U.S. patent application number 14/114076 was filed with the patent office on 2015-03-12 for intravenous infusion monitoring apparatus, system and method.
This patent application is currently assigned to Freddie Eng Hwee Lee. The applicant listed for this patent is Freddie Eng Hwee Lee. Invention is credited to Freddie Eng Hwee Lee.
Application Number | 20150073392 14/114076 |
Document ID | / |
Family ID | 46001700 |
Filed Date | 2015-03-12 |
United States Patent
Application |
20150073392 |
Kind Code |
A2 |
Lee; Freddie Eng Hwee |
March 12, 2015 |
INTRAVENOUS INFUSION MONITORING APPARATUS, SYSTEM AND METHOD
Abstract
An intravenous infusion system that shows infusion flow rate,
volume of medication infused, and alarming during malfunction. User
intervention to adjust flow rates deviation is possible, using the
data already stored in the system prior to the onset of making the
adjustment. The system detects flow rate by measuring temperature
dynamics in a section of the fluid path, unlike other systems that
measures the electromechanical output of the pumping source if the
counting of drops is not possible. This fundamental difference
allows the invention to be used in any system that has a pumping
source that provides a continuous fluid path as it measures actual
flow of fluid in a segment of the fluid path, independent of
pumping mechanism design.
Inventors: |
Lee; Freddie Eng Hwee;
(Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Freddie Eng Hwee |
Singapore |
|
SG |
|
|
Assignee: |
Lee; Freddie Eng Hwee
Singapore
SG
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140155867 A1 |
June 5, 2014 |
|
|
Family ID: |
46001700 |
Appl. No.: |
14/114076 |
Filed: |
April 10, 2012 |
PCT Filed: |
April 10, 2012 |
PCT NO: |
PCT/SG2012/000125 PCKC 00 |
371 Date: |
December 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61479629 |
Apr 27, 2011 |
|
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Current U.S.
Class: |
604/533 ;
73/204.22 |
Current CPC
Class: |
A61M 5/16804 20130101;
G01F 1/684 20130101; A61M 5/16831 20130101; G01F 1/6847 20130101;
G01F 15/001 20130101; A61M 5/16886 20130101 |
Class at
Publication: |
604/533 ;
73/204.22 |
International
Class: |
A61M 5/168 20060101
A61M005/168; G01F 1/684 20060101 G01F001/684 |
Claims
1. A device for measuring flow rate of a fluid passing through a
fluid channel, the device comprising: a housing having a coupling
interface to which the fluid channel is attachable; a thermal
source disposed in the housing and adjacent to the coupling
interface at a first location, wherein the thermal source is to
emit a first thermal signal from the coupling interface into the
fluid channel; a first thermal sensor disposed in the housing and
adjacent to the coupling interface at a second location spaced
apart from the first location with a first interval; wherein the
first thermal sensor is to receive a first thermal signal at the
coupling interface from the fluid channel; a microprocessor
disposed in the housing and coupled to the thermal source and the
first thermal sensor, wherein the microprocessor is to record a
first instant at which the first thermal signal is emitted from the
thermal source, a second instant at which a second thermal signal
is received by the thermal sensor, and to determine the flow rate
based on said first interval, the first instant, the first thermal
signal, the second instant and the second thermal signal
characterized in that the fluid channel includes a tubular member;
the device includes a first plate and a second plate connected to
each other with the tubular member sandwiched therebetween; wherein
the tubular member being resiliently deformable, a distance between
the first plate and the second plate is less than an external
diameter of the tubular member such that the tubular member is
compressed between the first plate and the second plate.
2. The device of claim 1, wherein the coupling interface includes a
first end and a second end, the thermal source is positioned
between the first end and the second end of the coupling
interface.
3. The device of claim 2, wherein the first thermal sensor is
positioned between the thermal source and the second end of the
coupling interface.
4. The device of claim 3, further comprising a second thermal
sensor disposed in the housing and adjacent to the coupling
interface at a third location spaced apart from the first location
with a second interval; wherein the second thermal sensor is
coupled to the microprocessor and to receive a second thermal
signal at the coupling interface from the fluid channel.
5. The device of claim 1, wherein the coupling interface is a slot
having a first side surface and a second side surface opposite to
each other for receiving the fluid channel therebetween.
6. The device of claim 5, wherein the thermal source and the first
thermal sensor are positioned at the first side surface.
7. The device of claim 5, wherein the thermal source is positioned
at the first side surface. and the first thermal sensor is
positioned at the second side surface.
8. A system for determining flow rate of an intravenous fluid
delivery, the system comprising: a flow cell having a sidewall
surrounding a fluid channel having an inlet and an outlet; a
controller including: a housing to which the flow cell is attached;
a thermal source disposed in the housing at a first position and
adjacent to a first portion of the sidewall of the flow cell,
wherein the thermal source is to emit a first thermal signal into
the fluid channel; a first thermal sensor disposed in the housing
at a second position and adjacent to a second portion of the
sidewall of the flow cell, wherein the first thermal sensor is to
receive a first thermal signal from the fluid channel; a
microprocessor disposed in the housing and coupled to the thermal
source and the first thermal sensor, wherein the microprocessor is
to record a first instant at which the first thermal signal is
emitted into the fluid channel, a second instant at which a second
thermal signal is received from the fluid channel, and to determine
the flow rate based on said first interval, the first instant, the
first thermal signal, the second instant and the second thermal
signal characterized in that the fluid channel includes a tubular
member; the device includes a first plate and a second plate
connected to each other with the tubular member sandwiched
therebetween; wherein the sidewall being resiliently deformable, a
distance between the first plate and the second plate is less than
an external diameter of the tubular member such that the tubular
member is compressed between the first plate and the second
plate.
9. The system of claim 8, wherein the thermal source is positioned
between the inlet and the outlet.
10. The system of claim 9, wherein the first thermal sensor is
positioned between the thermal source and the outlet.
11. The system of claim 10, wherein the housing having a first side
surface and a second side surface, the flow cell is disposed
between the first side surface and the second side surface, wherein
the thermal source is disposed on one of the first and second side
surfaces and the first thermal sensor is disposed on said one of
the first and second side surfaces.
12. The system of claim 10, wherein the housing having a first side
surface and a second side surface, the flow cell is disposed
between the first side surface and the second side surface, wherein
the thermal source is disposed on one of the first and second side
surfaces and the first thermal sensor is disposed on the other one
of the first and second side surfaces.
13. The system of claim 10, further comprising a second thermal
sensor disposed in the housing at a second position and adjacent to
a third portion of the sidewall of the flow cell, wherein the
second thermal sensor is coupled to the microprocessor and to
receive a second thermal signal from the fluid channel.
14. The system of claim 13, wherein the second thermal sensor is
positioned between the inlet and the thermal source.
15. The system of claim 14, wherein the housing having a first side
surface and a second side surface, the flow cell is disposed
between the first side surface and the second side surface, wherein
the thermal source is disposed on one of the first and second side
surfaces and the second thermal sensor is disposed on said one of
the first and second side surfaces.
16. The system of claim 14, wherein the housing having a first side
surface and a second side surface, the flow cell is disposed
between the first side surface and the second side surface, wherein
the thermal source is disposed on one of the first and second side
surfaces and the second thermal sensor is disposed on the other one
of the first and second side surfaces.
