Surgery – Truss – Perineal
Patent
1991-09-23
1993-11-09
Cohen, Lee S.
Surgery
Truss
Perineal
367147, A61B 1722
Patent
active
052593681
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to apparatus for comminuting concretions in the body of a patient, and includes a liquid-filled focusing chamber with a reflector having an inner wall in the form of an open revolution ellipsoid, and closed by a bellows at its open end. The bellows are placed against the patient's body. A spark gap is arranged at one focus point of the ellipsoidal reflector for generating as shock wave focused at the other focal area of the revolution ellipsoid.
BACKGROUND OF THE INVENTION
Apparatus for comminuting concretions is previously known, e.g. from DE, Al, 3220751.
In this type of apparatus it is important to achieve good comminuting effect on the concretions or calculi (kidney or gall stones) while the pain caused to the patient is sufficiently low so that anesthetics are not required. Analgestic and optional local anesthesia, e.g. EMLA cream (cylocain) on the skin where the wave inpinges should be sufficient for the procedure. In this way the cost of anesthetics is reduced.
It has been found that the effective frequency for adequate therapy is in the range 0.3-1 MHz. For the frequency of 1 MHz and a sound propagation velocity of 3000 m/s in kidney and gall calculi there is obtained a wavelength of .lambda.=3 mm at these sites. Disintegration in calculi is achieved in the range 1/4-1/2.lambda., i e. fragments of the size 0.75-1.5 mm, these being desired sizes. Of course, calculi are not homogeneous, i.e. disintegration can occur to an important degree due to inherent weakness bands. Fragments with the given sizes can subsequently be passed without causing further trouble.
Lower frequencies do not give satisfactory therapy, e.g. for 100 kHz there is magnitude of disintegration in the range of 0.75-1.5 cm, which gives fragments which are much too large to be passed easily.
Such low frequencies are not focused particularly well in the present size of the reflector and will thus pass into the body as a badly focused wave. They involve large displacements causing pain to the patient and by sudden jerks in the heart area they can cause the risk of cardiac arhythmia of different kinds, such as auricular fibrillation and flutter.
It is therefore an object of the invention to minimize the energy transmission at such low frequencies and concentrate it to the frequency range 0.3-1 MHz. Substantially higher frequencies than 1 MHz are attenuated too heavily in the body tissue for having a good effect on calculi.
SUMMARY OF THE INVENTION
This object is achieved with an apparatus of the kind including a liquid-filled focusing chamber, defined by a reflector with an inner wall having the shape of an open revolution ellipsoid. The open end is closed by a bellows intended to be placed against the patient's body. A spark gap is disposed at the focus (F.sub.1) of the ellipsoid reflector for generating a shock wave intended to be focused at the other focal area (F.sub.2) of the reflector. The wall thickness of the reflector is constant and equal to half the wave length of a predetermined frequency.
By forming the ellipsoidal reflector wall thickness in a suitable way, resonance between the waves reflected on the inside and outside of the reflector is achieved within a given frequency range, in the second focal area which is situated in a concretion opposite the spark gap. The reflected waves for other frequencies substantially reduce or cancel each other. A filter action is thus achieved in this way.
The simplest way to achieve such an effect is to form the reflector with a constant wall thickness equal to half the wavelength of the predetermined frequency, so that this frequency will be attenuated by half wave resonance less than other frequencies, and thus act with the greatest effect on the concretion.
According to a further development of the invention, the wall thickness of the ellipsoidal reflector varies with the angle of incidence and refractive index applicable for the shock wave from the spark gap placed in the first focus, so that the wall thickness passed through
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patent: 5095891 (1992-03-01), Reitter
patent: 5105801 (1992-04-01), Cathignol et al.
patent: 5111805 (1992-05-01), Jaggy et al.
Cohen Lee S.
Pfaffle Krista M.
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