EP0784447A1

EP0784447A1 - Device for measuring simultaneously the tissue blood flow rate and the extra-cellular liquid composition

Info

Publication number: EP0784447A1
Application number: EP95934184A
Authority: EP
Inventors: Jean-Pierre Villemot; Paul-Michel Mertes; Yves Jaboin; Jean-Pierre Carteaux; Georges Pinelli; Thierry Hubert
Original assignee: Universite Henri Poincare Nancy I
Current assignee: Universite Henri Poincare Nancy I
Priority date: 1994-10-06
Filing date: 1995-10-06
Publication date: 1997-07-23
Also published as: FR2725356A1; WO1996010948A1; FR2725356B1; AU3657195A

Abstract

The device for analysing the composition and the perfusion rate of an interstitial liquid comprises a coupled probe comprising an external sleeve (110); an exchange membrane (160), particularly for microdialysis and which is situated at the distal end of said coupled probe, an internal conduit (124; 134, 170) which can be connected at its proximal end to a supply source for supplying a perfusate liquid, particularly a dialysis liquid, means (120, 130) for measuring the interstitial liquid perfusion flow rate, introduction means (400) providing for the protection of the distal end of said probe.

Description

DEVICE FOR JOINT MEASUREMENT OF BLOOD TISSUE FLOW AND COMPOSITION OF EXTRA-CELLULAR LIQUID

The invention relates to a device suitable for the dynamic study or modification of the composition of the intercellular fluid by simultaneous analysis and at the same site of the composition of the extra cellular fluid, using a measurement of the type and the concentration of molecules exchanged by microdialysis of the interstitial fluid, and of the nature of the circulating regime, using a measurement of tissue perfusion. The invention also relates to a device for measuring the infusion rate as well as a device for analyzing the composition of the interstitial fluid.

Knowledge and modification of the composition of the interstitial fluid, a place of exchange between cells and between the cell and the blood system, results from the biological assay of the compounds present in the extra cellular fluid collected in vivo by microdialysis. This composition is strongly influenced by the intensity of extra vascular liquid exchanges which depends on the importance of the tissue perfusion rate. Microdialysis is a method of ultrafiltration of interstitial fluid through a permeable exchange membrane, placed between the extra cellular fluid and a fluid of known composition. However, knowing the change in the composition of the interstitial fluid can only be truly effective if cell perfusion rate data are available. With the device of the present invention, the combination of microdialysis and measurement of tissue flow at the same site can be used for determining and interpreting the concentration of the intercellular compounds studied.

The hydrogen clearance technique allows the measurement of the cell perfusion rate and is the subject of sustained medical research with the aim of improving the concept sufficiently to allow more extensive use. Because of the low traumatic nature, the simplicity of the implantation and the explantation of the probe that it implements, on the one hand, and because of its non-contaminating nature which allows an unlimited number of measurements, on the other hand, this technique constitutes a privileged medical tool.

Hydrogen is a gas usually absent from the body. Three modes of hydrogen administration are possible. The very low minimum ignition energy of hydrogen gas makes it inconceivable to use the inhalation of a mixture of hydrogen in human clinics, but remains usable in experiments. The importance of the total volume which results from repeated intravenous injections is likely to disturb the hemodynamic balance of the patient and makes the use of this technique inconceivable in human clinic and experimental in small animals. It has been shown that it is possible to generate hydrogen locally by the redox of the water contained in the tissues. This method was tested by Stossek (Stossek, 1971). The method described by Stossek uses on the one hand, a current-voltage amplifier of the measurements and on the other hand, a current generator. Fully independent, each of these modules operates in parallel from a different pair of electrodes.

Microdialysis has been successfully applied to the study of the kinetics of release of different neurotransmitters in different regions of the brain, in the study of the metabolism of adipose tissue at rest and at exertion, as well as in the field of cerebral ischemia in humans.

The perfusion liquid, of known hydro-electrolytic composition, close to that of the interstitial liquid studied, infuses the probe at a constant speed. He infuses a dialysis membrane, previously introduced into the tissue in question. Substances present in the interstitial fluid and absent from the perfusate will be able to cross the dialysis membrane and come to enrich the perfusion liquid. At the exit of the probe is thus collected a liquid called “dialysate”, capable of being analyzed.

The choice of pore size makes it possible to vary the cut-off thresholds and therefore to obtain a selective exchange of molecules previously determined. This choice also makes it possible to avoid the passage through the dialysate liquid of enzymes capable of degrading the molecules studied. Indeed, these enzymes are usually of a molecular weight higher than the chosen cutoff threshold. The size of the exchange surface and the infusion rate of the infusion liquid determine the efficiency of the exchange. This yield can be assessed in vitro using solutions of known concentration of the substance studied, or a control solution.

Microdialysis and hydrogen clearance techniques have been used in humans in various organs but in isolation.

The coupling of the two techniques in a single flexible probe, easily implantable and usable in humans as in animals is desirable. Indeed, this coupling could allow a simultaneous appreciation and at the same site of the variations of concentration of a substance in the interstitial fluid and of the perfusion rate of the tissue, flow rate which partly conditions the exchanges (supply or evacuation) between interstitium and sector vascular.

The present invention relates to a device for analyzing the composition and infusion rate of an interstitial fluid. This device comprises a coupled probe comprising an external sheath, an exchange membrane, an internal pipe, means for measuring the perfusion rate of the interstitial liquid and means for introducing the probe in situ.

The exchange membrane, in particular of microdialysis, is located at the distal (patient) end of the coupled probe. At least one part of its outer surface can be brought into contact with the interstitial fluid in situ.

The internal pipe can be connected at its proximal end to a source of supply of perfusate liquid, in particular a dialysis liquid. This pipe allows the circulation of the perfusate liquid in the coupled probe and the contacting of the perfusate liquid with the interior surface of the exchange membrane so as to perfuse the membrane and thus allow certain substances present in the interstitial liquid or in the liquid perfusate to cross the membrane thus modifying the composition of the perfusate liquid which can then be collected as modified perfusate liquid, and analyzed. The external pipe allows the collection of the modified perfusate liquid or enriched liquid without the enriched liquid coming into contact with the perfusate liquid.

