Pressure sensing
A biological fluid device comprises a pressure sensor, which is arranged on the device. The pressure sensor comprises a compressible container, the compression of which is indicative of the pressure, and is capable of wireless communication.
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The present invention relates to management of fluids used in a medical procedure and more specifically to pressure sensing in a biological fluid.
BACKGROUNDThere are a number of procedures in which biological fluids such as blood, blood components as well as mixtures of blood or blood components with other fluids as well as any other liquid comprising biological cells, are managed. Examples of such procedures include treatments where blood is taken out in an extracorporeal blood circuit. Such treatments involve, for example, hemodialysis, hemofiltration, hemodiafiltration, plasmapheresis, blood component separation, blood oxygenation, etc. Normally, blood is removed from a blood vessel at a blood access and returned to the same blood vessel. During these procedures it is often desirable and also important to monitor the pressure in the biological fluid system.
U.S. patent application 20020007137 describes a prior art dialysis pressure sensing system wherein the pressure in an extracorporeal blood circuit is measured with an ordinary pressure transducer.
Typically, when performing pressure sensing using arrangements according to prior art, the extracorporeal blood circuit is connected to a patient and a dialysis machine. The pressure sensor is located within the dialysis machine and operably and structurally connected to the extracorporeal blood circuit.
Even though the extracorporeal blood circuit typically is in the form of a disposable arrangement there is a risk of cross contamination between patients. Between the pressure sensor in the dialysis machine and the blood in the disposable extracorporeal circuit is arranged an air column in a connector line/column. The air column exerts a backpressure on the blood, thereby preventing blood from getting in contact with the pressure sensor/machine. The dialysis machine normally comprises pumps of roller type creating a pulsating flow of blood in such a way that blood is penetrating into the connector line to some extent. In case the blood flow is blocked there is a potential risk that the backpressure exerted on the blood by the air column in the connector line is overcome and that blood reach a protective filter, protecting the pressure sensor. In such a case, cross contamination could occur if this situation reoccurs with another patient connected to the machine and the machine has not been cleaned properly. Also there is a potential risk that bacteria could grow in blood residuals at the protective filter.
Another problem is that of leakage, which may occur due to operator mistakes during set-up of the system. Needless to say, leakage could be of danger to an operator of the system in case contaminated blood is present in the system. Leakage may also lead to erroneous or less accurate pressure measurements.
International patent application with publication number WO 02/22187 discloses a blood pump having a disposable blood passage cartridge with integrated pressure sensors. Signal wires convey information from pressure transducers to a controller.
Hence, electrical contact problems may occur due to presence of spillage (or contamination) of fluids such as blood as well as contamination of particles such as salt crystals and burrs. Moreover electric connector means imply that there exist edges, indentations, protrusions etc. in the vicinity of means for transporting fluids, which typically enhances the risk of spillage (or contamination) of fluids as well as particles collecting in the area of the connector means. Needless to say, electrical connectors open to touch by operator, may also constitute an added risk of an operator being subject to electric shock.
Moreover, electric wiring and connectors that are needed for transmission of pressure information from pressure sensors according to prior art are unnecessarily complicated and adds to the risk of mistakes during use.
Thus, there is a general problem of how to provide a disposable fluid arrangement which is electrically safe, avoids risks relating to accumulation of spillage (or contamination) of fluids as well as particles, is easy to set-up, avoid leakage and which reduces the risk of cross contamination between patients and/or operators of the system.
SUMMARY OF THE INVENTIONAn object of the present invention is to provide a system capable of overcoming problems related to prior art systems.
The object of the present invention is achieved in different aspects by way of a device, a use of a device, a system, a use of a system and a method according to the appended claims.
An inventive device for transporting biological fluid in at least a part of an extracorporeal circuit, where at least part of the extracorporeal circuit is disposable and comprises at least one pressure sensor configured to be in fluid communication with the biological fluid during use, is characterized in that the at least one pressure sensor is configured for sensing a difference between a pressure of the biological fluid and a reference pressure and comprises an electric circuit that is configured to be energized by an applied alternating first electromagnetic field and configured to communicate information indicative of a pressure from the pressure sensor via a second alternating electromagnetic field.
