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Biomedical subjects

W Irnich

Publications and source records attributed to W Irnich.

At least 19 recordsLinked to original sources
PubMed1991

[The programming of cardiac pacemakers--wish and reality].

To test the extent and quality of pacemaker programming, 340 programmable pacemakers were selected out of 1,204 impulse generators removed post-mortem. Their actual program was compared with the nominal parameters when first delivered. 177 (52.1%) of the 340 pacemakers still had the same parameters as on delivery. The multiply programmable impulse generators with telemetry were more frequently programmed (61.2%) than the simple programmable ones (43.0%) or the multiply programmable ones without telemetry (43.7%). Rate was the most frequently programmed parameter, followed by impulse amplitude, sensitivity and impulse duration. Refractory time and hysteresis were only rarely changed from the initial state. Apparently, programmability was not thought to be important enough. Programming without telemetry was seemingly too complicated. The reasons for this attitude should be investigated so that the discrepancy between wishes and reality can be overcome.

Equipment Design↗
PubMed1990

The fundamental law of electrostimulation and its application to defibrillation.

Around the turn of the last century, there was an intensive discussion among physiologists as to whether there is a law describing the phenomena of electrostimulation and which formula may best approximate it mathematically. J.L. Hoorweg found in 1892 that the voltage at which a capacitor must be charged to elicit an excitation, was a function of the capacitance in an inverse correlation. G. Weiss reported in 1901 that according to his investigations a linear relationship existed between the duration of a pulse and the corresponding quantity of electricity applied and called it "formule fondamentale." We are now able to give the "fundamental formula" a physical interpretation that yields, as result, the electric field produced by the electrode acting on the excitable membrane. The electric field in the extracellular space is transformed by the cell geometry ratio: cell length to membrane thickness yielding a high transmembrane field capable of reducing the inherent electric field to its threshold level. The consequences drawn from this hypothesis are remarkable and (should) have an influence on all applications of electrostimulation including the discussions on defibrillation. The application of the stimulation theory to defibrillation yields as results: (1) The basic engineering principle of defibrillation is to produce an electric field within the ventricles of 400 V/m or more. An orthogonal pulse application may reduce the energy requirements, as more fibers are longitudinally reached by the electric field; (2) The shape of the defibrillation pulse and its polarity plays no role. Consequently it follows that biphasic pulses must be less efficient than monophasic pulses, if they are close to the chronaxie; and (3) The most serious disadvantage in today's defibrillation practice is its dose characterization in "energy"; but this physical quantity cannot be justified in the light of the fundamental law of electrostimulation.

Animals↗
PubMed1978

[Incidence of spontaneous rhythm after pacemaker implantation for total A-V block (author's transl)].

Follow-up investigation over 12--84 months (mean 30 months) of 86 patients with the primary diagnosis of permanent total atrioventricular block revealed that spontaneous rhythm could be demonstrated in all but 17 patients. A-V conduction was re-established in 13, but in most of them it was on the basis of ventricular ectopic beats. These findings prove that in the described type of patient spontaneous rhythm after pacemaker implantation is common. Therefore, fixed-rate pacemakers are not indicated in these patients.

Atrioventricular Node↗
PubMed1978

Electromagnetic interference in implantable pacemakers.

The inhibited pacemaker (VVI or AAI) has become the most popular in recent years because of its ability to combine a physiological advantage with economical current consumption in cases with spontaneous activity. One of its disadvantages is its sensitivity to external electromagnetic interference. Though today's pacemakers possess effective protection against most interference signals there may be instances in which patients are subjected to uncomfortable or even life-threatening situations. This is the case of "amplitude modulated" or "pulsed" fields with modulation frequencies in the physiological range. Fields of that sort have been found in the vicinity of a welder, an electric steel plant, and in medical practice where therapeutic currents were applied. Even touch-actuated switches may influence a demand pacemaker. However, these situations may be overcome by a device within the pacemaker for simple time analysis which can be carried out with few components. If electromagnetic fields of diathermy equipment are applied, today's pacemakers may react with intolerably high or low rates. They should, therefore, be avoided.

Electromagnetic Phenomena↗