U.S. patent application number 09/899301 was filed with the patent office on 2002-02-14 for controlled force fluid delivery system.
This patent application is currently assigned to Fluidsense Corporation. Invention is credited to Carlisle, Jeffrey A., Patel, Keena B..
Application Number | 20020018720 09/899301 |
Document ID | / |
Family ID | 22808521 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018720 |
Kind Code |
A1 |
Carlisle, Jeffrey A. ; et
al. |
February 14, 2002 |
Controlled force fluid delivery system
Abstract
A controlled force fluid delivery system which provides fluid
delivery with continuity over a wide range of flow rate. The system
sets the force provided by an energy storage device, e.g. a spring
and the opening of system outlet valve in response to a low volume
due command. Specifically at a low flow rate, the controlled force
is decreased and/or the outlet valve of the system closes before
the fluid flow reaches stable velocity whereas at a high flow rate
the controlled force is increased and/or the outlet valve does not
close until the fluid stops flowing. The system also reduces fluid
flow rate variation in part by adjusting the timing and the level
of opening and closing the outlet valve, and the speed of pumping
the fluid out of system central cassette chamber.
Inventors: |
Carlisle, Jeffrey A.;
(Salsbury, MA) ; Patel, Keena B.; (N. Andover,
MA) |
Correspondence
Address: |
Pillsbury Winthrop LLP
Intellectual Property Group
1800 Tysons Boulevard
McLean
VA
22102
US
|
Assignee: |
Fluidsense Corporation
|
Family ID: |
22808521 |
Appl. No.: |
09/899301 |
Filed: |
September 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60216789 |
Jul 7, 2000 |
|
|
|
Current U.S.
Class: |
417/26 |
Current CPC
Class: |
A61M 5/16881 20130101;
A61M 5/14224 20130101; A61M 2205/12 20130101; A61M 2205/128
20130101; A61M 5/16877 20130101 |
Class at
Publication: |
417/26 |
International
Class: |
F04B 049/00 |
Claims
What is claimed is:
1. A fluid delivery system comprising: a central chamber with an
inlet valve and an outlet valve; a piston assembly moving in and
out of the central chamber; a force source connected to the piston
assembly, wherein the force source generates a force to move the
assembly in and out of the central chamber thereby moving fluid out
of and into the central chamber; a position sensor connected to the
piston assembly, wherein the position sensor determines a position
change of the piston assembly; and a processor connected to the
position sensor, and the force source, wherein the processor
receives the position change of the piston assembly, modifies the
amount and duration of force generated by the force source, and
controls the opening of the outlet valve.
2. The system of claim 1, wherein the force source comprises a
motor which generates a negative pressure in the central chamber
and pumps fluid into the central chamber via the piston assembly,
and an energy storage device which receives energy from the motor
and employs the stored energy to generate a positive pressure in
the central chamber and pump fluid out of the central chamber via
the piston assembly, wherein the processor controls the amount of
energy stored in the energy storage device.
3. The system of claim 2, wherein the energy storage device is a
spring.
4. The system of claim 2, wherein the motor simultaneously
generates the negative pressure and stores energy in the energy
storage device.
5. The system of claim 4, wherein the processor determines a flow
rate and directs the motor to generate a negative pressure based on
the flow rate.
6. The system of claim 2, wherein the energy storage device
generates a positive pressure when it is disconnected from the
motor.
7. The system of claim 2, wherein the motor opens the outlet
valve.
8. The system of claim 2, wherein the motor opens the outlet valve
in a pulsed mode.
9. The system of claim 2, wherein the processor directs the motor
to open the outlet valve in a pulsed mode in response to a low
volume due command.
10. The system of claim 9, wherein the low volume due command is
less than 40 .mu.l.
11. The system of claim 1, wherein the processor causes the outlet
valve to open in a pulse mode in response to a low volume due
command.
12. The system of claim 11, wherein the low volume due command is
less than 40 .mu.l.
13. The system of claim 1, wherein the processor causes the outlet
valve to close before the fluid finishes acceleration to a stable
velocity.
