U.S. patent application number 12/418914 was filed with the patent office on 2009-07-30 for aliquot correction for feeding set degradation.
This patent application is currently assigned to COVIDIEN AG. Invention is credited to Eric B. Holderle, Joseph A. Hudson, Christopher A. Knauper.
Application Number | 20090191066 12/418914 |
Document ID | / |
Family ID | 37497834 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090191066 |
Kind Code |
A1 |
Knauper; Christopher A. ; et
al. |
July 30, 2009 |
ALIQUOT CORRECTION FOR FEEDING SET DEGRADATION
Abstract
A peristaltic pump is able to deliver accurate volumes over the
life of a pump set that is operated on by the pump to drive the
flow of fluid. The pump delivers fluid in small volumes or
aliquots. In order to deliver fluid at any particular selected flow
rate, the pump determines how often the rotor will rotate. The pump
is able to calculate aliquot volume based on selected flow rate,
but also on a factor that compensates for changes in the dimensions
of the pump set over its life.
Inventors: |
Knauper; Christopher A.;
(O'Fallon, MO) ; Holderle; Eric B.; (St. Louis,
MO) ; Hudson; Joseph A.; (O'Fallon, MO) |
Correspondence
Address: |
TYCO HEALTHCARE - EDWARD S. JARMOLOWICZ
15 HAMPSHIRE STREET
MANSFIELD
MA
02048
US
|
Assignee: |
COVIDIEN AG
NEUHAUSEN AM RHEINFALL
CH
|
Family ID: |
37497834 |
Appl. No.: |
12/418914 |
Filed: |
April 6, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11240956 |
Sep 30, 2005 |
7534099 |
|
|
12418914 |
|
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Current U.S.
Class: |
417/44.1 |
Current CPC
Class: |
A61M 5/14232 20130101;
A61M 5/172 20130101; A61M 2205/702 20130101 |
Class at
Publication: |
417/44.1 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Claims
1. A pumping apparatus for use with a pump set to deliver fluid
through the pump set, the pumping apparatus comprising: a pumping
device capable of acting on the pump set to produce a fluid flow
within the pump set, the pumping device producing said fluid flow
in a series of aliquots; a housing capable of receiving at least a
portion of the pump set to be acted upon by the pumping device; a
controller programmed to control an electrical signal to the
pumping device, the controller including a pump set degradation
compensator for changing the electrical signal thereby altering
operation of the pumping device whereby the fluid flow rate
delivered by the pumping apparatus is more accurate over the useful
life of the pump set, the pump set degradation compensator
including a volume compensation element which is a function of the
entire time the pump set has been in use on the pumping device.
2. A pumping apparatus as in claim 1 further comprising an actuator
having at least one pump set engaging member for engaging the pump
set to force fluid to flow in the pump set.
3. A pumping apparatus as in claim 2 wherein the actuator comprises
a rotor adapted to receive a portion of the pump set into
engagement with the rotor.
4. A pumping apparatus as in claim 3, wherein there are plural
engaging members, each engaging member comprising a roller for
engaging the pump set and generating an aliquot of fluid flow.
5. A pumping apparatus as in claim 1, wherein the controller
includes a memory and a microprocessor in communication with the
memory, wherein said memory contains the pump set degradation
compensator.
6. A pumping apparatus as in claim 5, wherein the memory is
selected from a group consisting of: random access memory, flash,
EEPROM, PROM, or disk.
7. A pumping apparatus as in claim 5, wherein the pump set
degradation compensator is a software program operating in said
memory, the microprocessor being adapted to run the software
program.
8. A pumping apparatus as in claim 7, wherein the pump set
degradation compensator corrects the aliquot volume as a function
of feed rate selected and time of use of the pump set; the pump set
degradation compensator is an equation stored in the memory of the
controller; the equation is H.sub.i(x)=G.sub.i(x)+T*F.sub.i(x)
where G.sub.i(x) is the established aliquot volume as a function of
flow rate selected; T is time of pump set use; F.sub.i(x) is pump
set flow compensation of volume as a function of flow rate
selected; x is a user selected flow rate and H.sub.i(x) is the
corrected aliquot volume as a function of flow rate selected and
time of use of the pump set.