In particular, the internal pipe is formed by a double tubular pipe at the end of which the exchange membrane is fixed.

More particularly, the internal pipe comprises in its center a perfusate capillary forming a circuit for collecting the enriched liquid, the inlet circuit for the perfusate liquid being defined by the external surface of the perfusate capillary and the wall of the internal pipe. At least part of the means for measuring the perfusion rate of the interstitial liquid is located outside the internal pipe, in particular at the distal end of the coupled probe, so as to be in direct contact with the interstitial liquid.

In particular, means for measuring the perfusion rate of the interstitial liquid comprise a probe for measuring the perfusion rate by measuring the elimination of hydrogen at the measurement site or else a probe allowing the measurement of the partial oxygen pressure in the interstitial fluid analyzed.

The probe for measuring the infusion rate by measuring the elimination of hydrogen at the measurement site may include in particular: - a hydrogen clearance measurement module comprising a polarized measurement electrode which can be connected to an oxidation-reduction current amplifier. The measuring electrode is located at the distal end of the mixed probe and can be introduced to the site for measuring the infusion rate so that the hydrogen present at the measuring site can come into contact with the electrode. measures and undergoes oxidation, the current of which can be measured by a current amplifier; and

- a reference electrode which can be connected to the measurement module.

More particularly, the probe for measuring the infusion rate by measuring the elimination of hydrogen at the measurement site also comprises a hydrogen genesis module comprising a genesis electrode which can be connected to a current generator. This genesis electrode is located at the distal end of said coupled probe and can be introduced into the site for measuring the infusion rate to continuously release therein a current which can be varied so as to be sufficient to generate an electrochemical reaction generating l hydrogen at the infusion rate measurement site. Other techniques for measuring the tissue perfusion rate can also be associated with microdialysis in order to perform the joint analysis and at the same site of the composition of the intercellular fluid and of the tissue flow.

Among the techniques for measuring the tissue perfusion rate, there may be mentioned, for example, the laser-doppler techniques and the techniques for measuring the flow rate by heat exchange.

Thus, a beam of laser light brought to the measurement area by an optical fiber, diffuses and is the object of absorption by the tissue studied. The cells in motion in this area reflect light and modify the wavelength (doppler effect). The amplitude and the variations of frequency undergone by the initial wavelength, are proportional to the number and speed of circulating cells. This information collected by a so-called receiving fiber can be converted into an analyzable electronic signal, thus making it possible to assess tissue flow. The measurements are expressed in a relative unit proportional to the tissue perfusion. The proportionality factor being specific to the tissue studied.

Another possible method is represented by the measurement of cell tissue by heat exchange. The general principle resides in the genesis of a known quantity of heat in the tissues studied by means of genesis of heat, for example by means of a resistance placed at the measurement site and by the study of dissipation. of this volume of heat within the tissue. This technique uses the general principle of diluting an indicator where the fate of a known quantity of the indicator is analyzed by a proximity sensor. The measurements performed depend on the tissue perfusion and the characteristics of the tissue studied. A computer is used to measure the area under the heat-diffusion curve by integration relative to the baseline (initial temperature of the tissue) and thus to extrapolate the tissue perfusion rate. This type of measurement can be performed intermittently or continuously. In the case of local production of hydrogen by electrolysis of the water present in the interstitial liquid, the device of the invention can also include a switching interface separating the hydrogen genesis module and the clearance module. hydrogen. This interface allows alternating the genesis of hydrogen and the measurement of hydrogen clearance. It is preferably possible to include a calculation module making it possible to transform in real time the signal of the measurement of hydrogen clearance measured into digital information of infusion rate.

The invention also relates to a device for measuring the infusion rate by measuring the elimination of hydrogen at the site of measurement of the infusion rate. The device includes a hydrogen clearance probe comprising

. a hydrogen clearance measurement module,

. a reference electrode, as well as. introduction means allowing the protection of the distal end of said clearance probe during its release in situ. These elements correspond to the elements described above.

The clearance probe may also include a hydrogen genesis module, a switching interface, as well as a calculation module making it possible to transform the hydrogen clearance measurement signal in real time into digital information on the infusion rate. .

The invention also relates to a device for analyzing the composition of the interstitial fluid, said device including an analysis probe comprising:

- an outer sheath,

an exchange membrane, in particular a microdialysis membrane, situated at the distal end of the analysis probe and of which at least part of the external surface can be brought into contact with the interstitial liquid in situ;

- internal management as defined above, as well as

- introduction means allowing the protection of the distal end of the analysis probe during its release in situ. The invention also relates to a method for measuring the infusion rate by measuring the elimination of the hydrogen present at the site for measuring the infusion rate. The process includes:

- the introduction to the measurement site of a polarized electrode for measuring the hydrogen clearance; - the introduction at a site other than the measurement site of a reference electrode which can be connected to the measurement electrode; - the measurement at the measuring electrode of the current generated by the oxidation of the hydrogen produced during the contact of this hydrogen with the measuring electrode;

- processing of hydrogen oxidation measurements at the measurement electrode by digital processing so as to transform the measured signal in real time into digital information of the infusion rate.

More particularly, the digital processing of the hydrogen oxidation measurements at the measurement electrode is carried out by a differential, integral or neuromimetic method and the hydrogen present at the measurement site is generated by a hydrogen genesis electrode inserted. at the measurement site by means of an electric current produced by the electrode sufficient to generate an electrochemical reaction producing hydrogen at the site for measuring the infusion rate. The clearance clearance with hydrogen-microdialysis, in addition to allowing a finer local analysis since the quantitative measurement of hydrogen clearance is carried out at the same place as the qualitative analysis of the interstitial fluid by microdialysis, also makes it possible to associate the strengths of the two techniques and of improving the interpretation of the information obtained by means of a simultaneous appreciation of the variations in concentration of a substance in the interstitial fluid and of the rate of perfusion of the tissue, a rate which partly conditions the exchanges (supply or evacuation) between interstitial and vascular sector.