17. The system of claim 1, wherein the housing having a first plate
and a second plate, the first plate and the second plate being
movable relative to each other between a first position at which
the flow cell is received between the first plate and the second
plate, and a second position at which the flow cell is fixed
between the first plate and the second plate.
18. The system of claim 17, wherein when the first plate and the
second plate are at the second position, the fluid channel is
compressed between the first plate and the second plate.
19. A method of detecting flow rate in an intravenous fluid
delivery system, the method comprising: emitting a first thermal
signal into a first location of a fluid delivery channel at a first
instant, wherein the fluid delivery channel forms a segment of the
intravenous infusion system; receiving a second thermal signal from
a second location of the fluid delivery channel at a second
instant, the second location is positioned with a first interval
downstream from the first location; receiving a third thermal
signal from a third location of the fluid delivery channel at a
third instant, the third location is positioned with a second
interval downstream from the second location; receiving a fourth
thermal signal from a fourth location of the fluid delivery channel
at a fourth instant, the fourth location is positioned with a third
interval downstream from the third location; determining the flow
rate by comparing the thermal signals from the second, third and
fourth location of the delivery channel with predetermined
temperature signal values established for known flow rates.
20. The method of claim 19, further comprising comparing a
temperature difference between the second thermal signal and the
third thermal signal with a trigger level to determine an occlusion
situation.
21. The method of claim 19, wherein each thermal signal at the
second, third and fourth location of the fluid channel includes a
time taken for the fluid heated by the first thermal signal to pass
through the respective first, second and third interval, the
temperature amplitude at each of the second, third and fourth
locations, the temperature differences between the second, third
and fourth locations and the time taken for the temperature
difference to reach a trigger level.
22. The method of claim 19, wherein each flow rate is determined by
combinations of the predetermined thermal signal values established
for known flow rates.
Description
TECHNICAL FIELD
[0001] Embodiments of the invention relate to a system, apparatus,
and methods for monitoring intravenous (IV) infusion, in
particularly the flow rate and volume of infusion delivery to a
patient.
BACKGROUND
[0002] In infusion therapy, the patient could either be immobilized
at bed site or ambulatory. In the former, infusion consist of an
intravenous (IV) drip set with gravity means or with the aid of an
electronic IV pump while in the latter the patient is ambulatory
with a self powered pump like elastomeric or electronic pumps. The
inadequacies in either situations relate to the lack of the flow
rate display of a gravity IV drip set as well as flow rate drifts
of such, hence necessitating frequent drip rate checks and roller
clamp adjustments by a healthcare provider. In electronic pumps the
flow rate display relates to the functioning of the driving
mechanism of such pumps and not the monitoring of actual flow of
medication to the patient.
[0003] Therefore, improved infusion procedures that address these
inadequacies are desirable. In conventional mechanical infusion
apparatus like elastomeric, spring powered or gas powered pumps,
flow adjustments are non-existent while in electrically driven
pumps user/healthcare provider response relates to malfunctioning
of the pumping mechanism itself.
[0004] It is the object of this invention to provide monitoring of
IV infusion by measuring the actual flow of medication independent
of the driving mechanism of the source and using the techniques
disclosed to enhance patient safety and caregiver efficacy.
SUMMARY
[0005] According to one embodiment of the invention, a thermal
pulse (or heat pulse) is emitted into the fluid or medication whose
flow rate is determined by measuring the time taken for this
thermal pulse and any change in its level to be detected by a
thermal sensor (e.g. temperature sensor) located at a fixed
position downstream in relation to the flow direction. This time
duration and change in temperature and the fixed distance between
the emitting and sensing locations provide the inputs to determine
flow velocity. The volumetric flow rate of the fluid is then
derived from the product of the flow velocity (V) and the
cross-sectional area (A) for flow. Even when different types of
fluids with different thermal coefficient are used, the impact
arising from such variables has little or no influence as the
measurement involves taking time duration between successive
pulses. While flow rate is determined by time and temperature
measurements, occlusion is detected by comparing the temperature
detected by two temperature sensors located at one upstream
location and another downstream location in relation to the fluid
delivery channel or path. In the absence of occlusion, the
temperature at the two locations will be different, specifically
the temperature at the downstream site will be higher than the
temperature at the upstream site due to the thermal pulse emitted
between the two locations. The fluid absorbs thermal energy from
the pulse and flows downstream, resulting in a higher temperature
detected at the downstream location. On the other hand, the
presence of occlusion causes minimal or no flow which results in a
minimal temperature difference or substantially equal temperature
readings at the two sensor locations.
[0006] According to one embodiment of the invention, the section of
the fluid delivery channel or path that is used in the above
described measurements of flow rate and temperature difference is
enclosed within an in-line Flow Cell, which can be inserted or
attached to a control module (Flow Detection Unit) that measures
and displays the appropriate flow status. The Flow Detection Unit
comprises a thermal source that utilizes a Laser diode, infra-red
(IR) diode or any heat generating means. The thermal source emits
the thermal pulse(s) that transfers heat to the fluid in the
channel of the Flow. Cell. The temperature sensors in the Flow
Detection Unit measure the temperatures at the predetermined
locations in the Flow Cell and provide these as input data for
further processing by the microprocessor in the Flow Detection
Unit. The algorithm programmed in the microprocessor will convert
these temperature inputs into digital outcomes and display
instantaneous flow rate, mean flow rate and/or volume
delivered.
[0007] According to another embodiment of the invention, the Flow
Cell comprises a bar code that can be read as it is swiped along a
slot in the housing of the Flow Detection Unit. The bar code is
encoded to provide specific input data for the microprocessor or
MCU in the Flow Detection Unit, which obviates the need for manual
input by the user of such data, hence promoting plug and play
simplicity. The barcode, which can be preprinted on the Flow Cell,
can also contain unique identification such that when the Flow Cell
is swiped in the Flow Detection Unit, the patient data tagged to
the barcode is scanned/read by the Flow Detection Unit, which
displays patient data for nurse verification. This provides for
positive identification of patient to the IV pump, i.e. medication
prescribed to the patient. Barcode can also be tagged with a
desired flow rate of the medication for the patient. In the
situation where patient and medication data are managed in a server
with wireless connectivity, such information could be sent to the
Flow Detection Unit by remote means. This allows further means of
verifying that correct medication is administered to the patient as
the Flow Detection Unit is attached to the Flow Cell through which
medication flows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments of the invention will be readily understood by
the following detailed description in conjunction with the
accompanying drawings.
[0009] FIG. 1 is a schematic view of the intravenous (IV) infusion
monitoring system in accordance with one embodiment of the
invention.
[0010] FIG. 2 is a perspective view of the Flow Detection Unit and
Flow Cell in accordance with one embodiment of the invention.
[0011] FIG. 2A is a perspective view of the Flow Detection Unit
with Flow Cell attached in accordance to one embodiment of the
invention.
[0012] FIG. 2B is an unassembled perspective view of the Flow
Detection Unit with its associated components in accordance with
the one embodiment of the invention.
[0013] FIG. 2C is a perspective view of the Flow Detection Unit in
use with the flow cell in accordance with one embodiment of the
invention.