9. A pumping apparatus as in claim 8 wherein G.sub.i(x) is one of a
constant and a polynomial equation.
10. A pumping apparatus as in claim 8, wherein the established
aliquot volume G.sub.i(x) is at least one of: (i) a constant, the
constant being B and stored in a lookup table; the table being
indexed by user selected flow rate x; (ii) a linear function mx+B
of the user selected flow rate; and (iii) a nonlinear equation
Lx.sup.2+mx+B, wherein L is an empirically established constant for
a user selected flow rate x, the value of L for a plural of flow
rate x are stored in a table in the memory.
11. A pumping apparatus as in claim 10, wherein the constant B is
an empirically established constant for the user selected flow rate
x or a range thereof and stored in a table in the memory.
12. A pumping apparatus as in claim 10 further comprising an input
device operatively connected to the memory communicates user inputs
for x.
13. A pumping apparatus as in claim 10, wherein m in the linear
function is an empirically established constant for a user selected
flow rate x; the values of m for a plurality of user flow rates x
are stored in a table in the memory.
14. A pumping apparatus as in claim 8 wherein F.sub.i(x) is one of
a constant and a polynomial.
15. A pumping apparatus as in claim 14 wherein the F.sub.i(x) is a
linear function Ax+N, where A is a coefficient and N is a constant
selected from the memory based on the flow rate x selected by a
user.
16. A pumping apparatus as in claim 1 in combination with the pump
set, and wherein the pump set is disposable.
17. A pumping apparatus as in claim 1 in combination with the pump
set, wherein the pump set includes at least two tube sections.
18. A method of delivering accurate flow rates of fluid using a
pumping apparatus that acts on a pump set attached to the pumping
apparatus to produce flow of fluid in aliquots, the method
comprising: determining the amount of time the pump set has been in
use in the pumping apparatus; calculating the volume of fluid in
each aliquot delivered by the pumping apparatus including executing
instructions that are capable of correcting the aliquot volume
based on the amount of time the pump set has been in use in the
pumping apparatus, wherein said calculating the volume of the fluid
in each aliquot is calculated as a function of the time the pump
set has been in use; operating the pumping apparatus to deliver a
number of aliquots having the aliquot volume determined in the
preceding step to maintain a selected flow rate.
19. A method as in claim 18 further comprising inputting the flow
rate of fluid to be delivered into memory associated with the
pumping apparatus.
20. A method as in claim 19 wherein calculating the volume of fluid
in each aliquot is further based on the selected flow rate inputted
into the pumping apparatus memory.
21. A method as in claim 20 wherein calculating the volume of fluid
in each aliquot comprises establishing a range in which the
selected flow rate lies.
22. A method as in claim 21 wherein calculating the volume of fluid
in each aliquot further comprises using an equation corresponding
to the selected flow rate range to calculate a volume correction
factor based on the selected flow rate and multiplying the
correction factor by the amount of time the pump set has been in
use.
23. A method as in claim 22 wherein the step of calculating the
volume of the fluid in each aliquot is determined according to the
following equation: H.sub.i(x)=G.sub.i(x)+T*F.sub.i(x) where
G.sub.i(x) is the established volume as a function of flow rate
selected; T is the amount of time of pump set use; F.sub.i(x) is
pump set flow compensation of volume as a function of flow rate
selected; x is flow rate and H.sub.i(x) is the corrected aliquot
volume as a function of flow rate selected and time.
24. A method as in claim 23 wherein G.sub.i(x) is one of a constant
and a polynomial.
25. A method as in claim 24 wherein G.sub.i(x) is at least one of:
(i) a linear function of selected flow rate G.sub.i(x)=mx+B, where
m is a coefficient and B is a constant; (ii) a constant B; and
(iii) a nonlinear function of selected flow rate
G.sub.i(x)=Lx.sup.2+mx+B, where L and m are coefficients
corresponding to particular selected flow rate and stored in memory
and B is a constant corresponding to a particular flow rate and
stored in memory.
