U.S. patent application number 10/938486 was filed with the patent office on 2005-03-03 for method and apparatus for kidney dialysis.
Invention is credited to Bedient, Robert A., Connell, Mark E., Elsen, Raymond, Hogard, Michael E., Johnson, Harley D., Kelly, Thomas D., Long, Jean McEvoy, Peterson, Bruce A., Preston, William G. JR., Smejtek, Dalibor J..
Application Number | 20050045540 10/938486 |
Document ID | / |
Family ID | 24763405 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050045540 |
Kind Code |
A1 |
Connell, Mark E. ; et
al. |
March 3, 2005 |
Method and apparatus for kidney dialysis
Abstract
A number of improvements relating to methods and apparatuses for
kidney dialysis are disclosed. These include checking of dialysate
bypass status using flow measurement; using a flow sensor to
confirm the absence of ultrafiltration during bypass; automatic
testing of ultrafiltration function by removal of a discrete volume
from a portion of the dialysate flow path coupled with a pressure
test of that part of the flow path; using a touch screen user
interface; bar graph profile programming of ultrafiltration,
sodium, and bicarbonate parameters; using a RAM card to upload
treatment instructions to, and to download treatment data from, the
machine; automatic setting of proportioning mode (acetate or
bicarbonate) based on connections of concentrate lines; predicting
dialysate conductivity values based on brand and formulation of
concentrates; minimizing no-flow dead time between dialysate
pulses; initiating operation in a timed mode from a machine
power-off condition; preserving machine mode during machine
power-fail condition; calibration scheduling and reminding;
automatic level adjusting; and blood leak flow rate detecting.
Inventors: |
Connell, Mark E.; (Sandy,
OR) ; Bedient, Robert A.; (Portland, OR) ;
Elsen, Raymond; (Antwerp, BE) ; Hogard, Michael
E.; (Oregon City, OR) ; Johnson, Harley D.;
(Portland, OR) ; Kelly, Thomas D.; (Portland,
OR) ; Long, Jean McEvoy; (Portland, OR) ;
Peterson, Bruce A.; (Milwaukee, OR) ; Preston,
William G. JR.; (Portland, OR) ; Smejtek, Dalibor
J.; (Beaverton, OR) |
Correspondence
Address: |
Bell, Boyd & Lloyd LLC
P.O. Box 1135
Chicago
IL
60690-1135
US
|
Family ID: |
24763405 |
Appl. No.: |
10/938486 |
Filed: |
September 9, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10938486 |
Sep 9, 2004 |
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10695526 |
Oct 27, 2003 |
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10695526 |
Oct 27, 2003 |
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09711240 |
Nov 13, 2000 |
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09711240 |
Nov 13, 2000 |
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09067922 |
Apr 28, 1998 |
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09067922 |
Apr 28, 1998 |
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08479688 |
Jun 7, 1995 |
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5744027 |
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08479688 |
Jun 7, 1995 |
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08122047 |
Sep 14, 1993 |
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5486286 |
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08122047 |
Sep 14, 1993 |
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07688174 |
Apr 19, 1991 |
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5247434 |
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Current U.S.
Class: |
210/143 ;
210/646; 345/173 |
Current CPC
Class: |
A61M 1/1686 20130101;
G06F 3/0482 20130101; G16H 40/63 20180101; A61M 1/1664 20140204;
A61M 2205/505 20130101; A61M 1/1607 20140204; A61M 1/1684 20140204;
A61M 2205/3313 20130101; A61M 1/1656 20130101; A61M 1/1692
20130101; A61M 1/169 20130101; A61M 1/341 20140204; A61M 1/165
20140204; A61M 1/1688 20140204; A61M 1/168 20130101; Y10S 210/929
20130101; A61M 2205/3324 20130101; A61M 1/16 20130101; A61M
2039/1005 20130101; G06F 3/04847 20130101; A61M 2205/52 20130101;
A61M 2205/3368 20130101; A61M 1/1613 20140204; A61M 1/1666
20140204; A61M 2205/3334 20130101; A61M 1/1694 20130101; A61M
2205/3317 20130101; A61M 1/3626 20130101; G16H 20/40 20180101 |
Class at
Publication: |
210/143 ;
210/646; 345/173 |
International
Class: |
B01D 061/00 |
Claims
1-41. (cancelled).
42. A hemodialysis apparatus, comprising: (a) means for delivering
extracorporeal blood to a hemodialyzer and for controlling at least
one extracorporeal-blood parameter selected from the group
consisting of (i) blood-flow rate, (ii) arterial pressure, (iii)
venous pressure, and (iv) anticoagulant delivery to the
extracorporeal blood; and (b) a user/machine interface operably
connected to said means for delivering extracorporeal blood, the
user/machine interface comprising a touch screen adapted to display
an indicium corresponding to a parameter pertinent to operation of
the hemodialysis machine and to permit the user, by touching the
indicium, to cause a change in the parameter.
43. A hemodialysis apparatus, comprising: (a) a dialysate-delivery
system for supplying dialysate to a hemodialyzer, the
dialysate-delivery system comprising at least one unit selected
from the group consisting of (i) a dialysate preparation unit, (ii)
a dialysate-circulation unit, (iii) an ultrafiltrate-removal unit,
and (iv) a dialysate-monitoring unit; and (b) a user/machine
interface operably connected to the dialysate-delivery system, the
user/machine interface comprising a touch screen adapted to display
an indicium corresponding to a parameter pertinent to operation of
the hemodialysis machine and to permit the user, by touching the
indicium, to cause a change in the parameter.
44. A hemodialysis apparatus, comprising: (a) a dialysate-delivery
system connectable to a hemodialyzer for supplying dialysate to the
hemodialyzer, the dialysate-delivery system comprising at least one
unit selected from the group consisting of (i) a
dialysate-preparation unit, (ii) a dialysate-circulation unit,
(iii) an ultrafiltrate-removal unit, and (iv) a
dialysate-monitoring unit; (b) an extracorporeal blood-delivery
system connectable to the hemodialyzer for routing extracorporeal
blood to the hemodialyzer in coordination with the
dialysate-delivery system, the extracorporeal blood-delivery system
comprising at least one unit selected from a group consisting of
(i) a blood-circulating unit, and (ii) a blood-monitoring unit; (c)
a controller connected to and controllably operating the
dialysate-delivery system and the extracorporeal blood-delivery
system; and (d) a touch screen connected to the controller, the
touch screen adapted to display an indicium corresponding to a
parameter pertinent to operation of the hemodialysis apparatus and
to permit a user, by touching the indicium, to cause a change in
the parameter.
45. A hemodialysis apparatus, comprising: (a) first and second
systems operably connected with each other, the first system being
operable to deliver extracorporeal blood from a source to a blood
compartment of a hemodialyzer, and the second system being operable
to deliver dialysate from a source to a dialysate compartment of
the hemodialyzer; and (b) a touch screen connected to the first and
second systems, the touch screen adapted to display an indicium
corresponding to a parameter pertinent to operation of the first
and second systems and to permit a user, by touching the indicium,
to cause a change in the parameter.
46. A hemodialysis apparatus, comprising: (a) a dialysate-delivery
system for supplying dialysate to a hemodialyzer, the
dialysate-delivery system comprising at least one unit selected
from the group consisting of (i) a dialysate-preparation unit, (ii)
a dialysate-circulation unit, (iii) an ultrafiltrate-removal unit,
and (iv) a dialysate-monitoring unit; and (b) a user/machine
interface operably connected to the dialysate-delivery system, the
user/machine interface comprising a touch screen that displays
information corresponding to a setting of a parameter pertinent to
operation of the hemodialysis machine, the touch screen being
operable to display an indicium permitting the user to perform,
using the touch screen, at least one step of a procedure for
changing the setting of the parameter.
47. The apparatus of claim 46, wherein the parameter can have a
value that changes with time.
48. The apparatus of claim 46, wherein the touch screen, responsive
to an operator touching the indicium, is operable to display a
numerical keypad that is touchable by the operator in performing
the procedure for changing the setting of the parameter.
49. A hemodialysis apparatus, comprising: (a) an
extracorporeal-blood-deli- very system for supplying extracorporeal
blood to a hemodialyzer, the extracorporeal-blood-delivery system
comprising at least one unit selected from the group consisting of
(i) a blood-circulating unit, and (ii) a blood-monitoring unit; and
(b) a user/machine interface operably connected to the
extracorporeal-blood-delivery system, the user/machine interface
comprising a touch screen that displays information corresponding
to a setting of a parameter pertinent to operation of the
hemodialysis machine, the touch screen being operable to display an
indicium permitting the user to perform, using the touch screen, at
least one step of a procedure for changing the setting of the
parameter.
50. The apparatus of claim 49, wherein the blood-circulating unit
comprises a blood pump.
51. The apparatus of claim 49, wherein the blood-monitoring unit
comprises at least one of a blood-flowrate controller, a venous
pressure monitor, and an arterial pressure monitor.
52. A hemodialysis apparatus, comprising: (a) a dialysate-delivery
system connectable to a hemodialyzer for supplying dialysate to the
hemodialyzer, the dialysate-delivery system comprising at least one
unit selected from the group consisting of (i) a
dialysate-preparation unit, (ii) a dialysate-circulation unit,
(iii) an ultrafiltrate-removal unit, and (iv) a
dialysate-monitoring unit; (b) an extracorporeal-blood-deliver- y
system connectable to the hemodialyzer for routing extracorporeal
blood to the hemodialyzer in coordination with the
dialysate-delivery system, the extracorporeal blood-delivery system
comprising at least one unit selected from a group consisting of
(i) a blood-circulating unit, and (ii) a blood-monitoring unit; (c)
a controller connected to and controllably operating the
dialysate-delivery system and the extracorporeal-blood-delivery
system; and (d) a user/machine interface operably connected to the
dialysate-delivery system and the extracorporeal-blood-delivery
system, the user/machine interface comprising a touch screen that
displays information corresponding to a setting of a parameter
pertinent to the hemodialysis machine, the touch screen being
operable to display an indicium permitting the user to perform,
using the touch screen, at least one step of a procedure for
changing the setting of the parameter.
53. A hemodialysis machine, comprising: (a) means for controlling a
dialysate parameter selected from a group consisting of dialysate
temperature and dialysate concentration, and means for delivering
the dialysate to a dialysate compartment of a hemodialyzer; and (b)
a user/machine interface operably connected to said means for
controlling the dialysate parameter, the user/machine interface
comprising a touch screen adapted to display an indicium
corresponding to a parameter pertinent to operation of the
hemodialysis machine and to permit the user, by touching the
indicium, to cause a change in the parameter.
54. A hemodialysis apparatus, comprising: first and second systems
operably connected with each other, the first system being operable
to deliver extracorporeal blood from a source to a blood
compartment of a hemodialyzer, and the second system being operable
to deliver dialysate from a source to a dialysate compartment of
the hemodialyzer, the first and second systems each including a
pump to deliver the respective extracorporeal blood and dialysate;
a touch screen connected to the first and second systems, the touch
screen adapted to display an indicium corresponding to a parameter
pertinent to operation of the first and second systems and to
permit a user, by touching the indicium, to cause a change in the
parameter.
55. A hemodialysis machine, comprising: means for controlling a
dialysate parameter selected from a group consisting of dialysate
temperature and dialysate concentration, and means for delivering
the dialysate to a dialysate compartment of a hemodialyzer; a
user/machine interface operably connected to said means for
controlling the dialysate parameter, the user/machine interface
comprising a touch screen adapted to display an indicium
corresponding to a parameter pertinent to operation of the
hemodialysis machine and to permit the user, by touching the
indicium, to cause a change in the parameter; and a memory storing
at least one of firmware and software that enables the user/machine
to interface and control the means for controlling the dialysate
parameter.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/711,240 filed on Nov. 13, 2000, now
pending, which is a continuation of U.S. patent application Ser.
No. 09/067,922 filed on Apr. 28, 1998, now abandoned, which is a
continuation of U.S. patent application Ser. No. 08/479,688, filed
on Jun. 7, 1995, now U.S. Pat. No. 5,744,027, which is a divisional
of U.S. patent application Ser. No. 08/122,047, filed on Sep. 14,
1993, now U.S. Pat. No. 5,486,286, which is a divisional of U.S.
patent application Ser. No. 07/688,174, filed on Apr. 19, 1991, now
U.S. Pat. No. 5,247,434.
FIELD OF THE INVENTION
[0002] The present invention relates to improvements in kidney
dialysis machines.
BACKGROUND OF THE INVENTION
[0003] Kidney dialysis machines are well known in the art and are
illustrated, for example, in U.S. Pat. Nos. 3,598,727, 4,172,033,
4,267,040, and 4,769,134.
[0004] While machines according to the prior art provide a number
of advantageous features, they nonetheless have certain
limitations. The present invention seeks to overcome certain
drawbacks of the prior art and to provide new features not
heretofore available.
[0005] A discussion of the features and advantages of the present
invention is deferred to the following detailed description, which
proceeds with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a schematic hydraulic diagram of a preferred
embodiment of a kidney dialysis machine according to the present
invention.
[0007] FIG. 2 is a schematic diagram showing flow path locations
and components of a pre-dialyzer flow sensor and a post-dialyzer,
flow sensor according to the present invention.
[0008] FIGS. 3A and 3B are isometric and schematic diagrams,
respectively, of a concentrate-line proximity sensor comprising a
portion of the automatic proportioning mode setting feature of the
present invention.
[0009] FIG. 4 is a schematic diagram showing the interconnection of
input and output pressure equalizers into the hydraulic flow path
of the present invention.
[0010] FIG. 5 is a schematic diagram of the automated drip-chamber
level adjusters of the present invention.
[0011] FIG. 6 is a schematic diagram a preferred embodiment of a
means for increasing dialysate flow velocity through the dialyzer
without increasing the dialysate flow rate.
[0012] FIG. 7 shows a block diagram of a computer system used in
the preferred embodiment.
[0013] FIG. 8 shows a touch screen display used in the preferred
embodiment.
[0014] FIG. 9 shows the touch screen of FIG. 8 with a calculator
window for data entry.
[0015] FIG. 10 shows a profile entry screen used in the preferred
embodiment.
[0016] FIG. 11 shows a programming screen used in the preferred
embodiment.
