WO1997038751A1

WO1997038751A1 - Transcutaneous nerve stimulator

Info

Publication number: WO1997038751A1
Application number: PCT/DE1997/000721
Authority: WO
Inventors: Brigitte Stroetmann; Siegfried Kallert; Alessandra D'intino; Waltraud Lager
Original assignee: Siemens Aktiengesellschaft
Priority date: 1996-04-12
Filing date: 1997-04-09
Publication date: 1997-10-23

Abstract

A transcutaneous nerve stimulator is disclosed, as well as its use in artificial respiration or in combination with a conventional respirator to avoid diaphragmatic atrophy. The nerve stimulator has electrodes and a pulse generator. Complex stimuli composed of individual stimuli are generated. The individual stimuli which make up a complex stimulus have the same form and repetition frequency.

Description

Transcutaneous nerve stimulator

The invention relates to a transcutaneous nerve stimulator and its use for artificial ventilation or in combination with a conventional respirator to avoid the inactivity atrophy of the diaphragm that occurs during artificial ventilation.

As a rule, artificial ventilation is carried out as so-called "positive pressure ventilation". This means that for the inhalation the pressure pg in the breathing gas container is increased compared to the pressure p _L in the lungs (= overpressure) so that a gas flow into the lungs, namely the inhalation, takes place because of PB ^ PL. The lungs and thorax are stretched according to the increased intrathoracic pressure. Because of the elasticity of these tissues, exhalation can take place passively as soon as the "excess pressure" disappears.

In the case of the physiological form of the respiratory mechanics, the respiratory muscles create a negative pressure in relation to the ambient air pressure py by expanding the thoracic expansion in the thorax, so that inhalation takes place because of PL <PU. Here too, passive exhalation occurs when the forces of the respiratory muscles, which expand the thorax and lungs, cease.

Immediately after exhalation (this situation is defined as resting breathing), the pressure in the thorax is the same in both respiratory forms, but while in the physiological form of breathing for the inspiration phase, the pressure in the thorax drops, it increases in positive pressure ventilation. This pressure and of course its changes are also transferred to the blood vessels according to the superposition principle. It mainly affects the veins and auricles. It comes with the physiological form of breathing, namely during inspiration through the increased pressure gradient between the thorax and Abdominal cavity to an increased venous inflow into the thorax and thus to the heart. As a result, the cardiac output is increased under otherwise completely identical conditions. This is referred to as the pumping effect of breathing on the circulation. In the case of positive pressure ventilation, an opposite pressure gradient is being built up for inhalation, so there is rather a counter-rotating, ie circulating pumping effect.

Respiratory rhythmic activation of the diaphragm by corresponding excitation of the phrenic nerve, which triggers the contraction of the diaphragm, would bring the artificial respiratory mechanics closer to the physiological respiratory mechanics and thus enable the respiratory pump effect on the circulation. It is therefore a goal to manufacture devices that lead to ventilation by activating the diaphragm according to the normal, physiological breathing mechanism.

Inactivity atrophy of the diaphragm occurs to varying degrees in patients who are artificially ventilated for a long time using conventional positive pressure methods. The muscle fibers of the diaphragm (skeletal muscles) become weaker and this leads to weakness in breathing and requires that the patient has to be weaned from the ventilator again after the artificial respiration. Regular activation of the diaphragm during artificial ventilation via respiratory rhythmic stimulation of the phrenic nerve prevents this inactivity atrophy.

Electrostimulation of the phrenic nerve is already a clinically established method, but it is limited to implantable nerve stimulators.

As early as 1952, Siemens-Reiniger-Werke developed an electrical stimulation device called Phrenoton (DE-PS 919 961) that was used for transcutaneous nerve stimulation. A single phrenic nerve of the patient was removed with the phrenotone stimulates a stimulus generated by electron tubes. The stimulus composed of a modulation of three pulses Gl, G2 and G3 (each with different shapes and frequencies) had a duration of 4 ms (or 2 ms) and a repetition frequency of 50 Hz (or 150 Hz). The 4 ms pulse was obtained by chopping a low-frequency current of 5 kHz (or 7 kHz). This pulse was superimposed with rectangular pulses of frequency 10-60 / min generated by an RC element.

The result was a one-sided, intermittent and unnecessarily violent stimulation of the nerve, which is not physiological and which soon led to signs of fatigue in the nerve. A further

I.

So far, the device has not been wound because the phrenotone soon became obsolete due to the medicinal treatment of weakness in breathing in polio (see archive for physical therapy, edition of 1952, page 326/327). There is now an increased need for nerve stimulators that can also be used for artificial respiration or for supportive treatment in artificial respiration.