26. A method as in claim 23 wherein F.sub.i(x) is one of a constant
and a polynomial.
27. A method as in claim 26 wherein F.sub.i(x) is a linear function
F.sub.i(x)=Ax+N, where A is a coefficient and N is a constant
selected from the memory based on the flow rate x selected by a
user.
28. A method as in claim 18 wherein one or more computer-readable
media have computer executable instructions for performing the
method of claim 18.
Description
CROSS-REFERENCE OF RELATED APPLICATIONS
[0001] This is a continuation of co-pending U.S. patent application
Ser. No. 11/240,956 filed Sep. 30, 2005, the entirety of which is
hereby incorporated by reference.
BACKGROUND
[0002] This invention relates generally to peristaltic pumps used
to deliver fluids to patients by way of a pump set, and more
particularly to a peristaltic pump that compensates for physical
alteration of the pump set over time to maintain accuracy.
[0003] Administering fluids containing medicine or nutrition to a
patient is well known in the art. Typically, fluid is delivered to
the patient by a pump set loaded on a flow control apparatus, such
as a peristaltic pump, which delivers fluid to the patient at a
controlled rate of delivery. A peristaltic pump usually comprises a
housing that includes a rotor or the like operatively engaged to at
least one motor through a gearbox. The rotor drives fluid through
the tubing of the pump set by the peristaltic action effected by
rotation of the rotor by the motor. The motor is operatively
connected to a rotatable shaft that drives the rotor, which in turn
progressively compresses the tubing and drives the fluid at a
controlled rate through the pump set. The pump set may have a type
of valve mechanism for permitting or preventing fluid flow
communication through the pump set. A controller operates the motor
or motors used to drive the rotor and, if necessary, control fluid
flow as by operation of the valve mechanism.
[0004] Peristaltic pumps operate by delivering fluid in small
charges called "aliquots". The rotor engages tubing of the pump
set, pinching off a portion of the tubing and pushing fluid forward
of the pinch point (i.e., closer to the patient than to the source
of fluid) toward the patient. Typically, the volume of fluid to be
administered to the patient is controlled in the pump by counting
the number of aliquots, each being of substantially the same
volume, and stopping when the number reaches an amount
corresponding to the total desired volume of fluid to be delivered.
Peristaltic pumps are sanitary and generally highly accurate and
therefore very useful in the administration of medication and
therapeutic fluids to the patient. However, the accuracy of the
pump is dependent upon the dimensional stability of the tubing of
the pump set. Over time the pump set can be plastically deformed so
that the volume of each aliquot can change. As a result, the
accuracy of the volumes delivered to the patient degrades over the
course of the life of the pump set. By way of example, an
administration feeding set used for enteral feeding may be used for
up to 24 hours.
SUMMARY OF INVENTION
[0005] In one aspect of the present invention, a pumping apparatus
for use with a pump set to deliver fluid through the pump set
generally comprises a pumping device capable of acting on the pump
set to produce a fluid flow within the pump set. The pumping device
produces the fluid flow in a series of aliquots. A housing is
capable of receiving at least a portion of the pump set to be acted
upon by the pumping device. A controller programmed to control an
electrical signal to the pumping device includes a pump set
degradation compensator for changing the electrical signal thereby
altering operation of the pumping device. The pump set degradation
compensator includes a volume compensation element which is a
function of the entire time the pump set has been in use on the
pumping device.
[0006] In another aspect of the present invention, a method of
delivering accurate desired flow rates of fluid using a pumping
apparatus that acts on a pump set attached to the pumping apparatus
to produce flow of fluid in aliquots generally comprises
determining the amount of time the pump set has been in use in the
pumping apparatus. The volume of fluid in each aliquot delivered by
the pumping apparatus is calculated as a function of the time the
pump set has been in use. Instructions are executed that are
capable of correcting the aliquot volume based on the amount of
time the pump set has been in use in the pumping apparatus. The
pumping apparatus is operated to deliver a number of aliquots
having the aliquot volume determined in the preceding step to
maintain a selected flow rate.