DETAILED DESCRIPTION
Hydraulic Circuit
[0017] A hydraulic circuit 10 representing a preferred embodiment
of an improved hemodialysis machine according to the present
invention is illustrated in FIG. 1. The hydraulic circuit 10 is
comprised of the following principal components: an incoming water
pressure regulator 12, a water on/off valve 14, a heat exchanger
16, a heater 18, a safety thermostat 20, an "A" concentrate pump
22, a supply valve 24, an air gap chamber 26, an "A" rinse fitting
28, a "B" rinse fitting 30, a deaeration sprayer 32, an air removal
pump 34, a vented air trap 36, an "A" conductivity probe 38, a "B"
concentrate pump 40, a supply pump 42, a "B" mix chamber 44, a "B"
conductivity probe 46, a dialysate filter 48, a supply regulator
50, an input pressure equalizer 52, a flow equalizer 54, an output
pressure equalizer 56, end-of-stroke sensors 59, a dialysate
conductivity probe 60, a pre-dialyzer flow sensor 62, a dialysate
pressure transducer 64, a bypass valve 66, a dialysate sample port
68, a post-dialyzer flow sensor 70, a dialysate pressure pump 72, a
UF removal regulator 74, a UF flow meter 76, a blood-leak detector
78, and a rinse valve 80. The aforementioned components are
interconnected as shown in FIG. 1.
[0018] The incoming water pressure regulator 12 is coupled to a
pressurized water source 82 and reduces and stabilizes the water
supply pressure to a level of about 20 psig.
[0019] The water on/off valve 14 opens when machine power is on,
thereby allowing water to flow from the source 82 into the
hydraulic circuit 10. When the machine power is off, the water
on/off valve 14 is closed.
[0020] The heat exchanger 16 transfers heat from "spent" or
effluent dialysate, passing through conduit 84, to the cooler
incoming water passing through conduit 86 as these two liquids pass
countercurrently through separate but adjacent compartments in the
heat exchanger 16. In this way, the incoming water is warmed, which
reduces the amount of heat energy that must be supplied to the
water by the heater 18..
[0021] The heater 18 further warms the incoming water to a suitable
temperature for hemodialysis, which is about 38.degree. C. A
typical heater 18 is a resistance type known in the art, rated at
about 1500 watts. The heater 18 includes a downstream thermistor 20
or analogous temperature-sensing device. A thermistor as known in
the art is essentially a temperature-sensitive resistor which
experiences a change in electrical resistance that is inversely
proportional to a corresponding change in temperature. The
thermistor 20 is coupled to the machine's microprocessor (not shown
in FIG. 1) which utilizes signals from the thermistor for turning
the heater 18 on and off as required to maintain the water
temperature at the proper level.
[0022] The "A" concentrate pump 22 propels either "acid" or
"acetate" concentrate as known in the art from a container thereof
88 into the air gap chamber 26. The "A" concentrate pump 22 is a
fixed-volume cam-driven pump. A stepper motor 90 calibratable to
rotate a precise number of rotations per minute is preferably used
to drive the "A" concentrate pump 22. The stepper motor includes a
shaft (not shown) to which is mounted a cam (not shown) which
engages a flexible diaphragm 92, thereby delivering a known volume
of "A" concentrate per each rotation of the cam. An optical sensor
(not shown) on the cam monitors, the angular rotation of the cam
for processing by the microprocessor (not shown). The
microprocessor, using information pertaining to dialysate flow rate
and concentrate parameters entered by the machine operator using a
touch screen (described in detail hereinbelow), calculates the
amount of concentrate necessary to achieve a correct ratio of water
and "A" concentrate for hemodialysis therapy. The microprocessor
thereby adjusts the angular velocity of the stepper motor
shaft.
[0023] An "A" concentrate line 94 is used to deliver "A"
concentrate from the supply 88 thereof to the "A" concentrate pump
22. When rinsing the machine, the "A" concentrate line 94 is
coupled to the "A" rinse fitting 28 which serves as a source of
rinse water for the "A" concentrate line.
[0024] When disinfecting the machine, the "A" concentrate line 94
is coupled to a disinfect fitting 96 which enables the "A"
concentrate pump 22 to deliver a chemical disinfectant to the "A"
concentrate line 94.
[0025] Heated water enters the air gap chamber 26 through the
supply valve 24. The supply valve 24 is actuated by a lever 98. The
lever 98 is coupled to a float 100 inside the air trap 36. Thus,
the float 100 controls water flow into the hydraulic circuit 10 by
opening the supply valve 24 when the water level supporting the
float drops and by closing the supply valve 24 when the water level
in the air trap 36 rises.
[0026] The air gap 102 in the chamber 26 is at atmospheric
pressure. The air gap 102 helps prevent incoming water from flowing
backward (upstream) in the event of a pressure drop in the water
supply 82.
[0027] A proximity sensor (not shown in FIG. 1 but described in
further detail hereinbelow) is built into the "A" fitting 28. The
proximity sensor senses when the "A" concentrate line 94 is coupled
to the "A" rinse fitting 28 and when it is not, thereby serving as
an important safety interlock feature which prevents unsafe
operation of the machine.
[0028] The "B" rinse fitting 30 supplies water for rinsing the "B"
concentrate line 104. During rinse, the "B" concentrate line 104 is
coupled to the "B" rinse fitting 30. During acetate dialysis, the
"B" concentrate line 104 is also coupled to the "B" rinse fitting
30 for recirculation of acetate dialysate solution
therethrough.
[0029] The "B" rinse fitting 30 is also provided with a proximity
sensor (not shown in FIG. 1 but described in further detail
hereinbelow) similar to that provided with the "A" rinse fitting
28.
[0030] The hydraulic circuit includes components operable to remove
dissolved gases from the liquid passing therethrough. Otherwise, if
the liquid were not deaerated, dissolved gases therein could
adversely affect the course of a dialysis treatment, including the
accuracy at which the machine performs ultrafiltration of the
patient. To facilitate deaeration, liquid flows through the
air-removal sprayer 32 at a rate of about 1500 mL/min at a
subatmospheric pressure (about 500 mmHg). The reduced pressure is
attained by aspirating the liquid via the air-removal pump 34
through a flow restrictor 106 upstream of the air-removal sprayer
32. The air-removal sprayer 32 breaks the liquid into small
droplets as it is subjected to the subatmospheric pressure, which
favors the formation of air bubbles.
[0031] The air trap 36 vents air bubbles liberated from the liquid
by the deaeration sprayer 32 through a vent opening 108 open to the
atmosphere. The air trap also contains the float 100 discussed
hereinabove.
[0032] The "A" conductivity probe 38 measures the electrical
conductivity of the mixture of water and "A" concentrate.
Conductivity is an accurate way to ascertain whether the "A"
concentrate solution has been correctly proportioned. The
conductivity measured at the "A" conductivity probe 38 can vary
depending upon the ionic strength and electrolytic profile of the
"A" concentrate. Since conductivity will be affected by
temperature, the "A" conductivity probe 38 is also provided with a
thermistor 110. The thermistor 110 is coupled to the microprocessor
(not shown) which performs the necessary temperature
compensation.
[0033] The "B" concentrate pump 40 delivers bicarbonate concentrate
from a supply thereof 112 and is operable only during bicarbonate
dialysis therapy. The "B" concentrate pump 40 is a fixed-volume
cam-driven pump similar to the "A" concentrate pump 22. The "B"
concentrate pump 40 is driven by a stepper motor 114. As with the
"A" concentrate pump, the angular velocity of the stepper motor
shaft is monitored by an optical sensor. The optical sensor is
connected to the machine's microprocessor which calculates the
amount of "B" concentrate necessary to achieve a correct dialysate
composition for safe hemodialysis therapy and correspondingly
controls the angular velocity of the cam. The "B" concentrate pump
40 will automatically compensate for changes in dialysate flow rate
in the event that said flow rate is changed during a dialysis
treatment by increasing or decreasing the pump rate.
[0034] FIG. 1 also shows an optional third concentrate supply 116,
a third fixed-volume cam-driven concentrate pump 118 operable in
the same manner as the "A" and "B" concentrate pumps 22, 40, a
corresponding mixing chamber 120 and conductivity probe 122.
[0035] The "B" mix chamber 44 provides thorough mixing of the "B"
concentrate with the proportioned mixture of "A" concentrate and
water to form dialysate before the dialysate enters the "B"
conductivity probe 46.
[0036] The "B" conductivity probe 46 monitors dialysate
conductivity. Electronic circuitry (not shown) coupled to the "B"
conductivity probe 46 subtracts the conductivity measured at the
"A" conductivity probe 38 from the conductivity measured at the "B"
conductivity probe 46. During acetate dialysis, the difference in
these conductivity readings should be zero. Since conductivity
measurements are affected by temperature, a thermistor 124 is
included with the "B" conductivity probe 46 to provide temperature
compensation of the "B" conductivity reading. The thermistor 124
also comprises a portion of a redundant high temperature alarm
subsystem.
[0037] Before describing the hydraulic circuit any further, it is
appropriate to briefly describe the flow equalizer 54. The flow
equalizer 54 comprises a first chamber 126 and a second chamber 128
of substantially equal volume. Each chamber 126, 128 is comprised
of two compartments, one termed a "pre-dialyzer" or "pre"
compartment 130, 132 and the other a "post-dialyzer" or "post"
compartment 134, 136. Each pair of opposing "pre" and "post"
chambers is separated by a flexible diaphragm 138, 140.
Solenoid-actuated valves 142-149 control the filling and emptying
of each compartment. In general, each compartment 130, 132, 134,
136 is completely filled before its contents are discharged. Also,
the "pre" compartments 130, 132 are alternately filled and
discharged and the "post" compartments 134, 136 are alternately
filled and discharged. Also, filling a "pre" compartment 130, 132
causes a corresponding discharge of an opposing "post" compartment
134, 136, respectively. The "pre" compartments 130, 132 alternately
fill from the supply pump 42 and alternately discharge to the
dialyzer. The "post" compartments 134, 136 alternately fill with
"spent" dialysate returning from the dialyzer and discharge the
spent dialysate to a drain line 150. For example, dialysate from
the supply pump 42 enters the "pre" compartment 132, thereby
displacing the diaphragm 140 in FIG. 1 to the right, causing the
"post" compartment 136 to empty. Simultaneously, "post" compartment
134 fills while "pre" compartment 130 empties.
[0038] The flow equalizer 54 operates via a four-phase cycle. In
the first phase, valves 142, 145, 147, and 148 turn on, thereby
filling the "pre" compartment 130 with fresh dialysate and
displacing the diaphragm 138 to the right in FIG. 1. Such
displacement of the diaphragm 138 expels "spent" dialysate
contained in the "post" compartment 134, which has a volume equal
to the volume in the "pre" compartment 130, to pass to the drain
line 150. At the same time, effluent dialysate from the dialyzer
enters the "post" compartment 136, thereby forcing the diaphragm
140 to be displaced to the left in FIG. 1 to expel an equal volume
of fresh dialysate from the "pre" compartment 132 to the dialyzer.
In the second phase, all the solenoid valves 142-149 turn off for a
short period of time (about 125 m sec). This brief shut-off
eliminates adverse affects on ultrafiltration accuracy that would
otherwise result if at least two of said valves were open at the
same time. In the third phase, solenoid valves 143, 144, 146, and
149 are energized, causing the "post" compartment 134 to fill with
effluent dialysate from the dialyzer, thereby expelling fresh rash
dialysate from "pre" compartment 130 to the dialyzer. Also, the
"pre" compartment 132 simultaneously fills with fresh dialysate
from the supply pump 42, thereby expelling effluent dialysate from
the remaining "post" compartment 136 to the drain line 150. In the
fourth phase, all the solenoid valves 142-149 are again turned off
for about 125 msec.
[0039] Since the volumes of opposing "pre" and "post" compartments
130 134 and 132, 136 are equal, the flow equalizer 54
volumetrically balances the flow of dialysate to and from the
dialyzer. A further benefit of such volumetric equality is that
dialysate flow to the dialyzer can be accurately measured over a
wide range of flow rates.
[0040] The supply pump 42 has two functions: (a) to supply an
adequate dialysate flow volume and pressure to fill the flow
equalizer compartments with dialysate, and (b) to create a flow of
dialysate through a loop 152 comprised of the dialysate filter 48,
the supply regulator 50, the "B" mix chamber 44, and the "B"
conductivity probe 46. The supply pump 42 delivers dialysate at a
maximum regulated pressure of 12.5 psig and at a flow rate
approximately 50 mL/min higher than the dialysate flow rate set by
the operator using the touch screen.
[0041] The dialysate filter 48 is used to occlude downstream
passage of particulate foreign material into the flow equalizer 54.
The supply regulator 50 is adjusted to an output pressure of
approximately 16 psig. Whenever the "pre" and "post" compartments
of the flow equalizer 54 reach the end of a fill cycle during
phases 1 or 3, pressure builds up in the loop 152. As the pressure
increases to about 16 psig, the supply regulator 50 opens
sufficiently to pass the dialysate output of the supply pump 42
through the loop 152 until the next phase 1 or 3.
[0042] The input pressure equalizer 52 equilibrates hydraulic
pressures at the inlets 155 of the flow equalizer 54 so that the
compartments 130, 132, 134, 136 fill at the same rate. Likewise,
the output pressure equalizer 56 equilibrates hydraulic pressures
at the outlets 156 of the flow equalizer 54. The input and output
pressure equalizers are discussed in greater detail
hereinbelow.
[0043] The input pressure equalizer 52 also automatically
equilibrates the pressure of the dialysate flowing through the
downstream lines 158, 160 with the pressure of dialysate at the
flow equalizer inlets 154. Whenever the pressure at the flow
equalizer inlets 154 exceeds the pressure generated by the
dialysate pressure pump 72, the input pressure equalizer 52
restricts the flow of dialysate in lines 158, 160. Such
equilibration of pressures allows both chambers 126, 128 in the
flow equalizer 54 to be filled at identical rates.
[0044] End-of-stroke sensors 162, 164 are provided at the outlets
156 of the output pressure equalizer. The end-of-stroke sensors
162, 164 verify when the flow equalizer compartments have reached
the end of a fill cycle (end of stroke). When the compartments are
full, the end-of-stroke sensors 162, 164 send a no-flow signal to
the machine's microprocessor, indicating that the compartments are
full.