[0014] FIG. 3A and FIG. 3B are perspective views of the Flow Cell
in accordance with one embodiment of the invention.
[0015] FIG. 3C and FIG. 3D are side views of the Flow Cell
illustrated in FIG. 3A and FIG. 3B.
[0016] FIG. 3E is a cross-sectional view of the Flow Cell
illustrated in FIG. 3C along A-A.
[0017] FIG. 3F is a perspective view showing a Flow Cell according
to another embodiment of the present invention.
[0018] FIG. 3G is a perspective view showing a Flow Detection Unit
and the Flow Cell of FIG. 3F.
[0019] FIG. 4A is a perspective view of a Flow Cell in accordance
with yet another embodiment of the invention.
[0020] FIG. 4B is a side view of the Flow Cell illustrated in FIG.
4A.
[0021] FIG. 4C is a cross-sectional view of the Flow Cell taken
along line B-B in FIG. 4B.
[0022] FIG. 4D is a cross-sectional view of the Flow Cell taken
along line A-A in FIG. 4B.
[0023] FIG. 4E is a perspective view of a Flow Detection Unit in
use with the flow cell shown in FIG. 4A in accordance with one
embodiment of the invention.
[0024] FIG. 5A is a perspective view of the Flow Cell shown in FIG.
4A coupled to a flow regulating mechanism and a clamping mechanism
in accordance with one embodiment of the invention.
[0025] FIG. 5B is a top view of the Flow Cell shown in FIG. 5A with
a partial cross-sectional view of the clamping mechanism.
[0026] FIG. 5C is a side view of the Flow Cell illustrated in FIG.
5A.
[0027] FIG. 5D is a cross-sectional view of the Flow Cell viewed
from the line A-A in FIG. 5C.
[0028] FIGS. 6A and 6B are examples of temperature vs time graphs
of the temperature profiles in the Flow Cell.
[0029] FIGS. 6C and 6D are examples of temperature vs. time graphs
of the temperature difference in the Flow Cell.
[0030] FIG. 6E is an example of temperature vs. time graphs of
temperature difference measured with the Flow Cell and Flow
Detection Unit shown in FIG. 2B.
[0031] FIG. 7 is a block diagram of the Flow Detection Unit in
accordance with an embodiment of the invention.
[0032] FIG. 8 is a flow diagram illustrating the functions of the
Flow Detection Unit in accordance with an embodiment of the
invention.
[0033] FIGS. 9A and 9B are flow diagrams illustrating the
instantaneous flow rate mode in accordance with an embodiment of
the invention.
[0034] FIGS. 10A to 10C are flow diagrams illustrating the mean
flow rate mode in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION
[0035] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of various
illustrative embodiments of the invention. It will be understood,
however, to one skilled in the art, that embodiments of the
invention may be practiced without some or all of these specific
details. In other instances, well known intravenous delivery
processes and mechanisms have not been described in detail in order
not to necessarily obscure pertinent aspects of embodiments being
described.
[0036] Embodiments of the invention relate to an infusion
monitoring and measurement system that supports mobile or
ambulatory and bed side mode of infusion based on any mechanical or
electrical source of pumping fluid source. In an embodiment of the
invention, a control module (Flow Detection Unit), which is a
tablet or pod like device, displays data and alarms to provide
effective monitoring of a typical infusion procedure and allows
appropriate user response. In another embodiment, a flow section of
the fluid path (Flow Cell) is attachable to the Flow Detection Unit
to enable measurement and monitoring of the fluid flow, volume of
fluid delivered and other related parameters.
[0037] The Flow Detection Unit comprises at least one thermal or
heat source such as a laser diode or Infra Red (IR) diode or any
heat generating means, at least one thermal sensing means, and
electronic processing circuits to ascertain flow rates and
occlusion, and in certain application modes prompts the user or
healthcare provider to take specific actions in order to achieve
desired flow of medication or fluids to the patient. In one
embodiment, the Flow Cell is an in-line component of the fluid
delivery path between the fluid source and the patient. The Flow
Cell allows thermal energy/thermal signal emitted from the Flow
Detection Unit to be transferred to the fluid or medication that
flows through the flow cell. In one embodiment, certain portions of
the Flow Cell include heat transmission paths, e.g. contacts or
conductive probes, which facilitate the heating or temperature
measurement of the fluid or medication by the Flow Detection Unit.
The Flow Cell may function as an interface on the fluid delivery
path which allows specific measurement of the fluid (by the Flow
Detection Unit) while it is delivered to the patient, hence making
it amenable as a single use or disposable component that could be
easily assembled with the entire fluid delivery apparatus. In one
embodiment, the Flow Cell is bar-coded to allow automatic input of
relevant data related to the fluid delivery apparatus used, for
example flow rate and volume to be infused or even unique patient
or pump or medication related identification.
[0038] One advantage of the re-usable main body Flow Detection Unit
and a single use in-line installed Flow Cell allows all current
disposable mechanical pumps including and not limited to spring
powered, gas powered or elastomeric pumps to be equipped with a
safety feature indicating flow rates and occlusion that is not
available presently. The implication is significant as the use of
such pumps, which is well received for its ease of use could be
expanded to include infusion of medication with narrow therapeutic
tolerances. Without such means to show the flow status, and where
appropriate prompting user intervention the use of such medication
with such pumps would be limited, and even hazardous. Furthermore,
unlike monitoring systems in most electronic pumps that focuses on
the proper functioning of the pump itself, the Flow Cell and Flow
Detection Unit monitors the actual flow rate of infusion and in
some embodiments allow the necessary adjustment to the flow orifice
to achieve the desired flow.
[0039] For example, the Flow Detection Unit provides a display of
flow rates, such as instantaneous and mean rate of infusion, and
the volume delivered as means of alerting the healthcare provider
to undesirable deviations. It may also alert the healthcare
provider when occlusion is detected. The Flow Detection also allows
user/healthcare provider to make adjustments to correct the flow
rates as a means of addressing the risks associated with any
non-action.
[0040] In addition, the Flow Detection Unit supports positive
identification of patient/drug patency. Conventionally, drugs to be
infused are prepared in the pharmacy while the filled apparatus are
attached to patients by a separate healthcare provider. Patient and
intended medication data stored in the Flow Detection Unit by means
of a barcode wand or hand held scanner in the pharmacy can be
subsequently used as positive identification means when the
infusion monitoring is initiated. For example, the nurse will be
able to identify the correct matching of medication in the pump to
the patient when the Flow Detection Unit displays patient data that
is tagged to the barcode on the Flow Cell. This helps to reduce
incorrect infusion of medication to the patient. Barcode could also
be tagged with a desired or nominal flow rate data for the
medication to be administered to the patient. As an interface
between the Flow Detection Unit and the fluid delivery path, the
Flow Cell is not necessarily an integral part of the delivery
system. It could be configured as an in-line component of an
extension tube that could be connected to any infusion delivery
system to support monitoring of infusion described in this
invention.