[0007] Other objects and features of the present invention will be
in part apparent and in part pointed out hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a perspective of an enteral feeding pump;
[0009] FIG. 2 is a side elevation thereof showing a fragmentary
portion of an administration feeding set received in the pump;
[0010] FIG. 3 is the side elevation of FIG. 2 with the
administration feeding set removed;
[0011] FIG. 4 is an exploded perspective of the pump;
[0012] FIG. 5 is a perspective of the administration feeding
set;
[0013] FIG. 6 is a block diagraph of the components of the enteral
feeding pump; and
[0014] FIG. 7 is a flow chart of an aliquot correction routine.
[0015] Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0016] Referring now to the drawings, an enteral feeding pump
(broadly, "flow control apparatus") constructed according to the
principles of the present invention is generally indicated at 1.
The feeding pump comprises a housing generally indicated at 3 that
is constructed so as to mount an administration feeding set
(broadly, a "pump set") generally indicated at 5 (see FIGS. 2 and
5). The housing 3 includes a door 7 hinged to the remainder of the
housing for swinging between a closed position (FIG. 1) and an open
position (FIG. 2) which exposes a portion of the pump 1 that
receives the administration feeding set 5. It will be appreciated
that "housing" as used herein may include many forms of supporting
structures (not shown), including without limitation multi-part
structures and structures that do not enclose or house the working
components of the pump 1. The pump 1 also has a display screen
generally indicated at 9 on the front of the housing 3 that is
capable of displaying information about the status and operation of
the pump. Buttons 11 on the side of the display screen 9 are
provided for use in controlling and obtaining information from the
pump 1 and three light emitting diodes 13 also provide status
information for the pump. Legs 15 at the bottom front of the
housing 3 support the housing so that the display screen 9 is
angled slightly upward for ease of viewing.
[0017] It will be understood that although the illustrated pump 1
is an enteral feeding pump, the present invention has application
to other types of peristaltic pumps (not shown), including medical
infusion pumps. The general construction and operation of the
enteral feeding pump 1, except as set forth hereinafter, may be
generally the same as disclosed in co-assigned U.S. patent
application Ser. Nos. 10/853,958 filed May 24, 2004 and entitled
ADMINISTRATION FEEDING SET AND VALVE MECHANISM, 10/854,136 filed
May 24, 2004 and entitled FLOW CONTROL APPARATUS, and 10/853,926
filed May 25, 2004 entitled FLOW MONITORING SYSTEM FOR A FLOW
CONTROL APPARATUS, the disclosures of which are incorporated by
reference. Moreover, although an administration feeding set 5 is
shown, other types of pump sets (not shown) can be used within the
scope of the present invention.
[0018] Referring now also to FIG. 4, the display screen 9 is part
of a front panel (generally indicated at 19) of the housing 3
removably attached to a main compartment (generally indicated at
21) of the housing that holds most of the operating components of
the pump 1. The enteral feeding pump further includes a pumping
unit (shown exploded from the main compartment and indicated
generally at 23) comprising a pump motor 25 connected to a rotor
shaft 27 and also to a valve shaft 29 (see, FIG. 3). It will be
understood that the valve shaft 29 could be omitted, and/or that a
separate motor (not shown) could be provided to operate the valve
shaft within the scope of the present invention. A battery 31 may
be received in the main compartment 21 of the housing 3 for
powering the pump motor 25. A battery door 33 hingedly attached to
the rear of the main compartment 21 closes the battery 31 within
the compartment while providing access as needed. A bolt 35 holds
the battery door 33 closed so that access to the battery 31 is
normally blocked. Of course, a power source other than or in
addition to a battery could be used.
