Abstract:
An electro-stimulation apparatus comprises an electrode system for measuring local electrical impedance. The electrode system includes a multitude of electrode pads and a counter electrode held at a reference voltage. The electrode pads and the counter electrode are assembled in an electrode unit. A particular embodiment of the electro-stimulation apparatus comprises an electronic circuit including a source group of electrode pads and a sink group of electrode pads and a source conductor for applying a first electrical quantity to electrode pads of the source group. The electronic circuit also includes a sink conductor for receiving a second electrical quantity from electrode pads of the sink group. Switching elements couple individual electrode pads of the source group to the source conductor. Other switching elements couple individual electrode pads of the sink group to the sink conductor.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an electro-stimulation apparatus, comprising 
     an electrode system for measuring local electrical impedance including 
     a multitude of electrode pads and 
     a counter electrode held at a reference voltage. 
     Such an electro-stimulation apparatus is for instance used in the fields of electro-acupuncture and transcutale electronic nerve stimulation (TENS). In both electro-acupuncture and TENS electrical signals are locally applied to the body of a human so as to excite particular parts of the nervous system. In particular a small electrical current is locally applied to the skin of the person undergoing electro-stimulation. It has been found that such electro-stimulation has various beneficial effects, notably pain is substantially relieved. It has also been found that local electro-stimulation activates growth of muscular tissue and activates the healing of wounds. Furthermore, electro-stimulation is employed as an alternative to traditional acupuncture. In order to achieve optimum beneficial effects, the electrical signals are to be applied to particular, optimum positions on the person&#39;s skin. It is known that these optimum positions locally have a minimum electrical impedance. 
     Such an electro-stimulation apparatus is known from the abstract of the Soviet patent SU 1 219 086. 
     The cited abstract mentions that the person clasps the counter electrode in the palm of one hand and the electrode system is placed so that a number of electrode pads are in electrical contact with the person&#39;s skin. The cited abstract mentions that the resistance of the acupuncture point is comparatively low and that a current regulator sets the current for the acupuncture point search. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an electro-stimulation apparatus which is easier to use and can operate more accurately than the conventional electro-stimulation apparatus. A particular object of the invention is to provide an electro-stimulation apparatus with which the optimum position for electro-stimulation is more comfortably and more accurately found. 
     This object is achieved according to the invention by an electro-stimulation apparatus which is characterized in that the electrode pads and the counter electrode are assembled in an electrode unit. 
     Because the counter electrode and the electrode pads are assembled in a preferably compact electrode unit, the counter electrode is not situated far from the electrode pads. Hence, the electrical impedances between individual electrode pads and the counter electrode accurately represent the skin&#39;s local electrical impedance at the positions on the person&#39;s skin where the electrode pads are positioned. Preferably, the counter electrode and the multitude of electrode pads are integrated in the electrode unit. Notably, the counter electrode and the electrode pads cannot be readily detached from the electrode unit. Furthermore, the electro-stimulation apparatus according to the invention does not require a separate counter electrode. The electro-stimulation apparatus according to the invention is easier to use since the person using the electro-stimulation apparatus does not need to clasp the counter electrode in the palm of the hand. Moreover, the counter electrode is not a separate component of the electro-stimulation apparatus. Hence, the electro-stimulation apparatus according to the invention requires the manufacture and assembly of fewer separate components. In addition, there is no risk of loss of the counter electrode. 
     In order to determine the optimum position for electro-stimulation, the electrode system is placed on the person&#39;s skin. It has been found that there are various rather large regions on the person&#39;s skin which contain respective optimum electro-stimulation positions relating to particular ailments or disorders of the person. It appears that these regions have a diameter of from a few centimeters to some ten centimeters and that it is quite simple to indicate these regions for various ailments. In particular, among a huge number of examples, a region between the shoulder blades appears to be related to general fatigue, a region on the lower portion of the sternum appears to be related to asthmatic cough, and a region on the upper portion of the sternum appears to be related to bronchitis. When the electrode system is placed in the desired region on the person&#39;s skin, some of the electrode pads are activated so as to apply an electrical quantity, such as a voltage or an electrical current. Subsequently, the impedances at individual electrode pads are determined by measuring the difference between the electrical quantity applied at separate electrode pads and the counter electrode. In particular, the electrical potential difference between individual electrode pads and the counter electrode is measured or the electrical current passing between individual electrode pads and the counter electrode is measured. The electrode pad at which the impedance constitutes a local minimum is situated at or very close to the optimum position for electro-stimulation. The electro-stimulation can be applied through the same electrode pad as used to measure the impedance, but it is also possible to employ a separate stimulation electrode which is very close to or occupies substantially the same position as the electrode pad at which the impedance is locally minimum. 