For the physiological excitation of a muscle, a stimulus is given to the nerves innervating it. This simultaneously triggers action potentials in the individual nerve fibers that add up to a total action potential. Depending on the strength of the stimulus, none, several or all nerve fibers are excited, which is shown in the occurrence or the amplitude and duration of the total action potential of the nerve. Each motor nerve fiber divides into several muscle fibers. The excitation of a nerve fiber also triggers action potential on all of the muscle fibers innervated by it. A muscle fiber twitch occurs at a single muscle fiber action potential. While a single pull occurs on a single action potential via the electromechanical coupling, superposition and finally tetanus of the muscle occurs due to the superimposition of the mechanics on several action potentials that follow one another quickly enough (= smooth long-lasting contraction = tetanic muscle contraction). A complex stimulus that causes a tetanic muscle contraction is called tetanic stimulus.

The object of the present invention is to provide a device for transcutaneous nerve stimulation which specifically triggers tetanic stimuli.

The invention relates to a transcutaneous nerve stimulator which comprises a pulse generator and stimulation electrodes, the pulse generator generating complex stimuli which are composed of individual stimuli, the current strength, subsequent frequency and duration of which can be variably adjusted, and the individual stimuli within a complex Each stimulus has the same shape and repetition frequency. The invention furthermore relates to the use of such a nerve stimulator for contraction of the diaphragm via the stimulation of the phrenic nerve and the use of such a nerve stimulator for stimulation of the nerves on both sides. phrenici, the use of the nerve stimulator for artificial ventilation and finally the use of the stimulator in combination with a conventional ventilator to prevent diaphragmatic atrophy.

Preferably the nerve stimulator is designed to be current stabilized, i.e. that when the skin resistance changes, for example by sweating or skin reactions, the nerve is in each case stimulated with approximately the same current strength.

The following is set independently of one another via the pulse generator:

- the individual stimulus duration,

- the form of the individual stimuli, - the phase individual stimuli,

- the amplitude (s) of the individual stimuli and

- the repetition frequency of the individual stimuli. The duration of the individual stimuli can vary between 100 μs and 2ms. However, if the applications require it, it can also be longer or shorter than the specified range. The shape of the individual stimuli is also arbitrary, for example sinusoidal, trapezoidal or rectangular. The amplitudes of the individual stimuli vary, for example between 0 and 50 mA. The frequency of the individual stimuli is also variable and depends on the application of the nerve stimulator.

The form of the complex stimulus arises from the individual stimuli. The duration of the complex stimulus, the repetition frequency of the complex stimulus and the amplitude (s) of the complex stimulus (rise, fall slope and hold time) are also set via the pulse generator.

Although differently shaped complex stimuli can be contained in a series of stimulations, each complex stimulus per se consists of only a single pulse shape. According to the invention, pulse shapes are not superimposed.

In an embodiment according to the invention, the rise and fall time of each complex stimulus can be set such that, for example, a rise time of the complex stimulus of 2 s can be offset by a fall time of 1 s (see FIG. 1). The shape of the complex stimulus can thus be both symmetrical and asymmetrical. As I said, the complex stimuli do not have to be repetitive units that repeat themselves again and again.

In order to trigger the desired tetanic contraction of the muscle, in the case of the diaphragm contraction, a sequential frequency of the individual stimuli of approximately 30 Hz is required.

In order to avoid electrolytic processes in the irritated tissue, biphasic pulses with charge compensation used. For example, as a result of the complex stimuli, a positive stimulus will alternate with a negative stimulus, or the individual individual stimuli may already have alternating positive and negative phases.

The stimulation electrodes for transcutaneous use are optimized after quick placement and simple handling. They are created from the outside and can be fixed to the body and also in a holder. This holder can comprise one or more guide rails and fixing means for fixing the electrodes relative to one another and relative to the patient. The holder is preferably fastened to the patient's neck or fixed relative to the neck by a bracket placed around the neck. The guide rails are used for height, width and depth adjustment. This enables simple, quick and exact adjustment of the electrodes to the desired stimulus points on the patient's skin. The electrodes can be attached to the skin itself with plaster or integrated into a plaster.

In one embodiment, the stimulation electrode is integrated in a cushion, which is connected to an adjustable holder, in order to make an adjustment at the desired stimulus points and to enable an adjustment relative to the patient.

The stimulation electrodes consist of electrically conductive material and preferably have a porous surface for reducing the skin resistance. In the case of flat plaster electrodes, an anesthetic or another medicament can also be applied, which releases the medicament into the skin layer to be stimulated according to the principle of iontophoresis (for example an anesthetic for local anesthetic). The porous surface of the electrodes also allows devices to be created that allow automatic and uniform moistening of the electrodes. The stimulation electrodes are made of an electrically conductive material such as stainless steel, platinum, titanium, titanium nitride, carbon, electrically conductive plastic, ceramics and others. These can be both rod-shaped and flat electrodes, and for better fixation these can be applied, for example, to a plaster, which in turn may also have included medication.

