U.S. patent application number 10/864209 was filed with the patent office on 2005-06-16 for hemofiltration system and method based on monitored patient parameters, supervisory control of hemofiltration, and adaptive control of pumps for hemofiltration.
This patent application is currently assigned to Children's Hospital Medical Center. Invention is credited to Bissler, John J., Hemasilpin, Nat, Morales, Efrain O., Polycarpou, Marios M..
Application Number | 20050126961 10/864209 |
Document ID | / |
Family ID | 22451766 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050126961 |
Kind Code |
A1 |
Bissler, John J. ; et
al. |
June 16, 2005 |
Hemofiltration system and method based on monitored patient
parameters, supervisory control of hemofiltration, and adaptive
control of pumps for hemofiltration
Abstract
A multipurpose hemofiltration system and method are disclosed
for the removal of fluid and/or soluble waste from the blood of a
patient. The system continuously monitors the flow rates of drained
fluid, blood, and infusate. When necessary, the pumping rates of
the infusate, drained fluid and blood are adjusted to remove a
preselected amount of fluid from the blood in a preselected time
period. A supervisory controller can monitor patient parameters,
such as heart rate and blood pressure, and adjust the pumping rates
accordingly. The supervisory controller uses fuzzy logic to make
expert decisions, based upon a set of supervisory rules, to control
each pumping rate to achieve a desired flow rate and to respond to
fault conditions. An adaptive controller corrects temporal
variations in the flow rate based upon an adaptive law and a
control law.
Inventors: |
Bissler, John J.;
(Cincinnati, OH) ; Polycarpou, Marios M.;
(Strovolos, CY) ; Hemasilpin, Nat; (Cincinnati,
OH) ; Morales, Efrain O.; (Rochester, NY) |
Correspondence
Address: |
WOOD, HERRON & EVANS, L.L.P.
2700 Carew Tower
441 Vine St.
Cincinnati
OH
45202
US
|
Assignee: |
Children's Hospital Medical
Center
Cincinnati
OH
|
Family ID: |
22451766 |
Appl. No.: |
10/864209 |
Filed: |
June 9, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10864209 |
Jun 9, 2004 |
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10030011 |
Jun 11, 2002 |
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6780322 |
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Current U.S.
Class: |
210/87 ; 210/143;
210/96.2; 210/97; 604/65; 604/67 |
Current CPC
Class: |
A61M 1/1605 20140204;
A61M 2205/3331 20130101; A61M 2205/3393 20130101; A61M 1/1603
20140204; A61M 1/3437 20140204; G05B 13/0275 20130101; A61M 1/3413
20130101; A61M 1/342 20130101; A61M 1/3607 20140204; A61M 2205/50
20130101; A61M 1/3639 20130101; A61M 1/341 20140204; A61M 1/3441
20130101; A61M 1/1643 20140204; A61M 1/16 20130101; A61M 1/3434
20140204; A61M 2205/3344 20130101; A61M 1/1615 20140204; A61M
1/1611 20140204; A61M 1/1647 20140204; A61M 1/3451 20140204; A61M
1/34 20130101; Y10S 210/929 20130101; A61M 1/3496 20130101; A61M
2205/3334 20130101 |
Class at
Publication: |
210/087 ;
210/096.2; 210/097; 210/143; 604/065; 604/067 |
International
Class: |
B01D 061/32 |
Claims
What is claimed is:
1. A hemofiltration system for fluid removal from the blood of a
patient, comprising: a pump capable of pumping a liquid selected
from the group consisting of infusate, drained fluid, and blood in
the hemofiltration system; a sensor for measuring the flow rate of
fluid in the medical system generated by at least one pump, the
flow rate sensor providing flow rate data signals correlated to the
fluid flow rate; a supervisory controller operably connectable to
the at least one pump and operably connected to the flow rate
sensor; and at least one monitor for measuring at least one
predetermined patient parameter; said least one patient parameter
monitor providing patient parameter data signals correlated to said
at least one patient parameter, wherein the controller is operably
connected to said at least one monitor, the controller receiving
the flow rate data signals and the patient parameter data signals
and analyzing the flow rate data signals and the patient parameter
data signals utilizing fuzzy logic having at least one
predetermined supervisory rule, and then providing an output signal
for the at least one pump to adjust, as necessary on a periodic
ongoing basis, the flow rate of liquid generated by the at least
one pump for regulating fluid removal from the patient's blood.
2. The control system of claim 1, wherein said at least one patient
parameter monitor is selected from the group consisting of a blood
pressure monitor providing blood pressure data signals, a heart
rate monitor providing heart rate data signals, and combinations
thereof.
3. A hemofiltration system for fluid removal from the blood of a
patient, comprising: a pump capable of pumping a liquid selected
from the group consisting of infusate, drained fluid, and blood in
the hemofiltration system; a flow rate sensor for measuring the
flow rate of the liquid generated by the at least one pump, the
flow rate sensor providing flow rate data signals correlated to the
liquid flow rate; and an adaptive controller operably connectable
to the at least one pump and operably connected to the flow rate
sensor, the controller receiving the flow rate data signals and
generating an output signal for adjusting the pumping rate of the
liquid generated by the at least one pump, the controller providing
the output signal for the at least one pump on a periodic ongoing
basis, the controller using an adaptive law to generate a set of
controller parameters for correcting time-dependent deviations of
the flow rate from a predetermined flow rate, and using a control
law to generate the output signal from the set of controller
parameters for adjusting the pumping rate of the liquid generated
by the at least one pump to achieve the predetermined flow rate for
regulating fluid removal from the patient's blood.
4. The control system of claim 3, wherein the adaptive law further
includes parameter projections to limit the output signal to a
range between a predetermined minimum output signal and a
predetermined maximum output signal.
5. A method of controlling a pump in a hemofiltration system,
comprising: measuring the flow rate of a liquid selected from the
group consisting of infusate, drained fluid, and blood generated by
the pump to obtain flow rate data signals correlated to the fluid
flow rate; measuring at least one patient parameter to obtain
patient parameter data signals correlated to said at least one
patient parameter; analyzing the flow rate data signals and the
patient parameter data signals utilizing fuzzy logic having at
least one predetermined supervisory rule; and providing an output
signal to the pump to adjust, as necessary on a periodic ongoing
basis, the flow rate of liquid generated by the pump for regulating
fluid removal from the patient's blood.
6. A method of controlling a pump in an ultrafiltration system,
comprising: measuring a flow rate of a liquid selected from the
group consisting of infusate, drained fluid, and blood in the
hemofiltration system generated by the pump to obtain flow rate
data signals correlated to the liquid flow rate; generating a set
of controller parameters from the flow rate signals for correcting
time-dependent deviations of the flow rate from the predetermined
flow rate; generating an output signal using a control law from the
set of controller parameters, the output signal capable of
adjusting the pumping rate of liquid generated by the pump to
achieve a predetermined flow rate; and providing the output signal
to the pump on a periodic ongoing basis to correct the deviations
of the flow rate from the predetermined flow for regulating fluid
removal from the patient's blood.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of patent application
Ser. No. 10/030,011, which is the National Stage of International
Application No. PCT/US00/11620, filed Apr. 28, 2000, which claims
the benefit under 35 U.S.C. .sctn.119(e) of U.S. Provisional
Application No. 60/131,995, filed Apr. 30, 1999, each disclosure of
which is hereby expressly incorporated by reference herein in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention is directed to a system and method of
blood filtration, and more particularly supervisory control systems
and methods and an adaptive control systems and methods for
controlling the continuous filtration of fluid and/or soluble waste
from the blood of a patient based on one or more monitored patient
parameters and fluid flow rates.
BACKGROUND OF THE INVENTION
[0003] For various reasons, including illness, injury or surgery,
patients may require replacement or supplementation of their
natural renal function in order to remove excess fluid or fluids
containing dissolved waste products from their blood. Several
procedures known for this purpose are dialysis, hemodialysis,
hemofiltration, hemodiafiltration and ultrafiltration; another
related procedure is plasmapheresis. The specific procedure
employed depends upon the needs of the particular patient. For
example, dialysis is used to remove soluble waste and solvent from
blood; hemofiltration is used to remove plasma water from blood;
hemodiafiltration is used to remove both unwanted solute (soluble
waste) and plasma water from blood; ultrafiltration is a species of
hemofiltration; and plasmapheresis is used to remove blood plasma
by means of a plasmapheresis filter. Because the replacement of
renal function may affect nutrition, erythropoiesis,
calcium-phosphorus balance and solvent and solute clearance from
the patient, it is imperative that there be accurate control of the
procedure utilized. The accurate control of the rate of removal of
intravascular fluid volume is also important to maintain proper
fluid balance in the patient and prevent hypotension.
[0004] Various systems have been proposed to monitor and control
renal replacement procedures. For example, U.S. Pat. No. 4,132,644
discloses a dialysis system in which the weight of dialyzing liquid
in a closed liquid container is indicated by a scale. After the
dialyzing liquid flows through the dialyzer, the spent liquid is
returned to the same container and the weight is again indicated.
Since the container receives the original dialyzing liquid plus
ultrafiltrate, the amount of ultrafiltrate removed from the patient
is equal to the increase in total weight in the container. This
system is not driven by a weight measuring device and does not
offer precise control of the amount of liquids used in the
procedure.
[0005] U.S. Pat. No. 4,204,957 discloses an artificial kidney
system which utilizes weight measurement to control the supply of
substitute fluid to a patient. In this system, the patient's blood
is pumped through a filter and the filtrate from the blood is
discharged to a measuring vessel associated with a weighing device.
A second measuring vessel containing substitute fluid is associated
with a second weighing device and is connected to the purified
blood line. By means of a pump, the substitute fluid and the
purified blood are pumped back to the patient. The first and second
weighing devices are coupled to one another by a measuring system
in such a way that a fixed proportion of substitute is supplied to
the purified blood stream from the second measuring vessel
depending an the weight of the filtrate received in the first
measuring vessel. This system does not utilize circulating
dialysate fluid in the blood filtration.
[0006] U.S. Pat. No. 4,767,399 discloses a system for performing
continuous arteriovenous hemofiltration (CAVH). The disclosed
system relies upon utilizing a volumetric pump to withdraw a
desired amount of fluid from the patient's blood and return a
selected amount of fluid volume to the patient.
[0007] U.S. Pat. No. 4,923,598 discloses an apparatus for
hemodialysis and hemofiltration which comprises an extracorporeal
blood circuit including a dialyzer and/or filter arrangement. The
system determines fluid withdrawal per unit time and total amount
of fluid withdrawn by utilizing flow sensors in conjunction with an
evaluating unit located upstream and downstream of the dialyzer or
filter arrangement in the blood circuit.
[0008] U.S. Pat. No. 4,728,433 discloses a system for regulating
ultrafiltration by differential weighing. The system includes a
differential weighing receptacle having an inlet chamber and an
outlet chamber which allows a fixed amount of fresh dialysate, by
weight, to flow through the hemodialyzer. This system operates in a
sequence of weighing cycles during which the amount of
ultrafiltrate removed from the blood may be calculated.
Additionally, the ultrafiltration rate for each weighing cycle may
be calculated. This system provides a mechanism for determining and
regulating the amount of ultrafiltrate removed from the blood while
delivering dialysate to the patient in alternating fill and drain
cycles of the inlet and outlet chambers of the differential
weighing receptacle.