One of the major difficulties which has been resolved by the inventors in the context of the present invention lies in the implementation of a measurement / genesis switching interface of the hydrogen clearance probe. Indeed, a ratio of the order of 100 to 10,000 distinguishes the amplitude of the measurement current and that of the genesis current. The structure of the mixed probe of the present invention is the result of an innovative way of managing the use of the microcurrents necessary for the operation of a hydrogen clearance probe. while allowing its coupling to a microdialysis system of the interstitial fluid.

The rest of the presentation will be made with reference to the attached figures, and the captions of which follow: - Figure 1: schematic representation of the hydrogen microdialysis-clearance analysis device of the invention.

FIG. 2A: longitudinal section of a first preferred embodiment of a mixed probe of the invention,

FIG. 2B: cross section on line II-A of the preferred embodiment illustrated in FIG. 2A,

FIG. 3A: longitudinal section of a second preferred embodiment of a mixed probe of the present invention,

FIG. 3B: cross section through line III-A of the preferred embodiment illustrated in FIG. 3A, FIG. 4A: longitudinal section of a third preferred embodiment of a mixed probe of the present invention,

FIG. 4B: cross section of line IV-A of the preferred embodiment illustrated in FIG. 4A,

- Figure 5: schematic representation of the architecture of the system for measuring blood perfusion by hydrogen clearance.

A in “hydrogen genesis” mode B in “hydrogen generated measurement” mode

- Figures 6A, 6B: preferred schematic representation of the introducer. Hydrogen-microdialysis mixed-clearance probe

Whatever the field of application (cell metabolism, intercellular communication, pharmacology), the quality of the analysis of the results concerning the composition of the extracellular fluid depends on the ability to evaluate simultaneously and at the same site the variations in tissue perfusion. , which constitutes an important vector of the intake or evacuation of substances present in the extra cellular fluid. The device for analyzing the composition and the infusion rate of an interstitial liquid including a coupled measurement probe which is the subject of the present invention meets this need. Microdialysis of interstitial fluid is a technique allowing the collection in vivo, for analysis, of the compounds present in the extra cellular fluid. Its operation is based on the use of a probe operating according to a principle of conventional dialysis, similar to that adopted in human dialysis. The perfusion liquid, called perfusate, is of known hydroelectrolytic and biological composition. It crosses the probe at a constant flow. The perfusate infuses a dialysis membrane previously introduced into the tissue in question. The dialysis membrane is permeable for both directions of exchange. The liquid collected at the other end of the membrane, called dialysate, is enriched with molecules present in the interstitium but absent from the perfusate and depleted of the molecules present in the perfusate but absent by the interstitium. A biological assay of the dialysate gives its composition. The comparison of the composition of the perfusate and that of the dialysate provides information on the nature of the transmembrane exchanges. The efficiency coefficient of the probe makes it possible to interpret these exchanges qualitatively, and thus to estimate the interstitial composition.

The composition of the perfusate is close to that of the interstitial fluid studied, so as not to cause osmotic disturbance. The size of the membrane is small enough not to be traumatic and not to cause mechanical disturbance. The choice of the size of the pores, that is to say the cut-off threshold of the membrane, allows a selective exchange of the molecules. The choice of membranes with a low cut-off threshold makes it possible to avoid the passage into the dialysate of enzymes capable of degrading the molecules collected. For a type of given membrane, the efficiency of transmembrane exchanges is a function of the perfusion rate and the exchange surface of the probe. Referring now to FIG. 1, a schematic illustration of a preferred embodiment of the device for analyzing the composition and the infusion rate of an interstitial fluid of the present invention, represented generally by the reference numeral 300 comprises a coupled probe 310 of which various preferred embodiments will be described in detail below. The coupled probe 310 is connected via a conduit 321 to an infusion rate analysis device 320 comprising a communication interface 322, a current generator 324, a current amplifier 326 and a module for calculation of the infusion rate in real time 328.

The device 300 also includes an infusion line 312 connecting the coupled probe 310 to an infusion system 314 via a connection system which may be of the LUER type

LOCK. The device 300 also includes a conduit 330 which can connect the coupled probe 310 either to a refrigerated collection system 332 or to a biological dosage system 334, the collection and dosage elements as well as the perfusion system 314 not necessarily forming part of the device 300. The same applies to the device for measuring the perfusion rate of the interstitial liquid 320 which can subsequently be attached to the device 300.

One of the important features of the device for analyzing the composition and infusion rate of an interstitial liquid lies in the structural adjustments made so as to reduce the size of this device or mixed probe as much as possible. These structural arrangements of the various elements of the device of the invention, in particular the concentric assembly, make it possible to minimize the trauma caused by the in situ implantation of a probe. For example, analysis of the composition of an interstitial fluid by microdialysis can only work effectively if the trauma to the site of analysis by implanting a probe is minimal. However, the simple juxtaposition of a microdialysis probe and a probe for analyzing the perfusion rate of interstitial fluid is traumatic. The inventors have made it possible to eliminate this trauma by developing a mixed probe of very small size resulting from specific structural arrangements.

In order to ensure that the mixed probe of the invention functions effectively without there being any harmful effect resulting from the combination of a microdialysis probe and means for measuring the infusion rate, a certain number of parameters must be observed. In the situation where the means for measuring the perfusion rate of the interstitial liquid comprise a probe for measuring the infusion rate by hydrogen genesis and measuring the elimination of the hydrogen generated at the measurement site, it is observed that the Generation of hydrogen in the microdialysis stream seems to pose certain problems. In addition, it is important that the genesis of hydrogen and the measurement of the oxidation of the hydrogen generated are not carried out at the same time. The extreme proximity of the genesis and measurement electrodes produces phenomena of current interference which seem to modify the results. On the other hand, it seems necessary to avoid complete power cuts when measuring the infusion rate. A low current can be maintained at the genesis electrode without the latter considerably interfering with the measurement of the current generated by the oxidation of the hydrogen produced. In addition, it seems difficult to predict the hydrogen enrichment of the microdialysis liquid.