In an embodiment, the first and second alternating electromagnetic fields are one and the same electromagnetic field and also in an embodiment, the first and second alternating electromagnetic fields are in the radio frequency range.
In an embodiment, the sensor comprises a compressible container, the compression or expansion of which is indicative of the pressure. Preferably, the container is open, i.e. configured with an opening or passage etc., to introduce atmospheric pressure into the container.
According to an embodiment of the present invention the pressure sensor may include components in the form of a capacitance and/or an inductance, of which components at least one is a variable component which varies with the relative compression and/or expansion of the container, said capacitance and/or inductance being part of a resonance circuit.
By having such a sensor it is possible to measure, in a wireless manner, the magnitude of the variable component by measuring the resonance frequency. This is advantageous in that it avoids the drawbacks related to prior art devices as discussed above. Thus, either the variable capacitance or the variable inductance is measured. From earlier measurements, i.e. calibration measurements, of the variable components dependence of the pressure the pressure may be determined.
Although it is preferred that the container is open, it is feasible that in some embodiments the compressible container may include a gas such as air at any known pressure, i.e. a reference pressure in a closed container. Thereby the container may have a known fixed pressure therein, so as to have a reference.
The sensor may be tailored to have any predetermined resonance frequency in an unaffected state. This may be used in an identification procedure by way of radio frequency measurements, in order to provide for identifying between different disposables used in different applications, such as dialyser, cassette, bloodline, ultrafilter, tube, connector, container, chamber, fluid bag, blood bag, collection bags, pump segment part of lineset, oxygenator etc.
A system for managing biological fluids according to the invention comprises a device with at least one pressure sensor as discussed above, at least one transmitter configured to transmit an alternating electromagnetic field to the at least one sensor in the device, at least one receiver configured to receive radio frequency information from the device, wherein the received information is indicative of at least one pressure sensed by the device, and a control unit configured to control the transmitter and the receiver. In an embodiment, the at least one sensor is located in close proximity, e.g. 5 to 40 mm, to the at least one transmitter and the at least one receiver.
An advantage of the invention is that, by disposing with the need for structurally connecting a pressure sensor to an extracorporeal blood circuit, thereby minimizing the air-blood interface, risks of cross contamination between patients and/or operators are avoided.
Another advantage is that it is easy to set-up and thereby avoiding risks of leakage, which may be dangerous to an operator of the system.
Yet another advantage of the present invention is that it provides an integrated pressure sensor which is sufficiently inexpensive to allow each device to be disposed of after each use.
The above aspects may be separate or combined in the same embodiment. Embodiments of the present invention will now be described with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described initially by way of illustration of an extracorporeal blood circuit during the process of dialysis followed by a description of pressure sensors and concluding with a description of a system comprising a blood circuit, pressure sensors, a transmitter and a receiver.
An arterial needle 5 is placed in the fistula, in the enlarged vein close to the connected openings and a venous needle 6 is placed downstream of the arterial needle, normally at least five centimeters downstream thereof.
The needles are connected to a tube system 7 shown in
The extracorporeal blood circuit 7 shown in
Downstream of pump 8 is a dialyzer 11 comprising a blood compartment 12 and a dialysis fluid compartment 13 separated by a semi permeable membrane 14. Further downstream of the dialyzer is a drip chamber 15, separating air from the blood therein.
Blood passes from the arterial needle past the arterial clamp 9 to the blood pump 8. The blood pump drives the blood through the dialyzer 11 and further via the drip chamber 15 and past the venous clamp 10 back to the patient via the venous needle. The drip chamber may comprise air or air bubbles.
The dialysis compartment 13 of the dialyzer 11 is provided with dialysis fluid via a first pump 16, which obtains dialysis fluid from a source of pure water, normally RO-water, and one or several concentrates of ions, metering pumps 17 and 18 being shown for metering such concentrates.