[0009] For certain patients, renal replacement procedures may
extend over hours or even days. In general, current systems for
monitoring and controlling renal replacement procedures lack the
flexibility and accuracy required to perform such procedures on
neonates. This is mainly due to the absence of a satisfactory
automatic control of the pumps employed. Because of the patient
risk involved in using such equipment, health care personnel
measure the fluid removed from the patient on an hourly basis. The
continuing need to monitor the fluid removed leads to a significant
increase in nursing care and thus increases the cost of the
therapy. Therefore, there is a need to improve the level of
autonomy for the systems such that the procedure is less time
consuming for medical personnel, and consequently less costly.
However, the enhanced autonomy must not come at the expense of
patient safety.
[0010] Some conventional renal function replacement/supplementation
systems possess an elementary level of supervisory control that
simply detects the presence of a fault condition, sounds an alarm,
and de-energizes the system pumps to halt the procedure. If the
hemofilter clots while the pumps are de-energized, the tubing and
hemofilter must be replaced with a concomitant increase in the
chance of infection for the patient. Furthermore, the
hemofiltration procedure is delayed with a possibly negative impact
upon the patient's health.
[0011] Due to the time-varying nature of the renal function
replacement/supplementation system, the dynamics of fluid pumping
may change over time. For example, the characteristics of system
components such as tubing, filter, and connectors may vary slowly
over time due to aging or as occlusion of the path for fluid flow.
As the flow path becomes constricted, the pumping rate of the pump
must be altered to compensate for the increased flow resistance.
Furthermore, the replacement of a tubing set requires a rapid
change adjustment of the pumping rates that may be difficult to
initially establish as a relatively constant value due to
short-term transient variations. Current systems for monitoring and
controlling renal replacement procedures lack the ability to
autonomously correct these time-dependent flow rate variations with
high accuracy, rapid response, and minimal overshoot or transient
variations following correction.
[0012] The need exists for a multipurpose renal function
replacement/supplementation system which is accurate, reliable,
capable of continuous, long-term operation, and which can be used
effectively on adult, pediatric and neonatal patients. Further, the
need exists for a feedback control system for controlling the
multipurpose renal function replacement/supplementation system that
accurately regulates the transfer of fluid and monitors the overall
behavior of the system to improve patient care and provide greater
autonomy.
SUMMARY OF THE INVENTION
[0013] The present invention is directed to a multipurpose system
and method for removal of fluid and/or soluble waste from the blood
of a patient: ultrafiltration only, hemodiafiltration,
hemodiafiltration and ultrafiltration, hemodialysis, and
plasmapheresis with or without fluid replacement. The system and
method of the present invention can provide reliable, long term
operation (5-10 days) with a great degree of accuracy (on the order
of .+-.2 grams regardless of the total volume of fluid passing
through the system). The system and method of the invention are
advantageous because of the multipurpose nature thereof, the
repeatability and accuracy of the processes, and the simultaneous,
continuous flow of fluids in an extracorporeal blood circuit, while
being equally applicable to adult, pediatric and neonatal
patients.
[0014] As used herein the term "hemofiltration" is to be broadly
construed to include hemodialysis, hemofiltration,
hemodiafiltration, ultrafiltration and plasmapheresis processes. As
used herein, the term "infusate" is defined to include dialysate
fluid or any other replacement fluids which may be supplied to the
patient as a part of the hemofiltration procedures.
[0015] In a preferred embodiment, the system of the present
invention includes a hemofilter, a blood pump for pumping blood
from a patient through the hemofilter and back to the patient, and
suitable tubing for carrying the pumped blood to and from the
patent. The system further includes a first reservoir for
maintaining a supply of infusate, a first weighing means for
continuously monitoring the weight of the infusate and generating
weight data signals correlated to the monitored weight, and a first
pump for pumping the infusate from the first reservoir to the
hemofilter or appropriate blood tubing access port. A second
reservoir receives drained fluid (e.g., spent infusate or
ultrafiltrate, including the fluids and solutes removed from the
blood) from the hemofilter, and a second weighing means monitors
the weight of the drained fluid and generates weight data signals
correlated to the monitored weight. A second pump pumps the drained
fluid from the hemofilter to the second reservoir. The system also
includes a computerized controller operably connected to the blood
pump, the infusate pump, the drain pump and the first and second
weighing means.
[0016] The controller periodically, but on an ongoing basis during
the treatment, interrogates at predetermined intervals the weight
data signals that are continuously generated by the first and
second weighing means and is designed to determine therefrom the
weight of infusate and drained fluid in the first and second
reservoirs at the predetermined intervals. The rate of fluid
withdrawal from the blood is also determined. The controller
compares the infusate and drained fluid weights to corresponding
predetermined computed weights in the memory of the controller,
and, when necessary, the controller generates control signals which
automatically adjust the pumping rates of the infusate and drained
fluid pumps in order to achieve a preselected amount of fluid
removal from the patient's blood. Additionally, the controller is
programmed to operate the infusate and drained fluid pumps only
when the blood pump is operating. Furthermore, the blood pump is
operably connected to and is responsive to control signals
generated by the controller in response to or independent of the
weight data signals to vary the flow rate of the blood through the
hemofilter as required to achieve the desired level of fluid
removal from the blood.
[0017] In an alternative embodiment, the computer controller is, by
initial selection of the operator, interfaced with one or more of
the various monitoring systems that are operably connected to the
patient. These monitoring systems, which are well known in the art,
generate and output data signals corresponding to the monitored
patient parameters, and the computer controller receives such data
signals. During the hemofiltration operation, the interfaced
parameters are constantly monitored; however, the controller only
responds to specific parameter data that corresponds to the patient
parameters selected by the operator. The patient parameters which
may be monitored and interfaced with the computer controller
include the following: arterial pressure, central venous pressure,
pulmonary arterial pressure, mean arterial pressure, capillary
wedge pressure, systemic vascular resistance, cardiac output,
O.sub.2 and CO.sub.2 content and saturation (expired, venous or
arterial), blood pressure, heart rate, patient weight, external
infusion rates, and hematocrit. Numerous of these parameters may be
monitored and corresponding output data signals generated in known
manner utilizing an indwelling intravenous or intra-arterial
catheter. The remaining parameters are monitored and data signals
are generated by means well known in the art. The operator will
select one or more of the above parameters to interface with the
controller which will then periodically, but on an ongoing basis
during treatment, interrogate at predetermined intervals the
parameter data signals that are continuously generated by the
interfaced monitoring system(s). The controller then evaluates the
parameter data and in response thereto, when necessary, the
controller generates control signals which automatically adjust the
pumping rates of the infusate, drained fluid and blood pumps so as
to achieve a preselected amount of fluid removal from the patient's
blood for patient benefit and safety.
[0018] It will be appreciated that the system of the present
invention may utilize a combination of monitoring and responding to
the infusate and drained fluid weight data signals, as described in
connection with the first embodiment hereinabove, along with one or
more of the other patient parameters interfaced to the
controller.
[0019] By way of specific examples, in connection with monitoring
the patient's weight, the computer controller may be interfaced
with a bed scale which provides continuous values for the patient's
weight. In response to the overall patient weight data signals, the
computer controller may control the infusate and/or drained fluid
pumps to achieve a predesigned protocol for decreasing or
increasing the patient's weight over time. The increase or decrease
in patient's weight can be accomplished in either a linear or
non-linear manner with respect to time by appropriate pump control.
Similarly, the computer may be interfaced with a continuous
read-out device of the patient's O.sub.2 saturation and the
controller will receive, evaluate and respond to the O.sub.2
saturation data by controlling the infusate, drained fluid and
blood pumping rates accordingly to optimize patient
oxygenation.
[0020] In connection with all of the above-described monitored
parameters, the computer controller will receive data signals
corresponding and relating to each particular selected parameter
from an appropriate signal generating device or source operably
connected to the patient. The controller will then, after periodic
interrogation, compare the interrogated values with predetermined
desired values and will automatically make the appropriate,
predetermined changes in the infusate, drained fluid and blood
pumping rates in response to the monitored signals. Furthermore,
more than one of the above-referenced parameters can be
continuously monitored simultaneously and the computer may be
programmed with a hierarchy to consider one or more specific
parameters rather than others and will respond with the appropriate
and desired adjustments in infusate, drained fluid and blood
pumping rates based on those selected parameters.
[0021] The computer controller is designed and programmed to adjust
the pumping rates (pump speed) of the infusate, drained fluid and
blood pumps so as to provide a linear response or a non-linear
(curvilinear) response to the observed changes in the selected
monitored parameters. In this regard, "linear" is defined to mean a
fixed, non-exponential change, and "non-linear" or "curvilinear"
means anything other than linear. The selection of linear versus
non-linear response profile is made by the operator of the system
depending on the needs of the patient. For example, in certain
situations it may be desirable to have an initially fast fluid
removal rate that decreases over time. In that case a curvilinear
or exponential response would be utilized. In other circumstances,
consistent or constant fluid removal over time is desired, and so a
linear response profile is selected. It is further contemplated
that at the election of the operator the computer controller may
combine linear and curvilinear response signals so as to tailor the
pump rates to achieve a desired response profile. For example, a
non-linear initial response period for fast initial fluid removal,
followed by a linear response period for ongoing fluid removal at a
consistent rate.
[0022] In yet another alternative embodiment, the computer
controller receives data signals from one or more patient infusion
pumps that are otherwise independent of the hemofiltration system.
These infusion pumps are used for infusion to the patient of
intravenous fluids, medications, parenteral nutrition and/or blood
products. By monitoring the data output from the independent
infusion pumps, the extraneous total fluid volume per unit time may
be ascertained. The controller will then, as required, change the
pumping rates of the system infusate, drained fluid and blood
pumps, as necessary, so as to alter the ultrafiltration rate and/or
infusate fluid rate automatically in response to changes in
intravenous fluid therapy. This facilitates independent patient
management while hemofiltration is being performed. Proper
coordination of the controller with the independent infusion pumps
allows the desired or targeted fluid removal goals by
hemofiltration to be achieved automatically in concordance with
ongoing intravenous fluid therapy.
[0023] In an additional alternative embodiment, the computer
controller incorporates a supervisory control system operably
connected to one or more of the system infusate, drained fluid and
blood pumps for controlling the pumping rates of the respective
fluids. The supervisory controller receives and utilizes feedback
data signals, correlated with the fluid flow rates, regarding the
pumping rate of the blood pump that is provided by a flowmeter and
the pumping rate of the infusate and drained fluid pumps from the
rate change in weight data signals that is provided by electronic
scales. The supervisory controller also receives and utilizes
patient parameters derived from patient parameter monitors, such as
blood pressure data signals from a blood pressure monitor or heart
rate data signals from a heart rate monitor. The supervisory
controller analyzes these signals utilizing fuzzy logic, based on
at least one predetermined supervisory rule, and furnishes an
output signal to the appropriate pump to adjust, as necessary on a
periodic ongoing basis, the flow rate of fluid generated by that
pump. For example, a set of supervisory rules may decide, based
upon whether the heart rate and blood pressure are high, normal, or
low, to increase or decrease the ultrafiltration rate, or even to
discontinue the procedure due to a fault condition.
