The concentration of a substance or group of substances in a body fluid is monitored by means of an interface held in contact with a living human or animal body and a detector is positioned downstream from the interface. A profusion fluid is passed from the interface to and along the detector at a flow rate of less than 60 .mu.l/hour. A constant flow is maintained at the low flow rate with very little or no supply of energy, allowing for a compact construction and reduced measurement delay.
The invention concerns a method and an arrangement for determining the concentration of glucose in a body fluid. In the microdialysis technology used for this purpose, perfusate containing glucose is transported in intermittent delivery pulses through a microdialysis probe (10) inserted into the body fluid and dialysate obtained in this process is passed to a measuring cell (16) to record the glucose content. In order to achieve an exact determination of glucose even with a reduced dialysis period, it is proposed that the starting content of glucose in the perfusate is adapted to the glucose content of the body fluid by means of a control device (18, 20) in accordance with a command variable derived from the measurement signals of the measuring cell (16). When the control deviation is negligible the momentary starting content of glucose in the perfusate can be determined as a measure for the glucose content of the body fluid.
The present invention concerns a method for determining and monitoring tissue glucose concentration. Additionally, the present invention concerns a measuring apparatus to determine and monitor glucose concentration.
In a method and a device for electrochemical determination of the concentration of at least one dissolved chemical entity in a liquid medium, a measurement voltage U is impressed on a working electrode, in contact with the liquid medium, relative to a counter electrode, thereby causing the dissolved chemical entity to react by oxidation or reduction at the working electrode, producing a measurement evoked current. The measurement evoked current is compared to a predetermined value, and the measurement voltage U is adjusted so that the measurement evoked current is substantially equal to the predetermined value, and thus remains substantially constant during measurements. A difference .DELTA.U=U-U.sub.min is formed, which corresponds to an oxidation/reduction reaction at the working electrode, with U.sub.min being a minimum voltage selected as a reference level. This difference is used to calculate concentration variations of the chemical entity in the liquid. A therapy administering apparatus, such as a medical implant such as a pacemaker or the like, can be controlled dependent on the calculated concentration variations.
The invention concerns an arrangement for determining the concentration of glucose in a tissue fluid. In the microdialysis technology used for this purpose, perfusate-containing glucose is transported in intermittent delivery pulses through a microdialysis probe inserted into the tissue fluid and dialysate obtained in this process is passed to a measuring cell to record the glucose content. In order to achieve an exact determination of glucose even with a reduced dialysis period, it is proposed that the starting content of glucose in the perfusate is adapted to the glucose content of the tissue fluid by means of a control device in accordance with a command variable derived from the measurement signals of the measuring cell. When the control deviation is negligible the momentary starting content of glucose in the perfusate can be determined as a measure for the glucose content of the tissue fluid.
Sensors that are capable measuring the rate of flow of a fluid that passes over the electrodes of the sensor. In these sensors, an electrode, designated the flow rate-determining electrode, is used in conjunction with the conventional electrodes, e.g., the working electrode, the reference electrode, and the counter electrode, to determine the rate of flow of the fluid. In one aspect, this invention provides a sensor for measuring the concentration of an analyte in a sample of fluid when the sample flows continuously over the electrodes of the sensor, especially when the rate of flow of the sample is relatively low. In another aspect, this invention provides a method for measuring the concentration of an analyte in a sample of fluid, wherein the rate of flow of the sample varies during the period of time that the sensor is in place. In a preferred embodiment, the sensor employs four electrodes, namely, a working electrode, a reference electrode, a counter electrode, and a flow rate-determining electrode. Alternatively, a single electrode that performs both the function of the reference electrode and the function of the counter electrode can replace the reference electrode and the counter electrode. In addition, a dummy electrode or a blank electrode can be used to compensate for interference from electrochemically active species. The reagent(s) specific to the analyte of interest is required to be deposited on the working electrode.
