WO1999018851A1

WO1999018851A1 - Emg sensor and multichannel urethral emg-system comprising said sensor

Info

Publication number: WO1999018851A1
Application number: PCT/NO1997/000263
Authority: WO
Inventors: Egidija R. Nilsen
Original assignee: Nilsen Egidija R
Priority date: 1996-04-02
Filing date: 1997-09-26
Publication date: 1999-04-22
Also published as: NO961359D0; NO304404B1; NO961359L

Abstract

An EMG sensor (1) comprising on the surface a number of measurement electrodes (2a, b,...) which are partly imbedded in the surface of the sensor body (1a) and they are essentially levelled with said surface. The measurement electrodes (2a, 2b,...) are arranged in respective electrode configurations that mainly stretch along the long axis of the sensor body (1a). A multichannel urethral EMG sensor system, where the sensor system includes an EMG sensor (1) for detection of myoelectrical potentials, an amplifier unit (6) with a switching unit (6b) and a number of measurement channels (6c) with differential instrumentation amplifiers (6cl, .. 6cn). The switching unit (6b) is devised to connect the measurement electrodes (2) in pairs to the input of the respective differential instrumentation amplifiers (6cl, .. 6cn), so that each measurement channel performs a differential detection of the registered myoelectrical potentials. Clinically applied for instance for detection of myoelectric potentials in the urethral closing musculature and for diagnosing dysfunctions in the lower urinary tract.

Description

EMG sensor and multichannel urethral EMG-system comprising said sensor.

The invention relates to an EMG (electromyographic)-sensor for sensing myoelectrical potentials, more particularly to an EMG sensor embodiment mounted on a urethral catheter or integrated with a urethral catheter, and wherein the EMG sensor includes a tubular essentially cylindrical sensor body of a dielectric material. Further aspect of the invention relates to a multichannel urethral EMG sensor system, where the sensor system includes said EMG sensor according to the claims 1 -6 for sensing myoelectrical potentials, wherein said EMG sensor^'s measurement electrodes are connected over an electronic amplifier unit to the galvanically isolated data processing unit for EMG signal analysis. where the EMG sensor system consists of a set of measurement channels, wherein each measurement electrode is assigned to one measurement channel, and where the output of each measurement electrode is connected to one respective input on the electronic amplifier unit.

In several disorders of the lower urinary tract in both males and females, it is of great benefit to clarify different physiological situations important in aiding diagnostics and finding possible sources for the disorder.

One of the most problematic disorders of the lower urinary tract is urinary incontinence, i.e. unwanted loss of urine. Normal controlled urination or continence is dependent upon the complex co-ordination of the bladder and the urethral function. A failure in the co-ordination at some level causes urinary incontinence. Different measurement techniques have been applied to identify the sources for urinary incontinence and to find the exact cause of dysfunction. One such method is based on measuring the pressure conditions, e.g. the mechanical impedances in the lower urinary tract, while the other method measures myoelectrical (myographical) potentials in the muscles that are important for the lower urinary tract function. Detection of the myoelectrical potentials is usually performed by applying implantable electrodes, preferably needle- or wire electrodes which are inserted into the muscle tissue. This causes substantial pain to the patient and therefore alternative surface electrodes mounted on a catheter have been used by introducing the catheter in place into the urethral canal and the surface potentials from the surrounding muscle tissue are registered. As the muscles of different type are important for the urinary continence function, it has been shown that the surface electrodes used for detection of myoelectrical potentials, that is for the electromyographic surface investigations (EMG analysis), are less appropriate. There are for instance known urethral electromyographic surface electrodes in the form of ring urethral electrodes made and marketed by Dantec Medical from Copenhagen since 1980. However, these ring-shaped EMG electrodes enable only the measuring of an interference EMG pattern of electrical potentials across the striated muscle fibres and as such they are not suitable for longitudinal detection of myoelectrical potentials along fibres, which is believed to be of great importance to obtain satisfactory analysis of the myoelectric activity in the striated muscles. It is of interest to measure simultaneously the myoelectrical activity together with the pressure in the urethra and the bladder.

This can be achieved appropriately with a urethral catheter that includes both EMG electrodes and pressure measurement sensors.

