U.S. patent application number 12/163935 was filed with the patent office on 2008-10-23 for devices and methods for use in assessing a flow condition of a fluid.
This patent application is currently assigned to Abbott Diabetes Care, Inc.. Invention is credited to Benjamin M. Rush.
Application Number | 20080257063 12/163935 |
Document ID | / |
Family ID | 37087707 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080257063 |
Kind Code |
A1 |
Rush; Benjamin M. |
October 23, 2008 |
DEVICES AND METHODS FOR USE IN ASSESSING A FLOW CONDITION OF A
FLUID
Abstract
A device for use in assessing a flow condition of a fluid, or a
fluid in a flow path, is provided. The device comprises at least
one electrochemical cell, comprising a working electrode and at
least one other electrode, sufficient for communication with the
fluid, or sufficient for communication with a flow path, such that
when sufficient fluid is in the flow path, the cell is in
communication with the fluid. The fluid comprises a component
sufficient to affect a mass-transport limited electrochemical
reaction at the working electrode. The device also comprises at
least one microcontroller operably connected to the at least one
electrochemical cell for providing a potential or a current to the
working electrode and for assessing the electrochemical reaction. A
method of assessing a flow condition of a fluid, or a fluid in a
flow path, is also provided. The device and the method of the
present invention may be used in connection with the delivery of a
fluid-borne or fluidized drug or medicament to a subject.
Inventors: |
Rush; Benjamin M.; (Oakland,
CA) |
Correspondence
Address: |
JACKSON & CO., LLP
6114 LA SALLE AVENUE, #507
OAKLAND
CA
94611-2802
US
|
Assignee: |
Abbott Diabetes Care, Inc.
Alameda
CA
|
Family ID: |
37087707 |
Appl. No.: |
12/163935 |
Filed: |
June 27, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11106256 |
Apr 13, 2005 |
7399401 |
|
|
12163935 |
|
|
|
|
10683659 |
Oct 9, 2003 |
6916159 |
|
|
11106256 |
|
|
|
|
60417464 |
Oct 9, 2002 |
|
|
|
60424613 |
Nov 6, 2002 |
|
|
|
Current U.S.
Class: |
73/861.08 |
Current CPC
Class: |
F04B 51/00 20130101;
A61M 5/16886 20130101; G01F 1/708 20130101; A61M 2205/3569
20130101; A61M 5/14216 20130101; A61M 5/14244 20130101; G01F 1/7088
20130101; A61M 2205/3592 20130101; G01F 25/0007 20130101; A61M
2205/702 20130101; A61M 2005/1726 20130101; F05C 2251/08 20130101;
A61M 2205/3317 20130101; F04B 2205/09 20130101; F04B 49/065
20130101; F04B 43/043 20130101; A61M 2205/0288 20130101; G01F 1/64
20130101 |
Class at
Publication: |
73/861.08 |
International
Class: |
G01F 1/56 20060101
G01F001/56 |
Claims
1. A device for use in assessing a flow condition of a fluid
sufficient to support an electrochemical reaction, comprising: at
least one electrochemical cell comprising a working electrode and
at least one other electrode, the electrochemical cell sufficient
for communication with a path via which the fluid flows, such that
when sufficient fluid is in the path, the electrochemical cell is
in communication with the fluid; at least one microcontroller
operably connected to the at least one electrochemical cell, the at
least one device sufficient to provide a current or a potential to
the working electrode sufficient for the electrochemical reaction
to take place at the working electrode, the at least one
microcontroller sufficient to receive information concerning a
mass-transport limiting affect of a component of the fluid on the
electrochemical reaction.
2. The device of claim 1, wherein the working electrode comprises a
material selected from carbon, gold, silver, platinum, copper, a
conductive polymer, and any combination thereof.
3. The device of claim 1, wherein the at least one other electrode
comprises a counter electrode.
4. The device of claim 3, wherein the counter electrode comprises a
material selected from carbon, gold, silver, platinum, copper, a
conductive polymer, and any combination thereof.
5. The device of claim 1, wherein the at least one other electrode
comprises a reference electrode selected from an Ag/AgCl electrode,
an Hg/HgO electrode, an Hg/Hg.sub.2SO.sub.4 electrode, an
Hg/Hg.sub.2Cl.sub.2 electrode, a normal hydrogen electrode, and a
reversible hydrogen electrode.
6. The device of claim 1 wherein the at least one electrochemical
cell comprises at least two electrochemical cells.
7. The device of claim 1, wherein one electrochemical cell of the
at least two electrochemical cells is sufficient for communication
with the path at one location and another electrochemical cell of
the at least two electrochemical cells is sufficient for
communication with the path at another location.
8 . The device of claim 1, wherein the fluid comprises a drug, a
medicament, a nutrient, a dietary supplement, a health supplement,
any source thereof, and any combination thereof.
9. The device of claim 1, wherein the fluid comprises a material
selected from insulin, an antibiotic, a nutrient, a dietary
supplement, a health supplement, total parenteral nutrition, an
analgesic, an anesthetic, a pain reliever, a hormone, a hormonal
drug, a gene therapy drug, an anticoagulant, a cardiovascular drug,
AZT, a chemotherapeutic drug, and any combination thereof, any
source thereof, and any combination thereof.
10. The device of claim 1, wherein the component is sufficient to
participate in, promote, or interfere with the electrochemical
reaction.
11. The device of claim 1, wherein the component is sufficient to
change the rate of the electrochemical reaction from what it would
be were the component absent.
12. The device of claim 1, wherein the component comprises a
material selected from an ionic species, a metallic species, a
metal oxide species, an organic species, oxygen, water, any source
thereof, and any combination thereof.
13. The device of claim 1, wherein the component comprises at least
one bubble of gas.
14. The device of claim 1, wherein the component is dilute relative
to the fluid.
15. The device of claim 1, wherein the component is of a
concentration of from about 10.sup.-7 M to about 10.sup.-2 M
relative to the fluid.
16. The device of claim 1, wherein the fluid comprises a drug and
the component comprises a reactant in the electrochemical reaction
that is dilute relative to the fluid.
17. The device of claim 16, wherein the drug is insulin.
18. The device of claim 16, wherein the reactant is an ionic
species.
19. The device of claim 16, wherein the drug is insulin and the
reactant is ionic zinc.
20. The device of claim 1, wherein the fluid comprises a reactant
in the electrochemical reaction and the component is sufficient to
interfere with transport of the reactant to the working
electrode.
21. The device of claim 20, wherein the fluid comprises a drug and
the reactant is an ionic species.
22. The device of claim 20, wherein the fluid comprises insulin and
the reactant is ionic zinc.
23. The device of claim 20, wherein the component comprises at
least one bubble of gas.
24. The device of claim 1, wherein the electrochemical reaction at
the working electrode is a promoted electrochemical reaction, the
fluid comprises a reactant in the promoted electrochemical
reaction, and the component is sufficient to promote the promoted
electrochemical reaction and sufficient to affect the promoted
electrochemical reaction such that the promoted electrochemical
reaction is mass-transport limited.
25. The device of claim 24, wherein the fluid comprises a drug.
26. The device of claim 24, wherein the reactant is an ionic
species.
27. The device of claim 24, wherein the drug is insulin and the
reactant is ionic zinc.
28. The device of claim 24, wherein the component is dilute
relative to the fluid.
29. The device of claim 1, further comprising the path.
30. The device of claim 1, further comprising a source of the fluid
in communication with the path.
31. The device of claim 30, wherein the source comprises a
pump.
32. The device of claim 30, wherein the source is sufficient for
providing the fluid in a continuous manner.
33. The device of claim 30, wherein the source is sufficient for
providing the fluid in a non-continuous manner.
34. The device of claim 30, wherein the source is sufficient for
providing the fluid in at least two pulses.
35. The device of claim 34, wherein the information comprises an
indicator of the rate of the electrochemical reaction associated
with the at least one electrochemical cell and associated with each
of the at least two pulses.
36. The device of claim 34, wherein the information comprises an
indicator of the rate of the electrochemical reaction associated
with the at least one electrochemical cell and associated with the
at least two pulses at a predetermined interval.
37. The device of claim 1, wherein the information comprises an
indicator of the rate of the electrochemical reaction associated
with the at least one electrochemical cell.
38. The device of claim 1, wherein the information comprises an
indicator selected from a current, a potential, a charge, a
resistance, and any combination thereof.
39. The device of claim 1, wherein the at least one microcontroller
is sufficient to control a delivery of the fluid based on the
information.
40. The device of claim 1, further comprising a device sufficient
for determining a flow rate associated with the fluid in the
path.
41. The device of claim 40, wherein the device comprises a first
pair of electrodes at a first point relative to the electrochemical
cell and a second pair of electrodes at a second point relative to
the electrochemical cell, each of the first and the second pair of
electrodes in communication with the path, each of the first and
the second pair of electrodes sufficient for indicating an absence
or a presence of the fluid.
42. The device of claim 40, wherein the at least one
microcontroller is sufficient to control a delivery of the fluid
based on the flow rate.
43. The device of claim 1, further comprising a device sufficient
for determining a temperature of the fluid in the path.
44. The device of claim 43, wherein the at least one
microcontroller is sufficient to control a delivery of the fluid
based on the temperature.
45. The device of claim 1, further comprising a housing for the at
least one electrochemical device, the at least one microcontroller,
and a source of the fluid.
46. The device of claim 1, further comprising a housing for the at
least one electrochemical device, the at least one microcontroller,
a source of the fluid, and at least a portion of a device
sufficient for delivery of the fluid to a location outside of the
housing.
47. The device of claim 46, wherein the housing is sufficient for
wearing on a skin surface and the location is beneath the skin
surface.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional application of U.S.
application Ser. No. 11/106,256 filed Apr. 13, 2005, which is a
continuation-in-part of U.S. application Ser. No. 10/683,659 of
Benjamin M. Rush et al., filed on Oct. 9, 2003, which is related to
and claims priority based on U.S. Provisional Application No.
