U.S. patent application number 11/160403 was filed with the patent office on 2005-12-29 for medical treatment system and method.
This patent application is currently assigned to INTEGRATED SENSING SYSTEMS, INC.. Invention is credited to Najafi, Nader, Sparks, Douglas Ray.
Application Number | 20050284815 11/160403 |
Document ID | / |
Family ID | 35504465 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050284815 |
Kind Code |
A1 |
Sparks, Douglas Ray ; et
al. |
December 29, 2005 |
MEDICAL TREATMENT SYSTEM AND METHOD
Abstract
A treatment system and method for treating a fluid withdrawn and
then returned to a living body. The system includes outgoing and
incoming fluid lines connected to the living body for transporting
the fluid from the living body, through the treatment system, and
back to the living body, a device for altering at least the density
of the fluid as it flows through the system, and a sensing unit
within the system and comprising a device for sensing the density
of the fluid as the fluid flows through the sensing unit. The
sensing device may be a micromachined Coriolis-based sensor also
capable of sensing mass flow rate.
Inventors: |
Sparks, Douglas Ray;
(Whitmore Lake, MI) ; Najafi, Nader; (Ann Arbor,
MI) |
Correspondence
Address: |
HARTMAN & HARTMAN, P.C.
552 EAST 700 NORTH
VALPARAISO
IN
46383
US
|
Assignee: |
INTEGRATED SENSING SYSTEMS,
INC.
391 Airport Industrial Drive
Ypsilanti
MI
|
Family ID: |
35504465 |
Appl. No.: |
11/160403 |
Filed: |
June 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60582976 |
Jun 28, 2004 |
|
|
|
Current U.S.
Class: |
210/645 ;
210/646; 210/742; 604/4.01; 604/65 |
Current CPC
Class: |
A61M 1/3626 20130101;
A61M 1/1656 20130101; G01F 1/8445 20130101; A61M 1/3663 20130101;
A61M 1/3639 20130101; A61M 1/1647 20140204; B01D 61/32 20130101;
G01F 1/8472 20130101 |
Class at
Publication: |
210/645 ;
210/646; 210/742; 604/065; 604/004.01 |
International
Class: |
B01D 061/24 |
Claims
What is claimed is:
1. A treatment system in which a fluid is withdrawn and then
returned to a living body, the system comprising: outgoing and
incoming fluid lines connected to the living body for transporting
the fluid from the living body, through the treatment system, and
back to the living body; means for altering at least the density of
the fluid as it flows through the system; and a sensing unit within
the system and comprising means for sensing at least the density of
the fluid as the fluid flows through the sensing unit.
2. The treatment system according to claim 1, wherein the treatment
system performs a treatment chosen from the group consisting of
hemodialysis, peritoneal dialysis, hemofiltration, and assistance
to kidneys, lungs, liver, and artificial organs of the living
body.
3. The treatment system according to claim 1, wherein the sensing
means further comprises means for sensing the temperature of the
fluid.
4. The treatment system according to claim 1, wherein the altering
means comprises means for introducing an ingredient into the fluid
as the fluid flows through the system.
5. The treatment system according to claim 1, wherein the altering
means comprises means for removing an ingredient of the fluid as
the fluid flows through the system.
6. The treatment system according to claim 1, wherein the sensing
unit further comprises means for communicating a density output to
a remote unit.
7. The treatment system according to claim 1, wherein the sensing
unit further comprises means for sensing at least one of the flow
direction and the flow rate of the fluid as the fluid flows through
the sensing unit.
8. The treatment system according to claim 1, wherein the sensing
unit comprises: a tube comprising a freestanding tube portion
through which the fluid flows; means for vibrating the freestanding
tube portion of the tube at a resonant frequency thereof that
varies with the density of the fluid flowing therethrough, the
Coriolis effect causing the freestanding tube portion to twist
while being vibrated at resonance, the freestanding tube portion
exhibiting a degree of twist that varies with the mass flow rate of
the fluid flowing therethrough; and means for sensing movement of
the freestanding tube portion of the tube, the movement-sensing
means producing a first output signal based on the resonant
frequency of the freestanding tube portion and a second output
signal based on the degree of twist of the freestanding tube
portion.
9. The treatment system according to claim 1, wherein the treatment
system performs hemodialysis and the fluid is blood.
