U.S. patent application number 11/808287 was filed with the patent office on 2007-11-15 for pressure sensing.
This patent application is currently assigned to GAMBRO LUNDIA AB. Invention is credited to Johan Drott, Thomas Hertz, Lennart Jonsson.
Application Number | 20070261496 11/808287 |
Document ID | / |
Family ID | 31974218 |
Filed Date | 2007-11-15 |
United States Patent
Application |
20070261496 |
Kind Code |
A1 |
Jonsson; Lennart ; et
al. |
November 15, 2007 |
Pressure sensing
Abstract
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.
Inventors: |
Jonsson; Lennart;
(Furrulund, SE) ; Drott; Johan; (Lund, SE)
; Hertz; Thomas; (Lund, SE) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
GAMBRO LUNDIA AB
|
Family ID: |
31974218 |
Appl. No.: |
11/808287 |
Filed: |
June 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10589353 |
Aug 11, 2006 |
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PCT/SE05/00184 |
Feb 11, 2005 |
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11808287 |
Jun 8, 2007 |
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60544205 |
Feb 12, 2004 |
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Current U.S.
Class: |
73/723 ; 29/825;
604/31 |
Current CPC
Class: |
Y10T 29/49117 20150115;
A61M 1/3639 20130101; A61M 2205/12 20130101; A61M 2205/3569
20130101 |
Class at
Publication: |
073/723 ;
029/825; 604/031 |
International
Class: |
G01L 9/00 20060101
G01L009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2004 |
SE |
0400330-7 |
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.
Description
TECHNICAL FIELD
[0001] The present invention relates to management of fluids used
in a medical procedure and more specifically to pressure sensing in
a biological fluid.
BACKGROUND
[0002] There 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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 INVENTION
[0011] An object of the present invention is to provide a system
capable of overcoming problems related to prior art systems.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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
[0025] FIG. 1 shows schematically an extracorporeal blood circuit
connected to a patient.
[0026] FIG. 2 shows schematically an extracorporeal blood circuit
comprising a device according to an embodiment of the present
invention.
[0027] FIG. 3 shows schematically a part of an extracorporeal blood
circuit comprising a device with a sensor according to an
embodiment of the present invention.
[0028] FIG. 4 shows part of FIG. 3 in larger scale.
[0029] FIGS. 5a-5e show schematically a device comprising a
pressure sensor.
[0030] FIGS. 6a and 6b show a tube mounted pressure sensor
according to an embodiment of the present invention.
[0031] FIG. 6c shows a tube mounted pressure sensor according to an
embodiment of the present invention.
[0032] FIGS. 7a and 7b show a system according to the present
invention.
[0033] FIGS. 8a-8c show a respective system according to the
present invention.
DESCRIPTION OF EMBODIMENTS
[0034] 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.
[0035] FIG. 1 discloses a forearm 1 of a human patient. The forearm
comprises an artery 2, in this case the radial artery, and a vein
3, in this case the cephalic vein. Openings are surgically created
in the artery 2 and the vein 3 and the openings are connected to
form a fistula 4, in which the arterial blood flow is
cross-circuited to the vein. Due to the fistula, the blood flow
through the artery and vein is increased and the vein forms a
thickened area downstream of the connecting openings. When the
fistula has matured after a few months the vein is thicker and may
be punctured repeatedly. Normally, the thickened vein area is
called a fistula. As the skilled person will realize, an artificial
vein may also be used.
[0036] 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.
[0037] The needles are connected to a tube system 7 shown in FIG.
2, forming an extracorporeal circuit comprising a blood pump 8,
such as may be found in a dialysis circuit. The blood pump
transfers blood from the blood vessel, through the arterial needle,
the extracorporeal circuit, the venous needle and back into the
blood vessel.
[0038] The extracorporeal blood circuit 7 shown in FIG. 2 further
comprises an arterial clamp 9 and a venous clamp 10 for isolating
the patient should an error occur.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] FIG. 3 shows schematically a section of a part of a blood
circuit 30 with a pressure sensor 323 according to the present
invention. The sensor 323 may be attached inside a tubing line such
as line 70 in FIG. 2 after the pump 8 leading to the dialyser, as
indicated by reference numeral 23'' in FIG. 2. Alternatively the
sensor 323 may be arranged in a tubing line 70 before the pump 8,
as indicated by reference numeral 23' in FIG. 2. As further
alternatives the sensor 23 may be arranged after the dialyzer at
reference numeral 23''' or in a drip chamber such as drip chamber
15 in FIG. 2.