14. The system of claim 13, wherein the processor causes the outlet
valve to close before the fluid finishes acceleration to a stable
velocity in response to a low volume due command.
15. The system of claim 1, wherein the processor causes the outlet
valve to close after the fluid stops flowing.
16. The system of claim 1, wherein the processor causes the outlet
valve to open when the assembly is moved into the central
chamber.
17. The system of claim 1, wherein the processor causes the outlet
valve to open in a nudge mode in response to a low volume due
command.
18. The system of claim 2, wherein the processor directs the motor
to open the outlet valve in a nudge mode in response to a low
volume due command.
19. The system of claim 1, wherein the processor causes the outlet
valve to open in a period of time in response to a low volume due
command.
20. The system of claim 19, wherein the processor causes the outlet
valve to open in a period of time in response to a predetermined
speed of the piston assembly.
21. The system of claim 1, wherein the processor causes the outlet
valve to close in response to a position change of the piston
assembly.
22. The system of claim 21, wherein the processor causes the outlet
valve to close in response to a predetermined position change of
the piston assembly.
23. The system of claim 1, wherein the processor causes the outlet
valve to close in a period of time.
24. The system of claim 23, wherein the processor causes the outlet
valve to close in a period of time in response to a detected speed
of the piston assembly.
25. The system of claim 2, wherein the processor directs the motor
to close the outlet valve in a period of time in response to a
predetermined position change of the piston assembly.
26. The system of claim 2, wherein the processor directs the motor
to close the outlet valve in a period of time in response to a
detected speed of the piston assembly.
27. The system of claim 1, wherein the outlet valve is opened by an
amount in response to a low volume due command.
28. The system of claim 1, wherein the outlet valve is opened by an
amount determined by a detected speed of the piston assembly.
Description
[0001] This application is based on and claims priority from
Provisional Patent Application No. 60/216,789, filed Jul 7,
2000.
FIELD OF THE INVENTION
[0002] The present invention relates to a fluid delivery system,
especially a unique controlled force fluid delivery system capable
of displacing fluid at a wide range of flow rates.
BACKGROUND OF THE INVENTION
[0003] Infusion pumps are generally well known in the medical field
for administering medications to patients over an extended time
period. Typical medications may include antibiotics, anesthetics,
analgesics, cardiovascular drugs, chemotherapy agents,
electrolytes, narcotics, whole blood and blood products, etc.
Infusion pumps are typically designed for a particular clinical
application: e.g., many pumps are designed principally for use on
the hospital general floor; other pumps are designed for pediatric
use; other pumps are designed for critical care use; still other
pumps are designed for home healthcare use, etc. Also, infusion
pumps are typically designed for either large volume fluid delivery
(say from one liter bags or bottles of diluted medication) or for
small volume fluid delivery (typically from syringes filled with up
to 60 mL of undiluted medication), but not for both. Such a wide
variety of specialized pumps require hospitals and healthcare
facilities to maintain a large diverse inventory of pumps, to
ensure staff training is current on all pumps, and to provide a
wide variety of service training. This diversity of specialized
pumps leads to increased cost, increased capital investment, and
increased medication administration errors.
[0004] Therefore, there exists a need for a mechanism to control
fluid delivery in a manner such that a single infusion pump can
fully satisfy the drug infusion needs of multiple hospital and
healthcare applications (including home healthcare), can deliver
small volume as well as large volume doses over a wide range of
required flow rates, and can provide small size and weight,
power-efficient, cost-efficient implementation. The infusion pump
described in this invention in conjunction with a cassette, such as
the one disclosed in U.S. patent application Ser. No. 60/216,658
entitled "Cassette," filed Jul. 7, 2000, to Carlisle, Costa,
Holmes, Kirkman, Thompson and Semler, the contents of which are
incorporated herein by reference, allows a drug infusion system to
achieve these objectives.
