Surgery: kinesitherapy – Kinesitherapy – Contact-free comminution of concretion
Patent
1997-05-27
2000-09-05
Lateef, Marvin M.
Surgery: kinesitherapy
Kinesitherapy
Contact-free comminution of concretion
367147, A61B 1722
Patent
active
061135607
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and a device for producing shock waves by spark discharge between electrodes which are supplied with electrical current intermittently in a liquid medium such as water, the shock waves being focussed onto the object located in a body.
A method of this type is disclosed in DE-PS 23 51 247. This document describes a device for fragmentation of concretions in the body of a living being. A spark discharge in a liquid medium is used to produce shock waves at one focus of a truncated rotation ellipsoid, which are reflected on the ellipsoid and are focussed at the second focus. The concretions to be fragmented are positioned at this second focus.
In general, in systems of this type, the spark discharge takes place on a replaceable device in which there are at least two opposite electrodes, between which the discharge takes place.
DE-OS 26 35 635 discloses such a device, substantially comprising two axially arranged electrode tips, a low-induction power supply, and mechanical retention or embedding of the electrodes.
Incorporated in the associated system, the electrodes together with a high-voltage switch and a high-voltage-resistant capacitance form a circuit whose inductance and resistance are very low. During operation, the capacitance is charged to a voltage in the order of magnitude of about 10 kV to 30 kV. This voltage is applied intermittently, via the high-voltage switch, to the electrodes, which are located in an aqueous environment. If the distance between the two electrodes is not too great at the given voltage, then an electrical breakdown in the form of a spark discharge takes place between the electrodes. The electrical resistance between the electrodes in this case falls sharply, and the capacitance is discharged in a damped periodic oscillation. A certain amount of time, called the latency time, passes between the closing of the high-voltage switch and the sharp reduction in the resistance between the electrodes, during which time a small current flows which is essentially limited by the resistance of the liquid medium located between the electrodes.
In order that a voltage breakdown in the form of a spark discharge takes place between the two electrodes, the distance between them must not be less than a certain level, depending on the nature of the liquid medium and magnitude of the intermittently applied voltage. Each spark discharge leads to material being lost at the electrode tips, and thus to a greater electrode separation. As the separation approaches a critical level, then application of the voltage to the electrodes leads to a spark discharge less and less frequently until, finally, such a discharge no longer takes place at all. In addition, the average latency time is increased, with the consequence that some of the stored energy is lost, as a result of the current flowing in this case, even before the voltage breakdown, and correspondingly less energy is available to produce the shock wave.
In the past, there have been a number of attempts to obtain a voltage breakdown even with an electrode separation beyond the critical level, in order on the one hand to increase the life of the devices containing the electrodes and on the other hand to achieve an increase in performance in terms of the shock wave energy, by means of the longer discharge channel.
So-called wire discharge sources are known, in which thin wires are caused to vaporize explosively by a high-current discharge. However, especially in the case of hydraulic lithotripsy, these do not represent a practicable method since the wire has to be replaced after every discharge and a typical lithotripsy treatment involves several thousand discharges.
DE-PS 36 37 326 discloses the use of an auxiliary electrode which leads to a controlled leader geometry and, by virtue of this, to greater electrode separations. The leader is in this case an initially low-current channel which precedes the actual spark discharge and determines its local course. Since very considerable mechanical stresses occur in the vicin
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Beard, Jr. R. William
HMT High Medical Techologies
Lateef Marvin M.
Shaw Shawna J
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