60/417,464, entitled "Disposable Pump for Drug Delivery System,"
filed on Oct. 9, 2002, and U.S. Provisional Application No.
60/424,613, entitled "Disposable Pump and Actuation Circuit for
Drug Delivery System," filed on Nov. 6, 2002, each of which is
hereby incorporated herein, in its entirety, by this reference. The
present application is related to U.S. application Ser. No.
11/106,155 of Benjamin Rush et al., entitled "Variable Volume,
Shape Memory Actuated Insulin Dispensing Pump," and U.S.
application Ser. No. 11/105,711 of Benjamin M. Rush, entitled
"Fluid Delivery Device with Autocalibration," each of which was
filed Apr. 13, 2005, and are hereby incorporated herein, in their
entirety, by this reference.
FIELD OF THE INVENTION
[0002] This invention generally relates to a device and a method
for assessing flow of a fluid. The device and method may be used in
connection with fluid delivery devices, systems, and methods.
Merely by way of example, the device and method may be used in
connection with a small volume, disposable medical device for the
precision delivery of a medicine or a drug, such as insulin, and
associated systems and methods.
BACKGROUND
[0003] A wide variety of fluid delivery devices have been developed
for various applications, such as the delivery of medicine or
drugs. By way of example, automated infusion devices that can
deliver a fluidized or fluid-borne drug to a subject with extremely
high precision have been developed. (See, for example, the
above-referenced U.S. Patent Application Publication No.
2004/0115067 A1 and the above-referenced U.S. application Ser. No.
11/106,155 of Benjamin Rush et al, concurrently filed herewith.) If
these devices fail to deliver a drug to a subject at an acceptable
or intended rate, the consequences can be anywhere from relatively
minor to relatively major, even deadly. Thus, some means of
verifying that a drug is being delivered or has been delivered at
an acceptable or intended rate is typically incorporated into
automated drug infusion devices.
[0004] Drug delivery verification means may allow for the detection
of insufficient and/or excessive drug delivery or fluid flow.
Traditional means or methods for measuring fluid flow include
hot-wire anemometry, generation and detection of a heat pulse,
injection and detection of a tracer component, and electromagnetic
flow measurement, such as via passage of an ion-containing liquid
through a loop and detection of an associated current.
[0005] Other means for measuring fluid flow have been developed for
specific devices, as well. For example, means for detecting a
build-up of pressure within a drug delivery path, such as that
caused by a blockage in the path, have been incorporated into
portable insulin pumps. These means, which include a pressure
transducer, can detect insufficient fluid flow from the insulin
pump, such as insufficient flow caused by a blockage in the
delivery tubing or in the cannula, but cannot detect excessive
fluid flow from the pump. The pressure transducer adds to the cost
and complexity of this portable insulin pump.
[0006] Another method of detecting insufficient fluid flow from a
fluid delivery device, such as a drug delivery device, has been
disclosed. (See U.S. Pat. No. 6,692,457.) According to this method,
the fluid flows past a resilient chamber, such as a balloon or a
bubble, in the flow path. If the flow path is blocked at a point
downstream from the bubble, for example, the pressure in the flow
path increases, such that the bubble expands and a surface of the
expanded bubble activates a sensor to indicate a blockage
condition.
[0007] Methods of monitoring the rate of fluid delivery from a drug
delivery device have also been disclosed. (See U.S. Pat. No.
6,582,393 and U.S. Patent Application Publication No. 2004/0019321
A1.) According to one such method, a small amount of fluid is
heated via a heating element, such as a laser, and the presence of
this heated amount of fluid is detected downstream via a heat
sensor, such as another laser, and a rate of fluid flow is
determined and evaluated. According to another such method, the
flowing fluid is subjected to a magnetic field, such that ions in
the fluid produce a directional current, which is then detected and
associated with the volumetric flow rate. Compensating adjustments
to the flow rate may then be made accordingly.
[0008] Devices for measuring fluid flow have also been developed
for applications unrelated to drug delivery. By way of example, a
device for measuring the very slow flow associated with
hydrothermal systems, such as hydrothermal systems on the seafloor
or dilute hydrothermal systems, has been described at
http://gore.ocean.washington.edu/research/slow_flow_meter.html. In
the case of seawater, the seawater fluid enters the tubular device
and generates a "puff" of chlorine gas at a platinum electrode of
an electrode pair within the device, via the electrochemical
reaction, 2Cl.sup.-.fwdarw.C1.sub.2+2e.sup.-. The puff is confined
within the device, where it is detected via two sensing electrodes
placed at fixed distances from the platinum electrode along the
tubular device. The times required for the puff to travel known
distances along the device provide a measure of the flow velocity
of the seawater.
[0009] Devices for measuring various parameters of a moving fluid
have also been developed for various applications. By way of
example, a rotating disk electrode has been developed as a means of
producing a very regular and reproducible liquid flow profile when
immersed in a liquid. If the liquid contains a dilute species that
can react at the electrode, the rate of reaction will depend on the
speed of rotation associated with the rotating disk electrode. This
phenomenon may be used to determine the concentration of the dilute
species in the liquid. (See, for example, A. J. Bard and L. R.
Faulkner, Electrochemical Methods, 2nd Ed., John Wiley (2001).)
[0010] Further development of fluid flow measurement devices, and
associated systems, devices and methods, is desirable.
BRIEF SUMMARY OF THE INVENTION
[0011] According to an aspect of the present invention, a technique
for assessing, measuring, and/or monitoring flow of a medium is
provided. The flow of the medium may be relatively unconfined or
natural, such as the flow of water in a body of water, such as sea
or ocean water in a body thereof, or may be in a flow path, such as
the flow of insulin from an insulin pump through a delivery
channel, for example. An electrochemical cell is immersed in the
medium and is used to assess, measure, and/or monitor the state of
flow of the medium. According to an aspect of the invention, the
cell is used to assess, measure, and/or monitor the rate of an
electrochemical reaction associated with the medium. According to
an aspect of the invention, a device for carrying out the technique
is provided. The device may be a simple, inexpensive, qualitative
and/or quantitative device.
[0012] According to an aspect of the invention, the technique is
based on the notion of a mass-transport limited reaction. The rate
at which a chemical reaction proceeds is determined by at least one
of two things, the inherent kinetics of the reaction or the rate at
which reactants become available to react. Examples of the latter
include heterogeneous reactions, such as those that take place at a
catalytic or reacting phase boundary. By way of example, an
oxidation reaction in which ferrous ion in water is oxidized to
ferric ion (Fe.sup.2+.fwdarw.Fe.sup.3++e.sup.-) at an appropriate
working electrode, such as a gold working electrode at an
appropriate potential, for example, is such a reaction. Further by
way of example, a reduction reaction in which ferric ion in water
is reduced to ferrous ion (Fe.sup.3++e.sup.-.fwdarw.Fe.sup.2+) at
an appropriate working electrode, such as a gold working electrode
at an appropriate potential, for example, is such a reaction. In
either an oxidation reaction or a reduction reaction, if the
reactant were readily available without limitation, the reaction
would proceed at a rate dictated by the inherent reaction kinetics
of the reaction. However, if the reactant were not so readily
available, such as in the case where the concentration of the
reactant is sufficiently low so that the rate at which it diffuses
to the working electrode surface is slower that the rate at which
it reacts at the working electrode surface, then the rate of
reaction would be dictated by the transport rate of the reactant,
rather than by the inherent reaction kinetics of the reaction.
Thus, increasing the rate of mass transport of the reactant, such
as via water movement (for example, via forced flow or circulation
of water), would increase the rate of such a reaction. Accordingly,
the rate of a mass-transport limited reaction may serve as an
indicator as to the status or condition of fluid flow.
[0013] According to an aspect of the present invention, the rate of
a mass-transport limited reaction, such as the oxidation reaction
or the reduction reaction just described, serves as a measure or
monitor of the state of the fluid flow around it. According to
another aspect of the present invention, a device and a method for
assessing, measuring, and/or monitoring the flow of fluid based on
the principle just described, is provided. According to yet another
aspect of the present invention, a device and a method for
assessing, measuring, and/or monitoring the flow of a drug or a
medicament, such as insulin, for example, that is pumped through a
flow channel, such as via an automatic infusion pump, for example,
is provided. According to yet another aspect of the present
invention, a device and a method for assessing a flow condition of
a fluid, may be used to provide information concerning any of a
wide variety of flow conditions and parameters, may be used to
indicate or provide notification of a deviation from a desirable or
an intended flow condition, may be used in a feedback loop to
control, adjust, or maintain the flow condition, such as an
automated feedback loop, for example, and/or the like.
[0014] These and various other aspects, features and embodiments of
the present invention are further described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A detailed description of various aspects, features and
embodiments of the present invention is provided herein with
reference to the accompanying drawings, which are briefly described
below. The drawings are illustrative and are not necessarily drawn
to scale. The drawings illustrate various aspects or features of
the present invention and may illustrate one or more embodiment(s)
or example(s) of the present invention in whole or in part. A
reference numeral, letter, and/or symbol that is used in one
drawing to refer to a particular element or feature may be used in
another drawing to refer to a like element or feature.
[0016] FIG. 1 (FIG. 1) is a schematic illustration of a device
according to an embodiment of the present invention.
[0017] FIG. 2 (FIG. 2) is a schematic illustration of a device
according to an embodiment of the present invention.
[0018] FIG. 3 (FIG. 3) is a graphical representation of current
(amperes) versus time (seconds) associated with an example
concerning a device according to an embodiment of the present
invention.
[0019] FIG. 4 (FIG. 4) is a graphical representation of a
normalized integration of the current pulses versus pulse number
associated with an example concerning a device according to an
embodiment of the present invention.
[0020] FIG. 5 (FIG. 5) is a graphical representation of current
(amperes) versus time (seconds) associated with an example
concerning a device according to an embodiment of the present
invention.
[0021] FIG. 6A (FIG. 6A) is a schematic illustration of a device
according to an embodiment of the present invention. Each of FIG.
