Biomedical subjects

J Werner

Publications and source records attributed to J Werner.

At least 37 records · Page 2Linked to original sources

PubMed2004

Morphological detection algorithms for the automatic implantable cardioverter/defibrillator (AICD).

To prevent sudden cardiac death of patients who are at risk from long standing tachyarrhythmia the implantable cardioverter defibrillator (ICD) is the first choice therapy. ICDs use a range of electrostimuli up to defibrillation, which is a non synchronous high energy shock, whereas cardioversion is synchronous with the ECG. In order to know when and how to react, a detection algorithm, which analyses an intracardial electrocardiogram (ECG) and classifies the heart rhythm, is implemented in every ICD. All detection algorithms use the heart rate to classify the different heart rhythms roughly. If a tachycardia is detected, it is important to discriminate between a ventricular tachycardia, which is life threatening and a supraventricular tachycardia, which is much less threatening. To be able to make this distinction the detection algorithms analyse the behaviour of the heart cycle intervals, the ECG-morphology or in addition to the ventricular ECG, an atrial ECG. In this paper morphological algorithms will be evaluated and newly developed algorithms will be presented. Recent algorithms use the mathematical wavelet theory. The evaluation shows that these get better results than all but one of the simpler classical morphological algorithms. A new wavelet based algorithm, developed by the authors, exhibits the best detection results.

Algorithms↗

PubMed2004

A fiberoptic sensor system for cardiac monitoring and electrotherapy.

Commercially available cardiac pacemakers and implantable cardioverters/defibrillators (ICD) predominantly use the intracardiac derived electrocardiogram (ECG) for detection of arrhythmias. To achieve an automatic control of the heart frequency in accordance with cardiovascular strain and an improved detection of life-threatening arrhythmias, it is desirable to monitor the heart by an input signal correlated with the hemodynamic state. One possible approach to derive such a signal, is to measure the inotropy (mechanical contraction strength of the heart muscle). For this purpose an optoelectronic measurement system has been designed. The fundamental function of the system has been shown in earlier investigations using an isolated beating pig heart. In this paper further results showing the correlation of the fiberoptic sensor signal with the left ventricular stroke volume are presented. To make the system useful for implantable devices, further improvements with regard to power consumption and signal quality were achieved.

Animals↗

PubMed2004

Automatic control of the extra-corporal bypass: system analysis, modelling and evaluation of different control modes.

Automatic control of the blood gas parameters during extracorporeal circulation has the potential to improve the quality of this procedure and to relieve the personnel from a time consuming task. This paper describes a model of the underlying system for a standard clinical set-up and pinpoints the major difficulties which are the variations of the process gains and the blood- and gas-flow dependent dead times and time constants. Scheduled PI-controllers both for the arterial oxygen as well as for the carbon dioxide partial pressure were designed. Scheduling was based on the blood flow rate. These controllers were tested in a simulation environment. The control systems remained stable under all tested operating condition, but if the blood flow rate was changed abruptly rather large load errors occurred. The performance was improved markedly by adding a feed-forward control path which directly influences the actuating signals based on the actual blood flow rate and the hemoglobin contents, variables which are measured anyway. The major conclusion of this study is to use such direct feed-forward compensation even if more sophisticated control algorithms are used.

Algorithms↗

PubMed2004

Automatic control of isolated organ perfusion.

If provided with adequate physiological conditions explanted hearts may continue to operate in the regular beating mode. This property offers the opportunity to substitute extensive animal experiments by investigations on the isolated organs. At the same time it enables the development of an alternative method for the transport of donor hearts for transplantation. Experimental setups for both applications are described in this paper. The focus is laid on the optimisation of handling and effectiveness of these setups by means of automatic control. The method for investigating the controlled system ("plant") for blood gas exchange, and especially the determination of the transfer function for the partial pressure of oxygen are described. The plant was triggered with stepwise changes on the gas side at several operating points. A first order lag element with time delay was chosen as approximation of every transfer function. The parameter 'time delay', 'gain of the plant' and 'time constant' were analysed as to the dependency on blood flow rate, gas flow rate and partial pressure of oxygen at the blood outlet of the oxygenator. As a result an equation was found to calculate the time delay from gas flow rate and blood flow rate. Correlation of gain and time constant with parameters of the plant were obtained, too. The data is used for the design of a controller, adapting to the different operating points of the plant.

Algorithms↗

PubMed2004

Investigation of cardiac and cardio-therapeutical phenomena using a pulsatile circulatory model.

