WO2005087312A1

WO2005087312A1 - A device for peristaltic control

Info

Publication number: WO2005087312A1
Application number: PCT/EP2005/051110
Authority: WO
Inventors: Cristian Sevcencu; Nico J. M. Rijkhoff; Thomas Sinkjaer
Original assignee: Aalborg Universitet
Priority date: 2004-03-11
Filing date: 2005-03-11
Publication date: 2005-09-22

Abstract

The invention relates to a device for artificially inducing peristaltic movement by electric stimulation of the colon. In particular a device is disclosed in which two consecutive electrode pairs share an intermediate electrode.

Description

A DEVICE FOR PERISTALTIC CONTROL

Field of the invention

The present invention relates to electric stimulation of the gastrointestinal tract for artificially inducing peristaltic movement.

Background of the invention

For some persons parts of the gastrointestinal tract are unable to produce peristaltic movements sufficient for emptying the contents of a section of the gastrointestinal tract. A particular problem arises for colostomy patients having no voluntary control over the evacuation of the colon content. Therefore, they currently wear a colostomy bag attached to the stoma, or perform irrigation procedures to empty the colon. When successful, the irrigation allows an almost normal life for the patient. However, the majority of people with a colostomy do not perform irrigation because it is time consuming (1-2 hours) and sometimes ineffective, with episodes of faecal discharge between washouts. Moreover, bowel irrigation can induce varying degrees of local histopathologic alterations. Instead of irrigation, colostomy patients could use electrical stimulation to induce colon emptying. Colon peristalsis could be induced by electrical stimulation of parasympathetic nerves controlling colon motility. However, the pelvic parasympathetic branches - which innervate part of the transverse, and the entire descending colon - are usually destroyed after a colostomy operation. The alternative is to create artifi- cially induced peristalsis in the remaining part of the colon. Our experiments show this is doable by sequential stimulation of consecutive colon segments, using intramurally implanted electrodes. The stimulation system and pattern used to activate consecutive colon segments is presented in the following.

Many studies have been performed to investigate the effect of different stimulation patterns on different regions along the digestive tract. Most of the work has been performed with electrical stimulation to improve gastric emptying (Bel- lahsene el al. Am J Physiol, 1992, Eagon and Kelly Neurogastroenterol Motil, 1995, Lin et al., Am J Physiol, 1998, Mintchev et al., Gastroenterology, 2000, Abell et al., Digestion 2002), and artificial pacing of the stomach is already considered as promising alternative to the use of prokinetics in the management of gastroparesis (Rabine and Barnett, J Clin Gastroenterol, 2001). Several results have also been reported with electrical stimulation to induce propulsive contractions in the small intestine (Lin et al., Proc 19^th Int Conf IEEE/EMBS, 1997, Moritz et al., Artif Organs, 1989). With respect to colon stimulation, the early in vivo studies used electrical stimulation as a mean to activate smooth muscles and en- teric neurons, only in order to elucidate basic physiological mechanisms (Bennet, J Physiol, 1966, Niklasson et al., Acta Physiol Scand 1988). Only few and recent studies investigated the possibility to electrically activate the colon for therapeutic purposes. Hughes et al. reported successful results with electrical stimulation to improve colon continence and evacuation (Hughes et al., Br J Surg,1995). The authors worked with dog isolated colonic loops, and intramurally applied rectangular pulses (30-35 mA, 0.5 ms, 10 Hz) using 2 intramural stainless steel electrode pairs. The electrodes were placed longitudinally, one pair for each limb of a J shaped loop. According to their statement, stimulation induced colon contractions able to generate sufficient intraluminal pressure to support propulsion. Later studies performed by Riedy et al. (Riedy et al., Proc 79^th Int Oonf IEEE/EMBS; 1997, Riedy et al., Lab Anim Sci 1997) and Bruninga et al. (Bruninga et al., Spinal Cord, 1998) showed that stimulation of the colon wall with wire electrodes improved colonic transit in spinalized cats. A total of 3 electrode pairs were chronically sutured to the colonic serosa of the transverse and descending colon. Two electrode pairs were implanted in a semicircular fashion and a third electrode pair was implanted parallel to the longitudinal axis of the colon. Stimulation was performed using current pulses up to 50 mA, 0.1 to 1 ms long, at a frequency of 10 to 40 Hz, and significantly improved colon transit. The most recent results with electrical stimulation to induce colon propulsion were published by Amaris et al. (Amaris et al., Gut 50, 2002), and described by Mintchev et al. in U. S. Patent No. 6,243,607 B1 and U. S. Patent No. 6,449,511 B1. Based on previous theoretical studies performed by the group (Rashev et al., J Med Eng Technol 2001, Rashev et al., Dig Dis Sci, 2002.), the authors developed a method to elicit bi-directional propulsion of semisolid colon content in dogs. A 15 cm long segment of the descending colon was subjected to stimulation. On this segment, 4 sets of bipolar stainless steel electrodes (15 mm long and 0.25 mm in diameter) were implanted longitudinally into the serosa. Each set consisted of one active and one reference electrode. All active electrodes were placed along the longitudinal axis of the colon, with the reference counterparts implanted parallel and diametrically opposite on the other side. The distance between 2 neighboring pairs was of 1.5 cm. Stimulation was performed sequentially, according to the following stimulation pattern: bipolar voltage trains of 10 ms, 50 Hz, 20 V rectangular pulses, 18 s stimulus duration, 9 s phase lag between the stimuli applied to successive electrode sets.

