Field of technology The present invention relates generally to the area of human and veterinary medicine and pharmacology. In particular, it relates to a device that allows a detection of the presence of the fluids and the identification of the type of the fluids flowing in systems used in healthcare, such as extracorporeal blood circulation or dialysis systems. Background of the invention

Fluid flow measuring devices based on the electromagnetic, optical or colorimetric principle are known in the art, such as Keyence FS-N11N sensors (Keyence, Itasca, USA), Sensirion AG SLF3S-1300F (Sensirion, Staefa, Switzerland). However, these devices do not detect the presence of the fluid as such, nor do they identify the type of the fluid. Furthermore, devices are known which detect the presence of the fluid (e.g. from NEOL IT Solutions, Bischheim, France) operating on the optical principle. These devices detect the presence of the fluid but do not detect the type of the fluid. U.S. Patent No. 5,418,465 disclosed a capacitive sensor for measuring mixing ratios in a fluid. International patent application published as WO 2018/210402 disclosed a capacitive sensor for monitoring the properties of the fluids. However, none of these sensors is suitable for medical use, as the electrodes are in direct contact with the measured fluid.

In the extracorporeal circulation (ECC) system, there is usually not only blood but also blood substitutes, diluted blood, plasma or other infusion fluids, such as saline (possibly Ringer's lactate solution, Hartman's solution), exceptionally sterile distilled water or glucose solution, many of these fluids being optically indistinguishable from each other.

One of the problems is to distinguish blood from saline when initiating or terminating a subject's connection to the ECC. The ECC tubes are first filled with saline, which is gradually expelled by blood after the subject is connected. In contrast, when a subject is disconnected, blood is expelled from the ECC with saline. At these events, of course, the blood is diluted with saline, whereas it is not possible to tell whether diluted or full blood is flowing based only on the appearance/colour of the fluid in the ECC tubes (which are transparent). To ensure the maximum return of the subject's blood to its own bloodstream and the associated minimization of unnecessary blood dilution, it is important to have accurate information about the degree of blood dilution that is currently in the ECC.

Another problem is the considerable complexity of the ECC system, which, especially in a non-routine experimental setting, contains a number of components, such as one or more pumps, heat exchangers, connections and branches. The fluids are applied to the circuit tubes (hoses) from infusion bottles or bags (often simultaneously from several bottles) via connections that can be opened and closed. In addition, the fluids are applied not only before and after ECC operation (e.g. rinsing ECC for cleaning and sterilization), but also during ECC operation by mixing fluids with blood via stopcocks. This system is often not well viewable, during operation of the ECC there are often unforeseen situations where an ECC operator is busy in such a way that she/he may not have a good overview of which fluid is actually flowing through the tube. It would therefore be useful to have information on whether any fluid is present in the ECC system or in any of its branches, and at the same time which kind of fluid it is.

Summary of the invention

The above problems are solved by the non-contact sensor according to the present invention. This sensor can be used to detect the degree of blood dilution in the ECC and also to identify infusion fluids used in the ECC. The main advantage of the sensor according to the invention is non-contact, since metal parts of the sensor are not in contact with the measured/detected fluid, as they are located outside the tube through which the respective fluid flows. The term “tube” is used in the present specification as a common term for all kinds of tubing and hosing common in the EEC system. The sensor is able to identify whether saline or blood is flowing through the EEC system, or to what extent the blood is diluted with saline. In addition, the sensor is able to identify what type (of commonly used) fluids flows through the ECC system. The sensor according to the present invention is based on the principle of non-contact measurement of ionic conductivity of blood and infusion fluids used in therapeutic procedures in the interventional medicine. The term blood as used in the present specification also includes diluted blood. The term infusion fluid as used in the present specification includes all fluids used in the ECC, in particular plasma, artificial blood (blood substitute), saline (0.9% NaCl solution), Hartmann's solution, Ringer's lactate solution, sterile distilled water and glucose solutions.

The basic functional part of the sensor is a pair of electrodes mediating capacitive coupling with the fluid, the conductivity of which is measured. Capacitive coupling was used because it is not possible to place the metal electrodes directly into the measured fluid as in classic conductometry (maintaining sterility, affecting the chemical properties of the fluids, possible interactions or the risk of contamination). As a result, it is necessary to use an alternating high-frequency (HF) current to measure conductivity.