[0044] 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 FIG. 4.
The variable capacitor may have in one embodiment a number of
interdigital conductors 28 in the form of fingers arranged on two
opposing metal electrodes. A first of the electrodes 29 may be
arranged on the compressible wall 24 while a second of the
electrodes 31 may be fixed in relation to the wall 32 of the blood
circuit, e.g. may be affixed to an interior wall of a tubing line
70 or a drip chamber 15. As the pressure in the extracorporeal
circuit varies, the compressible wall of the container will move
and accordingly the first electrode 29 and the second electrode 31
will move in relation to each other and thus the capacitance will
vary. The resonance frequency of the resonance circuit constituted
by the capacitor and the inductor will then vary in accordance with
the capacitance of the capacitor.
[0045] Outside the blood circuit an exciter antenna 33 in FIG. 3 is
arranged connected to a tunable oscillator 34 which may be
controlled by a control unit 39. The oscillator may drive the
antenna to influence the electromagnetic field at one or more
different frequencies. In one embodiment the control unit 39 may
use the grid-dip oscillator technique according to which technique
the oscillator frequency is swept over the resonance frequency of
the sensor, or other techniques for analyzing resonance frequencies
of LC circuits. The oscillator is inductively coupled to the sensor
and at the resonance frequency the sensor will be energized and
thereby drain energy from the external circuit. A current-dip in
the oscillator circuit may then be detected. The resonance
frequency of the oscillator circuit may then be detected and may be
transformed into a pressure by an established, e.g. calibrated,
relationship between the frequency of the dip frequency and the
fluid pressure, i.e. the difference between blood pressure and
atmospheric pressure.
[0046] A device comprising a pressure sensor 500 will now be
schematically described with reference to FIGS. 5a-d. FIG. 5a shows
the sensor 500 in perspective view and FIGS. 5b-d shows the sensor
500 in cross section and forming part of a wall 530 of an
extracorporeal blood circuit having an inside surface 531, being in
contact with the blood, and an outside surface 532, being in
contact with the outside atmosphere.
[0047] 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.
[0048] 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 FIGS. 3 and 4.
[0049] FIG. 5c illustrates a situation where the sensor 500 is
located in an environment in which the pressure in the
extracorporeal circuit is higher than the pressure inside the
cavity 503, i.e. higher than atmospheric pressure. This leads to a
net pressure force 510 acting on the lid 502 resulting in a
decrease of the volume of the cavity 503. Consequently, the two
electrodes 504,505 are brought closer to each other, changing the
capacitance of the electrode arrangement and thereby changing the
resonance frequency of the resonance circuit.
[0050] FIG. 5d illustrates a situation where the sensor 500 is
located in an environment in which the pressure in the
extracorporeal circuit is lower than the pressure inside the cavity
503, i.e. lower than atmospheric pressure. This leads to a net
pressure force 520 acting on the lid 502 resulting in an increase
of the volume of the cavity 503. Consequently, the two electrodes
504,505 are brought further away from each other, changing the
capacitance of the electrode arrangement and thereby changing the
resonance frequency of the resonance circuit.
[0051] FIG. 5e illustrates schematically an alternative embodiment
of a device comprising a sensor configuration. A sensor 551 is
mounted, e.g. glued or welded, on the inside wall 550 of a
container for a biological fluid, for example a blood container
with, e.g., rigid walls. Similar to the embodiment described above,
electrodes 554 and 565 and an inductor 566 are located on a sensor
lid 554 and a substrate 561, respectively. A cavity 553 is formed
by the lid 552 and the substrate 561. As in the previous
embodiment, the cavity 553 is in pressure communication with the
outside of the container for biological fluid by means of a hole
555. A pressure differences between the cavity and the inside of
the container for biological fluid results in flexing of the lid
552 and consequent relative displacement of the electrodes 554 and
565.