[0045] The dialysate conductivity probe 60 measures the
conductivity of the dialysate before it enters the dialyzer. The
machine's microprocessor compares the measured conductivity with an
expected conductivity value (discussed in detail hereinbelow) based
upon concentrate-formulation information entered by the operator
using the touch screen. If the measured dialysate conductivity is
excessively above or below the expected conductivity value, the
machine's microprocessor activates a conductivity alarm. Also, the
bypass valve 66 is triggered during a conductivity alarm to divert
dialysate away from the dialyzer through conduit 166.
[0046] The dialysate conductivity probe 60 includes a thermistor
168 which allows temperature compensation of the conductivity
reading. The electronic signal from the thermistor 168 is also
utilized to provide a dialysate temperature display on the
machine's touch screen as well as primary high and low temperature
alarm limits. The dialysate conductivity as measured by the
conductivity probe 60 is also displayed on the machine's touch
screen.
[0047] The dialysate flow sensor 62 includes a self-heating
variable thermistor as well as a reference thermistor (not shown in
FIG. 1, but discussed in detail hereinbelow). The dialysate flow
sensor 62 is used mainly as a bypass monitor. Whenever the machine
is in bypass, the resulting lack of dialysate flow past the flow
sensor 62 serves as a verification that the bypass valve 66 is
functioning correctly.
[0048] The dialysate pressure transducer 64 senses dialysate
pressure and converts the pressure reading into an analog signal
proportional to the dialysate pressure. The analog signal is
utilized by the machine's microprocessor as the basis for a
dialysate pressure display on the touch screen, pressure alarms,
and other dialysate control functions (not shown in FIG. 1).
[0049] The bypass valve 66 protects the hemodialysis patient in the
event of a temperature or conductivity alarm by diverting dialysate
flow away from the dialyzer. The bypass valve 66 is a three-way
solenoid valve which, when triggered, occludes the conduit 170
leading to the dialyzer and shunts the dialysate flow through
conduit 166 to a location 172 downstream of the dialyzer.
[0050] The dialysate sample port 68 is an appliance which allows
the operator to obtain a sample of the dialysate using a syringe
for independent testing.
[0051] A second dialysate flow sensor 70 is located in the
post-dialyzer ("venous") line 174. The second flow sensor 70 is
constructed similarly to the first flow sensor 62 and is discussed
in detail hereinbelow. The second flow sensor 70 is utilized for
checking the accuracy of the machine's ultrafiltration
capability.
[0052] The dialysate pressure pump 72 is situated downstream of the
dialyzer. An accompanying recirculation loop comprising lines 158,
160 conducts effluent dialysate to the inlet pressure equalizer 52.
The recirculation loop 158, 160 thereby helps equilibrate pressure
differences that might otherwise be transmitted to the flow
equalizer 54 and also serves as a source of hydraulic pressure
sufficient to fill the UF flow meter 76 when demanded thereby.
[0053] The dialysate pressure pump 72 circulates dialysate at a
constant flow rate of 1500 mL/min through the recirculation loop
158, 160 without affecting the overall dialysate flow rate through
the hydraulic circuit 10. As a result, the dialysate pressure pump
72 is usable to adjust pressure differences across the dialyzer
membrane.
[0054] As long as the dialysate pressure pump 72 receives an
adequate volume of dialysate for pumping, the flow dynamics of
dialysate through the hydraulic circuit 10 are unaffected. However,
should liquid be removed from the recirculation loop 158, 160, the
dialysate pressure pump will attempt to replace that lost volume by
demanding more volume from the dialyzer. Since the flow equalizer
54 maintains volumetric constancy of dialysate passing to and from
the dialyzer, the only fluid available to replace any fluid lost
from the loop 158, 160 must come from the dialyzer itself. Hence,
by precisely controlling the amount of liquid removed from the
recirculation loop 158, 160 (using the UF flow meter 76), the
operator can precisely control the amount of liquid that must be
removed from the hemodialysis patient via the dialyzer.
[0055] Since the dialysate pumped by the dialysate pressure pump 72
has a partially restricted flow, a sufficient pressure is thereby
provided at the input of the UF removal regulator 74. The UF
removal regulator 74 regulates hydraulic pressure at the input 178
of the UF flow meter 76.
[0056] The UF flow meter 76 is comprised of a chamber 180 separated
into two subcompartments 182, 184 via a diaphragm 186. Each
subcompartment 182, 184 has a corresponding valve 188, 190,
respectively, associated therewith. Either subcompartment 182, 184
of the UF flow meter 76 can only fill when the corresponding valve
188, 190 is opened. Whenever a first subcompartment 182 is filling,
the opposing second compartment 184 is emptying its contents to a
drain line 192. The rate of UF removal through the UF flow meter 76
is governed by the rate at which the corresponding valves 188, 190
are alternately opened and closed.
[0057] Whenever liquid leaves the recirculation loop 158, 160
through the UF flow meter 76, correspondingly less liquid is
recirculated through the recirculation loop 158, 160. This causes a
corresponding "starvation" at the input 172 of the dialysate
pressure pump 72 which generates a corresponding decrease in
dialysate pressure in the dialyzer. The decreased dialysate
pressure causes a volume of liquid to be removed from the patient
that is equal to the volume of liquid removed from the
recirculation loop 158, 160 via the UF flow meter 76. These volumes
will be equal so long as the dialyzer has an ultrafiltration
capability sufficient to remove said volume from the patient at the
desired rate.
[0058] Effluent dialysate expelled from the flow equalizer 54
passes through and is monitored for the presence of blood by the
blood-leak detector 78. The blood-leak detector 78, discussed in
further detail hereinbelow, comprises a light source 194 and a
photocell 196 which monitors light transmitted through the effluent
dialysate solution passing therethrough. If blood leaks through the
dialyzer membrane from the patient into the dialysate the dialysate
passing through the blood-leak detector 78 will absorb a portion of
the light passing therethrough. The corresponding decrease in the
amount of light reaching the photocell 196, if the decrease is
excessive, triggers a blood-leak alarm by the machine.
[0059] Effluent dialysate from the blood-leak detector 78 is routed
through conduit 84 to the heat exchanger 16, then to a drain
198.
[0060] The rinse valve 80 allows the UF flow meter 76 to remove
rinse water from the recirculation loop 158, 160 at a rate of about
4 L/h. Such rinsing ensures an adequate flushing of the
recirculation loop 158, 160 and UF flow meter 76. However, since
liquid is removed from the loop 158, 160 at a relatively high rate
during rinse, the rinse valve 80 also allows an equivalent volume
of liquid to be added back to the loop 158, 160.
User Interface
[0061] In the preferred embodiment, a touch screen user interface
is employed.
[0062] Touch screens are known in the art and are commercially
available from a number of sources, including Elographics West of
San Diego, Calif. The use of touch screens in user interface
applications for medical equipment is also known, as shown for
example in U.S. Pat. Nos. 4,974,599 and 4,898,578, the disclosures
of which are incorporated herein by reference.
[0063] In the prior art, as illustrated by the above-referenced
patents, touch screens have been used in conjunction with computers
and CRTs to provide a control panel that can be changed under
computer control. The means by which a computer, a CRT, and a touch
screen can be cooperatively operated in this fashion is well known
and does not, per se, form a part of this invention.
[0064] FIG. 7 shows a block diagram of the computer system 500 that
is used to control the touch screen 501, CRT display 503, and other
components of the apparatus. This computer is programmed in the
language `C` in a conventional manner to accomplish the dialogue
and other functions subsequently described.
[0065] FIG. 8 shows the touch screen display that is usually
presented to the operator of the system of FIG. 7. As can be seen,
the primary treatment parameters are displayed. These include the
heparin pump rate, the dialysate flow rate, the dialysate
conductivity, the dialysate temperature, the elapsed treatment
time, the total ultrafiltrate removed, the transmembrane pressure,
and the ultrafiltration rate. Also displayed are the patient's
arterial and venous blood pressure (both in colunm of mercury form
and in numeric form). A linear indicator at the bottom of the
screen indicates the blood pump flow rate. A space at the top of
the screen is reserved for alarm and help messages. These elements
of the display are detailed more fully in Appendix A beginning at
page Reference 1.
[0066] Most of these display elements are in a bordered box. The
border serves as a visual alarm indicator and changes color and
flashes if a corresponding alarm limit is violated.
[0067] A number of buttons are displayed on the right hand side of
the display. The first is a RESET button and is used to reset alarm
conditions after an alarm condition is corrected. HELP guides the
user through a variety of help messages. SET LIMITS sets the alarm
limits for various parameters including arterial pressure, venous
pressure and TMP. MENUS replaces the buttons on the right hand side
of the display with additional buttons corresponding to additional
control functions, while maintaining the displayed parameters
elsewhere on the screen. RINSE initiates the rinse mode, provided
the interlocks are met. MUTE silences most audio alarms for 100
seconds. Additional buttons can appear in this part of the screen
and are detailed in the Reference Section of Appendix A. Button
locations are reprogrammable and can have multiple legends
associated with them. Also, their positions on the touch screen can
be varied by reprogramming.
[0068] If it is desired to change one of the displayed parameters,
such as the heparin pump rate, the operator simply touches the
corresponding indicator. A calculator-like keyboard then pops up in
a window superimposed on the display, as shown in FIG. 9. On this
keyboard, the user can enter the new value for the selected
parameter. Once the desired parameter is entered in this fashion,
the operator presses ENTER on the calculator display and the
calculator display disappears. The revised parameter is substituted
in the corresponding indicator (with its border highlighted) and
the user is prompted, through a button that appears at the lower
right hand side of the screen, to verify the entered change. If the
VERIFY button is not touched shortly after displayed, the VERIFY
button disappears and the machine continues with its previous
parameter. If timely verified, the change takes effect. In the
preferred embodiment, the user has between one and five seconds to
verify the parameter.
[0069] Some parameters are not susceptible to representation by a
single number displayed in a parameter window. Exemplary are
parameters that are programmed to change over time (so-called
profiled parameters). In this class are the sodium concentration of
the dialysate solution, the bicarbonate concentration of the
dialysate solution, kT/V, and the ultrafiltration rate.
[0070] In the preferred embodiment, such profiled parameters are
selectably displayed in the form of bar graphs on the display
screen. Using sodium as an example, the Y-axis represents sodium
concentrations in the range of 130-160 mEq/L. The X-axis represents
the treatment period, broken down into fifteen minute intervals.
Such a display is shown in FIG. 10.
[0071] The use of bar graphs to display profiled parameters is
known in the art. The prior art fails, however, to provide a
convenient manner by which data characterizing the profile curve
may be entered into the machine. Typically, such data entry has
been accomplished through a keypad on which data for each discrete
time period is entered. However, this approach requires dozens of
key presses and provides numerous opportunities for error.
[0072] In the preferred embodiment, in contrast, profiled
parameters are entered by simply tracing the desired profile curve
on the touch screen.
[0073] In more detail, programming of profiled parameters is
performed as follows:
[0074] From the main touch screen display of FIG. 8, the user
presses MENUS. The programming screen of FIG. 11 then appears,
which includes along its right hand side buttons corresponding to
the programming of sodium, bicarbonate, kt/V, and ultrafiltration.
The parameter desired to be programmed is then selected by touching
the corresponding button.
[0075] In response to this touch, the screen of FIG. 10 appears. If
a profile has already been programmed, it is displayed in bar graph
fashion on this screen. Otherwise, the graph is empty.
[0076] Before permitting the user to program the sodium profile,
the machine first solicits the sodium value of the sodium
concentrate being used. This data is entered on a pop-up keypad. If
the treatment time was not earlier programmed, the machine also
solicits this data by means of a pop-up keypad.
[0077] The user then traces the desired profile curve on the touch
screen, and the computer virtually simultaneously displays a series
of bars corresponding to the traced curve.
[0078] Alternatively, the user can touch the screen at discrete
points on the desired profile curve. To program a linear increase
in sodium from 140 to 160 mEq/L, for example, the user would touch
the graph at 140 at the ordinate corresponding to the beginning of
the treatment to interval, and 160 at the ordinate corresponding to
the end of the treatment interval. The computer would then fit a
linearly increasing series of bars between these points.
[0079] Discrete touches can also be used to program stepped
profiles. If the first hour of treatment is to be at 150 mEq/L and
the second hour is to be at 135 mEq/L, the user would first touch
the screen at 150 at the ordinate corresponding to the beginning of
the first hour. At the ordinate corresponding to the end of the
first hour, the user would press at two locations. First at 150 (to
cause the computer to fill in the intervening period with bars
corresponding to 150), and again at 135. Finally, the user would
touch the screen at 135 at the ordinate corresponding to the end of
the second hour. The computer would then fill in the second hour
with bars corresponding to 135.
[0080] After the desired profile curve has been entered, the ENTER
button is pressed to set the program in the machine.
[0081] In the preferred embodiment, the computer "snaps" the height
of each bar to one of a series of discrete values. In the case of
sodium, these discrete values are spaced in 1 mEq/L steps.
[0082] Displayed on the screen during this programming operation is
a numeric data window in which the numeric counterpart to a
particular bar may be displayed. When the curve is first traced,
the computer displays in this window the numerical parameter
corresponding to each bar as it is defined. After the profile has
been programmed, the numeric counterpart to any bar can be
displayed by first touching a LOCK button that locks the curve, and
then touching the bar in question.
[0083] After the profile has been set, the user may wish to alter
it in certain respects. One way, of course, is to simply repeat the
above-described programming procedure. Another is to adjust the
height of a particular bar. This can be accomplished in one of two
ways. The first is simply to touch the bar to be altered. The
height of the bar tracks movement of the user's finger. The second
way of adjustment is to first select a bar to be adjusted by
repeatedly touching (or pressing and holding) a Right Arrow button
until the desired bar is highlighted. (The Right Arrow button
causes highlighting to scroll through the bars, left to right, and
cycles back to the left-most bar after the right-most bar. The
highlighting indicates the bar that is selected.) The numeric
parameter corresponding to the selected bar is displayed in the
numeric data window. This value can then be adjusted by Up and Down
arrow keys that cause the displayed parameter to increase and
decrease, respectively. In the preferred embodiment, the Up and
Down arrow keys cause the sodium parameter to change in steps of
0.1 mEq/L, one-tenth the resolution provided in the original data
entry, procedure. A similar ratio holds with other parameters
programmed in this fashion. Again, the ENTER button is pressed to
complete the programming operation.
[0084] As with other parameters, profiled parameters must also be
verified before they take effect.