6B (FIG. 6B) and FIG. 6C (FIG. 6C), independently, is a schematic
illustration, in the form of a flow chart, of a method according to
an embodiment of the present invention.
[0022] FIG. 7 (FIG. 7) is a schematic illustration of a system
according to an embodiment of the present invention.
DETAILED DESCRIPTION
[0023] In the description of the invention herein, it will be
understood that a word appearing in the singular encompasses its
plural counterpart, and a word appearing in the plural encompasses
its singular counterpart, unless implicitly or explicitly
understood or stated otherwise. Further, it will be understood that
for any given component described herein, any of the possible
candidates or alternatives listed for that component, may generally
be used individually or in combination with one another, unless
implicitly or explicitly understood or stated otherwise.
Additionally, it will be understood that any list of such
candidates or alternatives, is merely illustrative, not limiting,
unless implicitly or explicitly understood or stated otherwise.
Still further, it will be understood that any figure or number
presented herein in connection with the invention is approximate,
and that any numerical range includes the minimum number and the
maximum number defining the range, unless implicitly or explicitly
understood or stated otherwise.
[0024] Various terms are generally described below to facilitate an
understanding of the invention. It will be understood that a
corresponding description of these various terms applies to
corresponding linguistic or grammatical variations or forms of
these various terms. It will also be understood that the general
description of any term below may not apply or may not fully apply
when the term is used in a non-general or more specific manner. It
will also be understood that the invention is not limited to the
terminology used herein, or the descriptions thereof, for the
description of particular embodiments. It will further be
understood that the invention is not limited to embodiments of the
invention as described herein or applications of the invention as
described herein, as such may vary.
[0025] The term "amperometry" generally refers to the determination
or measurement of the strength of a current and encompasses
steady-state amperometry, chronoamperometry, and Cottrell-type
determination or measurement.
[0026] The term "concentration" may generally refer to a signal
that is indicative of a concentration of a component in a medium,
such as a current signal or a voltage signal, for example, to a
more typical indication of a concentration of a component in a
medium, such as mass of the component per unit volume of the
medium, for example, and/or the like.
[0027] The term "control" generally refers to any type of control
and encompasses the maintenance of a condition or status and the
adjustment of a condition or status, which control may be
automated. In various embodiments of the present invention, a
microcontroller sufficient to control a delivery of a fluid or a
fluid delivery device based on any of a variety of parameters, such
as a current, a potential, a charge, a resistance, a rate of an
electrochemical reaction, a fluid flow rate, a fluid temperature,
and/or the like, is provided. The microcontroller may be sufficient
to control such delivery in an automated manner, such as via a
feedback loop.
[0028] The term "coulometry" generally refers to the determination
of charge passed or projected to pass during complete or nearly
complete electrolysis of a material, either directly on the
electrode or via at least one electron-transfer agent. The charge
is determined by measurement of electrical charge passed during
partial or nearly complete electrolysis of the material, or, more
often, by multiple measurements during the electrolysis associated
with a decaying current over an elapsed period. The decaying
current results from the decline in the concentration of the
electrolyzed species caused by the electrolysis.
[0029] A "counter electrode" generally refers to at least one
electrode that is paired with a working electrode and through which
passes an electrochemical current. In general, the counter
electrode is a conductor that completes the electrochemical cell or
circuit. The current that flows into the electrically conductive
solution via the working electrode leaves the solution via the
counter electrode. The term "counter electrode" encompasses a
counter electrode that also functions as reference electrode (i.e.,
a counter/reference electrode), unless the description provides
that a "counter electrode" excludes a counter/reference
electrode.
[0030] The term "current" generally refers to one type of measure
that can be used in connection with the present invention. It will
be understood that although current is often discussed as a type of
measure employed herein, current, potential or voltage, charge, or
resistance may be employed alone or in any suitable combination as
a type of measure herein.
[0031] The term "electroactive" generally refers to a species in
solution that can take part in an electrochemical reaction or that
can be adsorbed on the working electrode.
[0032] The term "electrochemical cell" generally refers to a cell
at which an electrochemical reaction may take place. In a
potentiostatic mode, a working electrode of such a cell may be
controlled or held at a certain potential or voltage and may
produce a current, which may be measured. In a galvanistatic mode,
a working electrode of such a cell may be controlled or held at a
certain current and produce a voltage, which may be measured. In
yet another mode, current, voltage, charge, and/or resistance
associated with such a cell, or with simply an electrode pair
(i.e., a pair of electrodes, neither of which is a reference
electrode, such that an electrochemical reaction at the pair may be
uncontrolled or undefined), may be measured, such as may be useful
to determine whether or not an electrochemical reaction is taking
place at the working electrode. In connection with an
electrochemical cell, any of these modes may be quantitatively or
qualitatively employed. In connection with a pair of electrodes,
the latter mode is generally qualitatively employed.
[0033] The term "electrolysis" generally refers to the
electrooxidation or electroreduction of a compound either directly
at an electrode or via at least one electron-transfer agent, such
as a redox mediator and/or an enzyme, for example. Examples of
electrolysis via an electron-transfer agent and/or an enzyme are
provided in U.S. Pat. Nos. 6,676,816, 6,605,200, and 6,605,201, and
U.S. patent application Ser. Nos. 10/251,513, 10/819,498, and
11/007,617, for example.
[0034] The term "flow path" generally refers to any path, pattern,
direction, way, manner, and/or the like, in which fluid may flow.
The flow path may be natural or unnatural, introduced, relatively
unconfined or relatively confined, anything in between, the like,
or any combination thereof, merely by way of example. The term
"flow path" encompasses a flow path of a fluid in a body of fluid,
such as the flow of water, ocean water, or sea water, in a body of
fluid, whether a natural flow, such as via a natural current, or an
artificially introduced flow, such as via artificial movement or
agitation of the fluid, or the flow path of a fluid in a flow
channel, such as a delivery channel from a source of fluid, which
may be naturally fed, gravity fed, pump fed, and/or the like,
merely by way of example.
[0035] The term "fluid" generally refers to any medium that can
support an electrochemical reaction at an electrochemical cell
within the fluid. In most cases, the term "medium" generally refers
to a liquid medium. The medium should be sufficiently ion
conductive to support an electrochemical reaction at the
electrochemical cell. For example, when the electrochemical
reactant is dilute, such as dilute ionic zinc in an insulin
preparation, the fluid may contain an inert ionic species or a
supporting electrolytic component that is sufficient to support the
electrochemical reaction at the electrochemical cell. A supporting
electrolyte is one that is added to a solution for the purpose,
such as the sole or predominant purpose, for example, of increasing
the conductivity of the solution and that does not participate in
the electrochemical reaction. Such a supporting electrolyte may be
referred to as an "inert" electrolyte, an "indifferent"
electrolyte, or a "swamping" electrolyte. Sodium chloride and
potassium are examples of supporting electrolytes, merely by way of
example. A supporting electrolyte may be present in an amount of
about 0.1M to about 1.0 M relative to the solution, merely by way
of example, and any suitable supporting electrolyte or combination
of supporting electrolytes may be used.
[0036] An "implantable" device generally refers to a fully
implantable device that is implanted fully within a body and/or an
at least partially implantable device that is at least partially
implanted within a body. An example of an at least partially
implantable sensing device is a transcutaneous sensing device,
sometimes referred to as a subcutaneous sensing device, that is
associated with a portion that lies outside of a body and a portion
that penetrates the skin from the outside of the body and thereby
enters the inside of the body. The sensing device may be a
continuous or in vivo analyte-sensing device that may be used to
sense an analyte, such as glucose, in the body or a portion
thereof, merely by way of example.
[0037] The term "measure," as in "to measure the concentration," is
used herein in its ordinary sense and generally refers to the act
of obtaining an indicator, such as a signal, that may be associated
with a value, such as concentration, for example, and to the act of
ascertaining a value, such as a concentration, for example. The
term "monitor," as in "to monitor the concentration," refers to the
act of keeping track of more than one measurement over time, which
may be carried out on a systematic, regular, substantially
continuous, and/or on-going basis. The term "assess" encompasses
the terms measure and monitor. The terms assess, measure, and
monitor may be used generally herein, such as alternately,
alternatively, or interchangeably, or more specifically, as just
described.
[0038] The term "measurement" may generally refer to a signal that
is indicative of a concentration of an analyte in a medium, such as
a current signal or a voltage signal, for example, to a more
typical indication of a concentration of an analyte in a medium,
such as mass of the analyte per unit volume of the medium, for
example, or the like. The term "value" may sometimes be used herein
as a term that encompasses the term "measurement."
[0039] The term "patient" generally refers to a living animal, and
thus encompasses a living mammal and a living human, for example.
The term "subject" may sometimes be used herein as a term that
encompasses the term "patient" and/or the term "user."
[0040] A "reference electrode" generally refers to at least one
electrode that is used as a reference against which the working
electrode potential is assessed or measured. The reference
electrode may be, and ideally is, non-polarizable, or has a
constant and known electrode potential even if current flows
through it. The term "reference electrode" encompasses a reference
electrode that also functions as a counter electrode (i.e., a
counter/reference electrode), unless the description provides that
a "reference electrode" excludes a counter/reference electrode.
[0041] The term "working electrode" generally refers to at least
one electrode at which a material is electrooxidized or
electroreduced. Generally, in a potentiostatic mode, the working
electrode is the electrode at which the potential is controlled and
the current is measured, and in a galvanistatic mode, the working
electrode is the electrode at which the current is controlled and
the potential or voltage is measured.
