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1. WO2004058057 - DISPOSITIF DE CAPTEUR POUR SURVEILLER UNE PERFUSION DANS UN TISSU

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

SENSOR DEVICE FOR MONITORING PERFUSION OF TISSUE

The invention relates to sensors for use in human or animal tissue, especially in muscular tissue, for example the myocardium.
The significance of efficient blood flow to effective organ function has been much studied. For example, it is well-known that effective reperfusion of ischaemic
myocardial tissue can be crucial to patient recovery following cardiac or coronary arterial surgery. The
concentrations in the tissue of certain analytes normally present in blood may be indicative of the level of perfusion of the tissue.
In one form of myocardial monitoring system (the Khuri Myocardial pH monitoring system made by Terumo
Cardiovascular Systems Corporation of Tustin California) a myocardial sensor has two electrochemical pH measurement probes and a reference electrode. The system can be used for the continuous monitoring of pH and temperature during cardiac surgery. The pH electrodes consist of a closed-ended glass tube made from pH sensitive glass, filled with a phosphate-based internal buffering solution in which a silver wire coated with silver chloride is inserted. The reference electrode consists of a silver/silver chloride wire inserted into a plastic tube of potassium chloride electrolyte solution. The tube is plugged with a semi-permeable material that prevents leakage of the bulk contents of the tube but maintains electrical contact with the patient during pH measurements.
In Clinical Science (2000) 98, 321-328 ("Myocardial tissue oxygen supply and utilization during coronary artery bypass surgery: evidence of microvascular no-reflow") there is described the use of an electrochemical sensor to determine regional variations in the oxygen concentration (tissue partial pressure of oxygen) in the myocardium. That sensor has an electrode having an insulated silver wire located within a stainless steel tube, a bevelled end portion of the silver wire being exposed to provide an electrochemically active surface. The electrode also includes an epoxy base portion which can be sutured to the surface of the myocardium. For the purpose of the
measurements, there is used a silver/silver chloride ECG electrode placed upon the patient' s skin on the right axilla, which electrode acts as reference and counter electrode .
The use of electrochemical sensor devices may be inappropriate in certain circumstances. For example, the measurements may become unreliable when the patient is subjected to, for example, defibrillation treatments or other treatments involving the application of a potential difference. Further, electrochemical sensors may consume the analyte to be measured and, where the concentration of the analyte to be measured is low, the measured value may be undesirably influenced by the rate of consumption of the analyte and the diffusion rate through the surrounding medium.
The invention provides a sensor device for monitoring perfusion of tissue, having a base portion and at least a first elongate probe member, the base portion and the first probe member being so arranged that, in use, the base portion can be positioned in abutment with a surface of said tissue whilst the first probe member extends into said tissue, and further comprising a first optical sensor housed within said first probe member for determining a first analyte in said tissue, and a second optical sensor for determining a second analyte in said tissue.
The use of an optical sensor to determine an analyte can offer advantages over the use of electrochemical sensors in that it can provide a more reliable indication of fluctuations in the analyte concentration, for example, if the patient undergoes any electrical treatment.