[0024] In yet an additional alternative embodiment, the computer
controller incorporates an adaptive control system for controlling
the pumping rate of at least one of the system infusate, drained
fluid and blood pumps. The adaptive controller is operably
connected to each pump to be adaptively controlled and to its
associated flow rate sensor. The adaptive control system receives
flow rate data signals correlated to the fluid flow rate from a
sensor, such as a flowmeter or weight scale, measuring the flow
rate of fluid generated by the pump being controlled. The adaptive
controller calculates a controller parameter vector using an
adaptive law to generate a set of controller parameters for
correcting time-dependent deviations of the flow rate from a
predetermined flow rate. Based on the controller parameters, the
adaptive controller then uses a control law to generate an output
signal for adjusting the pumping rate of fluid generated by the
pump to achieve the predetermined flow rate. Finally, the
controller provides the output signal to the pump on a periodic
ongoing basis for adjusting the fluid flow rate. In one aspect, the
adaptive controller may use parameter projections to limit the
range of the output signal for maintaining the pump in a linear
regime of pump operation.
[0025] In a preferred embodiment of the method of the present
invention, blood from a patient is pumped through a hemofilter and
a supply of infusate, which is maintained in a first reservoir, is
pumped from the first reservoir through the hemofilter,
countercurrent to the blood. The weight of infusate in the first
reservoir is continuously monitored and data signals correlated to
that weight are generated. Drained fluid (e.g., spent infusate) is
pumped from the hemofilter and is received in a second reservoir.
The weight of the drained fluid in the second reservoir is
continuously monitored and weight data signals correlated thereto
are generated. The signals correlated to the weight of infusate and
drained fluid are interrogated at regular intervals (for example
every minute) by a system controller and are compared to
corresponding predetermined computed weights in the memory of the
controller. The controller determines the amount and rate of fluid
withdrawal from the patient's blood. If those values differ from
preselected, preprogrammed desired values, the controller generates
control signals which independently adjust the pumping rates of the
infusate and drained fluid pumps so as to achieve the desired
amount of fluid removal. The control signals may also control the
blood pumping rate.
[0026] In an alternative embodiment of the method of the present
invention, independent of or in addition to the infusate and
drained fluid weight monitoring and pump control, the computer
controller may be interfaced with one or more of the previously
discussed monitoring systems. In this embodiment, the controller
will receive, evaluate and respond to the selected patient
parameter data by generating appropriate, responsive control
signals by which the infusate, drained fluid and blood pumping
rates are controlled to achieve the desired amount of fluid
removal. This may be accomplished in combination with or
independent of the infusate and drained fluid weight
monitoring.
[0027] In an alternative embodiment of the method of the present
invention, flow rate data signals for the fluid flow generated by a
pump in a hemofiltration system and patient parameter data signals,
such as heart rate and blood pressure, are supplied to a
supervisory controller. Flow rate data signals are derived from the
rate change in weight of either infusate or drained fluid or from
the blood flow rate. The signals are analyzed utilizing fuzzy logic
based on at least one predetermined supervisory rule and an output
signal is provided to the appropriate pump to adjust, as necessary
on a periodic ongoing basis, the flow rate of fluid generated by
that pump.
[0028] In yet another alternative embodiment of the method of the
present invention, flow rate data signals for the fluid flow
generated by a pump in a hemofiltration system are supplied to an
adaptive controller. Flow rate data signals are derived from the
rate change in weight of either infusate or drained fluid or from
the blood flow rate. A set of controller parameters is generated
from the flow rate signals for use in correcting time-dependent
deviations in flow rate from a predetermined flow rate. The signals
and parameters are analyzed using a control law to generate an
output signal. The output signal is provided to the adaptively
controlled pump on a periodic ongoing basis.
[0029] The advantages of the system and method of the present
invention are achieved at least in part due to the continuous
monitoring and periodic interrogation of the fluid weights, and
other selected patient parameters, and the adjustment of fluid
pumping rates in response thereto, including the blood pumping
rate, so as to achieve ideal or nearly ideal fluid removal and
replacement if necessary from a patient's blood. Further, the
supervisory system controller and adaptive system controller
implement closed-loop, feedback control systems that precisely and
accurately adjust and control the pumping rates. Further features
and advantages of the system and apparatus of the present invention
will become apparent with reference to the Figure and the detailed
description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a diagrammatic representation of one embodiment of
the system of the present invention; a variation is shown in
phantom.
[0031] FIG. 2 is a diagrammatic representation of an alternative
embodiment of the system of the present invention.
[0032] FIG. 3 diagrammatically illustrates the hierarchical control
architecture for a hemofiltration system.
[0033] FIG. 4 diagrammatically illustrates the fuzzy logic process
performed by the supervisory controller of FIG. 3.
[0034] FIG. 5 represents the supervisory control architecture
implemented in the supervisory controller.
[0035] FIG. 6A is a set of membership functions for blood pressure
data signals that are input into the fuzzy logic control
system.
[0036] FIG. 6B is a set of input membership functions for heart
rate data signals that are input into the fuzzy logic control
system.
[0037] FIG. 6C is a set of output membership functions for signals
representing changes in ultrafiltration rate that are output from
the fuzzy logic control system.
[0038] FIG. 7A is a graphical representation of the tracking error
of a blood pump for an ultrafiltration simulation.
[0039] FIG. 7B is a graphical representation of the control voltage
for an ultrafiltration simulation.
[0040] FIG. 7C is a graphical representation of the controller
parameters for an ultrafiltration simulation.
[0041] FIG. 8A is a graphical representation of the tracking error
of a blood pump for an ultrafiltration simulation.
[0042] FIG. 8B is a graphical representation of the tracking error
of a drain pump for an ultrafiltration simulation.
[0043] FIG. 8C is a graphical representation of the tracking error
of a first replacement pump for an ultrafiltration simulation.
[0044] FIG. 8D is a graphical representation of the tracking error
of a second replacement pump for an ultrafiltration simulation.
[0045] FIG. 9A is a graphical representation of the tracking error
of a drain pump for an ultrafiltration simulation.
[0046] FIG. 9B is a graphical representation of the control voltage
for an ultrafiltration simulation.
[0047] FIG. 9C is a graphical representation of the controller
parameters for an ultrafiltration simulation.
[0048] FIG. 10A is a graphical representation of the heart rate for
an ultrafiltration simulation.
[0049] FIG. 10B is a graphical representation of the blood pressure
for an ultrafiltration simulation.
[0050] FIG. 10C is a graphical representation of the desired drain
flow rate calculated by fuzzy system I for an ultrafiltration
simulation.
[0051] FIG. 11A is a graphical representation of the heart rate for
an ultrafiltration simulation.
[0052] FIG. 11B is a graphical representation of the blood pressure
for an ultrafiltration simulation.
[0053] FIG. 11C is a graphical representation of the desired drain
flow rate calculated by fuzzy system II for an ultrafiltration
simulation.
[0054] FIG. 12A is a graphical representation of the heart rate for
an ultrafiltration simulation.
[0055] FIG. 12B is a graphical representation of the blood pressure
for an ultrafiltration simulation.
[0056] FIG. 12C is a graphical representation of the desired drain
flow rate calculated by fuzzy system III for an ultrafiltration
simulation.
[0057] FIG. 13A is a graphical representation of the heart rate for
an ultrafiltration simulation.
[0058] FIG. 13B is a graphical representation of the blood pressure
for an ultrafiltration simulation.
[0059] FIG. 13C is a graphical representation of the desired drain
flow rate calculated by fuzzy system IV for an ultrafiltration
simulation.
[0060] FIG. 14A is a graphical representation of the heart rate for
an ultrafiltration simulation.
[0061] FIG. 14B is a graphical representation of the blood pressure
for an ultrafiltration simulation.
[0062] FIG. 14C is a graphical representation of the desired drain
flow rate calculated by FSIII for an ultrafiltration
simulation.
[0063] FIG. 14D is a graphical representation of the blood pump
flow rate for an ultrafiltration simulation.
DETAILED DESCRIPTION OF THE INVENTION
[0064] FIG. 1 shows a diagrammatic representation of a preferred
embodiment of the system of the present invention. The portion of
FIG. 1 shown in phantom represents an alternative embodiment of the
present invention which will be described hereinbelow.
Hemofiltration system 10 is operated and controlled by a suitable
controller designated generally as 12. Controller 12 may be a
programmable computer having a display 13 and is operably connected
to various components of hemofiltration system 10, as will be
described in greater detail hereinafter.
[0065] In operation, blood is pumped from a patient (not shown),
which may be an adult, pediatric or neonatal patient, through a
suitable catheter (not shown) and input tubing 14 by means of a
blood pump 16. Blood pump 16, which is preferably of the roller
type, is operably connected to controller 12 by line 18. One
suitable blood pump is the RS-7800 Minipump manufactured by Renal
Systems, Minneapolis, Minn. Input tubing 14 through which the
patient's blood is pumped preferably includes a pressure transducer
20 upstream of pump 16. Pressure transducer 20 is operably
connected to controller 12 via line 21. Means are included
downstream of blood pump 16 for accessing input tubing 14 to enable
the injection or infusion of desired fluids, including medications
and anti-clotting compounds such as heparin, into the patient's
blood. The injection or infusion of such fluids to the blood may be
accomplished in any suitable manner; FIG. 1 shows diagrammatically
a syringe and tube arrangement 22, but it will be appreciated that
other means could be employed for the same purpose.
[0066] The patient's blood is pumped through hemofilter 24 by blood
pump 16. Filters of the type suitable for use in the system of the
present invention are readily available; one example of a suitable
hemofilter is the Diafilter manufactured by AMICON, Denvers, Mass.
Where the present system is used to perform plasmapheresis, a
suitable plasmapheresis filter such as the Plasmaflo manufactured
by Parker Hannifin, Irvine, Calif. can be employed.
[0067] Input tubing 14 includes a second pressure transducer 26
slightly upstream of hemofilter 24. Pressure transducer 26 is
operably connected to controller 12 via line 28. The patient's
blood exits hemofilter 24, passes through output tubing 30 and is
returned to the patient via any suitable means such as a venous
catheter arrangement (not shown). Output tubing 30 preferably
includes a suitable blood flow detector 31 which verifies that
there is blood flow in the system and an air bubble/foam control
device such as air bubble clamp 32 to prevent the passage of air
bubbles to the patient. Blood flow detector 31 and air bubble clamp
32 may be operably connected (not shown) to controller 12 or
directly to the pumps to interlock all pumps upon detection of any
air bubbles in the blood or upon the cessation of blood flow. A
suitable foam-bubble detector is the RS-3220A manufactured by Renal
Systems. Output tubing 30 also preferably includes a pressure
transducer 34 immediately downstream of hemofilter 24. Pressure
transducer 34 is operably connected to controller 12 via line
36.
[0068] A first reservoir 50 maintains a supply of suitable
dialysate or other fluid, referred to herein generally as infusate
52. The infusate-containing reservoir 50 is supported by a weighing
device such as electronic scale 54 which is operably connected to
controller 12 via line 56. Infusate 52 is pumped from reservoir 50
via tubing 58 by means of infusate pump 60, which is preferably of
the roller variety. A suitable pump for this purpose is a 3 1/2"
Roller Pump manufactured by PEMCO, Cleveland, Ohio, Infusate pump
60 is operably connected to controller 12 via line 62 and pumps
infusate 52 through hemofilter 24 countercurrent to the blood
pumped therethrough. In accordance with known principles, infusate
52 may extract certain components (fluids and/or soluble waste)
from the blood passing through hemofilter 24. The fluid drained
from hemofilter 24 includes spent infusate and the components
removed from the blood, which are referred to herein as drained
fluid 76. In an alternative embodiment wherein system 10 is used as
a fluid or plasma replacement system, e.g., to perform
plasmapheresis, the infusate (which may be blood plasma) from
reservoir 50 is pumped via tubing 59 (shown in phantom) to blood
output tubing 30 or via tubing 59a (also shown in phantom) to input
tubing 14, thereby replacing the fluid volume removed from the
blood. In this embodiment, the drained fluid 76 from hemofilter or
plasmapheresis filter 24 does not include any spent infusate since
the infusate is pumped directly to blood output tubing 30 or input
tubing 14 and supplied to the patient.