SUMMARY OF THE INVENTION
[0005] The invention is based on the discovery that a system using
a controlled force for fluid delivery can employ inertial effects
of the fluid system and provide continuing fluid displacement over
a wide range of flow rates. The present invention provides a
controlled force fluid delivery system, especially a system with a
modifiable force provided by an energy storage device and modified
by feedback of fluid displacement. In particular, the system sets
the amount of controlled force and the opening of system outlet
valve in response to a flow rate command. At a low flow rate, the
controlled force is decreased and/or the outlet valve of the system
closes before the fluid flow reaches stable velocity whereas at a
high flow rate the controlled force is increased and/or the outlet
valve does not close until the fluid stops flowing. The system also
reduces fluid flow rate variation in part by adjusting the timing
and the level of opening and closing the outlet valve, and the
speed of pumping the fluid out of system central cassette
chamber.
[0006] The invention and its other advantages will be apparent from
the following detailed description, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] These and other objects and advantages of the invention will
become more apparent and more readily appreciated from the
following exemplary embodiment of the invention taken in
combination with the accompanying drawings, of which:
[0008] FIG. 1 is a diagram illustrating the fluid delivery
system.
[0009] FIG. 2 is a diagram illustrating a cross-sectional view of
the cassette assembly of an infusion pump.
[0010] FIGS. 3(a)-3(c) are block diagrams illustrating three
opening states of an outlet valve.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT
[0011] One of the applications of the controlled force fluid
delivery system is an infusion pump. FIG. 1 shows a block diagram
of one embodiment of the present invention. The fluid delivery
system 100 includes a cassette assembly 102 and a shuttle mechanism
104. A suitable cassette assembly is described in patent
application Ser. No. 60/216,658, filed Jul. 7, 2000, entitled
"Cassette" to Carlisle, Costa, Holmes, Kirkman, Thompson and
Semler, the entire contents of which are incorporated herein by
reference. Within the cassette assembly 102 is a cassette piston
106 and a cassette central chamber 108. An energy storage device,
such as a spring 110, biases the shuttle mechanism 104, which is
connected to the cassette piston 106. Piston 106 slides freely to
draw fluid into the cassette central chamber 108 and pump fluid out
of central chamber 108. A motor 112 is activated in one direction
to draw the cassette piston 106 out of cassette central chamber 108
via cam 114 and shuttle 104. When the cassette piston 106 is
withdrawn to the desired extent, shuttle 104 disengages from cam
114 and motor 112, so that spring 110 pushes the cassette piston
106 into the cassette central chamber 108 via shuttle 104 to apply
positive pressure to the fluid in the cassette central chamber 108.
The shuttle mechanism 104 is also operably linked to an optical
position sensor 116. A suitable position sensor is described in
patent application Ser. No. 60/217,885, filed Jul. 7, 2000,
entitled "Optical Position Sensor and Position Determination
Method", to Carlisle, Kaplan and Kirkman, the entire contents of
which are incorporated herein by reference. A processor 118 is
connected to motor 112 and the position sensor 116.
[0012] FIG. 2 shows a block diagram illustrating a cross-sectional
view of a cassette assembly 102. The cassette assembly 102 contains
an inlet valve 200, an outlet valve 210, a cassette central chamber
108, and a cassette piston 106. Cassette piston 106 is connected to
shuttle 104. The outlet valve 210 is operated by an actuator 212.
Actuator 212 is driven by cam 114 connected to motor 112.
[0013] In operation, the motor 112 is activated in one direction to
withdraw the cassette piston 106 against the force of spring 110
via cam 114, creating a relative vacuum in the cassette central
chamber 108 and pulling fluid through a one-way passive inlet valve
200 into the cassette central chamber 108. During this fill stroke,
the pressure in the cassette central chamber 108 is negative, e.g.,
between 0 and -10 psi. The amount of negative pressure depends on
the withdrawal speed of the piston, fluid resistance, fluid
viscosity, etc. The cassette piston can be withdrawn to different
positions or fill levels depending on the intended displacement
volume of the fluid. In one embodiment, the minimum fluid volume
pumped into the cassette central chamber 108 during each fill
stroke is about 50 .mu.l and the maximum fluid volume is about 500
.mu.l. In another embodiment, a turbo mode is used to increase the
maximum fluid volume by further withdrawing the cassette piston 106
to let the fluid fill up the entire cassette central chamber
108.