Bardy in U. S. Patent No. 6,238,423 B1 describes an apparatus and method to supply electrical stimuli to the muscles associated with a target portion of the patient's gut, from the esophagus to the anus, through an electrical lead and several pairs of electrodes. The stimuli may be provided sequentially, in a proximal to caudal direction, in order to initiate, enhance or artificially produce peristalsis. The device comprises an array of electrode comprising electrode pairs, which consist of electrodes with non-variable polarity, each electrode having one contact.

The device described by Mintchev et al. in U. S. Patent No. 6,449,511 B1 also uses for stimulation electrode pairs with non-variable polarity. In the stimulation system set up current is flowing in a direction transverse to the longitudinal direc- tion of the gastrointestinal tract.

Brief Description of the Drawings

The invention is disclosed more in detail with reference to the drawings in which

Fig 1 shows a schematic representation of the stimulation system coupled to an intestine portion. Fig. 2 shows the configuration of an electrode positioned into the colon wall, relative to the longitudinal axis of the intestine.

Fig 3 shows a schematic representation of the timing of a stimulation sequence. Fig 4 shows a schematic representation of a part of a stimulation session.

Detailed Description of the Present Invention

The present invention relates to a device for inducing serial contractions in a section of the gastrointestinal tract, said section of the gastrointestinal tract, defining a lumen and comprising a proximal end portion with a proximal opening, a distal end portion with a distal opening, and an intermediate portion extending between said proximal end portion and said distal end portion, said device comprising • a set of electrodes comprising a distal electrode adapted to be placed in said distal end portion, a proximal electrode adapted to be placed in said proximal end portion and at least one intermediate electrode adapted to be placed in said intermediate portion, each of said electrodes comprising at least one contact, • a contol unit for creating a potential difference between a contact of at least one first electrode, and a contact of at least one second electrode, said first electrode and said second electrode constituting an electrode pair for performing a stimulation session, wherein each intermediate electrode is comprised in two electrode pairs.

The section of the gastrointestinal tract may comprise a part of the esophagus, the stomach, the small bowel, the colon, the rectum and/or the anal sphincter. The section of the gastrointestinal tract may also comprise a part made by surgery, such as a stoma, e.g. colostomy. In a preferred embodiment of the invention said section of the gastrointestinal tract comprises at least a part of the colon. Said section of the gastrointestinal tract may also comprise at least a part of a colostomy. The section of the gastrointestinal tract has a lumen encircled by a tube-like wall of the section of the gastrointestinal tract, said wall extending from a proximal end to a distal end of the section of the gastrointestinal tract. The section of the gastrointestinal tract may be divided in a proximal end portion having a proximal opening and a distal end portion having a distal opening, said proximal opening and said distal opening connecting the lumen of said section of the gastrointestinal tract with lumens of adjacent parts of the gastrointestinal tract. A center axis of the section of the gastrointestinal tract may be defined roughly by the direction of mass transport through the gastrointestinal tract. As the gastrointestinal tract comprises curved sections, the center axis may also have a curvature. For a roughly cylinder-shaped section of the gastrointestinal tract, such as a part of the colon, the center axis and the longitudinal direction of the gastrointestinal tract coincide.