[0041] Referring to FIG. 1 and FIG. 2, a Flow Cell 200 according to
one embodiment of the present invention forms a segment of a fluid
path of a fluid delivery system, e.g. an intravenous infusion
system, from a fluid source 201 to a final receiving point, e.g. a
patient 20. The fluid source 201 can be an electrical fluid pump or
a mechanical fluid pump (e.g. spring powered, gas powered or
elastomeric fluid pumps) In one embodiment, the Flow Cell 200
includes a first plate 246 and a second plate 247 connected to each
other. In the context of a patient receiving medication, the Flow
Cell 200, when inserted into an opening or slot 103 in the Flow
Detection Unit 100, enables the flow rate of infusion to be
detected and shown on a display screen 108 of Flow Detection Unit
100. The display screen 108 could be a Liquid Crystal Display (LCD)
or Organic Light-Emitting Diode (OLED) display with or without
in-screen navigational options for displaying flow rates, flow rate
deviations, volume delivered and visual alarms for occlusions or
unacceptable deviations in flow rates, etc. The Flow Detection Unit
100 can also include an audio alarm that activates when unsafe flow
rates or occlusion are detected.
[0042] The Flow Detection Unit 100 with the Flow Cell 200 may be
dimensioned to be attachable to the patient 20 so that it allows
easy access to the caregiver, e.g., a physician or nurse, to adjust
the rate of infusion when needed, to reset an alarm button 104 or
merely to monitor the flow status on display screen 108. In one
embodiment, the Flow Detection Unit 100 starts automatically when
Flow Cell 200 is inserted or secured thereto, an in-built proximity
switch will initiate the MCU in the Flow Detection Unit 100 to
perform the preprogrammed logic.
[0043] Referring to FIG. 2B and FIG. 2C, the Flow Detection Unit
100 comprises a thermal source 109 and first, second, third and
fourth thermal sensors 110, 111, 112 and 113. The use of more
thermal sensors enables time and amplitude data to be recorded at
more positions along the fluid channel. This in turn increases the
permutations in the development of the algorithm for flow rate
detection. The thermal source 109 is a flexible resistive heater,
but it could be any source generating thermal energy, e.g. a laser
diode, an IR diode or the like. In one embodiment, the thermal
source 109 is positioned in substantially equidistant between the
first and second thermal sensors 110 and 111. However, it is also
possible that the distances from thermal source 109 to thermal
sensors 110 and 111 are not substantially equidistant. If this is
the case, an algorithm used to determine the measurement/monitoring
results could be developed to compensate for the impact of such
non-equidistance positioning relationship between thermal source
109 and first and second thermal sensors 110 and 111, in the data
recorded. The thermal sensors 110, 111, 112 and 113 are radiation
or temperature sensing means that uses, for example IR sensors,
laser sensors, film based resistance temperature detectors (RTD)
sensors, negative/positive temperature coefficient (NTC/PTC)
thermistors or any thermocouple.
[0044] During operation, when Flow Cell 200 is inserted into the
slot 103 of the Flow Detection Unit 100, the thermal source 109 and
thermal sensors 110, 111, 112 and 113 are aligned to the windows
portions 249, 250, 251, 252 and 253, respectively, that are
disposed along the flow direction of the fluid through the Flow
Cell 200 (FIG. 2B and FIG. 3B. The window portions 249, 250, 251,
252 and 253 may be openings formed on one or both of first and
second plates 246 and 247, transparent panels and/or other suitable
configurations that allow thermal radiation to be transmitted
between the fluid in the Flow Cell 200 and the thermal source 109
and sensors 100, 111, 112 and 113 through first and second plates
246 and 247, without substantial thermal energy losses. The slot
103 (FIG. 2) provides simplicity and ease of use for attaching Flow
Cell 200 to Flow Detection Unit 100, thus obviating the need for
additional protective means to prevent unintended visual and
physical exposure to the radiation waves from the thermal source
109.
[0045] In one embodiment, the Flow Cell 200 may be bar-coded and
together with a bar code reading feature, hence the need for manual
user inputs may be obviated. In an embodiment of the invention, the
Flow Detection Unit 100 comprises a barcode reading/scanning means
114 to read a barcode 312 on the Flow Cell 200 as the Flow Cell 200
is inserted into and swiped along the slot 103. The barcode 312 can
be encrypted by a commercially available printer, a laser marking
system or other means onto the Flow Cell 200. In one embodiment,
the barcode reading means 114 is a photocell comprising emitter and
receiver elements for sensing the barcode 312 as the Flow Cell 200
is swiped along the slot 103. The orientation of the barcode
reading means 114 in relation to the slot 103 may differ from the
illustrations in the context and in the drawings, depending on the
barcode position marked on the Flow Cell 200. Upon reading the
barcode 312, the barcode scanning means 114 generates an input
signal to a microprocessor or micro-controller unit (MCU) 130 in
the Flow Detection Unit 100. The input signal can be used to, for
example, set the reference value for calculation of flow rates,
infused volume as well as the interval frequency of the thermal
pulses (or heat pulses) to be emitted by thermal source 109.
[0046] In one embodiment, the display screen 108 is activated to
request user for inputs of flow rate and fill volume when the
barcode reading means 114 failed to generate input signals for MCU
130 after reading the barcode 312, or in a situation when wireless
transmission of such data from a server to the Flow Detection Unit
100 failed. In one embodiment, the Flow Detection Unit 100
comprises a membrane switch 107 or any other forms of user
input/control means, such as a scroll wheel which allows user to
select predetermined values shown in the display screen 108.
Alternatively, the display screen 108 may show in-screen options
that allow user selection, i.e. touch-screen features to allow user
input or selection.
[0047] In one embodiment, the Flow Detection Unit 100 includes a
housing 102 having a top lid 120 and a bottom shell 121. For
clarity purposes and to illustrate other components of Flow
Detection Unit 100, the top lid 120 is not shown in FIG. 2C. In one
embodiment, the Flow Detection Unit 100 comprises a power source
131 for the MCU 130, display screen 108, alarm button 104 and any
associated electrical components. For example, the power source 131
can be a Lithium polymer or Lithium Ion cells or any other
commercially available batteries. The power source 131 can be
retained within the bottom shell 121 by a hinged cover 122 over an
opening 123. Alternatively, the power source 131 could be connected
to a universal serial bus (USB) port for charging on board.
[0048] In an embodiment of the invention, the power source 131 can
be coupled to an electrical port 116, for example a USB port, which
may be used to recharge the power source 131. The electrical port
116 can also be configured to serve as a communication port to
store data in the MCU 130, for example, from a pen scanner. In
another embodiment, the electrical port 116 receives data from a
scanning wand or any equivalent barcode input, where the data could
be patient and medication information that are automatically stored
in the MCU 130. These data could be retrieved using the membrane
switch 107 and used as positive identification purposes for
patient-drug patency.
[0049] In an embodiment of the invention, the Flow Detection Unit
100 may be equipped with wireless connectivity means 105, e.g. a
blue tooth or wifi device etc., to allow data exchange between
itself and a remote server 35 wirelessly (FIG. 2A). In one
application, the server could send patient and medication data to
the Flow Detection Unit 100 when the Flow Cell 200 is swiped or
attached to it. This feature allows the caregiver to confirm that
the infusion system comprising the Flow Cell 200 as a segment of
the fluid channel carries the correct medication to the patient.