[0019] A rotor (generally indicated at 37) is mounted on the rotor
shaft 27 of the pumping unit 23 by a bolt 42. The rotor 37 includes
an inner disk 39, an outer disk 41 and three rollers 43 (only one
is shown) mounted between the inner and outer disks for rotation
about their longitudinal axes relative to the disks. In the
illustrated embodiment, the pump motor 25, rotor shaft 27 and rotor
37 may broadly be considered "a pumping device". It will be
understood that peristaltic pumps that use mechanisms other than
rollers may fall within the scope of the present invention. For
example, a linear peristaltic pump could be used within the scope
of the present invention. The roller 43 engages the administration
feeding set 5, which is also received in first and second chutes
(designated 45 and 47, respectively) formed on a faceplate 49 of
the pumping unit 23 on which the pump motor 25 is also mounted. The
first and second chutes 45, 47 receive portions of the
administration feeding set 5, as will be described in more detail
hereinafter. The door 7 covers the chutes 45, 47 and rotor 37 when
it is closed as it is in FIG. 1. Other bolts 51 hold various
components of the pump 1 together.
[0020] Referring now to FIG. 5, the administration feeding set 5
comprises tubing indicated generally at 55 that provides a fluid
pathway between at least one source of fluid and a patient. Tubing
55 can be made of a medical grade, deformable silicone and
comprises first tube section 57 connected between a valve mechanism
59 and mounting member 61. A second tube section 63 is connected to
the mounting member 61 and at an outlet of the tubing 55 to a
connector, such as a barbed connector 65, suitable for connection
to a gastrostomy device (not shown) attached to a patient. Third
tube section 67 is connected at an inlet of the tubing 55 to a bag
69 of feeding fluid and to valve mechanism 59, and fourth tube
section 71 is connected at an inlet of the tubing 55 to a bag 73 of
flushing fluid and to the valve mechanism. The valve mechanism 59
is operable to selectively permit flow of feeding fluid from bag 69
or flushing fluid from bag 73, or prevent any fluid flow
communication from the feeding or flushing fluid bags 69, 73 into
the first tube section 57. The valve mechanism 59 can be turned to
three positions. The first closes off all fluid flow from the third
and fourth tube sections 67, 71 to the first and second tube
sections 57, 63, the second allows feeding fluid to flow from the
bag 69 to the first and second tube sections, and a third allows
flushing fluid to flow from bag 73 to the first and second tube
sections. As previously stated, pump sets of different
constructions may be used, for example a recertification set may be
used to verify and/or correct the pump accuracy. The pump 1 can be
configured to automatically recognize what kind of set is installed
and to alter its operation to conform to that called for by the
particular administration set. Still further, the pump 1 can be
configured to recognize whether the first tube section 57 is
properly installed on the pump. Examples of suitable pump sets
(including valve mechanisms) are shown in co-assigned U.S. Ser. No.
10/853,958 previously incorporated by reference.
[0021] In use, the administration feeding set feeding fluid bag 69
and flushing fluid bag 73 can be hung from a suitable support, such
as an IV pole (not shown). The door 7 on the side of the pump 1 is
swung open and the valve mechanism 59 can be placed in the first
chute 45 so that the valve shaft 29 of the pump is engaged with the
valve mechanism. Thus, rotation of the valve shaft 29 controls in
which of the three positions the valve mechanism 59 is placed. The
first tube section 57 is placed around the lower part of the rotor
37 and the mounting member 61 is placed in the second chute 47. The
second chute is generally funnel-shaped so that the mounting member
61 can be placed into the chute 47 at a location in which the first
tube section 57 is substantially stretched around the rotor 37. The
first tube section 57 can relax slightly, pulling the mounting
member 61 further down in the second chute 47. However, the first
tube section 57 is maintained in a stretched condition around the
rotor when properly installed on the pump 1. The door 7 can be
re-closed to cover the first and second chutes 45, 47 and the rotor
37. The connector 65 at the end of the second tube section 63 can
be connected to a conduit (not shown) attached to the patient in a
known manner. It will be understood that any suitable connection to
the patient for delivering the fluid may be used without departing
from the scope of the present invention.
[0022] The pump 1 can be programmed or otherwise controlled for
operation in a desired manner. For instance, the pump 1 can begin
operation to providing feeding fluids from bag 69 to the patient.