Preferably the electrodes are adapted to be positioned serially, i.e. in a row in a longitudinal direction along the walls of the section of the gastrointestinal tract, the distal electrode being positioned in a distal end portion of said section of the gastrointestinal tract, the proximal electrode being positioned in a proximal end portion of said section of the gastrointestinal tract and the at least one intermedi- ate electrode being positioned in an intermediate portion of said section of the gastrointestinal tract, said intermediate portion extending between said distal end portion and said proximal end portion. Thus each intermediate electrode will have two neighbour electrodes, namely the two nearest electrodes being a distal neighbour electrode and a proximal neighbour electrode respectively. The distal electrode has only one neighbour electrode, being a proximal neighbour electrode and similarly the proximal electrode has only one neighbour electrode, being a distal neighbour electrode.

An electrode pair may typically be constituted by one electrode and one of its neighbour electrodes. In a preferred embodiment of the invention each electrode pair is constituted by a first electrode and a second electrode, said second electrode being one of the neighbour electrodes of said first electrode. The electrodes may be adapted to be implanted such that a pair of electrodes comprising a first electrode and a second electrode, defines a ring-shaped segment of the section of the gastrointestinal tract, said ring-shaped segment being bounded by a first cross section of the intestinal tract, said first cross section comprising the contacts of the first electrode, and a second cross section of the intestinal tract, said second cross section comprising the contacts of the second electrode. The cross sections are not necessarily plane as the contacts need not define a plane. One or both of the cross sections may be essentially perpendicu- lar to the longitudinal direction of gastrointestinal tract. However for some applications it is desirable that one or both cross sections are not perpendicular to the gastrointestinal tract, the segment thus having at least one oblique end portion.

In a preferred embodiment of the invention, one electrode comprises two or more contacts. Electrodes having two or more contacts distributed around a circumference of the section of the gastrointestinal tract are advantageous in order to induce contractions in all parts of a ring-shaped segment of said section of the gastrointestinal tract. One electrode may e.g. comprise three contacts, or even more than three contacts, such as 5, 10, 20 or even more than 20 contacts. By using many contacts evenly distributed in said ring-shapecfsegment, a more uniform contraction may be obtained in said segment, which may lead to more efficient propulsion. The electrodes could all have the same number of contacts. Alternatively the number of contacts could vary from one electrode to the other, e.g. in order to keep the distance between contacts roughly constant in spite of varying circumference of the gastrointestinal tract, or in order to stimulate some segment more than other segments. .

The contacts may be connected serially. An electrode may e.g. be made from a lead, said lead being de-insulated at a number of locations, each de-insulated portion of the lead corresponding to a contact. The electrode may be adapted to encircle the lumen of the section of the gastrointestinal tract, such that the elec- trade defines a loop around the said lumen. The contacts are thus distributed around said lumen of said section of the gastrointestinal tract.

The contacts may be elongated, having an appreciable length compared to the dimensions of the section of the gastrointestinal tract, such as in the order of 0.5 or even 1 cm. Due to this, the electrode may be exposed to mechanical stress when the section of the gastrointestinal tract is contracting and expanding. In one embodiment of the invention the contacts are elongated and the contacts are adapted to be implanted such that the direction of elongation is oblique relative to the longitudinal direction of the gastrointestinal tract at the implantation site. The direction of elongation may e.g. form an angle of 20-70°, such as 30-60°, such as 40-50°, such as around 45°, with the longitudinal direction of the gastrointestinal tract at the implantation site. When the contacts are implanted in an oblique direction relative to the longitudinal direction of the gastrointestinal tract, mechani- cal stress and hence the risk of breaking the electrodes is reduced. Angles around 45° between the center axis and the contacts minimize the mechanical stress exerted on the wire during longitudinal and circular contractions.

In a preferred embodiment of the invention the contacts of at least one electrode are serially connected, the electrode being capable of forming a loop encircling the section of the gastrointestinal tract in a loop. In a further embodiment of the invention the center axis defines an acute angle with the plane of said loop, such as an angle of 20-70°, such as 30-60°, such as 40-50°, such as an angle around 45°. This configuration is advantageous in order to obtain an oblique direction of the contacts relative to the longitudinal direction of the section of the gastrointestinal tract. However, the loop may also be perpendicular to the longitudinal direction of the colon.