One example of such a catheter being especially useful for acquiring the signals in tubular, content-transporting organs, such as oesophagus, bowel, urethra, etc. is known from the European patent application nr. 0 366 127 - Al. Similar to the above mentioned measurement electrodes from Dantec. these measurement electrodes are also formed as ring electrodes or arranged essentially ring-shaped around the catheter and they range a bit out of it. The sensors described in this publication are primarily intended to measure the pressure signals, which allow an investigation of time changing movements and peristaltic function (in gastro- esophogeal tract). These measurement electrodes can also be used for measuring myoelectrical signals as the catheter is assembled with biosignal transducers for multichannel registration of such signals. These measurement electrodes have the same weakness as the measurement electrodes from Dantec with respect to the detection of myoelectrical potentials. In addition to this as the measurement electrodes are ranging a bit over the surface, application of the catheter would cause discomfort for the patient.

One purpose of the present invention is therefore to obtain a sensor for detection of myoelectrical potentials or an EMG sensor where measurement electrodes enable sensing of myoelectrical potentials from both smooth and striated muscles and where the sensor can be easily integrated or mounted on a urethral catheter at a given longitudinal point along the catheter and can be introduced in the urethral canal without any form of pain or discomfort for the patient. Another purpose is that the EMG- sensor enables registration along the muscle fibres in the striated musculature.

The purpose of the invention is further to obtain a multichannel urethral EMG sensor system, where the EMG sensor according to the invention is used for measuring the myoelectrical potentials with a multichannel technique and particularly in this sense to obtain a differential detection of the myoelectrical potentials. These above mentioned and other objects are obtained with an EMG sensor, which is characterised by that the surface of the EMG sensor comprises a number of measurement electrodes that are partly imbedded in the surface of the sensor body and are essentially levelled with said surface, and that the measurement electrodes are arranged in respective electrode configurations that mainly stretch along the long axis of the sensor body, together with a urethral multichannel EMG sensor system which is characterised by that the amplifying unit comprises of an electronic switching unit together with a differential instrumentation amplifier for each measurement channel, and that the switching unit is devised to connect the measurement electrodes in pairs to the input of the respective differential instrumentation amplifier, so that each measurement channel performs the differential detection of the registered myoelectrical potentials.

Other features and advantages with the EMG sensor according the present invention are described by the claims 2-7 and other characteristics and advantages with the multichannel urethral EMG sensor system according the invention are described with the dependant claims 9-12.

The invention will now be better described in the following, relating to one design example and the following drawings, where:

Figure 1 shows the first design version of the EMG sensor according to the invention.

Figure 2 shows the second design version of the EMG sensor with reference to the invention.

Figure 3 shows the third design version of the EMG sensor according to the invention, Figure 4 shows the forth design version of the EMG sensor according to the invention,

Figure 5 shows examples of the embodiment of the EMG sensor in the form of a urethral catheter according to the invention,

Figure 6a shows the clinical application of the urethral catheter provided with the EMG sensor in the place in a male urethral canal according to the invention.

Figure 6b shows the schematic drawing of the musculature of the lower urinary tract,

Figure 6c shows the multicore cable with the EMG sensor according to the invention. Figure 7 shows a clinical application of the urethral catheter provided with the EMG sensor in the place in a female urethral canal according to the invention,

Figure 8 shows an embodiment of the EMG sensor multichannel system according to the invention,

Figures 9a, 9b are two examples of the connections of the individual electrodes ot the EMG sensor to the inputs of the amplifying unit of the EMG- system according to the invention.

Figure 10 shows another example of the connection of the individual measurement electrodes in a configuration for 4 channel differential detection.

Figure 1 shows in a side view the first version of the EMG sensor according to this invention. The EMG sensor 1 consists of a longitudinal, cylindrical sensor body l a of dielectric material, e.g. of epoxy material. Disposed on the surface of the sensor body la are longitudinal band shaped electrodes 2 parallel to the sensor^'s body axis. In this example there are 4 electrodes 2a, 2b, 2c. 2d, which are levelled with the surface of the sensor body la. On the distal end of the sensor body l a ring-shaped reference electrode 3 is mounted and further a pressure sensor 4a is shown, for example as a microtip transducer or a piezoelectric transducer. A partially shielded cable 5 connects the different electrodes and emerges out from the sensor body la at the distal end.