The invention is in no way intended to be limited to such types of electrodes, but rather can encompass all types of electrode systems.

The nerve to be stimulated is preferably stimulated symmetrically, i.e.

I Both the right and left phrenic nerves are stimulated. One advantage of bilateral or symmetrical stimulation compared to the one-sided stimulation is that both diaphragmatic aids are stimulated equally and on an equal footing. In the case of one-sided irritation, only the corresponding half of the diaphragm contracts. The other part contracts only slightly due to the mechanics.

With the symmetrical contraction of the diaphragm, the Nn. phrenici with two counter electrodes each at their left and right motor points in the neck area and with one electrode at the exit point in the cervical area at C3 / C5. The electrodes can be applied so that

- either one electrode lies at the point of exit of the nerve and two counter electrodes lie at both motor points in the neck area,

- Or the electrodes are placed on both sides in the neck area and the counter electrode at a suitable location, possibly in the neck. The invention is described in more detail below on the basis of various exemplary embodiments and the associated five figures.

Figures 1 and 2 explain the device by way of example using various stimulus pulse patterns to trigger a tetanic diaphragm contraction and

Figures 3 to 5 indicate different configurations for stimulation electrodes and their holders.

1 shows the current strength of the complex stimulus as a function of time. The period, which here comprises 10s,

I shows two complex stimuli, each composed of biphasic individual stimuli. This can be seen from the fact that the complex stimuli are each mirror-symmetrically depicted in the positive as well as in the negative ampere range. As can be seen, there are no impulse blocks within the envelope (= complex stimulus), but there is a uniform rectangular impulse sequence.

The individual stimuli composing the complex stimulus have a repetition frequency of approx. 30 Hz. The amplitude of the resulting complex stimuli is variable like that of the individual stimuli and is 30 to approx. 35 mA here. The duration of the complex stimulus at the max. Ampere number and the time interval between two complex stimuli, which can also be expressed in such a way that the repetition frequency of the complex stimuli is variable. The individual stimuli, shown on the top right in the picture, have an amplitude of 0 to approx. 35 mA and a duration of approx. 100 μs to 2 ms, which are simple square-wave pulses in this example. The entire current curve from 0 to 5000 ms is referred to as a complex stimulus.

The first complex stimulus from FIG. 1 is shown again in FIG. 1 a, a rectangle R being inserted at the leftmost edge. is drawing. FIG. 1b shows an enlargement of this rectangle 1 from FIG. La, in which the individual biphasic rectangular stimuli which result in the complex stimulus become visible.

2 again shows a trapezoidal complex stimulus, the shape of the stimulus according to the invention not being fixed to a trapezoidal or rectangular shape, but being variable. It can be seen here that, in contrast to FIGS. 1, 1a and 1b, there are no biphasic individual stimuli, but two successive complex stimuli are positive and negative. The individual stimulus repetition frequency is again approximately 30 Hz, the amplitude of the individual stimuli between 0 and 35 mA and the duration of the individual stimuli can vary between 100 μs and 2 ms. With the sequence of complex stimuli shown, a tetanic shredding contraction occurs when the Nn are stimulated. phrenici, in which case the time up to 2.8s can be referred to as the inhalation phase and the time from 2.8 to 5.0s can be referred to as the passive exhalation time.

FIGS. 2a and 2b show, analogously to FIGS. 1a and 1b, the marking of the rectangle R in the left complex stimulus of FIG. 2 (FIG. 2a) and the enlargement of this rectangle (FIG. 2b) so that the individual pulses become visible.

FIG. 3 shows the schematic representation of a pillow 4, the pillow being able to be ergonomically shaped, even without the details being discussed here. In the middle of the pillow is the flat electrode 1, which is embedded in the pillow with a remaining increase of a few centimeters. Also in the middle is the metal bracket 2 on which the counter electrodes are attached. The electrode 1 is guided and fixed in a rasterized guide and fixing rail 3. In the case of nerve stimulation of the Nn. phrenicii it can be individually adapted to the neck or spine course of the respective patient. The electrode 1 is connected to the pulse generator of a nerve stimulator via a contact 5.

The two counter electrodes are mounted on an insulated metal bracket 2, which stands vertically on an extra fixing rail 6. By means of a special grid at both ends of the metal bracket 2 (this can be clearly seen in FIG. 2), the latter can be lowered into the cushion 4 by the fixing rail 6 and its width setting can thus be changed. An individual adjustment to the neck circumference of the patient is easily possible.