The control unit is adapted to activate the electrodes in order to perform at least one stimulation session. The control unit may comprise a pulse generator, for generating a pulsed signal. The pulse generator may comprise a current source. The serial stimulation sequence comprises stimulating consecutive segments of the section of the gastrointestinal tract. A device according to this embodiment of the invention may be operated to perform a serial stimulation sequence comprising the steps of: 1. providing a first electrode with a first polarity, said first electrode being the proximal electrode, 2. providing a second electrode with the opposite polarity, said second electrode being the distal neighbour of said first electrode, 3. performing a stimulation session activating the electrode pair comprising said first electrode and said second electrode, 4. inactivating the first electrode, 5. switching the polarity of the second electrode, said second electrode taking the place of the first electrode in the following stimulation session,

Some of the steps may be carried out simultaneously. Steps 2-5 are repeated a number of times depending on the number of electrodes, such that in the last repetition, the second electrode of the electrode pair is the distal electrode. In the last repetition step 5 is replaced by a step in which the second electrode is inactivated. This stimulation sequence may induce serial contractions propagating from the proximal end to a distal end of the gastrointestinal tract. Thus by this procedure serial propulsive contractions may be induced, i.e. expulsion of a part of the content of the gastrointestinal tract may be obtained.

The device may thus be adapted to perform at least a first stimulation sequence for inducing propulsive contractions, for expulsion of a part of the content of the gastrointestinal tract. In some cases it may be advantageous to perform a reversed stimulation sequence in order to avoid expulsion of the content of the gastrointestinal tract. Thus in one embodiment of the invention, the device is capable of performing a second stimulation sequence for avoiding expulsion of the con- tent of the gastrointestinal tract. In the second stimulation sequence the order of stimulation sessions may be reversed as compared to the first stimulation se- quence. Thus the device may e.g. be used to promote emptying of the colon as well as providing faecal continence between episodes of emptying.

A reversed serial stimulation sequence may be obtained by an operation of the device similar to the operation summarised in the above described procedure, replacing in step 1 the proximal electrode with the distal electrode, in step 2 the distal neighbour electrode with the proximal neighbour of the first electrode. Furthermore in the last repetition, the second electrode of the electrode pair should be the proximal electrode rather than the distal electrode.

In a preferred embodiment of the invention the device is capable of switching the polarity of said intermediate electrodes. This is advantageous as contractions seems to propagate within a segment from one electrode to the other, the direction of propagation depending on the polarity of the electrodes. Thus the direction of propagation of contractions within one segment should preferably coincide with the direction corresponding to the consecutive order of stimulation sessions in a stimulation sequence.

In order to switch the polarity of intermediate electrodes, the control unit may comprise a switchboard for switching the polarity of the intermediate electrodes.

In a preferred embodiment of the invention, the stimulation session comprises a number of electric pulses and a number of pulse intervals between said electric pulses, the electrode receiving no appreciable signal from the control unit during the pulse intervals. In the pulse intervals the electrodes are essentially inactive except for a passive discharge. Usually a difference in potential will build up in the tissue during a pulse. The pulse intervals allow a passive discharge, whereby current may flow in a direction opposite to the direction of current flow during the pulse. In a few milliseconds this passive discharge result in a reduction or elimi- nation of said difference in potential within the tissue. Allowing the discharge by means of the pulse intervals has the advantage that the need for accurately bal- ancing the current e.g. by application of very uniform pulses of alternating polarity, is eliminated.

The stimulation session may comprise only one pulse. However the stimulation session typically comprises at least two pulses, e.g. a number of pulses in the range of 10-100. The pulses may be rectangular. However other pulse shapes may also be used. The pulses of a stimulation session may be of the same polarity. The pulses of a stimulation session may further be of the same duration and/or the same amplitude and/or of the same pulse shape. Typically the pulses of a stimulation session are essentially identical. The pulse intervals between pulses comprised in a stimulation session may also be of essentially the same duration.

The pulse duration may be 0.01 to 30 ms, such as 0.1 to 10 ms, such as 0.3 to 5 ms. In one embodiment of the invention the pulse duration is around 3 ms. A short pulse duration is desirable in order to avoid inducing irreversible changes in the tissue.

In one embodiment of the invention the duration of each pulse interval is at least 20 ms, such as at least 25 ms, such as at least 50 ms, such as between 25 and 500 ms, such as 50-200 ms, such as in the order of 100 ms. It is advantageous to provide a stimulation session in which the duration of the pulse interval is relatively long as this reduces the exposure of the tissue to charges and will allow the tissue to recover between the electric pulses, e.g. by restoring the original ion distribution.