10. The treatment system according to claim 9, wherein the sensing
unit senses the concentration of a component of the blood chosen
from the group consisting of urea, hematocrit, blood cells, water,
and anticoagulant.
11. The treatment system according to claim 9, further comprising
means for controlling the altering means based on the sensed
density of the blood.
12. The treatment system according to claim 9, wherein the altering
means comprises means for introducing an anticoagulant into the
blood, and the sensing unit senses the concentration of the
anticoagulant introduced into the blood by the introducing
means.
13. The treatment system according to claim 12, further comprising
a second sensing unit comprising means for sensing the flow rate of
the anticoagulant into the blood.
14. The treatment system according to claim 9, wherein the altering
means comprises a dialyzer through which a dialysate solution and
the blood flow to perform dialysis on the blood, and the treatment
system further comprises a second sensing unit that senses the
density and flow rate of the dialysate solution entering the
dialyzer.
15. The treatment system according to claim 9, wherein the altering
means comprises a dialyzer through which a dialysate solution and
the blood flow to perform dialysis on the blood, and the treatment
system further comprises a second sensing unit that senses the
density of the dialysate solution leaving the dialyzer.
16. The treatment system according to claim 15, further comprising
a source of water, a source of dialysate concentrate, means for
combining the water and dialysate concentrate to form the dialysate
solution, a third sensing unit comprising means for sensing the
flow rate of the water to the combining means, and a fourth sensing
unit comprising means for sensing the flow rate of the dialysate
concentrate to the combining means.
17. The treatment system according to claim 9, wherein the sensing
unit is sufficiently sensitive to the density of the blood to
detect sterilization fluids in the blood flowing through the
treatment system.
18. The treatment system according to claim 9, wherein the sensing
unit is sufficiently sensitive to the density of the blood to
detect air bubbles in the blood flowing through the treatment
system.
19. The treatment system according to claim 9, wherein the sensing
unit further comprises means for sensing the flow rate of the blood
through the treatment system, the treatment system further
comprising means in communication with the sensing unit for
detecting leakage of blood from the treatment system based on the
flow rate sensed by the sensing unit.
20. The treatment system according to claim 1, further comprising
means for receiving a density output from the sensing unit and
controlling the altering means based on the density output.
21. A method of treating a fluid of a living body, the method
comprising the steps of: withdrawing the fluid form the living body
and into a treatment system; altering at least the density of the
fluid as it flows through the treatment system; sensing at least
the density of the fluid as it flows through the treatment system;
and then returning the fluid to the living body.
22. The method according to claim 21, wherein the method performs a
treatment chosen from the group consisting of hemodialysis,
peritoneal dialysis, hemofiltration, and assistance to kidneys,
lungs, liver, and artificial organs of the living body.
23. The method according to claim 21, further comprising the step
of sensing the temperature of the fluid as it flows through the
system.
24. The method according to claim 21, wherein the altering step
comprises introducing an ingredient into the fluid as the fluid
flows through the system.
25. The method according to claim 21, wherein the altering step
comprises removing an ingredient of the fluid as the fluid flows
through the system.
26. The method according to claim 21, further comprising the step
of communicating the density to a remote unit.
27. The method according to claim 21, further comprising the step
of sensing at least one of the flow direction and the flow rate of
the fluid as the fluid flows through the treatment system.
28. The method according to claim 21, wherein the sensing step is
performed with a sensing unit comprising: a tube comprising a
freestanding tube portion through which the fluid flows; means for
vibrating the freestanding tube portion of the tube at a resonant
frequency thereof that varies with the density of the fluid flowing
therethrough, the Coriolis effect causing the freestanding tube
portion to twist while being vibrated at resonance, the
freestanding tube portion exhibiting a degree of twist that varies
with the mass flow rate of the fluid flowing therethrough; and
means for sensing movement of the freestanding tube portion of the
tube, the movement-sensing means producing a first output signal
based on the resonant frequency of the freestanding tube portion
and a second output signal based on the degree of twist of the
freestanding tube portion.
29. The method according to claim 21, wherein the method performs
hemodialysis on a patient and the fluid is blood of the
patient.
30. The method according to claim 29, wherein the sensing step
senses the concentration of a component of the blood chosen from
the group consisting of urea, hematocrit, blood cells, water, and
anticoagulant.