Figure l b shows the cross-section through the sensor body la along the line I-I in Figure l a and it shows the band-shaped measurement electrodes 2a. 2b. 2c. 2d on the surface of the sensor body. Figure 2a shows another version of the EMG sensor than Figure 1, where the electrodes 2a. 2b, 2c. 2d are not parallel with the sensor body length axis but helically shaped on the surface of the sensor body la.

Figure 2b shows the cross-section through the sensor body la along the line II-II in Figure 2a and the corresponding section along the line III-III. In Figure 2a with the electrode arrangements on the sensor body la surface as it is showed at the respective cross-sections. In Figure 2a there are also shown two pressure sensors 4a, 4b. Naturally, there could be arranged several not shown pressure sensors.

Figure 3 shows the third version of the EMG sensor according to the invention. Here the measurement electrodes are not formed as bands but instead as dots on the surface, where two electrodes 2d and 2g are not seen. An alternative position of the reference electrode 3 is given stippled and marked as 3'.

Figure 4a shows the fourth version of the EMG sensor 1 according to the invention. As shown in Figure 4a, a first version includes a sensor body la parted in two segments by the ring-shaped reference electrode 3. In the first segment, there are 4 band electrodes 2a,...,2d. where 2d is not seen. In the other segment there are 4 band electrodes 2e,..,2h. where 2g, 2h are not seen. Electrodes 2e,..,2h are moved radially towards the electrodes 2a,..,2d. Figure 4b shows another version of this embodiment, where the 4 electrodes 2e,..,2h are formed in the extension of the measurement electrodes 2a,..,2d of the first segment. The arrangement of the electrodes is additionally shown in Figure 4c along the line IV-IV in Figure 4a, and along the line VI-VI in Figure 4b. while Figure 4d shows the electrode arrangement along the line V-V in Figure 4a. The EMG sensor in Figure 4 includes in each version 8 separate band electrodes 2a,..,2h imbedded on the sensor body la surface.

Figure 5a shows EMG sensor 1 according to the invention, integrated with a urethral catheter 9 and close to the catheter tip 9a. In addition to the pressure sensors 4a, 4b. which are a part of the EMG sensor 1. there are also shown two pressure sensors 10a, 10b, the first on the catheter tip 9a in front the EMG sensor and the second on the catheter itself behind to the EMG sensor. It should be understood that the EMG sensor can be integrated in the catheter 9 itself and that it is forming a part of it. or it can be the separate part, which is mounted on the catheter 9, behind the catheter tip 9a. Alternatively the sensor body la and the catheter tip 9a can form one unit which is fastened on the catheter 9. Correspondingly Figure 5b shows the catheter with the integrated EMG sensor 1. this being a balloon catheter. Behind the catheter tip 9a, there is a balloon 11, which can be inflated and used to retain the catheter in position after introducing it into the urethral canal, for example after the catheter tip with the balloon is introduced into the bladder, and the balloon is inflated and positioned in physical contact with the bladder neck. There are also in this case employed pressure sensors on the catheter 9. the pressure sensor 10a on the catheter tip. and the pressure sensor 10b inbetween the balloon and the EMG sensor 1 and the pressure sensor 10c behind of the EMG sensor 1.

Figure 6a illustrates the EMG sensor 1 according to the invention, mounted on a catheter 9 of the same type as shown on Figure 5b, introduced into the urethral canal in a man. It is seen that the catheter tip with the catheter balloon is introduced into the bladder and that the balloon 11 is inflated to retain the catheter 9 in place, by that the balloon is fitted to the wall of the bladder and the bladder neck. In the bladder wall itself there are smooth muscles which are under the control of the autonomous nervous system. Some of this musculature is made up of the muscle in the triangle (trigonum) between the urethras opening in the bladder wall and the bladder neck and it functions like a kind of sphincter. Besides, in the bladder wall there is smooth musculature which contracts at a certain bladder pressure and contributes under the control of the autonomous nervous system to bladder emptying. The urethral canal in a man extends through the prostate, as shown in Figure 6a. and then passes the pelvic floor muscles. The urethra continues further through the pelvic floor muscles or urogenital diaphragm which includes the so called pelvic floor (E) or the urethral sphincter, the external sphincter, which is striated and which is under voluntary control. Under normal conditions it can resist the urge for voiding stimulated by the autonomous nervous system, e.g. when on the basis, that the bladder pressure exceeds a certain threshold or because of other circumstances that are not under person^'s voluntary control. When the bladder volume and the bladder pressure are above a certain value, the person gets a conscious need for voiding and at the same time a subconscious reflex from the autonomous nervous system takes place; this reflex is known as micturition reflex and it causes activation of the muscles in the bladder, both the emptying muscle or trigonum muscle and the internal sphincter which relaxes. Basically the only thing which can prevent the urine emptying is a contraction of the external sphincter E, and different forms of urinary incontinence are caused by malfunction of the external sphincter E, which itself is under voluntary control, so that unwillingly emptying takes place. It can be mentioned, that around the urethral canal there is also smooth musculature which is not under voluntary control, the function of these muscles has been little investigated, but it would be of benefit to be able to detect this myoelectrical activity. This is schematically shown in Figure 6b, which for simplicity reasons shows the important part of the musculature of the lower urinary tract, with the current musculature in women.