[0042] According to the present invention, a device and a method
for use in assessing a flow condition of a fluid are provided. The
device 100 comprises an electrochemical cell 102, which comprises a
working electrode (WE) 104 and at least one other electrode 106, as
shown in FIG. 1. The at least one other electrode 106 may comprise
a counter/reference electrode (not shown), which may be encompassed
by the term counter electrode or reference electrode, as indicated
previously, or a counter electrode (CE) 108 and a reference
electrode (RE) 110, as shown in FIG. 1. Independently, each of the
working electrode 104 and the counter electrode 108 comprises a
material that is an electrical conductor and may be selected from
the group consisting of carbon, gold, silver, platinum, copper, a
conductive polymer, and any combination thereof, merely by way of
example. The reference electrode 110 may be any of the following
types, namely, an Ag/AgCl electrode, an Hg/HgO, an
Hg/Hg.sub.2SO.sub.4 electrode, an Hg/Hg.sub.2Cl.sub.2 electrode, a
normal hydrogen electrode, and a reversible hydrogen electrode,
merely by way of example. Each of the electrodes of the
electrochemical cell may be comprised of any suitable material or
any suitable combination of materials. Generally, any suitable
electrodes for the electrochemical cell 102 may be used and any
selection of same may be based on the nature of the electrochemical
reaction that is to take place at the electrochemical cell 102 and
any condition that may affect that electrochemical reaction.
[0043] The electrochemical cell 102 is sufficient for communication
with the fluid 202. Merely by way of example, when the fluid is in
a flow path 200, the electrochemical cell 102 is sufficient for
communication with the fluid path 200, such that when sufficient
fluid 202 is in the flow path 200, the cell 102 is in communication
with the fluid. The device 100 may be independent of the flow path
200 and/or of a source (not shown) of the fluid. Merely by way of
example, the device may be adapted for use with an existing flow
path, such as an outlet of a fluid delivery device or pump that is
in communication with a source of fluid or has its own supply of
fluid, or a natural flow path that is in communication with a
source of fluid or has its own supply of fluid, such as a blood
vessel, for example. Such an adaptation may comprise putting the
electrochemical cell into communication with the existing flow
path, such as introducing the electrochemical cell into the flow
path, preferably in a manner that substantially avoids the leakage
of fluid from the flow path in the vicinity of the cell components.
Alternatively, the device may itself comprise a flow path and/or a
source of the fluid.
[0044] A device 100 according to the present invention may comprise
one electrochemical cell 102, as described above and shown in FIGS.
1 and 2, or two or more electrochemical cells (not shown). Multiple
electrochemical cells may be located in the same general vicinity
relative to the flow path 200, or at different locations relative
to the flow path 200. Multiple electrochemical cells may be used
for redundant assessment, measurement, and/or monitoring of the
flow condition of the fluid 202 in the flow path 200.
[0045] According to an embodiment of the present invention, the
device 100 may be used in connection with an existing source of
fluid and an existing fluid delivery device or pump, as described
above and as will be understood with reference to FIG. 2. According
to another embodiment of the present invention, a device 600 may
comprise a source of fluid 300, such as a fluid reservoir 300, and
a fluid delivery device 400, such as a pump 400, in communication,
such as via a conduit 350, as shown in FIG. 2. The fluid delivery
device or pump 400 is in communication with the flow path 200 for
the delivery of fluid 202 thereto, as shown in FIG. 2. In such a
case, the flow path 200 is in communication with the outlet 402 of
the fluid delivery device or pump 400.
[0046] The pump 400 may be one sufficient for delivering the fluid
in a continuous manner, or in a non-continuous manner, such as in
two or more pulses, or two or more periodic discrete pulses. It
will be understood that appropriate pump parameters may vary
according to the fluid to be pumped and the application of that
fluid. Merely by way of example, in the case of the delivery of a
fluid that comprises a drug, a medicament, a nutrient, a dietary or
health supplement, any source thereof, any combination thereof,
and/or the like, to a subject, such parameters may vary according
to the drug, medicament, nutrient, or supplement, etc., the
characteristics of the subject, the characteristics of the
condition the drug, medicament, nutrient, or supplement, etc., is
intended to address, and/or the like, all of which may be highly
variable. It will be appreciated that via a fluid, a wide variety
of drugs or medicaments may be delivered to a subject, such as an
antibiotic, a nutritional fluid, a dietary supplement, a health
supplement, total parenteral nutrition (TPN), an analgesic, an
anesthetic, a pain reliever, such as morphine, for example, a
hormone, a hormonal drug, a gene therapy drug, an anticoagulant, a
cardiovascular drug, AZT, a chemotherapeutic drug, any source
thereof, and any combination thereof, merely by way of example.
[0047] Merely by way of example, the pump 400 may comprise a
micro-pump sufficient for the delivery of fluid in small
quantities, such as from about 1 to about 10,000 microliters
(.mu.L) per day, or from about 100 to about 1000 .mu.L per day or
around 400 .mu.L per day on average, as may be suitable for the
delivery of insulin to a diabetic person. The pump 400 may comprise
a micro-pump sufficient for the delivery of fluid in periodic
pulses, such as from about 0.1 to about 10 .mu.L per pulse or from
or from about 0.5 to about 1 .mu.L per pulse, as may be suitable
for the delivery of insulin to a diabetic person. Suitable pulse
periods and repetition rates are quite variable depending on the
application. By way of example, the fluid may be delivered at a
rate of from about every second for a fast multi-dose bolus to
about every 10 minutes for a slow basal rate, as may be suitable
for the delivery of insulin to a diabetic person.
[0048] Preferably, the pump is a micro-pump when the fluid to be
delivered is a drug or a medicament for a subject, such as insulin
for a diabetic subject. In general, a device of the present
invention may be run by a relatively modest battery or other power
source (see FIG. 7, for example), such as a very small 357 silver
oxide battery that has a lifetime of about a few weeks, as the
power consumption of the device is very low. Merely by way of
example, in a device of the present invention that is used in
connection with a micro-pump (see FIG. 7, for example), the power
consumption may be relatively minor, trivial, or negligible
relative to that of the micro-pump, particularly in the case of a
small micro-pump that is worn on a subject, such as via patch
disposed on the subject's skin, and delivers a drug or medicament
to the subject.
[0049] The fluid 202 is sufficient to support an electrochemical
reaction at the working electrode 104 of an electrochemical cell
102 that is in communication with the fluid. The fluid comprises a
component 204 (FIG. 1) sufficient to the electrochemical reaction
such that it is mass-transport limited. Upstream of the
electrochemical cell 102, as generally indicated by the arrow 206
(FIGS. 1 and 2), the fluid and the component may be integral, or
the fluid may comprise the component and a substituent that is free
of the component. Merely by way of example, at that upstream point,
the fluid may comprise an insulin preparation that comprises an
electroactive component, such as ionic zinc (Zn.sup.+), for
example, or the fluid may comprise an electroactive component and a
substituent, such as an insulin preparation, that is free of an
electroactive component.
[0050] The component 204 of the fluid 202 may be sufficient to
participate in, promote, or interfere with an electrochemical
reaction at the working electrode 104, where participating
encompasses reacting, promoting encompasses catalyzing, and
interfering encompasses inhibiting and suppressing. The component
may be sufficient to change the rate of an electrochemical reaction
at the working electrode 104 from what it would be were the
component absent. The component of the fluid may be relatively
dilute in concentration, such as from about 10.sup.-7 M to about
10.sup.-2 M, merely by way of example, as may be the case for an
electroactive component of ionic zinc in an insulin preparation,
for example.
[0051] Merely by way of example, the component 204 of the fluid 202
may be electroactive. Such an electroactive component may comprise
an ionic species, a metallic species, a metal-oxide species, an
organic species, oxygen, water, any source thereof, and any
combination thereof. By way of example, such an electroactive
component may comprise any suitable material from a complete table
of standard electrode potentials, such as any of a variety of
metals, metal ions, metal oxides, and any combination thereof.
(See, for example, A. J. Bard and L. R. Faulkner, Electrochemical
Methods, 2.sup.nd Ed., John Wiley (2001), Appendix C.) Further by
way of example, such an electroactive component may comprise any
suitable organic material or compound, such as glucose for use in
connection with a working electrode that comprises a glucose
oxidase enzyme, may be used. An example of a fluid 202 that
comprises an electroactive component 204 is insulin preparation
that comprises the drug insulin, which is not electroactive, and an
electroactive component, such as an ionic species, such as ionic
zinc, for example. The electroactive component may participate in
the electrochemical reaction at the working electrode 104 of the
electrochemical cell 102. The electroactive component may be
sufficiently dilute relative to the fluid, such that the
electrochemical reaction is mass-transport limited.
[0052] Further, merely by way of example, the component 204 of the
fluid 202 may comprise a gas, such as air, which may be in the form
of at least one gas bubble, such as an air bubble, which interferes
with an electrochemical reaction by interfering with the transport
of an electrochemical reactant toward the working electrode 104.
For example, as mentioned above, the fluid, such as an insulin
preparation described above, may comprise an ionic species, such as
ionic zinc, that participates in the electrochemical reaction at
the working electrode, and an air bubble component of the fluid may
interfere with transport of the ionic species to the working
electrode. Further, merely by way of example, the fluid may
comprise an electroactive component, such as water, suitable for an
electrochemical reaction (such as electrolysis to produce H.sub.2
and O.sub.2, for example) at the working electrode 104, and may
further comprise a component that impedes the electrochemical
reaction at the working electrode such that it becomes
mass-transport limited.
[0053] Still further, merely by way of example, the electrochemical
reaction of interest at the working electrode 104 may be a promoted
electrochemical reaction. For example, the fluid may comprise a
participant in the electrochemical reaction at the working
electrode 104 and a component sufficient to promote the
electrochemical reaction of interest and to affect it such that it
is mass-transport limited. Such a case may be exemplified by a
fluid that comprises a drug, such as an insulin preparation that
comprises insulin and a reactant ionic species, such as ionic zinc,
as described above, and that comprises a component that promotes
the reaction of the reactant at the working electrode. In this
case, the component is sufficiently dilute relative to the fluid
that it causes the electrochemical reaction of interest to be
mass-transport limited. For example, the rate of the promoted
electrochemical reaction is affected by the dilute concentration of
the promoter component of the fluid.