31. The method according to claim 29, further comprising the step
of controlling the altering step based on the sensed density of the
blood.
32. The method according to claim 29, wherein the altering step
comprises introducing an anticoagulant into the blood, and the
sensing step senses the concentration of the anticoagulant
introduced into the blood.
33. The method according to claim 32, further comprising the step
of sensing the flow rate of the anticoagulant into the blood.
34. The method according to claim 29, wherein the altering step
comprises a dialyzer through which a dialysate solution and the
blood flow to perform dialysis on the blood, and the method further
comprises sensing the density and flow rate of the dialysate
solution entering the dialyzer.
35. The method according to claim 29, wherein the altering step
comprises flowing a dialysate solution and the blood through a
dialyzer to perform dialysis on the blood, and the sensing step
senses the density of the dialysate solution leaving the
dialyzer.
36. The method according to claim 35, further comprising the steps
of: combining water and a dialysate concentrate to form the
dialysate solution; sensing the flow rate of the water being
combined with the dialysate concentrate; and sensing the flow rate
of the dialysate concentrate combined with the water.
37. The method according to claim 29, wherein the sensing step
detects sterilization fluids in the blood.
38. The method according to claim 29, wherein the sensing step
detects air bubbles in the blood.
39. The method according to claim 29, further comprising sensing
the flow rate of the blood in the system and detecting leakage of
blood based on the flow rate.
40. The method according to claim 29, further comprising the step
of sensing the density of urine excreted by the patient and then
initiating or controlling the method in response to the density of
the urine.
41. The method according to claim 21, further comprising the step
of controlling the altering step based on the sensed density of the
fluid.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/582,976, filed Jun. 28, 2004.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to medical treatment
systems that receive and return fluids to a patient. More
particularly, this invention relates to a medical treatment system
suitable for use in dialysis and other therapies in which a fluid
is withdrawn and then returned to a living body, and flow rates,
fluid concentrations, temperature, and other process parameters can
be accurately sensed with flow rate sensors.
[0003] Hemodialysis and peritoneal dialysis are used to remove
impurities from the blood, such as in the treatment of renal
failure and various toxic conditions. In hemodialysis, a patient's
blood is shunted from the body through a machine for diffusion and
ultrafiltration before being returned to the patient's circulation
system. Peritoneal dialysis requires access to the peritoneal
cavity, and involves the use of a catheter to fill the peritoneal
cavity with a dialysis solution. Waste products pass from the blood
into the dialysis solution through the peritoneum, and are then
removed from the peritoneal cavity when the dialysis solution is
drained.
[0004] Traditional hemodialysis is performed by accessing the blood
stream through an external shunt or arteriovenous fistula. The
external shunt is constructed by inserting two cannulas through the
skin into a large vein and artery. When performing dialysis the two
cannulas are used separately, allowing arterial blood to flow to a
dialyzer with which wastes (urea, creatinine, etc.) are removed
with a dialysate solution, after which the dialyzed blood is
returned to circulation through the cannula in the vein. A blood
pump is used to maintain flow through the dialysis system, and
various sensors are used to monitor the system, such as to monitor
the rate of heparin (anticoagulant) infusion, the conductivity and
temperature of the dialysate solution, and blood leak rates in the
dialysate solution leaving the dialyzer. Pressure sensors, air
bubble detectors, temperature monitors, leak detectors, and
conductivity meters have all been used, each usually as a separate
individual sensor that often must accommodate the relatively high
blood flow rates that must be maintained within the system to avoid
clotting. High dialysate flow rates through the dialyzer and the
dialysis membrane are also desirable to maximize the removal rate
of urea and other wastes. Consequently, accurate flow rate
measurement is required, which in the past have included the use of
ultrasonic flow sensors, optical sensors, and volumetric
containers. Finally, additional sensors, equipment, and procedures
have been used to monitor the efficiency and progress of dialysis
procedures, such as the slow-flow method, saline-dilution method,
blood temperature modules, monitoring urea and hematocrit levels,
and the occlusion method.
[0005] It would be desirable to improve yet simplify accurate
monitoring of dialysis treatments while avoiding clouting and other
dialysis-related problems that can occur include hemorrhaging,
hypotension, infection, thrombophlebitis, etc.
BRIEF SUMMARY OF THE INVENTION
[0006] The present invention provides a treatment system and method
for treating a fluid withdrawn and then returned to a living body.
