WO2019202488A1

WO2019202488A1 - Output stage for electrical stimulation of the neuromuscular system

Info

Publication number: WO2019202488A1
Application number: PCT/IB2019/053110
Authority: WO
Inventors: Marco GAZZONI; Giacinto Luigi CERONE
Original assignee: Politecnico Di Torino
Priority date: 2018-04-16
Filing date: 2019-04-16
Publication date: 2019-10-24
Also published as: IT201800004526A1

Abstract

An output stage of a stimulation unit (27) for applications of electrical stimulation of the neuromuscular system is described, which is implemented with a switched capacity circuit (40) comprising a first switch (SW1) interposed between a high- voltage generator (VCHG) and a capacitor (C) adapted to store the energy required for applying electrical stimuli by means of stimulation electrodes (28), through which current is delivered to cause muscle contraction, a second switch (SW2) connected in series to the first switch (SW1), downstream of the capacitor (C), and a closed -loop current control system (45) comprising current intensity control means (46) connected to the second switch (SW2) and adapted to detect the current intensity (II) in the circuit (40) and to control the activation/deactivation of the second switch (SW2) depending on the detected current intensity (II).

Description

OUTPUT STAGE FOR ELECTRICAL STIMULATION OF THE NEUROMUSCULAR SYSTEM

DESCRIPTION

The present invention relates to an output stage for electrical stimulation of the neuromuscular system. In particular, the invention relates to an output stage of a system for functional electrical stimulation of an individual’s neuromuscular system.

Electrical stimulation of the neuromuscular system involves the application of electrical stimuli, by means of stimulation electrodes, to one or more muscles in order to cause them to contract. Functional electrical stimulation is a type of electrical stimulation aimed at causing the contraction of a person’s muscles in order to induce a movement that is functional for the execution of a given movement and/or exercise.

Electrical stimulators are known which consist of a single device, to which stimulation electrodes are connected by means of cables.

However, such electrical stimulators are not satisfactory and suffer from the following problems:

they require a wired connection between the stimulation control unit and the stimulation site;

- the person’s freedom of movement is limited because of the bulkiness and length of the connection cables between the stimulator and the electrodes.

Electrical stimulators are known which solve these problems by using a modular, as opposed to centralized, architecture, so that each muscle is stimulated through a miniaturized device placed in proximity thereto.

However, these latter electrical stimulators suffer from the drawback that they require a miniaturized, battery-powered and highly efficient output stage (a circuit that allows outputting a given voltage or current, set beforehand according to a given stimulation pattern).

The present invention aims at solving the above-mentioned problems of the prior art by providing an output stage for neuromuscular stimulators which is small in size, battery- powered and highly efficient, and allows controlling the electrical charge injected into the individual during the stimulation.

These and other objects and advantages of the invention, which will become apparent in the light of the following description, are achieved through an output stage for electrical stimulation of the neuromuscular system as described in claim 1. Some preferred embodiments and non-obvious variants of the present invention are set out in dependent claims.

It is understood that all the appended claims are an integral part of the present description.

It will become immediately apparent that what is described herein may be subject to innumerable variations and modifications (e.g. in shape, dimensions, arrangements and parts having equivalent functionality) without departing from the protection scope of the invention as set out in the appended claims.

The present invention will be described in detail below through a preferred embodiment thereof, which is only provided by way of non-limiting example with reference to the annexed drawings, wherein:

Figure la is a schematic view of a programmable modular system for functional electrical stimulation applications;

- Figure lb shows an example of application of a programmable modular system for functional electrical stimulation applications in FES-Rowing protocols;

Figure 2 is a block diagram of an electrical stimulation module of a programmable modular system for functional electrical stimulation applications;

Figure 3 is a block diagram of an output stage of the stimulation module of a programmable modular system for functional electrical stimulation applications according to the present invention; and

Figure 4 is a block diagram of an acquisition module of a programmable modular system for functional electrical stimulation applications.