[0054] The fluid 202 and the component 204 should be of suitable
compatibility with one another. Merely by way of example, a
pharmaceutical insulin preparation and an ionic zinc component
thereof are generally compatible with one another, such that the
preparation is relatively stable, for example. It will be
understood that when the fluid is delivered to a flow path that
communicates with a living subject or lies within a living subject,
the fluid and the component should be of suitable compatibility
with one another, and should be of suitable biocompatibility with
the living subject when the life of the living subject is to be
relatively uncompromised. It will also be understood that the
device or any component thereof or any adaptation thereof, and the
fluid and the component thereof, should be compatible with one
another. Merely by way of example, when the fluid is insulin, which
may be inclined to adsorb out of solution onto certain surfaces,
the surfaces of the electrodes in the electrochemical cell should
be selected to minimize or substantially avoid such adsorption. It
will further be understood that when the device is associated with
a flow path of a living subject, the device or any component
thereof or any adaptation thereof that comes into intimate contact
with the living subject should be of suitable biocompatibility with
the living subject when the life of the living subject is to be
relatively uncompromised. It will be also understood that when the
electrochemical reaction takes place within or in intimate contact
with a living subject, any product of the electrochemical reaction
should be of suitable biocompatibility with the living subject when
the life of the living subject is to be relatively uncompromised.
Still further, it will be understood that any product of the
electrochemical reaction, and the fluid and the component thereof,
should be of suitable compatibility with one another.
[0055] A temperature of the fluid in the flow path may be taken to
provide additional information about the flow condition of the
fluid. Thus, the device of the present invention may comprise a
temperature probe 112, as shown in FIG. 1, that is sufficient for
communication with fluid 202 in the flow path 200. The temperature
of the fluid in the flow path may affect mass transport of the
component 204 of the fluid to the electrochemical cell. In some
cases, the effect of temperature on such mass transport may be
fairly minimal, as may be the case in various drug delivery
applications, such as the delivery of an insulation preparation
that contains ionic zinc. In such cases, information regarding
temperature may not be needed or desired. In other cases, the
effect of temperature may be more pronounced or significant, such
that obtaining information regarding the temperature of the fluid
may be desirable or necessary. When temperature information is
obtained, it may be used to calibrate or to control the fluid
delivery device or pump. Merely by way of example, the temperature
reading may be received by a microcontroller (further described
herein) and used to correct data concerning a condition of the flow
of the fluid accordingly, via an empirically- or a
theoretically-based algorithm, for example. Merely by way of
example, the algorithm may be used to correct current or voltage
data received from the electrochemical cell 102 by some level or
percentage for each degree of temperature deviation from a baseline
temperature.
[0056] A fluid delivery device or pump may not need calibration.
Merely by way of example, it may be quite feasible to determine the
relationship between a flow of fluid from a fluid delivery device
and an indication of a characteristic of that flow that is obtained
from a device of the present invention, without calibration. In
some cases, such as when the relationship just described cannot be
feasibly or adequately determined, it may be desirable or necessary
to calibrate a fluid delivery device or pump. Merely by way of
example, the manufacture and/or performance of fluid delivery
devices or pumps may not be sufficiently reliable or consistent
such that the calibration of each manufactured device can feasibly
be avoided. Calibration of a fluid delivery device or pump may
comprise obtaining an indication of the fluid delivery associated
with the fluid delivery device, such as a volume or a flow rate of
fluid that flows from the fluid delivery device, for example, and
substantially simultaneously, obtaining an indication of a
characteristic of that flow of the fluid, such as a current or
voltage, for example. The indication of the fluid delivery
associated with the fluid delivery device may be obtained using a
device or a method of the above-referenced U.S. application Ser.
No. 11/105,711 of Benjamin M. Rush, entitled "Fluid Delivery Device
with Autocalibration." The indication of a characteristic of the
flow of the fluid may be obtained using a device or a method of the
present invention, as described herein. The two indications may be
obtained over time, via monitoring, using the first and the second
of the above-described devices, respectively, for example.
[0057] The information obtained, such as temperature, fluid volume
or flow rate, current, voltage, and/or the like, as described
above, may be provided to the microprocessor of the device of the
present invention for use in the calibration of the fluid delivery
device and/or the control of the fluid delivery device. Merely by
way of example, the reaction rate associated with a component of
the fluid, as may be related to the current or voltage obtained, of
a known quantity of fluid, as may be related to the volume
obtained, may be used, with or without temperature compensation, as
appropriate, to assess a flow condition of the fluid, for use in
the calibration and/or the control of the fluid delivery device.
Calibration of the fluid delivery device may comprise performing a
calibration according to an algorithm that is stored in a
microprocessor (further described herein), or the like. Control of
the fluid delivery device may comprise providing an indication of
proper or improper fluid delivery, which may be based on a
predetermined set of limits or a predetermined range that may be
stored in a microprocessor (further described herein), such as via
a display of information or an alarm, for example, such that a
recipient of the information or alarm can adjust the fluid delivery
device or the flow of fluid therefrom, or automatically adjusting
the fluid delivery device or the flow of fluid therefrom via a
feedback loop. A suitable microprocessor, or multiple
microprocessors, may handle all of the foregoing. In the case of
drug delivery, redundant microprocessors may be used, as may be
desirable or required for safety, for example.
[0058] A particular embodiment of the present invention is now
described. According to this embodiment, a fluid from a fluid
delivery pump is delivered to a subject. As shown in FIG. 2, a
device 600 comprising an electrochemical cell 102, including a
working electrode (WE) 104, a counter electrode (CE) 108, and a
reference electrode (RE) 102 is disposed at at least one location
in a fluid flow path. The at least one location may include a
location that is relatively near the point where the fluid leaves
the pump and/or a location that is relatively near the point where
the fluid enters the body of the subject. In this embodiment, the
electrochemical cell 102 is a micro-electrochemical cell wherein
the working area of the working electrode 104 is about 0.1 mm.sup.2
or less.
[0059] As also shown in FIG. 2, the device 600 comprises at least
one microcontroller 500 operably connected to the at least one cell
102 for providing a current or a potential to the working electrode
104 of the cell sufficient for the electrochemical reaction to take
place there, and for receiving information concerning the
electrochemical reaction, such as the rate of the electrochemical
reaction. One such microcontroller 500 may be used in connection
with one cell or multiple cells 102. Further, more than one
microcontroller 500 may be used in connection with one cell or
multiple cells 102. Still further, a microcontroller 500 and a cell
102 may be associated with one another, another microcontroller 500
and another cell 102 may be associated with one another, and so on.
Generally, any suitable association of at least one microcontroller
500 and at least one electrochemical cell 102 may be employed. The
microcontroller 500 may also be operably connected to a temperature
probe 112 for receiving information concerning temperature of the
fluid 202, as previously described.
[0060] At least one microcontroller 500 of the device 600 is
sufficient for providing a potential to the working electrode 104
and for receiving information concerning an electrochemical
reaction associated with the electrochemical cell 102. The working
electrode potential may be any suitable potential and may be
selected from any of a variety of potentials suited to the
particular electrochemical reaction contemplated and/or suited to
the particular reference electrode contemplated, merely by way of
example. The microcontroller 500 may be sufficient for providing an
indication related to a current or charge associated with the
electrochemical reaction, or an assessment of a change in the
electrochemical reaction rate, by way of example. Merely by way of
example, when the fluid 202 is delivered to the flow path 200 in at
least two pulses, the at least one microcontroller 500 of the
device 600 is sufficient for providing a current or a potential to
the working electrode 104 to facilitate the electrochemical
reaction and for assessing the electrochemical reaction associated
with each of the at least two pulses, and/or with the at least two
pulses at a predetermined interval, such as every few minutes, for
example. The microcontroller 500 may be operably associated with a
display device, a recording device, a printing device, and/or any
device sufficient for communicating information concerning the
electrochemical reaction and/or temperature. The microcontroller
500 may be operably connected with the pump 400 for feedback
control, such as to adjust a pumping parameter such as flow volume,
flow rate, pulse frequency, or pulse duration, merely by way of
example, based on information concerning the flow condition and/or
temperature of the fluid 202 in the flow path 200.
[0061] In an example of the use of this embodiment of the device
600, the fluid in the flow path is an insulin preparation that
contains a dilute ionic zinc component, namely, ionic zinc. A
pharmaceutical insulin preparation often contains ionic zinc (for
example, from ZnCl), which happens to be suitable for
electrochemical reaction (Zn.sup.++e.sup.-.fwdarw.Zn) at the
electrochemical cell. In this example, the insulin preparation is
delivered via the flow path in consecutive doses, in between which
there is an absence of flow. When a dose of the insulation
preparation is delivered and the ionic zinc component thereof first
reaches the electrochemical cell, the rate of electrochemical
reaction at the electrochemical cell, which may be measured as a
current, is initially that associated with the bulk (maximum)
concentration of the ionic zinc in the fluid. Thereafter, the rate
of electrochemical reaction at the electrochemical cell, as
reflected by current, for example, will begin to diminish, as ionic
zinc in the vicinity of the electrochemical cell is consumed, such
that ionic zinc must diffuse to the electrochemical cell from
further and still further points upstream. When a new dose of the
insulation preparation is delivered and the ionic zinc component
thereof first reaches the electrochemical cell, the rate of
reaction, as reflected by current, for example, will return to that
associated with the bulk concentration of the ionic zinc in the
fluid. The above-described diminishment and return of the rate of
reaction, or current signal, may occur quite rapidly.
[0062] A functional model of the above-described device of the
present invention was constructed and tested according to the
above-described example. A flow path was constructed out of a
length of Teflon tubing with ID of 0.0625 of an inch. The
electrochemical cell comprised a carbon counter electrode and an
Ag/AgCl reference electrode both screen-printed on plastic film,
and a gold wire working electrode of 0.010 of an inch in diameter.
