Apparatus for shock wave therapy

Apparatus for shock wave therapy comprises an electroacoustic therapeutic transducer for generating ultrasonic shock waves, which are transmitted by way of a coupling medium shock wave transmission section of the transducer, bounded by a membrane, to the body of a patient reclining on a therapy table. In the interest of hygiene the membrane is releasably attached by its marginal area to the therapy table, being thereby exchangeable so that a new membrane can be provided for each patient. The extraction of gas from the coupling medium following exchange of the membrane is provided for.

FIELD OF THE INVENTION 
The invention relates to a apparatus for shock wave therapy comprising an 
electroacoustic therapeutic transducer for generating shock waves in the 
ultrasonic range, which are transmitted to the body of a patient to be 
treated by means of the shock waves, through a coupling medium shock wave 
transmission part of the transducer, bounded by an elastic membrane 
covering a porthole formed in a therapy table on which the patient 
reclines. 
BACKGROUND OF THE INVENTION 
There is disclosed in EP-A-0084093, a shock wave generator disposed in a 
bath filled with coupling medium, a patient reclining on a couch and being 
immersed in said bath so that the focus of the shock wave generator is 
directed on to a concretion in the patient, which concretion is to be 
disintegrated by means of the shock waves. 
DE-A-2351247 discloses a shock wave generator located at one focal point of 
a focusing chamber in the form of part of an ellipsoid of revolution, said 
chamber being covered by an elastic membrane. By way of this membrane, the 
focusing chamber is applied to the patient's body, without the 
interposition of an air gap, in such a way that the concretion to be 
destroyed is positioned at the second focal point of the ellipsoid. 
According to EP-A-0131654, alignment can be effected by axial displacement 
of the focusing chamber covered by a membrane, in a coupling cylinder 
which is applied to the patient's body and is likewise bounded by a 
membrane, a coupling medium being provided between the two membranes and 
within the focusing chamber itself. 
DE-A-3220751 discloses the use of a shock wave generator comprising a 
flexible, coupling medium transmission part bounded by a film which is 
adaptable to the patient's body. Coupling is performed manually by the 
application of a coupling gel. 
An object of the present invention is to provide improved apparatus for 
shock wave therapy in which the transmission of bacteria and pathogens is 
avoided, coupling of the shock waves to the patient's body being achieved 
simply, and with virtually loss-free transfer of acoustic radiation from 
said transmission part to the patient's body. 
According to the invention the membrane is releasably attached at its 
marginal area to the therapy table, the membrane being thereby 
replaceable. 
The membrane is thus a disposable article, a new membrane being provided 
for each patient. 
The marginal area of the membrane may be pneumatically clamped to the 
therapy table. The membrane may be placed over a trough, surrounding the 
porthole in the therapy table, the trough being arranged to be connected 
to a vacuum source. Said trough may be formed on a ring in the form of an 
upwardly projecting pad surrounding and defining the porthole. The 
membrane may comprise a ready-made section of film, or a web of film 
comprising a series of such sections and which can be moved a section at a 
time across the porthole. The membrane preferably has a thickness of the 
order of 50 to 500 .mu.m. 
For low-loss coupling of the therapeutic transducer to the patient's body 
any gas which may collect in the transmission part when the membrane is 
changed must be removed. The gas may be removed by means of a device which 
operates beneath the membrane and within the transmission part to extract 
gas therefrom. Recesses may be machined into the upper marginal area of 
the part of the therapy table surrounding the porthole, so that gas in 
said transmission part can be extracted by way of the recesses, or an 
annular pipe having perforations in its inwardly and upwardly facing 
surface may be provided for extracting the gas. When using such gas 
extraction means, the membrane must be distended so that gas extraction 
takes place at the highest point of the membrane, at which gas bubbles 
collect. 
Another means for extracting the gas comprises a tube which is extensible 
from the center of the therapeutic transducer, and which has a perforated 
extractor head at its tip. By extension of that tube the membrane 
undergoes a pyramid-shaped distortion, so that any gas bubbles which may 
be present in said transmission part make their way to the perforated 
extractor head located at the highest point that is to say at the apex of 
the pyramid. Such an effect can also be attained by the provision of a 
cranked extractor tube opening radially into said transmission part, and 
having a perforated extractor head at its free end, the extractor tube 
being rotatable about a radially guided part thereof. The extraction means 
described above are not, however, needed if the membrane is made of a 
material which is microporous and gas-permeable, but is impervious to 
water, being of polyurethane for example.