The system includes outgoing and incoming fluid lines connected to
the living body for transporting the fluid from the living body,
through the treatment system, and back to the living body, means
for altering at least the density of the fluid as it flows through
the system, and a sensing unit within the system and comprising
means for sensing the density of the fluid as the fluid flows
through the sensing unit. In preferred embodiments of the
invention, the sensing means is also capable of sensing flow rates
and temperature. According to the invention, a preferred sensing
means comprises a micromachined Coriolis-based mass flow rate and
density sensor capable of extreme accuracy.
[0007] A significant advantage of this invention is that various
sensors previously required in medical treatment systems used for
biological fluids can be replaced by sensing means capable of
accurately sensing density. In the context of a dialysis treatment
system, density sensors can be used to sense additives (e.g.,
anticoagulants), wastes (e.g., urea and hematocrit), contaminants
(e.g., sterilization fluids), and air bubbles in the blood, sense
the concentration of the dialysate used to cleanse the blood,
detect blood leakage through the dialyzer, and generally monitor
the efficiency and progress of the dialysis procedure. Additional
system monitoring capabilities are achieved by including the
capability to accurately sense flow rates and temperature, such as
ensuring the proper flow rates, dosage rates, mixing, and
temperatures of the various fluids, with the result that multiple
functions are incorporated into a flow sensor capable of replacing
a variety of sensors previously used in dialysis treatment systems,
as well as other treatment systems and methods used in the medical
field.
[0008] Other objects and advantages of this invention will be
better appreciated from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic representation of a dialysis treatment
system in accordance with an embodiment of this invention.
[0010] FIG. 2 is a perspective view of a sensing unit for use in
the treatment system of FIG. 1.
[0011] FIGS. 3 and 4 are perspective and cross-sectional views,
respectively, of a Coriolis-type mass flow rate sensor suitable for
use in the sensing unit of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Illustrated in FIG. 1 is a dialysis treatment system 10
capable of making use of multiple sensing units 12 of a type or
types in accordance with this invention. The system 10 is
represented as being generally configured similar to traditional
hemodialysis. The blood stream of a patient 14 is accessed through
an external shunt or arteriovenous fistula, such as by inserting
two cannula 16 and 18 through the skin into a large vein and
artery. Arterial blood flows into the system 10 through the cannula
16 and is returned to the patient 14 through the cannula 18 in the
vein. The system 10 includes a blood pump 20 connected to a
dialyzer 22 with which wastes (urea, creatinine, etc.) are removed
from the blood with a dialysate solution. The blood pump 20 is
necessary to maintain acceptable flow rate through the system 10
and particularly through the dialyzer 22 to avoid clotting. As is
also generally conventional, the system 10 may include an arterial
drip chamber 24 and arterial pressure monitor 26 between the pump
20 and dialyzer 22. An anticoagulant is infused into the blood
flowing into the dialyzer 22 with an infusion pump 28. Before being
introduced into the dialyzer 22, the dialysate solution is prepared
by mixing purified water 30 and a dialysate concentrate 32 at a
controlled rate. The dialysate solution is drawn from the dialyzer
22 with a pump 34 and monitored with a blood leak detector 36.
Finally, an air bubble detector 38 is shown between the dialyzer 22
and venous cannula 18 to check for air bubbles in the blood that,
if delivered to the patient's blood stream, can cause venous air
embolisms that may lead to stroke or death.
[0013] While the invention will be described with reference to the
hemodialysis treatment system 10 shown in FIG. 1, the invention is
also applicable to other treatment systems in which a fluid is
withdrawn and then returned to the human body, including but not
limited to peritoneal dialysis, hemofiltration and assistance to
the kidneys, lungs, liver and artificial organs.
[0014] According to a preferred aspect of the invention, each
sensing unit 12 employs a sensor that can accurately measure
density, and preferably also flow rate and optionally temperature
of a fluid passing through it. More particularly, using the density
output of the units 12, the chemical concentration of any fluid
flowing in the system 10 (blood, dialysate, anticoagulant, water,
dialysate solution, etc.) can be measured. For example, density
output can be used to indicate the urea or hematocrit content
within the blood before and after passing through the dialyzer 22
to monitor the effectiveness and progress of a dialysis treatment.