From an electrical point of view, the sensor appears to be a combination of two capacitors connected in series by a conductive fluid. The sensor is realized as an assembly of two electrodes, preferably annular electrodes (i.e. ring/sleeve-shaped), which are arranged concentrically on the tube through which the measured fluid passes so as to be in close contact with the tube wall, wherein there is a gap between the electrodes in the longitudinal direction (parallel to the longitudinal axis of the tube). The width of the gap, i.e. the distance between adjacent edges of the electrodes, determines the size of the measured column of fluid. The optimal distance between the edges of the electrodes is given by somewhat conflicting requirements for the maximum sensitivity of the sensor to changes in ionic conductivity and for still acceptable dumping of the chain of the input coupling capacity - measured column of the fluid - output coupling capacity. If the column of fluid increases, its impedance and its changes depending on changes in specific conductivity increase, but at the same time the output voltage decreases and thus the conditions for accuracy and stability of measurements deteriorate. The distance between the electrodes is optimized with regard to the highest possible sensitivity and at the same time the stability of the measurement. The optimal distance between the edges of the electrodes may be in the range of a few millimetres to a few tens of centimetres, preferably a few centimetres. In a preferred embodiment, the distance is about 20 to 60 mm, more preferably about 40 mm. The electrodes are equipped with contacts for electrical connection to the excitation and measuring circuit.

The tube is made of an electrically non-conductive material, preferably a biocompatible material. The tube is preferably made of plastic, more preferably PVC certified for medical use.

The electrodes are made of metal, preferably aluminium or copper.

The term annulus as used in this specification refers also to an incomplete, partial annulus, in general the electrodes can embrace only a part of the tube circumference, e.g. a quarter, half or three quarters of the tube circumference, but annular electrodes represented by a closed annulus (ring) appear to be the most suitable.

The assembly of the two electrodes is enclosed in a shielding housing formed by an outer shell and a baffle separating the electrodes so as to minimize parasitic transmission of the high frequency (HF) signal outside the measured fluid. The space between the electrodes and the shielding is filled with non-conductive insulating material (plastic, air, etc.). Preferably, the sensor is embodied as a fixed module comprising the tube with two annular electrodes and electrical conductors, all "sealed" in a plastic block, which is provided with a fluid inlet and outlet (e.g. LUER type connectors for connecting medical device tubes) for connection to the EEC and electrical contacts for connecting detection electronics - excitation and measuring circuit. The whole module is also equipped with a shielding sleeve, which also extends into the space between the electrodes.

In another embodiment, the sensor may be in the form of a split sensor, which consists of two identical parts, each of which comprises only one annular electrode, which forms one capacitor with the wall of the tube and the liquid inside the tube. Each of the two parts can be moved along the tube. The split sensor was used to verify the optimal longitudinal distance of the electrodes, but it turned out that the optimal distance is rather small (corresponding to the distance in the non-split sensor illustrated bellow). However, in certain applications, it may be advantageous to use a split sensor.

In an alternative embodiment, the sensor could be arranged in the form of "pliers" or "clamp", the jaws of which, when snapped onto the tube, form an electrode in contact with the tube, either an annular or a partially annular electrode. In such a case the sensor tube is directly the ECC tube.

The sensor according to the present invention is a passive circuit element which must be connected to the excitation and measuring circuit for measurement, i.e. it must be equipped with high-frequency (HF) voltage generator with low output impedance and a load resistor on the output side of the sensor connected with suitable HF voltage detector. Suitable voltage detectors are available from commercial production of a number of companies (e.g. Boonton 9240 RF Voltmeter, Boonton, Parsippany, NJ, USA), or it is possible to use one of the available detection integrated circuits, e.g. AD8318 from Analog Devices. For the maximum achieved sensitivity, the suitable HF voltage detector should have input impedance comparable to the impedance of the sensor used for a given operating frequency.