In Figure 4, the exact embodiment of the metal bracket 2 can be seen namely the grids at both ends and the straight course above. The two electrodes 14 (counter electrodes) are each attached to the round metal bracket 2 with the aid of an annular hook 3, the hooks 3 being freely displaceable over the bracket. The two rod-shaped electrodes 14 can be displaced and fixed along the bracket 2 as desired via the positioning aid 10, which can optionally be a screw. With this arrangement, the electrodes can be variably positioned on the stimulation points on the right and left in the neck area and then fixed with the screw 10 (positioning aid). After the stimulus point has been found, the rod electrodes 14 are pressed onto the motor point (stimulus point) of the nerve with the aid of the variable depth setting 7, which can change the length of the rod. The pressure can be variably set using the depth setting 7. The electrodes 14 are again connected to the pulse generator of the nerve stimulator via a cable 5. On both sides of the bracket 2, which is preferably an insulated metal bracket, the catches 9 can be seen, with the aid of which the depth adjustment of the bracket, ie how far the bracket is sunk into the cushion, can be adjusted. FIG. 5 shows another variant of the electrode fixation, this arrangement consisting of two round, insulated metal brackets, namely the electrode bracket 2 and the counterelectrode bracket 2 '. The electrode bracket 2 is placed tightly around the patient's neck in such a way that the electrode 12 lies well against the exit point of the nerve (s) in the neck. The counter electrode bracket 2 ', which rests on the motor point (s) of the nerve (s), is placed loosely at the front around the patient's neck. The two counter electrodes are in turn attached to the round counter electrode bracket 2 'with the aid of an annular fastening 3 and can be freely moved over the bracket. Both brackets 2, 2 'are attached to the pair of guide and fixing rails 17 with the aid of the fixing

I attached 8 rings. The advantage of this arrangement is that the patient can sit down for example during the duration of the stimulation and thus have a little more freedom of movement.

With the new stimulator, both inhalation and exhalation are controlled and an even breathing process is achieved. The invention is not limited to the irritation of the phrenic nerve, but rather can be used for all possible nerve irritations, in each case using the repetition frequency that is required for tetanic irritation of the muscle in question that is to be contracted. With the proposed holder, a simple adaptation of the stimulation electrodes to the patient's body or its stimulation points is possible. Compared to implanted electrodes, the patient is less stressed and the electrodes are easier to apply.

Claims

claims

1. Transcutaneous nerve stimulator, which comprises a pulse generator and stimulation electrodes for attachment to the skin of a patient, the pulse generator comprising means for generating complex stimuli, the stimuli being composed of individual stimuli, the current strength, repetition frequency and duration of which are variable are adjustable and the individual stimuli within a complex stimulus each have the same shapes and repetition frequencies.

2. Nerve stimulator according to claim 1, which is current stabilized.

3. Nerve stimulator according to one of claims 1 or 2, in which the amplitude and the shape of the complex stimuli can be set independently of one another by the pulse generator.

4. nerve stimulator according to any one of the preceding claims, in which by the pulse generator the rise, fall and

The holding times of the complex stimuli are variably adjustable.

5. A nerve stimulator according to one of the preceding claims, which sends complex stimuli, positive and negative stimuli alternating as a result of the complex stimuli.

6. nerve stimulator according to one of claims 1 to 4, in which in the sequence of the individual stimuli alternate positive and negative stimuli.

7. nerve stimulator according to one of the preceding claims, the stimulation electrodes are made of electrically conductive material with a porous or smooth surface.

8. Nerve stimulator according to one of claims 2 - 7, wherein at least one stimulation electrode is flat and medication is stored in the surface of the at least one stimulation electrode are that they become effective on the skin at the starting point of the electrode.

9. Nerve stimulator according to one of the preceding claims, in which three stimulation electrodes are provided, which are provided for the attachment so that an electrode is to be arranged above the point of exit of the nerve from the spine and two further electrodes at two motor points of the nerve .

10. Nerve stimulator according to one of the preceding claims, the electrodes of which are provided such that two electrodes at the motor points of the nerve and a counter electrode are to be arranged over a large area in the neck or shoulder area.

11. Nerve stimulator according to one of the preceding claims, in which a holder is provided for the stimulation electrodes, which comprises guide rails and fixation means for adjusting the stimulation electrodes relative to one another and relative to a patient.

12. Use of the nerve stimulator according to one of the preceding claims for contraction of the diaphragm.

13. Use of the nerve stimulator according to one of the preceding claims for symmetrical (bilateral) stimulation of the nerves. phrenici, the right and left motor points of the nerve in the neck area being stimulated simultaneously with two counterelectrodes and additionally the electrode exit point of the nerve from the spine in the cervical area at C3 / C5.

14. Use of the nerve stimulator according to one of the preceding claims for artificial ventilation.

15. Use of the nerve stimulator according to one of claims 1 to 11 in combination with a conventional ventilator for preventing diaphragmatic atrophy.