Likewise, any adverse events pertaining to infusion irregularities
or any event that may require imminent attention could be
communicated remotely to the server, hence allowing care givers to
plan and schedule work ahead. The possibilities arising from
wireless connectivity associated with the means of monitoring
status of infusion as described in this invention is encompassing
for anyone ordinarily skilled in the art.
[0050] The Flow Cell 200 forms a segment of the fluid path from the
fluid source 201 to the patient 20, either as an integral part of
the infusion system or as a separate standalone component that is
connected to the infusion system. In a preferred embodiment, the
Flow Cell 200 is flat paneled in shape. Referring to FIGS. 3A-3E,
the flow Cell 200 includes a tubular member, e.g. a soft flexible
tube 243, a first plate 246 and a second plate 247. Soft flexible
tube 243 defines a fluid channel 241 therethrough. First and second
plates 246 and 247 are constructed with substantially rigid
material. When assembled together, first and second plates 246 and
247 form a space therebetween which is narrower than an external
diameter of soft flexible tube 243. Accordingly, first and second
plates 246 and 247 press against soft flexible tube 243 disposed
between plates 246 and 247. As plates 246 and 247 are rigid, soft
flexible tube 243 is compressed into a thin channel shaped
configuration from its original round cross sectional geometry in
the section where plates 246 and 247 and soft flexible tube 243 are
in contact. The rigid plates 246 and 247 are held firmly together
by means of claws 254, 255 and 256 and adjacent openings or slots
257, 258 and 259 such that these features will engage each other to
produce a locking action when the plates 246 and 247 are firmly
pressed against each other. The positions and number of claws and
slots may vary from those shown in the drawings and maybe subject
to tool design considerations suitable for manufacturing.
Connection of first and second plates 246, 247 by the claws and
openings also enables easy assembly and when necessary, also allows
first and second plates 246, 247 to be detached from each other
for, e.g. checking or replacement of soft flexible tube 243.
Compressed by plates 246 and 247, the cross section of the soft
flexible tube 243 along a direction perpendicular to the fluid path
it communicates is approximately a thin rectangular space 242 with
a thickness of about 0.05 to 0.35 mm and is created between the
inner walls of the soft flexible tube 243. Second plate 247 may
have a slightly raised section 248 facing first plate 246. Raised
section 248 is to provide uniform compression displacement onto the
soft flexible tube 243. The soft flexible tube 243 is typically
constructed from materials that allow transmission and detection of
infrared radiation through its walls. The plates 246 and 247 could
also be part of a clamp shell or hinged-like contraption as a means
to achieve a thin channel-like cross section in the soft flexible
tube 243 such that the fluid channel created allows thermal
radiation to be transmitted to and from the fluid in a manner and
extent that data could be recorded and used to develop an algorithm
for flow rate determination. Window portion 249 formed on first
plate 246 may be the type of thin panel to give improved proximity
or an opening to allow direct access and physical contact between
the heat source 109 and the soft flexible tube 243. Window portions
250, 251, 252 and 253 formed on second plate 247 may also be the
types of thin panels or openings at locations adjacent to the
thermal sensors 110, 111, 112 and 113 in the Flow Detection Unit
100, to allow direct access and physical contact between thermal
sensors 110, 111, 112 and 113 and soft flexible tube 243.
[0051] The soft flexible tube 243 has an inlet 243a for coupling to
the fluid source 201 via inlet tube 204, and an outlet 243b for
coupling to outlet tube 205. On the sidewall of soft flexible tube
243, there are defined thermal conductive portions 243c, 243d,
243e, 243f and 243g. When soft flexible tube 243 is sandwiched
between first and second plates 246 and 247, thermal conductive
portion 243c is in alignment with, and become at least partially
overlapped to, window portion 249. Similarly, thermal conductive
portions 243d, 243e, 243f and 243g are also in alignment with, and
become at least partially overlapped with, window portions 250,
251, 252 and 253, respectively. This structure allows thermal
signals to transmit between Flow Detection Unit 100 and Flow Cell
200 through thermal conductive portions 243c, 243d, 243e, 243f and
243g, when Flow Cell 200 is attached to Flow Detection Unit 100 and
that thermal source 109, first, second, third and fourth thermal
sensors 110, 111, 112 and 113 face respective window portions, 249,
250, 251, 252 and 253.
[0052] Outlet tube 205 can be coupled to a patient 20 through
common means like a patient connector and catheter. The inlet 243a
and outlet 243b are also means to allow improved manufacturability
when the soft flexible tube 243 and the fluid tubes 204 and 205 are
of different dimensions (primarily inner and/or outer diameters) or
materials. The soft flexible tube 243 and fluid tubes 204 and 205
could also be connected directly without separately formed inlet
243a and outlet 243b.
[0053] According to another embodiment of the present invention, as
shown in FIG. 3F, there is provided a Flow Cell in the form of a
tubular member 270 to enable thermal signal transmission with an
external device, e.g. a Flow Detection Unit, for flow rate
measurement, detection and monitoring in a fluid delivery system
e.g. an intravenous infusion system. Tubular member 270 includes a
sidewall 273 surrounding a fluid channel 271. Tubular member 270
may form a segment of a fluid path of a fluid delivery system, e.g.
an intravenous infusion system. Tubular member has an inlet 273a at
one end of sidewall 273, and an outlet 273b at opposite end of
sidewall 273, and allows fluid to flow through fluid channel 271
from inlet 273a to outlet 273b. Sidewall 273 has a first portion
273c and a second portion 273d adjacent to first portion 273c.
First portion 273c is to allow a first thermal signal to transmit
into fluid channel 271, and second portion is to allow a second
thermal signal to transmit out from fluid channel 271. It should be
appreciated that although shown in FIG. 3F as separate regions on
sidewall 273, first portion 273c and second portion 273d may also
join together as one region.
[0054] FIG. 3G shows a flow detection unit 170 for flow rate
detection using tubular member 270 shown in FIG. 3F. Flow detection
unit 170 includes a housing 171, a thermal source 173c, a thermal
sensor 173d and a controller e.g. a microprocessor 172 disposed in
housing 171. Microprocessor 172 is coupled to thermal source 173c
and thermal sensor 173d. In use, tubular member 270 is placed
proximate to flow detection unit 170 by, e.g. attaching to housing
171 of flow detection unit 170 such that thermal source 173c is
aligned with first portion 273c, and thermal sensor 173d is aligned
with second portion 273d. When activated, thermal source 173c emits
a first thermal signal into fluid channel 271 through first portion
273c. Meanwhile or subsequently, thermal sensor 173d receives a
second thermal signal from fluid channel 271 through second portion
273d. First and second thermal signals, the time instant at which
the thermal signals are emitted/received as well as the time
intervals taken in between may then be recorded by microprocessor
172 for determining the flow rate based on methods as hereinafter
described.