The characteristics of the coupled probe of the invention are determined according to the intended use. Indeed, the probe can be used in various modes of application such as implantations: • percutaneous (fat, brain),

• endoscopic (digestive tract) • endomuscular,

• direct approach to the organ (heart, open chest)

or for physiological or pharmacological monitoring of the administration of substances in situ. Three preferred embodiments of the coupled probe of the invention are described below and some possible variations of the main structural characteristics are also stated.

Referring now to Figure 2A, the coupled probe, illustrated generally by reference 100, includes an outer sheath 110, a hydrogen clearance measurement electrode 120, a hydrogen genesis electrode 130, a insulating film 140, a dialysate tube 150, a microdialysis membrane 160, a perfusate capillary 170 as well as a plug 180. The outer sheath 110 is used to protect the metal wires for connection (not shown) to the clearance measurement electrodes d hydrogen 120 and hydrogen genesis 130. The outer sheath 110 also protects the dialysate collection conduit (not shown) and provides connection to the injection system and delivery of the infusion set (not shown).

The hydrogen clearance electrode 120 includes a platinum electrode 122 partially covered with a Teflon sheath 124. The Teflon sheath 124 separates the platinum electrode 122 from the outer sheath 110 and from the dialysate tube 150 With regard to the hydrogen genesis electrode 130, its structure is similar to that of the hydrogen clearance electrode 120. In fact, the hydrogen genesis electrode 130 comprises a platinum electrode 132 partially covered with a Teflon sheath 134. The portion of the electrodes 122 and 132 not covered with a Teflon sheath 124 or 134 is in direct contact with the interstitial liquid when the mixed probe 100 is implanted in a patient. Pre-treatment of measurement and genesis electrodes

In a preferred embodiment of the invention, it seems that better results are obtained when the platinum electrode undergoes additional platinization before being used in genesis or in hydrogen measurement, for example by means of the platinum oxide deposition by electrolysis. For example, the distal end of a teflon-coated platinum wire is stripped, constituting the active part of the electrode. Traces of fatty substances are eliminated by passage through alcoholic potash. In order to improve the sensitivity, the response time and the stability of the electrode, the latter is platinized by electrolysis in a solution of hexachloroplatinic acid at 5% for an exposure time of 1 minute under a current of 5mA. The electrode is then washed and then stabilized by electrolysis in a 0.5 M sulfuric acid solution and saturated with hydrogen for 3 minutes. The electrode is kept protected from all dirt.

Pretreatment of the reference electrode

In another preferred embodiment of the invention, the inventors have found that a pre-treatment of a reference electrode of the Ag-AgCI type (not illustrated) made it possible to obtain more precise results during use. of the probe, the hydrogen clearance perfusion rate probe of the invention, in particular, it seems desirable to cover the electrode with a deposit of silver halide, for example chloride silver through electrolysis processes. For example, the distal end of a Teflon-coated silver wire is stripped, constituting the active part of the electrode. Traces of fatty substances are eliminated by passage through alcoholic potash.

The electrode is covered with a silver chloride deposit by slow electrolysis in a 0.5 M hydrochloric acid solution under a voltage which varies linearly and continuously, first from 0 to 30 volts in 15 seconds then 30 to 9 volts in 15 seconds. This deposit is stabilized by rapid electrolysis in the same 0.5 M hydrochloric acid solution as above under a voltage which varies linearly and continuously, first from 0 to 15 volts in 7.5 seconds then from 15 to 0 vol t in 7.5 seconds. The electrode is then washed and stored away from all dirt.

The microdialysis membrane 160 is located at the patient end of the probe 100. A portion of the outer surface 162 of the microdialysis membrane 160 is exposed so that it can be contacted with the interstitial fluid of a patient. The size of this outer surface portion 162 through which the exchange takes place (dialysis) is determined as a function of the organ studied and of the expected concentration of the desired substance (the exchange yield being conditioned by the surface ). The material of the microdialysis membrane 160 is also to be taken into consideration. It must be biocompatible, have pores of sufficient size to allow the test substance to pass through and not interact with the test substance. The patient end of the microdialysis membrane 160 is closed by a plug 180.

The central part of the mixed probe 100 comprises an inlet duct 190 for the microdialysis liquid defined by the internal wall 152 of the dialysate tube 150 and the internal wall 164 of the microdialysis membrane 160 on the one hand and the external wall 172 of the capillary perfusate 170 on the other hand. A circuit 194 for collecting the dialysis liquid is delimited by the internal wall 174 of the perfusate capillary 170. The insulating film 140 separates the electrodes for measuring hydrogen clearance 120 and for hydrogen genesis 130 from the dialysate tube 150.