As shown in Figure 6a. the urethral catheter 9 is introduced with the EMG sensor 1 mounted into the urethral canal so that the EMG sensor is placed in the region of the striated, voluntary controlled external sphincter E for the urinary bladder or the pelvic floor. The positioning of the catheter can advantageously be performed aided by the pressure sensors. In the striated external sphincter E the band-shaped measurement electrodes 2 in the EMG sensor 1 will be positioned across the muscle fibres, allowing the detection of the myoelectrical activity along the muscle fibres, which could not be possible with the ring-shaped electrodes referenced as prior art. However, the EMG sensor 1, according to the invention, and positioned on the catheter 9 and shown in Figures 6a, c. can also be employed to detect the myoelectrical activity in the smooth musculature around the urethral canal and the bladder neck. The cable 5 from the EMG sensor 1 is shown in Figure 6c and it contains the wires where the number n of the wires corresponds to the number of the electrodes 2,3. The wires or the leads from the electrodes are preferably led on the outer side of the catheter 9 and a medical wire is employed. The segment of the cable 5 that does not reach the urethral canal is shielded with a shield 5b and a protecting cable sheet 5c, for example made of silicon can be wrapped around the cable. The cable 5 would contain altogether n leads 5a_n for the electrodes and the shielding wire 5b'. The EMG sensor 1 with the 4 electrodes 2a,.., d and the reference electrode 3 would have the cable 5 with altogether :> wires. It would not cause any discomfort for the patient that the cable 5 is not inside the catheter itself, and this construction makes it easier to repair, if the lead would be damaged.

As shown in Figure 6a the EMG sensor 1 is used simultaneously with the measurement probe 12 which is introduced into the rectum and equipped with electrodes for detection of the myoelectrical activity in the anal sphincter. This kind of simultaneous recording of the electromyographic potentials in the closing muscle of the bladder as well as in the rectum is appropriate for investigating dysfunctions in the lower urinary tract and the anal canal to elucidate the physiological condition which can be the source for this kind of functions.

Figure 7 shows similar to Figure 6a a clinical application of the EMG sensor 1. according to the present invention, mounted on the catheter 9. and introduced into the urethra of a woman. Also here the rectal probe 12 is used, for simultaneous detection of the electromyographic activity in the external anal sphincter. Similar to the illustration in Figure 6, the EMG sensor 1 is introduced into the urethra in the place of the pelvic floor muscles E. while the catheter tip 9a with the balloon 11 is introduced into urinary bladder for retention. The musculature and the function would be approximately the same in women and in men, so that the description with reference to Figure 6 is relevant also for the situation in Figure 7, with adjustments for the physiological and anatomical differences between men and women. It should be pointed out that for example so called stress incontinence - that is the incontinence appearing when the pressure in the abdominal cavity and with that the bladder pressure is higher than the maximal pressure in the urethra, for example during coughing or heavy lifts, is a more common state for women who has had childbirth or after menopause, so that incontinence is generally assumed to be a bigger problem in women then in men. however this may be disputable. It is however a fact that the maximal urethral pressure is inclined to decrease with the age in women while it is remaining constant or may increase somewhat in men.