The care giver may select (for example) the amount of fluid to be
delivered, the rate at which the fluid is to be delivered and the
frequency of fluid delivery. The pump 1 has a controller 77 (see,
FIG. 6) including a microprocessor 79 that allows it to accept
programming and/or to include pre-programmed operational routines
that can be initiated by the care giver. The controller 77 is in
communication with an administration set positioning sensor 81 that
detects whether the administration feeding set 5 has been
positioned properly, as previously described. Other sensors (not
shown), such as a sensor that determines the type of administration
set that has been placed in the pump 1 and a flow monitoring sensor
can be in communication with the controller 77 to facilitate
accurate operation of the pump. The controller 77 is also connected
to the pump motor 25 for controlling its operation to actuate the
valve mechanism 59 and the rotor 37. The pump motor 25 can operate
the valve mechanism 59 and rotor 37 independently of each
other.
[0023] If the pump 1 is to deliver feeding fluid from the bag 69 to
the patient, the valve shaft 29 is rotated so that the valve
mechanism 59 is moved to the second position in which fluid
communication from the feeding fluid bag 69 to the first tube
section 57 is open. The amount of feeding fluid that is delivered
to the patient is controlled by the number of rotations of the
rotor 37 (in a counterclockwise direction as viewed in FIG. 2). In
the illustrated embodiment, the rotor 37 includes the three rollers
43 so that each one-third of a rotation delivers one aliquot of
fluid to the patient. As each roller 43 first engages the first
tube section 57, it pinches off the first tube section thereby
closing off an amount of fluid forward (i.e., toward the patient)
from the fluid coming from the feeding fluid bag 69. The roller 43
continues to the right, pushing fluid forward of the roller toward
the patient. Finally, the roller 43 releases engagement with the
first tube section 57 at about the same time the trailing roller
engages the first tube section for pinching it off for delivering
the next aliquot of fluid. Thus, when the microprocessor 79
receives a command to deliver a fluid flow rate, it calculates the
number of rotations within a given period of time that will deliver
a number of aliquots producing the desired flow rate. More
specifically in the illustrated embodiment, the controller 77
determines the amount of time between rotations of the rotor 37.
The amount of time between rotations is dependent upon the volume
of the aliquots delivered in a single rotation. It is to be
understood that other ways of changing rotor operation could be
used to maintain a constant flow rate. It has been determined that
if the microprocessor assumes that the volume of each aliquot is
the same or varies only as a function of flow rate, this will lead
to errors in the actual flow rate of fluid delivered.
[0024] Accordingly, the controller 77 of the present invention
includes a timer 83 and a memory area 84 including an aliquot
volume degradation compensator 85. In the illustrated embodiment,
the degradation compensator 85 includes degradation compensation
instructions 86 and degradation compensation functions 87. The
timer 83 is initiated in a suitable manner when the administration
feeding set 5 is first installed in the pump 1. The initiation is
preferably automatic. For example, the timer 83 may initiate when
the mounting member 61 is detected as being in the proper position
for a certain period of time. Upon initiation, the timer 83 begins
to count the amount of time the administration feeding set 5 has
been in use. The degradation compensator 85 uses this information
and the selected flow rate to compensate or correct the volume
associated with each aliquot over the life of the administration
feeding set 5. Thus, the microprocessor 79 can use a different
aliquot volume amount over the life of the administration feeding
set 5 to keep the flow rates delivered by the pump 1 substantially
accurate.
[0025] The degradation compensator 85 operates to correct for
time-dependent variation in the volume associated with each aliquot
of fluid delivered by the pump 1 to the patient. However, the
time-dependent variation is also dependent upon selected flow rate.