With reference to the drawings, the programmable modular system 10 for neuromuscular functional electrical stimulation (FES) applications is preferably a multi-channel system and comprises at least one wireless module 20, 30 adapted to be positioned on a person; preferably, the system 10 comprises a plurality of wireless modules 20, 30 adapted to make up a network of wearable modules (body network - BN) connected to one another in wireless mode. The system 10 is a multi-channel one (i.e. it may comprise multiple stimulation and/or bio-signal acquisition channels), since it is possible to use as many modules as the number of necessary channels and/or signals. In the example of Figure lb, two stimulation modules 20 and five signal acquisition modules 30 are used. The signal acquisition modules 30 serve to acquire the position of the person’s arm and forearm (by means of inertial sensors) and the positions of the seat, handle and carriage of the rowing ergometer. The system 10 comprises two different types of wireless modules 20, 30: 1) stimulation module 20 (Stimulation Unit - SU), shown in Fig. 2; 2) bio-signal acquisition module 30 (Bio-signal acquisition Unit - BU), shown in Fig. 4. Said module 20, 30 is adapted to receive data from bioelectrical and/or biomechanical sensors and/or to generate a stimulation pattern based on said data and on an algorithm defined beforehand by the user during the programming stage, according to the acquired signals, the type of stimulation protocol to be implemented (FES-Rowing, FES-Cycling, etc.) and the type of muscles to be stimulated; said module 20, 30 is also adapted to be programmed independently through the use of a high-level programming language, e.g. Python, for which a set of libraries are provided in order to simplify the programming task (e.g. Master/Slave mode management, data acquisition or reception, etc.), and can operate in Master or Slave mode.

A stimulation module 20 or a bio-signal acquisition module 30, if configured in Master mode, receives data from sensors, processes them, and drives other sensors configured in Slave mode; conversely, when configured in Slave mode, the module 20, 30 only behaves as a stimulator (module 20, SU) or as a data acquisition unit (module 30, BU), receiving commands from the Master module 20, 30 and generating the required outputs. The functions of the Master module may also be carried out by any mobile device 1, e.g. a smartphone or a tablet, or by a PC connected to the wireless module 20, 30, should high performance be required for processing the acquired data and applying the (user- defined) algorithm for generating the stimulation pattern.

Figure la schematically shows an example of a programmable modular system 10 consisting of a network of four modules 30 of the BU type, two modules 20 of the SU type, and one PC 1. Figure lb shows an example of application of the system 10 of the invention within a FES-Rowing context, consisting of combining the voluntary exercise of the upper part of the body with electrical stimulation of the lower part of the body, e.g. of a paraplegic person. In this example, the system 10 comprises a sensorized rowing ergometer 11 with three bio-signal acquisition modules 30 (BU) that acquire the positions of a carriage 14 and a handle 15, as well as the force exerted on the latter. Two more BU modules 30 are arranged on the user’s upper limbs and are used in order to acquire kinematic variables (displacement, speed, acceleration) relating to the movements of the upper limbs while rowing. A mobile device 1 placed on the rowing ergometer 11 processes the data received from the bio-signal acquisition modules 30 (BU) and appropriately controls the stimulation modules 20 (SU) that stimulate the muscles of a person’s lower limbs.

In brief, the stimulation module SU 20 performs the following functions:

- Electrical stimulation of a muscle with constant current (preferably programmable and comprised between 0,1 mA and 100 mA);

- Generation of stimulation patterns according to a predefined program that can be customized by the user;

- Reception of the stimulation start/stop command, if configured in Slave mode;

- Reception of signals from BU modules 30, if configured in Master mode.

In brief, the bio-signal acquisition module 30 performs the following functions:

- Acquisition of bioelectrical signals (e.g. EMG) and/or biomechanical signals (force, displacement, etc.);

- Transmission of the signals acquired by the module configured in Master mode;

- Transmission of the stimulation start/stop command to other SU modules 20, if configured in Master mode;

- Reception of signals from other BU modules 30, if configured in Master mode.

Preferably, the stimulation module (SU) 20, shown in Fig. 2, comprises the following units: a power unit 22, comprising electric energy supplying means adapted to supply power to the stimulation module 20, e.g. a single-cell lithium-polymer (LiPo) battery, e.g. with a no-load voltage of 3.7 V; a power management unit 21 and a control unit 23 connected thereto; a stimulation unit 27 comprising an output stage according to the invention, connected to stimulation electrodes 28, a synchronization unit 24, and a storage unit 25, e.g. an SD Card, said stimulation unit 27, synchronization unit 24 and storage unit 25 being connected to the control unit 23.

Preferably, the power management unit 21 comprises means 26 for connection to an electric power supply, and is adapted to recharge the power unit 22; for example, the battery is recharged by means of an element 26 for wireless inductive charging.