In a preferred embodiment of the invention, the duration of each pulse interval is at least twice the duration of the previous pulse. It may be advantageous to provide a stimulation session in which the duration of each pulse interval is at least three times the duration of the previous pulse, such as at least five times, at least ten times or even at least thirty times the duration of the previous pulse. The control unit may comprise a current source for delivering the current for the stimulation sessions. The current amplitude of the pulse may be 2 to 50 mA, such as 5 to 30 mA, such as 10-20 mA, such as in the order of 15 mA. For some applications the current amplitude may be around 5 mA.

A device according to the present invention may be adapted to perform a stimulation sequence comprising at least two stimulation sessions, such as at least three stimulation sessions, or even at least five stimulation sessions. In one embodiment of the invention each electrode pair perform one stimulation session in the stimulation sequence. A serial stimulation sequence may be obtained by performing the stimulation sessions in consecutive order corresponding to the consecutive order of serially arranged electrode pairs. The stimulation sequence may be repeated a number of times in order to provide the desired result, e.g. faecal discharge.

In a preferred embodiment of the invention the device is adapted to perform a stimulation sequence comprising at least two stimulation sessions, the timing of the stimulation sessions being such that within the stimulation sequence one stimulation session starts immediately after the termination of the previous stimu- lation session, only one session being performed at a time.

A second aspect of the invention relates to a device for inducing serial contractions in a section of the gastrointestinal tract, said section of the gastrointestinal tract, defining a lumen and comprising a proximal end portion with a proximal opening, a distal end portion with a distal opening, and an intermediate portion extending between said proximal end portion and said distal end portion, said device comprising • a set of electrodes, each electrode comprising at least one contact, • a contol unit for creating a potential difference between a contact of at least one first electrode, and a contact of at least one second electrode, said first electrode and said second electrode constituting an electrode pair for performing a stimulation session, said set of electrodes constituting at least three electrode pairs, said electrode pairs being adapted to be arranged serially in the longitudinal direction of the gastrointestinal tract, said device being capable of delivering a serial stimulation sequence comprising at least two stimulation sessions, each stimulation session involving one electrode pair, wherein a stimulation session comprises a number of electric pulses and a number of pulse intervals between said electric pulses.

The electrode pairs may be adapted to be arranged serially along the gastrointestinal tract, a proximal pair being placed in the proximal end portion, a distal pair being placed in the distal end portion and at least one intermediate pair being placed in the intermediate portion of the section of the gastrointestinal tract. The electrode pairs may be arranged so that current flow essentially in the longitudinal direction of the gastrointestinal tract. It may be advantageous to arrange the electrodes such that current flow in the longitudinal direction of the gastrointesti- nal tract as contractions induced in a stimulation session seems to propagate from one electrode to the other of the pair of electrodes performing a stimulation session, thus enhancing the propulsive movement. However, the electrode pairs may alternatively be arranged so that current flow essentially transverse relative to the longitudinal direction of the gastrointestinal tract.

The serial stimulation sequence comprises stimulating consecutive segments of the section of the gastrointestinal tract. A device according to the invention may be operated to perform a serial stimulation sequence comprising a number of stimulation sessions, each stimulation session involving one pair of electrodes, the order of stimulation sessions corresponding to the order of electrodes pairs.

Any feature or parameter related to the stimulation session as previously described may also be a feature of a device according to the second aspect of the invention. The timing of the stimulation sessions may be such that within the stimulation sequence one stimulation session starts immediately after the termination of the previous stimulation session, only one session being performed at a time. In one embodiment of the invention the set of electrodes comprises a distal electrode, a proximal electrode and at least one intermediate electrode, each of said intermediate electrodes being comprised in two electrode pairs. The device may further have any feature previously described for a device according to the first aspect of the invention.

In a preferred embodiment of the invention, at least a part of a device according to the first or the second aspect of the invention, is implantable. The implantable part of the device may at least comprise the electrodes. The electrodes are preferably implanted in the serosa. The control unit may be an external member. In this case, the electrode leads could be percutaneously brought outside the body and connected to the external control unit. Alternatively the implantable part of the device may also comprise at least a part of the control unit. The control unit may be operated by an external control member, e.g. via an inductive link.