An exchange of substances between the blood and the dialysis fluid takes place in the dialyzer through the semi permeable membrane. Notably, urea is passed from the blood, through the semi permeable membrane and to the dialysis fluid present at the other side of the membrane. The exchange may take place by diffusion under the influence of a concentration gradient, so called hemodialysis, and/or by convection due to a flow of liquid from the blood to the dialysis fluid, so called ultrafiltration, which is an important feature of hemodiafiltration or hemofiltration.
The pressure sensor 323 comprises a container 25 with a compressible wall 24. A hole 35 in the wall 32 of the blood circuit ensures that the pressure within the container 25 is equal to atmospheric pressure. A resonance circuit is enclosed by the compressible container and comprises a variable capacitor 26 and an inductor 27. Such a sensor is shown in even larger scale in
Outside the blood circuit an exciter antenna 33 in
A device comprising a pressure sensor 500 will now be schematically described with reference to
The sensor 500 comprises a substrate 501 on which a lid 502 is arranged. A cavity 503 is formed between the substrate 501 and the lid 502, whereby the substrate 501 and the lid 502 form walls of the cavity 503, defining a container. The substrate 501 and the lid 502 are made of an electrically isolating material and the cavity 503 has been formed by way of, e.g., micro machining, as is known in the art. The cavity 503 is in pressure communication with the surroundings by means of a hole 535 in the substrate 501 in the sense that exchange of gas, i.e. air, is possible between the cavity 503 and the outside of the cavity 503. The container is also compressible, where the term compressible is used in the meaning that the volume of the container may increase as well as decrease depending on the pressure in the extracorporeal circuit.
A first electrode 504 and a second electrode 505 are arranged on two opposing walls of the cavity 503 forming a capacitive arrangement. These electrodes 504,505 form, together with an inductor 506, a resonance circuit similar to the one described above in connection with
An alternative embodiment of a device according to the invention is illustrated in a perspective view in
The device, i.e. housing and sensor described above in
Yet an alternative embodiment of a device according to the invention is illustrated in a cross sectional view in
Turning now to
In operation, the device 703 is arranged at a dialysis apparatus 704, only a part of which is shown in
In
In
In
After manufacture of a device comprising a pressure sensor as described above, there might be a wish to test the sensor so that one may be certain that it functions properly. One way of doing this is to apply a pressure to the sensor and measure the resonance frequency of the sensor. The sensor is made to have a certain resonance frequency without any applied pressure. If the pressure sensor has a different resonance frequency when a pressure is applied to the sensor this may be taken as an indication that the pressure sensor is functioning. However, it may be that the pressure sensor has a different resonance frequency without any applied pressure and still is non-functioning. Thus, in order to be more certain at least two different testing pressures may be applied to the sensor while the resonance frequency is measured.
The testing pressure may be applied in a number of different ways, for example as a static pressure in a pressure chamber.
By trimming during manufacturing of the pressure sensor it may be given different resonance frequencies which can thus be used to distinguish between different disposable sets. Thus, different tubing sets for use on the same machine may be identified as different tubing sets by discernment of the different resonance frequencies. Moreover, different medical procedures may also make use hereof.
As mentioned above the calibration at manufacturing and/or at the beginning of use at startup of a dialysis session can also provide for ensuring that the pressure sensor is working. This can be a function test like process to see if a proper response to the application of varying pressures by the blood pump or other mechanical alteration. The mechanical alteration may be the appliance of a mechanical force to test the electronic response frequency. The force for altering the sensor mechanically may be applied, e.g., by applying an ultrasound wave on the sensor.
The described embodiments are intended as examples only and may be modified by the man skilled in the art in a number of different ways without departing from the scope and the spirit of the invention which is defined by the appending claims.
For example the resonant sensor described above may be modified in that the inductance is made variable while the capacitance is fixed.
Another example is that the device for transporting biological fluid may be used in other extracorporeal management and/or treatments of biological fluids than specified above. Such other extracorporeal management and/or treatments may include: separation of blood into blood components; treatment to reduce pathogens such as viruses in biological fluids; absorption of specific cells or substances in blood; cell sorting and treatment of selected cells.