[0085] After the above-detailed data profiling operations are
completed, data corresponding to the programmed profile is stored
in the computer's memory. Periodically, such as once every fifteen
minutes, a timed interrupt in the system's software program causes
the computer to poll this memory for the value of the programmed
parameter for the next time interval (here fifteen minutes). The
physical parameter is adjusted accordingly using conventional
adjustment mechanisms.
[0086] Once treatment has begun, the system only permits bar
graph-bars corresponding to upcoming time intervals to be
programmed. Bars corresponding to past time intervals reflect
treatment history and cannot be changed. To readily distinguish
past from future, the bars corresponding to each are displayed in
different colors.
[0087] Additional details on sodium programming, as well as details
of bicarbonate and ultrafiltration programming, are contained in
Appendix D.
[0088] In all aspects of the interface, the user is guided from one
touch to the next by a feature of the preferred embodiment wherein
the button that the user is most likely to press next is
highlighted. For example, when the machine is in Rinse mode and is
nearing completion of these operations, the Self-Test button is
highlighted, indicating that this is the next likely operation.
Similarly, when the Self-Test operation is nearing completion, the
Prime button is highlighted. By this arrangement, even novice users
are easily guided through the machine's various phases of
operations.
[0089] In addition to the above-described user interface,
communications with the dialysis machine can also be effected by an
RS-232C serial data interface 530 and by a data card.
[0090] Data cards (also known as memory cards or RAM cards) are
known in the art, as represented by U.S. Pat. Nos. 4,450,024,
4,575,127, 4,617,216, 4,648,189, 4,683,371, 4,745,268, 4,795,898,
4,816,654, 4,827,512, 4,829,169, and 4,896,027, the disclosures of
which are incorporated herein by reference. In the preferred
embodiment, a data card can be used both to load treatment
parameters into the machine and to download logged patient
parameters from the machine for therapy analysis.
[0091] Among the treatment parameters that can be provided to the
machine by a data card are the ultrafiltration profile, the sodium
profile, the bicarbonate profile, the blood pump flow rate, the
treatment time, the desired ultrafiltration removal volume, the
dialysate flow rate, the dialysate temperature, the blood pressure
measurement schedule and alarms, and the heparin prescription.
[0092] Among the patient parameters that are logged by the machine
and that can be downloaded to a memory card for later therapy
analysis are: temporal data relating to dialysate temperature and
conductivity (both of which are typically measured at several
points in the fluid circuit), venous, arterial, dialysate, systolic
and diastolic pressures, blood flow rate, total blood processed,
ultrafiltration rate, total ultrafiltrate removed, the
ultrafiltrate goal, and the machine states.
[0093] Additionally, the data card can convey to the machine
certain codes that, when read by the machine, initiate special
operations. These operations include calibration mode, technician
mode, enabling the blood pressure monitoring function, modifying
the parameters transmitted over the serial port for diagnostics,
and others.
[0094] The card used in the preferred embodiment is commercially
available from Micro Chip Technologies under the trademark ENVOY
and provides 32K of data storage in EEPROM form. Similar cards are
also available from Datakey.
[0095] When a card containing treatment parameters is read by the
machine, the stored parameters do not immediately take effect.
Instead, each is displayed on the screen and the operator is asked,
through prompts that appear on the screen, to verify each
individually. If a parameter is not verified, that aspect of
machine operation is left unchanged. In the preferred embodiment,
the parameters loaded from a memory card are displayed in their
respective parameter windows and each is highlighted in sequence,
with the system soliciting verification of the parameter in the
highlighted window. In alternative embodiments, a plurality of
parameters are be displayed for verification as a group.
[0096] Returning now to FIG. 7, the computer system 500 that
controls the user interface and other aspects of machine operations
is built around an IBM-AT compatible motherboard 502 that includes
an Intel 80286 microprocessor 504 and 256K of RAM 506
interconnected by an AT bus 508. Into expansion slots in this
motherboard plug seven additional boards: a memory board 510, an
RS-232 board 512 (which is dedicated to controlling a patient blood
pressure monitor), an Input/Output system controller board 514, an
ultrafiltration/proportioning system controller board 516, a blood
pump system controller board 518, a touch screen interface board
520, and an EGA display adapter board 522.
[0097] The computer system has five primary responsibilities: (1)
user interface (i.e., through the CRT display and the touch
screen); (2) state machine control (i.e., rinse, prime, dialyze,
etc.); (3) microcontroller communications; (4) conducting of
self-tests; and (5) calibrations. These functions are carried out
by the AT-computer in conjunction with the above-listed expansion
boards.
[0098] Turning now to a more detailed description of each
component, the memory board 510 contains the firmware for the 80286
microprocessor. The memory board can hold up to 384K of read only
memory (ROM) 524 and 8K of nonvolatile static random access memory
(RAM) 526. Also included on the memory board is a memory interface
528, an RS-232C interface 530, and a time of day clock 532. The
interface 528 is conventional and simply handles the addressing of
memories 524 and 526. The RS-232C interface is for general purpose
use (as opposed to the RS-232 interface 512 that is dedicated to
use with a blood pressure monitor) and is typically used to
remotely provide programming instructions to, and to interrogate
patient treatment data from, the machine. The time of day clock 532
is used, inter alia, to time/date stamp patient data as it is
acquired and to provide a time of day reference by which automated
machine operations (such as unattended warm-up) may be
controlled.
[0099] The host control program is written in the `C` programming
language. This code is compiled, linked and loaded into the ROM
524. The purpose of the host control program is to:
[0100] Gather data from the Input/Output, Blood Pump and
Ultrafiltration controller sub-systems, and output control
functions to the various controller sub-systems;
[0101] Input data from the user interface touch screen;
[0102] Monitor the data for violation of alarm limits and usage
operating conditions, and to set the appropriate program alarm
condition indicators;
[0103] Evaluate the data to determine the current operating state
of the control program, i.e., Standby, Rinse, Self-Test, Prime, and
Dialyze; and
[0104] Update the display data to the CRT portion of the user
interface.
[0105] The RAM memory 526 is used to store calibration and machine
parameters.
[0106] In order for the memory board to operate without conflict
with the host AT-motherboard, the motherboard must be modified by
disabling the data buffers above address 256K. The memory
controller's ROM space is mapped into the address space from 256K
to 640K, with the portion between 256K and 312K being mapped also
to address range 832K to 888K. The code at this upper address range
is configured as a BIOS extension, which results in the ROM being
given control by the motherboard's BIOS software following power-on
initialization. Unlike the standard BIOS extensions, the host code
does not return to the BIOS after being given control.
[0107] The RS-232 board 512 permits computerized remote control of
a patient blood pressure monitor. Suitable blood pressure monitors
that are adapted for RS-232 control are available from Spacelabs of
Hillsboro, Oreg.
[0108] The touch screen interface board 520 is commercially
available as part number E271-400 from Elographics and is designed
to operate with the E272-12 touch panel 501 that is used in the
preferred embodiment. The function of the interface board 520 is to
translate signals returned from the touch screen into a data format
suitable for use by the 80286 microprocessor 504. Terminate and
stay resident software for driving the interface board 520 is
available from Elographics.
[0109] The EGA display adapter card 522 is conventional and
provides RGB signals to the CRT display 503.
[0110] The three microcontroller subsystems (the blood pump system
518, the ultrafiltration/proportioning system 516, and the I/O
system 514) are particularly detailed in the following
discussion.
Blood Pump System
[0111] The blood pump controller 518 is built using an Intel 8040
microcontroller and is responsible for controlling or monitoring
five subsystems. They are (1) the blood pump; (2) the blood
pressure measurement (arterial, venous and expansion chamber): (3)
heparin delivery: (4) level adjust; and (5) ambient temperature.
The blood pump controller operates in conjunction with a blood pump
power board (not shown) that controllably provides operating power
to devices controlled by the blood pump controller.
[0112] In still more detail, the primary operation of the blood
pump controller 518 is to supply power to the blood pump motor such
that the pump head will turn and pump at a rate selected by the
operator.
[0113] The blood pump controller system consists of the following
major components:
1 Description Location User parameter entry Host controller
Software Speed Error Control Blood Pmp Controller Hardware Speed
Error Control BP Power Board Optical speed sensor On motor shaft
Motor Power Driver Circuitry BP Power Board
[0114] The operator enters the desired blood pump rate information
on the video screen (CRT) touch panel. The host controller (80286
microprocessor) converts this information to the appropriate motor
rate which it then sends to the Blood Pump controller (8040) on the
Blood Pump controller board. The 8040 controller converts the motor
rate information to an analog level, which is fed to a motor speed
control IC (LM2917-8) on the Blood Pump Power board.
[0115] An optical speed sensor is mounted on the rear shaft of the
blood pump motor, with an LED being positioned on one side of the
shaft, and a photo transistor on the opposite side. The shaft has
two holes drilled through it, with each hole being perpendicular to
the shaft and to each other. This results in four optical pulses
received per shaft revolution.
[0116] This tachometer signal is monitored by both the LM2917-8 and
the 8040 controller. The LM2917-8 provides quick responding speed
control by comparing the motor speed with the desired speed
information from the 8040. The result of this comparison is an
error signal which provides an input to the motor power driver
circuit.
[0117] The motor power driver provides a +24 V pulse width
modulated drive to the motor at a frequency of approximately 30
KHz. This drive is current limit protected, to prevent damage in
the event of a stalled motor.
[0118] The 8040 compares the tachometer motor speed information
with the desired speed commanded by the 80286 and corrects the
level provided to the LM2917-8 accordingly. In this way the 8040
guarantees the ultimate accuracy of the pump, with the LM2917-8
circuit not requiring any calibration. In addition, the 8040 can
monitor for control problems, such as under speed or over speed,
which may result from failures in the LM2917-8 or motor drive
circuitry.
[0119] The 8040 also monitors the motor speed independent of the
tachometer signal using the motor's back EMF. Periodically (every
0.5 second) the motor drive is turned off for approximately 6
millisecond and the voltage at the motor terminals is measured.
Though this does not result in as precise an indication as the
tachometer signal, gross failures can be determined, such as when
the tachometer signal is lost.
Blood Pressure Measurement
[0120] The blood pressure measurements include the venous, arterial
and expansion chamber (for Single Needle treatment) pressures. All
three measurement systems include identical hardware. Each pressure
is sensed by a SenSym SCX15 gauge sensing pressure transducer
mounted to the Blood Pump Power board. Each transducer is connected
to a differential amplifier designed to provide a measurement range
from -400 to +600 mmHg. The output of each amplifier drives an A/D
input channel of the Blood Pump Control system, at which point it
is converted to a 10 bit digital value. The calibration of each of
the pressure inputs is handled entirely in software, requiring that
the design of each amplifier guarantee that its output remain
within the A/D input range of 0 to +5 V over the input pressure
range and over all component tolerances.
Heparin Delivery
[0121] Heparin delivery is accomplished by stepping a stepper motor
which rotates the pinion of a rack and pinion mechanism. The pinion
moves the rack, and the mechanical fixture is such that the plunger
of the heparin syringe moves the same distance. The stepper motor
is controlled by the 8040 microcontroller located on the Blood Pump
Controller board 518. When the operator enters a desired heparin
rate in milliliters per hour (mL/h) via the front panel touch
screen, the host 80286 microprocessor converts this information to
the appropriate motor step rate and passes it to the Blood Pump
microcontroller. The Blood Pump microcontroller outputs a motor
step rate logic signal to the Blood Pump Power board where the
heparin motor power drive circuitry energizes the appropriate
stepper motor coil.
[0122] The motor step rate logic signal from the Blood Pump
microcontroller 518 is also input to the I/O Controller board 8040
microcontroller 514. The I/O microcontroller monitors this signal
to determine if the heparin motor is going the appropriate speed.
If it determines that an overspeed condition exists, it disables
the heparin motor via a disable line that goes to the Blood Pump
Power board.
[0123] There are two optical sensors to provide information about
the state of the heparin pump. The disengage sensor detects when
the front panel syringe holder arm is in the disengage position.
The end-of-stroke sensor detects when the pinion is raised up on
the rack, which occurs when the gear teeth are not meshed. This is
an indication of an overpressure condition. The Blood Pump
microcontroller monitors the state of these sensors and passes the
information to the host 80286 microprocessor.
Level Adjust
[0124] The level adjust system allows the operator to change the
blood level in the arterial and venous drip chambers. A level up
and level down button exists for each drip chamber. The 8040
microcontroller on the Blood Pump Controller board 518 monitors the
button positions. When a button is pressed, a valve selects that
drip chamber power is supplied to the motor such that the pump head
of a peristaltic pump rotates to apply a positive or negative
pressure to the drip chamber. The software logic only accepts one
button press at a time. If two buttons are pressed simultaneously,
both are ignored.
[0125] The motor drive circuitry is located on the Blood Pump Power
Board. The motor may be driven in the forward or reverse direction.
A direction signal from the Blood Pump Controller Board, along with
a pulse width modulated motor rate signal controls two bipolar half
bridge motor drivers. Both half bridge motor drivers receive the
same motor rate signal, while the motor direction signal is high at
one and low at the other to determine the direction the motor runs.
The half bridge drivers provide a 24 V pulse width modulated drive
voltage of approximately 30 KHz to the motor.
[0126] Other details of the level adjusts are described
hereinbelow.
Ambient Temperature Control
[0127] The purpose of the cabinet cooling system is to keep the
internal temperature of the cabinet lower than the 50.degree. C.
maximum temperature at which the electronic components are
guaranteed to operate. (Most electronic components are rated to
operate at 60.degree. C., the exception is the solid state relay
used for heater control.) A fan is located at the base of the
cabinet and exhausts the warm cabinet air. An intake vent for the
ambient room temperature is located below the CRT on the back of
the machine.
[0128] The cabinet cooling system consists of the following major
components:
2 Description Location Cabinet Fan Base of cabinet Blood Pump
Temperature IC Blood Pump Power Board Misc I/O Temperature IC Misc
I/O Electronics Pwr Bd. Software Fan Control Host controller
Cabinet Fan Drive Blood Pump Power Board
[0129] The two LM35DZ temperature ICs are located on the Blood Pump
and Misc I/O Electronics power boards. This IC outputs a voltage
linear with temperature in .degree. C. (10.0 mV/.degree. C.). These
temperature readings are input to the fan control software.
[0130] The fan control software always responds to the higher of
the two temperatures. Typical values are as follows. At 46.degree.