The electrodes were inserted into the Teflon tube by drilling a
small hole in the side of the tube and sealing the electrodes in
place with epoxy. A pharmaceutical insulin preparation (U100
Humalog from Eli Lilly (Indianapolis, Indiana)), containing ionic
zinc at a concentration of 0.0003 M, was delivered through the flow
path in a pulsed manner, with a pulse volume of approximately 2
.mu.Ls and a pulse period of 235 seconds. The electrode potential
was held at -0.6V versus the Ag/AgCl reference electrode in an
attempt to reduce Zn.sup.+ ion to Zn metal on the surface of the
gold working electrode.
[0063] The current associated with the electrochemical reaction at
the electrochemical cell was recorded during the pulsed delivery of
the insulin preparation through the flow channel, as shown in FIG.
3. Each pulse of fluid delivered from the pump corresponded with a
distinct current pulse of large amplitude, as illustrated by the
current peaks shown in FIG. 3. The data obtained may be assessed
qualitatively and/or qualitatively. By way of example, the area of
under the curve associated with each current pulse shown in FIG. 3,
or the integral of each current pulse, can be viewed and an
assessment can be made as to whether the areas or integrals appear
to be the same or substantially the same on a qualitative basis, as
is the case in FIG. 3, or not. Further by way of example, the
integral of each current pulse shown in FIG. 3 can be determined,
as shown in FIG. 4, and an assessment can be made as to whether the
integrals are the same or substantially the same on a quantitative
basis, as is the case in FIG. 4, or not. Any suitable means or
method may be used to assess the data, be it human, machine,
automated, and/or otherwise.
[0064] The functional model just described was also tested as
described above, with the exception that the pulsed delivery of the
insulin preparation was unrestricted and then partially restricted
by compressing the Teflon tubing at the end upstream relative to
the electrochemical cell. Each pulse of fluid delivered from the
pump in this manner corresponded with a distinct current pulse, as
shown in FIG. 5. The first peak, corresponding to a pulse of fluid
from the unrestricted tube, is of significant amplitude, while the
second peak, corresponding to a pulse of fluid from the restricted
tube, is of relatively reduced amplitude. A test involving
compressing the Teflon tubing at different points, whether upstream
or downstream relative to the electrochemical cell, could also be
undertaken, and would be expected to give similar results
regardless of the location of the restriction. Further, it is
believed, although this was not tested, that if the pump in the
above-described embodiment were to fail such that a continuous flow
of insulin was delivered, a continuous current value corresponding
to that of the peak amplitudes of the current pulses shown in FIG.
3 would result. In this manner, the device of the present invention
may be used to detect insufficient fluid flow from a pump, such as
an insulin pump, and/or to detect excessive fluid flow from a pump,
in a qualitative and/or quantitative manner.
[0065] Any of the devices and methods described herein may be used
to assess, measure, and/or monitor the flow of any fluid that
comprises, or has added to it, an electrochemically reactive
component, such as a dilute electrochemically reactive component,
for example. Any such devices and methods may be used to assess,
measure, and/or monitor such flow of any magnitude and of any flow
characteristic, such as a type of flow, such as continuous or
non-continuous flow, for example, an example of the latter being
pulsed flow, a direction of flow, a current or force associated
with or influencing flow, and the like, and any combination
thereof. Merely by way of example, any such devices and methods may
be used to assess, measure, and/or monitor pulsed flow to ascertain
whether or not each pulse of fluid has a suitable volume, such as
whether or not such each pulse of fluid is of substantially the
same volume, for example. Any such devices and methods may be used
to assess, measure, and/or monitor an impediment to a desirable or
an intended delivery of fluid, such as by way of a gaseous bubble,
such as an air bubble, for example, that interferes with such
delivery (for example, the bubble displaces the fluid so that the
delivery of the fluid is less than what would otherwise be
delivered). The presence of such a bubble may significantly affect
an indicator associated with the electrochemical cell, such as
current, for example, such as reducing the current significantly or
to zero. This may be useful in assessing whether such a bubble is
present in the flow path of, or from, a fluid delivery device, for
example.
[0066] Any such devices and methods are particularly well suited to
flow of a small scale, such as the flow of a liquid drug from an
automatic portable drug delivery device to a subject. Examples of
such drug delivery devices and methods, and the flow associated
therewith, include those of the above-referenced U.S. application
Ser. No. 10/683,659 and U.S. application Ser. No. 11/106,155 of
Benjamin Rush et al, which may be calibrated according to the
devices and methods of the above-referenced U.S. application Ser.
No. 11/105,711 of Benjamin M. Rush, merely by way of example.
Further, any such devices and methods may be used in connection
with an automatic portable drug delivery device, which in turn, may
be associated with an implantable device, such as an implantable
sensing device that is used to sense an analyte, such as glucose,
within a subject, such as a diabetic subject. Examples of such
implantable devices, and associated methods, include those of
several U.S. patent Nos. and U.S. patent application Nos., as
follows: U.S. Pat. No. 6,175,752 of Say et al., filed on Apr. 30,
1998; U.S. Pat. No. 6,329,161 of Heller et al., filed on Sep. 22,
2000; U.S. Pat. No. 6,560,471 of Heller et al., filed on Jan. 2,
2001; U.S. Pat. No. 6,579,690 of Bonnecaze et al., filed on Jul.
24, 2000; U.S. Pat. No. 6,654,625 of Say et al., filed on Jun. 16,
2000; U.S. Pat. No. 6,514,718 of Heller et al., filed on Nov. 29,
2001; U.S. Pat. No. 6,605,200 of Mao et al., filed on Nov. 14,
2000; U.S. Pat. No. 6,605,201 of Mao et al., filed on Nov. 14,
2000; Ser. No. 10/146,518 of Mao et al., filed on May 14, 2002;
Ser. No. 10/819,498 of Feldman et al., filed on Apr. 6, 2004; and
Ser. No. 11/007,617 of Feldman et al., filed on Dec. 7, 2004, for
example, each of which is hereby incorporated herein, in its
entirety, by this reference.
[0067] Any of the devices and methods described herein may be used
to assess, measure, and/or monitor the flow of any liquid that
comprises, or has added to it, a dilute electrochemically reactive
component, in a qualitative and/or quantitative manner. In a
qualitative assessment, a general observation of the presence or
absence of a current signal, or the amplitude of a current signal,
may be used to assess flow condition, merely by way of example. In
a quantitative or semi-quantitative assessment, the presence or
absence of a current signal, or the amplitude of a current signal
or the integral of a current peak, or a portion thereof, may be
used to assess flow condition, merely by way of example. An
assessment of a current signal or a charge generated, such as a
charge generated in connection with electrolysis, may be obtained
by any suitable means, such as amperometry or coulometry, merely by
way of example.
[0068] An assessment of flow condition that is obtained via any of
the devices and methods of the present invention may be used as a
basis for adjusting the flow of the fluid in the flow path, or
adjusting a device, such as a pump, that generates the flow of the
fluid in the flow path, by any suitable means or methods. Such an
adjustment may comprise any of those described in the
above-referenced U.S. Pat. No. 6,582,393 and U.S. Patent
Application Publication No. 2004/0019321 A1. Merely by way of
example, when the fluid in the flow path is delivered in a pulsed
manner, such as via discrete periodic pulses of nominally identical
volumes of fluid, and an assessment of the flow condition shows the
pulse volume to be 5% larger than the nominal volume, the pulse
period may be decreased by 5% so as to reestablish the intended
overall flow condition, or delivery rate, or some other fluid
delivery or pulse parameter may be controlled or changed to obtain
desirable results. Further by way of example, when the fluid in the
flow path is delivered in a continuous manner, such as in a
continuous flow via gravity or via pressure from a source of fluid,
such as a reservoir or a bladder, that is controlled, such as via
opening or closing or adjusting of a control device, such as a
valve, and an assessment of the flow condition shows the flow
volume or rate to be 5% smaller than the nominal volume, the
control device may be adjusted so as to increase the flow volume or
rate to obtain suitable or desirable results.
[0069] The microcontroller of the device of the present invention
may comprise any appropriate elements or components for achieving
any of its intended purposes. Examples of such elements or
components include any one or more of the following: electronic
circuitry, componentry, storage media, signal- or data-processing
elements, algorithmic elements, software elements, logic devices,
wired or wireless communication elements, devices for operable
communication between elements or components, and the like.
Examples of such intended purposes include any one or more of the
following: providing a potential or a current to a working
electrode, obtaining information from the electrochemical cell,
obtaining information from a fluid delivery device, obtaining
information from a temperature probe, obtaining information
pertinent to calibration and/or control of a fluid delivery device,
assessing or processing any obtained or internal information,
communicating with the electrochemical cell or another device, such
as a fluid delivery device, a display device, an alarm or
notification device (sensory or otherwise), and/or a calibration
device, such as an autocalibration device, communicating via a
feedback loop, such as an automated feedback loop, and calibrating
and/or controlling another device, such as a fluid delivery device.
A microcontroller may be configured to include any suitable
elements described herein, or any suitable elements for achieving
any of the purposes described herein, in a conventional manner. Any
device with which the microcontroller may communicate may be
equipped with complementary elements, such as any suitable
communication elements, components, or devices, such as wired or
wireless communication elements, merely by way of example, as may
be afforded or accomplished in a conventional manner.
[0070] Any of the devices or methods of the present invention may
be suited or adapted to be suited for use in connection with an
electrochemical reaction at the electrochemical cell that is
continuous or intermittent. Merely by way of example, the working
electrode of the cell may be biased in order to start an
electrochemical reaction at the electrochemical cell prior to an
anticipated pulse of fluid flow and to terminate the
electrochemical reaction at some time after the pulse of fluid
flow. Further by way of example, an electrochemical reaction at the
electrochemical cell may be assessed, measured, and/or monitored in
connection with every pulse of fluid flow, or in connection with
one or more pulse(s) of fluid flow at some regular interval, such
as at every hour or at every hundredth pulse, as may be useful in
terms of optimizing or reducing consumption of a battery and/or
other power source (not shown) associated with the pump or the
device of the invention, optimizing or extending the life of the
electrodes of the device of the invention, minimizing consumption
of the component of the fluid, and/or minimizing production of one
or more reaction product(s), for example.