Claims
1-28. (canceled)
29. A disposable sensor system, comprising:
- a substrate;
- a capacitor and an inductor fixed to said substrate to form a disposable pressure sensor thereof, wherein said inductor comprises an inductor surface, at least one electrode of a capacitor and a compressible wall, wherein when said compressible wall is exposed to a pressure, said compressible wall moves close to said inductor surface and/or said at least one capacitor electrode, thereby resulting in an increase in an inductance and/or a capacitance and a decrease in a resonant frequency associated with said capacitor and said inductor, wherein said increase and said decrease are detectable by external interrogation; and
- interrogation electronics associated with said inductor and said capacitor, wherein said interrogation electronics externally detect said increase in said inductance and/or said capacitance and said decrease in said resonant frequency.
30. The system of claim 1 further comprising a trimming mechanism for trimming said capacitor in order to calibrate data based on said decrease in said resonant frequency.
31. The system of claim 1 further comprising a trimming mechanism for trimming said inductor in order to calibrate data based on said increase in said inductance.
32. A device for transporting biological fluid in at least a part of an extracorporeal circuit, said at least part of the extracorporeal circuit being disposable and comprising:
- at least one disposable sensor configured to be in fluid communication with the biological fluid, the at least one disposable sensor comprising: a substrate, a capacitor and an inductor fixed to said substrate to form a disposable pressure sensor thereof, wherein said inductor comprises an inductor surface, at least one electrode of a capacitor and a compressible wall, wherein when said compressible wall is exposed to a pressure, said compressible wall moves close to said inductor surface and/or said at least one capacitor electrode, thereby resulting in an increase in an inductance and/or a capacitance and a decrease in a resonant frequency associated with said capacitor and said inductor, wherein said increase and said decrease are detectable by external interrogation, and interrogation electronics associated with said inductor and said capacitor, wherein said interrogation electronics externally detect said increase in said inductance and/or said capacitance and said decrease in said resonant frequency.
33. The disposable sensor of claim 1 further comprising a trimming mechanism for trimming said capacitor in order to calibrate data based on said decrease in said resonant frequency.
34. The system of claim 1 further comprising a trimming mechanism for trimming said inductor in order to calibrate data based on said increase in said inductance.
35. A disposable sensor method, comprising the steps of:
- providing a substrate;
- fixing a capacitor and an inductor fixed to said substrate to form a disposable pressure sensor thereof;
- configuring said substrate to include an inductor surface, at least one capacitor electrode and a compressible wall, wherein when said compressible wall is exposed to a pressure, said compressible wall moves close to said inductor and/or a surface of said at least one capacitor electrode, thereby resulting in an increase in an inductance and/or a capacitance and a decrease in a resonant frequency associated with said capacitor and said inductor, wherein said increase and said decrease are detectable by external interrogation; and
- associating interrogation electronics with said inductor and said capacitor, wherein said interrogation electronics externally detect said increase in said inductance and/or said capacitance and said decrease in said resonant frequency.
36. The method of claim 35 further comprising the step of calibrating data based on said decrease in said resonant frequency utilizing a trimming mechanism for said capacitor.
37. The method of claim 35 further comprising the step of calibrating data based on said increase in said inductance utilizing a trimming mechanism for said inductor.
38. A disposable flow sensor comprising:
- at least one pressure sensing device for detecting fluid pressure in a channel, wherein said at least one pressure sensing device comprises: a compressible wall, and a capacitor electrically coupled to an inductor to form an LC tank circuit, said capacitor and/or inductor being mechanically coupled to said compressible wall such that a deflection of said diaphragm in response to fluid pressure applied thereto causes a change in the LC tank circuit inductance and/or capacitance and a change in the resonant frequency thereof, and wherein, when said at least one pressure sensing device is operatively coupled to said channel, said fluid pressure and said flow rate can be determined by detecting changes in said resonant frequency using interrogation.
39. The sensor of claim 38, wherein said capacitor comprises a pair of spaced apart conductive plates, one of said plates being carried on or forming said compressible wall.