C. the fan turns on in the low speed mode and at 48.degree. C. it
turns on in the high speed mode. There is a 2.degree. C. of
hysteresis at these threshold temperatures, i.e., the fan returns
to low speed at 46.degree. C. and turns off at 44.degree. C. In
addition, at 60.degree. C. a cabinet temperature alarm occurs that
results in the machine shutdown state.
[0131] The fan power driver is located on the Blood Pump Power
board. A motor rate signal from the Blood Pump Controller board
determines the duty cycle of a 30 KHz pulse width modulated signal.
This signal is input into a passive filter to provide a DC signal
to the motor.
UF/Proportioning Control System
[0132] The ultrafiltration/proportioning (UF/PROP) controller 516
is built using an Intel 8040 microcontroller and is responsible for
controlling the systems associated with ultrafiltration and
dialysate preparation. This controller operates in conjunction with
an ultrafiltration/ proportioning power card (not shown) that
controllably provides operating power to devices controlled by the
ultrafiltration/proportioning controller. Six subsystems are
controlled or monitored by the UF/Proportioning controller 516.
They are:
[0133] a. Temperature Control
[0134] b. Proportioning Control
[0135] c. Flow Control
[0136] d. UF Removal Control
[0137] e. Conductivity Monitoring
[0138] f. Temperature Monitoring
Temperature Control
[0139] The UF/PROP system 516 controls the dialysate temperature by
enabling a zero voltage crossing solid state relay, which provides
the power to a 1500 W heater (item 18 in FIG. 1), with a 5 Hz pulse
width modulated digital signal (heater-enable signal). The duty
cycle of the heater-enable signal is updated every 0.5 seconds with
the sum of the past duty cycle and a temperature error correction
value. The correction value is proportional to the difference
between the desired temperature (stored by the host) and the
measured control temperature (measured immediately down stream of
the heater housing).
[0140] The host-determined desired temperature is calculated using
the user-entered desired temperature and the stable "B"
conductivity probe (item 46 in FIG. 1) temperature. If the stable
"B" conductivity probe temperature is different from the
user-entered desired temperature by more than 0.05.degree. C., then
the control temperature threshold sent to the UF/PROP controller is
updated so that the "B" conductivity probe temperature will equal
the user-entered desired temperature. In this way, the dialysate
temperature at the "B" conductivity probe will be adjusted so that
flow rate and ambient temperature effects on the "B" conductivity
probe temperature (and the primary temperature, displayed on the
video screen) will be compensated. This control temperature
adjustment is performed a maximum of every 5 minutes.
Proportioning Control
[0141] The UF/PROP system 516 controls the concentrate(s) to water
proportioning ratios by controlling the dialysate flow rate, the
"A" concentrate 5 flow rate, and the "B" concentrate flow rate.
[0142] The "A" and "B" concentrate pumps (items 22 and 40,
respectively, in FIG. 1) are stepper-motor driven (each by a
cam/follower) diaphragm pumps which deliver a calibrated volume of
concentrate per stepper motor revolution. Their flow rates are
controlled by controlling the speed of the stepper motors. The
concentrate pumps are unidirectional and utilize the proper
actuation of a three-way valve for their intake and output pumping
strokes. The intake stroke is synchronized by a signal that is
generated by an optical interrupter sensor which senses a pin
mounted on the cam of the pump assembly. Further details pertaining
to the "A" and "B" concentrate pumps are described hereinbelow.
[0143] The UF/PROP controller 516 utilizes the fact that the
stepper motors require 200 motor steps per revolution (between each
synchronization pulse) to check the concentrate pumps for stepping
errors. If late or early synchronization pulses are received then
the associated error conditions are reported on the screen during
the Technician Mode of the machine (further details provided
hereinbelow).
[0144] During the Rinse Mode, the host determines the concentrate
treatment mode based on the "A" and "B" rinse port interlock
information (further details provided hereinbelow). If the "B"
concentrate line (FIG. 1, item 104) is not coupled to the "B" rinse
port (FIG. 1, item 30), a bicarbonate treatment is initiated by
setting the proportioning ratios and the conductivity alarm limits
appropriately. Conversely, if the "B" concentrate line is coupled
to the "B" rinse port, an acetate treatment is initiated (further
details provided hereinbelow). Using the dialysate flow rate and
the proportioning ratios, the host determines the associated
concentrate flow rates and stores the concentrate pump speeds in
the UF/PROP controller. The proportioning mode (for acetate or
bicarbonate dialysis) cannot be changed in the Prime or Dialyze
Modes.
[0145] The control of the dialysate flow rate is described in the
following Flow Control section of the UF/PROP controller
description.
Flow Control
[0146] The UF/PROP system 516 controls the dialysate flow rate by
controlling the time between the switching of the flow equalizer
(FIG. 1, item 54) valves (provided that all the fluid within the
flow equalizer chambers has been exchanged).
[0147] The average flow equalizer volume is calibrated (measured)
during the Calibration Mode. The time between the switching of the
flow equalizer valves (FIG. 1, items 142-149) is scaled by the host
(according to the calibration constant) and stored in the UF/PROP
controller so that the user entered desired dialysate flow rate is
achieved.
[0148] To guarantee the complete fluid transfer to/from the flow
equalizer chambers (FIG. 1, items 126, 128) two flow sensors (FIG.
1, items 58, 59; described in further details hereinbelow) are
located within the fluid path to detect the absence of dialysate
flow. The time at which both sensors detect no flow has been
defined as end of stroke. The end-of-stroke time has been defined
as the time between the moment an end of stroke was sensed and the
desired flow equalizer valve switch time. Since the supply pump
speed controls the instantaneous dialysate flow rate, the UF/PROP
controller servos the supply pump speed in order to maintain a
consistent end-of-stroke time.
[0149] Since the flow equalizer volume is calibrated and the
end-of-stroke time is controlled, the UF/PROP system 516 can
accurately control the dialysate flow rate to the user-entered
value.
UF Removal Control
[0150] The UF/PROP system 516 controls the UF removal rate by
controlling the time between the switching of the UF flow meter
valves (FIG. 1, items 142-149). The UF/PROP system controls the
accumulated UF volume by counting the number of UF flow meter
strokes.
[0151] Since the UF flow meter volume is calibrated (measured) in
the Calibration Mode, the rate which the host (80286
microprocessor) passes to the UF/PROP controller (number of seconds
between valve switches) is scaled so that the user-entered UF
removal rate is achieved.
[0152] In the same way, the user-entered UF removal volume is
scaled by the UF flow meter's stroke volume to a number of UF meter
strokes. The host passes the number of UF meter strokes to the
UF/PROP controller. The UF/PROP controller will then switch the UF
flow meter valves and decrement the stroke number, at the desired
rate, as long as the stroke number is greater than zero. The host
can then calculate the UF removal volume accumulated by subtracting
the number of UF flow meter strokes remaining, scaled by the stroke
volume, from the operator-entered desired UF removal volume. The
accumulated volume is displayed during the Dialyze Mode. This value
remains during the Rinse Mode and is cleared upon the entry of the
Self Test Mode.
[0153] In Rinse, the UF removal rate is 3.6 L/h and the video
screen indicates no UF volume accumulated. During the Self Test
Mode, no UF removal occurs except during specific self tests
performed by the machine (no UF volume is accumulated). In the
Prime Mode, the UF removal rate is set by the operator and is no
greater than 0.5 L/h (no UF volume is accumulated). During the
Dialyze Mode, the UF removal rate is set by the operator and is
limited to between 0.1 and 4.00 L/h. For UF removal to occur in the
Dialyze Mode the following conditions must be met:
[0154] 1. A target UF volume and a UF rate have been entered (or
treatment time and target UF volume have been entered and a
machine-calculated UF rate is used).
[0155] 2. The blood pump is pumping.
[0156] 3. The target UF volume has not been reached.
Conductivity Monitoring
[0157] Conductivity is used as a measurement of the electrolyte
composition of the dialysate. Conductivity is usually defined as
the ability of a solution to pass electrical current. The
conductivity of dialysate will vary due to the temperature and the
electrolyte composition of the dialysate.
[0158] The UF/PROP system measures conductivity at two locations
(conductivity probes) in the hydraulic circuit using
alternating-current resistance measurements between each of the
conductivity probes' electrode pairs. The two flow path locations
are at the "A" conductivity probe (FIG. 1, item 38) and the "B"
conductivity probe (FIG. 1, item 46).
[0159] One electrode of each of the probes is stimulated with a 1
kHz ac voltage while the other is held at virtual ground (current
sense electrode). Two voltages are produced by the resistance
measurement circuit. The ratio of the voltages is proportional to
the resistance of the respective probe. The resistance of the
probes has been modeled as a function of temperature and
conductivity. Since each of the conductivity probes contains a
thermistor, the temperature at each of the probes is known. Using
the model that was derived for the probes, the temperature measured
at the probes, and the resistance measured at the probes the
conductivity is calculated.
[0160] Each conductivity probe is calibrated during the Calibration
Mode, at which time the resistance of each probe is measured at a
known conductivity and temperature (by the use of an external
reference meter) for the scaling of the probe's base resistance in
the relationship described previously.
[0161] The UF/PROP system 516 generates alarms from the measured
conductivities at the "A" and "B" probes. Since these conductivity
alarms are used to verify the proportioning ratios, the alarms are
generated by testing the "A" conductivity and the "B" portion of
the total conductivity ("B" portion="B" conductivity-"A"
conductivity). The alarm limits are determined from the concentrate
treatment mode and are stored in the UF/PROP controller by the
host. Therefore only during a bicarbonate dialysis treatment would
the host store a non-zero expected "B" conductivity portion.
[0162] The host determines the concentrate treatment mode during
the Rinse Mode by reading the "All and "B" rinse port interlock
information. If the "B" concentrate line is not on the "B" rinse
port; a bicarbonate treatment is initiated by setting the
proportioning ratios and the conductivity alarm limits
appropriately. Conversely, if the "B" concentrate line is coupled
to the "B" rinse port, an acetate treatment is initiated. Upon
exiting the Rinse Mode the concentrate treatment mode is set for
the remainder of the dialysis treatment (concentrate treatment mode
is only adjusted in the Rinse Mode).
Temperature Monitoring
[0163] The UF/PROP system 516 measures the dialysate temperature at
three locations in the fluid path. The first location is directly
after the heater (FIG. 1, item 18) and this thermistor, the heater
thermistor (FIG. 1, item 20), is used for the primary temperature
control feedback. The next two thermistors (FIG. 1, items 110 and
124) are contained in the "A" and "B" conductivity probes (FIG. 1,
items 38 and 46, respectively). These temperatures are used to
temperature-compensate the "A" and "B" conductivity measurements.
The "B" conductivity temperature is also used to generate a backup
high temperature alarm.
[0164] The temperature measurement circuit used throughout the
machine consists of a voltage divider with a Thevenin Equivalent
circuit of 3062.OMEGA. in series with a 7.55 V supply. The voltage
divider circuit when connected to the thermistor used in the
temperature measurement system referenced to ground produces the
voltage to temperature relationship of T(.degree.
C.)-(3.77V-Vtemp)(12.73)(.degree. C./V)+37.degree. C.
[0165] The tolerance on the component parameters used in the
temperature measurement system can be as great as 10%, therefore
the temperature-to-voltage relationship must be calibrated.
Calibration of the temperature measurements is a two-point
calibration done at 30 and 40.degree. C. The calibration procedure
results in a calibration constant for both the slope and the offset
for each temperature probe/circuit.
[0166] In the UF/PROP controller the voltage described above as
Vtemp is measured for the three temperature probes in its system on
a scheduled basis (every 0.2 seconds for the "A" and "B"
temperatures and every 1 second for the heater temperature).
[0167] The temperature that is displayed on the video screen is
measured at the primary ("dialysate") conductivity probe, located
just before the bypass valve (see FIG. 1), by the I/O
controller.
Input/Output Control System
[0168] Nine subsystems are controlled or monitored by the I/O
control system 514. They are:
[0169] Air detector
[0170] Blood leak detector
[0171] Dialysate pressure monitor
[0172] Heparin pump overspeed monitor
[0173] Bypass system and flow sensor
[0174] Conductivity monitor
[0175] Temperature monitor
[0176] Line clamp
[0177] Power fail alarm
Air Detector
[0178] The air detector assembly utilizes a set of 2 MHz piezo
crystals. One crystal functions as an ultrasonic transmitter and
the second crystal functions as a receiver. The transmitter and
receiver are housed in separate but identical assemblies. There is
a distance of 0.20 inch between these assemblies into which the
venous blood line is placed during dialysis. The emitter is driven
by a 2 MHz squarewave that is derived from a crystal oscillator
located on an I/O Electrical Power board 536 that is connected to
the I/O controller 514 by a ribbon cable. When there is fluid in
the blood line between the crystal assemblies, the 2 MHz signal is
coupled to the detector assembly. The return signal from the
detector assembly is amplified and rectified by two independent
circuits also located on the I/O Electrical Power board 536. These
dc output levels are monitored using two different methods. The
first method is the software generated alarm and the second is the
hardware generated alarm.
Software Alarm Detection (Primary Alarm)
[0179] One output is fed from the I/O Electrical Power board 536 to
an A to D converter and read by the 8040 microcontroller on the I/O
Controller board 514. This value is averaged over a 400 msec time
period and reduced by multiplying it by 15/16 and subtracting 50 mV
(for noise immunity). This new value is then converted back to an
analog level to be used as an alarm limit. This software generated
limit is compared to the rectified dc signal from the detector. The
output state of this comparator is monitored by the on-board 8040.
When the unaveraged signal falls below the software generated limit
for longer than a calibratable time period, an alarm occurs.
Sensitivity of the software alarm is 10 microlitres at 300 mL/min
blood flow.
Hardware Alarm Detection (Secondary Alarm)
[0180] The hardware alarm is redundant to the software generated
alarm. This alarm uses two comparators on the I/O Electrical Power
board 536. One comparator looks for a minimum dc level from the
rectified detector signal which guarantees the presence of fluid in
the venous tubing. The second comparator is ac-coupled to react to
a large air bubble in the tubing. Sensitivity of this detector is
approximately 300 microliters at 300 mL/min blood flow. Both
comparator outputs are wire OR'd together so that either comparator
will generate an alarm.