[0071] As previously described, any of the devices or methods of
the present invention can be used in connection with a fluid
delivery device such as a pump. According to a preferred
embodiment, as now described, a device or method of the present
invention may be used in connection with a fluid delivery device,
or pump, that has automatic calibration and/or control capability.
Information concerning the construction and the operation of such a
fluid delivery device may be found in the above-referenced U.S.
application Ser. No. 11/105,711 of Benjamin M. Rush filed
concurrently herewith.
[0072] A schematic illustration of a device 1000 that may comprise
or be used in association with a fluid delivery device 700, is
shown in FIG. 6A, and a flow chart describing the operation of such
a fluid delivery device 700 is shown in FIG. 6B. The fluid delivery
device 700 may be of any suitable type, such as a fluid pump, for
delivery of a fluid from an outlet thereof to a flow path 202. It
may be preferable to use a fluid pump that is driven by a shape
memory actuator in certain cases, for example, when cost is a
driving factor or when the device is used in connection with
applications, such as medical applications, in which devices may be
disposed of and replaced relatively frequently for various reasons.
Information concerning the construction and the operation of such a
fluid delivery device may be found in the above-referenced U.S.
application Ser. No. 10/683,659 and the above-referenced U.S.
application Ser. No. 11/106,155 of Benjamin Rush et al filed
concurrently herewith. The fluid delivery device 700 may comprise
or be used in association with a user interface (not shown) for
setting one or more operating parameter(s), such as a fluid
delivery rate, an activation or deactivation of the fluid delivery
device, and the like, and any combination thereof.
[0073] According to a preferred embodiment, the fluid delivery
device has automatic calibration and/or control capability, as now
described in connection with the device 1000 shown in FIG. 6A. The
device 1000 comprises at least two sensors, an upstream sensor 800,
and a downstream sensor 802 that are in communication with the flow
path 200. This communication may be similar to that associated with
the electrochemical cell 102, as previously described. Each of the
sensors comprises a pair of conductive electrodes. The electrodes
may be made of a material suitable for a particular application.
Merely by way of example, when the fluid to be delivered is an
insulin solution, gold or gold-plated electrodes may be used. A
current and/or a voltage passing between the electrodes of the
pair, and/or a charge and/or a resistance associated with the
electrode pair, may indicate the presence of a fluid that has at
least some measure of electrical conductivity (such as an insulin
preparation that contains ionic zinc, for example) at the
electrodes. Thus, an indication of current, voltage, charge, and/or
resistance, such as zero current, voltage, charge, and/or
resistance, versus some amount of current, voltage, charge, and/or
resistance, from an electrode pair may be detected and used to
indicate the absence or presence of a fluid at the electrodes. Any
of the electrode pairs just described is typically used to provide
a qualitative measure of the existence or non-existence of fluid,
based on the existence or non-existence of electrical continuity in
the electrode pair circuit.
[0074] It will be understood that any of the electrode pairs may be
employed as part of an electrochemical cell if a quantitative
measure is desired, although this may be more complicated than is
desirable or necessary where a simple indication of existence or
non-existence of fluid is desired. Further, it will be understood
that a flow-monitoring electrode may serve as a current-sensing
electrode, and that a current-sensing electrode may serve as a
flow-monitoring electrode.
[0075] The volume of the flow path between the two sensors, or the
calibration region 708, is known or ascertainable. Merely by way of
example, when the distance 704 between the two sensors and the
diameter 706 of the flow path 200 are known, the volume of the flow
path between the two sensors, or of the calibration region 708, can
be determined or known. It will be understood that while the flow
path 200 may be cylindrical, as depicted in FIG. 6A, merely by way
of example, such that the volume associated with the calibration
region 708 may be determined or known in the manner just described,
the flow path 200 may be of any geometric (regular or irregular)
shape or configuration, such that the volume associated with the
calibration region 708 may be otherwise known or ascertainable. It
may be desirable to have the volume of the calibration region 708
much greater than the volume of fluid to be delivered in the flow
path. Merely by way of example, when the fluid to be delivered is
an insulin solution, the volume of the calibration region 708 is
preferably much greater than the volume of an individual dose of
insulin solution to facilitate good resolution and accuracy in the
detection or measurement of the flow rate or the current.
[0076] The two sensors 800 and 802 and the fluid delivery device
700 are connected to a control unit 900. The control unit 900
comprises drive circuitry 902 and logic unit 904, which is
preferably in the form of a microcontroller or microprocessor, such
as that previously described in connection with FIG. 2. The control
unit 900 may be used for the general control of the fluid delivery
device 700 and its operation. The control unit 900 may also be used
to initiate and control calibration of the fluid delivery device
700.
[0077] Control 1100 of the fluid delivery device 700 may proceed as
depicted in FIG. 6B, merely by way of example. Such a control
process 1100 may be performed at any time. Merely by way of
example, such a process 1100 may be carried out in conjunction with
priming the fluid delivery device 700. The control 1100 comprises
the detection 1102 of the arrival of fluid at a point A, which
corresponds to a location of the up-stream sensor 800. The
detection 1102 may be via the control unit 900 described above. In
association with this detection 1102, the flow stream may be
allowed to advance to the upstream sensor 800 or may be interrupted
before it reaches the upstream sensor 800. Merely by way of
example, the flow may be interrupted via the introduction of a gas
bubble into the flow stream. The control 1100 also comprises the
detection 1104 of the arrival of fluid at a point B, which
corresponds to a location of the downstream sensor 802. The
detection 1104 may be via the control unit 900 described above.
[0078] The control 1100 also comprises the determination 1106 or
measurement of the time it takes for the fluid to travel from point
A to point B. The determination 1106 may be via the control unit
900 described above. As described previously, the volume of the
flow path in the calibration region 808 is known or ascertainable.
Data concerning this volume may be entered via a user interface
(not shown) and/or stored in memory in the control unit 900. The
control 1100 also comprises determining 1108 or calculating the
flow rate associated with the fluid, such as a volumetric flow
rate, based on these time and volume parameters. The determination
1108 may be via the control unit 900 described above.
[0079] The control 1100 may comprise the adjustment 1110 of the
fluid delivery device 700, or the fluid flow therefrom, based on
the fluid flow rate, or no adjustment of the fluid delivery device
700 where such is undesirable or unnecessary. The adjustment 1110
may comprise providing the fluid flow rate to a user, who could
then adjust the pump, if and as may be appropriate, such as via a
user interface (not shown), in any appropriate manner, or
automatically adjusting the pump, such as via an automated feedback
loop, in any appropriate manner. Control 1100 of the fluid delivery
device 700 may take place at any suitable time, such as before or
at the time fluid delivery from the device 700 commences, or at any
time during fluid delivery from the device 700. Further information
concerning control of a fluid delivery device may be found in the
above-referenced U.S. application Ser. No. 11/105,711 of Benjamin
M. Rush filed concurrently herewith.
[0080] Calibration 1200 of the fluid delivery device 700 may
proceed as depicted in FIG. 6C, merely by way of example. Such a
calibration process 1200 may be performed at any time. The
calibration 1200 comprises determining 1202 a fluid flow rate, such
as a volumetric flow rate, which may be performed as described
previously in relation to FIG. 6B. The determination 1202 may be
via the control unit 900 described above. The calibration 1200 may
comprise determining 1204 a suitable or desirable fluid delivery
amount, such as a volume or a dose volume, for example, or a
suitable or desirable fluid delivery rate. This volume or rate may
be known. Data concerning the volume or rate may be entered via a
user interface (not shown) and/or stored in memory in the control
unit 900. The determination 1204 may be via the control unit 900
described above.
[0081] The calibration 1200 also comprises determining 1206 a
calibration factor based on this determined fluid flow rate. The
calibration factor may, and preferably does, comprise a ratio of an
expected or nominal amount or volume of fluid to be delivered, such
as a dose volume, for example, and an actual volume of fluid
delivery delivered. The determination 1206 may be via the control
unit 900 described above. The calibration 1200 also comprises
applying 1208 the calibration factor in connection with operation
of the fluid delivery device 700, such as in connection with
delivering a suitable or desirable amount or volume of fluid, such
as a dose, from the fluid delivery device. The application 1208 of
the calibration factor may be via the control unit 900 described
above.
[0082] The calibration factor may be applied 1208 in connection
with an adjustment of the fluid delivery device 700, if desirable
or necessary, which may be performed as described previously in
relation to FIG. 6B. The calibration 1200 may comprise the
adjustment of the fluid deliver device 700 based on the determined
fluid flow rate and/or the calibration factor, or no adjustment of
the fluid delivery device 700 where such is undesirable or
unnecessary. The adjustment may comprise providing the determined
fluid flow rate and/or calibration factor to a user, who could then
adjust the fluid delivery device, if and as may be appropriate, in
any appropriate manner, or automatically adjusting the fluid
delivery device, such as via an automated feedback loop, in any
appropriate manner. Calibration 1200 of the fluid delivery device
700 may take place at any suitable time, such as before or at the
time fluid delivery from the device 700 commences, or at any time
during fluid delivery from the device 700. Further information
concerning calibration of a fluid delivery device may be found in
the above-referenced U.S. application Ser. No. 11/105,711 of
Benjamin M. Rush filed concurrently herewith. Preferably, a
suitable or desirable amount or volume of fluid, such as a dose, is
delivered 1300, from the fluid delivery device 700, whether or not
an actual adjustment of the device is performed, as also shown in
FIG. 6C.
[0083] According to the present invention, a device and a method
for assessing a flow condition of a fluid are provided. The device
and the method are drawn from more or less discrete disciplines,
such as the disciplines of electrochemistry, micro-fluidics, mass
transport, kinetics, fluid pumping, fluid flow, pulsed flow, pump
monitoring, and flow measurement, merely by way of example.
Although each of these disciplines has its own nuances and
complexities, the device and the method of the present invention
may be rather simple and inexpensive and may provide useful
qualitative and/or quantitative assessments of the flow condition
of a fluid.