[0069] The drained fluid 76 is pumped from hemofilter 24 through
outlet tubing 64 by means of drain pump 66, which is preferably a
roller-type pump, and may be the same as infusate pump 60. Drain
pump 66 is operably connected to controller 12 via line 68. Output
tubing 64 preferably includes a pressure transducer 70 downstream
of hemofilter 24, but upstream of drain pump 66. Pressure
transducer 70 is operably connected to controller 12 via line 72.
Output tubing 64 also preferably includes a blood leak detector 67
which detects the presence of blood in the drained fluid 76, as may
occur if hemofilter 24 ruptures. A suitable blood leak detector is
sold by COBE, Lakewood, Co as model 500247000. Blood leak detector
67 may be operably connected (not shown) to controller 12 or
directly to the pumps to interlock all pumps upon the detection of
blood in the drained fluid. Drained fluid 76 pumped from hemofilter
24 is pumped into a second reservoir 74 which collects the drained
fluid. Second reservoir 74 is supported by a weighing device such
as electronic scale 78, which is operably connected to controller
12 via line 80.
[0070] Scales 54 and 78, which may be model 140 CP sold by SETRA of
Acton, Mass. continuously generate weight data signals correlated
to the weight of infusate and drained fluid contained in reservoirs
50 and 74, respectively. Those weight data signals are continuously
fed to controller 12, to which the scales are linked through an
interface having a data protocol, such as an RS-232 interface. It
will be appreciated that a single scale could be utilized in place
of the two scales whereby the weight differential between reservoir
50 and 74 is monitored and a corresponding data signal is
generated. Pressure transducers 20, 26, 34 and 70 all continuously
measure the pressure at their respective locations in
hemofiltration system 10 and generate pressure data signals
correlated thereto which are fed to controller 12. A suitable type
of pressure transducer is model number 042-904-10 sold by COBE of
Lakewood, Colo. When certain predetermined alarm or danger
conditions exist in the system 10, as represented by the pressure
data signals, the controller will either adjust the infusate,
drained fluid, or blood pumping rate, or a combination thereof, or
will shut the system down entirely.
[0071] Controller 12 is preferably a programmable computer that is
capable of sending and receiving signals from auxiliary equipment
including pressure transducers 20, 26, 34 and 70, first and second
scales 54 and 78, respectively, and blood pump 16, infusate pump
60, and drain pump 66. In operation, controller 12 interrogates, at
regular intervals, the weight data signals generated by first and
second scales 54 and 78. From these signals, controller 12
determines the weight of infusate and drained fluid in the first
and second reservoirs 50 and 74 at that point in time, and compares
those weights to corresponding predetermined computed weights which
have been programmed into and are stored by controller 12. By
monitoring the weight of infusate in reservoir 50 and the weight of
drained fluid in reservoir 74 at regular intervals, the rate of
change of those weights and the rate of hemofiltration can be
calculated by the computer portion of controller 12. When the
weights deviate from the predetermined computed weights and/or the
rate of hemofiltration deviates from a preselected, preprogrammed
desired rate, controller 12 generates control signals which control
or adjust the rates at which blood pump 16, infusate pump 60 and
drain pump 66 are operated, as necessary, to adjust the
hemofiltration rate to the desired rate, or to stop the pumps when
preselected limits have been reached. This is accomplished in a
continuous manner; i.e., continuous weight data signal generation,
periodic interrogation of those weight data signals and computation
of the required weight and/or rate information, comparison to
predetermined computed values and automatic adjustment of the
pumping rates of the pumps, as necessary, to achieve the desired
amount and/or rate of hemofiltration.
[0072] Controller 12 is programmed so that infusate pump 60 and
drain pump 66 are operated only when blood pump 16 is being
operated. In the case when ultrafiltration is being performed, the
pumping rate of drain pump 66 must equal the pumping rate of
infusate pump 60 plus the desired ultrafiltration rate.
[0073] Controller 12 continuously receives pressure data signals
from pressure transducers 20, 26, 34 and 70 and is programmed to
generate alarm signals when high and low pressure limits are
exceeded at any of the monitored locations. Furthermore, an alarm
signal is generated when the pressure differential across
hemofilter 24 exceeds a predetermined upper limit, as monitored
specifically by pressure transducers 26, 34 and 70. Additionally,
controller 12 may stop the pumps when preselected pressure limits
(high or low) are exceeded, as for example may occur if the system
tubing becomes occluded or ruptures or if pump occlusion occurs.
Finally, controller 12 may signal when the infusate level in
reservoir 50 reaches a predetermined lower limit and when the
drained fluid level in reservoir 76 reaches a predetermined upper
limit. Hemofiltration system 10 may also include suitable blood
warmer and infusate warmer devices (not shown) to adjust and/or
maintain the blood and infusate temperatures at desired levels.
Such devices may also generate alarm signals when the fluid
temperatures are outside of preselected limits.
[0074] Display 13 offers updated display of measured and computed
parameters such as pressures, pressure differentials, temperatures,
flow rates and amounts of infusate, drain and ultrafiltration, and
alarm conditions. Controller 12 generates both visual and audible
alarms and all the pumps are interlocked to prevent operation
thereof under alarm conditions. Users have the option of disabling
or unabling the alarms (the audible part of the alarm and its
interlock with the pumps) to perform a procedure under close
supervision. A printer (not shown) is operably connected (not
shown) to controller 12 to generate a hard copy of procedural data
currently displayed or stored at regular intervals, at the
completion of a procedure or at any desired time.
[0075] Hemofiltration system 10 can be operated in one of two
modes: 1) a manual mode wherein the pumping rates of blood pump 16,
infusate pump 60 and drain pump 66 are provided by controller 12
when fixed voltages are applied; and 2) an automatic mode wherein
the pumps are controlled by controller 12 when the desired
hemofiltration amount or rate has been programmed into the
controller. The automatic mode allows the system to be paused and
later continued without losing previously measured and computed
data.
[0076] FIG. 2 shows a diagrammatic representation of several
alternative embodiments of the hemofiltration system 10 of the
present invention. Because of the commonality of many of the system
components in FIG. 2 vis-a-vis the system depicted in FIG. 1, like
reference numerals are intended to indicate like components.
Furthermore, the system components in FIGS. 2 operate in the same
manner as the corresponding system components shown in FIG. 1 and
described hereinabove. Input tubing 14 further includes a flowmeter
or flow probe 27 slightly upstream of hemofilter 24. The flow probe
27 is operably connected to controller 12 via line 29. A suitable
flow probe 27 is an ultrasonic flow probe manufactured by Transonic
Systems, Inc. Other suitable types of flowmeters include a
bearingless rotary flowmeter, a Doppler flowmeter, and a
differential electromagnetic flowmeter.
[0077] The hemofiltration system of FIG. 2 further includes
interfaces between controller 12 and monitoring systems which
generate parameter data signals corresponding to selected patient
parameters such as blood gas 100, hematocrit 110, patient heart
rate 120, patient blood pressure 130 and numerous other patient
parameters (designated generally as 140), which other parameters
may be one or more of the following: arterial pressure, central
venous pressure, pulmonary arterial pressure, mean arterial
pressure, capillary wedge pressure, systemic vascular resistance,
cardiac output, end tidal O.sub.2 and CO.sub.2, core and peripheral
body temperature, and patient weight. While the blood gas sensor
100 and hematocrit sensor 110 are shown as being connected to the
input tubing 14, these parameters can also be monitored by means
associated directly with the patient rather than via tubing 14. In
fact, whereas venous O.sub.2 saturation could be measured as
indicated, arterial O.sub.2 saturation would require the monitor to
be located elsewhere. The overall patient weight parameter can be
monitored utilizing a standard patient bed scale (not shown) as is
well known in the art.
[0078] During the hemofiltration procedure, one or more of the
various patient parameters will be monitored continuously and the
controller will, at the selection of the operator, be responsive to
selected parameter data supplied to the controller. The parameter
data may be evaluated and responded to by the controller
independent of the infusate and drained fluid weight data signals;
i.e., the system may operate and respond based on one or more of
the selected parameters and not the weight data signals; or the
system may respond to a combination of the weight data signals and
one or more selected specific parameters.
[0079] One or more independent patient infusion pumps 150 may be
interfaced with computer controller 12 to supply data signals
correlated to the infusion to the patient of intravenous fluids,
medications, parenteral nutrition and/or blood products. The
controller 12 may evaluate this data and make modifications to the
infusate, drained fluid and blood pumping rates so as to compensate
for the extraneous fluid being delivered to the patient by means of
the infusion pumps. In this regard, the overall fluid balance in
the patient can be managed concurrent with the hemofiltration
procedure.
[0080] In an alternative embodiment wherein system 10 is used to
perform an ultrafiltration procedure or hemodialysis procedure, the
infusate (which may be one or more replacement fluids such as a
calcium replacement fluid or a bicarbonate replacement fluid) from
reservoir 50 is pumped via tubing 59 (shown in phantom) to blood
outlet tubing 30 or via tubing 59a (also shown in phantom) to input
tubing 14, thereby offsetting substances and fluid volume removed
from the blood. In this embodiment, the drained fluid 76 from
hemofilter 24 does not include any spent infusate since the
infusate is pumped directly to blood output tubing 30 and supplied
to the patient. In yet another alternative embodiment, a distinct
replacement fluid may be provided by a system having more than one
infusate pump 60. For example, infusate pump 60 may be a first
infusate pump for delivering a first replacement fluid to blood
outlet tubing 30 via tubing 59 and the system 10 may further
include a second infusate pump (not shown) for delivering a second
replacement fluid to blood outlet tubing 30 via a length of tubing
(not shown but similar to tubing 59).
[0081] FIG. 3 represents a hierarchal control architecture that may
be implemented by the computer controller 12 of FIG. 2 for
controlling the pumping rates in the hemofiltration system 10 to
perform an ultrafiltration or hemodialysis procedure, referred to
hereinafter collectively as an ultrafiltration procedure. Because
of the commonality of many of the system components in FIG. 3,
vis-a-vis the system depicted in FIGS. 1 and 2, like reference
numerals are intended to indicate like components. Furthermore, the
system components in FIG. 3 operate in the same manner as the
corresponding system components shown in FIGS. 1 and 2 and
described hereinabove. The hierarchal control architecture
disclosed herein is further described in "Intelligent Contol of
Continuous Venovenous Hemofiltration," Efrain O. Morales, Master's
Thesis, University of Cincinnati, Department of Electrical &
Computer Engineering and Computer Science, and in "Hierarchical
Adaptive and Supervisory Control of Continuous Venovenous
Hemofiltration," Efrain O. Morales, Marios M. Polycarpou, Nat
Hemasilpin, and John. J. Bissler, submitted to IEEE Transactions on
Control Systems Technology, to be published, both of which are
hereby incorporated by reference in their entirety.