A third aspect of the invention relates to a method of inducing serial contractions in a section of the gastrointestinal tract, the method comprising applying at least one serial stimulation sequence to said section of the gastrointestinal tract, said stimulation sequence comprising at least one stimulation session, said stimulation session comprising a number of electric pulses and a number of pulse intervals between said electric pulses.

The serial stimulation sequence and the stimulation session applied in a method according to the third aspect of the invention may have any features previously described in relation to the first and second aspect of the invention. In particular the serial stimulation sequence may be produced by a device according to the first or second aspect of the invention.

A fourth aspect of the invention relates to a kit comprising - a set of electrodes capable of generating electric pulses when controlled by a control unit, and - instructions for using the electrodes in a method according to the third aspect of the invention.

In one embodiment of the invention the kit further comprises a package holding the set of electrodes and the instructions.

The electrodes may be disposable in the sense that they are used for one patient only, being implanted in said patient only one time.

A fifth aspect of the invention relates to a kit comprising - a control unit comprising a pulse generator operable for being connected to at least two electrodes for stimulation of intestinal smooth muscle, and - instructions for using the control unit in a method according to the third aspect of the invention.

In one embodiment of the invention the kit further comprises a package holding the control unit and the instructions.

The control unit may be disposable in the sense that is used for one patient only, being implanted in said patient only one time.

A sixth aspect of the invention relates to a kit comprising - a set of electrodes capable of generating electric pulses when controlled by a control unit, - a control unit comprising a pulse generator operable for being connected to at least two electrodes for stimulation of intestinal smooth muscle, - instructions for using the electrodes and/or the control unit in a method according to the third aspect of the invention.

In one embodiment of the invention the kit further comprises a package holding the set of electrodes, the control unit and the instructions. The control unit and/or the set of electrodes may be disposable in the sense that is used for one patient only, being implanted in said patient only one time.

A seventh aspect of the invention relates to the use of at least two electrodes for the preparation of an implantable, disposable medical device for producing peristaltic movement of intestinal smooth muscle by a method according to the third aspect of the invention.

An eighth aspect of the invention relates to the use of a control unit comprising a pulse generator for the preparation of an implantable, disposable medical device for producing peristaltic movement of intestinal smooth muscle by a method a method according to the third aspect of the invention.

A ninth aspect of the invention relates to the use of at least two electrodes and a control unit comprising a pulse generator for the preparation of an implantable, disposable medical device for producing peristaltic movement of intestinal smooth muscle by a method according to the third aspect of the invention.

Description of the Preferred Embodiments The invention is now explained morein detail with reference to the drawings showing preferred embodiments of the invention.

Referring to figure 1 , the stimulation system comprises a control unit 1 connected by the leads 41-4n to an array of electrodes 51-5n located serially along an intes- tine portion 7. The leads 4 are flexible wires coated with biocompatible isolator, such as Teflon coated multistranded stainless steel wires, 0.3 mm in diameter (AS634 Cooner Wire Inc. Chatwoth, CA). Electrodes 51-5n may be formed by removing the insulation at the tip of the leads. The tip of a wire 4 is deinsulated at 3 locations 611, 612, and 613. These locations represent the contacts of the electrode. Each contact has a length of 10 mm. Between the contacts, the Teflon insulation is preserved. Each of the 2 insulated portions 621 and 622 has a length of 20 mm. The electrodes are adapted to be placed intramurally, in oblique direction relative to the longitudinal axes of the intestine (the angle α is about 45°).

Fig. 2. b. shows an electrode attached to the colon wall. The contacts of the elec- trade are located under the colon serosa 8, whereas the insulated portions remain outside the colon. In order to allow dilatation of the gut during displacement of intraluminal content, the insulated portions can be longer than 20 mm, and coil- shaped. The knots 9 serve to secure the electrode to the colon serosa. Corroborating the images a) and b), one can understand that the electrode is semi- spirally placed around and in the intestine wall. The semi-spiral positioning of the electrode reduces the mechanical stress exerted on the wire during longitudinal and circular contractions. Thus, the risk of electrode breaking is minimized. The solution was tested with good results in acute experiments on the descending colon of the pig. However, stimulation using electrodes placed perpendicular to the longitudinal axis of the colon (angle β in Fig. 2. c. has about 90°) is also possible, and was tested with similar good results in acute experiments on rats and P'gs-

Two neighboring electrodes located at a distance d between one to another de- limitate a ring-shaped segment s. Experiments with colon stimulation in pigs showed that a suitable distance d between 2 neighboring electrodes is of about 20 mm. In a stimulation system used to induce colon emptying in colostomy patients, the first electrode 51 should be placed orally to the hepatic flexure and the last electrode 5π in the proximity of the stoma. Considering that a stoma can be performed at any point on the transverse or descending colon, the total number of the electrodes will depend on the distance d and on the length of the colon subjected to stimulation.