     These and other aspects of the invention will be further elaborated with respect to the embodiments of an electro-stimulation apparatus according to the invention as defined in the dependent claims. 
     Various geometries of the arrangement of the electrode pads and the counter electrode are useful for integration in the electrode unit. In a particularly simple arrangement the counter electrode surrounds a part of or all of the electrode pads. The counter electrode is formed as a conducting loop; for example, the loop has a circular, oval or rectangular shape. A part of or all electrode pads are located within the loop. Because the arrangement is simple, it is easy and hence inexpensive to manufacture the integrated electrode unit. The counter electrode can also be positioned between individual electrode pads. For example, the counter electrode is formed as one or more conducting strips which are positioned between individual electrode pads, or the conducting strip(s) meander(s) between the individual electrode pads. 
     The counter electrode in another embodiment is formed as a plurality of counter electrode elements; in particular, a sink group of the electrode pads is employed as the counter electrode elements and a source group of the electrode pads is employed to apply the electrical quantity, such as the voltage or the electrical current, to the person&#39;s skin. The counter electrode elements, notably the electrode pads of the sink group, are maintained at the substantially constant reference voltage, for example, at ground potential. The distances between neighbouring counter electrode elements and electrode pads of the source group are substantially equally small throughout the electrode system. Hence, the electrical impedances between electrode pads of the source and the sink group accurately represent the local electrical skin impedance of the person. Usually, the size of the electrode system is about 2×2 cm, or 5×5 cm. As more electrode pads having smaller sizes are provided, the spatial resolution for measuring the local electrical impedance is increased and, consequently, the optimum position for electro-stimulation can be found more accurately. The more accurately electro-stimulation is performed at the optimum stimulation position, the more effective beneficiary effects are achieved. 
     The electrode pads and the counter electrode are part of the electrode system which is incorporated in an electronic circuit. Preferably, the electrode pads of the electrode system are incorporated in a matrix structured electronic circuit. For example, the electrode pads are arranged in a two-dimensional square or triangular pattern. Preferably, 8×8, 16×16 or 512×512 electrode pads are provided. A source conductor is provided to apply the first electrical quantity in the form of the voltage or the electrical current to electrode pads of the source group. A sink conductor is provided to receive the second electrical quantity in the form of the electrical current or the voltage from the electrode pads of the sink group. The second electrical quantity at the sink electrode pads is caused by applying the first electrical quantity to the source electrode pads so that the electrical impedance between source and sink electrode pads can be derived from the electrical quantity received from the sink electrode pads. Electrode pads in the sink and source groups will be designated as source and sink electrode pads, respectively. The source electrode pads and the sink electrode pads have the same construction and electrode pads are arranged in the source group by connecting them electrically to the source conductor so that the first electrical quantity can be applied to the source electrode pads. Similarly, electrode pads are arranged in the sink group by electrically connecting them to the sink conductor so that the second electrical quantity can be received from the sink electrode pads. The source electrodes are switchably coupled to the source conductor and the sink electrodes are switchably coupled to the sink conductor. Electrode pads are selected to apply or receive the voltage or the electrical current by closing relevant switching elements between said electrode pads and the source conductor or the sink conductor. Preferably, the switching elements are transistors, e.g. thin-film field effect transistors, which are controlled by applying addressing signals to the gate contacts of the transistors. The addressing signals are conveniently supplied over addressing lines which can be incorporated in the electronic circuit. By controlling appropriate switching elements, source electrode pads are selected to apply the first electrical quantity, for example to apply the voltage. By controlling appropriate switching elements sink electrode pads are selected to receive the second electrical quantity, for instance to receive the electrical current. The electrical impedances between source electrode pads and sink electrode pads are determined by measuring the electrical currents generated at the sink electrode pads and measuring the applied voltages at the source electrode pads, subsequently, the optimum stimulation position is found at the position of the sink electrode pad having the lowest electrical impedance with respect to the source electrode pads. It is also to be noted that the sink electrode pads function as the counter electrodes, but a separate counter electrode which is maintained at a constant reference voltage, for example at ground potential, can also be used. 