For many years computer models of the cardiovascular system have existed with which the complex physiological interrelations of regulation processes may be studied. However, one major disadvantage of these models is the simplified modeling of the heart kinematics whereby the short term regulation effects of the heart itself on varying physical strains may only be simulated rudimentarily. The developed pulsatile model emphasizes the detailed description of the systolic wall tension progression subject to the Hill/Frank-Starling mechanisms and the simulation of the cardiac valves. Moreover, to be able to describe long term effects the pulsatile model was coupled to the established cardio vascular model of Guyton. Using the coupled system the influences of impaired valve function and ventricular relaxation disorders on the cardiac output as well as the need for an implementation of a physical strain dependent av-delay in existing pacemaker types were investigated. Both the dynamics and the steady-state values of a subset of variables (pressure, volume, flow) were successfully validated by comparing them to published experimental and clinical recordings.

Biomechanical Phenomena↗

PubMed2003

Specific properties of fine SnO2 powders connected with surface segregation.

The effect of surface segregation in Sb- and In-doped SnO2 fine-grained powders has been analyzed in comparison with single-crystalline samples. The kinetics and thermodynamics of the Sb and In segregation processes were studied as a function of annealing temperature by X-ray photoelectron spectroscopy (XPS) after annealing in an oxygen-containing atmosphere. Significant differences between diffusion and segregation were revealed for doped powders and single crystals, obviously because of simultaneous diffusion and particle-growth processes proceeding during annealing of powders. For doped single crystals the thermodynamic equilibrium is approached after 24 h annealing above 850 degrees C and at 1000 degrees C for Sb and In, respectively. Higher effective activation energies of diffusion are observed for doped powders and the thermodynamic equilibrium is not achieved under technologically relevant annealing conditions. On the basis of dopant profile measurements anomalies in the electrical resistivity at 300 degrees C of Sb-doped SnO2 powders annealed at 700 and 900 degrees C were attributed to an Sb-depleted zone formed beneath the segregated surface during the kinetic regime. To achieve optimum resistivity behavior for commercial application, inhomogeneous doping of powders must be avoided by appropriate preparation steps.

Journal Article↗

PubMed2003

Determination of the s-wave scattering length of chromium.

We have measured the deca-triplet s-wave scattering length of the bosonic chromium isotopes 52Cr and 50Cr. From the time constants for cross-dimensional thermalization in ultracold atomic samples, we have determined the magnitudes |a(52Cr)|=(170+/-39)a(0) and |a(50Cr)|=(40+/-15)a(0), where a(0)=0.053 nm. By measuring the rethermalization rate of 52Cr over a wide temperature range and comparing the temperature dependence with the effective-range theory and numerical single-channel calculations, we have obtained strong evidence that the sign of a(52Cr) is positive. Rescaling our 52Cr model potential to 50Cr strongly suggests that a(50Cr) is positive also.

Journal Article↗

PubMed2003

Accuracy of diagnostic laparoscopy for early diagnosis of abdominal complications after cardiac surgery.

BACKGROUND: In the early postoperative period after major cardiac surgery using extracorporal circulation, abdominal complications can have serious consequences with a mortality rate of up to 70%. Early diagnosis and the timely institution of therapy are the most important factors to improve the outcome; however, clinical evaluation of the abdomen is difficult in these patients. Diagnostic laparoscopy is a minimally invasive procedure with low procedure-associated morbidity, even in critically ill patients. The aims of our study were to investigate the safety of laparoscopy in critically ill patients suspected to have intraabdominal pathology following cardiac surgery and to evaluate the accuracy of diagnostic laparoscopy compared to laparotomy in this setting. METHODS: A total of 17 patients were included (13 male, four female, age 52-80 years) in the early (3-30 days) postoperative period after cardiac surgery using extracorporal circulation (10 ACVB, four valve replacement, one aorto-coronary-venous-bypass (ACVB)+ valve replacement, two cardiac transplantation). Clinical and laboratory findings included distended abdomen (17 of 17), elevated white blood cells (12 of 17), elevated C-reactive protein (CRP) (13 of 17), and elevated lactate levels (11 of 17). The decision to perform laparotomy was taken in all patients on the basis of their clinical condition. Diagnostic laparoscopy was always performed immediately before laparotomy. The laparoscopic findings were then compared to the laparotomy findings. RESULTS: In one patient, laparoscopy showed no abnormal findings, this was confirmed on laparotomy. Five patients were found to have massive distension of the large bowel without ischemia on both laparoscopy and laparotomy. Colonic ischemia of the right hemicolon was found laparoscopically in six patients, which was confirmed in all cases by open resection and histological workup. Three patients suffered from acute cholecystitis, which was correctly diagnosed by laparoscopy in all cases. In one patient, laparoscopy revealed fibrinous peritonitis without other findings. Open exploration failed to identify the cause of the peritonitis in this patient. Laparoscopy showed no pathological findings in one patient, but laparotomy then revealed necrotizing pancreatitis confined to the lesser sac. There was one laparoscopy-associated intraoperative complication (6%) in this series. CONCLUSIONS: Diagnostic laparoscopy is a minimally invasive procedure that can be performed at low intraoperative risk in critically ill patients and has a high sensitivity (94%) for the correct diagnosis of intraabdominal complications after major cardiac surgery. These results suggest that bedside laparoscopy should be considered for all patients with equivocal abdominal symptoms in this setting.

