Abstract:
A method and system for the determination of the pH of a fluid by measuring the pH of the fluid and thereafter correcting the pH based upon the determination of measured and/or adjusted values of at least one other parameter, such as PO 2  and PCO 2 , which relate to the fluid.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for measuring by means of at least one electrode, such as an ambulatory measuring, the pH-value in the gastrointestinal tract. 
     The invention also relates to a system to perform such a method. 
     Units for the ambulatory registration for medical purposes are already known. Such a unit is known as Synectics MicroDigitrapper for the measuring of the pH-value, the PO 2  content and further such parameters. Several units also exist for measuring only the pH-value in different regions of the gastrointestinal tract. Such a unit is Synectics ED Digitrapper™ and Synectics ED Digitrapper MkII™. The sensor for the pH-value usually being applied are based on glass electrodes from Ingold, Switzerland and electrodes with an antimony crystal from Synectics according to USEA∃4,119,498. Said publication describes an electrode for measuring the pH-value, and the PO 2  - and PCO 2  -content in fluids. The known methods for measuring the pH-value, however, are presenting essential measuring errors in certain measuring situations, e.g. in respect to measurements in the gastrointestinal tract. 
     SUMMARY OF THE INVENTION 
     The present invention provides the possibility to essentially improve the measuring accuracy in determinating e.g. the pH-value by means of monocrystal metallic electrodes. 
     The invention thus relates to a method according to the preambles of the attached claim 1. The method is especially characterized in what is stated in the characterizing part of said claim. 
     Moreover, the invention relates to a system according to the preambles of the attached claim 9. The system is especially characterized in what is stated in the characterizing part of said last mentioned claim. 
     The invention is described herein below with reference to execution examples and to the attached drawings, in which 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows schematically an axial section of a rodlike monocrystal electrode; 
     FIG. 2 shows schematically an arrangement of electrodes with reference bag and a reference electrode; 
     FIG. 3 shows schematically the ambulatory measuring according to the invention of e.g. the pH-value in the gastrointestinal tract; 
     FIG. 4 shows schematically a first embodiment of a system according to the invention with two monocrystal electrodes; 
     FIG. 5 shows schematically a second embodiment of a system according to the invention with two variables are determined with one single monocrystal electrode and two different circuit designs; and 
     FIG. 6 shows schematically a monocrystal measuring electrode arranged within a potentiostat with a counter electrode. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 a metal monocrystal electrode is designated 1 generally according to the previously mentioned U.S. patent, the metal preferably being antimony, a crystal 2 of the metal being arranged to be exposed at the end 3 of the electrode and the plane crystal surface 4 adapted to be exposed to a fluid coinciding with a certain crystallographic constellation of the crystal. By means of a conductor 5 the crystal is coupled to an electric circuit. Between a reference electrode 6, FIG. 2, and the measuring electrode a potential difference is created under certain conditions and the electrode can be used to measure the pH-value, and the PO 2  - and PCO 2  -content. According to one embodiment the determination of the pH-value is to be perform by means of the measuring electrode 1. According to a special embodiment, FIGS. 3 and 4, the electrode is adapted and provided to be lowered into the gastrointestinal tract 8 of a patient 9, e.g. by means of a catheter 7, for an ambulatory and continuous determination of the pH-value in the gastrointestinal tract, a portable unit 10 being provided for the registeration of certain variables. 
     Measuring values related to the pH-value are meant to be corrected for the oxygen influence in the fluid within the actual measuring region, the oxygen content there being expressed as the partial pressure related to O 2  and is here expressed in that way, and means being provided for the determination of even PO 2  to be described further down. 
     By means of a counter 11, which preferably is comprised in the registration unit 10, the measuring result of the pH-value are meant to be corrected based on preferably generally all obtained measuring values related to PO 2 , e.g. according to an empirically determined correlation: ##EQU1## 
     Also other correlations can possibly be provided for the correction, the correction correlation then preferably being adapted to the actual measuring environment and the actual variables of the integral parameters. 