The EMG sensor system according to the second aspect of the invention will now be described: Figure 8 illustrates the preferred design of the EMG sensor system, where the EMG sensor 1 according to the first aspect of the invention is connected to the inputs of an electronic amplifier unit 6, where the input connections are arranged in an input unit 6a, 6b, which is further schematically depicted in the Figure 9b. The electronic amplifier unit 6 comprises the differential preamplifiers for the measurement channels 6c and the electronic switching unit, which provides connections of the measurement electrodes 2 in pairs to the inputs of the respective differential amplifiers όcι,...,όc_n , so that each measurement channel gives differentia! registration of the detected myoelectrical potentials. The electronic amplifier unit 6 is connected over a two-way signal line to the isolated signal conditioning unit 7, which is further connected to the dataprocessing unit 8, for example through the data bus 8a. The switching unit 6a, 6b on the Figure 9a or Figure 9b can be configured automatically through the dataprocessing unit 8 onto measurement channels 6cι,...,6c_n , which can be configured with the measurement electrodes 2 for differential detection of the myoelectrical potentials. The signal conditioning unit 7 is generally shown with a filter 7a, filter meaning a signal altering device, including isolation amplifier, or for example analog to digital converters or other signal conditioning devices. Advantageously the electronic amplifier unit 6 and the signal-conditioning unit 7 can be integrated into one unit which is aiso the interface to the data bus 8a.

Figure 9b shows the inputs of said input part 6a, 6b to the preamplifiers 6cι,..,6c₄, which can be commercially available. On Figure 9b said input part 6a, 6b is made for differential inputs with 4 measurement electrodes 2a,.., 2d. a ground input for the shield 5b and the reference electrode 3.

I^'he input part 6a,6b of the electronic amplifier unit 6 can be constructed for larger number of the measurement electrodes, for example 8. Further, it should be understood that in the case that said EMG sensor 1 also comϋrises one or more pressure sensors 4, the electronic amplifier unit 6 should provide the measurement channels for the pressure detection, and the inputs for the pressure sensors should be available in the input part 6a.

Figure 10 is schematically presenting a preferred construction of an EMG- sensor system according to the invention, wherein the EMG sensor 1 is connected with a 5-core cable 5 to the input unit 6a of an electronic amplifier unit 6, where the electronic amplifier unit here comprises 4 channels 6cj,..6c₄ for 4-channel differential detection, where each measurement channel includes one instrumentation amplifier, shown here as operational amplifiers 6cι,..6c₄. By utilising 4 measurement electrodes one can use up to 6 measurement channels with pairwise combination of the measurement electrodes for differential detection. The reference electrode 3 is connected to the ground of the amplifier unit, as shown (reference ground 3a).

The set up in Figure 10 is presenting the EMG sensor system according to the invention for 4 measurement channels 6cι,..6c₄ in the electronic amplifier unit 6. From the EMG sensor 1, shown here with 4 measurement electrodes 2 placed on the surface of the sensor body, the 5-core cable connects them to the input unit 6a of the electronic amplifier unit 6. The reference electrode is naturally grounded and the measurement electrodes 2 connected to the inputs of the measurement channels 6c for differential detection. Again it is used as many measurement channels as the number of the electrodes and in practice it is sensible to use 4- 10 measurement channels. With an increasing number of the electrodes, the possible combinations of connections in pairs for the differential detection would naturally increase and with 8 measurement electrodes 28 different measurement channels can be used.

The frequency components present in the myoelectrical surface signal, which consists of an interference pattern, can be extracted with the help of different methods for frequency analysis, and this can make it possible to find out which type of muscle fibres are active and which remain passive. In this way it is possible with the help of the EMG sensor system according to the invention to diagnose muscle function without using an invasive needle electrode, which is painful for the patient. Applied on striated urethral musculature the EMG sensor according to the invention may provide a simple way to detect the presence of any dysfunction in the lower urinary tract. The EMG sensor according to the invention can be employed to measure superficially in contact with the urethral wall the myoelectrical potentials of both striated musculature in the urethra and also smooth musculature in the urethral wall. It should be mentioned that the signal conditioning would be a bit different for striated and smooth musculature respectively. This is due to the differences in the frequency content. In the striated electromyographic potentials the region between 10- 1000 Hz is used, while detection of the myoelectrical potentials in the smooth musculature lies in the region between 0. 1- 40 Hz.