Aged↗

PubMed2003

Angiogenesis inhibition with TNP-470, 2-methoxyestradiol, and paclitaxel in experimental pancreatic carcinoma.

INTRODUCTION: Inhibition of tumor angiogenesis is a novel therapeutic modality for various malignancies. AIM: To investigate the effect of different antiangiogenic agents (TNP-470, 2-methoxyestradiol, and paclitaxel) on growth and neovascularization of experimental pancreatic cancer. METHODOLOGY: In 25 male Lewis rats, tumor induction was achieved by orthotopic and subcutaneous tumor fragment implantation of ductlike pancreatic cancer DSL6A. Four weeks after tumor implantation, the animals were randomly treated with TNP-470, 2-methoxyestradiol, or paclitaxel. After 2 weeks of antiangiogenic therapy, total tumor volume, vital tumor surface, vascular density, and apoptosis were measured. RESULTS: Total tumor volume and vital tumor surface were not significantly different in any of the treatment groups. Similarly, vascular density and apoptosis were not altered by treatment with the various angiogenesis inhibitors at the specific doses used. CONCLUSION: We conclude that in contrast to many earlier studies, angiogenesis inhibition by a single-drug application and by the doses used in the present model did not reveal a favorable therapeutic effect on pancreatic cancer DSL6A. The combination of different angiogenesis inhibitors or higher doses might be more effective.

2-Methoxyestradiol↗

PubMed2003

Inhibition of alcohol-associated colonic hyperregeneration by alpha-tocopherol in the rat.

BACKGROUND: Chronic alcohol consumption results in colorectal mucosal hyperregeneration, a condition associated with an increased risk for colorectal cancer. Possible mechanisms may involve the effects of acetaldehyde and/or free radicals generated during alcohol metabolism. Vitamin E is part of the antioxidative defense system, and its concentration is decreased or its metabolic utilization increased in various tissues after chronic alcohol consumption. We wondered whether alpha-tocopherol supplementation may prevent ethanol-induced colorectal cell cycle behavior and whether these changes were related to alterations in protein synthesis. METHODS: Five groups of male Wistar rats, each consisting of 14 animals, received liquid diets as follows: group 1, alcohol; group 2, alcohol + alpha-tocopherol; group 3, control (i.e., isocaloric glucose); group 4; control (i.e., isocaloric glucose) + alpha-tocopherol. Group 5 was fed a solid chow diet ad libitum. After 4 weeks of feeding, immunohistology was performed with anti-proliferating cell nuclear antigen (PCNA) or anti-BCL2 antibodies. Fractional (k(s)) and absolute (V(s)) rates of protein synthesis and rates of protein synthesis relative to RNA (k(RNA)) and DNA (k(DNA)) were measured with a flooding dose of L-[4-3H] phenylalanine with complementary analysis of protein and nucleic acid composition. RESULTS: The PCNA index was increased significantly in the colon after ethanol administration compared with controls (ethanol, 10.3 +/- 2.3 vs. control, 6.51 +/- 1.6% PCNA positive cells, p < 0.05), although neither the protein, RNA, and DNA concentrations nor k(s), k(RNA), k(DNA), and V(s) were affected. This increase in PCNA index was significantly diminished by coadministration of alpha-tocopherol (ethanol + alpha tocopherol, 7.86 +/- 1.71% PCNA positive cells, p < 0.05) without significant alterations in protein synthetic parameters. A similar result was obtained for the PCNA index in the rectal mucosa (ethanol, 14.6 +/- 4.4 vs. control, 12.1 +/- 4.2% PCNA positive cell), although this did not reach statistical significance. Neither ethanol nor alpha tocopherol feeding had any significant effect on BCL-2 expression in the colorectal mucosa. As with the colon, protein synthetic parameters in the mucosa were not affected by alcohol feeding at 4 weeks. These effects on colonic cell turnover without corresponding changes in protein synthesis thus represent a specific localized phenomenon rather than a general increase in anabolic processes in the tissue and reaffirm the hyperregenerative properties of chronic alcohol consumption. CONCLUSIONS: Alcohol-associated hyperproliferation could be prevented, at least in part, by supplementation with alpha-tocopherol. This may support the hypothesis that free radicals are involved in the pathogenesis of alcohol-associated colorectal hyperproliferation.

