed. Electrochemical determination of the glucose concentration is effected by measurement of the impedance, which at given potentials is directly dependent on the glucose concentration in the solution. For evaluation and determination of long-term stability, the sensor was first implanted in the carotid artery in the form of a flow-through cell, and was later inserted into the vena cava of a sheep in the form of a catheter. Sensor response was checked periodically by performing glucose tolerance tests. During the implantation period, we also tested the sensitivity of the sensor towards various blood components and medicaments. By adapting sensor calibration, it proved possible to suppress these cross-sensitivity effects. The flow-through cell type of sensor remained functional for up to 71 days post-implantation. So far, data for the catheter-type sensor cover an indwelling time of up to 30 days.

Animals↗
PubMed1992

Influence of paracetamol, sulfanilamide and ascorbic acid on the electrocatalytic glucose sensor.

An electrocatalytic glucose sensor for in vivo application has been developed. The principle of measurement is based on the direct electrochemical oxidation of glucose at a platinum electrode without an enzymatic reaction. In an in vivo experiment with sheep the glucose sensor was tested with respect to its cross-sensitivity towards ascorbic acid, paracetamol and sulfanilamide. The influence of these substances could be reduced by an adapted calibration to such an extent, that the sensor performance could be ensured.

Acetaminophen↗
PubMed1991

Human atherosclerotic coronary artery xenografts: a model for investigation of transluminal recanalization.

A model for testing transluminal recanalization techniques was developed. Fragments of human atherosclerotic coronary arteries were transplanted into carotid arteries of dogs and evaluated by angiographic, angioscopic, and histologic study within a three-month period. An inflammatory response was most intense within the first week. By two weeks no inflammation was noted. Total occlusion (n = 13) and stenosis (n = 11) of the carotid arteries were achieved without complications. The model is easy to produce within a short period and the arterial occlusion resembles human vascular disease. This model has been used to evaluate laser recanalization of vascular obstructions.

Animals↗
PubMed1991

Influence of urea on the glucose measurement by electrocatalytic sensor in the extracorporeal blood circulation of a sheep.

In an animal experiment with the electrocatalytic glucose sensor, measurements were carried out over one week in the extracorporeal circulation of a sheep. Glucose tolerance tests were performed, and the influence of increased urea concentrations in the blood on the glucose determination was investigated. The sensor constructed as a flow-through cell was integrated via a vascular graft outside the body into the carotid artery of the animal and activated by an external electronic unit of measurement. The glucose concentration was determined by measuring the impedance of the electrode/membrane system at various potentials. By means of a subsequent correlation analysis of the measured values obtained over one week, a calibration valid for the entire measurement period was established. After a zero adjustment, it was even possible to adopt the calibration from the glucose measurement of the preceding animal experiment. The investigations of the influence of urea on the glucose measurement showed that the error in measurement of the sensor, which is 20% on average, is only insignificantly increased when the urea level is raised beyond the maximum physiological concentration.

Animals↗
PubMed1991

[Improved model of a fecal collection device for the prevention of coprophagia in the rat].

Previous fecal collection cups with tape fixation frequently led to serious necroses of the rat tail due to strangulations, and did not allow for growth of the tail. A recently developed new model gives space for rapidly growing tails and is securely fixed by a cannula perforating both fecal collection cup and tail. It is transparent, cheap to be made, and easy to empty and was tested in 118 animals for two and four weeks. In no case the cup did loosen or had to be removed due to infections, strangulations or any local problems.

Animals↗
PubMed1990

Laser balloon angioplasty: technical realization and vascular tissue effects of a modified concept.

A modified concept using a movable fiber with radial light dispersion was developed for combining mechanical balloon dilatation and intraluminal circumferential Nd-Yag laser irradiation of the arterial wall. The aims of the study were the technical feasibility and the acute and chronic vascular tissue effects of laser-assisted balloon dilatation. The carotid arteries (n = 9 dogs) and femoral arteries (n = 5 dogs) of dogs were mechanically dilated and simultaneously circumferentially irradiated through the balloon by 1,064 nm Nd-Yag laser (20-25 W). Temperature at the adventitial surface was kept constant at 50 degrees C, 60 degrees C, 70 degrees C, or 80 degrees C for either 8 or 15 seconds by a computerized feedback system for temperature control. Angiographic and histological results were available acutely, subacutely (2 days), and at 3 months. Angiographically, stable and smooth enlargement of the lumen was demonstrated acutely. At 3 months, occlusions, probably thrombotic in origin, had occurred in 5 of the carotid arteries and none of the femoral arteries. Histologically, laser-induced coagulation of the arterial wall with loss of cellular elements was demonstrated. Collagen and elastic fibers remained relatively intact. In two carotid arteries intimal proliferation was observed at the treated site. Thus, this technique appears to be technically feasible, yet further study is needed to assess its potential to reduce or repair acute vascular complications (dissections) and to reduce restenoses after percutaneous transluminal coronary angioplasty (PTCA). However, the clinical value of this technique appears to be limited in view of the thromboses and reactive proliferations observed in this preliminary study.

Angioplasty, Balloon↗
PubMed1987

Improvement of endoscopic laser therapy in gastrointestinal ulcer bleeding by tissue infiltration. Basic experiments on the dog stomach in vivo.

The therapeutic effect of Nd-YAG laser coagulation in arterial ulcer bleeding seems to be improved by local epinephrine infiltration. The purpose of this animal study was to evaluate the safety of this new therapeutic modality. The effect of Nd-YAG laser on normal and on infiltrated gastric mucosa was compared in acute and chronic experiments on 14 beagle dogs. On exposed normal gastric wall, perforation time and power output were inversely correlated. The required energies are nearly constant at different power levels. After infiltration of sodium chloride as well as of epinephrine into the mucosa, however, perforation time increased four- to five-fold. Volumes of mucosa defects and of the coagulation zones were also lower after pretreatment by infiltration. The results encourage further clinical use of this new therapeutic approach.

Animals↗