Advantageously, there is at least one further sensor for at least one further analyte in said tissue.
Advantageously, there is a first elongate probe member housing the first optical sensor and a second elongate probe member housing the second optical sensor. Advantageously, there is a third sensor, said third sensor being housed in one of said first and second elongate probe members.
Advantageously, there is a third elongate probe member comprising a third optical sensor. Thus, it is preferred for there to be two or three elongate probe members, with each probe member housing a respective optical sensor, or with at least one of the elongate probe members housing two or three optical sensors.
Advantageously, the device comprises at least one sensor for a physical parameter, for example, temperature. Advantageously, the device comprises a thermistor or a thermocouple. Temperature measurements may be of clinical interest. In addition, or instead, they may be used to correct sensor readings in respect of any temperature dependent characteristics, for example, having regard to the temperature coefficient of chemical indicator systems used in the sensor (s) . The sensor for a physical parameter may be housed in an elongate probe member, which may or may not be a probe member housing one or more optical sensors. The sensor for a physical parameter may be associated with the base portion.
If desired or necessary, one or more additional elongate members may be provided to enhance securing of the device into the tissue to be monitored. In addition or instead, the base portion may be so arranged that it can be affixed to the surface of the myocardium, for example, by suturing.
The or each optical sensor may be an optical sensor for determination of an analyte. Suitable optical sensors include, for example, those containing absorption or fluorescent indicators, the optical characteristics of which are dependent upon the concentration of the analyte of interest. Where placed in direct, or more usually indirect, contact with tissue or bodily fluid the behaviour of those sensors, containing the indicators, on interrogation by light of an appropriate wavelength or wavelengths depends on the local concentration of the analyte to be monitored. It will be appreciated that when those sensors are used in indirect contact with fluid or tissue it will be necessary for any medium between the sensor and the fluid or tissue to be permeable to the analyte to be determined. In the preferred sensors, the indicators have a relatively long life in the sense that they are not consumed in the analyte measurement, that is, they remain substantially unchanged by the analyte measurement process.
The optical sensor may comprise an optical fibre comprising one or more voids filled with an indicator.
Advantageously, each sensor comprises an optical fibre which carries light transmitted to and received from a distal extremity of the fibre.
The device may be suitable for determination of blood gas concentrations. For example, the device may be suitable for determination of one or more parameters selected from oxygen partial pressure (p02) , carbon dioxide partial pressure (pC02) and hydrogen ion concentration (pH) .
Advantageously, the device comprises at least one sensor selected from optical p02 sensors, optical pC02 sensors and optical pH sensors. Preferably, the device comprises a p02 sensor, a pC02 sensor and a pH sensor.
Advantageously, the pH and p02 sensors are located in a common elongate probe member. If desired, a p02 sensor, a pC02 sensor and a pH sensor are housed in a common elongate probe member, although such arrangements may in practice be less preferable because of the increased diameter of the probe member required to accommodate three or more sensors.

The configuration and dimensions of each elongate probe member are selected so as to permit insertion of the probe members into the tissue to be monitored without an
unacceptable extent of disruption or damage to the tissue.

Advantageously, the or each elongate probe member comprises a cylindrical casing. A distal end portion of the or each probe member may be shaped, for example, tapered, to facilitate insertion of the device into the tissue and to reduce tissue damage during insertion. Advantageously, the cylindrical casing is of circular cross-section.
Advantageously, the or each elongate probe member is closed at its distal end. For example, where as is preferred the probe member comprises a cylindrical or tubular casing, that casing may be filled at its distal end by a plug of any suitable material, for example, a medically approved epoxy compound. Preferably, the probe member comprises at least one access aperture for permitting ingress of the analyte to be measured. The or each elongate probe member
advantageously has a length of at least 5mm and
advantageously not more than 12mm. Advantageously, the or each probe member has a housing with an external diameter of not exceeding 1mm, and preferably not exceeding 2mm.
Advantageously, the external diameter is at least 0.3mm, and preferably at least 0.5mm. It is preferred for the external diameter to be from 0.5 to 1mm. The internal diameter of each probe member may be, for example, up to 1mm, advantageously up to 0.5mm, and preferably in the range of from 0.2 to 0.5mm.
Advantageously the or each elongate probe member comprises a housing of a biocompatible material, for example, medical grade stainless steel or titanium.
Advantageously, the base portion is of a synthetic polymer material. Advantageously, the base portion is disk-shaped. The base portion may comprise attachment means for
attachment of the sensor device to tissue, for example, apertures through which sutures may be passed to secure the device when in use.
The invention further provides a method of monitoring a human or animal patient comprising inserting into a heart wall of said patient an optical sensor for determining at least one analyte selected from p02 and pC02 and monitoring said at least one analyte in said heart wall.
Moreover, the invention provides a method of monitoring a human or animal patient comprising inserting into a heart wall a sensing arrangement for determining first and second analytes and monitoring said first and second analytes.
Advantageously, said sensing arrangement comprises first and second optical sensors which are inserted into said heart wall in fixed, spaced relationship and retained in said relationship whilst in situ in said heart wall.

Advantageously, a third sensor is inserted into said heart wall. The third sensor may be inserted in fixed, spaced relationship with respect to said first and second sensors and retained in said relationship whilst in situ in said heart wall.
In a further aspect, the invention provides a sensor device for monitoring perfusion of tissue, comprising a base portion and at least a first elongate probe member, the base portion and the first probe member being so arranged that, in use, the base portion can be positioned in abutment with a surface of said tissue whilst the first probe member extends into said tissue, the device further comprising optical sensor means housed for determining two or more analytes in the tissue.
Two illustrative embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:
Fig. 1 is a section through a first form of device according to the invention positioned in monitoring position relative to a region of myocardium;
Fig. 2 is a perspective view from above of a lower part of the device of Fig. 1;
Fig. 3 is a perspective view from below of the device of Fig. 1;