As illustrated in FIG. 2B, the various elements constituting the mixed probe 100 are arranged concentrically so as to form an easily implantable assembly. Referring now to FIG. 3A, another preferred embodiment of the mixed probe of the invention, illustrated generally by the reference numeral 200, is presented. In this preferred embodiment, the architecture of the mixed probe 210 is similar to the architecture of the mixed probe 100 illustrated in FIG. 2A except for the fact that the dialysate tube 150 illustrated in FIG. 2A has been eliminated . In the mixed probe 200 illustrated in FIG. 3A, the inlet duct 190 for the dialysis liquid is formed by the Teflon sheaths 124 and 134 of the hydrogen clearance measurement electrodes 120 and 130 and the internal wall 164 of the microdialysis membrane 160 on the one hand and the outer wall 172 of the perfusate capillary 170 on the other hand. A mixed probe 200 of reduced size is therefore obtained, the implantation of which in vivo is easier. As illustrated in FIG. 3B, the elements of the mixed probe 200 are also arranged concentrically. Referring now to FIG. 4A, another preferred embodiment of an even smaller size of the mixed probe of the invention, illustrated generally by the reference 300 is presented. Here, the inlet duct 190 of the dialysis liquid is defined by the internal surface 112 of the protective envelope 110 and the internal wall 164 of the microdialysis membrane 160 on the one hand and the external wall 172 of the dialysate capillary 170 on the other hand. The hydrogen clearance 120 and hydrogen genesis 130 electrodes were placed inside the inlet duct 190. The platinum electrodes 122 and 132 are protected inside the inlet duct 190 by the Teflon sheaths 124 and 134. The platinum electrodes 122 and 132 are only discovered at their patient end which is located outside the inlet duct 190. A plug 180 is located at the patient end of the mixed probe 300. As shown in FIG. 4B, the various elements of the mixed probe 220 are again arranged concentrically. As illustrated above, the central portion of the mixed probe of the invention comprising the dialysis membrane and the Measuring and genesis electrodes can be subject to several modifications linked to the field of application of the technique and to the principle of clinical installation of the probe without however departing from the initial concept of the invention. In this regard, different configurations are possible depending on the expected use of the probe. Generally, these configurations can be classified according to two categories. First, it is possible to modify the central portion of the probe by incorporating into an accessory chamber any part of the probe, more particularly the electrodes for measuring hydrogen clearance and hydrogen genesis, used to determine the blood flow. tissue. Secondly, the very structure of the probe can be modified depending on the final conditions of implantation and use, for example whether it is an endoscopic or endovascular catheter or an intratissular implantation system. The operation of the mixed probe of the invention will now be described with reference to the preferred embodiment illustrated in FIG. 2A. Referring to FIG. 2A, once the probe 100 has been implanted at the tissue site to be analyzed (the reference electrode can be implanted subcutaneously), a virgin perfusion liquid is introduced into the inlet conduit 190 so as to circulate in the direction indicated by the arrow 196. The virgin perfusion liquid therefore comes into contact with the interior surface 164 of the microdialysis membrane 160 which will have the effect of perfusing the microdialysis membrane 160 and allowing certain substances present in the interstitial fluid or in the infusion fluid to pass through the microdialysis membrane 160 and to enrich either the infusion fluid or the interstitial fluid. The infusion fluid may have a composition close to the composition of the intercellular fluid. It is for example a Ringer type liquid capable of being enriched with various substances such as proteins or antioxidants. The virgin infusion liquid injection system is a syringe pump available on the clinic market (not shown). It must be able to inject at very low flow rates, preferably flows of the order of a few μl / min. The syringe and associated infusion extension line are also part of traditional clinical equipment. In the case of surgical implantation, the extension is chosen so as to be long enough to keep the injection system out of the operating field.

Referring again to FIG. 2A, after the infusion liquid has been enriched with substances present in the interstitial fluid following its contact with the microdialysis membrane 160, it is then conveyed towards the outside of the probe 100 by l 'via the collection duct 194 as illustrated by the arrow 198. The enriched perfusion liquid leaving the probe 100 is then collected as dialysate and analyzed. During the infusion of the microdialysis membrane 160, the hydrogen clearance 120 and hydrogen genesis measurement electrodes 130 are alternately activated as described above so as to simultaneously record the tissue blood flow. This allows simultaneous assessment of variations in the concentration of a substance in the interstitial fluid and the rate of tissue perfusion.

It should be noted that additional modifications to the structure and the probe of the invention as well as various applications can be envisaged by those skilled in the art. For example, the hydrogen clearance and hydrogen genesis electrodes can be used for biological assay purposes. One can also consider the use of a gas other than hydrogen to perform the measurement of tissue blood flow. It may be a locally generated gas which requires the use of different electrodes or else a gas generated by inhalation in which case it may be sufficient to use only one electrode for measuring the inhaled or injected gas. . We can also consider the use of the mixed probe of the invention for the subtraction of interstitial liquids or else to couple the elements of the probe used for microdialysis with an optical probe for measuring the flow rate. It is also possible to envisage coupling the probe to systems for constant evaluation of substances present in the interstitial fluid or also to on-line dosing systems for these various substances. All these modifications will be readily apparent to the person skilled in the art.

Introducer description

When placing the probe, the distal end

(active) of the probe is inserted into an introducer which protects it and allows its release in situ. The introducer is then removed so as to release the exchange membrane. Referring to FIGS. 6A and 6B, the introducer 400 consists of:

- A flexible plastic tubular body which can be produced either from a piece 402 or from the glued assembly of a tube 404, and a rod 406; and

- A bevelled needle made of stainless steel 408 and glued to the tubular body 402. The use of an introducer is important given the very small diameter of the probes of the invention. The introducer makes it possible in certain cases to avoid a traumatic incision at the place of implantation of the probe without the latter being damaged during its introduction.

Holder infusion rate measurement device

The invention also relates to a probe making it possible to directly estimate the rate of tissue perfusion by measuring the rate of elimination of a gas, such as hydrogen, from the tissues. The measurement of tissue perfusion by the hydrogen clearance technique is based on the calculation of the kinetics of elimination of hydrogen in the tissues. This calculation is applied to successive measurements of the concentration of hydrogen contained in the tissues.

The preferred method chosen by the inventors for estimating tissue blood flow consists in locally generating hydrogen by redoxing the water contained in the tissues. Alternatively, local saturation of hydrogen is obtained by hydrolysis of the water contained in the tissues, then the tissue concentration of hydrogen after the desaturation time is measured using an anodic oxidation-reduction method. . The use of an original real-time calculation method allows immediate estimation of tissue perfusion. Hydrogen is an inert gas, that is to say, not metabolized by the body. The only vector for eliminating this gas, when it is present in a tissue, is therefore the blood flow which perfuses this tissue. The kinetics of gas desaturation in the tissues is therefore proportional to the tissue blood flow. It has been shown that the proportionality ratio known as the blood-tissue partition coefficient is unitary. Therefore, tissue blood flow is equal to the kinetics of hydrogen desaturation.