[0052] An alternative embodiment of a device according to the
invention is illustrated in a perspective view in FIG. 6a and in a
cross sectional view in FIG. 6b. A pressure sensor 601, similar to
the sensors described above in connection with FIGS. 5a-e,
comprises a cavity 603 and a hole 635 for allowing the cavity 603
to obtain atmospheric pressure. A part of an electrode pattern 605
is formed on the sensor 601. The sensor 601 is attached to a tube
602, of which only a short section is shown, by way of a housing
610. The difference between a pressure of a fluid within the tube
602 and the atmospheric pressure is sensed via a membrane 612 as
described above in connection with FIGS. 5a-e.
[0053] The device, i.e. housing and sensor described above in FIGS.
6a and 6b, is manufactured, for example, by way of techniques that
employ insert molding.
[0054] Yet an alternative embodiment of a device according to the
invention is illustrated in a cross sectional view in FIG. 6c. A
pressure sensor 681, similar to the sensors described above in
connection with FIGS. 5a-e, comprises a cavity 683 and a hole 685
for allowing the cavity 683 to obtain atmospheric pressure. A part
of an electrode pattern is formed on the sensor 681. The sensor 681
is attached to a tube 682, of which only a short section is shown,
at a location where the tube 682 is provided with a hole 690 as
described, e.g., in the international patent application published
with number WO 00/72747. The difference between a pressure of a
fluid within the tube 682 and the atmospheric pressure is sensed as
described above in connection with FIGS. 5a-5e.
[0055] Turning now to FIGS. 7a and 7b, a system 701 according to
one embodiment of the present invention will be briefly described.
The system 701 comprises a device 703, such as a cassette, which
forms part of an extracorporeal blood circuit 711, 712. Two
pressure sensors 702, such as the sensors described above, are
arranged in a side wall of the device 703, the arrangement being
such that the sensor is mounted flush with both an inside surface
and an outside surface of the wall of the device 703. It is to be
noted, however, that it is not necessary that the sensor is mounted
flush with the surfaces.
[0056] In operation, the device 703 is arranged at a dialysis
apparatus 704, only a part of which is shown in FIGS. 7a and 7b,
secured by means of mechanical coupling devices 708, 709. Within
the dialysis apparatus 704 is an electromagnetic wave transmitter
and a receiver located, schematically illustrated by a coil
structure 705. The transmitter and receiver is controlled by a
control unit (not shown) within the apparatus 704.
[0057] FIGS. 8a-c illustrate schematically, by way of a respective
block diagram, systems according to the present invention. The
systems may for example form part, as described above, of a
dialysis machine of which only a respective side wall 806, 826 and
846 is illustrated. Moreover, the systems are controlled by means
of a respective controller 801, 821 and 841.
[0058] In FIG. 8a, a first tunable oscillator 808 connected to a
first transmitting and receiving antenna 810 communicates by way of
a first alternating electromagnetic field with a first sensor 802.
A second tunable oscillator 812 connected to a second transmitting
and receiving antenna 814 communicates by way of a second
alternating electromagnetic field with a second sensor 804. The
tunable oscillators 808, 812 thereby provide a respective signal to
the controller 801 indicative of the conditions sensed by the
sensors 802 and 804, respectively.
[0059] In FIG. 8b, a transmitter 828 connected to a transmitting
antenna 830 generates, i.e. transmits, an alternating
electromagnetic field which interacts with a sensor 822. A receiver
832 receives, via a receiving antenna 834, the alternating
electromagnetic field, as modified by interaction with the sensor
822, and thereby provides a signal to the controller 821 indicative
of the conditions sensed by the sensor 822.
[0060] In FIG. 8c, a transmitter 848 connected to an antenna 850
generates, i.e. transmits, an alternating electromagnetic field
which interacts with a sensor 842. A receiver 852 receives, via the
same antenna 850, the alternating electromagnetic field, as
modified by interaction with the sensor 842, and thereby provides a
signal to the controller 841 indicative of the conditions sensed by
the sensor 842.
[0061] 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.
[0062] The testing pressure may be applied in a number of different
ways, for example as a static pressure in a pressure chamber.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] For example the resonant sensor described above may be
modified in that the inductance is made variable while the
capacitance is fixed.
[0067] 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.
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