The measuring system according to the present invention comprises the sensor described above and further comprises a generator of excitation HF voltage, a load resistor to which a detector, i.e. a meter of alternating current flowing through the fluid, is connected in parallel way, and connecting means. All components of the measuring system except the sensor can be arranged in an electronic module, which is located in a separate housing outside the sensor housing, whereas the sensor and module housings are connected by connecting means. In addition, the electronic module is provided with connecting means (wire or wireless, e.g. IR or Bluetooth means) for communication with an external electronic device (e.g. a computer, tablet, telephone or peripheral connected to a vital signs monitor). The electronic module may comprise two parts, the first part comprising an electronic circuit providing the measuring system with alternating (AC) voltage of the desired amplitude and frequency, and the second part comprising an electronic measuring circuit which measures the AC voltage at the load resistor. Other electronic components can be used to digitize and indicate the resulting value (e.g. voltage, output to input voltage ratio), as well as to communicate with the external electronic devices.

In one preferred embodiment, the measured signal is digitized by means of an A/D converter and may be indicated or further processed by any suitable computer device. In another preferred embodiment, the output signal from the measuring system is indicated by a system of at least two FEDs, preferably of different colours, located e.g. on the sensor housing and/or the electronic module housing, wherein the activation of one diode (e.g. blue or green) corresponds to a signal characteristic for "correct" fluid (i.e. the fluid that is supposed to be in the ECC in the given arrangement at a given moment) and the activation of the second diode (e.g. orange or red) corresponds to a signal outside the setpoint, i.e. a signal for another, "wrong" fluid in a given place and at a given moment. The measuring system arranged in this way simply and clearly indicates whether the fluid which should be there is present in a certain part of the ECC system (in a certain hose) at a certain moment.

The creation of suitable electronic circuits and possibly suitable software for operating these circuits and thus the measuring system according to the invention, which comprises a sensor according to the invention, is fully within the routine ability of a person skilled in the field of electrical and software engineering and, therefore, it is not discussed in detail here.

The present invention also relates to a method for detecting and identifying blood and infusion fluids in the ECC, wherein a sensor according to the invention is connected to a fluid conduit tube in the ECC, the electrodes are connected to the excitation and measuring circuit comprising the HF voltage generator, the load resistor and the excited AC voltage meter, wherein the sensor, the excitation HF voltage generator and the load resistor are connected in series and the excited AC voltage meter is connected in parallel to the load resistor, and after activating the excitation HF voltage the fluid flowing in the ECC is detected and identified based on the value of the excited AC voltage.

The present invention relates in particular to the sensor for detecting and identifying blood and infusion fluids as defined in appended claims 1 to 8 and to the measuring system for detecting and identifying blood and infusion fluids as defined in appended claims 9 and 10, and further to the method for detecting and identifying blood and infusion fluids in extracorporeal circulation circuit as defined in claim 11. Brief description of the figures in the drawings

FIG. 1: Schematic illustration of an embodiment of a sensor comprising two annular electrodes on a tube, input and output parts for connection to ECC tubes, wires and contacts for connecting power and measuring electronics, shielding cover, all placed in a housing. FIG. 2: Wiring diagram of a sensor connected to a HF power supply and to an additional, load resistor on which the output voltage is measured.

FIG. 3: It shows a schematic comparison of two variants of the sensor design. A. Compact sensor with two annular electrodes, where the whole system is enclosed in a shielding cover. B. Split sensor that consists of two identical parts, each of which contains only one annular electrode.

FIG. 4: It shows the connection of the sensor for measuring. The sensor shown is the split sensor of FIG. 3B, nevertheless, the measuring connection of the compact sensor of FIG. 3A would be analogous.

Examples of the invention

Example 1

Measurement principle and sensor design

From an electrical point of view, the sensor shown in FIG. 1 appears as a series combination of two capacitors connected by a conductive fluid - see the electrical model in FIG. 2.

The sensor 1 comprises two annular electrodes 2 and 3, which form, together with the wall of the tube 4, two capacitors with capacitances Cl and C2. The electrical model in FIG. 2 shows the sensor 1 arranged in a closed circuit, wherein the capacitors Cl and C2 are connected in series together with a generator of excitation HF voltage L (with frequency f) and load resistor RL, to which a detection circuit of HF voltage UOUT is connected in parallel. UOUT signal is measured after passage of the input HF signal through the fluid represented by the resistor Rp. From an electrical point of view, it is a two-port network, while its continuous damping characterizes the type of measured fluid. Equation (1) applies to the diagram in FIG. 2: where co= 2pΐ; C = C _/s CAAC _/ + Ci)\ Ei =\! tύ€

For the used frequency and the size of the design capacitance of the electrodes (Ci = C2 = approx. 35 pF) it is obvious that the impedance of the column of the most conductive fluid (e.g. 0.9% NaCl) is almost 300 times larger and can therefore be neglected in equation (1). For the frequency used, the conductivity of the column of the measured fluid shows practically no reactance component or a measurable non-linear dependence and can therefore be represented by a purely ohmic resistance. In a practical implementation, it is necessary for the whole set of two electrodes 2, 3 to be enclosed in a shielding cover 8 in order to minimize parasitic transmission of the HF signal outside the measured fluid.