[0082] Referring to FIG. 3, the supervisory controller 160 controls
a blood pump 16, a drain pump 66, and a pair of infusate pumps 60,
namely a bicarbonate replacement pump 60a and a calcium replacement
pump 60b. Pumps 60a, 60b provide replacement fluids to replace
fluid volume removed from the patient during the ultrafiltration
procedure. The actual weight .omega..sub.rep1(n),
.omega..sub.rep2(n) of each replacement fluid supplied to the
patient is respectively monitored by an electronic scale 54a, 54b
(where each scale is similar to scale 54 shown in FIG. 2) with a
frequency of a sample period n. In a typical ultrafiltration
procedure, the sample period is on the order of one second. The
actual weight .omega..sub.dra(n) of the drained fluid is monitored
by an electronic scale 78. The ultrafiltration rate is calculated
as the difference between the rate change in drained fluid weight
and the rate change in the replacement fluid weight. The actual
flow q.sub.blo(n) from blood pump 16 is indicated by a flow probe
27.
[0083] Blood pump 16 is controlled by an adaptive pump controller
162, implemented in the controller 12, which receives a desired
fluid flow rate q.sub.blo.sup.*(n) calculated by the supervisory
controller 160 as a reference command input. The pump controller
162 is operably connected to the blood pump 16 via line 18 for
transmitting a voltage u.sub.blo(n) which corresponds to the
desired pumping rate and which is proportional to
q.sub.blo.sup.*(n). The actual flow q.sub.blo(n) measure by the
flow probe 27 is provided as a feedback signal via line 29 to the
supervisory controller 160 and to the pump controller 162. The pump
controller 162 further provides a controller parameter vector
.theta..sub.blo, indicative of the tracking performance, to the
supervisory controller 160.
[0084] Drain pump 66 is controlled by an adaptive pump controller
170, implemented in the controller 12, which receives a desired
weight signal .omega..sub.dra.sup.*(n) calculated by the
supervisory controller 160 as a reference command input. The pump
controller 170 is operably connected to the drain pump 66 via line
68 for transmitting a voltage u.sub.dra(n) which corresponds to the
desired pumping rate and is proportional to the rate change of
.omega..sub.dra.sup.*(n). The actual weight .omega..sub.dra(n)
measured by the scale 78 is provided as a feedback signal via line
80 to the supervisory controller 160 and to the pump controller
170. The pump controller 170 further provides a controller
parameter vector .theta..sub.dra, indicative of the tracking
performance, to the supervisory controller 160.
[0085] Bicarbonate replacement pump 60a and calcium replacement
pump 60b are controlled by a respective adaptive pump controller
180a, 180b, both implemented in the controller 12, which receives a
desired weight signal .omega..sub.rep1.sup.*(n),
.omega..sub.rep2.sup.*(n) calculated by the supervisory controller
160 as a reference command input. The pump controller 162 is
operably connected via a respective line 62a, 62b (similar to line
62 shown in FIG. 2) to the respective pump 60a, 60b for
transmitting a respective voltage u.sub.rep1(n), u.sub.rep2(n)
which corresponds to the desired pumping rate and is proportional
to the rate change of .omega..sub.rep1.sup.*(n),
.omega..sub.rep2.sup.*(n), respectively. The actual weight
.omega..sub.rep1(n), .omega..sub.rep2(n) measured by the respective
scale 54a, 54b is provided as a feedback signal via line 56a, 56b,
respectively, to the supervisory controller 160 and to the
respective pump controller 180a, 180b. Each pump controller 180a,
180b further provides a respective controller parameter vector
.theta..sub.rep1, .theta..sub.rep2 indicative of the tracking
performance between desired and actual flow rates, to the
supervisory controller 160.
[0086] The supervisory controller 160 uses a parameter projection
feature to remove an input saturation nonlinearity, such that the
pumps 16, 60a, 60b, 66 can each be viewed as a linear system. The
adaptation of the controller parameters enables enhanced tracking
of the pump controllers 162, 170, 180a, 180b in the presence of
time variations in flow due to, for example, changes in tubing
diameters and wear, changes in hemofilter characteristics, or
changes in flow resistance in the blood line.
[0087] If the respective applied voltage u.sub.dra(n),
u.sub.rep1(n), u.sub.rep2(n) is limited to the linear regime of
pump operation, the replacement pumps 60a, 60b and the drain pump
66 are each adequately modeled by a time-varying auto-regressive
moving average (ARMA) adaptive control algorithm. The adaptive
control algorithm can be expressed as:
.omega.(n)-b.sub.1.sup.*(n-1).omega.(n-1)+b.sub.2.sup.*(n-1).omega.(n-2)=a-
.sub.0.sup.*(n-1)+a.sub.1.sup.*(n-1)u(n-1)
[0088] that relates the actual weights .omega..sub.dra(n),
.omega..sub.rep1(n), .omega..sub.rep2(n) and the corresponding
applied voltages u.sub.dra(n), u.sub.rep1(n), u.sub.rep2(n). A
unique set of respective system parameters a.sub.0.sup.*,
a.sub.1.sup.*, b .sub.1.sup.*, b.sub.2.sup.* is ascribed to each
pump 60a, 60b, 66. The system parameters a.sub.0.sup.*,
a.sub.1.sup.*, b.sub.1.sup.*, b.sub.2.sup.* are unknown
time-varying parameters assumed to vary slowly in the absence of
disturbances and a.sub.1.sup.* is assumed to be positive since the
pump motor never turns the rollers in a reverse direction. The bias
parameter a.sub.0.sup.* is included in the equation because it is
possible for a pump to induce no fluid flow for a non-zero
voltage.
[0089] Employing a direct adaptive control scheme, designed to
track the desired weight signal .omega..sup.*(n), the control
voltage is determined from:
u(n-1)=.theta..sup.T(n-1).phi.(n-1)
.theta..sup.T(n-1):=[.theta..sub.1(n-1).theta..sub.2(n-1).theta..sub.3(n-1-
).theta..sub.4(n-1)]
.theta..sup.T(n-1):=[1-.omega.(n-1)-.omega.(n-2).omega..sup.*(n)],
[0090] where .theta.(n) is a vector whose components are the
controller parameters generated by an adaptive law and .phi.(n) is
a regressor vector, where .vertline..phi.(n).vertline..gtoreq.1 for
all n.gtoreq.0. If e(n):=.omega.(n)-.omega..sup.*(n) denotes the
tracking error for the accumulated fluid weight, then the tracking
error satisfies:
e(n)=a.sub.1.sup.*(.theta.(n-1)-.theta..sup.*).sup.T.phi.(n-1),
[0091] where .theta..sup.* represents the unknown "optimal"
parameter vector 1 * = 1 a 1 * [ - a 0 * - b 1 * - b 2 * 1 ] T
[0092] Although the dependence of .theta..sup.* on sample time n is
not explicit, .theta..sup.* will vary slowly with time, which is
one of the main motivations for the utilization of on-line
parameter estimation and adaptive control techniques. In general,
the derivation of provably stable adaptive control algorithms for
linear time-varying systems is complex. Due to the slowly
time-varying nature of the pump dynamics, standard adaptive control
methods with .theta..sup.* constant were found to be satisfactory
for the present invention.
[0093] Pumps in an ultrafiltration system typically exhibit
saturation behavior at the lower and upper end of the operation.
Specifically, below a certain voltage level the rollers of the pump
cease to rotate and fluid flow ceases. Similarly, there is a
maximum allowable control voltage, typically specified by the pump
manufacturer. Due to saturation in the control signal for pumps,
the standard adaptive control must be modified such that the
inequality u.sub.1 .ltoreq..theta..sup.T(n).phi.(n).ltoreq.-
u.sub.h holds, where the positive constants u.sub.1 and u.sub.h
are, respectively, the minimum and maximum allowable control
voltages. To address the time-varying parametric uncertainty and
input saturations, the following normalized gradient adaptive law
with planar projections apply: 2 ( n ) = ( n - 1 ) - 0 e ( n ) ( n
- 1 ) 2 ( n - 1 ) - p ( n ) p ( n ) := I ( T ( n ) ( n - 1 ) , u l
) [ T ( n ) ( n - 1 ) - u l ( n - 1 ) 2 ] ( n - 1 ) + I ( u h , T (
n ) ( n - 1 ) ) [ T ( n ) ( n - 1 ) - u h ( n - 1 ) 2 ] ( n - 1 ) (
n ) := ( n - 1 ) - 0 e ( n ) ( n - 1 ) 2 ( n - 1 )
[0094] where adaptive step-size .gamma..sub.0 is chosen such that
it satisfies
0<.gamma..sub.0<2[sup.sub.na.sub.1.sup.*(n)].sup.-1, where an
upper bound of a.sub.1.sup.* is assumed to be known. The indicator
function I(.,.) is defined as: 3 I ( x 1 , x 2 ) := { 1 if x 1 <
x 2 0 otherwise
[0095] The projection term p(n) guarantees that the controller
parameters .theta.(n) will be projected onto the hyperplane
.theta..sup.T.phi.(n-1)-- u.sub.1=0 if
.mu..sup.T(n).phi.(n-1)<u.sub.1. Similarly, the controller
parameters .theta.(n) will be projected onto the hyperplane
.theta..sup.T.phi.(n-1)-u.sub.h=0 if .mu..sup.T(n)
.phi.(n-1)>u.sub.h. Thus the parameter estimates .theta.(n) are
adapted such that the control voltage is restricted to a value
between u.sub.1 and u.sub.h.
[0096] If the applied voltage u.sub.blo(n) is limited to the linear
regime of pump operation, the blood pump 16 is adequately modeled
by on ARMA adaptive control algorithm, that may be expressed
as:
q.sub.blo(n)+b.sub.1.sup.blo(n-1)q.sub.blo(n-1)=a.sub.0.sup.blo(n-1)+a.sub-
.1.sup.blo(n-1)u.sub.blo(n-1).
[0097] that relates the actual flow q.sub.blo(n) and the applied
voltage u.sub.blo(n) at the n.sup.th sample time. The system
parameters a.sub.0.sup.blo, a .sub.1.sup.blo, b.sub.1.sup.blo are
assumed to vary slowly over time in the absence of disturbances and
a.sub.1.sup.blo is assumed to be positive.
[0098] A minimum applied voltage is chosen as a value slightly
above the voltage for which the rollers of the blood pump 16 can
overcome friction and rotate. If the applied voltage never falls
below the minimum voltage, the blood flow is never static during
the ultrafiltration procedure and the possibility of clotting is
reduced. The minimum voltage will depend upon the properties of the
tubing used. A typical minimum voltage is 0.3 volts. A maximum
voltage will be provided by the pump manufacturer. A typical
maximum voltage is 3.2 volts.
[0099] The control law is expressed by
u.sub.blo(n)=.theta..sub.blo.sup.T(- n).phi..sub.blo(n), where
.theta..sub.blo(n) is a vector consisting of the three controller
parameters, as known for a direct adaptive control scheme, and
.phi..sub.blo(n) is given by:
.phi..sub.blo.sup.T(n-1)=[1-q.sub.blo(n-1)q.sub.blo.sup.*(n)].
[0100] The desired fluid flow q.sub.blo.sup.*(n) is the output of a
low-pass filter 4 L blo ( z ) = 0.2514 z + 0.99 z - 0.5
[0101] which provides a smooth response to required changes in the
desired flow rate. For example, the blood pump 16 start-up will be
smooth so that the catheter will not draw against the vessel
wall.
