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Biomedical subjects

P Wach

Publications and source records attributed to P Wach.

67 records · Page 4Linked to original sources
PubMed1982

[Experimental studies of signal fields of ultrasound broad band transducers].

Quantitative analysis of ultrasonic signals, as increasingly practised, makes it necessary to increase the band width as well as the efficiency of ultrasonic transducers. An broad band ultrasonic transducer is presented which meets the requirements by double lambda/4 layer matching and was specially designed for medical ultrasonic spectroscopy. In an extended measurement programme transmitter characteristic, spatial dependence of the spectral content of the transmitter signals as well as beam geometry and its frequency dependence are investigated and compared with conventional transducers.

Fourier Analysis↗
PubMedDate not supplied

Three-dimensional computer model of the entire human heart for simulation of reentry and tachycardia: gap phenomenon and Wolff-Parkinson-White syndrome.

A computer model of the entire human heart has been developed for simulation of the excitation and repolarization process. Spatial distribution of refractory periods and conduction velocities in the different cardiac tissues, the anisotropy of conduction in the ventricles, and the cycle length dependence of refractory periods and conduction velocities are taken into account. The algorithm calculating the activation process is based on a modified version of Huygen's principle for constructing wavefronts. This study presents simulations concerning the gap phenomenon of the conduction system and the initiation of tachycardias in a heart with Wolff-Parkinson-White syndrome. Results are compared for different basic cycle lengths and for normal and prolonged refractory periods in the His-Purkinje system. The gap phenomenon was found to be present only when using the prolonged refractory periods in the His-Purkinje-system at a cycle length of 700 ms. Induction of tachycardia by a single extrastimulus in the high right atrium in a heart with a bidirectionally conducting accessory pathway is possible by properly timed extrastimuli. The coupling interval of the stimulus for initiating a reentrant tachycardia depends on the cycle length, the conduction velocities and the set of refractory periods used. The same parameters determine whether or not a gap phenomenon in atrioventricular conduction occurs. The model may be useful for investigating similar questions concerning the reentry phenomena of tachycardia.

Atrioventricular Node↗
PubMedDate not supplied

A computer model of human ventricular myocardium for simulation of ECG, MCG, and activation sequence including reentry rhythms.

A computer model is presented for simulation of the spread of activation and repolarization in ventricular myocardium. The program calculating the activation sequence is based on an algorithm similar to Huygen's principle of constructing wavefronts. Physiological parameters of the heart, such as areas of early activation on the endocardium, conduction velocity, anisotropy of propagation, duration of action potentials and refractory periods are taken into account. The time-course of ECG and MCG is calculated using the equations of the bidomain model. Simulation of pathologic cases of activation is performed through variation of the physiological heart parameters. The simulations presented here show good agreement of ECG and MCG with measurements in the normal case, the case of bundle branch block and abnormal repolarization. A special feature of the model is the possibility of simulating reentry rhythms following a premature stimulus in ventricular myocardium. Two kinds of reentry are simulated: reentry around an anatomical obstacle and the leading-circle model. The widespread capability for investigating not only ECG but also MCG and various kinds of pathologic activation patterns including reentry rhythms indicates that the model may be useful in studying numerous problems in cardiologic research.

Action Potentials↗
PubMedDate not supplied

Realtime measurement of stroke volume--an adaptive monitoring system and its application.

A variety of monitoring systems is available for special fields of clinical application and scientific research. Whenever requirements change data acquisition and handling of signal analysis have to be adapted or even completely new structured, especially in real-time applications. This can be a time consuming procedure. In order to be able to focus on the development of algorithms without taking care how data are acquired a monitoring system has been developed which can be adjusted in terms of signal acquisition, analysis and user handling. New algorithms can be added and polygraphical presentation of results can be adjusted for special clinical requirements. As a specific application the online and real time calculation left ventricular ejection time (LVEJT), stroke volume (SV), cardiac output (CO), mean blood pressure and total peripheral resistance (TPRI) is presented.

Algorithms↗