PubMed Health⌕ Search

Biomedical subjects

W Niederlag

Publications and source records attributed to W Niederlag.

18 recordsLinked to original sources
PubMed2000

[Evaluation of PC-based radiologic diagnosis workstations].

PURPOSE: Evaluation of PC based Radiology Diagnostic Workstations performed by medical users using detailed lists of functional requirements. MATERIAL AND METHODS: During February 1999 and September 1999 medical users at the hospital Dresden-Friedrichstadt Germany had tested 7 types of radiology diagnostic workstations. Two types of test methods were used: In test type 1 ergonomic and handling functions were evaluated impartial according to 78 selected user requirements. In test type 2 radiologists and radiographers (3 + 4) performed 23 work flow steps with a subjectively evaluation. RESULTS: By using a progressive rating no product could fully meet the user requirements. As a result of the summary evaluation for test 1 and test 2 the following compliance rating was calculated for the different products: Rad Works (66%), Magic View (63%), ID-Report (58%), Impax 3000 (53%), Medical Workstation (52%), Pathspeed (46%) and Autorad (39%). CONCLUSIONS: As a basis for a purchasing decision a detailed functional specification an importance rating is required. Especially industrial development effort for improving the workstations is required for DICOM Supplements 33, image printing, integration teleradiology functions for compatible interoperability between different workstations, support for classroom demonstrations, system administration and data security.

Computer Communication Networks↗
PubMed1992

Right ventricular conductance to establish closed-loop pacing.

Innovations in pacing technology, which include the addition of rate-responsive features to programmable pacemakers, can improve the quality of life of patients suffering from sick sinus syndrome. Among the strategies providing rate-adaptive cardiac pacing, the most attractive is the physiological restoration of closed-loop chronotropic control. This paper describes how autonomic nervous system (ANS) control information is extracted from dynamic measures of myocardial contractile performance obtained from unipolar conductance measurements using the stimulation electrode in the right ventricular cavity. The pacemaker uses the ANS information to modulate pacing rate and restore normal physiological control of heart rate. A new algorithm, regional effective slope quantity (RQ), for isolating the ANS signal was developed. The resulting signal, ventricular inotropic parameter (VIP), is a normalized parameter proportional to the strength of the ANS inotropic signals to the myocardium. The efficacy of the ANS control concept was evaluated in multi-centre studies. Patients with AV block and VIP-controlled pulse generators performed defined exercise protocols. The ANS-controlled pacing rate and the spontaneous sinus rate were closely correlated. Blood pressure and subjective patient reports further indicated that good control of the cardiovascular circulation was achieved.

Autonomic Nervous System↗
PubMed1992

Autonomic nervous system controlled closed loop cardiac pacing.

A multicenter clinical study is presented, which focuses on the reestablishment of closed loop cardiac control in patients with chronotropic insufficiency. Using the information about sympathetic tone contained in the myocardial contractility, it is possible to reconnect the heart rate to the physiological control mechanisms. Intracardiac impedance is measured with the ventricular electrode and the ventricular inotropic parameter (VIP) is derived from that. The VIP serves directly as input to the control of heart rate by the pacemaker. Over 200 patients have received autonomic nervous system (ANS) controlled pacemakers. The patient-pacemaker system was investigated in different ways. This included standard exercise tests, long-term studies of every day activities over 24 hours, psychological, and pharmacological challenges. To prove the validity of the approach we specifically looked at (1) the appropriateness of changes in paced heart rate with sympathetic tone during exercise, (2) the correlation between heart rate and sinus rate, if detectable, and (3) the correlation between the echocardiographically determined preejection period (PEP) and the VIP controlled heart rate.

Autonomic Nervous System↗
PubMed1992

[Measuring intracardiac impedance for the determination of sympathetic nerve activity in frequency-adapted electrostimulation--Part 2: Clinical results].

The results of a multicenter clinical study involving patients receiving the first ANS controlled rate adaptive pacemaker are presented. In the patients with primary or secondary chronotropic insufficiency, it is possible to reestablish the closed loop control system that includes the baroreceptors, the medulla oblongata, the cardiac output and the mean arterial blood pressure. This system serves to keep the blood pressure constant in the face of changing demands on the circulation. Utilizing intracardiac impedance measurements, the myocardial contractility can be determined, which contains information about the current sympathetic tone, and thus represents an excellent physiological input for a rate adaptive mechanism. The results presented are taken from a study population of over 200 patients. The objective evaluation of this new approach was performed echocardiographically, by ergometry and 24-hour Holter monitoring.

Adult↗
PubMed1989

[Intracardiac recording of potentials in placing a thermodilution catheter].

It is reported on methods of positioning our former described flow directed thermodilution (TD) catheter by the intracardiac ECG derived from two electrodes, one at the tip of the catheter near the temperature sensor and the other six centimeter proximally of it. The typical criterion of the intracardiac ECG in the outflow tract of the right ventricle and in the pulmonary artery are listed, especially the amplitudes, the QRS-splits, T-wave inversion and P-wave configuration.

Cardiac Catheterization↗
PubMed1989

Improved rate responsive algorithm in QT driven pacemakers--evaluation of initial response to exercise.