Animals↗

PubMed2002

New sensor based on fibre optics for measurement of heart movement.

Innovative fibre-optic sensor technology for measuring the movement of the myocardial walls, and from this the heart chamber volumes, was developed. An optical fibre, with a mirror at its end, is inserted into a catheter located in the heart. An opto-electrical control unit positioned outside the heart contains both the light source and the signal receiver. It generates and couples the light into the fibre and transforms and analyses the reflected signal. With such a system, the movement of the cardiac wall can be continuously measured during each cycle, because the fibre moves synchronously with the heart, and this movement bends the fibre, changing the optical attenuation. Experiments where the fibres were wound around metal cylinders of different diameters revealed a maximum sensitivity of 4% mm(-1), diameter. The noise signal corresponded to about 1% of the diameter. First tests in a working pig heart showed a high correspondence of the fibre signal with cardiac parameters. Although these tests are promising, further long-term, extensive experiments in preclinical test devices, and later in clinical tests, must be carried out before the new sensor is used in clinical practice. The fibre-optic technique could be used in monitoring devices, assist devices, pacemaker systems or cardioverter defibrillators.

Animals↗

PubMed2002

[Biventricular defibrillation using transvenous electrodes].

This study investigated the feasibility of transvenous biventricular defibrillation using an electrode in a left ventricular vein. The standard lead configuration with a coil in the right ventricle (RV) and a coil in the superior vena cava (SVC) was compared with an additional unipolar coil in an accessible epicardial vein. Only biphasic shocks were used with different shocking modes between the coils in the RV, LV, SVC and the ICD-generator (CAN). Shocks were applied starting with 30 J, decreasing till the DFT was reached. As a result there is a lower DFT when defibrillation is performed including the left ventricular electrode. The impedance did not show a significant increase after more then 20 consecutive shocks. It is a feasible and workable application that might help to reduce the energy demand and increase the safety of such a system.

Animals↗

PubMed2002

[Rate-responsive pacemaker concept: parametric system identification].

The focus of this paper is the design of a rate-responsive pacemaker which uses the atrio-ventricular conduction time (AVCT) as an exertion related sensor signal. AVCT can be easily obtained from an intracardial electrogram. During atrial pacing AVCT shortens with exercise but increases with the stimulation rate. Hence, an AVCT based pacemaker always establishes a closed-loop system. General design rules for an AVCT pacemaker have been developed from our experimental results and a system-theoretical treatment. Topics addressed were the controller gain, uncertainties concerning the dynamics of the AVCT, the attenuation of disturbances, the closed-loop bandwidth and stability.

Algorithms↗

PubMed2002

[Blood gas regulation in isolated beating pig hearts].

Continuous perfusion with oxygenated blood is required to supply isolated beating pig hearts. To meet physiological conditions the blood gas parameters pH, pO2 and pCO2 should correspond with values usually found in pigs, respectively. Controlling these parameters manually is a very time consuming task and is therefore done best by a control system consisting of gas blender, oxygenator and blood gas sensors. As this control system should be used with an transportable perfusion apparatus, this paper describes an approach where the gassing is realized only with air and oxygen. In this approach pO2 and pH are measured on blood side so that the control system can change oxygen concentration and gas flow adequately on the gas side.

Acid-Base Equilibrium↗

PubMed2002

[Ultrasound-based imaging modalities for thermal therapy monitoring].

Thermal therapy has been established as an alternative and minimally invasive approach for the treatment of tumors. During a thermal therapy tissue is heated locally up to above 60 degrees C. Cancerous tissue can thus be destroyed by coagulation. At present there are no suitable imaging modalities available for an accurate real-time monitoring of the coagulation process. A subproject of the Ruhr Center of Competence for Medical Engineering (KMR Bochum) aims at developing an ultrasound-based, real-time capable monitoring system for thermal therapy. Therefore several tissue characterizing imaging modalities will be combined in a new multimodal concept. Initial experiments with porcine liver in vitro have shown that real-time monitoring of a thermal therapy using various imaging methods simultaneously will be possible.