[0084] According to a preferred embodiment, the device and the
method of the present invention may have useful application in the
delivery of a drug or medicament to a subject, such as the
automated delivery of such a drug or medicament to a subject, and
more particularly, the precise automated delivery of such a drug or
medicament to a subject, with optional feedback control, such as
automated feedback control. It is contemplated that the present
invention may be used in connection with an analyte-sensing device,
such as an implantable analyte-sensing device, and an associated
drug delivery device that is provided in a patch that may be worn
by a subject, such as an adhesive patch that may be affixed to the
skin of a subject. Merely by way of example, the present invention
may be used in connection with any of the devices and methods
disclosed in U.S. Provisional patent application Ser. No.
11/105,711 of Benjamin Rush et al., entitled "Method and Apparatus
for Providing Integrated Infusion Device and Monitoring System,"
filed on Mar. 21, 2005, which is hereby incorporated herein, in its
entirety, by this reference. Further, merely by way of example, the
analyte-sensing device may comprise a glucose-sensing device, the
drug delivery device may comprise an insulin delivery device, the
subject may be afflicted with diabetes, and the device and method
may be associated with a flow channel of the drug delivery device,
a natural flow channel of the subject, or any suitable flow path,
as described herein. Still further, merely by way of example, the
present invention may be used in connection with any of the devices
and methods associated with an in vivo FreeStyle.RTM. Navigator.TM.
glucose monitoring device (Abbott Diabetes Care, formerly known as
TheraSense, Inc., of Alamada, Calif.), that is currently in
clinical trials, though not now commercially available, and is
based on or related to several of the above-referenced U.S. patents
and patent applications, namely, U.S. Pat. Nos. 6,175,752,
6,329,161, 6,560,471, 6,579,690, 6,654,625, 6,514,718, 6,605,200,
and 6,605,201, and U.S. patent application Ser. Nos. 10/146,518,
10/819,498, and 11/007,617, for example.
[0085] According to a preferred embodiment of the present
invention, a system 1400 as shown in FIG. 7 is provided. The system
1400 comprises a patch 1500 that may be used on a portion of a
subject's body (not shown). The patch 1500 may be appended or
attached to the portion of the subject's body in any suitable
manner, such as via adhesive that adheres to the skin of the
subject, merely by way of example. The patch may comprise a portion
1600 (shown with solid outline), which may be reusable, and another
portion 1700 (shown in broken outline), which may be disposable.
The patch 1500 may house a number of components, such as any of the
components shown in FIG. 7, and any combination thereof.
[0086] The portion 1600 comprises a battery 1602 and a
microcontroller 1604, such as any of same previously described. The
portion 1600 may also comprise a transceiver 1606 for the
communication of information, which may be a wired transceiver (not
shown) or a wireless transceiver suitable for communication with a
remote unit 1800 or a transceiver 1802 thereof, such as via
signals, for example, as represented by arced lines. The portion
1700 comprises a fluid reservoir 1702, such as an insulin
reservoir, a fluid delivery device 1704, such as a pump, a
calibration device 1706, which may be a calibration device as
previously described, an infusion set 1708, a flow measurement or
monitoring device 1710, which may be such a device as previously
described, and a continuous analyte-sensing device 1712, such as a
continuous blood glucose-monitoring device as previously described.
An infusion set generally refers to a device that connects a fluid
delivery device to subcutaneous tissue of a subject, which may
comprise a piece of tubing having a luer connection or lock on one
end for connection to the fluid delivery device and a needle or
soft flexible plastic tube on the other end for insertion into the
subcutaneous tissue, merely by way of example, at least part of
which may be associated with a patch, such as an adhesive patch
that secures at least the insertion needle or tube in place, for
example. An infusion set is typically a disposable device that is
replaced periodically, such as every three or so days.
[0087] It will be understood that the solid lines between any two
components of the patch 1500, as shown in FIG. 7, represent any
suitable method or device for operable communication between those
components. Further, it will be understood that the two solid lines
with a grey or shaded interior between any two components of the
patch 1500, as shown in FIG. 7, or from the infusion set 1708 of
the patch 1500, represent any suitable method or device for
operable fluid communication between those components, or from the
infusion set, respectively.
[0088] As mentioned above, a remote unit 1800 may be used in
connection with the patch 1500. This may be a remote, handheld or
easily portable unit. The remote unit 1800 comprises a transceiver
1802 for the communication of information, which may be a wired
transceiver (not shown) or a wireless transceiver suitable for
communication with a patch 1500 or a transceiver 1606 thereof, such
as via signals, for example, as represented by arced lines. The
remote unit 1800 may also comprise a user interface 1804 for
receiving information from a user, for communicating information
(such as flow parameter (rate, pulse, duration, etc.) instructions
or adjustments, for example) from a user to the fluid delivery
device 1704, and/or for communicating information to the user. The
remote unit also comprises a data storage device for storing data,
such as any data received from the patch 1500 and/or any data
received from the user interface 1804. Any appropriate operable
connections between the components of the remote unit 1800 may be
used.
[0089] The system 1400 may be used for delivery of a fluid to a
subject, for calibration associated with such delivery, for control
associated with such delivery, for communication of information
associated with such delivery, for fluid delivery based on
information from a continuous analyte-sensing device, automated
fluid delivery, automated fluid delivery control, automated fluid
delivery calibration, automated feedback fluid delivery based on
information from a continuous analyte-sensing device, and/or the
like, as will be understood from the description herein.
Preferably, the micro-controller 1604 is sufficient for
facilitating or carrying out any or all of these various functions.
The system 1400 may be used for any such applications in a
convenient manner, in that the system 1400 may be small, compact,
partially disposable, partially reusable, relatively low in energy
consumption, relatively convenient in communication, such as
wireless communication, and/or the like, merely by way of
example.
[0090] According to another embodiment of the present invention, a
transient electric double-layer charging current may be used to
measure or monitor fluid flow. By way of explanation, when an
electrode is immersed into an electrolyte, an accumulation of ions
from the electrolyte forms spontaneously at the electrode surface
as a result of the disturbance in the electrical environment of the
ions that is caused by the electrode. The accumulation of ions
consists of a layer of ions adsorbed directly on the electrode
surface and a diffuse arrangement of ions in the electrolyte just
off the surface of the electrode. Accordingly, this accumulation of
ions is known as the electric double layer. When the electric
double layer is initially forming, a transient current will flow
through the electrode as mobile charges in the electrode adjust to
the new electrical environment of the electrolyte. The arrangement
of ions in the double layer is a function of the potential of the
electrode and will change if the potential or current,
respectively, of the electrode is changed. This potential-dependent
structure of ions in the double layer will also generate a
transient current if the potential of the electrode is changed.
Furthermore, flow of the electrolyte near the electrode can disturb
the ions in the diffuse layer of ions which will generate a
transient current as the diffuse layer of ions are reordered.
Measurement of this transient current can be used as a measure
and/or monitor of fluid flow. The electric double layer may be
associated with any of numerous electrochemical phenomena, such as
double-layer charging, electrochemical capacitance,
electrophoresis, and electroosmosis.
[0091] As to methods of the present invention, a method of
assessing a flow condition of a fluid is disclosed herein. Such a
method comprising providing a fluid sufficient to support an
electrochemical reaction at a working electrode of an
electrochemical cell, wherein the fluid comprises a component
sufficient to affect the electrochemical reaction such that the
electrochemical reaction is mass-transport limited. Such a method
further comprises providing at least one electrochemical cell
comprising the working electrode and at least one other electrode
in communication with the fluid and obtaining an indicator of a
rate of the electrochemical reaction. As previously described, the
method may comprise adjusting a parameter of the flow of the fluid,
as may be done in view of the indicator obtained, for example.
[0092] Another method of assessing a flow condition of a fluid is
also provided. Such a method comprises providing a flow path for
the fluid described above and/or a source of fluid in communication
with such a flow path for delivering the fluid to the flow path. In
this method, the fluid may be provided continuously or
non-continuously, such as in at least two pulses. In the latter
case, such a method may comprise obtaining an indicator of the rate
of the electrochemical reaction associated with the at least one
electrochemical cell and associated with each of at least two
pulses, such as doing so at a predetermined interval, for example.
As previously described, the indication may be related to a
current, a potential, a charge, or any combination thereof,
associated with the electrochemical reaction. The method may
further comprise feedback control of the source of fluid, such as
feedback control based on the indication obtained, as previously
described herein.
[0093] Various devices, systems, and methods have been described
herein. It will be understood that a method of use or application
is naturally contemplated in connection with any device or system
described herein, and a device or system for carrying out a method
is naturally contemplated in connection with any method described
herein.
[0094] It will be appreciated that each of the device and the
method of the present invention has many useful medical
applications, as well a wide variety of other useful applications
that involve the flow of fluid. Merely by way of example, any of
various aspects that affect the performance of a flow assessment,
measurement, and/or monitoring device of the present invention,
could be assessed, measured, and/or monitored, in cases where other
aspects of such performance are known and/or constant. Such aspects
include reactant concentration, temperature, fluid viscosity, and
laminar flow velocity distribution, merely by way of example.
[0095] Various modifications, processes, as well as numerous
structures to which the present invention may be applicable will be
readily apparent to those of skill in the art to which the present
invention is directed, upon review of the specification. Various
references, publications, provisional and/or non-provisional United
States or foreign patent applications, and/or United States or
foreign patents, have been identified herein, each of which is
hereby incorporated herein, in its entirety, by this reference.
Various aspects and/or features of the present invention have been
explained or described herein in relation to understandings,
beliefs, theories, underlying assumptions, and/or working or
prophetic examples, although it will be understood that the
invention is not bound to any particular understanding, belief,
theory, underlying assumption, and/or working or prophetic example.
Although the various aspects and features of the present invention
have been described with respect to various embodiments and
specific examples herein, it will be understood that the invention
is entitled to protection within the full scope of the appended
claims.
* * * * *
References