On contact with a platinum anode, positively polarized with respect to a reference electrode, for example a silver reference electrode, the hydrogen undergoes electrochemical oxidation, the current of which is proportional to the hydrogen concentration in the vicinity of the anode. If the measurement circuit has a low impedance, the expression of the measured oxidation current is proportional to its physical expression. This proportionality coefficient is the gain of the acquisition chain. The presence of a residual current which would be due to proteins binding to the probe has been shown. Therefore, the current of redox hydrogen is an affine function of its concentration. It therefore follows that the value of the tissue blood flow can be calculated from the signal for measuring the redox current of tissue hydrogen over time. This current is usually a few tens of nano amps.

One of the important characteristics of the hydrogen clearance measuring device of the present invention is the fact that the clearance probe can use the same reference electrode alternately for genesis and then for measuring the gas making it possible to determine the blood flow. This system makes it possible to locally generate hydrogen at the very place where it will be measured, using a simple space-saving probe. The use of a switching interface which will be described in detail below, makes it possible both to protect the measurement module against an overload current, without breaking (electronically) the fabric measurement loop: anode: measurement: reference : tissue and suspend the genesis without breaking the loop fabric: anode: genesis: reference: tissue.

Referring now to Figure 5A, the hydrogen clearance device of the invention, generally represented by reference numeral 10 includes a clearance probe which includes a hydrogen genesis electrode 20 and a measurement electrode of hydrogen clearance 22 independently connected to a switching interface 30. The device 10 may also include a hydrolysis current generator 32 as well as a redox current amplifier 34 connected on the one hand to the interface of communication 30 and on the other hand to a reference electrode 26.

The hydrogen genesis electrode 20 advantageously consists of platinum. The hydrogen clearance measurement electrode 22 is for its part a polarized platinum electrode. As for the reference electrode 36, it is normally an electrode of the Ag-AgCI type. The hydrolysis current generator 32 is advantageously a constant current generator. The electronic architecture of the current generator used in the context of the invention was developed from the application note illustrated in the “Analog device” catalog under the reference LM 369. The modification made to this diagram of the manufacturer is the following: the recommended reference voltage generator has been replaced by a precision component referenced LM336. The hydrolysis current generator 32 therefore makes it possible to generate currents which can vary between 10 and .300 μA. The redox current amplifier 34 implements a microcurrent: voltage converter. The electronic architecture of the redox current amplifier 34 was developed from the application note illustrated in the “Analog device” catalog under the reference AD515. The three modifications to this manufacturer's diagram are as follows: the recommended operational amplifier has been replaced by a precision component (AD549 JH), the bias voltage is adjustable via a potentiometer and the amplification gain can be selected from a predefined range of 1 millivolt for 1, 2, 3 or 4 nanoamps. The role of the switching interface 30 is to avoid the transient effects generated by the passage from genesis → measurement or measurement → genesis.

The genesis electrode 20 and the reference electrode 26 are permanently connected to the current generator 32. This makes it possible to avoid the connection and disconnection transients.

The current generator 32 is permanently active at nominal current. This avoids switching transients on and off.

In the measurement state, the communication interface makes the current generator 32 inoperative by short-circuiting its terminals through the drain and the source of a field effect transistor including the gate is polarized. The transition from the measurement state to the genesis state (respectively genesis → measurement) results from the controlled opening (respectively closing) of this short circuit. This avoids switching transients. As mentioned earlier, the switching interface

30 makes it possible to alternate the genesis of hydrogen and the measurement of hydrogen clearance by alternating the formation of the measurement electrode loop: current detector: reference electrode and the formation of the genesis electrode loop: current generator: reference electrode, which allows the use of a single reference electrode.

When using the device 10, the genesis 20 and measurement 22 electrodes of the clearance probe are implanted in the tissue analyzed while the reference electrode 36 is implanted at another site of the same tissue. A current which can vary between 1 μA and 100 μA is then applied to the genesis electrode 20 via the current generator 32, which has the effect of locally generating hydrogen by oxidation-reduction of the water contained in the tissue analyzed. The hydrogen generated is conveyed, through the tissue blood flow, to the measurement electrode 22 where it undergoes an oxidation, the current of which is measured by the current amplifier 34.

The genesis and the measurement of hydrogen are carried out alternately via the communication interface 30 which momentarily connects either the genesis electrode 20 or the measurement electrode 22 to the reference electrode 36. The hydrogen oxidation current at the measuring electrode 22 and detected by the current amplifier 34 is then digitized, calculated and displayed so as to: omit the user of the probe 10 to obtain a direct measurement of the tissue blood flow at the site of implantation of the genesis 20 and measurement electrodes 22. The “genesis” state of the device of the invention is illustrated in FIG. 5A and the measurement state is illustrated in FIG. 5B, the arrow representing the course of the current. A description of the digitization and calculation modules is presented below.

Digitization module This quantization module makes it possible to digitize the signal according to a resolution (16 bit) and at a given frequency (1 measurement per second). This module allows synchronous conversion from one to sixteen channels. This module is marketed by several constructions (eg NATIONAL INSTRUMENTS). This module is optional in the case of analog signal processing. This module allows the conditioning of the measurements, so as to make them compatible with a digital calculation mode.

Calculation module The recognized hydrogen clearance calculation model is: y = A. (e ^'F, + B) where y is the signal, A the amplification gain and B the residual current, t the variable time and F the desired tissue blood flow.

We have developed in the laboratory three new methods of calculation in real time, while all the classic methods of evaluation are deferred time.

The differential method

The differential method can be applied to both analog and digital signals. This method consists in determining the flow

F by calculating the ratio of the first and second derivatives of the signal.