Preferably, the control unit 23 comprises a microcontroller of a known type comprising wireless connectivity means (e.g. Texas Instruments CC3200 or CC3220), said microcontroller incorporating firmware programmed by using a programming language comprising a high-level language interpreter, e.g. the Python language, for programming the main functions of the system (signal acquisition, stimulation pattern generation, etc.), which allows the user to configure the behaviour of each stimulation module 20. In particular, said control unit 23 is adapted to interpret the program set by the user, manage the Master/Slave modes, transmit/receive data and commands, generate the stimulation pattern, and control the output stage of the stimulation unit 27.

Preferably, the synchronization unit 24 is of a known type and is adapted to control the synchronization of multiple modules 20, 30 making up a system 10. For example, the modules may be synchronized by means of a digital trigger signal simultaneously sent from the outside to all the modules 20, 30 in use. Such signal prompts the modules to start the operations for which they have been programmed (signal sampling, stimulation pattern generation, etc.). The trigger signal can be obtained by connecting a push-button or a device (e.g. an infrared one) for command transmission/reception. In particular, in the case of a stimulation module 20 in Master mode, said synchronization unit 24 is adapted to send a digital signal (trigger signal) simultaneously to the control units 23 of each module in Slave mode, which signal may be sent, for example, by pressing a key or via an infrared optical command of a remote control, and indicates the beginning/end of a work session.

Preferably, the storage unit 25 comprises memory means, e.g. an SD Card unit, and is adapted to store the user-defined program files.

The stimulation unit 27 is connected to the control unit 23 and comprises the output stage of the invention, which includes a switched capacity circuit 40 providing control over the current being applied to the load. The block diagram of the output stage of the stimulator according to the invention is shown in Figure 3.

The switched capacity circuit 40 comprises a first switch SW1, e.g. a transistor-based electronic switch, preferably of the MOSFET type, interposed between a high-voltage generator (200V - 350V) VCHG, consisting of the power unit 22, e.g. a Boost -type DC/DC converter like those used for recharging camera flashes (LT3468 chip - Linear Technology), and a capacitor C adapted to store the energy required for applying electrical stimuli through the stimulation electrodes 28 that deliver the current that causes muscle contraction.

The switched capacity circuit 40 comprises a second switch SW2, e.g. a transistor-based electronic switch, preferably of the MOSFET type, connected in series to the first switch SW1, downstream of the capacitor C, and a closed-loop current control system 45 comprising current intensity control means 46, e.g. consisting of a conditioning circuit for acquisition of the current applied to the load Z_L (46, e.g. based on the LT6100 chip - Linear Technology) and a circuit for comparing said current with the predefined threshold via the STIM AMP command (I-Lim, e.g. obtained through a classical Schmitt trigger hysteresis comparator), connected to the second switch SW2 and adapted to detect the current intensity I_I in the circuit 40 and to control the activation (if I_L<=STIM_AMP) or deactivation (if I_L>STIM_AMP) of the second switch SW2 depending on the detected current intensity I_I.

During the operation of the switched capacity circuit 40, the first switch SW 1 switches in the period during which no stimulation command is applied (STIM CMD = Off), while the second switch SW2, on the contrary, is disabled. During such period, the capacitor C is charged to the voltage VC_HG, e.g. 150V. When the stimulation command is activated (STIM CMD = On), the first switch SW1 is disabled and the second switch SW2 switches. During this phase, the energy stored in the capacitor C is discharged through the load Z_L, which represents the electrode-skin impedance across the stimulation electrodes 28. At the same time, based on the STIM AMP command, which is proportional to the current amplitude to be injected into the load during the stimulation, the current I_I injected into the load Z_L is monitored.

Control of the current intensity is effected by the control means 46 by disabling the second switch SW2 whenever the limit of the injected current monitored by a closed- loop current control system 45 comprising current intensity control means 46, set through the STIM AMP command, is exceeded.

Preferably, the bio-signal acquisition module (BU) 30, shown in Fig. 4, comprises the following units, which are similar to those of the stimulation module (SU) 20 already described: the power unit 22, adapted to supply power to the bio-signal acquisition module 30, e.g. a rechargeable single-cell lithium-polymer (LiPo) battery, e.g. with a no- load voltage of 3.7 V; the power management unit 21 and the control unit 23 connected thereto; the synchronization unit 24 and the storage unit 25, e.g. an SD Card, connected to the control unit 23.