The control unit 1 comprises a current source 2 coupled to a switchboard 3. The current source generates charge balanced rectangular pulses of controlled amplitude, duration and frequency. The switchboard switches distribution of current pulses to consecutive electrode pairs in the array, simultaneously changing the polarity of the electrodes shared by consecutive electrode pairs.

Fig. 3 shows a stimulation sequence constituted by stimulation sessions S1-Sn sequentially applied to the colon segments s1-sn through consecutive electrode pairs consisting of the electrodes 51 -5n. The first stimulation session uses electrodes 51 and 52, and induces contraction in the stimulated segment s1. During stimulation session S1 , the electrode 51 is the cathode and the electrode 52 is the anode. After a stimulation time of 5 to 15 s, distribution of the current pulses is switched to the second pair consisting of electrodes 52 and 53, and stimulation session S2 starts. Simultaneously, the polarity of the electrode 52 is switched from positive (anode) to negative (cathode). In response to stimulation session S2, contraction in the stimulated segment s2 follows. Stimulation continues until the last segment sn is stimulated in stimulation session Sn. Hence, two adjacent electrode pairs consist of 3 electrodes. The middle electrode is shared by the 2 pairs and has a variable polarity. Thus, except for the first electrode 51 and the last electrode 5n, all of the electrodes in the array have a variable polarity.

All of the stimulation sessions have the same duration. The termination of one stimulation session coincides with the start of next stimulation session. Thus, no time delay between 2 consecutive stimulation sessions occurs. The consecutive contractions of adjacent intestine segments result in a continuous contraction wave.

Fig 4 shows a part of a stimulation session comprising rectangular pulses of a pulse amplitude A, a pulse of pulse duration PD and a pulse interval of duration PI. One pulse and one pulse interval constitute a pulse cycle of duration PC.

Claims

1. A device for inducing serial contractions in a section of the gastrointestinal tract, said section of the gastrointestinal tract, defining a lumen and comprising a proximal end portion with a proximal opening, a distal end portion with a distal opening, and an intermediate portion extending between said proximal end portion and said distal end portion, said device comprising • a set of electrodes comprising a distal electrode adapted to be placed in said distal end portion, a proximal electrode adapted to be placed in said proximal end portion and at least one intermediate electrode adapted to be placed in said intermediate portion, each of said electrodes comprising at least one contact, • a contol unit for creating a potential difference between a contact of at least one first electrode, and a contact of at least one second electrode, said first electrode and said second electrode constituting an electrode pair for performing a stimulation session, wherein each intermediate electrode is comprised in two electrode pairs.

2. A device according to claim 1, said device being adapted to switch the polarity of said intermediate electrodes.

3. A device according to any of the preceding claims, wherein at least one electrode comprises two or more contacts.

4. A device according to claim 3, wherein said contacts are elongated, said contacts being implantable such that the direction of elongation is oblique relative to the longitudinal direction of the gastrointestinal tract at the implantation site.

5. A device according to any of the preceding claims, wherein said stimulation session comprises a number of electric pulses and a number of pulse intervals between said electric pulses.

6. A device according to claim 5, wherein the duration of each pulse interval is at least 20 ms.

7. A device according to any of claims 5-6, wherein the duration of each pulse interval is at least twice the duration of the previous pulse.

8. A device according to any of the preceding claims, said device being adapted to perform a stimulation sequence comprising at least two stimulation sessions, the timing of the stimulation sessions being such that within the stimulation se- quence one stimulation session starts immediately after the termination of the previous stimulation session, only one session being performed at a time.