     Preferably, a source and a sink conductor share a common line conductor. The common line conductor is at option coupled to the source unit so as to function as the source conductor and coupled to the sink unit so as to function as the sink conductor. The electronic circuit has a comparatively simple architecture with a rather small number of lines. Preferably, there is provided a plurality of common line conductors which at option function as one or more of source conductors or as one or more sink conductors. When a plurality of common line conductors is employed it is simultaneously possible to supply the first electrical quantity and to receive the second electrical quantity from separate electrode pads of the source group and of the sink group, respectively 
     In a more elaborate embodiment of the electronic circuit the electrical current is applied to electrode pads of an activation source group and the electric current is received from electrode pads of an activation sink group. Electrode pads of the activation group are switchably coupled to the source conductor or to the sink conductor. Electrode pads of the probe group are switchably coupled to a source voltage line or to a sink voltage line. Electrode pads in the activation and probe group, respectively are designated activation electrode pads and probe electrode pads, respectively. Activation electrode pads which are coupled to the source conductor or to the sink conductor are named activation source and activation sink pads, respectively. The electrical current flows from one or more electrode pads of the activation source group to one or more electrode pads of the activation sink group. Voltages are probed from electrode pads of a probe group. Thus, voltages at electrode pads of a probe group are measured at electrode pads of the probe group due to an electrical current flowing between electrode pads of the activation group. The voltages at the probe electrodes are caused by the current flowing between the activation electrode pads. Notably the measurement of voltages at electrode pads between which the electric current flows is avoided. In this set up the measurement of the voltages hardly influences the electrical current so that the voltages area measured reliably and accurately. 
     In a more simple circuit architecture the source voltage line and the drain voltage line are formed as a common voltage line. The common voltage line is switchably coupled to separate voltage probes so as to act at option as the source voltage line and the drain voltage line. Preferably, a plurality of common voltage lines is provided so that different voltages from separate probe electrode pads can be probed simultaneously. Electrode pads are selected for probing voltages by closing relevant switching elements between said electrode pads and the source voltage line or the drain voltage line. The electronic circuit having common voltage lines instead of separate source and drain voltage lines has a simple circuit lay-out because the number of conducting lines is comparatively small. Hence, such an electronic circuit can be more easily manufactured. 
     Advantageously, the electrode unit comprising the electrode pads and the counter electrode is provided on a flexible substrate. The electrode unit can then be easily placed on the person&#39;s body, for example, wrapped around an arm or leg. Preferably, the electrode unit on the flexible substrate is incorporated on an inflatable band which will help to accurately maintain the correct location during the electro-stimulation. 
     Additionally, the invention relates to an electronic circuit comprising a source group of electrode pads and a sink group of electrode pads with a source conductor for applying a first electrical quantity to the electrode pads of the source group and a sink conductor for receiving a second electrical quantity from the electrode pads of the sink group. A first group of switching elements couple individual electrode pads of the source group to the source conductor and a second group of switching elements couple individual electrode pads of the sink group to the sink conductor. This inventive electronic circuit is particularly useful when employed in an electro-stimulation apparatus as disclosed above. 
    
    
     These and other aspects of the invention will be elucidated by way of example with reference to the embodiments described hereinafter and with reference to the accompanying drawing, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a first embodiment of the electro-stimulation apparatus according to the invention, 
     FIG. 2 is a schematic representation of a second embodiment of the electro-stimulation apparatus according to the invention, and 
     FIGS.  3 , 4  and  5  are schematic representations of embodiments of the electro-stimulation apparatus according to the invention in which advantageous electronic circuits are employed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a schematic representation of a first embodiment of the electro-stimulation apparatus according to the invention. The electro-stimulation apparatus comprises an electrode system  1  which is placed on a person&#39;s skin such that most or all of the electrode pads  2  and the counter electrode  3  make electrical contact with the skin. One or more electrode pads  2  apply a voltage locally to the skin. The voltage is supplied by a voltage source  11  and as a consequence of the applied voltage an electrical current is received by the counter electrode  3 . The electrical current is carried off to ground and is measured by a current meter, e.g. an ammeter. The current meter  12  generates a current signal (CS) whose signal level represents the measured current. The current signal is applied to a micro-controller  13 . 