Density output can also be utilized to monitor and control the
mixing of the water 30 and dialysate concentrate 32 to make the
dialysate solution, and to monitor and more accurately control the
flow of anticoagulant from the infusion pump 28 into the blood. The
sensing units 12 can also be used to detect sterilization fluids
like formaldehyde, solvents, and other cleaning solutions and
chemicals placed in the system 10 prior to use. If not entirely
removed, these cleaning solutions can be potentially injected into
the patient 14 causing injury or death. The ability to accurately
measure density with the sensing units 12 also enables the
detection of air bubbles and estimation of their volume.
[0015] In view of the above, the sensing units 12 of this invention
are able to supplement and/or replace many of the sensors
previously required by dialysis treatment systems. As replacements
for traditional sensing devices in a dialysis treatment system,
sensing units 12 of this invention are shown in the individual
lines from the water 30 and dialysate concentrate 32 and the line
carrying the resulting dialysate solution, thereby taking the place
of conductivity and temperature sensors typically used to monitor
the dialysate solution before being introduced into the dialyzer
22. Because of its density-sensing capability, the sensing unit 12
shown in the line connecting the air bubble detector 38 to the
venous cannula 18 can replace the bubble detector 38. As
supplemental sensors capable of improving the safety and efficacy
of the dialysis treatment, sensing units 12 are shown placed
between the arterial cannula 16 and the blood pump 20, immediately
downstream of the drip chamber 24 and in the line downstream of
where the anticoagulant enters the blood stream before being
introduced into the dialyzer 22, in the outlet line from the
dialyzer 22, in a discharge line connected to the line between the
dialyzer 22 and the bubble detector 38, and between the bubble
detector 38 and the venous cannula 18. These installations are
discussed in more detail below.
[0016] A suitable configuration for a sensing unit 12 for this
invention is depicted in FIG. 2. The unit 12 is shown as comprising
a housing 44 adapted for inline installation, though other
configurations are also possible and within the scope of this
invention. The housing 44 is formed to have a fluid inlet 46 and
outlet 48, both of which can be adapted for a fluidic connection
through such fittings as a Luer, threaded, compression, barbed,
lock or other type of fitting. The housing 44 contains a sensor 50
and electronic circuitry 52 located and enclosed within a cavity
defined within the housing 44 and closable with a cover (not
shown). The sensor 50 is the structure through which the fluid
being sensed flows and provides a measurable response to the
density and preferably the flow rate of the fluid. The circuitry 52
is preferably configured to communicate with and control the sensor
50 and output information regarding the operation of the sensing
unit 12. The unit 12 further includes an electrical connector 54 by
which the circuitry 52 can be coupled to a control unit (not shown)
such as a computer or another suitable electronic device capable of
controlling and receiving signals from the sensing unit 12. Such a
control unit may be hard-wired to the sensing unit 12 with the
connector 54, or the connector 54 can be replaced with a wireless
communication device of a type known in the art, such as an IR, RF,
optical, magnetic, etc. Power for the sensor 50 and circuitry 52
can be provided with a battery (not shown) within the housing 44,
delivered through a cable connected via the connector 54, or
delivered telemetrically using known tele-powering techniques.
[0017] The sensor 50 is represented as comprising a tube 56 that
serves as a conduit through which the fluid flows as it flows
between the inlet 46 and outlet 48 of the housing 44. In a
preferred embodiment of the invention, the sensor 50 and its tube
56 are part of a Coriolis mass flow sensor. FIGS. 3 and 4 depict a
preferred Coriolis mass flow sensor 50 taught in commonly-assigned
U.S. Pat. No. 6,477,901 to Tadigadapa et al., whose discussion of
the construction and operation of the flow sensor thereof is
incorporated herein by reference. In Tadigadapa et al., wafer
bonding and silicon etching techniques are used to micromachine the
tube 56 and its freestanding portion 58, which is suspended over a
silicon substrate 60. The freestanding portion 58 of the tube 56 is
vibrated at resonance such that, as fluid flows through an internal
passage 62 within the tube 56, the freestanding portion 58 twists
under the influence of the Coriolis effect. As explained in
Tadigadapa et al., the degree to which the freestanding portion 58
twists (deflects) when vibrated can be correlated to the mass flow
rate of the fluid flowing through the tube 56 on the basis of the
change in the amplitude of a secondary resonant vibration mode. The
density of the fluid is proportional to the natural frequency of
the fluid-filled vibrating portion 58, such that controlling the
vibration of the portion 58 to maintain a frequency at or near its
resonant frequency will result in the vibration frequency changing
if the density of the fluid flowing through the tube 56 changes. As
depicted in FIGS. 2 and 3, the freestanding portion 58 is
preferably U-shaped, though other shapes--both simpler and more
complex--are within the scope of this invention.