[0055] Housing 171 may have a first plate 280 on which thermal
source 173c and first thermal sensor 173d are fixed, and a second
plate 281 opposite to first plate 280. First plate 280 is fixed to
housing 171, second plate 281 is movable relative to first plate
280. When second plate 281 is at a position away from first plate
280, e.g. with a distance d greater than an external diameter of
tubular member 270, tubular member 270 can be placed between first
plate 280 and second plate 281. When second plate 281 move towards
first plate 280, i.e. by decreasing distance d, tubular member 270
will be clamped between first and second plates 280, 281 such that
tubular member 270 is fixed to housing 171. At this position, first
portion 273c is aligned with thermal source 173c, and second
portion 273d is aligned with first thermal sensor 173d such that, a
first thermal signal from thermal source 173c can be emitted into
tubular member 270 through first portion 273c, and a second thermal
signal from tubular member 270 through second portion 273d can be
received by second thermal sensor 173d.
[0056] Flow detection unit 170 may include a second thermal sensor
173e disposed at the opposite side of first thermal sensor 173d
about thermal source 173c. Tubular member 270 includes a third
portion 273e between inlet 273a and first portion 273c. When
tubular member 270 is clamped between first plate 280 and second
plate 281, third portion 273e is aligned with second thermal sensor
173e such that a third thermal signal from tubular member 270
through third portion 273e can be received by second thermal sensor
173e.
[0057] In a further embodiment, as shown in FIGS. 4A-4E, a Flow
Cell 200' is tubular in shape and comprises a housing 208 having an
inlet 214, an outlet 215, and a fluid channel 213 in fluid
communication with the inlet 214 and outlet 215. Housing 208 is
formed of rigid material, by injection molding for instance.
Housing 208 includes a sidewall 217 defining the channel 213, and
with three window portions 209, 210, 211 formed on sidewall 217.
The window portion 209 allows thermal energy to be transmitted to
the fluid flowing through channel 213, at the window portion 209 of
the channel 213. The window portions 210 and 211 allow the
detection of respective thermal energy levels (i.e. temperature) of
the fluid at the window portions 210 and 211. When the Flow Cell
200' is attached to a Flow Detection Unit, e.g. a Flow Detection
Unit 100' shown in FIG. 4E, the window portions 210, 211 and 209
are substantially aligned to the thermal sensors 110, 111 and
thermal source 109 respectively (FIG. 4E). In one embodiment, the
housing 208 of the Flow Cell 200' includes a protrusion or handle
219 that eases the insertion or removal of the Flow Cell 200'
into/from the slot 103 of the Flow Detection Unit 100'.
[0058] In one embodiment where the thermal source 109 utilizes an
IR diode, the Flow Cell 200' can be made from materials with
minimal IR absorption characteristics. In other words, Flow Cell
200' can be made of materials that allow a large percentage of the
IR radiation to be transmitted to the fluid. For example, the
window portions 209,210, 211 are made of polyethylene materials.
Alternatively, the entire Flow Cell 200' can be made of
polycarbonate materials. In another embodiment, the window portions
209, 210, 211 are each formed as a recess on the sidewall 217 such
that the window portions 209, 210, 211 have smaller thickness than
the other portions of the sidewall 217. The smaller thickness helps
to reduce the absorption of radiation by the window portions 209,
210, 211.
[0059] If a laser diode is used as the thermal source 109, heat
transfer probes 209a (only one is shown) may be used to improve the
transfer of heat to the fluid in the channel 213, as shown in FIG.
4C. The probes are made of good heat conducting material, e.g.
stainless steel, and at least one probe is integrated into each of
the window portions 209, 210, 211, for example by insert molding
techniques. The probe 209a extends across the thickness of portion
209 such that it has an exposed surface in contact or in close
proximity to the thermal source 109 when the heat pulse is emitted,
and an opposite surface in contact with the fluid path so that the
fluid receives the heat pulses. Similarly, probes at the portions
210 and 211 has an exposed surface in contact or in close proximity
to the thermal sensors 110 and 111, and opposite surfaces in
contact with the fluid to conduct heat from the fluid to the
thermal sensors 110 and 111.
[0060] In one embodiment, the Flow Cell 200, 270 or 200' may
include a clamping mechanism 220 at one end, for example at the
inlet 214, and a flow rate regulating mechanism 230 at the other
end, for example the outlet 215 (FIGS. 5A-5D). The clamping
mechanism 220 offers a means of stopping fluid flow from the fluid
source 201 to the patient 20, while the flow regulating mechanism
230 provides a means of adjusting the flow rate of the fluid. In an
embodiment of the invention, the flow regulating mechanism 230
includes a barrel 232 inside which a rotatable axle 231 is
disposed. A fluid tube can be coupled to the opening 234 of the
flow regulating mechanism 230. Rotation of the axle 231 about its
axis will move a stem 233 (solid or hollow) into the fluid tube in
a longitudinal direction such that the effective lumen of the fluid
tube will vary, hence modifying the flow rate of the fluid passing
through it. This action of rotating the axle 231 could be done
manually or by means of an actuating mechanism, for example a
robotic arm interface that receives signals from the MCU 130 of the
Flow Detection Unit 100 to effect the necessary rotation. The
adjustment in the flow rate can be made automatically and optimized
using data of the infusion stored in the Flow Detection Unit
100.
[0061] In an embodiment of the invention, the clamping mechanism
220 includes a tubular construction 225 with a silicone or pliable
material as an over sleeve 226. The tubular construction 225 can be
made from any hard plastics. In one embodiment, the over sleeve 226
is secured in position with respect to the tubular construction 225
by O Rings 228a and 228b (FIG. 5D) made of elastic material or any
constrictive means such that the fluid path along the axis of the
Flow Cell 200 is not compromised due to leakages. The O Rings 228a,
228b can be protected by retainers 222a and 222b which may be
designed to be part of a single molded piece. The clamping function
is achieved by a lever 223 which includes a protrusion 229 on its
underside. When the lever 223 is pushed towards the over sleeve
226, the protrusion 229 will press against the wall of the over
sleeve 226. There is a notch 227 that permits the protrusion 229 to
extend into the tubular construction 225 and cause a partial or
full blockage of the fluid flow. The lever 223, when pushed
downwards, is held in place by a catch 224. The lever 223 can be
released by pushing the catch 224 away from the lever 223. To avoid
accidental activation of the lever 223, there are side shields 221a
and 221b formed on both sides of the lever 223.
[0062] The use of the clamping mechanism 220 and flow regulating
mechanism 230 allows the function of stopping or regulating flow to
be grouped within close proximity to the Flow Cell 200, hence
offering convenience for the healthcare provider. However, it can
be appreciated that the Flow Cell 200 can be used without the
clamping mechanism 220 or flow regulating mechanism 230.
[0063] FIG. 6A to FIG. 6D illustrate an exemplary temperature vs.
time graphs according to embodiments of the present invention, e.g.
for the temperature readings by the thermal sensors 110 and 111 of
Flow Detection Unit 100 shown in FIG. 4E. Taken from a direction of
flow of the fluid to be measured, thermal sensor 110 is situated in
a downstream position in relation to the thermal source 109, while
thermal sensor 111 is situated upstream in relation to thermal
source 109.
[0064] The temperature readings detected at thermal sensor 110
(represented by line T2) and at thermal sensor 111 (represented by
line T1) vary according to the thermo diffusion of the fluid heated
by thermal source 109 and also the flow of fluid passing through
the thermal sensors 110, 111 locations in the channel 213. In FIG.
