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Biomedical subjects

W Irnich

Publications and source records attributed to W Irnich.

At least 55 records · Page 3Linked to original sources
PubMed1989

[The perception threshold for 50 Hz alternating voltage and current].

The perception threshold for 50 Hz alternating voltage and current was investigated in male and female volunteers. The results demonstrate that the voltage thresholds for males and females are practically identical, while the current thresholds are significantly higher for males than for females. In the light of these results, the hypothesis that current is the only reliable parameter for describing electric hazards can no longer be sustained.

Electricity↗
PubMed1989

[Classification of implants with reference to safety considerations].

Implants are listed both in the German Drug Law (Arzneimittelgesetz) and in the Regulations of the Safety of Medical Technical Equipment (Medizingeräteverordnung). In recent time, various guidelines concerning implants have been under discussion in Europe. It is surprising to note that more than one set of guidelines has been thought to be necessary. The present article discusses possible definitions of some of the terms employed in connection with implants, and attempts to identify the differences and common features of implants under aspects of safety, thus providing a broader base for public discussions. An analysis of the implants presently available has shown that it is useful to establish a hierarchy of possible hazards that takes into account the danger to the patient under worst-case conditions. A survey has demonstrated that in the worst case, most implants are associated with only an impairment or inconvenience for the patient, but no threat to life. In contrast, a minority of implants are of such a nature that in the case of severe failure, a life-threatening situation can develop for the patient. Such a hazard is not dependent upon whether the implant has a driving energy source or not. These findings indicate that within the framework of safery considerations, more attention need to be paid to "passive" implants than has been the case so far.

Accident Prevention↗
PubMed1988

A new principle of rate adaptive pacing in patients with sick sinus syndrome.

The most "natural" rate adaptive pacemaker is VDD for patients with AV block. Nothing equivalent exists for patients with sick sinus syndrome (SSS). Even if they are paced in the AAI mode, the AV synchrony is often lost under exercise if nodal rhythms develop which cause the atria to contract against closed valves by retrograde conduction. We tried to develop a concept of rate adaptive pacing which is applicable in SSS patients by guaranteeing AV synchrony. It is known that AV delay shortens with increasing rate under exercise in normal subjects. Three AAI paced patients were evaluated to find out whether a similar correlation is valid between exercise and AV delay with constant rate. A nonconventional ECG was registered during the whole procedure by using an analog tape recorder. The pacing rate was changed with and without exercise on a bicycle to determine its influence on AV delay and by calculating the AV delay averaged over the last 8 beats. In all three patients a reproducible correlation existed between exercise and shortening of the AV delay. This effect was already detectable after 10 s. Increasing the pacing rate above "physiological" rates caused prolongation of the AV delay (over-stimulation phenomenon). We, therefore, concluded that measuring the AV delay in atrial paced patients with SSS by means of a ventricular electrode can be used as a fast parameter for rate adaptive pacing with AV synchrony. The "over-stimulation" phenomenon can additionally be utilized for controlling "physiological" rates depending on individual needs.

Atrioventricular Node↗
PubMed1987

Muscle noise and interference behavior in pacemakers: a comparative study.

Inhibition of VVI pacemakers by muscle noise, though known since 1972, has attracted increased interest in recent years. More sensitive dual chamber atrial synchronized pacemakers have proved to be more susceptible to interference and will further enhance the effort at improving pacemaker resistance to interference of all kinds. To study the reaction of 16 pacemakers of 10 different manufacturers with respect to muscle noise, we stored a noisy episode on a 16-second endless loop tape. Each pacemaker was subjected to an identical muscle noise signal, with amplitude varied to reach the response threshold. The results are: The range of muscle noise thresholds consists of more than one decade, varying from 0.4 mV to 4.6 mV. Only 4 of 16 pacemakers remained unaffected if a noise signal of 3 mV maximum is assumed. In 11 out of 16 pacemakers, the threshold amplitude for muscle noise is lower than that for intracardiac electrographic signals which can be explained by a sensitizing mechanism caused by noise. Five pacemakers were so sensitive that even a sensitivity setting of 4 mV would not reject muscle noise. Filtering muscle noise, 50-Hz signals, and intracardiac electrograms with a 12 dB filter of variable upper cut-off frequency revealed that heart signals are always attenuated more than interference signals.

Electricity↗
PubMed1986

Sensing properties of pacemaker leads.