[0102] FIG. 4 generically illustrates the fuzzy logic process that
may be implemented in a microprocessor, such as by supervisory
controller 160 implemented in computer controller 12, for
decision-making to control a process, such as an ultrafiltration
procedure. As is familiar from fuzzy logic theory, a fuzzy logic
control system 190 generally comprises a fuzzifier 192, an
inference engine 194, and a defuzzifier 196 for controlling a plant
198. The fuzzifier 192 accepts one or more discrete input data
signals 200 and forms a fuzzy set by assigning degrees of
membership in a set of input membership functions. The inference
engine 194 makes one or more fuzzy inferences from the input
signals 200 based on a fuzzy rule base 202. The defuzzifier 196
defuzzifies the fuzzy inferences based upon a set of output
membership functions and provides a discrete output control signal
204 to the plant 198. The fuzzy rule base 202 comprises expert
knowledge regarding the operational protocol of the system being
controlled and comprises sets of "if-then" rules for controlling
the plant 198. The defuzzifier 196 may apply various mathematical
techniques known in the art of fuzzy logic to defuzzify the fuzzy
inferences. The plant 198 may supply feedback signals 206, relating
to performance of the plant 198, to the fuzzy logic control system
190 for use by the inference engine 194.
[0103] Fuzzification and defuzzification compose the interface
needed between measured physical quantities (inputs 200 and outputs
204) and the fuzzy inference engine 194. The resulting mathematical
relation is a fuzzy system. The fuzzy system accepts as inputs
crisp values, forms fuzzy sets from these values, makes an
inference from the specified rule base 202, and provides a crisp
output by defuzzifying the inferred fuzzy output.
[0104] In the present invention, the plant 168 is the
hemofiltration system 10, the fuzzy logic control system 190 is
implemented by software in the computer controller 12 for
controlling the pumps 16, 60a, 60b, 66, and the input data signals
200 are the patient heart rate 120 and the patient blood pressure
130. The patient heart rate 120 is typically measured in beats per
minute (bpm) and the patient blood pressure 130 is typically
measured in millimeters of mercury (mmHg). Relying upon the expert
clinical knowledge of a physician, an exemplary fuzzy rule base 202
for modifying the ultrafiltration rate based upon the heart rate
120 (R.sub.h) and the blood pressure 130 (P.sub.b) has the
following set of Supervisory Rules:
[0105] Supervisory Rule (1): If R.sub.h is high and P.sub.b is
normal or low, then decrease ultrafiltration. Wait 10 minutes.
[0106] Supervisory Rule (2): If P.sub.b is low and R.sub.h is
normal or high, then decrease ultrafiltration. Wait 10 minutes.
[0107] Supervisory Rule (3): If both P.sub.b and R.sub.h are low
then provide the user with a choice between a decrease or increase
of the ultrafiltration rate. Wait 5 minutes.
[0108] Supervisory Rule (4): If both P.sub.b and R.sub.h are high
for 30 consecutive minutes, then provide the user with a choice
between a decrease or increase of the ultrafiltration rate.
[0109] Supervisory Rule (5): If P.sub.b is high and R.sub.h is low
for 60 consecutive minutes, then increase ultrafiltration.
[0110] Supervisory Rule (6): The lowest possible value of
ultrafiltration is 0 ml./hr. The highest possible value of the
ultrafiltration rate is 30% above that of the ultrafiltration rate
specified by the physician, and can thus be changed during the
ultrafiltration procedure if so desired.
[0111] Supervisory Rule (7): If an increase in ultrafiltration
occurs such that the filtered fraction (proportional to the ratio
of the desired drained rate to the desired blood flow rate) is
greater than 20%, increase the blood pump flow such that the
filtered fraction equals 0.2.
[0112] Supervisory Rules 1-5 were implemented using fuzzy logic
techniques while Supervisory Rules 6 and 7 were incorporated into
the supervisory algorithm based on standard switching (crisp) logic
methods. The instructions to wait in Supervisory Rules 1-5 are
local to each rule. For example, if the ultrafiltration is
decreased because Supervisory Rule 1 is satisfied, Supervisory Rule
1 cannot operate again until 10 minutes have lapsed. However, the
ultrafiltration rate may be modified if one of Supervisory Rules
2-7 is subsequently triggered. Other sets of Supervisory Rules
would be apparent to one of ordinary skill in the art and the
Supervisory Rules may be so varied without departing from the scope
and spirit of the present invention. For example, a
time-independent set of Supervisory Rules is formulated below.
[0113] High and low thresholds of heart rate (R.sub.high,
R.sub.low) and blood pressure (P.sub.high, P.sub.low) are specified
to the supervisory controller 160 based on the size and
cardiovascular state of the patient. These thresholds are used by
the supervisory controller 160 to characterize the magnitudes of
the heart rate 120 and the blood pressure 130 according to the
following inequalities. If R.sub.low<R.sub.h<R- .sub.high,
then the heart rate 120 is deemed normal. If R.sub.low>R.sub.h,
then the heart rate 120 is characterized as being low, and if
R.sub.h>R.sub.high then the heart rate 120 is high. Similar
inequalities apply to characterize the blood pressure 130. The
thresholds may be changed during the ultrafiltration procedure to
respond to changes in the patient's cardiovascular state.
[0114] FIG. 5 diagrammatically illustrates the supervisory
controller 160 according to the principles of the present invention
in which time has been eliminated as an input parameter. The
supervisory controller 160 comprises four separate fuzzy systems
210, 220, 230, 240 that a switch logic 250 activates based upon
whether the heart rate 120 and blood pressure 130 are low, normal,
or high. Only one of the fuzzy systems 210, 220, 230, 240 may be
active at a given time. The switch logic 250 also performs the
operation of waiting the required duration before or after a
supervisory adjustment to the ultrafiltration as required by the
Supervisor Rules.
[0115] FIGS. 6A and 6B are two sets of input membership functions
defined for the input data signals of heart rate 120 and blood
pressure 130, respectively, provided to the supervisory controller
160. FIG. 6C is a set of output membership functions defined for
the output data signal connoting the change 135 in ultrafiltration
rate for use in defuzzifying the fuzzy inferences made by fuzzy
systems 210, 220, 230, 240. Points on each membership function
represent the degree of confidence, ranging between 0 and 1, that
any single input data signal 120, 130 or output control signal 135
belongs to a particular fuzzy region. Due to overlaps, one input
data signal 120, 130 or output data signal 135 may belong to more
than one membership function. The membership functions may be
varied to have differing gradations as understood by one of
ordinary skill in the art of fuzzy logic.
[0116] Each individual input membership function and output
membership function is defined as a distinct curve having a center
and a full-width. In the example of this description, individual
membership functions are chosen from curves having characteristic
shapes such as a triangular (T) function, a right trapezoidal (RT)
function, a left trapezoidal (LT) function, or a constant value (C)
function. Alternative characteristic shapes could be selected
depending upon the desired response without departing from the
spirit and scope of the present invention.
[0117] With reference to FIGS. 6A-C, Table 1 summarizes the input
and output membership functions for the following universe of
discourse:
U.sub.1=(-.infin.,R.sub.h.sup.low]U.sub.2=(R.sub.h.sup.low,R.sub.h.sup.hig-
h)U.sub.3=[R.sub.h.sup.high,+.infin.)
V.sub.1=(-.infin.,P.sub.b.sup.low]V.sub.2=(P.sub.b.sup.low,P.sub.b.sup.hig-
h)V.sub.3=[P.sub.b.sup.high,+.infin.)
Y.sub.1=(-0.2q.sub.ult.sup.*-0.05
q.sub.ult.sup.*Y.sub.2=(+0.05q.sub.ult.s-
up.*+0.2q.sub.ult.sup.*]
[0118] where q.sub.ult.sup.*(n) is the desired ultrafiltration rate
at the time the supervisory controller 160 is activated.
1TABLE 1 Name Defined in Type Centroid Width
.mu..sub.11.sup.u(R.sub.h) U.sub.1 RT 0.85 R.sub.h.sup.low 0.15
R.sub.h.sup.low .mu..sub.12.sup.u(R.sub.h) U.sub.1 T 0.925
R.sub.h.sup.low 0.15 R.sub.h.sup.low .mu..sub.13.sup.u(R.sub.h)
U.sub.1 T R.sub.h.sup.low 0.15 R.sub.h.sup.low
.mu..sub.2.sup.u(R.sub.h) U.sub.2 C 1/2 (R.sub.h.sup.high -
R.sub.h.sup.low) (R.sub.h.sup.high - R.sub.h.sup.low)
.mu..sub.31.sup.u(R.sub.h) U.sub.3 T R.sub.h.sup.high 0.15
R.sub.h.sup.high .mu..sub.32.sup.u(R.sub.h) U.sub.3 T 0.925
R.sub.h.sup.high 0.15 R.sub.h.sup.high .mu..sub.33.sup.u(R.sub.h)
U.sub.3 LT 0.85 R.sub.h.sup.high 0.15 R.sub.h.sup.high
.mu..sub.11.sup.v(P.sub.b) V.sub.1 RT 0.85 P.sub.b.sup.low 0.15
P.sub.b.sup.low .mu..sub.12.sup.v(P.sub.b) V.sub.1 T 0.925
P.sub.b.sup.low 0.15 P.sub.b.sup.low .mu..sub.13.sup.v(P.sub.b)
V.sub.1 T P.sub.b.sup.low 0.15 P.sub.b.sup.low
.mu..sub.2.sup.v(P.sub.b) V.sub.2 C 1/2 (P.sub.b.sup.high -
P.sub.b.sup.low) P.sub.b.sup.high - P.sub.b.sup.low
.mu..sub.31.sup.v(P.sub.b) V.sub.3 T P.sub.b.sup.high 0.15
P.sub.b.sup.high .mu..sub.32.sup.v(P.sub.b) V.sub.3 T 0.925
P.sub.b.sup.high 0.15 P.sub.b.sup.high .mu..sub.33.sup.v(P.sub.b)
V.sub.3 LT 0.85 P.sub.b.sup.high 0.15 P.sub.b.sup.high
.mu..sub.11.sup.y(.DELTA.) Y.sub.1 T -0.2q.sub.ult* 0.15q.sub.ult*
.mu..sub.12.sup.y(.DELTA.) Y.sub.1 T -0.125q.sub.ult*
0.15q.sub.ult* .mu..sub.13.sup.y(.DELTA.) Y.sub.1 T -0.05q.sub.ult*
0.15q.sub.ult* .mu..sub.21.sup.y(.DELTA.) Y.sub.2 T 0.05q.sub.ult*
0.15q.sub.ult* .mu..sub.22.sup.y(.DELTA.) Y.sub.2 T 0.125q.sub.ult*
0.15q.sub.ult* .mu..sub.23.sup.y(.DELTA.) Y.sub.2 T 0.2q.sub.ult*
0.15q.sub.ult*
[0119] The inputs to the fuzzy systems are the patient heart rate
and blood pressure. The output of each fuzzy system 210, 220, 230,
240 is derived by combining the singleton fuzzifier, the fuzzy
inferences from each invoked rule, and the center-averarge
defuzzifier. The output of the fuzzy systems, .DELTA.(n), is a
recommended change 135 to the ultrafiltration rate. The change is
implemented by keeping the replacement fluid flows constant and
adding .DELTA.(n) to the drain flow rate. That is, once a change in
ultrafiltration .DELTA.(n) is calculated at sample time n, it is
applied as follows:
q.sub.rep1.sup.*(n+1)=q.sub.rep1.sup.*(n)
q.sub.rep2.sup.*(n+1)=q.sub.rep2.sup.*(n)
q.sub.dra.sup.*(n+1)=q.sub.dra.sup.*(n)+.DELTA.(n)
q.sub.ult.sup.*(n+1)=q.sub.dra.sup.*(n+1)-q.sub.rep1.sup.*(n+1)-
q.sub.rep2.sup.*(n+1),
[0120] resulting in an ultrafiltration rate changed by .DELTA.(n)
between sample time n and sample time n+1. The output membership
functions may change from sample time to sample time because they
are dependent on q.sub.ult.sup.*(n), and thus the fuzzy system
mappings built upon these may also change. This feature was
designed such that the ultrafiltration system may be used for any
size patient. For example, a neonate requires much smaller changes
in flow rates than an adult, a fact reflected by the width of some
membership functions being dependent upon the desired
ultrafiltration rate.