More specifically, the controller 77 employs the following function
to determine the volume in each aliquot:
H.sub.i(x)=G.sub.i(x)+T*F.sub.i(x)
G.sub.i(x) is the established volume as a function of flow rate
selected. T is the time of feeding set use and F.sub.i(x) is the
administration set flow compensation of volume as a function of
flow rate selected. The variable x is flow rate and H.sub.i(x) is
the corrected aliquot volume as a function of flow rate selected
and time. The equation has been established through testing and
curve-fitting the data from the tests. It will be appreciated that
flow rate shows up in the function F.sub.i(x) which is used to
calculate time-dependent variations. G.sub.i(x) is independent of
how long a particular administration feeding set has been in use,
and can be a different equation depending upon the flow rate
selected and is used from the very beginning of operation of the
pump 1 to calculate aliquot volume. It is also possible that
G.sub.i(x) can always be the same equation (regardless of flow
rate) or a constant. For example, if the flow rate selected is low
(e.g., a few milliliters per hour), then G.sub.i(x) may be
constant, i.e., G.sub.i(x)=B. At higher flow rates, the equation
takes on a polynomial form that may vary depending upon the flow
rate selected. The equation may be linear, e.g., mx+B, or
non-linear, e.g., Lx.sup.2+mx+B, where L and m are empirically
determined coefficients and B is an empirically determined
constant. The coefficients and equations are stored in the
controller 77 so that when the flow rate is known, the
microprocessor 79 can look up the associated equation and
coefficients in, for example, a look up table in the controller
memory. The flow rate is plugged into the selected equation
G.sub.i(x) to find the aliquot volume compensation. Preferably,
each equation G.sub.i(x) is operable over a range of flow
rates.
[0026] The degradation compensator 85 provides computer-executable
instructions 86 for use in calculating T*F.sub.i(x), and operates
in a similar way as the microprocessor in calculating G.sub.i(x).
The degradation compensator 85 looks at the selected flow rate and
selects a previously stored function from a look up table or other
source represented by the degradation compensation functions 87 in
FIG. 6. However unlike the calculation of G.sub.i(x), the selected
equation is multiplied by the time T the administration feeding set
5 has been in operation. In one embodiment, the time T increments
once per hour, but any frequency of updating the time T may be used
without departing from the scope of the present invention. It will
be appreciated that even at high flow rates within a time in which
T=0 (i.e., for a newly installed administration feeding set 5), the
compensation of aliquot volume based on degradation of the
dimensions of the administration feeding set over time is zero.
Thus, initially the degradation compensator 85 has no affect on the
calculation of aliquot volume because the pump set 5 is relatively
dimensionally stable.
[0027] Referring now to FIG. 7, the degradation compensation
instructions 86 of the degradation compensator 85 used to account
for time based variations in aliquot volume are shown. In other
words, the flow chart shows how T*F.sub.i(x) is calculated. The
degradation compensation instructions 86 are machine readable
instructions on any suitable medium, broadly identified as the
memory area 84. These instructions can be carried out by the
microprocessor 79. After a particular flow rate x is selected at
block 89, the degradation compensation instructions 86 first look
at decision block 91 to see if the flow rate x is greater than some
minimum threshold flow rate x.sub.0 (e.g., 40 ml/hr). If the
selected flow rate x is less than threshold x.sub.0, F.sub.i(x) is
set to zero at process block 93 and the aliquot volume calculation
performed by the microprocessor becomes:
H.sub.i(x)=G.sub.i(x)
[0028] Therefore, no matter how long the administration feeding set
5 has been in operation, if the flow rate x is low enough, only the
standard flow rate based function G.sub.i(x) is used. If the
selected flow rate is greater than the threshold (x.sub.0) in
decision block 91, the program moves on to decision block 93 where
it inquires whether the flow rate x is above a next higher
threshold (x.sub.1). If the flow rate x is less than x.sub.1, then
the degradation compensator 85 looks up the equation and
coefficients and constants in the degradation compensation
functions 87 that are associated with that particular flow rate
threshold x.sub.1. For example, the equation can be:
F.sub.i(x)=Ax+N, where A is a coefficient, N is a constant and x is
the selected flow rate. The solution to this equation is multiplied
by the time T to arrive at the time-dependent aliquot volume
correction in process block 97. Other equations could be used for
F.sub.i(x) depending upon their ability to model experimentally
determined aliquot volume alteration over time and as a function of
flow rate. For the embodiment described herein, the coefficients of
the equations and the constants have been empirically determined
(i.e., by curve-fitting test data) and are different for different
selected ranges of flow rates.