In particular, the power management unit 21 is adapted to recharge the battery 22, as already described with reference to the stimulation module 20, and the battery 22 is adapted to supply power to the bio-signal acquisition module 30, as already described with reference to the stimulation module 20.

The control unit 23 is also similar to the one already described with reference to the stimulation module 20, and allows the user to configure the behaviour of each bio-signal acquisition module 30. In particular, said control unit 23 is adapted to interpret the program set by the user, manage the Master/Slave modes, and transmit/receive data and commands.

The bio-signal acquisition module 30 further comprises a bio-signal acquisition unit 31 connected to the control unit 23 and adapted to acquire data relating to biomechanical parameters from sensors connected thereto, preferably via a connector 32, e.g. inertial sensors, optical encoders, generic analogue signals (0 V - 3,3 V dynamics) or digital signals (e.g. from external triggers).

Preferably, the synchronization unit 24 is similar to the one already described with reference to the stimulation module 20 and is adapted to manage the synchronization of multiple modules 20, 30 making up a system 10, and the storage unit 25 is similar to the one already described with reference to the stimulation module 20 and is adapted to store the user-defined program files.

The output stage for neuromuscular stimulation according to the invention offers the following advantages:

no circuits are necessary for generating high-voltage direct (DC) potentials;

- during the stimulation, rising edges are steeper by at least one order of magnitude

(-100 ns) than in existing technologies;

the high efficiency of the circuit (-90%) ensures minimal power dissipation, so that the capacity and size of the battery can be reduced.

The preferred embodiment of the invention described herein is of course susceptible of further modifications and variations without departing from the inventive idea. In particular, numerous functionally equivalent variations and modifications will be immediately apparent to those skilled in the art, which will still fall within the protection scope of the invention as set out in the appended claims, wherein any reference signs between brackets should not be considered to limit the scope of the claims. Furthermore, the word“comprising” does not exclude the presence of elements and/or steps other than those listed in the claims. The article“a”,“an” or“one” before an element does not exclude the presence of a plurality of such elements. The simple fact that some features are mentioned in different dependent claims does not suggest that a combination of such features cannot be used to advantage.

Claims

1. Output stage of a stimulation unit (27) for applications of electrical stimulation of the neuromuscular system implemented with a switched capacity circuit (40) comprising: a first switch (SW1) interposed between a voltage generator (VCHG) and a capacitor (C) adapted to store the energy required for applying, through stimulation electrodes (28), electrical stimuli that cause muscle contraction; a second switch (SW2) connected in series to the first switch (SW1), downstream of the capacitor (C), and a closed-loop current control system (45) comprising current intensity control means (46) connected to the second switch (SW2) and adapted to detect the current intensity (I_I) in the circuit (40) and to control the activation/deactivation of the second switch (SW2) depending on the detected current intensity (I_I).

2. Output stage of a stimulation unit (27) for applications of electrical stimulation of the neuromuscular system according to claim 1, characterized in that the voltage generator (VCHG) is a DC/DC converter.

3. Output stage of a stimulation unit (27) for applications of electrical stimulation of the neuromuscular system according to any one of the previous claims, characterized in that it is connected to the electrodes (28) of a stimulation module (20).

4. Output stage of a stimulation unit (27) for applications of electrical stimulation of the neuromuscular system according to any one of the preceding claims, characterized in that the first switch (SW1) is adapted to switch in the period during which no stimulation command (STIM CMD) is applied, while the second switch (SW2), on the contrary, is disabled, in order to charge the capacitor (C).

5. Output stage of a stimulation unit (27) for applications of electrical stimulation of the neuromuscular system according to any one of the preceding claims, characterized in that the first switch (SW1) is disabled and the second switch (SW2) switches when the stimulation command is activated (STIM CMD) in order to discharge the energy stored in the capacitor (C) through the stimulation electrodes (28), while the current (I_I) is monitored.

6. Output stage of a stimulation unit (27) for applications of electrical stimulation of the neuromuscular system according to any one of the preceding claims, characterized in that the control of the current intensity is effected by the control means (46) by disabling the second switch (SW2) whenever an injected current limit (I-Lim) is exceeded.