As best be seen in FIG. 1, apparatus for shock wave therapy comprises a 
therapy table 1 for receiving a reclining patient and which has therein a 
porthole 2 of preferably circular cross-section. A focusing therapeutic 
transducer 3 for generating shock waves in the ultrasonic range, is 
arranged under the porthole 2 for positioning along three axes, X, Y and 
Z, relative to the therapy table 1. The transducer 3 is connected to the 
underside of the therapy table 1 by means of a flexible casing 4, which 
encloses the shock wave source of the therapeutic transducer 3, and is 
attached to the peripheral area of the port-hole 2 in (i.e. tightly 
sealed) fashion. A receptacle is thereby provided which when filled with a 
coupling medium 6, for example, water, constitutes a transmission part 5 
for conducting shock waves generated by the therapeutic transducer 3 to 
the patient's body. In order to avoid contact between the patient's body 
and the coupling medium 6, the transmission part 5 is covered by an 
elastic membrane 7 in the region of the porthole 2, the membrane 7 also 
being connected to the casing 4 in tightly sealed fashion. 
According to the embodiment shown in FIG. 1, the membrane 7 is provided by 
a web 8 in the form of a film drawn from a feed roll 9 along the underside 
of the therapy table 1 and over the porthole 2. The web 8 is passed 
between the underside of the therapy table 1 and a clamping ring 8' 
arranged to be pressed against the table 1. The clamping ring 8' is 
releasable for exchanging the membrane 7, by advancing the web 8 to allow 
an unused section thereof to be clamped in place by means of the clamping 
ring 8'. The extraction of any gas bubbles that may be present in the 
transmission part 5, which is necessary for its proper functioning is 
described below. 
As shown in FIG. 2 a membrane 7 for bounding the transmission part 5 
comprises a ready-made section of film which is pneumatically clamped 
between the upper end of the transducer 3 and the peripheral area of the 
porthole 2 in the therapy table 1, by a ring element 10. The element 10 
extends upwardly from the coupling medium 6 and flexible casing 4 to the 
height of the upper surface of the therapy table and widens out defining a 
pad which surrounds and defines the porthole 2. The ring element 10 has a 
trough 11 the bottom of which is formed with an annular groove 12 
connected by way of a hose connection 13 to a vacuum source (not shown). 
Evacuation of the annular groove 12 causes the membrane to be sucked down 
into the trough 11 and held fast therein in fluid-tight fashion. The 
membrane can easily be released again by turning off the vacuum. Any gas 
bubbles trapped in the coupling medium can be extracted through slots 14 
in the upper part of the ring element 10 by means of an extraction hose 15 
communicating with the slots 14, by causing the membrane 7 to distend 
downwards. 
Another embodiment of the invention is shown in FIGS. 3 and 4. In this 
embodiment the membrane 7 is fastened at a ring 16 which can be clamped 
between a bayonet ring 17 and a support ring 18. After initially removing 
the bayonet ring 17 with its ring 16, the periphery of the membrane 7 is 
laid in a recess in the support ring 18. The ring 16 and the bayonet ring 
17 are placed thereover, with tooth elements 12 on the periphery of the 
ring 17 engaging in matching recesses 22 in a retaining ring 21 
surrounding the porthole 2 (FIG. 4). The bayonet is axially tightened by 
twisting it into place. 
The coupling medium may be degassed in various ways. For example as shown 
in FIG. 5, a circular pipe 23 may be provided, surrounding the upper 
peripheral area of the porthole 2, the pipe 23 having perforations in its 
inwardly and upwardly facing surfaces, and having means for connecting it 
to a vacuum source. For extracting gas bubbles from the coupling medium 
the membrane 7 may, for example, be made to distend downwards by weighting 
it at its center, so that the gas bubbles rise up to the pipe 23, which is 
the highest level in the transmission part 5, when the membrane 7 is so 
distended. 
In the embodiment shown in FIG. 6, an extensible tube 24 capable of being 
extended from the center of the shock wave source of the therapeutic 
transducer 3, is provided at its tip with a perforated extractor head 25. 
By extending the tube 24 its extractor head 25 can be brought into contact 
with the membrane 7 thereby distending it upwardly so that gas bubbles in 
the coupling medium collect at the extractor head 25, from which they can 
be extracted. 
According to FIG. 7, a degassing device comprises a cranked extractor tube 
26, opening radially into the transmission part 5, and being provided with 
a perforated extractor head 27 at its free end. The extractor tube 26 can 
be turned through 90.degree. about a radial guided part 28 thereof, so 
that the extractor head 27 can be brought from a lateral position just 
below the undistended membrane 7 into a position in which the membrane 7 
is distened upwardly as shown in FIG. 7. 
For initially fixing the membranes 7 when in the form of ready-made 
sections of film, as described above with reference to FIGS. 2 to 7, 
before they are finally fixed in place by the means described above, the 
margins of these membranes may be provided with a self-adhesive coating. 
In the embodiments described above the thickness of the membrane 7 is 
preferably of the order of 50 to 500 .mu.m. 
As another means for extracting gas from said coupling medium, the membrane 
may be microporous so that it is gas permeable but is water impervious, 
the membrane being made, for example, of polyurethane.