Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-11-01
2001-11-27
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S115000, C607S048000, C600S546000, C600S372000
Reexamination Certificate
active
06324432
ABSTRACT:
The invention concerns an electrical neuromuscular stimulator for measuring muscle reactions generated by electrical stimulation pulses. The stimulator includes an electrical pulse generator arranged in a case, at least one pair of stimulation electrodes intended to be placed on the skin of an user in the vicinity of the motor points of the muscles to be stimulated, each electrode being connected to one end of an electric cable, the other end of which is connected to the case to receive the electric pulses from the generator, at least one sensor sensitive to the muscle reactions caused by the electric stimulation pulses and arranged for transmitting electric measuring signals representative of said muscle reactions to electronic means in the stimulator case.
The invention also concerns an electric cable and a stimulation electrode for a neuromuscular electric stimulator.
The sensor supplies data regarding the useful muscle reactions in particular in order to know the fatigue level of the electrically stimulated muscles. The measurements obtained from the sensor allow the parameters of the electric stimulation pulses to be adjusted either manually by viewing the shape of the signals received by the sensor on a display or automatically by adjusting the electric stimulation parameters as a function of the muscle fatigue. Adjusting the parameters consists in correcting either the frequency of the pulses, or the amplitude or duration of the voltage or current pulses, or the duration of muscle contraction and relaxation, or the number of contraction/relaxation cycles, or any combination of the preceding parameters.
The object of electric stimulation or electrostimulation is to control working of the muscles by the intermediary of electric voltage or current pulses as a function of programmed parameters. Each voltage or current pulse provides excitation of the nerve fibres which control the muscle fibres via the motor end-plate This excitation causes an elementary mechanical muscle response called a twitch with a duration of the order of 0.1 seconds.
The voltage or current pulse is repeated over time at an adjustable frequency. If this frequency is low, for example 10 Hz, the working power of the muscles is slight, whereas for a high frequency, for example 100 Hz, the working power of the stimulated muscle fibres is very high. This very high power corresponds to a powerful tetanic contraction. The muscle fibre twitches can no longer be separated after each pulse at this high frequency, which means that a temporal summation of the twitches occurs which leads to a tetanic contraction.
If the stimulated muscles are stimulated at a high frequency, they will tend to become tired. In this case, the exercising session consists in alternating contraction periods and rest periods. The rest phase allows the fibres to relax and recover prior to the next contraction phase.
In the medical field, electric stimulators are used to assist handicapped persons or accident victims so as to overcome deficiencies in muscular activity or to allow them to rehabilitate withered musculature. Electric current or voltage pulses are transmitted to said muscles via the electrodes placed on the skin or subcutaneously in order to make them work passively. Measurements of the muscle reaction caused by the electrically evoked twitch allows the electric pulses to be transmitted to the electrodes to be adjusted as a function of the level of the electrical or mechanical amplitude measured on the innervated muscles without thereby excessively tiring the muscles stimulated. This adjustment of the electrical parameters of the stimulator is used in particular for handicapped persons or accident victims, to prevent them being continually obliged to ask for external help when they have to move one or other of their deficient limbs.
A stimulator of this type is shown in U.S. Pat. No. 5,070,873 which discloses a control loop for the electric pulses to be supplied to the muscles to give them sufficient motricity. In a first phase, electromyographic sensors detect the voluntary muscle activity which in the case of a handicapped person is lacking. The voltage measurement obtained by the sensors represents the low contraction state of the activated muscles which leads to adjusting the electric pulses from the pulse generator to send voltage pulses adjusted to the expected reaction to the muscle motor nerves, in particular to allow automatism in the coordination of movements desired by the handicapped person.
The electromyographic sensors can be separated from the stimulation electrodes, but may also be combined therewith. In the latter case, a third electrode is necessary. If the same active surface of the electrode is used both as stimulation electrode and sensor, this involves controlling, with difficulty, the signals originating from the sensor following the electric pulses sent across the electrode.
The combination of the sensor with the electrode requires rectangular biphasic voltage pulses to be sent to perform the measurements by the sensor. It is to be noted that in this case, for voltage pulses, the stimulation current provided depends on the impedance of the electrode and the skin. This impedance is not the same from one person to another, or can vary rapidly over time in the same person, which leads to different muscle reactions for identical voltage pulses sent to the electrodes.
The use of a current pulse generator allows one to be rid of the drawbacks of a voltage pulse generator, since the pulse is kept constant whatever the impedance of the skin and the electrode, and thus allows the same number of fibres recruited for stimulation to be maintained.
One drawback of this combination of active surfaces of the sensor and the electrode lies in the fact that after the sequence of sent biphasic voltage pulses, there remains a residual voltage which can have a value of ten volts, whereas the measurement voltage drawn from the muscles by the sensor is of the order of a few millivolts. It is thus necessary to attenuate this residual voltage in order to be able to make an accurate measurement in particularly of the fatigue level of the stimulated muscles. This is why sensors separated from the electrodes provide better results than those combined as described hereinbefore.
French Patent No. FR 2 425 865 also discloses a bioelectrically controlled electric muscle stimulator. A carrier frequency generator provides an electric signal to the muscles to be stimulated which is adjusted as a function of the bioelectrical activity of the innervated muscles. With this adjustment of the electric pulses as a function of the measured muscle reaction, this stimulator offers a wide range of uses. It allows, in particular, a certain motor automatism of movements for example during sports exercising or for assisting handicapped persons.
The measurement sensors are of the electromyographical type and can also be combined with the stimulation electrodes, but in this case, since the voltage pulses sent to the muscles are mainly voltages of the sinusoidal order, drawing the EMG signals originating from the same stimulation electrodes using filters does not pose too much of a problem, which is not the case with rectangular voltage pulses.
The muscular contraction measurement means for providing data as to the state of reaction of the stimulated muscles can be performed in many ways. The measurement can be either electrical using electromyographical sensors, or mechanical followed by an electrical conversion for example using acoustic sensors (microphones). Such an arrangement is shown in U.S. Pat. No. 4,805,636 in which the vibrations of the contracting muscles are measured.
In this Patent document, two microphones are placed at different locations where the innervated muscles respond mechanically by a twitch to the voltage pulse generated by an electric pulse generator. A feedback circuit takes account of the voltage signals given by the two microphones in order to adjust the twitch or the electric pulses which the generator generates for the mu
Buhlmann Félix
Müller Pierre-Yves
Rigaux Pierre
Compex SA
Evanisko George R.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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