Fig. 4 is a perspective view from above of a lower part of a second form of device according to the invention.
With reference to Fig. 1, a device 1, being used for monitoring myocardial perfusion, has a base portion 2 and three probe members 3, 4, 5. Only probe members 3 and 4 are shown in Fig. 1. The device is positioned in monitoring contact with the myocardium M, with the lower surface of base portion 2 in contact with the external surface of, and the three probe members 3, 4, 5 penetrating into, the myocardium M.
Referring to Figs. 1 and 2, each of the probe members 3, 4, 5 has a housing 6, 7, 8, with a respective proximal end 9, 10, 11, fixedly located in a respective aperture in a lower wall of base portion 2. The housings 6, 7, 8 are generally circular cylindrical at proximal ends 9, 10, 11, and in respective mid-regions 12, 13, 14. Distal ends 15, 16, 17 are tapered. Apertures 18, 19, 20 are provided in the mid-regions 12, 13, 14. The housings 6, 7, 8 define bores 21, 22, 23.
Located in bore 21 of probe member 3 are a first optical sensor 24 for dissolved oxygen (that is, oxygen partial pressure p02) and a second optical sensor 25 for pH (see Fig. 3) . Located in the bore of probe member 4 is a third optical sensor 26, for dissolved carbon dioxide (that is, carbon dioxide partial pressure pC02) . The optical sensors may, for example, be of the kind having an optical fibre pierced by apertures that are filled with an indicator material whose optical characteristics, for example, absorption or fluorescence characteristics, are dependent upon the concentration of an analyte to be determined. For example, sensor 25 may be a pH sensor comprising an optical fibre through a sensing portion of which extends a helical array of apertures, which are so arranged that all parts of the cross sectional area of the fibre are interrupted by at least one of the apertures. Each of the apertures is filled with a pH sensitive indicator, for example, phenol red in gel. A mirror is provided embedded in the end of the fibre and optical radiation transmitted along fibre is reflected by the mirror and passes back along the fibre. The
transmitted and reflected light passes through the
indicator-containing apertures and the amount of light absorbed gives an indication of the pH of the medium in which the sensor is located. Sensor 24 may, for example, be of similar construction to sensor 25 except that it contains an indicator sensitive to oxygen, for example, a fluorescent indicator. Sensor 26 is a pC02 sensor which may be of broadly similar construction to sensor 25 except that the indicator is suitable for detection of C02. For example, the indicator may be phenol red, in a solution which is a source of bicarbonate ions.
Analyte sensors of the kind described above are present, for example, in the sensor devices described in US 5 596 988.
The optical sensors, 24, 25, 26 are optically connected by optical fibres 27, 28, 29 via base portion 2 and a cable 30 to processing means (not included in Figs. 1 to 3). The probe member 3 is filled with a polyacrylamide gel which surrounds the sensors 24 and 25 at least in the region of apertures 18. The sensors 24, 25 may be enclosed within a microporous membrane, with any void spaces inside the membrane advantageously being filled with a hydrogel which permits passage of the analytes of interest. Void areas within the probe member, for example, between the internal wall surface of the probe member and the sensors, are preferably also filled with a hydrogel which permits passage of the analytes of interest. That prevents the formation of air bubbles within the probe member, which would interfere with measurement of the analyte. The hydrogel may be a polyacrylamide gel. The apertures 19 in the housing 7 of probe member 4 and the end of the housing 7 are closed by a non-microporous membrane (not shown in the drawings) which is permeable to carbon dioxide but not to hydrogen ions, for example, polyethylene. The sensor 26 may be surrounded by a snugly fitting non-microporous membrane, and any voids within that membrane or between that membrane and the housing 7 are filled with a hydrogel, such as a
polyacrylamide gel, the membrane and the hydrogel being permeable to carbon dioxide. Located in the bore of probe member 5 is a thermistor 31. If desired, the ends of the probe members 3, 4, 5 may be filled by an impermeable medically approved filler, for example, a medically approved epoxy compound.
With reference to Fig. 3, the optical fibres 27, 28, 29 and a cable 32 from thermistor 31 converge within the base portion 2 and exit that portion through an aperture 33 in a side wall thereof from which cable 30 carries them to the processing means.
Referring now to Fig. 4, a second embodiment of the invention has four probe members. The arrangement is similar in many respects to that of Figs. 1 to 3 and the same reference numerals indicate features which are
essentially common between the two devices. In the
embodiment of Fig. 4, however, there is an extra probe member 3' and the sensors 24, 25 are separately located in respective probe members 3 and 3' .