     Furthermore, the electrode system  1  includes voltage lines  14  and addressing lines  15 . Preferably, the electrode pads  2  are configured in a square two-dimensional matrix. By way of example, a 4×4 matrix is shown, but in practice larger matrices such as 8×8 or 16×16 matrices can be employed. Such comparatively small matrices are advantageously manufactured from discrete electrical components mounted on a printed circuit board. The electrode pads can be mounted on one side of the printed circuit board and the conductor lines and switching elements are provided on the other side of the printed circuit board. Separate electrode pads  2  are coupled to one of the voltage lines  14  via respective switching elements, such a thin-film transistors  4 . The source contact of each of the thin-film transistors  4  is coupled to the relevant voltage line  14  and the drain contact of each of the thin-film transistors  4  is coupled to the relevant electrode pad  2 . The thin-film transistors  4  are coupled to respective addressing lines  15  via their gate contacts. Separate addressing lines  15  are coupled to thin-film transistors  4  in respective rows of the matrix. The electrode system also includes a source selection circuit  16  and a row addressing circuit  17  which are controlled by the micro-processor  13 . The source selection circuit  16  applies the voltage (V) to one or more selected voltage lines  14 . The row addressing circuit  17  applies gate signals (GS) to selected addressing lines  15 . When a gate signal is applied to one of the addressing lines, the transistors coupled to that addressing line are closed, i.e. rendered conductive. Hence, the voltage is applied to electrode pads  2  which are coupled to a voltage line  14  that is activated and to an addressing line  15  that is activated. By way of example, activated voltage lines and activated addressing lines are marked with an asterisk (*) in the drawing. 
     The micro-controller  13 , e.g. successively activates the voltage lines  14  and the addressing lines  15  so as to apply the voltage to successive electrode pads  2  or combinations of several electrode pads  2 . The current meter  12  measures the electrical currents received from the counter electrode  3  and the current signals (CS) representing the electrical currents caused by applying the voltage to respective electrode pads are applied to the micro-controller  13 . The micro-controller computes the skin impedance at the respective electrode pads, derives the local minimum of the skin impedance values, and selects the electrode pad at which the local minimum skin impedance occurs. Subsequently, the micro-controller activates the voltage line and the addressing line whereto the selected electrode pad, situated at or close to the position of minimum skin impedance is coupled. The selected electrode pad is then activated so as to apply a voltage to the skin at the optimum stimulation point, characterized by a locally minimum skin impedance, in order to perform an electro-acupuncture of transcutaneous electro nerve stimulation procedure. Notably, more than one local minimum skin impedance may be detected. In such a situation several electrode pads, each of them being situated at a locally minimum skin impedance, can be selected and the voltage can be applied to several optimum stimulation points. 
     In the embodiment shown in FIG. 1, the counter electrode  3  is arranged in the form of a more or less rectangular loop which surrounds the electrode pads  2 . It is to be noted that the counter electrode  3  can also be arranged as a loop of a different shape, for example, a round loop. The counter electrode  3  may enclose all or a part of the electrode pads  2 . 
     FIG. 2 shows a schematic representation of a second embodiment of the electro-stimulation apparatus according to the invention. The counter electrode  3  in the embodiment shown in FIG. 2 is arranged as a conducting strip which meanders between the electrode pads  3 . Although only a single meandering strip is shown in FIG. 2, in practice several counter electrodes may be provided between the electrode pads and/or one or more straight conductive strips may be used as counter electrodes. 
     The electrode pads and the counter electrode are preferably formed from an electrically conductive rubber. Such electrically conductive rubbers are easily integrated in electrically isolating rubber so as to form physically and electrically separated electrode pads. Moreover, electrically conductive rubbers are not poisonous. 