9. A device for inducing serial contractions in a section of the gastrointestinal tract, said section of the gastrointestinal tract, defining a lumen and comprising a proximal end portion with a proximal opening, a distal end portion with a distal opening, and an intermediate portion extending between said proximal end portion and said distal end portion, said device comprising • a set of electrodes, each electrode comprising at least one contact, • a contol unit for creating a potential difference between a contact of at " least one first electrode, and a contact of at least one second electrode, said first electrode and said second electrode constituting an electrode pair for performing a stimulation session, said set of electrodes constituting at least three electrode pairs, said electrode pairs being adapted to be arranged serially along said longitudinal axis, and said device being capable of delivering a serial stimulation sequence comprising at least three stimulation sessions, each stimulation session involving one electrode pair, wherein a stimulation session comprises a number of electric pulses and a number of pulse intervals between said electric pulses.

10. A device according to claim 9, wherein the duration of each pulse interval is at least 20 ms.

11. A device according to any of claims 9 - 10, wherein the duration of each pulse interval is at least twice the duration of the previous pulse.

12. A device according to any of claims 9 - 11, wherein the timing of the stimula- tion sessions is such that within the stimulation sequence one stimulation session starts immediately after the termination of the previous stimulation session, only one session being performed at a time.

13. A device according to any of the claims 9 - 12, wherein the set of electrodes comprises a distal electrode, a proximal electrode and at least one intermediate electrode, each of said intermediate electrodes being comprised in two electrode pairs.

14. A device according to any of the claims 9 -13, said device being adapted to switch the polarity of said intermediate electrodes.

15. A device according to any of the claims 9 - 14, wherein at least one electrode comprises two or more contacts.

16. A device according to any of claims 9 - 15, wherein" said contacts are elongated, said contacts being implantable such that the direction of elongation is oblique relative to the longitudinal direction of the gastrointestinal tract at the implantation site.

17. A device according to any of the preceding claims, wherein said section of the gastrointestinal tract comprises at least a part of colon.

18. A device according to any of the preceding claims, wherein said section of the gastrointestinal tract comprises at least a part of a colostomy.

19. A method of inducing serial contractions in a natural or artificial section of the gastrointestinal tract, the method comprising applying at least one serial stimula- tion sequence to said section of the gastrointestinal tract, said stimulation sequence comprising at least one stimulation session, said stimulation session comprising a number of electric pulses and a number of pulse intervals between said electric pulses.

20. The method according to claim 1 , wherein the duration of each pulse interval is at least 20 ms.

21. A method according to any of claims 19 - 20, wherein the duration of each pulse interval is at least twice the duration of the previous pulse.

22. A method according to any of claims 19 - 21, wherein the serial stimulation sequence comprising at least two stimulation sessions, the timing of the stimulation sessions being such that within the stimulation sequence one stimulation session starts immediately after the termination of the previous stimulation session, only one session being performed at a time.

23. The method according to any of claims 19 - 22, wherein the serial stimulation sequence is produced by a device according to any of claims 1 - 18.

24. A kit comprising - a set of electrodes capable of generating electric pulses when controlled by a control unit, and - instructions for using the electrodes in a method according to any one of claims 19-23.

25. A kit according to daim 24, further comprising a package holding the set of electrodes and the instructions.

26. A kit according to claims 24 or 25, wherein said set of electrodes is disposable.

27. A kit comprising - a control unit comprising a pulse generator operable for being connected to at least two electrodes for stimulation of intestinal smooth muscle, and - instructions for using the control unit in a method according to any one of claims 19-23.

28. A kit according to daim 27, further comprising a package holding the control unit and the instructions.

29. A kit according to daims 27 or 28, wherein said control unit is disposable.

30. A kit comprising - a set of electrodes capable of generating electric pulses when controlled by a control unit, - a control unit comprising a pulse generator operable for being connected to at least two electrodes for stimulation of intestinal smooth muscle, - instructions for using the electrodes and/or the control unit in a method according to any one of claims 19-23.

31. A kit according to daim 30, further comprising a package holding the set of electrodes, the control unit and the instructions.

32. A kit according to claim 30 or 31, wherein the set of electrodes and/or the control unit is disposable.

33. Use of at least two electrodes for the preparation of an implantable, disposable medical device for producing peristaltic movement of intestinal smooth mus- de by a method according to any of claims 19-23.

34. Use of a control unit comprising a pulse generator for the preparation of an implantable, disposable medical device for producing peristaltic movement of intestinal smooth muscle by a method according to any of claims 19-23.

35. Use of at least two electrodes and a control unit comprising a pulse generator for the preparation of an implantable, disposable medical device for producing peristaltic movement of intestinal smooth muscle by a method according to any of daims 19-23.