[0014] Once the cassette piston 106 has been withdrawn, cam 114
disengages from the shuttle 104, enabling the spring mechanism 110
to urge shuttle 104 to drive piston 106 into the cassette central
chamber 108. The pressure in the chamber then moves from a negative
value through zero to a positive value. The one-way passive inlet
valve 200 is now fully closed. The positive pressure in the
cassette central chamber 108 is typically between +2 and +7 psi
depending on the spring force applied to the cassette piston 106
through the shuttle 104 which is directly related to the length of
the withdrawal stroke, e.g., the further the withdrawal stroke the
stronger the spring force.
[0015] Upon finishing withdrawal of the cassette piston 106, cam
114 disengages from the shuttle 104 and engages actuator 212 so
that the motor 112 operates the outlet valve 210 through actuator
212. The outlet valve 210 opens incrementally, partially or fully
as shown in FIGS. 3(a)-3(c) depending on the amount of activation
force received from motor 112 through actuator 212. When the outlet
valve 210 opens incrementally as shown in FIG. 3(a), the outlet
valve 210 opens in a pulse mode, e.g., it opens on and off, and
closes before the fluid finishes its acceleration. The outlet valve
210 is in a nudge mode when it opens partially as shown in FIG.
3(b) or fully as shown in FIG. 3(c). When the outlet valve 210 is
in a nudge mode, it opens continuously and does not close before
the fluid reaches stable velocity. The fluid flow through a
partially opened outlet valve 210 can be precisely metered out and
is controlled by the distance between the tapered surface and the
valve seat. Once the outlet valve 210 is fully opened, the fluid
flow through the outlet valve 210 is controlled by the distance
between valve stem 310 and valve-housing seat 320, although fluid
flow is usually dominated by higher resistance in the circuit, such
as an IV needle or catheter.
[0016] According to the present invention, the force that generates
the positive pressure in the cassette central chamber is controlled
based on the length of the withdrawal stroke and is directly
related to shuttle position. Thus, the force is modifiable in
response to various conditions of a fluid delivery system, e.g.,
desired flow rate, volume of fluid displacement, and flow
continuity. For example, the processor 118 receives a flow rate
command and feedback position changes provided by the position
sensor 116 and directs motor 112 to cock the spring 110 to various
degrees thus modify the spring force applied to the cassette piston
106.
[0017] In one mode, the force generating the positive pressure is
decreased in response to a desired low flow rate. Specifically the
processor 118 directs the motor 112 to conduct a partial withdrawal
stroke, e.g., less than full length, therefore generating less than
the full amount of the spring force, thus pumping less fluid out of
the cassette central chamber 108.
[0018] In another mode, if the volume of fluid due the patient for
the next opening of the outlet valve 210 is less than 40 .mu.l, the
processor 118 directs the motor 112 to provide a corresponding
spring force and/or directs the outlet valve 210 to open in a pulse
mode. The duration of the pulse is modifiable based on the position
change of the cassette piston 106 which represents the volume of
fluid displacement. For example, the amount of time that the motor
112 is energized to open the outlet valve 210 is adjusted on an
ongoing basis based on the position change provided by the position
sensor 116 to the processor 118, so that the cracking point of the
outlet valve 210 is reached. At a low flow rate, the inertial
component of the fluid flow is significant because the fluid flow
is constrained mainly by the acceleration of the moving mass of the
system instead of the resistance of the pathway. That is, the fluid
does not achieve a steady state flow rate instantly. Instead, the
mass of all moving components (e.g., the fluid, piston 106 and
shuttle 104) must be accelerated by the force of spring 110. This
dynamic adjustment accommodates a wide tolerance in mechanics and
fluidics.