[0121] Fuzzy system 210 (FSI) applies where the heart rate 120 is
high and/or the blood pressure 130 is low, as defined in
Supervisory Rules 1 and 2, to output a negative number to add to
the ultrafiltration rate. Fuzzy system 210 comprises three fuzzy
subsystems 210a, 210b, 210c (FSIA, FSIB, FSIC). The switch logic
250 activates fuzzy system 210 if the heart rate 120 is high and
the blood pressure 130 is high or low, or if the heart rate 120 is
high or low and the blood pressure 130 is low. The switch logic 250
also disables the selection of fuzzy system 210 for 10 minutes and
chooses which fuzzy subsystem 210a, 210b, 210c will calculate the
decrease in the drain flow rate.
[0122] The switch logic 250 activates fuzzy subsystem 210a if
R.sub.h is high and p.sub.b is normal. The fuzzy rule base for
fuzzy subsystem 210a is:
[0123] FSIA Rule (1): If R.sub.h is .mu..sub.31.sup.u then .DELTA.
is .mu..sub.13.sup.y.
[0124] FSIA Rule (2): If R.sub.h is .mu..sub.32.sup.u then .DELTA.
is .mu..sub.12.sup.y.
[0125] FSIA Rule (3): If R.sub.h is .mu..sub.33.sup.u then .DELTA.
is .mu..sub.11.sup.y.
[0126] The switch logic 250 activates fuzzy subsystem 210b if
R.sub.h is normal and P.sub.b is high. The fuzzy rule base for
fuzzy subsystem 210b is:
[0127] FSIB Rule (1): If P.sub.b is .mu..sub.11.sup.v then .DELTA.
is .mu..sub.11.sup.y.
[0128] FSIB Rule (2): If P.sub.b is .mu..sub.22.sup.v then .DELTA.
is .mu..sub.12.sup.y.
[0129] FSIB Rule (3): If P.sub.b is .mu..sub.33.sup.v then .DELTA.
is .mu..sub.13.sup.y.
[0130] The switch logic 250 activates subsystem fuzzy subsystem
210c if R.sub.h is high and P.sub.b is low. The fuzzy rule base for
fuzzy subsystem 210c is:
[0131] FSIC Rule (1, 1): If P.sub.b is .mu..sub.11.sup.v and
R.sub.h is .mu..sub.31.sup.u then .DELTA. is .mu..sub.11.sup.y.
[0132] FSIC Rule (1, 2): If P.sub.b is .mu..sub.11.sup.v and
R.sub.h is .mu..sub.32.sup.u then .DELTA. is .mu..sub.11.sup.y.
[0133] FSIC Rule (1,3): If P.sub.b is .mu..sub.11.sup.v and R.sub.h
is .mu..sub.33.sup.u then .DELTA. is .mu..sub.11.sup.y.
[0134] FSIC Rule (2,1): If P.sub.b is .mu..sub.12.sup.v and R.sub.h
is .mu..sub.31.sup.u then .DELTA. is .mu..sub.12.sup.y.
[0135] FSIC Rule (2,2): If P.sub.b is .mu..sub.12.sup.v and R.sub.h
is .mu..sub.32.sup.u then .DELTA. is .mu..sub.12.sup.y.
[0136] FSIC Rule (2,3): If P.sub.b is .mu..sub.12.sup.v and R.sub.h
is .mu..sub.33.sup.u then .DELTA. is .mu..sub.11.sup.y.
[0137] FSIC Rule (3,1): If P.sub.b is .mu..sub.13.sup.v and R.sub.h
is .mu..sub.31.sup.u then .DELTA. is .mu..sub.13.sup.y.
[0138] FSIC Rule (3,2): If P.sub.b is .mu..sub.13.sup.v and R.sub.h
is .mu..sub.32.sup.u then .DELTA. is .mu..sub.12.sup.y.
[0139] FSIC Rule (3,3): If P.sub.b is .mu..sub.13.sup.v and R.sub.h
is .mu..sub.33.sup.u then .DELTA. is .mu..sub.11.sup.y.
[0140] The switch logic 250 activates fuzzy system 220 (FSII) if
the heart rate 120 and blood pressure 130 are low, as defined in
Supervisory Rule 3, to calculate the change 135 in ultrafiltration
rate and disables fuzzy system 220 for 10 minutes. Fuzzy system 220
comprises two fuzzy subsystems 220a, 220b (FSIIA, FSIIB). Since the
direction of the change 135 in ultrafiltration rate is
indeterminate, the switch logic 250 must query the user whether the
ultrafiltration rate should be increased or decreased. The user
selects fuzzy subsystem 220a to increase the ultrafiltration rate.
The fuzzy rule base for fuzzy subsystem 220a is:
[0141] Rule (1): If R.sub.h is .mu..sub.11.sup.u then .DELTA. is
.mu..sub.23.sup.y.
[0142] Rule (2): If R.sub.h is .mu..sub.12.sup.u then .DELTA. is
.mu..sub.22.sup.y.
[0143] Rule (3): If R.sub.h is .mu..sub.13.sup.u then .DELTA. is
.mu..sub.21.sup.y.
[0144] Alternatively, the user selects fuzzy subsystem 220b to
decrease the ultrafiltration rate. The fuzzy rule base for fuzzy
subsystem 220b is:
[0145] Rule (1): If P.sub.b is .mu..sub.11.sup.v then .DELTA. is
.mu..sub.11.sup.y.
[0146] Rule (2): If P.sub.b is .mu..sub.12.sup.v then .DELTA. is
.mu..sub.12.sup.y.
[0147] Rule (3): If P.sub.b is .mu..sub.13.sup.v then .DELTA. is
.mu..sub.13.sup.y.
[0148] The switch logic 250 activates fuzzy system 230 (FSIII) if
the heart rate 120 and blood pressure 130 are both high for 30
consecutive minutes, as defined in Supervisor Rule 4, to calculate
the change 135 in ultrafiltration rate. Fuzzy system 230 comprises
two fuzzy subsystems 230a, 230b (FSIIIA, FSIIIB). Since the
direction of the change 135 in ultrafiltration rate is
indeterminate, the user is queried whether the ultrafiltration rate
should be increased or decreased. The user manually selects fuzzy
subsystem 230a to decrease the ultrafiltration rate. The fuzzy rule
base for fuzzy subsystem 230a is:
[0149] Rule (1): If P.sub.b is .mu..sub.31.sup.v then .DELTA. is
.mu..sub.21.sup.y.
[0150] Rule (2): If P.sub.b is .mu..sub.32.sup.v then .DELTA. is
.mu..sub.22.sup.y.
[0151] Rule (3): If P.sub.b is .mu..sub.33.sup.v then .DELTA. is
.mu..sub.23.sup.y.
[0152] The user selects fuzzy subsystem 230b to increase the
ultrafiltration rate. The fuzzy rule base for fuzzy subsystem 230b
is:
[0153] Rule (1): If R.sub.h is .mu..sub.31.sup.u then .DELTA. is
.mu..sub.13.sup.y.
[0154] Rule (2): If R.sub.h is .mu..sub.32.sup.u then .DELTA. is
.mu..sub.12.sup.y.
[0155] Rule (3): If R.sub.h is .mu..sub.33.sup.u then .DELTA. is
.mu..sub.11.sup.y.
[0156] Finally, fuzzy system 230 (FS IV) calculates increases in
ultrafiltration rate as a consequence of improvement in the
patient's condition. The switch logic activates fuzzy system 240 if
R.sub.h is low and P.sub.b is high. The fuzzy rule base for fuzzy
subsystem 240 is:
[0157] Rule (1): If P.sub.b is .mu..sub.31.sup.v then .DELTA. is
.mu..sub.21.sup.y.
[0158] Rule (2): If P.sub.b is .mu..sub.32.sup.v then .DELTA. is
.mu..sub.22.sup.y.
[0159] Rule (3): If P.sub.b is .mu..sub.33.sup.v then .DELTA. is
.mu..sub.23.sup.y.
[0160] The supervisory controller 160 also adjusts the filtered
fraction such that the filtered fraction is always less than or
equal to 20%, as prescribed by Supervisory Rule 7.
[0161] In another aspect, the supervisory control system 160 also
validates the measured flow rates by comparing those flow rates
with prediction errors based on the pump model. The supervisory
control system 180 must ignore inaccurate fluid weight
measurements, which are the result of, for example, inadvertent
bumps to the electronic scales 54, 78, while accurately detecting
significant leaks in the fluid pathways or a disconnected tubing.
In the latter instances, the supervisory control system 160 halts
the ultrafiltration procedure and triggers audible and visual
alarms.
[0162] The prediction error for the drain pump 66 and the infusate
pump 60 is defined as the difference in the measured accumulated
fluid weight and the predicted weight forecast by the pump model.
The tracking error is defined as the difference in the predicted
fluid weight and the desired fluid weight. For the blood pump 16,
fluid flow rates are measured by flow probe 27 and the prediction
error and the tracking error are referenced with respect to fluid
flow rate.
[0163] If, for a given minimum number of consecutive sample
periods, the prediction error is greater than a positive constant
provided by the pump model and the tracking error is greater than a
second positive constant also provided by the pump model, the
supervisory controller 160 triggers a supervisory action. If only
the prediction error or only the tracking error is large, the
parameter estimates by the supervisory controller 160 are not yet
tuned to the hemofiltration system 10. If both errors are large and
are of the same sign, the pumps 16, 60a, 60b, 66 of the
hemofiltration system 10 are halted. If the prediction error and
the tracking error are large and of opposite sign, the parameter
estimates by the supervisory controller 160 are marginally tuned to
the undisturbed hemofiltration system 10, and either an inaccurate
measurement or a sudden drastic change in the dynamics of the
hemofiltration system 10 has likely occurred. A drastic change in
the pump dynamics can only be caused by a significant system fault
such as a tubing leak. If an inconsistent weight or flow is sensed
for any pump 16, 60a, 60b, 66 for more than a predetermined number
of consecutive samples, the supervisory controller 160 disables the
hemofiltration system 10 and triggers audible and visual
alarms.
[0164] Implementation of either or both of the aforementioned
adaptive control or supervisory control can increase the autonomy
of a hemofiltration system. Various advantages follow from the
enhanced autonomy. For example, the continuous monitoring and
control reduces medical costs and improves the quality of medical
care by reducing the need for intermittent supervision of the
ultrafiltration procedure by clinical staff. Further details of the
invention will be described in the following examples.