The electrical potentials, detected with the EMG sensor system described in the invention, are after appropriate signal conditioning fed into necessary signal analysis in the data processing unit 8. For this purpose a special PC-based realtime programme MAF (Muscle Activation Function programme) for frequency analysis, display of the extracted signals, analysis results and report generation and optionally a possibility for an automatic diagnostic system (expert system) has been developed.

Claims

1. An EMG sensor for detection of myoelectrical potentials, in particular an EMG sensor mounted on a urethral catheter (9) or integrated with a urethral catheter (9), and where the EMG sensor is comprised of an elongated, mainly cylindrical sensor body (la) of a dielectric material, characterised by that the surface of the EMG sensor comprises a number of measurement electrodes (2a,b,...) that are partly imbedded in the surface of the sensor body and are essentially levelled with said surface, and that the measurement electrodes (2a.b....) are arranged in respective electrode configurations that mainly stretch along the long axis of the sensor body.

2. An EMG sensor according to claim 1, characterised by measurement electrodes (2) made in platina.

3. An EMG sensor according to claim 1, characterised by that each measurement electrode (2) is configured as a narrow band running parallel to the long axis of the sensor body.

4. An EMG sensor according to claim 1, characterised by that each measurement electrode (2) is configured as a helical narrow band of an electrically conducting material.

5. An EMG sensor according to claim 1, characterised by that each measurement electrode (2) is configured essentially as a dot. in that the dot-shaped measurement electrode is arranged in configurations that constitute lines parallel to the long axis of the sensor body (la) or helical lines around the sensor body (la) or evenly distributed throughout the surface of a sensor body (la).

6. An EMG sensor according to claim 1, characterised by that the surface of the EMG sensor (1) has a ring-shaped reference electrode (3), in that the reference electrode (3) is arranged around the long axis of the sensor body (la) and is partially imbedded in the surface of the sensor body and is essentially levelled with said surface.

7. An EMG sensor according to claim 1, characterised by at least one pressure detecting sensor (4a,b,...), preferably in the form of a microtip transducer mounted on the sensor body (la).

8. A multichannel urethral EMG sensor system, where the sensor system includes an EMG sensor (1) according to claims 1-6 for detection of myoelectric potentials, where the EMG sensor's measurement electrode (2) is connected through an amplifier unit (6) to an isolated data processing unit (8) for EMG signal analysis, where the EMG sensor system includes a number of measurement channels (6c). where each measurement electrode (2) is assigned to a measurement channel (6c), and where the output of each measurement electrode is connected to the corresponding input of the amplifier unit (6), characterised by that the amplifier unit (6) includes a switching unit (6b) together with a differential instrumentation amplifier(6cι-6c_n ) for each measurement channel, and that the switching unit is devised to connect the measurement electrodes (2) in pairs to the input of the respective differential instrumentation amplifiers (6cι-6c_n ), so that each measurement channel performs a differential detection of the registered myoelectrical potentials.

9. An EMG sensor system according to claim 8. characterised by that it comprises at least 4-10 separate measurement channels (6c), where each measurement channel constitutes pairs of measurement electrodes (2) for differential detection of the registered myoelectrical potentials.

10. An EMG sensorsystem according to claim 8, characterised by that the amplifier unit is connected with an isolating signal conditioning unit (7). where the signal-conditioning unit is connected isolated with dataprocessing unit (8).

11. An EMG sensorsystem according to claim 8. characterised by that the switching unit (6b) is devised to automatically connect the measurement channels (6c) through the dataprocessing unit (8) by connecting the measurement electrodes (2) pairwise for differential detection of the registered myoelectrical potentials.

12. An EMG- sensor system according to claim 8. where the EMG sensor (1) is mounted on a urethral catheter (9) or is an integrated part of a catheter (9), characterised by that the catheter (9) together with the EMG sensor (1) comprise at least one pressure detecting sensor (4a ), preferably in the form of a microtip transducer. AMENDED CLAIMS

[received by the International Bureau on 26 January 1999 (26.01.99); original claims 1-9 and 11 amended; remaining claims unchanged (3 pages)]