40. The sensor of claim 39, wherein said inductor comprises a patch or layer of conductive or magnetic material carried on or forming said compressible wall, such that a deflection of said compressible wall causes a change in inductance of said inductor.
41. The sensor of claim 39 further comprising a substrate coupled to said compressible wall, said inductor and/or at one least one of said capacitor plates being carried on said substrate.
42. The sensor of claim 41 further comprising a calibration capacitor and/or calibration inductor carried on said substrate, said calibration capacitor and/or inductor being trimmable or adjustable for calibrating said pressure sensing device.
43. A differential pressure flow sensor system comprising:
- a disposable flow sensor comprising upstream and downstream pressure sensing devices for detecting a differential pressure between upstream and downstream locations of a flow channel;
- wherein each of said pressure sensing devices comprises a compressible wall, a capacitor and an inductor electrically coupled to said capacitor so as to form an LC tank circuit, said capacitor and/or inductor being mechanically coupled to said compressible wall such that a deflection of said diaphragm in response to fluid pressure applied thereto causes a change in the inductance and/or capacitance of said LC tank circuit and a change in the resonant frequency thereof and, wherein, when said upstream and downstream pressure sensing devices are operatively coupled to said upstream and downstream channel locations, respectively, said differential pressure and said flow rate can be determined by detecting changes in said resonant frequency using interrogation.
44. The system of claim 43 further comprising external interrogation electronics for wirelessly detecting said change in resonant frequency of each of said pressure sensing devices.
45. The system of claim 43, wherein said compressible wall of said pressure sensing devices are molded in a wall of said channel at upstream and downstream locations, respectively.
46. The system of claim 43 further comprising a substrate coupled to said compressible wall and, wherein said inductor and/or or at least one electrode plate of said capacitor is/are carried on said substrate.
47. The system of claim 46 further comprising a calibration capacitor and/or calibration inductor formed on said substrate, said calibration capacitor and/or inductor being trimmable or adjustable for calibrating said pressure sensing device.
48. The system of claim 43, wherein said capacitor comprises a pair of spaced apart conductive plates, one of said plates being carried on or forming said compressible wall.
49. The system of claim 43, wherein said inductor includes a patch or layer of conductive or magnetic material coupled to said compressible wall such that deflection of said diaphragm causes a change in inductance of said inductor.
50. The system of claim 43, wherein said inductor includes a single patch or layer of conductive or magnetic material coupled to both compressible wall of said pressure sensing devices such that deflection of said compressible wall causes a change in inductance of said inductors of said pressure sensing devices.
51. The system of claim 43 further comprising a transceiver for wireless transmitting an electromagnetic interrogation signal to said pressure sensing devices and/or for receiving resulting resonant electromagnetic signals therefrom so as to detect said changes in resonant frequency.
52. A method of manufacturing a flow sensor system for measuring the flow rate of fluid in a channel, said method comprising:
- forming a pair of disposable pressure sensing devices for measuring the pressure differential in a flow channel; and
- mechanically coupling said pressure sensing devices to said channel at upstream and downstream locations, respectively.
53. The method of claim 52, wherein forming each disposable pressure sensing device comprises: forming a compressible wall; forming a capacitor and inductor; electrically coupling said capacitor to said inductor so as to form an LC circuit; and mechanically coupling said capacitor and/or inductor to said compressible wall such that a deflection of said compressible wall caused by pressure applied thereto causes a change in said capacitance and/or inductance of said LC circuit.
54. The method of claim 52 further comprising configuring external interrogation electronics for wireless detecting the resonant frequencies of said pressure sensing devices.
55. The method of claim 52 further comprising forming a trimmable capacitor and/or trimmable inductor on said pressure sensing devices for calibration thereof.
Type: Application
Filed: Jun 8, 2007
Publication Date: Nov 15, 2007
Applicant:
Inventors: Lennart Jonsson (Furrulund), Johan Drott (Lund), Thomas Hertz (Lund)
Application Number: 11/808,287
International Classification: G01L 9/00 (20060101);