Long-term responses of canine lungs to acidic particles.

Sixteen beagle dogs were housed in four large chambers under minimum restraint. They were exposed for 16 months to clean air and individual baseline data of markers were obtained. For 13 months, eight dogs were further exposed to clean air and eight dogs for 6 h/d to 1-microm MMAD (mass median aerodynamic diameter) acidic sulfate particles carrying 25 micromol H(+) m(-3) into their lungs. To establish functional responses (lung function, cell and tissue integrity, redox balance, and non-specific respiratory defense capacity), each exposed animal served as its own control. To establish structural responses, the eight non-exposed animals served as controls. Acidic particles were produced by nebulization of aqueous sodium hydrogen sulfate at pH 1.5. Only subtle exposure-related changes of lung function and structure were detected. A significant increase in respiratory burst function of alveolar macrophages points to a marginal inflammatory response. This can be explained by the significant production of prostaglandin E(2), activating cyclooxygenase-dependent mechanisms in epithelia and thus inhibiting lung inflammation. The non-specific defense capacity was slightly affected, giving increased tracheal mucus velocity and reduced in vivo dissolution of moderately soluble test particles. Hypertrophy and hyperplasia of bronchial epithelia were not observed, but there was an increase in volume density of bronchial glands and a shift from neutral to acidic staining of epithelial secretory cells in distal airways. The acidic exposure had thus no pathophysiological consequences. It is therefore unlikely that long-term inhalation of acidic particles is associated with a health risk.

Performance evaluation of IVC systems.

An expert Working Group was set up in December 2000 to develop recommendations for users and industry on the evaluation of proper function and operation of individually ventilated cage (IVC) systems. The full report of their recommendations is in two parts--'Part 1: Test Instructions' and 'Part 2: Evaluation Criteria'--both of which have been published in full on the Laboratory Animals Ltd website. They can be found at http://www.lal.org.uk/IVC/index.html. Evaluation of and feedback on the recommendations to further refine their use and scientific basis is encouraged. This Summary Report provides a brief overview of the background to the development of the full report and the issues it addresses.

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.

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.

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.

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.

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.

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.

[Improved model of a fecal collection device for the prevention of coprophagia in the rat]. / Verbessertes Modell einer Kotfalle zur Unterbindung der Koprophagie bei dei Ratte.

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.

[Development and evaluation of an electrocatalytic glucose sensor for diabetes therapy]. / Entwicklung und Erprobung eines elektrokatalytischen Glucosesensors für die Diabetes-Therapie.

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.

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.

Image guided interstitial laser thermotherapy: a canine model evaluated by magnetic resonance imaging and quantitative autoradiography.

OBJECTIVE: To determine the applicability and safety of a new canine model suitable for correlative magnetic resonance imaging (MRI) studies and morphological/pathophysiological examination over time after interstitial laser thermotherapy (ILTT) in brain tissue. MATERIAL AND METHODS: A laser fibre (Diode Laser 830 nm) with an integrated temperature feedback system was inserted into the right frontal white matter in 18 dogs using frameless navigation technique. MRI thermometry (phase mapping i.e. chemical shift of the proton resonance frequency) during interstitial heating was compared to simultaneously recorded interstitial fiberoptic temperature readings on the border of the lesion. To study brain capillary function in response to ILTT over time quantitative autoradiography was performed investigating the unidirectional blood-to-tissue transport of carbon-14-labelled alpha amino-isobutyric acid (transfer constant K of AIB) 12, 36 hours, 7, 14 days, 4 weeks and 3 months after ILTT. RESULTS: All laser procedures were well tolerated, laser and temperature fibres could be adequately placed in the right frontal lobe in all animals. In 5 animals MRI-based temperature quantification correlated strongly to invasive temperature measurements. In the remaining animals the temperature fibre was located in the area of susceptibility artifacts, therefore, no temperature correlation was possible. The laser lesions consisted of a central area of calcified necrosis which was surrounded by an area of reactive brain tissue with increased permeability. Quantitative autoradiography indicated a thin and spherical blood brain barrier lesion. The magnitude of K of AIB increased from 12 hours to 14 days after ILTT and decreased thereafter. The mean value of K of AIB was 19 times (2 times) that of normal white matter (cortex), respectively. CONCLUSION: ILTT causes transient, highly localised areas of increased capillary permeability surrounding the laser lesion. Phase contrast imaging for MRI thermomonitoring can currently not be used for reliable temperature readings in vivo. The suggested new canine model proved to be safe, accurate, easy to use, and provides clinical, radiographic, pathological and physiological correlations.

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.

Laser versus radiofrequency catheter ablation of ventricular myocardium in dogs: a comparative test.

To compare the effects of laser light with those of radiofrequency (RF) current on ventricular myocardium, a total of 36 lesions (endocardial approach n = 10 each and epicardial approach n = 8 each) were produced by either transcatheter laser (Nd:YAG, 1,064 nm, 30 W, 30 s) or RF (70 degrees C, 30 s) catheter applications in the beating hearts of 4 dogs. Volumes of coagulated myocardium in endo-/epicardial approaches were 996 +/- 73/1,075 +/- 82 (laser) and 111 +/- 38/44 +/- 5 mm3 (RF). RF lesions showed intramural bleeding, rupture and dissociation of myocardial fibers, tissue vaporization with crater and thrombus formation. Transcatheter application of laser light produced significantly larger and better reproducible lesions than RF current, without undesirable effects on the ventricular walls.

In vivo temperature measurement during transcatheter endomyocardial Nd-YAG laser irradiation in dogs.

Intramural temperatures were monitored during catheter-directed endomyocardial non-contact laser irradiation by means of an array of thermocouples inserted epicardially. Via a novel electrode-laser catheter, a total of 30 Nd-YAG laser pulses, 1064 nm, 25 W/15 s, 20 W/30 s, 15 W/45 s,n = 10 each, were aimed at various endocardial sites in the ventricles of four dogs. Temperatures increased gradually after the onset of the laser pulses. Maximum values were measured in the central area of the irradiated spots: 100 +/- 15 double daggerC at 25 W, 78+/- 23 double daggerC at 20 W and 80 +/- 13 double daggerC at 15 W. Application of 300 J of laser energy induced significantly higher temperatures at 25 W (p< 0.02) than at 20 or 15 W (20vs 15 W: p> 0.05). Initial temperature rise and lesion formation was accompanied by dwindling of local electrical potentials. There was no crater formation. Transcatheter non-contact Nd-YAG laser coagulation of healthy ventricular myocardium can be performed in a safe and controllable manner at power settings up to 20 W and laser energies up to 675 J.

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.

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.

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.

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.