[0029] If at decision block 95 the flow rate x is greater than the
threshold x.sub.1, then the instructions 86 proceed to the final
decision block 99 which inquires whether the selected flow rate x
is greater than the maximum threshold x.sub.n1. It will be
appreciated that other decision blocks (not shown) prior to the
maximum threshold decision block 99, and associated process blocks
(not shown) providing different time-dependent aliquot volume
corrections based on selected flow rate may be used without
departing from the scope of the present invention. Similar to the
prior steps, if the selected flow rate x is not above the (maximum)
threshold x.sub.n-1, the program at process block 101 applies a
particular function F.sub.n-1(x) associated with that range of flow
rates (i.e., above x.sub.n-2 and below xn-1) from the degradation
compensation functions 87, in a similar fashion as the prior
process block 97. On the other hand, if the flow rate x exceeds the
maximum threshold x.sub.n1, the degradation compensation
instructions 86 move to process block 103 where a final
compensation function Fn (x) is selected from the degradation
compensation functions 87 for use in calculating the time based
aliquot volume compensation. The flow rate x.sub.n1 above which
this function F.sub.n(x) is employed may be at or near the maximum
flow rate at which the pump 1 is capable of operating. As in all
cases, the result of the equation F.sub.n(x) is multiplied by time
T and added by the microprocessor 79 to the result of G.sub.n(x) to
produce the aliquot volume H.sub.n (x). This aliquot volume amount
can be used to signal the pump motor 25 to control the period of
time between rotations of the rotor 37 to accurately deliver the
desired flow rate of fluid.
[0030] Thus it may be seen that the various objects and features of
the present invention are achieved by the embodiment of the pump 1
disclosed herein. The pump controller 77 has the degradation
compensator 85 that allows the microprocessor 79 to compensate for
changes in aliquot volume of the pump 1 based on flow rate, and
also using a compensation factor for the amount of time the
administration feeding set 5 has been in use. The time compensation
factor is able to allow for the degradation (or simply changes) in
the dimensions of the administration feeding set 5 over time.
Therefore, the patient can receive accurate flow rates of fluid
over the entire life of the administration feeding set (e.g., 24
hours).
[0031] Embodiments of the invention may be described in the general
context of computer-executable instructions, such as program
modules, executed by one or more computers or other devices. The
computer-executable instructions may be organized into one or more
computer-executable components or modules including, but not
limited to, routines, programs, objects, components, and data
structures that perform particular tasks or implement particular
abstract data types. Aspects of the invention may be implemented
with any number and organization of such components or modules. For
example, aspects of the invention are not limited to the specific
computer-executable instructions or the specific components or
modules illustrated in the figures and described herein. Other
embodiments of the invention may include different
computer-executable instructions or components having more or less
functionality than illustrated and described herein.
[0032] Further, the order of execution or performance of the
operations in embodiments of the invention illustrated and
described herein is not essential, unless otherwise specified. That
is, the operations may be performed in any order, unless otherwise
specified, and embodiments of the invention may include additional
or fewer operations than those disclosed herein. For example, it is
contemplated that executing or performing a particular operation
before, contemporaneously with, or after another operation is
within the scope of aspects of the invention.
[0033] In operation, microprocessor 79 of the controller 77
executes computer-executable instructions such as those illustrated
in the figures to implement aspects of the invention. Aspects of
the invention may also be practiced in distributed computing
environments where tasks are performed by remote processing devices
that are linked through a communications network. In a distributed
computing environment, program modules may be located in both local
and remote computer storage media including memory storage
devices.
[0034] When introducing elements of the present invention or the
preferred embodiment(s) thereof, the articles "a", "an", "the" and
"said" are intended to mean that there are one or more of the
elements. The terms "comprising", "including" and "having" are
intended to be inclusive and mean that there may be additional
elements other than the listed elements. Moreover, the use of "up",
"down", "top" and "bottom" and variations of these terms is made
for convenience, but does not require any particular orientation of
the components.
[0035] As various changes could be made in the above without
departing from the scope of the invention, it is intended that all
matter contained in the above description and shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
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