Blood Leak Detector
[0181] The detector assembly consists of a high-efficiency green
LED and a photocell. These components are installed into a housing
through which spent dialysate passes. Both of these components
connect to the I/O Hydraulic Power board. The LED is connected to a
voltage-to-current converter on an I/O Hydraulic Power board 534
(which is also connected to the I/O controller 514 by a ribbon
cable). The input to this circuitry comes from the I/O Controller
board 514. The photocell is tied to the +5 V reference supply
through a 750k ohm resistor. This provides a voltage divider which
is monitored on the I/O Controller board.
[0182] The current through the LED is adjustable and controlled via
a D to A output from the I/O Controller board. The light intensity
of the LED is adjusted to illuminate the photocell to a point where
its resistance is below the alarm threshold. During a blood leak,
the presence of blood in the housing attenuates the light striking
the photocell which causes an increase in both the photocell
resistance and voltage. The increase in voltage (monitored by the
microcontroller on the I/O controller board) results in a
blood-leak alarm.
[0183] Further details on the blood-leak detector are provided
hereinbelow.
Dialysate Pressure Monitor
[0184] The dialysate pressure is sensed by a resistive bridge
pressure transducer (FIG. 1, item 64) located just upstream of the
dialyzer. The transducer is connected to a differential amplifier
circuit on the I/O Hydraulics Power board 534 designed to provide a
measurement from -400 to +500 mmHg. The differential amplifier
circuit also has an offset input that comes from a software
calibratable variable, DAC_OFFSET. The output of the amplifier
drives an A/D input channel of the I/O Controller system, at which
point it is converted to a 10 bit digital value. The calibration of
the pressure input is handled entirely in the software, requiring
that the design of the amplifier guarantee that the output remains
within the A/D input range of 0 to +5 V over the input pressure
range and over all component tolerances.
Heparin Pump Overspeed Monitor
[0185] To ensure that the heparin pump does not exceed its set
speed, the I/O controller board software monitors a clock signal
from the Blood Pump Controller board that is equivalent to 1/4th
the heparin pump step rate. In the event that a heparin pump
overspeed occurs, the I/O controller board disables the heparin
pump via a hardware line that goes to the Blood Pump Power board
and notifies the host of the alarm.
[0186] To determine if the heparin pump is running at the correct
speed, the time required for ten clock signals to occur is measured
(and stored in variable HEPTIMER) and compared against a minimum
time period that is set by the host (HP_P_MIN). If the measured
period is less than the host set limit, a normal-speed alarm
occurs. The host is notified of the normal-speed alarm and the
heparin pump is disabled via the hardware line to the Blood Pump
Power board.
[0187] When the heparin pump rate changes, the host resets the
minimum time period, HP_P_MIN, and the I/O controller waits for the
first clock signal to restart the timer (this first clock is not
counted as one of the ten). In this way, the alarm logic is
resynchronized with the heparin pump stepper motor.
[0188] The I/O controller board 514 also monitors the total amount
of heparin delivered in the high-speed bolus mode. When it receives
clock signals at a rate faster than a predetermined speed, it
assumes the pump is operating in the high-speed mode. It has a
high-speed counter, H_SPD_CNTR, that is set by the host. If more
high-speed counts occur than are in the counter, a high speed alarm
occurs. The host is notified of the high-speed alarm and the
heparin pump is disabled via the hardware line to the Blood Pump
Power board.
Bypass System and Flow Sensor
[0189] The bypass mode is initiated when a primary dialysate alarm
is detected by the I/O Controller board, when a redundant dialysate
alarm is detected by the UF/PROP Controller board 516, when the
host requests bypass, or when the manual bypass button is
pushed.
[0190] The bypass valve (FIG. 1, item 66) is in the bypass position
when deenergized. It is driven from the nominal +24 V supply with a
straight on/off transistor control on the I/O Hydraulics Power
board.
[0191] To verify that there is not a failure in the bypass system,
a flow sensor (FIG. 1, item 62) located upstream of the dialyzer
and just downstream of the bypass valve checks for flow. If flow
exists during bypass, a Bypass Fail Alarm is triggered and the
machine is put in the safe, nonfunctional, Shutdown state. If there
is no flow when not in the bypass mode, a No Flow alarm is
generated. (Further details on the flow sensor are provided
hereinbelow.)
[0192] This flow sensor consists of two thermistors. The first is a
reference thermistor used to determine the fluid temperature. The
second thermistor uses thermal dilution to sense the fluid flow.
The voltage outputs from the thermistors on the I/O Hydraulics
Power board 534 drive A/D input channels on the I/O Controller
board where they are converted to 10 bit digital values. A software
algorithm in the I/O Controller code uses these inputs to determine
the flow condition. The design of the voltage divider guarantees
that the output remains within the A/D input range of 0 to +5 V
over the input temperature/flow range and over all component
tolerances.
Conductivity Monitoring
[0193] The dialysate conductivity probe (FIG. 1, item 60) comprises
two stainless steel probes inserted into the flow path just prior
to the dialyzer. The drive signal for the conductivity probes is a
capacitive-coupled squarewave generated on the I/O Hydraulic board
534. This signal is sent to the conductivity probe and a monitor
circuit. Both the monitor circuit and the return signal are
rectified and filtered. These dc values are routed to I/O
Controller board 514 along with the temperature signal.
[0194] On the I/O controller board, the temperature, conductivity,
and conductivity reference signals are input to an A-to-D converter
that is monitored by the on-board 8040 microcontroller. The
microcontroller calculates the temperature-compensated
conductivity. This value is then displayed on the CRT as the
conductivity in milliSiemens per centimeter (mS/cm).
Temperature Monitoring
[0195] The thermistor (FIG. 1, item 168) installed in the dialysate
conductivity probe (FIG. 1, item 60) changes its resistance in
response to changes in temperature. The values for dialysate
conductivity and temperature measured at this probe are displayed
on the CRT and are used to generate the primary alarms for patient
safety. If either value is outside preset alarm limits, a bypass
condition and an audio alarm occur.
[0196] The thermistor is wired to a resistor divider network on the
I/O hydraulic board. The output of this divider network is sent to
the Miscellaneous I/O controller board 514 where it is monitored by
the onboard 8040 microcontroller via an A-to-D converter network.
From this information, the controller calculates, the temperature
using offset and gain parameters stored in the host from the
calibration. Calibration of the temperature measurement is a
two-point procedure done at 30 and 40.degree. C.
Line Clamp
[0197] The line clamp opens with a solenoid and clamps with a
spring return. When the solenoid is not energized, the spring
pushes the plunger away from the solenoid. This causes the plunger
to clamp the blood tubing. When the solenoid is energized, it pulls
the plunger in with enough force to overcome the spring force. This
unclamps the blood tubing. In the event of a power failure, the
solenoid is de-energized causing the blood line to be clamped.
[0198] The solenoid is controlled by the line clamp board. On the
line clamp board is a pulse-width modulated current controller.
This circuit applies sufficient current to the line clamp solenoid
to pull in the plunger. After pull in, the controller ramps the
current down to a level capable of holding the line clamp open.
This cutback in current reduces the temperature of the solenoid,
resulting in a more reliable device. Also located on the line clamp
board, is a quick-release circuit which helps dissipate the power
stored in the solenoid. The result of this circuitry is a quicker
and more repeatable clamp time over the life of the machine.
[0199] Control for the line clamp comes from the Miscellaneous I/O
controller board 514 via the I/O power board 536. The control
signal for clamp and unclamp is optically coupled on the line clamp
board. This provides electrical isolation between the high voltage
used to operate the line clamp and the low voltage used for the
control signals from the microprocessor.
Power Fail Alarm
[0200] The power-fail alarm circuitry is located on the Misc I/O
Electrical Power board 536, and includes a CMOS power state flip
flop powered by a 1 Farad (F) capacitor. The flip flop, which can
be toggled by either the front panel power button or the 80286
system controller, provides the following functions:
[0201] Whenever power is not supplied to the machine (i.e., when
the +5 V supply is off) and the flip flop is in the on state, power
is supplied from the 1 F capacitor to the audio alarm device.
Whenever power is supplied to the machine, the flip flop's output
state is ready by the 80286, which provides indication of the
intended machine power state. Also, when the flip flop is in the on
state, power is supplied to the front panel power switch LED.
[0202] The first function listed above results in the power fail
alarm. The alarm occurs either if the machine loses power while it
is running, or if the front panel power button is pressed "on" when
there is no power supplied to the machine. The alarm can be
silenced by toggling the flip flop off via pressing "off" the front
panel power button.
[0203] Additional details of the preferred computer system 500 are
provided, inter alia, in Appendix C.
[0204] Reference has been made to five appendices (A-E) which form
part of the specification hereof and which further detail certain
aspects of the preferred embodiment.
Bypass Valve Flow Sensor
[0205] The dialysis machine of the present invention includes a
bypass valve flow sensor which is utilized to confirm that
dialysate flow to the dialyzer is completely interrupted during
bypass. The bypass valve flow sensor comprises a first thermistor
202 and a second thermistor 204, as shown schematically in FIG. 2.
FIG. 2 also shows in simplified schematic form the flow equalizer
54, the bypass valve 166, and a dialyzer 208. The first and second
thermistors 202, 204 are of a negative-temperature coefficient
(NTC) type known in the art. The first, or "sensing," thermistor
202 is energized with a 20 mA constant current while the second, or
"reference," thermistor 204 is driven with a negligibly small
current.
[0206] The electrical resistance of both thermistors 202, 204 is
measured using electronic circuitry (not shown). The resistance
R(T) of each thermistor 202, 204 at a given temperature T is
determined by the following relationship:
R(T)=(K.sub.1) exp (-K.sub.2T)
[0207] where K.sub.1 and K.sub.2 are constants. Hence, the
thermistor resistance is a function of its temperature.
[0208] Since the electrical power input to the reference thermistor
204 is negligibly small, the temperature of the reference
thermistor 204 will be substantially equal to that of the liquid
surrounding it, whether flowing or not, at all times. The sensing
thermistor 202, on the other hand, is powered by a substantial
constant current. Hence, the sensing thermistor 202 will undergo
appreciable self-heating. During conditions of no dialysate flow
past the thermistors 202, 204, such as during bypass, the
temperature of the reference thermistor 204 will be equal to the
temperature of the dialysate surrounding the reference thermistor
204. However, the no-flow temperature of the sensing thermistor
202, as a result of self-heating, will be substantially greater
than the temperature of the reference thermistor 204. During
conditions when dialysate is flowing past the thermistors 202, 204,
the temperature of the reference thermistor 204 will, again, be
equal to the temperature of the dialysate. The temperature of the
sensing thermistor 202, while greater than that of the reference
thermistor 204, will be somewhat lower than the temperature thereof
would otherwise be during no-flow conditions. This is because
dialysate flowing past the sensing thermistor 202 will conduct a
portion of the self-heating energy away from the thermistor 202,
thereby lowering the temperature of the thermistor 202. The bypass
flow sensor can detect flow as low as about 3 mL/min.
[0209] Since the sensing thermistor 202 is driven with a
constant-current source, the amount of power input into the
thermistor 202 is limited according to the relationship P=I.sup.2R.
As a result, the ultimate self-heating temperature achievable by
the sensing thermistor 202 will self-limit, thereby protecting the
sensing thermistor 202 from a damaging thermal runaway
condition.
[0210] The two thermistors 202, 204 are calibrated by measuring the
electrical resistance across them individually under conditions of
no dialysate flow at both 30 and 40.degree. C. A mathematical
relationship is utilized during calibration which equates the
resistance of the sensing thermistor 202 and the resistance of the
reference thermistor 204 at any temperature between 30 and
40.degree. C. If Rh(t) represents the sensing thermistor resistance
at T=t, and Rr(t) represents the reference thermistor resistance at
T=t, then, at no dialysate flow, Rh(t)-A Rr(t)+B, where A and B are
calibration constants determined by the equations shown below
(since Rh(30), Rh(40), Rr(30), and Rr(40) are measured during
calibration):
Rh(30)=A.multidot.Rr(30)+B
Rh(40)-A.multidot.Rr(40)+B
[0211] Hence, if the thermistor resistances are equal, then the
electronic circuitry (not shown) coupled to the thermistors 202,
204 recognizes such equal resistance as indicating a "no dialysate
flow" condition. However, if 5 the resistances of the first and
second thermistors 202, 204 are not equal, which occurs when any
dialysate flow (greater than about 3 mL/min) is passing by the
first and second thermistors 202, 204, the electronic circuitry
recognizes a "dialysate flow" condition. Therefore, whenever the
machine is in bypass, if the electronic circuitry senses that the
resistances across the first and second thermistors 202, 204 is
unequal, indicating flow, the machine will trigger an alarm
condition to notify the operator of failure of the bypass valve
66.
[0212] The advantage of the bypass valve flow sensor 62 as
described hereinabove is that it enables the dialysate bypass valve
66 to be tested functionally, i.e., via a determination of whether
or not the bypass valve 66 actually shut off the flow of dialysate
to the dialyzer 208. This is the first known use of such a flow
sensor in a hemodialysis machine. Other bypass valve sensors known
in the relevant art merely test whether or not, for example, the
bypass valve has been energized. One example of such a mechanism is
a sensor that determines whether or not a solenoid controlling the
valve has shifted position in response to application of current
thereto. In the present invention, in contrast, the bypass valve
flow sensor verifies that the bypass valve 66 has actually seated
properly.
[0213] Further details and engineering data pertaining to the
bypass valve flow sensor can be found in Appendix A, pp. ET 52-ET
57 ("Flow Sensing"), ET 75 ("Bypass Fail Alarm"), Hydraulic Theory
9 ("Flow Sensor" and "Bypass Valve"), EC 13 ("Bypass Fail
Detection"), and EA 11 ("Bypass System and Flow Sensor").
No-Ultrafiltration-During-Bypass Sensor
[0214] This feature, shown schematically as item 70 in FIGS. 1 and
2, utilizes a first and a second thermistor 210, 212 in a manner
similar to the bypass valve flow sensor 62 discussed above. The
first and second thermistors 210, 212 are exposed to dialysate
flowing through conduit 174 just downstream of the dialyzer 208 but
upstream of the bypass line 166.
[0215] This feature 70 is utilized during automatic testing of
machine functions, as controlled by the machine's microprocessor.
During such a test, dialysate flow is bypassed from the dialyzer
208. The flow equalizer 54 volumetrically matches the volume of
dialysate that would ordinarily enter the dialysate compartment
(not shown) of the dialyzer 208 with the volume of dialysate
exiting the dialyzer 208. During bypass, the volume of dialysate
passing through the bypass valve 66 and bypass line 166 is equal to
the volume passing back through the flow equalizer 54 via line 158.