CLAΪMS

1. An EMG sensor for detection of myoelectrical potentials, in particular an EMG sensor mounted on a urethral catheter (9) or integrated with a urethral catheter (9), and wheie the EMG sensor is comprised of an elongated, mainly cylindrical sensor body ( 1 a) of a dielectric material, characterised by that the surface of the EMG sensor comprises more than one pair of measurement electrodes (2a.2b.2c.2d...) that are partly imbedded in the surface of the sensor body and are essentially levelled with said surface, and that the measurement electrodes (2a.2b....> are arranged in respective electrode configurations that mainly stretch along rhe long axis of the sensor body as helical or parallel narrow band of an electrically conducting material, and that the surface of the EMG sensor ( I) has a ring-shaped reference electrode (3), in that the reference ring electrode 3) of an electrically conducting mateπal is arranged around the long axis of the sensor body (la) and is partially imbedded in the surface of the sensor body and is essentially levelled with said surface, and is a ring band of at least the same width as measurement electrodes

2. An EMG sensor according to claim 1, characterised by that measurement electrodes (2) and the reference electrode (3) are made in platina.

3. An EMG sensor according to claim ^characterised by that up to four measurement electrodes (2) arc configured around the said sensor at the same area of the said sensor as narrow bands running in lines parallel to the long axis of the sensor body or in helical lines.

4. An EMG sensor according to claim I. characterised by that up to four measurement electrodes (2) are placed symmetrically and equidistantly around the said sensor.

5. An EMG sensor according to claim 1. characterised by that each measurement electrode (2) is configured essentially as a dot, in that the dot-shaped measurement electrodes are arranged in configurations that constitute parallel lines to the long axis of the sensor body (l ) or helical lines around the sensor body ( la) or are evenly distributed throughout the surface of said sensor body (la) so that at least four measurement electrodes are distributed essentially on a circle radialy equidistantly around the said sensor.

6. An EMG sensor according to claim 1, characterised by that its size is well fitted to the urethrai size of children, adult men or women and that it fits smoothly into urethra and can be mounted on or can be a part of a measurement urethral catheter of minimal size.(la) with a reference ring-shaped electrode positioned at the end or in the middle of the said sensor, enabling isometric orientation of the measurement electrode arrangement. An EMG sensor according to claim 1. characterised by more than one pressure detecting sensor Ma.4b....). preferably in the form of a number of microup transducers mounted on the sensor body ( 1 a) at several places to allow to measure the pressure changes along the urethra and help at the same time in positioning and localising the said sensor within the urethra. A mu iti channel urethra! FMG sensor system, where me sensor system includes an EMG censor ( 1) according lo claims 1-6 for detection of myoelectric potentials, where the FV1G sensor^'s measurement electrode (2) is connected through an amplifier unit (6) to an isolated data processing unit (8) for EMG signal analysis, where the EMG sensor system includes a number of measurement channels (6c). where each measurement electrode (2) is assigned to two measurement channels (6c). and where the outυut of each measurement electrode is connected to the corresponding input of the amplifier unit (6), characterised by that the amplifier unit (6) includes a separate switching unit (6b) together with a differential instrumentation amplifier(όe_!-όc_R ) for each measurement channel, and that rhe switching unit is devised to connect the measurement electrodes (2) in pairs to the input of the respective differential instrumentation amplifiers (6c 6c_π ), so that each measurement channel performs a differential detection of the registered myoelectrical potentials. An EMG sensor system according to claim 8. ch racterised by that it comprises at least 4-10 separate measurement channels (6c) around the same area of the said sensor, where each measurement channel constitutes pairs of measurement electrodes (2) together with a reference electrode (3) for differential detection of the registered myoelectrical potentials located around the said sensor,

10. An EMG sensor system according to claim 8, characterised by that the amplifier unit is connected with an isolating signal conditioning unit (7), where the signal-conditioning unit is connected isolated with data processing unit (8).

11. An EMG sensor system according to claim 8, characterised by that the separate switching unit (6b) is devised to automatically connect the measurement channels (όc) through the data processing unit (8) by connecting the measurement electrodes (2) pairwise for differential detection of the registered myoelectrical potentials.

12. An EMG- sensor system according to claim 8. where the EMG sensor

( 1) is mounted on a urethral catheter (9) or is an integrated part of a catheter (9), characterised by that the catheter (9) together with the EMG sensor (1) comprise at least one pressure detecting sensor (4a,....), preferably in the form