The capacitances Ci and C2 are determined by geometry of the transport tubes used in clinical practice, so the only variable parameter is the length of the electrodes 2 and 3.

Example 2

Embodiment of the sensor

The sensor 1 in FIG. 1 comprises two annular electrodes 2, 3, which are arranged concentrically on the middle part of the tube 4 so as to be in close contact with the wall of the tube 4. The electrodes 2, 3 are made of copper, they are identical and have dimensions: a length 25 mm (the length means the dimension in the axis parallel to the longitudinal axis of the tube 4), an inner diameter 9.4 mm, an outer diameter 11.7 mm. The tube 4 is made of the plastic (PVC certified for medical use), has an outer diameter of 9.3 mm and an inner diameter of 6.4 mm and is provided with an inlet part 5 and an outlet part 6 for connecting the sensor 1 to the ECC tubes. The length of the tube 4 is adapted to the placement of the two electrodes 2, 3 so that the distance between the adjacent edges of the electrodes 2, 3 is 40 mm. The electrodes 2, 3 are connected by electrical conductors to contacts 7, which are exposed on the outer surface of a cylindrical housing 8, which encloses the whole sensor 1 and contains an electrical shielding 9, in the form of a 0.1 mm thick Cu sheet cylinder which is in this particular embodiment 20 mm from the centre of the tube 4. The contacts 7 are designed to allow the connection of a standardized plug (e.g. PSS 254/03G).

Under normal operation, usually the tubes with internal diameters: 1/8" (3.2 mm), 3/16" (4.8 mm), 1/4" (6.4 mm) are used. The sensor 1 described above can be easily implemented in alternative embodiments adapted to these tubes or any other kind of tubes.

Example 3

Verification of sensor performance

For the purpose of verifying the functionality of the sensor, a measuring circuit shown in FIG. 5 was constructed, which substantially corresponds to the electrical model depicted in FIG. 2.

In this example, the sensor 1 described above and the HF spectrum analyzer SIGLENT SSA 302 IX (Batronix GmbH, Preetz, Germany), were used. This device has two parts, one of which generates a variable HF signal (tracking generator) according to the set parameters, the other serves as a sensitive and selective HF voltmeter. The analyzer can be used to measure the HF characteristics of frequency-dependent circuits and display them graphically.

Blood, diluted blood or infusion fluids were passed through a PVC tube with an inner diameter of 9.4 mm and an outer diameter of 11.7 mm with a flow rate of 100 - 500 ml/min.

The output impedance of the tracking generator of the used spectrum analyzer was 50 W, wherein the reference level is 0 dBm (for 50 W 1 mW, i.e. voltage of 223 mV), with a frequency of 5 MHz.

The results achieved are summarized in the following table (relative values of dBm in relation to the reference value of the trace generator output and percentage values in relation to the value of sterile distilled water - aqua pro inj., average values from 5 repetitions are plotted):

Experimental verification of the sensor function showed that a) An optimum for the functioning of the sensor according to the invention is the frequency about 5 MHz; b) Using the sensor, it was possible to clearly (statistically significantly) distinguish between an empty tube (i.e. comprising air) and a tube containing saline, pure water and a tube containing full blood; c) If more stringent conditions for the stability of detection and discriminating electronic circuits are met, the degree of blood dilution with saline would be also detectable.

List of the reference numbers

1... non-contact sensor for detection and identification of blood and infusion fluids

2... first annular electrode

3... second annular electrode 4... tube

5... sensor fluid inlet

6... sensor fluid outlet

1... electrical contacts

8... sensor housing 9... sensor electrical shielding

Ci ... capacitance created by the first electrode C2... capacitance created by the second electrode R _f ... resistance of the fluid R _L - .. load resistance Ui _N - · · input (excitation) HF voltage U _OUT · · · output (measured) HF voltage