[0018] As known in the art, micromachining techniques a capable of
forming very small elements by bulk etching a substrate (e.g., a
silicon wafer), or by surface thin-film etching, the latter of
which generally involves depositing a thin film (e.g., polysilicon
or metal) on a sacrificial layer (e.g., oxide layer) on a substrate
surface and then selectively removing portions of the sacrificial
layer to free the deposited thin film. Accordingly, suitable
materials for the tube 56 include glass (e.g., quartz and Pyrex),
ceramic, metal or a semiconductor, including micromachined silicon,
germanium, Si/Ge and GaAs. The substrate 60, tube 56, and
freestanding portion 58 of the tube 56 are micromachined so that
the passage 62 connects ports 64 (one of which is shown) located on
the lower surface of the substrate 60. As previously noted,
micromachining technologies are preferably employed to fabricate
the tube 56, enabling the size of the tube 56 and its freestanding
portion 58 and passage 62 to be extremely small, such as lengths of
about 0.5 mm and cross-sectional areas of about 100 square
micrometers, with the result that the sensor 50 is capable of
processing very small quantities of fluid.
[0019] The resonant frequency of the freestanding tube portion 58
is determined in part by its mechanical design (shape, size,
construction and materials). Suitable frequencies are in the range
of 1 kHz to over 100 kHz, depending on the particular fluid being
analyzed. Under most circumstances, frequencies above 10 kHz,
including ultrasonic frequencies (those in excess of 20 kHz), will
be preferred. The amplitude of vibration is preferably adjusted
through means used to vibrate the tube portion 58. For this
purpose, FIG. 3 shows an electrode 66 located beneath the
freestanding portion 58 on the surface of the substrate 60. In the
embodiment shown, the tube 56 serves as an electrode (e.g., is
formed of doped silicon) that is capacitively coupled to the
electrode 66, enabling the electrode 66 to electrostatically drive
the freestanding portion 58. However, it is foreseeable that the
tube 56 could be formed of a nonconductive material, requiring a
separate electrode formed on the freestanding portion 58 opposite
the electrode 66 for vibrating the freestanding portion 58
electrostatically. Furthermore, the freestanding portion 58 could
be driven capacitively, piezoelectrically, piezoresistively,
acoustically, ultrasonically, magnetically, optically, or by
another actuation technique. Also shown in FIGS. 3 and 4 are
sensing electrodes 68 for providing feedback to enable the
vibration frequency and amplitude to be controlled with the
circuitry 52 within the sensing unit 12. While capacitive sensing
is preferred, the sensing elements 68 could sense the proximity and
motion of the freestanding portion 58 in any other suitable
manner.
[0020] FIG. 4 schematically represents the micromachined tube 56
enclosed by a cap 70 bonded or otherwise attached to the substrate
60. In a preferred embodiment, the bond between the cap 70 and
substrate 60 is hermetic, and the resulting enclosure is evacuated
to enable the freestanding portion 58 to be driven efficiently at
high Q values without damping. A suitable material for the cap 70
is silicon, allowing silicon-to-silicon bonding techniques to be
used, though other cap materials and bonding techniques are
possible and within the scope of the invention.
[0021] The resonating tube flow sensor 50 of Tadigadapa et al. is
preferred for use in the sensing units 12 of this invention, though
it is foreseeable that other types of flow sensors could be
employed. However, particularly advantageous aspects of the
resonating tube sensor of Tadigadapa et al. include its very small
size and its ability to precisely measure extremely small amounts
of fluids, in contrast to prior art Coriolis-type flow sensors.