     FIG. 3 is a schematic representation of an embodiment of the electro-stimulation apparatus according to the invention in which an advantageous electronic circuit is employed. The electronic circuit comprises a plurality of electrode pads  2 . The electronic circuit comprises a number of common line conductors  30 . Electrode pads  2  in one column of the matrix are coupled to the same common line conductor  30  by respective thin-film transistors  4 . The common line conductors  30  are coupled to the voltage source  11  by switching elements, preferably transistors  22 , which are controlled by a source selection circuit  16 . The common line conductors  30  are also coupled to the current meter  12  by switching elements, preferably transistors  23 , which are controlled by a sink selection circuit  18 . The electronic circuit also includes a row addressing circuit  17  which is coupled to addressing lines  15 . Separate addressing lines  15  are coupled to electrode pads  2  in the same row of the matrix. The addressing lines are coupled to the gate electrodes of the thin-film transistors  4 . The row-addressing circuit  17  controls the thin-film transistors  4 . 
     The source selection circuit  16  selects one or more common line conductors  30  to supply the voltage from the voltage source  11 . To that end the relevant transistors  22  are closed so that the voltage is applied to the selected common line conductor  30 . Such a selected common line conductor  30  then functions as the voltage line in the examples of the FIGS. 1 and 2 so as to apply the voltage to one or more electrode pads  2 . The row addressing circuit  17  selects one or more rows of electrode pads  2  which are coupled to a common line conductor to which the voltage is applied. The row addressing circuit  17  applies a gate signal (GS) to the addressing line(s)  15  of the selected row(s) so as to close the thin-film transistors  4  in the selected row(s) so that the voltage is applied to the selected electrode pads  2 . 
     The sink selection circuit  18  selects one or more common line conductors  30  to receive a current caused by the application of the voltage to one or more electrode pads  2 . To that end, the relevant transistors  23  are closed so that the current received is led to the current meter  12 . Such a selected common line conductor functions as a sink conductor which receives the electrical current caused by the applied voltage. The row addressing circuit selects one or more row electrode pads  2  which are coupled to a common line conductor which is electrically connected to the current meter so as to lead the electrical current to the current meter. The row addressing circuit applies a gate signal to the addressing line(s) of the selected row(s) so as to close the thin-film transistors  4  in the selected row(s) so that the voltage is applied to the selected electrode pads  2 . The current meter generates a current signal (CS) which represents the electrical currents from electrode pads on common line conductors that are selected as sink conductors and are caused by voltages applied to electrode pads on common line conductors that are selected as source conductors. The current signals are generated for several selections of electrode pads and applied to the micro-controller. From the current signals the micro-controller computes the local minimum impedances which represent the optimum stimulation points. 
     FIG. 4 shows a schematic representation of an embodiment of the electro-stimulation apparatus according to the invention in which another advantageous electronic circuit is employed. The electronic circuit comprises several separate sink conductors  20  and several separate source conductors  21 . The sink conductors  20  are electrically coupled to the current meter  12  and the source conductors  21  are electrically coupled to the voltage source  11 . The source conductors  21  are coupled to the voltage source  11  by switching elements, such as transistors  22  which are controlled by the source selection circuit  16 . The electrode pads  2  that are switchably coupled to the voltage source  11  form one or more source groups. The sink conductors  20  are electrically coupled to the current meter  12  by switching elements  23 , such as transistors, which are controlled by the sink selection circuit  18 . The electrode pads  2  that are switchably coupled to the current meter  12  form one or more sink groups. 