The integral method

The integral method can be applied to both the analog signal and the digital signal. The integral method determines the flow rate F from the ratio of the signal integral evaluated over three consecutive windows of the same width T over time.

The neuromimetic method

The identification method by neuromimetic network can only be applied to the digital signal. This method consists in determining the numerical value of the flow F by a succession of weighted sums of the value of the signal at given times in time. Each of the weights is calculated a priori by learning using a backpropagation algorithm of the error gradient, for example.

Claims

1. Device for analyzing the composition and the perfusion rate of an interstitial liquid, said device including a coupled probe (310) comprising the following elements: - an external sheath (110);

- An exchange membrane (160), in particular of microdialysis, situated at the distal end of said coupled probe (100) and of which at least part of the external surface can be brought into contact with the interstitial liquid in situ; an internal pipe (190, 194) which can be connected at its proximal end to a source of supply of perfusate liquid, in particular a dialysis liquid, said pipe allowing the circulation of said perfusate liquid in said coupled probe and the bringing into contact of said perfusate liquid with the inner surface (164) of said exchange membrane (160) so as to perfuse said membrane and thus allow certain substances present in the interstitial liquid or in the perfusate liquid to pass through said membrane (160), thus modifying the composition of the perfusate liquid which can then be collected as a modified perfusate liquid and analyzed; said external line allowing the collection of the modified perfusate liquid without said enriched liquid coming into contact with the perfusate liquid;

- means for measuring the perfusion rate of the interstitial liquid (320) at least part of which is situated outside the internal pipe (190, 194) in particular at the distal end of said coupled probe, so as to be in direct contact with the interstitial fluid; and

- introduction means allowing the protection of the distal end of said coupled probe during its release in situ, said elements being assembled, in particular concentrically, to form a unitary unit implantable in situ, the unitary assembly of said elements allowing to reduce the structural size of the coupled probe and thus minimize the trauma during the implantation of the coupled probe in situ.

2. Device according to claim 1, characterized in that the means for measuring the perfusion rate of the interstitial liquid comprise a probe for measuring the perfusion rate by measuring the elimination of hydrogen at the measurement site.

3. Device according to claim 1, characterized in that the means for measuring the perfusion rate of the interstitial liquid comprise a probe for measuring the perfusion rate by measuring the reflection of a beam of light on the moving cells near said probe.

4. Device according to claim 1, characterized in that the means for measuring the perfusion rate of the interstitial liquid comprise a probe for measuring the perfusion rate by measuring the dissipation of a volume of heat generated within the tissue.

5. Device according to claim 1, characterized in that the means for measuring the perfusion rate of the interstitial fluid comprise a probe allowing the measurement of the partial pressure of oxygen in the interstitial fluid analyzed.

6. Device according to any one of claims 1 to 5, characterized in that said internal pipe (190, 194) is formed by a double tubular pipe at the end of which the exchange membrane (160) is fixed.

7. Device according to claim 6, characterized in that said internal pipe comprises in its center a perfusate capillary

(170) forming a circuit for collecting the enriched liquid, the inlet circuit for the perfusate liquid being defined by the external surface (172) of the collection pipe (194) and the wall of the internal pipe.

8. Device according to any one of claims 1 to 7, characterized in that the said introduction means consist of an introducer (400) comprising a hollow flexible body (402, 404), in particular tubular, capable of receiving at least the distal end of said probe when it is released in situ, said introducer (400) then being able to be removed so as to release said exchange membrane (160).

9. Device according to claim 8, characterized in that said introducer (400) comprises, at its distal end, a bevelled portion, in particular a stainless steel needle (408).

10. Device according to any one of claims 2 and 6 to 9, characterized in that the probe for measuring the infusion rate by measuring the elimination of hydrogen at the measurement site comprises: - a module for measuring hydrogen clearance

(326) comprising a polarized measuring electrode (120) which can be connected to an oxidation-reduction current amplifier, said measuring electrode (120) being located at the distal end of said mixed probe and can be introduced to the site measuring the infusion rate so that the hydrogen present at the measurement site can come into contact with said measurement electrode (120) and undergoes oxidation, the current of which can be measured by said current amplifier (326); and

- a reference electrode which can be connected to the measurement module (326).

11. Device according to claim 10, characterized in that the probe for measuring the infusion rate by measuring the elimination of hydrogen at the measurement site also comprises a hydrogen genesis module (324) comprising an electrode for genesis (130) can be connected to a current generator, said genesis electrode (130) being located at the distal end of said coupled probe and can be introduced at the site for measuring the infusion rate, said electrode (130) being continuously releasing a current which can be varied so as to be sufficient to generate an electrochemical reaction generating hydrogen at the site for measuring the infusion rate.

12. Device according to claim 11, characterized in that the genesis (130) and measurement (120) electrodes are located inside of said internal pipe (190, 194) so that a portion of the electrodes located at the distal end of the coupled probe is exposed to the interstitial liquid during the in situ introduction of said coupled probe.

13. Device according to claim 10, characterized in that the measurement electrode (120) is located inside said internal pipe so that a part of said electrode being at the distal end of the coupled probe is exposed to the interstitial liquid during the in situ introduction of said probe.

14. Device according to any one of claims 11 or 12, characterized in that the genesis electrode (130) is a platinum electrode (132).

15. Device according to claim 14, characterized in that the platinum electrode (132) has undergone a platinization pre-treatment, in particular by the electrolytic deposition of a platinum oxide.

16. Device according to claim 12 or 13, characterized in that the reference electrode is an Ag-AgCI type electrode.

17. Device according to claim 16, characterized in that the reference electrode is covered with a layer of a silver halide, in particular silver chloride.

18. Device according to any one of claims 10 or 1 1, characterized in that it comprises a switching interface (322) separating the hydrogen genesis module (324) and the hydrogen clearance module ( 326), said interface (322) making it possible to alternate the genesis of hydrogen and the measurement of hydrogen clearance.

