WO2001019453A1

WO2001019453A1 - Constant energy pulse nerve stimulation device

Info

Publication number: WO2001019453A1
Application number: PCT/ZA1999/000091
Authority: WO
Inventors: Stevaun Coetzee
Original assignee: Gideon Medical Enterprises (Pty) Limited
Priority date: 1999-09-16
Filing date: 1999-09-16
Publication date: 2001-03-22
Also published as: AU6299899A

Abstract

A nerve stimulation device (10) which includes an electric energy source which is typically in the form of a battery (12) and a control means (14) arranged in electrical communication with the battery (12) to allow substantially constant amounts of energy to be released or discharged periodically from the battery (12) source via or between a pair of terminals (20a) and (20b) independently of a resistance across or between said terminals (20a) and (20b).

Description

Constant Energy Pulse Nerve Stimulation Device

This invention relates to a nerve stimulation device and, more specifically, to the generation of constant energy pulses by such a device which may be used in a Transcutaneous Electrical Nerve Stimulation (TENS) apparatus or in a passive exercise unit.

The applicant is aware of prior art in which the output from a TENS apparatus is either not controlled at all or has either a constant voltage or constant current output. In particular, using a constant voltage output may result in changes in the effect of the apparatus meaning that if, for example, the contact resistance of the electrodes is decreased due to a user leaning back against a chair, this may cause an effect ranging from slight discomfort to severe muscle spasms. Alternatively, using a constant current output may result in current burn should the electrodes become even slightly detached. Furthermore, conventional nerve stimulation apparatus are generally not used over prolonged periods of time thereby to avoid any negative side effects such as muscle spasms and electrolysis.

The applicant therefore believes that a need exists for a nerve stimulation device for pain relief which is safe to use over prolonged periods of time, which can be adjusted according to each subject's specific needs and which is comfortable to use as well as being portable . The applicant further believes that it would be advantageous to produce a nerve stimulation device which may be used to relieve pain and which may alternatively be used as a passive exercising device.

Thus, according to the invention, there is provided a nerve stimulation device which includes :- an electric energy source; and a control means arranged in electrical communication with the electric energy source to allow substantially constant amounts of energy to be released or discharged periodically from the electric energy source via or between a pair of terminals independently of a resistance across or between said terminals.

The nerve stimulation device may include a plurality of control means to permit independent supplying of substantially constant amounts of energy to a plurality of pairs of terminals and wherein the energy supplied via each pair of terminals may be variable according to a user's requirements.

The electric energy source may preferably be a DC energy source, typically a battery having a voltage range of between 1 ,5V and 12V, preferably between 2 and 3,1 V, typically 3 V. Typically, the amount of current supplied by the battery may be between 5 mA and 25 mA depending on the amount of energy drawn by the user . However, the electric energy source may also be a 9 V battery or have a suitable multiplier circuit to imitate such a battery, in which case the amount of current supplied by the battery may be between 1 mA and 30 mA depending on the amount of energy drawn by the user .

The control means may include a voltage control means for maintaining a desired, substantially constant change in voltage across a capacitor or terminals over a predetermined period of time, the amplitude of the change in voltage across the capacitor or terminals being variable according to the resistance across or between the terminals to permit energy pulses supplied by the nerve stimulation device are of a substantially constant magnitude .

The voltage control means may include an energy storage means, preferably a capacitor, and a switching means for regulating the time period for which the capacitor is allowed to charge and discharge. The capacitance of the capacitor may be between 10 and 100 μF, preferably 22 μF. The charging of the capacitor, and hence the capacitor voltage, may be variable according to the resistance across the terminals to enable constant amounts of energy to be released therefrom, thereby to permit self-regulation in a manner corresponding to a feedback system.

The capacitor voltage for every energy pulse supplied may be determined by a microprocessor.

The control means may further include a switching means which may include an input and output transistor arranged in communication with a timer of the microprocessor.

In particular, the timer may serve to regulate the magnitude of the change in the potential difference across the capacitor and hence the maintenance of the desired determined potential difference across the terminals by controlling the switching time periods of the switching means, the desired potential difference being such that the energy pulses supplied by the nerve stimulation device are of a substantially constant magnitude. Typically, this period of time may be a predetermined variable value between 0 and 10 ms.

The output transistor, typically an NPN or FET transistor may also serve to permit a discharge of pulsed DC to flow from the energy storage means to a voltage step up transformer that is connected to the terminals and which steps up the potential difference between said terminals in a desired ratio. This ratio is typically 10 when using a 3 V electric energy source. The input transistor is typically a PNP transistor.