     The electronic circuit also includes source addressing lines  33  and sink addressing lines  34 . The source addressing lines  33  are coupled to the gate contacts of respective thin-film transistors  4  of electrode pads  2  that are coupled to one of the source conductors  21 . The sink addressing lines  34  are coupled to the gate contacts of respective thin-film transistors  4  of electrode pads  2  that are coupled to one of the sink conductors  20 . A source addressing circuit  31  is coupled to the source addressing lines  33  and a sink addressing circuit  32  is coupled to the sink addressing lines  34 . By applying gate signals (GS) to source addressing lines  33 , thin-film transistors  4  of the selected electrode pads  2  in the source group are selected for application of the voltage from the voltage source. By applying gate signals (GS) to sink addressing lines  34 , thin-film transistors  4  of the selected electrode pads in the sink group are selected wherefrom the current caused by application of the voltage to electrode pads in the source group is measured. Electrode pads  2  in the source group and the sink group, respectively, can be present in different columns or in the same column of the matrix, because separate source and sink conductors are provided with separate sink addressing and source addressing circuits. Electrode pads to which the voltage is applied and from which the electrical current is received can be present in different rows or in the same row of the matrix, because separate sink and source addressing lines are provided. The micro-controller  13  controls the source and sink selection circuits  16 , 18  and the source and sink addressing circuits. The micro-controller also derives the local impedance minima from the current signal (CS) from the current meter. 
     FIG. 5 shows a schematic representation of an embodiment of the electro-stimulation apparatus according to the invention in which another advantageous electronic circuit is employed. The electronic circuit shown in FIG. 5 is in particular arranged to perform four-point measurements. The electrode pads  2  are arranged in a matrix. The electronic circuit also comprises several common line conductors  30 . Common line conductors  30  of a first group are switchably coupled to the current source  51  and to the current meter  12 . The common line conductors of the first group are coupled to the current meter  12  and to the current source  51  by transistors  22 , 23 . The transistors  22 , 23  are controlled by the source selection circuit  16  and the sink selection circuit  18 . The common line conductors that are selected to be coupled to the high-voltage source function as activation source conductors. The common line conductors that are selected to be coupled to the low-voltage source function as activation sink conductors. Furthermore, the electronic circuit comprises a second group of common line conductors which are switchably coupled to a high-voltage source  52  and a low-voltage source  53 . For example, use is made of a DC voltage of 40V, and an AC voltage of 25V at 400 Hz or 50V at 1.5 kHz. The common line conductors  30  of the second group are coupled to the high-voltage source  52  and the low-voltage source  53  by means of transistors  54 , 55 . The transistors  54 , 55  are controlled by a high-voltage selection circuit  56  and a low-voltage selection circuit  57 . The electronic circuit also includes source addressing lines  33  and sink addressing lines  34 . The electrode pads  2  are coupled to separate common line conductors by means of respective thin-film transistors  4 . The source and sink addressing circuits  31 , 32  apply gate signals via the source and sink addressing lines  33 , 34  so as to close thin-film transistors  4  whose gate contacts are coupled to the source and sink addressing lines. The gate signals close the relevant thin-film transistors  4  to connect electrode pads  2  electrically to the relevant common line conductors. The electrode pads that are switchably coupled to the high-voltage source  52  or to the low-voltage source  53  form the activation group. The common line conductors that are selected to be coupled to the high-voltage source and to the low-voltage source function as source voltage lines and drain voltage lines, respectively. The electrode pads  2  that are switchably connected to the current source  51  and the current meter  12  form the probe group. The electronic circuit shown in FIG. 5 is arranged to measure local impedances by means of a so-called four point measurement. To that end, under control of the high-voltage selection circuit  56  one or more separate common line conductors  30  are electrically connected to the high-voltage source  52  and, under control of the low-voltage selection circuit  57  one or more separate common line conductors are electrically connected to the low-voltage source  53 . The source addressing circuit  31  selects electrode pads  2  to be electrically connected to their respective common line conductors. Thus, a high-voltage and a low-voltage are applied to electrode pads  2  that are coupled to the activated source addressing line  33 . Furthermore, one or more separate common line conductors are coupled to the current source  51  under the control of the source selection circuit and one or more common line conductors are coupled to the current meter  12  under the control of the sink selection circuit  18 . The sink addressing circuit  32  applies gate signals, via selected sink addressing lines  34 , so as to close thin-film transistors whose gate contact is coupled to the respective sink addressing lines  34 . Thus, the sink addressing circuit  32  selects electrode pads  2  whereto the electrical current is applied or wherefrom the electrical current is received from depending on the setting of the transistors  22 , 23 . Hence, the current meter measures the electrical current that flows between two (or more) separate electrode pads in the probe group, while an electrical potential difference is maintained between two (or more) electrodes in the activation group. From the current signals the micro-controller computes the local minimum impedances which represent the optimum stimulation points.