19. Device according to any one of claims 11 to 18, characterized in that it comprises a calculation module (328) making it possible to transform in real time the signal of the hydrogen clearance measurement measured into digital information of infusion rate.

20. Device for measuring the infusion rate by measuring the elimination of hydrogen at the site for measuring the infusion rate, said device including a hydrogen clearance probe comprising the following elements: - a measurement module ( 326) of hydrogen clearance comprising a polarized measurement electrode (120) which can be connected to an oxidation-reduction current amplifier, said measurement electrode (120) being located at the distal end of said clearance probe and being able to be introduced into the site for measuring the infusion rate so that the hydrogen present at the site of measurement can come into contact with said measuring electrode (120) and undergo an oxidation whose current can be measured by said amplifier current ;

- a reference electrode which can be connected to the genesis module (324) or to the measurement module (326) so as to alternate the genesis of hydrogen and the measurement of hydrogen clearance at the site for measuring the perfusion rate of the liquid interstitial without completely interrupting the current generated by the genesis electrode (130), this current being weak when measuring the hydrogen clearance; and

- introduction means (400) allowing the protection of the distal end of said clearance probe during its release in situ.

21. Device according to claim 20, characterized in that the clearance probe also comprises a hydrogen genesis module (324) comprising a genesis electrode (130) which can be connected to a current generator, said genesis electrode ( 130) being located at the distal end of said probe and being able to be introduced into the site for measuring the infusion rate, said electrode (130) being able to continuously release a current which can be varied so as to be sufficient to generate an electrochemical reaction generating hydrogen at the infusion rate measurement site.

22. Device according to claim 20 or 21, characterized in that the introduction means consist of an introducer (400) comprising a hollow body (402, 404), in particular tubular, flexible, capable of receiving at least the distal end of said clearance probe when it is released in situ, said introducer (400) then being able to be removed so as to release the hydrogen genesis and / or hydrogen clearance measurement modules (326).

23. Device according to claim 22, characterized in that said introducer comprises at its distal end a bevelled portion, in particular a stainless steel needle.

24. Device according to any one of claims 21 to 23, characterized in that the genesis electrode (130) is a platinum electrode (132).

25. Device according to claim 24, characterized in that the platinum electrode (132) has undergone a platinization pre-treatment, in particular by the electrolytic deposition of a platinum oxide.

26. Device according to any one of claims 20 to

25, characterized in that the reference electrode is an Ag-AgCI type electrode.

27. Device according to claim 26, characterized in that the reference electrode is covered with a layer of silver halide, in particular silver chloride.

28. Device according to any one of claims 21 to

27, characterized in that it comprises a switching interface (322) separating the genesis module (324) of hydrogen from the measurement module (326) of the hydrogen clearance, said interface (322) making it possible to alternate the genesis of hydrogen and the measurement of hydrogen clearance.

29. Device according to any one of claims 20 to

28, characterized in that it comprises a calculation module (328) making it possible to transform the hydrogen clearance measurement signal in real time into digital information on the infusion rate.

30. Device for analyzing the composition of the interstitial fluid, said device including an analysis probe comprising the following elements:

- an outer sheath (110); - An exchange membrane (160), in particular of microdialysis, located at the distal end of said analysis probe and of which at least part of the external surface (162) can be brought into contact with the interstitial liquid in situ ;

an internal pipe (190, 194) which can be connected at its proximal end to a source of supply of liquid, in particular a dialysis liquid, said pipe allowing the circulation of said perfusate liquid in said coupled probe and the bringing into contact of said liquid perfusate with the interior surface (164) of said exchange membrane (160) so as to perfuse said membrane and thus allow certain substances present in the interstitial liquid or in the perfusate liquid to pass through said membrane and to enrich the perfusate liquid perfusion which can then be collected, in particular as a dialysate, and analyzed; said external pipe allowing the collection of the enriched liquid without said enriched liquid coming into contact with the perfusate liquid; introduction means allowing the protection of the distal end of said analysis probe when it is released in situ.

31. Device according to claim 30, characterized in that said internal pipe (190) of said analysis probe is formed by a tube at the end of which the exchange membrane is fixed.

32. Device according to claim 31, characterized in that said collection conduit is constituted by a perfusion capillary (170) disposed in the center of said internal conduit so as to form an inlet circuit for the dialysis liquid defined by the external surface (172) of the collection pipe and the wall of the internal pipe.

33. Device according to any one of claims 30 to

32, characterized in that said introduction means are constituted by an introducer (400) comprising a hollow body (402, 404), in particular tubular, flexible, capable of receiving at least the distal end of said analysis probe during its release in situ, said introducer (400) then being able to be removed so as to release said exchange membrane (160).

34. Device according to claim 33, characterized in that said introducer (400) comprises, at its distal end, a bevelled portion, in particular a stainless steel needle (408).

35. Method for measuring the infusion rate by measuring the elimination of the hydrogen present at the site for measuring the infusion rate, said method comprising:

- the introduction to the measurement site of a polarized electrode for measuring the hydrogen clearance;

- the introduction at a site other than the measurement site of a reference electrode which can be connected to the measurement electrode;

- the measurement at the measuring electrode of the current generated by the oxidation of the hydrogen produced during the contact of this hydrogen with the measuring electrode;

- the processing of hydrogen oxidation measurements at the measurement electrode by digital processing so as to transform in real time the measured signal into digital information of the infusion rate.

36. Method according to claim 35, characterized in that the digital processing of the hydrogen oxidation measurements at the measurement electrode is carried out by a differential, integral or neuro-mimetic method.

37. Method according to any one of claims 35 and 36, characterized in that the hydrogen present at the measurement site is generated by a hydrogen genesis electrode inserted at the measurement site by means of an electric current produced by said electrode sufficient to generate an electrochemical reaction producing hydrogen at the site of measurement of the infusion rate.

38. Method according to claim 37, characterized in that the genesis of hydrogen is alternated with the measurement of hydrogen while maintaining at least one weak electric current at the genesis electrode.