The QT pacemaker is a rate modulated pacemaker that uses the evoked QT interval as an indicator to determine its optimal pacing rate. Despite the generally favorable clinical results with this form of pacing, some flaws in the system have been reported, such as the frequently observed rather slow initial response of the pacing rate to physical exercise, and the phenomenon of oscillation of the heart rate. These problems can be attributed to the rate adaptive algorithm used in the current QT pacemaker. Recently, in a reexamination of the relationship between evoked QT interval and pacing rate, a curvilinear relationship between these parameters has been demonstrated. As a result, a new algorithm has been developed for the next generation of the QT pacemaker. Before this new algorithm was implemented in new implantable devices, it was evaluated in a multicenter clinical investigation, with emphasis on the initial response of the pacing rate to exercise. This study was carried out by means of special software in the programmer of the QT pacemaker. By employing real-time bidirectional telemetry, it was possible to submit the study population, consisting of 37 patients with implanted QT pacemakers of the current generation, to identical exercise tests. Comparing these exercise tests, it appears that a considerable gain in speed of response to exercise can be achieved by using the same sensor with a faster reacting, nonlinear rate adaptive algorithm.

Aged↗
PubMed1987

[Physiologic frequency adaptation of cardiac pacemakers using systolic time intervals].

Of the parameters in consideration for control of physiological rate responsive pacing special interest is directed to stroke volume. In search of indirect parameters which are correlated to stroke volume it is demonstrated on principle that systolic time intervals could be used. From the relation ejection time versus pre-ejection time (LVET/PEP) which is known for its correlation to stroke volume a simple algorithm is derived which is based on the realization that PEP is related to the reciprocal of cardiac output. First investigations with patients demonstrated the possibility of the computation of heart rate from PEP only, with good physiological significance.

Electrocardiography↗
PubMed1987

[A new catheter for hemodynamic studies].

It is reported on a new catheter technique for the determination of the cardiac output by means of the method of thermodilution. It consists of a thin sensorcatheter (3 Ch), which contains a microthermistor as temperature sensor and additionally two electrodes. The insertion of the catheter is carried out via puncture of the subclavian vein by means of a special introducer set, the outer sheath of which can used for injecting the cold solution. The positioning of the sensor catheter into the pulmonary artery may be done by intracardiac ECG monitoring with the help of the two electrodes. By means of these electrodes, however, also an electric stimulation of the right ventricle is possible, so that, for instance, haemodynamic investigations depending on stimulation parameters can be performed by only one catheter. The clinical test of the new catheter-set was very successful.

Cardiac Catheterization↗
PubMed1987

[Possibilities for frequency adjusted heart stimulation].

In the sick sinus syndrome, in sinu-atrial conduction defects or in atrial flutter or fibrillation a stress-adapted, frequency-adapted stimulation cannot be obtained by the processing of the atrial potential. Here one depends on partly extracardiac parameters which contain informations about the metabolic and stress situation, respectively. A survey of the parameters for a frequency-adapted stimulation discussed at present is given and a critical valuation of them is carried out. It is shown that all parameters up to now experimentally and clinically, respectively, tested are more or less problematic and that the way out of the difficulty most consist in deriving the controlled variable for a stress adapted stimulation rate from several parameters.

Bradycardia↗
PubMed1986

[Insertion behavior of miniature IBW-79 pressure transducers in the left heart].

It is reported on the properties of the new catheter-tip pressure transducer IBW-79 (Ch 5) for applications in the left heart. The approach to the left ventricle was carried out with the help of Seldinger-technique (Ch 10) via A. femoralis. In all cases positioning of the pressure transducer in the left ventricle succeeded, but in 2 out of 12 patients there were complications after diagnostic program caused by the puncture. The pressure measurements were from a high quality and high fidelity. Zero shifts during the measurements were in the order of -0.5 kPa (-3.8 mm Hg), directions are given for correction or compensation. In our opinion the IBW-79 is a valuable new sensor-catheter for measuring the pressure in the left heart, above all for scientific applications.

Adult↗
PubMed1986

[For and against physiologic heart stimulation].

Issuing from the own experiences on 110 patients with a heart stimulation including the atrium, advantages and disadvantages as well as possibilities of a complication in physiological stimulation system are discussed. From the differential indications for the pacemaker therapy are derived. It is estimated that approximately 20% of the new implantations in critical indication should be performed by a form of physiological stimulation.

Arrhythmias, Cardiac↗
PubMed1986

[Hysterosalpingography with simultaneous intrauterine pressure measurement. A contribution to invasive sterility diagnosis].

There will be demonstrated a method in order to contrast the cavum uteri and the uterine tubes by means of a x-ray TV amplifier in combination with simultaneous intrauterine pressure monitoring. We could demonstrate that measuring the intrauterine pressure during continuous flow of radio-opaque material at hysterosalpingography results in additional informations about tubal patency.

Constriction, Pathologic↗
PubMed1984

[URO-103--a new uroflow measuring device].

A new uroflow measuring instrument produced in the GDR by W. Rentsch , the Uroflow -Recorder URO-103, is presented and compared with thermistor and capacity-measuring apparatuses. The Uroflow -Recorder gives strictly linear measurements and requires extremely little maintainence . Over the test period of 8 months it functioned free from disturbance. The new apparatus is recommended for use, whereby it is suitable for combined urodynamic measurements.

Humans↗
PubMed1982

[Micro-tip transducer for simultaneous pressure and temperature measurements].

It is reported on a new semiconductor-microtransducer with integrated pressure and temperature sensor for simultaneous intracorporal pressure and temperature measuring. The properties of the pressure and temperature canal are described in short and first clinical applications (pressure measuring of the right heart, determination of cardiac output by means of thermodilution). Further applications are discussed.

Cardiac Catheterization↗