6A, the temperature T2 is higher than T1 as the fluid passing
thermal sensor 110 would have predominantly being heated by thermal
source 109, while the temperature T1 would represent the
temperature of fluid at thermal sensor 111 before it is heated by
thermal source 109. Measuring the difference in the temperatures T2
and T1 allows the confirmation of flow of fluid. In a similar
fashion, the minimal or lack of temperature difference between T2
and T1 is an indication of no flow or an occurrence of occlusion
(see FIG. 6B and FIG. 6C).
[0065] Further referring to FIG. 6C, a temperature difference
threshold level representing a predetermined quantum in the
differential in temperatures between T2 and T1 could be used to
determine flow or no flow situations. This threshold level could
also be used, in conjunction with the thermal pulse duration of the
thermal source 109 to determine the flow rate of the fluid passing
through the channel 213. The fluid passing through the channel 213
or alternatively thin rectangular space 242 acts as a carrier of
thermal energy or heat emitted by the thermal source 109. The time
taken for the fluid heated by the thermal source 109 to pass
through fixed distance between thermal source 109 and thermal
sensor 110 will be measured and the electronic circuitry of the
Flow Detection Unit 100 can be designed to have repetitions of such
measurements to achieve better accuracy. Since the cross section of
the fluid path (i.e. channel 213) in the Flow Cell 200 is fixed,
the time taken for the thermal pulse to appear at thermal sensor
111, or to flow cells with more sensors e.g. thermal sensors 112 or
113, and the amplitude of such a thermal pulse at each of the
sensor locations would vary according to the flow rate of the fluid
And could be determined. In similar fashion, the approximate volume
of fluid delivered can be derived from the flow rate and duration
lapsed. Trigger level is a predetermined reference level to ensure
that time measurements are consistent, i.e. time is measured when
this level is reached.
[0066] Referring to FIG. 7, input ports of MCU 130 receive a signal
J1 from thermal sensor 110, a signal J2 from thermal sensor 111,
and a signal J3 from the barcode reading means 114, a signal J4
from membrane switch 107 and an alarm reset signal J5 from alarm
button 104. In embodiments having more thermal sensors, e.g.
thermal sensor 112, 113, MCU 130 also receive signals J6 and 17
from respective thermal sensors 112 and 113. A display latch and
driver controls the display screen 108. The MCU 130 sends signals
O1 to display screen 108, O2 to a buzzer 140 to indicate occlusion,
end of infusion and unacceptable flow rate detected; O3 to trigger
thermal source 109 to emit at a desired time interval based on the
expected flow rate of the fluid in the channel 213 or alternatively
channel 242. The input signal for the expected flow rate is made
possible via the barcode signal J3. To conserve power consumption,
a signal from the MCU 130 will control the power source 131 to
operate intermittently. The power source 131 can be coupled to the
MCU 130 via a voltage regulator.
[0067] A software program is stored in a Flash Memory to work with
the arithmetic logic unit (ALU) to generate the output signals O1,
O2, O3 and O4. O4 represents a signal to display patient data when
the barcode 212, tagged to some patient data, is read by the
barcode reading means 114. Signals J1 and J2 are compared and a
differential is referenced with a predetermined threshold giving an
output O2 when there is an occlusion. In the absence of occlusion,
the time taken for J2 to reach a trigger level will produce a
signal O1 which displays the flow rate in, for example, mL per
hour.
[0068] Referring to FIG. 8, in a method of detecting flow rate of
intravenous fluid delivery system according to one embodiment of
the present invention, the Flow Detection Unit 100 is powered on
automatically when the Flow Cell 200 is inserted, e.g. inserted
into an opening (or slot 103) of the Flow Detection Unit 100 or
suitably attached to the Flow Detection Unit 100 (step 410). The
MCU 130 then undergoes a reset (step 411) before activating the
barcode reading means 114 to decode the nominal flow rate (Q.sub.N)
and nominal volume (V.sub.N) at step 412. The barcode 212 or
alternatively 312 is decoded by the barcode reading means 114 to
provide nominal flow rate data (Q.sub.N) as well as nominal volume
(V.sub.N) for calculations to be performed by the MCU 130. Data
from the barcode 212 or alternatively 312 is decoded by blocking
and transmitting IR light from the barcode reading means 114 during
Flow Cell 200 insertion into the Flow Detection Unit 100. Next, the
MCU 130 checks whether the reading or data decoded from the barcode
212 or alternatively 312 is valid (step 413). For example, the MCU
130 comprises a checksum function to ensure that any dirt or blur
on the barcode 212 or alternatively 312 area does not cause wrong
readings. In the event such decoding fails or the data is not
valid, manual input via the membrane switch 107 will be prompted
(step 415). Otherwise, the display screen 108 would display
automatically a mode selection option (step 414) for instantaneous
flow rate (step 420) or mean flow rate (step 440) measurements.
User then selects the desired mode by manipulating the membrane
switch 107.
[0069] Referring to FIG. 9A, the Flow Detection Unit 100 is
programmed to display instantaneous flow rate (step 420). Next, the
MCU 130 sets the initial instantaneous flow rate (Q.sub.i) to
"null" (step 421) and sets the measurement variables by looking up
the nominal flow rate (Q.sub.N) value from a reference table stored
in the Flash Memory of the Flow Detection Unit 100 (step 422). The
measurement variables comprises the duration the thermal source 109
is switched on (T.sub.IRON), the time interval between each
measurement (T.sub.INT), the maximum time laps for detecting the
presence of an occlusion (T.sub.EXP), the trigger level of
temperature difference between T1 and T2 (T.sub.DIFF), and the
constant for the calculating the instant flow rate (C.sub.Q). In
embodiments where the Flow Cell 200 is predisposed with more
temperature measurement locations along its fluid channel,
additional permutations of T.sub.DIFF could be developed to further
improve the accuracy of flow rate determination.
[0070] When the measurement cycle starts (step 423), the thermal
source 109 will be turned ON and OFF intermittently to emit heat
pulses to the fluid in the channel 213. In one embodiment, the
thermal source 109 turns on for the duration of T.sub.IRON then
turns off. The temperature difference (T.sub.DIFF) between the
readings at thermal sensors 110 (T2) and 111 (T1) is measured and a
timer starts to count time interval (T.sub.INT) for the start of
the next measurement cycle (step 424), which helps to ensure that
the measurements are taken at equal intervals. At step 425, the
measured temperature difference (T2-T1) is compared against a
predetermined trigger level (T.sub.DIFF) to confirm the existence
of fluid flow versus occlusion. In other words, the MCU 130 checks
whether the temperature difference between T1 and T2 exceeds the
trigger level (T.sub.DIFF).
[0071] If there is occlusion, the difference in the temperature
readings taken by thermal sensors 110 and 111 will be below the
trigger level (T.sub.DIFF), which activates the buzzer/alarm on the
Flow Detection Unit 100. A suitable display indicator, e.g.
"OCCLUSION" will be shown on the display screen 108 (step 427). In
one embodiment, the MCU 130, at step 426, checks whether the number
of time laps, from the time the thermal source 109 turned on, has
reached the maximum laps for occlusion detection (T.sub.EXP) before
activating the buzzer at step 427. In other words, the buzzer
activates after the maximum waiting time had lapsed without the
temperature difference (T2-T1) reaching or exceeding the trigger
level (T.sub.DIFF).