Furthermore, the preferred flow sensor can attain flow rate
measurement accuracies of under +/-1%, in contrast to other types
of infusion pumps whose accuracies can range from about +/-15% for
volumetric pumps and +/-3% for syringe pumps. While the high cost
and the high flow rate requirements for prior art Coriolis-type
flow sensors have restricted their use in the drug delivery arena,
the flow sensor of Tadigadapa et al. is able to sense the extremely
low flow rates (e.g., less than 1 ml/hr) required by infusion
therapy applications, and can be used to sense the flow rates
associated with the dialysis treatment system 10 of FIG. 1. Because
of its tube configuration, the sensor 50 also has a bidirectional
flow capability that enables the sensing unit 12 to detect
incorrect flow direction in the system 10. The sensing unit 12 can
be used in a similar manner with peritoneal dialysis and other
forms of patient treatment for renal failure and other renal
applications, and for a variety of artificial organs and filtration
treatments for the kidneys, lungs and liver. For example, an
additional sensing unit 12 is shown in FIG. 1 as being employed
with a urinary catheter 17 to indicate the specific gravity and
concentration of the patient's urine, enabling the patient's health
and renal activity to be closely monitored. In this manner, the
output of the sensor 50 can be used to indicate a need for further
medical treatment, including dialysis. The sensing unit 12 can be
mounted in-line as part of the urinary catheter 17, or used to
analyze samples drawn from the catheter 17.
[0022] In order to provide the temperature-sensing capability
desired for the sensing unit 12, the sensor 50 is shown in FIG. 3
as including an on-chip thin film temperature sensor 72, such as a
resistance temperature detector (RTD), in close proximity to the
resonating tube 56. The temperature sensor 72 is shown integrated
on to the same substrate 60 as the tube 56 to provide an accurate
fluid temperature output, which in addition to providing useful
temperature data also enables temperature to be factored into the
fluid density measured by the sensor 50. Alternatively, a
temperature sensing capability can be achieved by fabricating a
second cantilevered tube on the substrate 60. According to
commonly-assigned U.S. Pat. No. 6,647,778 to Sparks, vibrating the
cantilevered tube at resonance enables the tube to measure the
temperature of the fluid flowing therethrough on the basis that the
Young's and shear modulus of the materials used to form the tube
change with temperature, causing the resonant frequency of the tube
to detectably shift with temperature.
[0023] From the above, it can be appreciated that sensing units 12
equipped with the sensor 50 and a temperature-sensing capability
(such as with the sensor 72) can be advantageously employed in the
hemodialysis treatment system 10 of FIG. 1 to monitor the blood and
the various fluids added to and removed from the blood. In
particular, it can be seen that the sensing units 12 shown in the
individual lines from the water 30 and dialysate concentrate 32 and
the line carrying the resulting dialysate solution to the dialyzer
22 are able to accurately monitor and provide feedback control for
the flow and subsequent mixing of the water 30 and concentrate 32
before the resultant dialysate solution is introduced into the
dialyzer 22, thereby replacing conductivity and temperature sensors
typically used to monitor the dialysate solution.
[0024] The density-sensing capability of the sensing unit 12 shown
in the line connecting the air bubble detector 38 to the venous
cannula 18 can be used to sense the density and temperature of the
blood returning to the patient 14, the former of which can be used
to sense the chemical concentration of urea, hematocrit, blood
cells, water, anticoagulants, etc., as well as the presence of
other desired and undesired components in the blood. The preferred
sensing unit 12 is also sufficiently sensitive to detect fine air
bubbles, as reported in commonly-assigned U.S. patent application
Ser. No. 10/248,839 to Sparks and U.S. patent application Ser. No.
10/708,509 to Sparks et al. As such, this sensing unit 12 can
entirely replace the bubble detector 38 represented in FIG. 1.
[0025] The sensing units 12 placed adjacent the arterial and venous
cannulas 16 and 18 are shown as being connected to an analyzer 42
capable of comparing the flow rates sensed by these sensing units
12, enabling the system 10 to detect blood leakage within the
system 10 as well as occlusions. As such, these sensing units 12
can replace the blood leak detector 36 represented as being
conventionally placed in the outlet line of the dialyzer 22.
Alternatively, FIG. 1 shows a sensing unit 12 placed in the outline
line of the dialyzer 22 to directly sense blood leak rates in the
dialysate solution leaving the dialyzer 22 by monitoring the
density of the dialysate solution.
