Surgery – Truss – Perineal
Patent
1991-09-20
1993-08-03
Cohen, Lee S.
Surgery
Truss
Perineal
367147, 181113, A61B 1722
Patent
active
052319768
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an apparatus for triggering shock waves used for therapeutic purposes.
The invention thus relates to apparatus for triggering shock waves generated with the aid of spark discharge in a liquid synchronously with the heart ECG in connection with extracorporal comminution of calculi, e.g. gall stones or kidney stones.
The apparatus includes a signal analyzer, which filters through the R peaks in the patient's ECG. The analyzer is connected to a pulse generator, which creates a trigger pulse for each detected R peak. The respective shock wave is triggered with the aid of this trigger pulse. Using this procedure the shock waves will not occur at the vulnerable period of the ECG cycle, i.e. the shock wave will be in the part of the heart beat where the heart has not had time to be repolarized after its latest activity, see FIG. 1 depicting the typical appearance of an ECG. Utilizing the R peak in conjunction with triggering shock waves is already known, e.g. from EP-A1-0 081 051.
In FIG. 2 there is shown an already known, usual embodiment of the discharge circuit. A low-inductive capacitor C is charged with a suitably selected high tension DC voltage via a resistor R or a current limiter arranged in some other way. The maximum charging current must be sufficiently high to enable charging the capacitor C fully before each new shock wave. If it is assumed that the patient's pulse is 1 Hz (60 beats/minute), each heart beat takes 1,000 ms, i.e. the time between R peaks for this patient is 1,000 ms. The capacitor C is also connected in series with a first spark gap 8, 10 in the triggering apparatus, and is furthermore connected in series with a second spark gap 4, 6, which is placed in one focus of the ellipsoidal reflector 2 used in the type of apparatus in question for comminuting calculi. When flashover occurs at the gap 8, 10 there is obtained an extremely rapid voltage build-up at the second spark gap 4, 6 in the ellipsoid, and the liquid inside it is gasified very rapidly, like an explosion, the shock wave thus being generated. This type of apparatus is described in the Swedish patent application 8900994-8 filed concurrently with this application. Too slow voltage build-up at the second spark gap 4, 6 results in the worst case in a resistive discharge of the capacitor C or to a shock wave having an unsuitably slow pressure front. In the type of apparatus in question, a voltage derivative is desired where the voltage attains its maximum value in about 8.5 microseconds. This is a condition for generating a shock wave which will effectively disintegrate calculi.
The trigger spark gap in this previously known apparatus thus includes two spherical balls 8, 10 of which one 8 is connected to the high voltage pole of the spark gap in the liquid. These balls are arranged at a mutual spacing such that spontaneous flashovers normally do not occur, irrespecxtive of air pressure and humidity.
An auxiliary electrode 12 is arranged in or adjacent the electrode gap between electrodes 8 and 10. As a response to the occurrence of the R peak a high voltage is applied via a high-ohmic resistor R.sub.1 to this auxiliary electrode 12, irrespective of the feed voltage to the capacitor C, so that an avalanche ionizing spark is generated in the area between the electrodes 8, 10 and the electrode gap will be conductive, the capacitor C being discharged across the gap 4, 6 for generating a shock wave. With this arrangement the avalanche ionizing spark is generated sufficiently rapidly after a detected R peak for the shock wave in the reflector 2 to be triggered with a sufficiently short lag, which does not exceed some milliseconds after the R peak maximum.
A drawback with this known technique is that it is sensitive to air pressure and humidity, which requires conditioning the trigger circuit environment by placing it in a nitrogen gas atmosphere, and it has been found difficult to make it function satisfactorily for different voltages across the capacitor C.
The object of the present invention is to elim
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Cohen Lee S.
Pfaffle Krista M.
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