[0019] In yet another mode, if the volume of fluid due the patient
for the next opening of the outlet valve 210 is greater than 40
.mu.l, the processor 118 directs the motor 112 to provide a
corresponding spring force and/or directs the outlet valve 210 to
be opened partially, e.g., in a nudge mode so that fluid is metered
out through the outlet valve 210. The amount of partial opening of
the outlet valve 210 depends on the duration of motor 112 actuation
through actuator 212, which is controlled by processor 118 based on
the position change received from the optical position sensor
116.
[0020] In still another mode, the processor 118 of the system
adjusts the force and/or the outlet valve 210 to provide a desired
low flow rate with a desired flow continuity. Specifically, at a
low flow rate, e.g., less than 5 ml/hr, the system of the present
invention, dispenses fluid at intervals no longer than about 8
seconds.
[0021] Similarly, the force that generates the positive pressure in
the cassette central chamber can also be increased to provide
continuing fluid delivery at a high flow rate. For example,
increasing the length of the withdrawal stroke increases the spring
force applied to the cassette piston, thus pumping more fluid out
of the central chamber. In one mode, the outlet valve 210 is not
closed until the fluid stops flowing. As spring 110 causes the
central chamber 108 to empty, the force of the spring, and
therefore, the pressure within the central chamber 108, decreases.
Ignoring the effects of momentum, this continues until the pressure
in the central chamber 108 equals the pressure downstream of outlet
valve 210. However at high flow rate, the moving mass has momentum
which allows the fluid to continue traveling for a short time even
after the pressure differential between the cassette central
chamber 108 and the downstream of the outlet valve 210 has
decreased to zero. Thus to maximize the fluid flow, the outlet
valve 210 is kept open even after the pressure is equalized between
the cassette central chamber 108 and the downstream of the outlet
valve 210 and is closed only after the fluid stops flowing.
[0022] Another feature of the present invention reduces fluid flow
rate variation, e.g., pulsatile flow rate changes. In one
embodiment, the processor 118 adjusts the timing of opening and
closing the outlet valve 210 to reduce fluid flow rate variation.
Specifically, the processor 118 adjusts the amount of time the
motor 112 is energized to open the outlet valve 210 before being
shut off over a period of time to allow the outlet valve 210 to
return to its normally closed position. For example, during fluid
delivery the processor 118 directs the motor 112 to open the outlet
valve 210 for a period of time, then directs a brake force on the
motor 112. Once a brake force is applied the outlet valve 210 is
kept open for a period of time until the shuttle 104, i.e., the
cassette piston 106 reaches a targeted position. The period of time
in which the motor 112 is energized is adjusted by the processor
118 based on the maximum fluid flow rate during an empty or outlet
cycle. In one embodiment, the processor adjusts the outlet valve
210 based on the targeted maximum shuttle speed which can be
readily measured by the position sensor 116. Usually the targeted
maximum shuttle speed is 10 mm/sec during a nudge mode outlet cycle
for a controlled force fluid delivery system of the present
invention.
[0023] The processor 118 adjusts the shuttle speed by adjusting the
level of openness of the outlet valve 210 based on the minimum time
period between the digital interrupts recorded by the optical
position sensor 116. Normally, the minimum time period between the
digital interrupts is about 8 msec. If it is less than 8 msec, then
the shuttle is moving too fast and the outlet valve is opened to a
lesser degree or closed to a larger degree; on the other hand if it
is more than 8 msec, then the shuttle is moving too slowly and the
maximum force or power to pump fluid out of the central chamber is
increased.
[0024] Another feature of the invention includes providing a steady
power output of the motor 112. In one embodiment, pulse width
modulation (PWM) value is modulated as f(Vb1), where the power
input to the motor 112 is a function of the main battery voltage
Vb1. Over a period of time, as the main battery voltage decreases
the PWM is adjusted to achieve a steady power output from the motor
112.
[0025] Other Embodiments
[0026] Although several exemplary embodiments of this invention
have been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiment without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention as defined in the following claims.
* * * * *