The transformer may be connected to the terminals, preferably in the form of a pair of electrodes. The set of electrodes are typically conventional electrodes which may be connected to a user. The transformer's output is typically in the form of pulses, each pulse containing the same amount of electrical energy. Typically, the pulse frequency may be between 70 and 120Hz, preferably 80Hz. Typically, the output current of the transformer is between 0,01 and 100 mA, depending on the user's specific energy requirements at the time. The transformer may be configured in such a way as to inhibit energy above a certain amount to pass through it by becoming saturated.

The transformer may serve to permit galvanic isolation of the user.

The nerve stimulation device may have zero direct current offset due to the transformer only being capable of delivering alternating current .

The period of time that the input transistor is in a closed position may be determined by the microprocessor in accordance with the user's desired energy requirements.

The period of time that the output transistor is in a closed position is determined by the microprocessor . Typically, this period of time may be a set value of between 0,01 to 0,1 ms, but preferably 0,02 ms.

A key pad and display means forming a control panel may be provided to enable the user to control the energy to be supplied.

The display means may include a visual and/ or audible alerting means for alerting the user should the voltage in the nerve stimulation device increase above acceptable levels, or should one of the electrodes become disconnected or the capacitor discharge fully so as to alert the user of a potentially hazardous condition. The alerting means may typically be in the form of randomly chosen codes which are displayed on the display means such as Ε ' to indicate that one of the electrodes has become disconnected, "E₂" to indicate an electrical short in the device's circuitry and so forth . The nerve stimulation device may be operable in one of three modes, namely continuous, pulse or passive exercise. Typically, the nerve stimulation device stimulates sensory nerves when operating in the continuous or pulse mode and motor nerves when operating in the passive exercise mode.

The nerve stimulation device may include a wave form generator capable of generating a wave form including a sequence of pulses having parameters as follows : a repetition rate of 70 to 120 Hz, a pulse width of 0,01 to 0,1 ms, a pulse decay which is stepped, an amplitude of between 0 and 80 volts with no DC offset, and an output current of 0,01 to 100 mA and a control means arranged in communication with the wave form generator for varying any one or combinations of the parameters.

The invention will now be described by way of non-limiting examples with reference to the accompanying drawings.

In the drawings:-

Figure 1 is a schematic circuit diagram of a nerve stimulation device in accordance with the invention;

Figure 2 is a plan view of a control panel of a nerve stimulation device having two separately controlled pairs of electrodes;

Figure 3 is a detailed circuit diagram of a nerve stimulation device in accordance with the invention Figures 4 ^nd 5 are time domain representations of various wave forms generated byihe nerve stimulation device; and

Figure 6 is a strength-duration curve for sensory, motor and noxious nerve responses.

Referring now to the drawings, reference numeral 10 generally indicates a nerve stimulation device in accordance with the invention. The nerve stimulation device 10 includes an electric energy source in the form of a battery 12 and a control means 14 in the form of a microprocessor 16 and a circuit 18 arranged in electrical communication with the battery 12 to allow substantially constant amounts of energy to be released or discharged periodically to a user via a pair of terminals in the form of electrodes 20a and 20b independently of a resistance between the electrodes 20a and 20b. It is to be appreciated however, that a plurality of independently controlled and isolated circuits may be provided to permit more than one area of a user to be stimulated at the same time.

The control means 14 further includes a voltage control means which is typically part of the microprocessor 16 for maintaining a desired, substantially constant change in voltage across an energy storage means in the form of a capacitor 22 and a switching means in the form of input (PNP) and output (NPN or FET) transistors 24 and 26 respectively for regulating the time period over which the capacitor 22 is allowed to charge and discharge.

The input 24 and output transistor 26 are arranged in communication with a timer (not shown) of the microprocessor 16 for controlling the opening and/ or closing of the transistors 24 and 26 thereby to control the time periods for which the capacitor 22 is allowed to charge and discharge .

The timer serves to regulate the magnitude of the change in the potential difference across the capacitor 22 and hence the maintenance of a desired calculated potential difference across the terminals 20a and 20b by controlling the switching time periods of the transistors 24 and 26, the desired potential difference being such that the energy pulses supplied are of a substantially constant magnitude.

The period of time that the input transistor 24 is in a closed position is determined by the microprocessor 16 in accordance with the user's desired energy requirements. The microprocessor 16 also determines the period of time for which the output transistor 26 is in a closed or open position.

The charging of the capacitor 22, and hence the capacitor voltage, is variable according to the resistance across the terminals 20a and 20b to enable constant amounts of energy to be released therefrom, thereby to permit self-regulation in a manner corresponding to a feedback system.