Animals↗

PubMed2002

[Model construction for reperfusion of the isolated pig liver].

In recent years thermal ablation of liver tumors as a minimally invasive method became a promising alternative to conventional strategies such as chemotherapy or resection of liver tissue. Thereby an electrode is placed inside the tumor delivering energy in the form of high frequency current into the target volume to achieve and maintain a tissue temperature between 60 and 100 degrees C. Cells exposed to this thermic stress undergo coagulation necrosis and are irreversibly damaged. To protect vital liver structures from heat, it is necessary to develop an online temperature monitoring system. An experimental setup perfusing isolated pig livers under physiological conditions with 0.9% NaCl solution was established to develop and evaluate the measuring technique.

Animals↗

PubMed2002

The effect of combination treatment with acarbose and glibenclamide on postprandial glucose and insulin profiles: additive blood glucose lowering effect and decreased hypoglycaemia.

This study compared the effects of acarbose plus glibenclamide combination therapy with acarbose or glibenclamide treatment alone on postprandial blood glucose, serum insulin and C-peptide levels, and the tendency to develop hypoglycaemia. A total of 84 patients with Type 2 diabetes (fasting blood glucose: 120-180 mg/dl; postprandial blood glucose: 140-240 mg/dl) was included in this two-centre, double-blind, double-dummy, placebo-controlled study. Patients were randomised to one of 4 treatment groups: acarbose (100 mg); glibenclamide (3.5 mg); acarbose plus glibenclamide; or placebo. Treatment was administered before a standard breakfast, and fasting (07.30 h, 08.00 h) and postprandial (09.00, 10.00, 11.00, 12.00 h) blood glucose, serum insulin and C-peptide levels were determined. Acarbose plus glibenclamide treatment significantly reduced the mean increase in postprandial blood glucose levels (23.7+/-17.3 mg/dl) compared with either acarbose (58.4+/-31.6 mg/dl), glibenclamide (56.9+/-42.8 mg/dl) or placebo (101.6+/-49.2 mg/dl) (p<0.05 for all). Serum insulin levels (mean AUC(7.30-12 h)) observed with acarbose plus glibenclamide combination therapy were significantly lower than those observed with glibenclamide monotherapy (243.5+/-161.1 vs 383.4+/-215.8 hr x microU/ml; p=0.02), and comparable with the values seen with placebo (226.0+/-166.6 hr x microU/ml), suggesting that acarbose modifies the insulin secretion induced by glibenclamide. Glibenclamide monotherapy resulted in a significantly higher rate of decrease in blood glucose level than with acarbose plus glibenclamide (71.8+/-29.9 vs 46.2+/-18.0 mg/dl x h(-1); p=0.0003), and blood glucose levels at 11.00 h were also markedly lower with glibenclamide (84.4+/-29 mg/dl) than acarbose plus glibenclamide (102.0+/-41 mg/dl), suggesting a reduced tendency for hypoglycaemic episodes with acarbose plus glibenclamide than with glibenclamide alone. In all, 6 (29%) hypoglycaemic episodes occurred with glibenclamide, 2 (10%) with acarbose plus glibenclamide and none with acarbose. Acarbose plus glibenclamide combination therapy results in an additive glucose lowering effect and reduced risk for hypoglycaemia. Acarbose modifies the insulin secretion induced by glibenclamide, which explains the lower risk of hypoglycaemia compared with glibenclamide monotherapy.

Acarbose↗

PubMed2002

[Fiberoptic measurement of myocardial contraction--correlation of the signal with hemodynamic values].

In addition to the intracardial ECG, the mechanical myocard contraction should be used as another input signal for cardiac pacemakers and implantable defibrillators. Therefore a fiberoptical measurement system was designed. A sensor-fiber was placed in the coronary venous system. An opto-electronic system converts the optical losses, caused by bending of the fiber, into a proportional voltage. This method allows measuring of the left ventricular myocard contraction strength. By theoretical calculations it was shown, that a good correlation of the sensor-signal and the left ventricular radius can be expected. Additional investigations using an isolated beating pig heart were performed. A high correlation of the sensor-signal and the left ventricular stroke volume was shown.

Animals↗