     According to an embodiment the PO 2  is determined preferably by digital sensors 12, e.g. from Catalyst Research, the measuring being primarily related to the PO 2  in the blood, with the measuring based on transillumination, with the thus determined PO 2  being possibly correlated to the PO 2  in the measuring region. 
     According to another embodiment, FIG. 4, there is provided a further monocrystal electrode 13 for the determination of PO 2 , the electrode preferably being of the same type as in the U.S. patent, FIG. 2, and comprizing a buffer solution 14 as a reference solution for the determination of PO 2 , regardless of the pH-value in the fluid in accordance with the description in the patent. 
     According to a further, preferred embodiment, FIG. 5, the measuring electrode for the pH-value is also adapted to be used for the determination of PO 2 , various different electrical circuits being provided for the determination of the pH-value and the determination of PO 2 . According to the illustrated embodiment i.a. the measuring electrode is connected to a voltage source 15 adapted to provide a voltage with an AC-component, the voltage preferably not being the same for the determination of the pH-value and the determination of PO 2 . The output signal 16 from the circuit in the configuration for the determination of the pH-value is sent to a pH-value amplifier 17 and means 18 of a convenient design for the analysis of preferably both the amplitude and the phase condition for a separation of the pH-values. In a corresponding way the output signal 16 is transmitted from the circuit in the configuration for the determination of PO 2  to a PO 2  -amplifier 19 and means 20 of a convenient design for the analysis of preferably both the amplitude and the phase condition for a separation of the PO 2  -values. There are also means 21 for an alternating between said configuration for the determination. 
     According to a further embodiment with the same electrode 1 for several variables, FIG. 6, a potentiostat arrangement is used, the counter resistor CE of the potentiostat is adapted and provided to be varied using control means CA to vary the voltage. The potentiostat is then arranged in such a way that during a change of the counter electrode voltage and even the frequency, with which the counter electrode voltage is changed, it becomes possible to separate any components which are specific for the pH-value, and the PO 2  - and PCO 2  -content, e.g. a double layer capacitance and a charging transmission resistance, kinetic constants possibly to be calculated and related to measuring variables, i.e. the concentrations of the corresponding substance, i.e. the pH, the PO 2  and the PCO 2 . For a further information of the potentiostat and the measuring procedures here is referred to Bioelectronics--Principles of Bioenergetics and Bioelectrochemistry, Oxford Press, 1990, especially pages 33-37. 
     According to a further embodiment there is also provided a fluid impermeable diaphragm 22 provided with a monocrystal electrode, FIG. 2, for the determination of PCO 2 , even the PCO 2  being in applicable cases adapted to form the basis for a correction of the determination of the pH-value. 
     The method and the function of the system according to the invention has been generally clarified in the description above. A measuring with a monocrystal electrode is thus supplemented by a measuring of at least one further parameter with simultaneously mutually dependent parameters, such as the pH-value and the PO 2 , the measuring result being corrected on the basis of the performed determination and the correction relation stated for the actual parameters. 
     Thus, the invention provides a possibility to use metal monocrystal electrodes with an essentially improved accuracy, which already are providing extremely accurate measuring. 
     The invention has been described above with reference to execution examples. Further embodiments can of course be imagined as well as smaller changes and supplements without leaving the scope of the invention. 
     The invention is also applicable for other types of electrodes besides metal monocrystal electrodes, and in the case of metal electrodes the invention is applicable even for polycrystal and amorph metal electrodes and not only for monocrystal electrodes. 
     Moreover, other circuitries than the already described ones can possibly be used for embodiments using various electric circuitries for the determination of the pH-value and of the PO 2  with the same electrode, the electrode then in most cases being electrically energized in different ways during the corresponding determination as a result of the various circuitries. Embodiments using various circuitries for different parameters with the same electrode are also applicable to other parameters than PO 2  and the pH-value. 
     Therefore, the invention is not limited to the already above state embodiments but can be varied within the scope of the attached claims.