The capacitor 22 voltage for every energy pulse supplied is determined by the microprocessor 16 as embodied in an algorithm, hardware or software.

The capacitor 22 voltage (V₂ : see figures 4 and/ or 5 ) determined by the microprocessor 16 is calculated as follows :

V₂ = ( V₁ ² + k) ⁰'⁵

where k is a constant which is typically between 0 and 20 000 and which is directly proportional to the intensity setting of the nerve stimulation device 10 chosen by the user, V₂ is the capacitor 22 voltage and V₁ is voltage at which the capacitor begins 22 to charge (see figures 4 and/ or 5) and which is measured by the microprocessor 16 in order to solve the above equation.

The change in voltage (ΔV) of the capacitor 22 is related to the current (I) supplied by battery 12 as well as the length of time (t^ for which the input transistor 24 remains closed and allows the capacitor 22 to charge and can be represented by the following formula:

ΔV = (I x t) / C

where I is the current in Ampere, t is time in seconds and C is capacitance in Farads. The output transistor 24 serves to permit a discharge of pulsed DC to flow from the capacitor 22 to a voltage step up transformer 28 that is connected to the terminals 20a and 20b and which steps up the potential difference between the terminals 20a and 20b in a desired ratio.

The transformer 28 serves to permit galvanic isolation of the user and permits the output of the nerve stimulation device 10 to have zero direct current offset .

The energy (E) transferred to the user via the isolating terminals 20a and 20b during the time period (t₂) for which the output transistor 26 is closed can be represented by:

ΔE = 0,5 x C x ( V₂ ² - V,² )

A key pad 30 and display means 32 form a control panel 34 which is provided to enable the user to select and/ or to control the energy to be supplied .

The user can select the mode of operation as well as the intensity of the energy pulses supplied by nerve stimulation device 10 by means of manipulating the keypad 30 which is in electrical communication with the microprocessor 16. The display means 32 will indicate to the user the settings he has chosen.

The nerve stimulation device 10 is operable in one of three modes, namely continuous, pulse or passive exercise which can be chosen by the user via key 36.

The display means 32 includes a visual and/ or audible alerting means

38 for alerting a user to disconnected electrodes 20a and/ or 20b or to indicate an electrical short in the device's 10 circuitry 18 or the like. The key pad 30 further includes keys 40a, 40b, 42a and 42b for manipulating the pulse intensity according to the user's desire. Keys 40a and

42a increase the pulse intensity supplied, while keys 40b and 42b decrease the pulse intensity supplied. Key 44 is used to turn the nerve stimulation device 10 on and off.

The nerve stimulation device 10 is adapted to stimulate sensory nerves when operating in the continuous or pulse mode and motor nerves when operating in the passive exercise mode.

Referring now to figure 4, if the effective resistance between the terminals 20a and 20b shown in figure 1 connected to the user increases (e.g. due to poorly connected electrodes) the capacitor 22 will not discharge as much electrical energy as it did for the previous pulse as indicated by region 46 on the graph . The microprocessor 16 will, after having measured V-,¹, calculate the value of V₂ ¹ to which the capacitor 22 will have to be charged in order to maintain a constant energy pulse output from the nerve stimulation device 10 . This means that the magnitude of V¹ will be smaller than that of V in order to compensate for the higher voltage at which the nerve stimulation device will then be operating. Should no further disturbances to the resistance between the terminals 20a and 20b occur, the magnitude of V¹ and with it the values of V.,¹ and V₂ ¹ will remain constant as shown in figure 4.

Referring now to figure 5 if the effective resistance between the terminals 20a and 20b shown in figure 1 connected to the user decreases (e.g. due to the user leaning back against a chair, thereby increasing the pressure on the electrodes) the capacitor 22 will discharge more electrical energy than it did for the previous pulse as indicated by region 54 on the graph . The microprocessor 16 will, after having measured V.,¹, calculate the value of V₂ ¹ to which the capacitor 22 will have to be charged in order to maintain a constant energy pulse output from the nerve stimulation device 10. This means that the magnitude of V¹ will be larger than that of V in order to compensate for the lower voltage at which the nerve stimulation device will then be operating. Should no further disturbances to the resistance between the terminals 20a and 20b occur, the magnitude of V¹ and with it the values of V-,¹ and V₂ ¹ will remain constant as shown in figure 5.

The applicant believes, that a nerve stimulation device in accordance with the invention is advantageous in that it provides constant energy pulses which fall within a designated zone "A" as shown in figure 6 below the noxious nerve curve 50 whilst still permitting stimulation of the sensory and motor nerves (indicated by curves 52 and 54 respectively) thereby not to harm the user.