Since the UF line 178 is occluded by the UF flow meter 76, any
dialysate flow past the first and second thermistors 210, 212 in
either direction must be due to dialysate flow passing through the
dialyzer membrane (not shown) into the blood compartment (not
shown) thereof or from the blood compartment thereof into the
dialysate compartment thereof. If such flow is detected, the
machine triggers an operator alarm.
[0216] Further details and engineering data pertaining to the
no-UF-during-bypass sensor can be found in Appendix A, pp. ET 52-ET
57 ("Flow Sensing"), and Hydraulic Theory 10 ("Flow Sensor").
Automatic Testing of Ultrafiltration Function
[0217] This feature is utilized during automatic testing of machine
functions that occurs before the machine is used for patient
treatment. This automatic test is controlled by the machine's
microprocessor along with other self-test routines. One example of
when ultrafiltration-function testing is automatically engaged is
when the machine is in rinse and producing dialysate without any
prevailing dialysate alarms such as temperature and conductivity. A
complete self-test routine begins when the operator touches the
"test" button on the touch screen before beginning a dialysis
treatment. (See Appendix A, pp. Operation 3 (Step 10).)
[0218] In order to test the ultrafiltration function, the dialysate
lines 174, 206 (FIGS. 1 and 2) must be connected together, enabling
dialysate to circulate therethrough without having to use a
dialyzer. Because a dialyzer is not used, the flow equalizer 54
discharges a volume of dialysate into line 206 that is
substantially equal to the volume of dialysate passing through line
174. Hence, a volumetrically closed loop is formed wherein
dialysate exits the flow equalizer 54 through the outlets 156
thereof, passes through lines 206 and 174 coupled together, and
reenters the flow equalizer 54 through the inlets 154 thereof.
Included in this closed loop is the UF flow meter 76. The UF flow
meter 76 permits a discrete volume of fluid to be removed from the
closed loop. Also included in the closed loop is the dialysate
pressure transducer 64.
[0219] To perform the test, the UF flow meter 76 removes about 3 mL
of dialysate from the closed loop. This removal of 3 mL is
sufficient to lower the dialysate pressure measured at the
transducer 64 by about 200 to 300 mmHg. If there are no leaks in
the closed loop, this lowered pressure will remain substantially
constant. The machine will monitor the depressed dialysate pressure
for about 30 seconds during which the pressure must remain within a
.+-.50 mmHg limit of the initial low value. If the pressure rises
and passes a limit, the machine will trigger an operator alarm.
[0220] Further pertinent details concerning this feature and the UF
flow meter can be found in Appendix A, pp. EA 7 ("UF Removal
Control"), EC 25-EC 26 ("UF Protective System"), EC 29-EC 30 ("UF
Test"), M 6 ("Flow Equalizer"), M 9 ("UF Removal Flowmeter"), M
17-M 19 ("Dialysate Flow Control System Performance"), and
Hydraulic Theory 7 ("Flow Equalizer").
Automatic Setting of Proportioning Mode Based Upon Connection of
Concentrate Lines
[0221] As described hereinabove, the concentrate rinse fittings,
e.g., the "A" and "B" rinse fittings 28, 30, respectively (FIG. 1),
are equipped with proximity sensors which sense whether or not the
corresponding concentrate lines 94, 104, respectively, are
connected thereto. Such information regarding whether or not a
concentrate line is coupled to a corresponding rinse fitting is
utilized by the machine's microprocessor to set the correct
proportioning mode, e.g., acetate or bicarbonate dialysis.
[0222] For example, during the machine's "dialyze" mode, if the
machine's microprocessor receives a signal indicating that the "B"
concentrate line 104 is coupled to the "B" rinse fitting 30, the
machine will operate only the "A" concentrate pump 22. If the "B"
concentrate line 104 is not coupled to the "B" rinse fitting 30,
the machine will operate both the "A" and "B" concentrate pumps 22,
40, respectively. See Appendix A, pp. EA 5-EA 6 ("Proportioning
Control"), and EA 7-EA 8 ("Conductivity Monitoring").
[0223] Such connections of the "A" and "B" concentrate lines 94,
104 also dictate the proportioning ratio of "A" concentrate. During
acetate dialysis, the volumetric ratio of "A" concentrate to
dialysate is 1:35. During bicarbonate dialysis with Drake Willock
brand concentrates, for example, the volumetric ratio of "A"
concentrate to dialysate is 1:36.83. Hence, the machine
automatically adjusts the pumping rate of the "A" concentrate pump
22 in response to whether or not the "B" concentrate line 104 is
coupled to the "B" rinse fitting 30.
[0224] The proximity sensors are shown in FIGS. 3A and 3B. FIG. 3A
is an isometric depiction of, for example, the "A" and "B" rinse
fittings 28, 30 situated on the right side 218 of the machine. (ee
Appendix A, pp. Components & Functions 11). On the annular
surface 220, 222 of each rinse fitting is an angled depression 224,
226, respectively. As depicted in the right-side elevational view
of the "A" rinse fitting 28 shown in FIG. 3B, beneath the angled
depression 224 is a light-emitting diode (LED) 228 (shown
schematically). A photosensor 230 of a type known in the art is
also situated beneath the angled depression 224. The LED 228 is
energized with a pulsatile signal in the kilohertz range (so as to
not be fooled by 60 Hz illumination). The LED 228 and photosensor
230 are oriented such that light 232 from the LED 228 passes
through a first face 234 of the angled depression 224, is-
reflected off an annular surface 236 of a connector 238 on the end
of the "A" concentrate line 94, passes through a second face 240 of
the angled depression 224 to be sensed by the photosensor 230.
[0225] So long as the photosensor 230 receives reflected light from
the LED 228, the machine's microprocessor circuitry (not shown)
"interprets" such a condition as indicating that the "A"
concentrate line 94 is coupled to the "A" rinse fitting 28. If the
light 232 does not reflect so as to impinge the LED 230, the
microprocessor circuitry "interprets" such a condition as
indicating that the "A" concentrate line 94 is not coupled to the
"A" rinse fitting 28 but is coupled to, e.g., a supply of "A"
concentrate.
Prediction of Dialysate Conductivity
[0226] The software controlling the operation of the machine's
microprocessor includes a routine for predicting correct dialysate
conductivity. Such predictions automatically reflect the particular
brand of concentrate being used, since different groups of
concentrate brands require different proportioning to yield a
dialysate having a correct ionic strength and electrolytic
profile.
[0227] Various groups of concentrates are currently marketed. These
include: (1) bicarbonate concentrates manufactured by Cobe
(utilizable for variable sodium and variable bicarbonate dialysis
and intended to be diluted at a ratio of 1 part "A" concentrate to
1.43 parts "B" concentrate to 45 parts dialysate); (2) bicarbonate
concentrates manufactured by Drake Willock (utilizable for variable
sodium dialysis only and intended to be diluted at a ratio of 1
part "A" concentrate to 1.83 parts "B" concentrate to 36.83 parts
dialysate); and (3) acetate concentrates intended to be diluted at
a ratio of 1 part acetate concentrate to 35 parts dialysate. The
machine is "instructed" or programmed by a technician as to which
brand of concentrate is being used. Such programming is done using
the touch screen with the machine in the "calibration" mode. See,
e.g., Appendix A, pp. Preventive Maintenance 8, Calibration Screen
#1, item 17.
[0228] The software utilizes a different algorithm for each group
of concentrates and for acetate or bicarbonate dialysis using
concentrates within any single group, to calculate a baseline
"calculated" conductivity value. Each algorithm requires that
certain data be entered by the operator using the touch screen. For
example, for bicarbonate dialysis, the machine will "ask" the
operator to enter baseline (i.e., not adjusted up or down relative
to a standard, or non-variable, proportioning ratio) values for
sodium and bicarbonate ion concentrations. Assuming proper
proportioning of the concentrates, the machine will determine a
"calculated" dialysate conductivity. Before beginning a dialysis
treatment, when the machine is proportioning concentrate and
producing dialysate at the proper temperature, the touch screen
will display an "actual" dialysate conductivity value as measured
by the dialysate conductivity probe 60 (FIG. 1) and "ask" the
operator to verify the correctness of that value against the value
stated to be correct by the concentrate manufacturer on the
concentrate label. See Appendix A, pp. operation 3. If the operator
responds that the displayed conductivity value is correct, the
machine will compare the displayed "actual" value with the
"calculated" value. If the "calculated" value is different from the
displayed value, the machine will regard the displayed baseline
value as correct since the operator "told" the machine that the
displayed value is correct. The machine will also calculate the
ratio of the displayed baseline value over the calculated baseline
value and will multiply any subsequently determined calculated
value during the dialysis treatment by the ratio to obtain new
"expected" conductivity values. For example, for variable sodium
dialysis, the operator will program the variable sodium profile to
be delivered to a patient over the course of the upcoming dialysis
treatment. Whenever the machine changes the sodium concentration
during the course of treatment as programmed by the operator, which
accordingly changes the dialysate conductivity, the machine will
redetermine a "calculated" conductivity value and apply said ratio
to determine a new "expected" conductivity value. These expected
conductivity values are used by the machine to calculate and set
upper and lower conductivity alarm limits at .+-.5% of the initial
or adjusted "expected" conductivity value.
[0229] For Cobe brand bicarbonate concentrates, the calculated
baseline dialysate conductivity is determined by the following
algorithm:
calculated conductivity in mS/cm=[-0.036+3.7.times..sup.10-5
([Na.sup.+]-130)][HCO.sub.3]+[14.37 +0.101([Na.sup.+]-130)]
[0230] where the operator enters the baseline concentrations of
sodium and bicarbonate using the touch screen.
[0231] For Drake Willock brand bicarbonate concentrates, the
calculated baseline conductivity of bicarbonate dialysate is
determined by the following algorithm:
calculated conductivity in mS/cm=0.1038[Na.sup.+]-0.54
[0232] where the operator enters the baseline concentration of
sodium using the touch screen.
[0233] For all brands of acetate concentrates, the calculated
baseline conductivity of acetate dialysate is determined by the
following algorithm:
calculated conductivity in mS/cm=0.0895[Na.sup.+]+1.41
[0234] where the operator enters the baseline concentration of
sodium using the touch screen.
[0235] For bicarbonate dialysis, the machine will also
automatically set alarm limits around the conductivity measured at
the "A" conductivity probe 38 (FIG. 1) in a similar manner. (During
acetate dialysis, the conductivity at the "A" conductivity probe 38
is equal to the conductivity at the dialysate conductivity probe
60, so setting of alarm limits around the conductivity at the "A"
conductivity probe is not necessary.) For bicarbonate dialysis, the
machine "assumes" that the "A" concentrate is being proportioned
properly (at the correct proportioning ratio), based upon the
operator having verified that the displayed dialysate conductivity
value is correct. The machine determines a baseline "calculated"
conductivity at the "A" conductivity probe based on baseline sodium
and bicarbonate concentrate information provided by the operator
via the touch screen. The machine then calculates a ratio of the
actual conductivity as measured at the "A" conductivity probe 38
over the calculated conductivity at the "A" conductivity probe.
Then, whenever the machine changes the sodium concentration during
the course of a dialysis treatment as programmed by the operator,
the machine will determine a new calculated conductivity value and
apply said ratio to determine a new "expected" conductivity value
at the "A" conductivity probe.
[0236] For Cobe brand bicarbonate concentrates, the calculated
baseline conductivity at the "A" conductivity probe is determined
by the following algorithm:
calculated conductivity in mS/cm=[0.110+9.7.times.10.sup.-5
([Na.sup.+]-130)][HCO.sub.3]+[15.04+0.105([Na.sup.+]-130)]
[0237] where the operator enters the baseline sodium and
bicarbonate concentrations using the touch screen.
[0238] For Drake Willock brand bicarbonate concentrates, the
calculated baseline conductivity at the "A" conductivity probe is
determined by the following algorithm:
calculated conductivity in mS/cm=0.1114[Na.sup.+]-5.90
[0239] where the operator enters the baseline sodium concentration
using the touch screen.
[0240] Further information on this feature is in Appendix A, pp. ET
23-ET 28 ("UF/Proportioning System"), and EC 34 ("Conductivity
Verify Test").
Controlling Flow Equalizer End-Of-Stroke Time
[0241] As discussed hereinabove, the flow equalizer 54 (FIG. 1)
operates via a four-phase cycle. In the first and third phases,
"pre" compartments 130, 132 and "post" compartments 134, 136
alternately fill and discharge their contents. In the second and
fourth phases, the valves 142-149 controlling liquid ingress and
egress from the "pre" and "post" chambers are all in the off
position for about 125 msec. During these brief second and fourth
phases, therefore, no dialysate is flowing to the dialyzer.
[0242] Preferably, at the beginning of the second and fourth
phases, the diaphragms 138, 140 will have already reached end of
stroke. Further preferably, the diaphragms 138, 140 will have
reached end of stroke at the same instant.
[0243] End of stroke is the moment when, for example, the "post"
compartment 134 has reached a completely full condition during a
phase after starting from a completely empty condition at the start
of the phase. In accordance with the above, it is preferable, for
example, that the filling of the "post" compartment 134 reach end
of stroke at the same instant as filling of the "pre" compartment
132 during a phase and that filling of the "post" compartment 136
reach end of stroke at the same instant as filling of the "pre"
compartment 130 during a different phase. Such simultaneous
reaching of end of stroke eliminates ultrafiltration inaccuracies
that otherwise could result if the "pre" and "post" compartments
(e.g., 130 and 136) being, say, filled during a phase are not
filled at exactly the same rate.
[0244] Since valves 143, 144, 146, and 149 all turn on at the same
instant that valves 142, 145, 147, and 148 turn off, and vice
versa, and since each pair of compartments 130, 134 and 132, 136
have exactly the same volume, it is possible to have pairs of
compartments (130, 136, and 134, 132) reach end of stroke at the
same instant. However, assuming that each chamber 126, 128 has
exactly the same flow restriction therethrough, achieving
simultaneous end of stroke requires at least that pressures at the
inlets 154 be matched and that pressures at the outlets 156 be
matched.
[0245] To achieve such pressure matching, the inlets 154 are
provided with an input pressure equalizer 52 and the outlets 156
are provided with an output pressure equalizer 56, as shown in FIG.