[0072] In the absence of occlusion (430), the time taken for the
temperature difference (T2-T1) to reach the predetermined trigger
level (T.sub.DIFF) will be measured (step 431) and stored as
T.sub.LAP (step 431), and subsequent readings of this duration are
taken (see FIG. 9B). In other words, the MCU 130 records the time
lapsed or time duration from the moment the thermal source 109 is
turned on until the temperature difference (T2-T1) reached the
trigger level (T.sub.DIFF), and sets the time lapsed as T.sub.LAP.
Next, at step 432, the instantaneous flow rate (Qi) is calculated
as Qi=T.sub.LAP.times.C.sub.Q. The number of measurement cycle
completed is represented as N=N+1, where initially N is defined as
zero. A timer in the Flow Detection Unit checks whether the
measurement time has reached the selected T.sub.INT (step 433),
which helps to control the measurement interval. If the interval
has reached a preset value of T.sub.INT, the measurement cycle
restarts at step 423 in FIG. 9A. The measurement intervals are
optimized to the timing of the pulses emitted by thermal source
109, and different nominal flow rate (Q.sub.N) entry registered by
the MCU will result in different measurement intervals.
[0073] Referring to FIG. 10A, the Flow Detection Unit 100 is
programmed to display mean flow rate (Q.sub.M) (step 440). Next, at
step 441, the nominal volume (V.sub.N) is defined either by reading
the barcode 212 or alternatively barcode 312 at step 412 (FIG. 8)
or manually input by the user at step 442. Furthermore, manual
input allows user to set the nominal volume (V.sub.N) in case of an
invalid reading of the barcode 212 by the barcode reading means
112. The MCU 130 then sets the variables at step 443, which
comprises the number of completed measurements (N), nominal time
(T.sub.N), total volume delivered (V.sub.D), volume delivered
within one completed measurement cycle (Vi), instant flow rate
(Qi), mean flow rate (Q.sub.M) and the accumulated instant flow
rate (Q.sub.ACC). Subsequently, the MCU 130 sets the measurement
variables T.sub.IRON, T.sub.INT, T.sub.EXP, T.sub.DIFF, C.sub.Q,
and C.sub.V (constant value for calculating the volume delivered
within one completed measurement cycle), which are retrieved by
looking up T.sub.N from a reference table stored in the Flash
Memory of the Flow Detection Unit 100 (step 444). The algorithm
developed is clearly not restricted to the use of the measurement
of variables described above. The presence of more sensors and
their locations relative to the heat source or sources will allow
other permutations in the development of the algorithm for flow
rate detection. For example, the determination of flow rates could
be realized by comparing the variables or its derivatives or
combinations of such resulting from a specific fluid flow with
predetermined values established for known flow rates in a table.
Referring to FIG. 6E, a 20 m L/hour fluid flow would manifest
varying T.sub.Lap as well as temperature amplitudes, when measured
at different sensor locations in a flow cell using four thermal
sensors which, generate four temperature readings T1, T2, T3 and
T4. These recordings could form inputs for developing an algorithm.
For example, in situations where the flow rate is relatively fast,
e.g. 100 mL/Hour, or relatively slow, e.g. 1 mL/Hour, it is
possible that the temperature of the location at which one of the
sensors is disposed is too close to or too far from the thermal
source, and temperature measurements at this location may not be
able to detect a clear signal. Embodiments with more sensors
disposed at different locations along the fluid channel, provide
solutions to enable temperature measurements at multiple locations.
Shown in FIG. 6E as an example, multi-location measurement of
temperature generates temperature difference comparison curves with
respect to a reference location. This provides data to the Flow
Detection Unit to record temperature measurements with meaningful
readings for the purpose of flow rate detection and monitoring.
[0074] Referring back to FIG. 10A, at step 445, the thermal source
109 will be turned ON and OFF intermittently at the start of the
measurement cycle. The subsequent steps 446-450 shown in FIG. 10B
are similar to steps 424-427 of FIGS. 9A and 431 of FIG. 9B, and
thus will not be described.
[0075] Next, at step 451, the volume delivered (V.sub.D) is
compared against 75% of the nominal volume (V.sub.N). The mean flow
rate (Q.sub.M) is the arithmetic mean of the all instantaneous flow
rate (Qi) readings obtained as described above if the volume
delivered (V.sub.D) is less than 75% of the nominal volume
(V.sub.N) (step 452). The total volume delivered (V.sub.D) since
the start of the first measured is also calculated. By definition,
the mean flow rate (Q.sub.M) shown will change when each subsequent
reading of instantaneous flow rate (Qi) changes.
[0076] When the volume delivered (V.sub.D) exceeds 75% of the
nominal volume (V.sub.N) (step 453), the mean flow rate (Q.sub.M)
displayed will be the cumulative volume over time. The cumulative
volume is the sum of each unit of volume that is derived from the
instantaneous flow rate (Qi) and the time interval (T.sub.INT)
between each of these readings. The result of this is that the mean
flow rate (Q.sub.M) displayed will approach a value that eventually
represents the volume delivered (V.sub.D) over time. The total
volume delivered (V.sub.D) since the start of the first measured is
also calculated. One of the considerations in selecting a 75%
threshold volume is that it corresponds to definition of mean flow
rate in the International Organization for Standardization ISO
28620. By definition, averages of instantaneous flow rate (Qi)
during the initial 75% of volume delivered (V.sub.D) will show more
fluctuations in the readings. It can be appreciated that other
threshold volume levels, such as 70% or 80% may be applicable.
[0077] At step 461, the MCU 130 checks if a DC motor module is
attached to the flow rate regulating mechanism 230. If the DC motor
module is available, the MCU checks whether any flow rate
adjustment is required (step 462) based on Q.sub.M, T.sub.INT, N,
and V.sub.D and calculates the number of turns and direction of
turns for the DC motor (step 463) to, for example, adjust the axle
231 of the flow rate regulating mechanism 230.
[0078] If no DC motor module is available, the MCU 130 proceeds to
determine whether the infusion is complete. For example, at step
464, the difference between the nominal volume (V.sub.N) and volume
delivered (V.sub.D) is compared with a threshold level of, for
example, 10 ml. If the difference of V.sub.N and V.sub.D is less
than 10 ml, the buzzer is turned on and the display screen 108
indicates "Infusion Completed" (step 465). The remaining volume of
medication fluid can be considered as residue volume. On the other
hand, if the difference is more than 10 ml, the timer checks
whether the measurement has reached the selected time interval
T.sub.INT (step 466), which helps to control the measurement
interval. If the interval has reach T.sub.INT, the measurement
cycle restarts at step 445 in FIG. 10A.
[0079] It can be appreciated that the algorithm used may differ
according to specific needs as it also relates to the performance
characteristics of the fluid pump to which the device is attached
and as such does not limit the scope of the invention. Furthermore,
several embodiments of the invention have thus been described.
However, those ordinarily skilled in the art will recognize that
the invention is not limited to the embodiments described, but can
be practiced with modification and alteration within the spirit and
scope of the appended claims that follow.
* * * * *