The invention is not limited to the precise constructional details as hereinbefore described.

Claims

1. A nerve stimulation device which includes :- an electric energy source; and a control means arranged in electrical communication with the electric energy source to allow substantially constant amounts of energy to be released or discharged periodically from the electric energy source via or between a pair of terminals independently of a resistance across or between said terminals.

2. A nerve stimulation device as claimed in claim 1 wherein a plurality of control means are provided to permit independent supplying of substantially constant amounts of energy to a plurality of pairs of terminals, the energy supplied via each pair of terminals being variable according to a user's requirements.

3. A nerve stimulation device as claimed in claim 1 or claim 2 wherein the electric energy source is a DC energy source, typically a battery .

4. A nerve stimulation device as claimed in any one of claims 1 to 3 wherein the electric energy source includes any suitable multiplier circuit .

5. A nerve stimulation device as claimed in any one of the preceding claims wherein the control means includes a voltage control means for maintaining a desired, substantially constant change in voltage across a pair of terminals over a predeterminable period of time, the amplitude of the change in voltage across the terminals being variable according to the resistance across or between the terminals to permit energy pulses supplied to be of a substantially constant magnitude .

6. A nerve stimulation device as claimed in claim 5 wherein the voltage control means includes an energy storage means, preferably in the form of a capacitor, and a switching means for regulating the time period for which the capacitor is allowed to charge and discharge, charging of the capacitor, and hence the capacitor voltage, being variable according to the resistance across the terminals to enable constant amounts of energy to be released therefrom, thereby to permit self-regulation in a manner corresponding to a feedback system.

7. A nerve stimulation device as claimed in claim 6 wherein a voltage regulator, typically a microprocessor, is provided to determine and regulate the capacitor voltage for every energy pulse supplied.

8. A nerve stimulation device as claimed in claims 6 or 7 wherein the switching means includes an input and output transistor preferably arranged in communication with a timer of the microprocessor.

9. A nerve stimulation device as claimed in claim 8 wherein the timer serves to regulate the magnitude of the change in the voltage across the capacitor and hence the maintenance of the desired calculated potential difference across the terminals by controlling the switching time periods of the switching means, the desired potential difference being such that the energy pulses supplied are of a substantially constant magnitude.

10. A nerve stimulation device as claimed in claim 8 or 9 wherein the output transistor serves to permit a discharge of pulsed DC to flow from the energy storage means to a voltage step up transformer that is connected to the terminals and which steps up the voltage between said terminals in a desired ratio.

1 1. A nerve stimulation device as claimed in claim 10 wherein the terminals are in the form of a pair of electrodes and which are connectable to a user .

12. A nerve stimulation device as claimed in claim 10 or 1 1 wherein the transformer permits galvanic isolation of the user.

13. A nerve stimulation device as claimed in any one of claims 10 to 12 wherein the transformer permits a wave form generated to have a zero direct current offset.

14. A nerve stimulation device as claimed in any one of claims 8 to 13 wherein the period of time that the input transistor is in an open and/ or closed position is determined by the microprocessor in accordance with the user's desired energy requirements.

15. A nerve stimulation device as claimed in any one of claims 8 to 14 wherein the period of time that the output transistor is in an open and/ or closed position is determined by the microprocessor .

16. A nerve stimulation device as claimed in any one of the preceding claims wherein a key pad and display means forming a control panel is provided to enable the user to control the energy to be supplied.

17. A nerve stimulation device as claimed in claim 16 wherein the display means includes a visual and/ or audible alerting means for alerting a user to current and/ or voltage surges or to indicate an electrical short in the device's circuitry and so forth .

18. A nerve stimulation device as claimed in any one the preceding claims which is adapted to be operable in one of three modes, namely continuous, pulse or passive exercise for stimulating sensory nerves when operating in the continuous or pulse mode and motor nerves when operating in the passive exercise mode.

19. A nerve stimulation device which inciudes:- a wave form generator capable of generating a wave form including a sequence of pulses having parameters as follows, a repetition rate of 70 to 120 Hz, a pulse width of 0,01 to 0,1 ms, a pulse decay which is stepped, an amplitude of between 0 and 80 volts with no

DC offset, and an output current of 0,01 to 100 mA ; and a control means arranged in communication with the wave form generator for varying any one or combinations of the parameters.

20. A nerve stimulation device according to the invention, as hereinbefore generally described.

21. A nerve stimulation device as specifically described with reference to or as illustrated in the accompanying drawings.

22. A nerve stimulation device including any new and inventive integer or combination of integers, substantially as herein described.