[0165] The following examples are simulated ultrafiltration
procedures performed with an ultrafiltration system having adaptive
controll and supervisory controll, as described above, wherein
either tap water or expired blood functioned as a virtual patient.
Since the pump model utilized is based on actual fluid weights or
flows and not from pump roller angular speeds, the control
performance is independent of the fluid's rheology. While the range
of achievable flows may change, the type of fluid used for the
simulations is irrelevant from the point of view of flow
tracking.
[0166] A sampling period of n=1.75 seconds was used in these
examples. This specific sampling period was selected after some
initial experimentation, taking into consideration the fact that
the instantaneous pump flow is impulsive and only the average flow
is of interest. Too small a sampling period may give large
variations in flow from sample to sample, resulting in a control
signal that varies too rapidly, causing a non-smooth operation. On
the other hand, a sampling time of more than a few seconds may
result in slow response and large tracking errors.
[0167] At the beginning of the simulation in each example, all
tubing segments were primed with water, or 150 mEq/L sodium
chloride solution if blood is used in the example, to eliminate air
bubbles in the lines. A source of measurement noise for the drained
weight is the evaporation of drained fluid, which can be prevented
by sealing the drain container. Other sources of measurement noise
include the swinging of replacement fluid bags due to air drafts,
which introduces uncertainty in the weight measurements. Placing
the bags and the scales inside an enclosure minimizes this
uncertainty and enables the practical use of the scales' accuracy
(.+-.0.5 gr) as the sole source of uncertainty in the weight
measurements. Flow measurements are taken by an ultrasonic
flow-probe (Transonic Systems, Inc.) which is calibrated by the
manufacturer for the fluid being used. The accuracy of the
flow-probe is .+-.7% of the measured value, which is a source of
blood flow error but not of ultrafiltration error.
[0168] The simulation flow rates for the blood, drain, and
replacement pumps are chosen to be consistent with those typically
used with a neonate as the patient. Ultrafiltration is beneficial
to smaller patients if small flow rates and a small extracorporeal
blood line volume are used. The type and size of tubing and
connectors for the blood line are chosen according to the magnitude
of the flow rates needed. These components determine the ARMA
equation parameters for each pump, which in general will vary in
time as the physical characteristics of the components vary over
time. Values of adaptive step-size .gamma..sub.0, maximum voltage
u.sub.h, and minimum voltage u.sub.1, for purposes of the
simulations in the example, are given in Table 2.
2 TABLE 2 Pump .gamma..sub.0 u.sub.l [volts] u.sub.h [volts] Drain
0.1 0.6 10.0 Replacement 1 0.1 0.2 10.0 Replacement 2 0.1 0.4 5.0
Blood -- 0.3 3.2
EXAMPLE 1
[0169] For a ultrafiltration procedure simulated with a container
full of blood as the "patient", the tracking error, the control
voltage and the controller parameters are shown in FIGS. 7A, 7B,
and 7C, respectively. The tracking error goes to zero within thirty
seconds, while the voltage remains steady. A large negative blood
pump tracking error at the beginning of the ultrafiltration
procedure is tolerated because the patient will not be adversely
affected by a slow blood clearance of a few seconds. A large
positive tracking error could result in decreased tissue perfusion,
and the patient may or may not react adversely to the decrease of
nutrients reaching various tissues. Hence, a transiently large
negative error at the beginning of the ultrafiltration procedure is
tolerated in exchange for preventing tracking overshoot.
EXAMPLE 2
[0170] A ultrafiltration procedure lasting approximately one hour,
with the blood flow rate set at 40.0 ml/min, the drain flow rate
set to 230.0 ml/hr, and both replacement flow rates set to 100.0
ml/hr simulates an ultrafiltration procedure performed on a
neonate. Typical flow rate and weight tracking errors of a
simulation utilizing water as a substitute for all fluids are shown
in FIGS. 8A, 8B, 8C and 8D. The blood pump tracking error at the
beginning of this simulation differs in character from the
beginning of the simulation shown in FIGS. 7A-7C because the
flowmeter low pass filter choices provided by the manufacturer were
not identical for this time period in the two simulations. Given
the precise duration of the procedure, the expected ultrafiltration
was 30.1 ml. The ultrafiltration measured by comparing the initial
(269.3.+-.0.5 gr) and final weight (241.0 .+-.0.5 gr) of the
"patient" was 28.3.+-.0.7 gr, which results in a difference of
1.7.+-.0.7 ml from the desired ultrafiltration. The expected
ultrafiltration measured by comparing the initial and final weights
of drain and replacement fluids was 28.4.+-.1.2 ml. The expected
ultrafiltration rate is calculated from the initial weights for the
drain and replacement containers 0.0.+-.0.5 gr, 345.2.+-.0.5 gr,
and 341.3.+-.0.5 gr, respectively, and the corresponding final
weights 230.5.+-.0.5 gr, 243.4.+-.0.5 gr, and 241.0.+-.0.5 gr,
respectively, as
[(230.5.+-.0.5)-(0.0.+-.0.5)]-[345.2.+-.0.5)-(243.4.+-.0- .5)
]-[341.3.+-.0.5 ) -(241.0.+-.0.5)]=28.4.+-.1.2 gr.
EXAMPLE 3
[0171] FIGS. 9A, 9B, and 9C present a simulation where the scale is
bumped twice and a tubing leak occurs. Threshold values for
determining an incongruent weight change are given in Table 3.
3TABLE 3 Minimum No. of Samples for Maximum Validating An Tracking
Maximum Incongruent Pump Error Prediction Error Measurement of Flow
Blood 20 ml/min 20 ml/min 5 Drain 3 gr 3 gr 5 Replacement 1 3 gr 3
gr 5 Replacement 2 3 gr 3 gr 5
[0172] A brief disturbance of a large magnitude is introduced at a
n=10 (by placing a large weight on the scale and removing it), and
the supervisory controller does not react. At n=60, a similar,
smaller disturbance is introduced for a brief period, and again,
the supervisory controller does not respond. At n=90, a similar
small disturbance is introduced, but for a prolonged period. This
simulates a leak in the tubing, and is a much smaller disturbance
than is generally encountered when leaks occur during actual
ultrafiltration procedures. The controller detects the incongruent
weight change and decides, in this case, to discontinue
ultrafiltration.
EXAMPLE 4
[0173] FIGS. 10A, 10B, and 10C show simulated patient data and the
desired drain rate for a simulation of ultrafiltration performed on
a neonate. The patient heart rate and blood pressure are generated
with computer software. The blood flow rate is set to 40 ml/min,
and the replacement rates are both set to 100 ml/min. The
thresholds for the heart rate are chosen as 90 bpm and 105 bpm, and
the thresholds for the blood pressure are chosen as 70 mmHg and 95
mmHg. At the beginning of the simulation, R.sub.h and P.sub.b are
within their normal ranges. Around n=40, R.sub.h rises to above the
threshold while P.sub.b stays normal. The supervisory controller
makes a correction due to the high heart rate and waits for a
reaction. During an actual ultrafiltration procedure, the
supervisory controller would wait about 10 minutes before taking
any other actions because of a high heart rate. For purposes of the
simulation, the wait is shortened to about 30 seconds. The switch
logic once again activates FSIA 30 seconds after the first
correction since the patient's heart rate remains high. The
supervisory controller waits 30 more seconds, and the switch logic
rechecks R.sub.h and P.sub.b. This time, the heart rate is high and
the blood pressure is low, so the switch logic activates FSIC. The
fuzzy subsystem FISC decreases the ultrafiltration rate at about
n=100, and shortly thereafter R.sub.h and P.sub.b begin to return
to normal. Since the patient parameters return to normal before the
supervisory controller checks if the reactivation of FSI is
necessary, no further corrections are made.
EXAMPLE 5
[0174] FIGS. 11A, 11B and 11C show a simulation where the heart
rate and blood pressure are both low and the user has specified a
decrease of ultrafiltration when queried by the supervisory
controller. The blood flow rate is set to 40 ml/min, and the
replacement rates are both set to 100 ml/min. The minimum and
maximum thresholds for the heart rate are chosen as 90 bpm and 105
bpm, and the minimum and maximum thresholds for the blood pressure
are chosen as 70 mmHg and 95 mmHg. At the beginning of the
simulation, R.sub.h and P.sub.b are within their normal ranges. At
about n=80, R.sub.h and P.sub.b drop below their respective low
thresholds, and FSIIB calculates an ultrafiltration rate decrease.
The switch logic forces FSII to wait 10 seconds (5 minutes for an
actual ultrafiltration procedure) before another adjustment is
made. Since the patient parameters never return to their respective
normal ranges, the supervisory controller lowers the drain rate
until the ultrafiltration rate is zero.
EXAMPLE 6
[0175] FIGS. 12A, 12B and 12C show a simulation where the patient
parameters are both high and the user specifies an increase of the
ultrafiltration rate. The blood flow rate is set to 40 ml/min, and
the replacement rates are both set to 100 ml/min. The thresholds
for the heart rate are chosen as 90 bpm and 105 bpm, and the
thresholds for the blood pressure are chosen as 70 mmHg and 95
mmHg. At the beginning of the simulation, R.sub.h and P.sub.b are
within their normal ranges. At about n=60, both the patient heart
rate and blood pressure rise above their respective upper
thresholds. After 20 seconds (30 minutes in an actual
ultrafiltration procedure), the condition for activating FSII is
met and the ultrafiltration rate is increased. Since the patient
parameters never return to their respective normal ranges, the
supervisory controller raises the drain rate until the
ultrafiltration rate is 30% above the rate initially given. At this
point, the hemofiltrator alerts the user that the maximum
ultrafiltration rate has been set as the desired rate.
EXAMPLE 7
[0176] FIGS. 13A, 13B and 13C present a simulation where the
patient is getting well enough to increase the ultrafiltration
rate. The blood flow rate is set to 40 ml/min, and the replacement
rates are both set to 100 ml/min. The thresholds for the heart rate
are chosen as 90 bpm and 105 bpm, and the thresholds for the blood
pressure are chosen as 70 mmHg and 95 mmHg. At the beginning of the
simulation, R.sub.h and P.sub.b are within their normal ranges.
Once the heart rate and blood pressure are in the favorable
regions, the supervisory controller waits 120 seconds (about 60
minutes in an actual ultrafiltration procedure) to detect transient
behavior before increasing the drain pump flow rate. Since the
heart rate and the blood pressure return to their normal ranges, no
further adjustments are made.
EXAMPLE 8
[0177] FIGS. 14A, 14B and 14C depict a simulation where the
supervisory controller adjusts the ultrafiltration due to a high
filtered fraction. The patient parameters are both high for an
extended period of time and the initial ultrafiltration rate of
132.6 ml/hr is increased to 172.4 ml/hr by increasing the drain
rate from 332.6 ml/hr to 372.4 ml/hr. The latter flow rate would
give a filtered fraction of 22.2% if the blood pumping were held at
40.0 ml/min. In order to bring the filtered fraction down to 20%,
the blood pump flow rate must be increased to 44.3 ml/min.
[0178] The supervisory control system and the adaptive control
system described above are not limited to use in a ultrafiltration
procedure, but may find application in other medical systems that
employ a pump for transferring a fluid, such as a heart-lung
machine. Other suitable medical applications would be apparent to
one of ordinary skill in the art.
[0179] It will be appreciated by persons skilled in the art that
various modifications can be made to the systems and methods of the
present invention without departing from the scope thereof which is
defined by the appended claims.
* * * * *