[0026] The sensing units 12 placed immediately downstream of the
drip chamber 24, downstream of the anticoagulant fusion pump 28,
and in the line downstream of where the anticoagulant enters the
blood stream before entering the dialyzer 22 enables the flow rates
of the blood and anticoagulant to be accurately monitored to ensure
a proper amount of anticoagulant is present in the blood entering
the dialyzer 22. Dose and dose rates can also be calculated based
on the flow rate measured with these sensors. As noted previously,
this capability is advantageous because the preferred sensor 50 is
capable of greater accuracy than conventional infusion pumps.
[0027] Finally, FIG. 1 shows a sensing unit 12 placed in a
discharge line connected to the line between the dialyzer 22 and
the bubble detector 38. A valve 40 is represented as being placed
in the discharge line to allow limited quantities of blood to be
drawn from the system 10 and analyzed with the sensing unit 12 for
the purpose of measuring the density of the blood, with the
capability of sensing waste, sterilization fluids, etc., in the
blood before being returned to the patient 14.
[0028] With the system 10 shown, algorithms relating flow rate,
flow direction, fluid density, chemical concentration, and
temperature can be developed with each individual sensing unit 12
or inputs from several of these sensing units 12 placed as shown at
different points in the dialysis system 10. These algorithms can be
developed to provide better control the treatment that the patient
14 receives than is possible with a single parameter sensor, such
as the ultrasonic or optical flow sensors used in the past. The
sensing units 12 and their control unit(s) also enable dosage rates
of the anticoagulant and dialysate solution to be programmed
wirelessly via IR, RF, magnetic, optical, or other communication
approach, as can the flow rates and concentrations be monitored to
detect malfunctions in the system 10. With an appropriate control
interface, programming can be performed by the physician, care
giver, nurse, or pharmacist, such as with a wireless two-way data
communication system. In this manner, the dose rate of any additive
can be adjusted at any time before or during use and can be
recorded for later retrieval and evaluation of the treatment. With
the sensing units 12, safety limits can also be programmed into the
system 10 to prevent overdose or warn if occlusions, leaks, or an
unsafe urea or drug concentration is detected. The control
interface can also receive inputs from other sensors integrated
into the system 10 to sense bodily responses, such as glucose,
urea, hematocrit, oxygen, respiration rate, pulse, and other
chemical or physiological responses to the treatment, and then
adjust or halt the medication delivery rate if necessary. Along
this approach, the sensing unit 12 shown in FIG. 1 as monitoring
the density (specific gravity) of the patient's urine can be used
to indicate when dialysis is needed and/or control the dialysis
treatment, e.g., increase or decrease the flow rate of the
dialysate solution, anticoagulant, etc.
[0029] In some of the above applications, the sensing unit 12 and
its sensor 50 must accommodate the relatively high blood flow rates
maintained within the system 10 to avoid clotting. High dialysate
flow rates through the dialyzer 22 and its dialysis membrane are
also desirable to maximize the removal rate of urea and other
wastes. Such higher flow rates can be accommodated by designing and
inserting the sensing unit 12 as a bypass unit, in which a fraction
of the fluid is drawn through the sensing unit 12. Some of the
applications within the system 10 also require only density as the
sensed parameter. The sensing unit 12 shown in FIG. 2 and described
above can be used for this limited purpose, or other density meters
can be used such as meters available from the assignee of the
present invention. These sensing units 12 can be used to measure
density, specific gravity, or chemical concentration of all the
fluid flowing through a line, or used in a by-pass mode to sample a
portion of the fluid, or sample small portions of fluid from a
line, in which case the sample can be discarded as waste. If the
sample does not return to the patient 14, the sensing unit 12 can
be a durable, reusable portion of the dialysis system 10.
Otherwise, the sensing unit 12 can be manufactured as a disposable
unit that can be removed after each use of the system 10. Reusable
sensing units 12 can be coupled with a valve to admit small test
samples of the fluid of interest, which can then be tested for the
presence of sterilization fluid, intentionally added drugs, and/or
the chemical concentration of such additives as heparin or another
anticoagulant, dialysate concentration, or blood hematocrit/red
blood cells. In view of the small size of the preferred sensor 50,
only very small sample volumes are required for analysis, typically
on the order of nanoliters to milliliters in volume.
[0030] While the invention has been described in terms of a
preferred embodiment, it is apparent that other forms could be
adopted by one skilled in the art. Therefore, the scope of the
invention is to be limited only by the following claims.
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