It is already general practice to attribute sensing properties to geometry and surface structure of pacemaker leads. We have to analyze critically whether claims of having found leads with high sensitivity are in accordance with experimental and theoretical findings. From a model can be derived what kind of typical signal structure will originate from an electrode when an excitation wave crosses it, and what of this signal is influenced by electrode parameters. With decreasing surface area, the frequency content of the signal, the impedance, and, theoretically, the amplitude, increases. If the pacemaker characteristics are not matched to the lead properties, this inverse relationship becomes a direct one: If the input impedance is too low or the upper cut-off frequency of the bandpass is not high enough, the effective heart signal seems to be diminished with decreasing size. This, however, is more a pulse generator than a lead problem. If all pacers would possess an input impedance of greater than or equal to 100 K omega and an upper cut-off frequency of greater than or equal to 350 Hz, an attenuation of the heart signal would be less than or equal to 10% and thus, the results with different leads would be very similar and of equally high sensitivity.

Electrocardiography↗
PubMed1985

[Programming of pacemakers: a gain or a passtime?].

Seventy-seven programmable pacemakers, selected at random from a reservoir of 1051 explanted pacemakers, made available by health-offices, institutes of pathology and institutes of forensic medicine, were examined for alterations made since the time of delivery. The results motivated our choice of title. In 41 of 74 (55.4%) no parameter was changed and in 36.5% the frequency was altered. Of the two- or multi-programmable pacemakers, the amplitude was altered in 13 of 61 (21.3%), the pulse duration in 9 out of 38 (23.7%), the sensitivity in 10 out of 32 (31.3%), hysteresis in one out of 31 (3.2%) and the refractory time in none of 30. None of the 10 pacemakers with programmable operation mode were reprogrammed although they included a DDD that was delivered, however, in the VVI state. Nine of 69 pacemakers (13%) were double- and 2 of 33 (6%) triple-programmed. The two physiological parameters (frequency and hysteresis) were clearly not utilised to the extent that would be desirable. All other programmable parameters serve exclusively for the technical adjustment to the heart.

Humans↗
PubMed1985

Intracardiac electrograms and sensing test signals: electrophysiological, physical, and technical considerations.

Until now, the characterization of intracardiac electrograms was carried out mainly in the frequency domain by which filtering and sensitivity testing was decidingly influenced. The typical structure of the intracardiac electrogram derived with unipolar electrodes that is normally responsible for synchronization can be explained theoretically by assuming two dipoles perpendicular to each other moving along with an excitation wave. An abstraction of this typical structure yields, as a sensitivity test signal, an asymmetric triangle with a 4-ms decay time and a 16-ms rise time. A correlation of different test signals and real heart signals applied to 16 different pacemakers demonstrates that the proposed test signal is superior to all others known so far.

Cardiac Pacing, Artificial↗
PubMed1984

Development of a coding system for pacemakers.

Since the establishment of the first pacemaker coding system (The Three-Letter Code, 1974) with its nine different pacemaker modes, the number of available modes has increased remarkably. As a consequence, even the expanded "Five-Letter-Code" is no longer adequate to describe the different modes with sufficient precision. To overcome these difficulties, we tried to construct a coding system that represents each mode in a pictorial form, which is simultaneously and precisely defined by a schematic circuit and a number within a numerical matrix.

Cardiac Pacing, Artificial↗
PubMed1984

Interference in pacemakers.

We attempt here to outline the different sources of interference and the methods of interference detection and protection with their advantages and disadvantages. A proposal is made as to how a better interference suppression could be established. A comparison of 16 pacemakers from ten manufacturers tested with different interference sources revealed a great variety, which does not allow one to generalize the problem of interference. As an example, an electric steel furnace with its magnetic field is described and how its influence on pacemakers can be estimated. Rules are given as to how pacemaker patients may be treated by electrotherapy. A test procedure for characterizing the specific interference behavior is proposed.

Electricity↗
PubMed1983

Comparison of pacing electrodes of different shape and material--recommendations.

Recommendations for comparing different pacing electrodes to one another are presented. In most reported studies, such comparisons fall short of the intended goal because they are made with electrode parameters that are not constant. The suggestions presented include timetables for acute and chronic threshold measurements, conditions for measuring lead impedance, and the relationship between rheobase and chronaxy. In addition, the effects of polarization of the electrodes are discussed.

Animals↗
PubMed1983

Polyurethane leads: facts and controversy.

A comparison of polyurethane and silicone cardiac pacing leads is presented. In comparing mechanical and electrical properties, friction coefficient and hydrolytic stability, both are highly qualified for use as electrode sheaths. The occurrence of surface cracking of polyurethane leads is examined. Several suggestions are proposed for dealing with the manufacture of new leads, the technique of implantation, and the follow-up required for successful surveillance.

Animals↗