4. The input pressure equalizer 52 is comprised of a flexible
diaphragm 246 separating first and second enclosed cavities 248,
250. A stem 252 is attached to the center of the diaphragm 246 and
terminates with a flow-restricting element 254. The output pressure
equalizer 56 is likewise comprised of a flexible diaphragm 256
separating first and-second enclosed cavities 258, 260. Extending
from the center of the diaphragm 256 on both sides thereof are
stems 262, 264, each terminating with a flow-restricting element
266, 268.
[0246] Dialysate from the supply pump 42 flows unimpeded through
the second cavity 250 on into a "pre" compartment of the flow
equalizer 54. The first cavity 248 passes dialysate from the
dialyzer to a "post" compartment of the flow equalizer 54. The
first cavity 248 is also part of a loop including the dialysate
pressure pump 72. This hydraulic configuration has been found to
maintain identical pressures and therefore identical flow rates at
the inlets 154 of the flow equalizer 54.
[0247] With respect to the output pressure equalizer 56, when the
pressure is equal in both cavities 258, 260, the flow rates through
each is identical. When the pressure, say, in the first cavity 258
exceeds that in the second cavity 260, the flow-restricting element
268 impedes flow into line 150, thereby increasing the pressure in
the second cavity 260. This hydraulic configuration has been found
to maintain identical pressures and therefore identical flow rates
at the outlets 156 of the flow equalizer 54.
[0248] Therefore, since pressures and flow rates are identical as
described above, both diaphragms 138, 140 (FIG. 1) come to end of
stroke at the same time.
[0249] The time required to attain end of stroke can also be
controlled. The dialysate flow rate is set by the operator using
the touch screen. This flow rate determines the shift frequency of
the valves 142-149. The higher the dialysate flow rate, the more
frequently the valves 142-149 shift. However, a machine malfunction
or occlusion of a hydraulic line could cause an excessive
end-of-stroke time for one or both diaphragms 138, 140.
[0250] As discussed hereinabove, flow sensors 162, 164 (FIG. 1) are
provided at the outlets 156 of the flow equalizer 54 for verifying
when the diaphragms 138, 140 have reached end of stroke. When a
diaphragm 138 or 140 has reached end of stroke, the corresponding
flow sensor 162 or 164, respectively, sends a no-flow signal to the
microprocessor. The flow sensors 162, 164 are each comprised of a
reference and sensing thermistor (not shown) and work in a manner
similar to the bypass valve flow sensor 62 and sensor 70 discussed
hereinabove.
[0251] If the valves 142-149 receive a signal from the
microprocessor to shift before the flow sensors 162, 164 have
detected end of stroke, the valves are prevented by the
microprocessor from shifting until the end-of-stroke signal(s) are
received by the microprocessor. In the event of an excessively long
end-of-stroke time, the microprocessor triggers an increase in the
pumping rate of the supply pump 42 to speed up the time to end of
stroke.
[0252] Controlling the end-of-stroke time not only increases the UF
removal accuracy of the machine but also keeps dialysate flowing
through the dialyzer as much as possible to maintain the desired
osmotic gradient therein, and ensures accurate proportioning and
mixing of concentrates with water to form dialysate.
[0253] Further details on this feature can be found in Appendix A,
pp. EA 6 ("Flow Control"), ET 28-ET 32 ("Dialysate Flow Control"),
M 17-M 19 ("Dialysate Flow Control System Performance"), and
Hydraulic Theory 6-8 ("Input Pressure Equalizer," "Flow Equalizer,"
"Output Pressure Equalizer," "End of Stroke Sensors").
Timed Mode Initiate From Power-Off
[0254] The microprocessor programming as described herein can be
conventionally implemented to accomplish a timed mode initiation
from a power-off condition. As is known in the art, machine
disinfection, rinsing, and "coming up" on concentrate and
temperature to produce dialysate in a condition to begin treatment
are burdensome tasks that typically must be performed before the
start of a treatment day. In large clinics having multiple dialysis
machines, performing these tasks manually can require a substantial
expenditure of time and other personnel resources.
[0255] The electronics of the machine are continuously powered,
even when the machine is "off," unless the mains switch has been
turned off or unless the machine's power cord is unplugged. As a
result, the programming is readily adapted to include use of the
key pad display on the touch screen by the operator to enter the
desired time at which certain designated machine functions are
automatically initiated. These functions include disinfection (such
as heat-cleaning), rinsing, and beginning the production of
dialysate at the desired temperature and ionic strength for
dialysis treatment.
Preservation of Machine Parameters During Brief Power-Off
[0256] The hemodialysis machine of the present invention is
provided with a battery back-up which preserves certain operational
parameters previously entered by the operator in the event of a
temporary power interruption (less than about 20 minutes). Upon
restoration of power, the machine is in the stand-by mode.
[0257] All of the following parameters are saved in static RAM
every 30 seconds or upon any major change in machine state. Upon
restoration of power after less than 20 minutes after the last
"time stamp" (time at which parameters were saved) by the machine,
the following parameters are restored:
[0258] Temperature correction
[0259] Accumulated UF volume removed
[0260] Desired UF removal volume
[0261] UF removal rate
[0262] UF override flag
[0263] Current machine state
[0264] Previous machine state
[0265] Self-test pass/fail flag
[0266] Time stamp
[0267] Prescribed dialysis time
[0268] Elapsed treatment time
[0269] Prescribed or elapsed treatment time display flag
[0270] Manual or calculated UF rate display flag
[0271] Heparin pump rate
[0272] Accumulated blood
[0273] Accumulated heparin
[0274] Alarm window limits for conductivity, temperature,
prescribed treatment time, heparin, etc.
[0275] Profile settings for variable sodium and bicarbonate
[0276] Upon restoration of power, the "dialyze" mode can be
restored by the operator touching the appropriate "button" on the
touch screen.
Drip-Chamber Level Adjusters
[0277] As is known in the art, hemodialysis treatment requires use
of an extracorporeal blood-line set. Blood-line sets are available
from a number of manufacturers in a variety of different
configurations. Virtually all blood-line sets have at least a
venous drip chamber. Usually, an arterial drip chamber is also
included. The drip chambers serve several functions, including
providing a means for removing air and foam from the extracorporeal
blood before the blood is returned to the patient, and providing
convenient sites at which extracorporeal arterial and venous blood
pressure can be measured.
[0278] A portion of the extracorporeal blood-line set, including
drip chambers, is normally fitted to the front of a hemodialysis
machine in an orderly and convenient arrangement using special
clips and the like. See Appendix A, pp. Components & Functions
4-5. Each drip chamber typically includes a short tubing segment
terminated with a female fitting of a type known in the art as a
Luer fitting. The female Luer is adapted for connection to a male
Luer fitting on or near the front of the machine (see Appendix A,
pp. Components & Functions 2-3), thereby providing the
requisite connection of the drip chamber to a pressure-measuring
component in the machine.
[0279] Drip chambers must be provided with a means for adjusting
the blood level therein, particularly to ensure that the blood
level does not drop so low in the drip chamber that air becomes
re-entrained in the blood. Dialysis machines as currently known in
the art require that the operator manually rotate one or more knobs
on the machine to rotate a peristaltic pump coupled to the
corresponding drip chamber. Such a manual operation has proven to
be a cumbersome annoying task, especially since the peristaltic
pumps can be difficult to rotate.
[0280] The machine of the present invention overcomes this problem
by providing, as shown schematically in FIG. 5, an electrically
driven reversible positive-displacement pump such as a peristaltic
pump 272 which replaces the hand-operated peristaltic pumps found
on conventional hemodialysis machines. The peristaltic pump 272 is
fitted with flexible tubing 274, one end 276 of which is open to
the atmosphere. The opposite end 278 is coupled in parallel to an
"arterial" valve 280 and a "Venous" valve 282 coupled to an
arterial drip chamber 284 and a venous drip chamber 286,
respectively. The valves 280, 282 are preferably solenoid valves of
a type known in the art. Each drip chamber 284, 286 is coupled via
a corresponding Luer fitting 288, 290 to the corresponding valve
280, 282. Included upstream of each Luer fitting 288, 290 is a
pressure-measuring device 292, 294, such as a pressure transducer,
which communicates with the microprocessor (not shown).
[0281] On the front of the machine are arterial and venous "up"
buttons 296, 298, respectively, and arterial and venous "down"
buttons 300, 302, respectively, which control operation of the
corresponding valves 280, 282 and the peristaltic pump 272. See
Appendix A, pp. Components & Functions 2-3. For example,
pressing the arterial "up" button 296 opens valve 280 and initiates
rotation of the peristaltic pump 272 so as to raise the blood level
in the arterial drip chamber 284. Pressing the arterial "down"
button 300 opens valve 280 and initiates an opposite rotation of
the peristaltic pump 272 so as to lower the blood level in the
arterial drip chamber 284. The venous "up" and "down" buttons 298,
302 operate in the same way to control the blood level in the
venous drip chamber 286.
[0282] Further details pertaining to this feature are in Appendix
A, pp. EA 4 ("Level Adjust"), ET 11-ET 12 ("Level Adjust"), and M
2-M 3 ("Level Adjusters").
Increasing Dialysate Flow Velocity Through the Dialyzer Without
Increasing Dialysate Flow Rate
[0283] Most hemodialyzers currently in use are hollow-fiber types
which generally have a more compact shape than parallel-plate or
coil dialyzers used previously. Hollow-fiber dialyzers as known in
the art typically comprise a bundle of fine hollow fibers, each
fiber made of a semipermeable membrane material, encased in an
outer cylindrical shell. The shell defines a space surrounding the
fibers termed the "dialysate compartment" through which flows the
dialysate prepared by a dialysis machine. The patient's blood is
conducted through the lumens of the hollow fibers, propelled by a
blood pump on the dialysis machine.
[0284] Clearance of metabolic solutes from the blood through the
fiber membrane to the dialysate depends on a number of factors,
including the osmotic gradient across the semipermeable membranes.
The osmotic gradient is dependent on a number of factors including
ionic strength and ionic profile of the dialysate, dialysate flow
rate through the dialysate compartment, and flow dynamics of the
dialysate as it flows through the dialysate compartment.
[0285] It is important that the dialysate flow rate be high enough
to expose the fibers to a sufficient supply of fresh dialysate to
effect satisfactory clearance of toxic solutes from the patient's
blood at a satisfactory rate. Any dead spaces or areas of blockage
in the dialysate compartment which are not exposed to a continuous
supply of fresh dialysate will adversely affect clearance. Such
dead spaces can be reduced by merely increasing the dialysate flow
rate. However, increasing the dialysate flow rate also increases
the rate at which expensive dialysate concentrates are consumed.
Therefore, it is advantageous, especially with large dialyzers, to
increase dialysate flow velocity through the dialysate compartment
without necessitating a corresponding increase in net dialysate
flow through the dialysate compartment.
[0286] An embodiment of the dialysis machine of the present
invention solves this problem by incorporating a dialysate
recirculation pump parallel with the dialyzer as shown
schematically in FIG. 6.
[0287] FIG. 6 depicts a typical hollow-fiber dialyzer 208 having an
outer shell 306 defining a dialysate compartment. Extracorporeal
blood is pumped by the machine's blood pump (not shown) through an
arterial blood line 308 from the patient (not shown), through the
hollow fibers (not shown) of the dialyzer 208, then returned
through a venous blood line 310 to the patient. FIG. 6 also shows
the "arterial" dialysate line 206 and "venous" dialysate line 174
(see also FIG. 1). A dialysate recirculation pump 312, such as an
electrically driven gear pump, is coupled to the dialysate lines
206, 174 parallel with the dialyzer 208. The pump 312 can be driven
with a variable-speed controller to adjust the pumping rate of the
pump 312 relative to the flow rate of the dialysate as delivered by
the dialysis machine (not shown).
[0288] By recirculating a portion of the "spent" dialysate from the
"venous" dialysate line 174 to the "arterial" dialysate line 206
for repassage through the dialysate compartment 306, the flow
velocity of the dialysate through the dialysate compartment can be
increased without making a corresponding increase in dialysate
flow. Hence, it is possible with this feature to improve clearances
with a particular dialyzer without increasing the consumption of
expensive dialysate concentrates.
Blood-Leak Detector
[0289] Virtually all dialysis machines in current use employ a
blood-leak detector to monitor dialysate flowing from the dialyzer
for the presence of blood that might have leaked from the blood
compartment into the dialysate compartment of the dialyzer.
[0290] Most dialysis machines currently in use are capable of
delivering only a fixed rate of dialysate flow, usually 500 mL/min.
The blood-leak detectors on those machines operate with a detection
sensitivity that is set at a fixed level and not changed during the
course of treating a patient or even a series of patients. At a
dialysate flow rate of 500 mL/min, many conventional blood-leak
detectors are set to detect blood having a 25% hematocrit flowing
at 0.35 mL/min into the dialysate.
[0291] The dialysis machine of the present invention is capable of
delivering dialysate at flow rates ranging from 500 to 1000 mL/min,
adjustable in 100 mL/min increments. At various dialysate flow
rates, a fixed leak rate of blood from the patient will be diluted
a different amount by the dialysate. Therefore, a blood-leak
detector having a fixed sensitivity level enabling it to detect a
small blood leak in dialysate flowing at 500 mL/min may not be able
to detect the same blood leak in dialysate flowing at 1000
mL/min.
[0292] The dialysis machine of the present invention is provided
with a blood-leak detector 78 employing a green LED 194 and a
photosensor 196 (FIG. 1). (A green LED is used because of the
strong absorbance of green light by red blood, yielding a greater
contrast in the blood-leak detector between the presence and
absence of blood.) The blood-leak detector has a sensitivity that
is automatically adjusted in a proportional manner to sense a given
leak rate of blood into dialysate having any dialysate flow rate
between the 500 to 1000 mL/min adjustability range. Such automatic
adjustment of the blood-leak detector sensitivity is performed by
the microprocessor in response to the operator selecting a desired
dialysate flow rate. The microprocessor adjusts the blood-leak
detector sensitivity by altering the illumination level of the LED
194.
[0293] Further details on this feature can be found in Appendix A,
pp. EA 10 ("Blood Leak Detector"), EC 20 ("Blood Leak Detector"),
EC 29 ("Blood Leak Detector Test"), and ET 46-ET 52 ("Blood Leak
Detector").
Calibration Scheduler and Data Logger And Warning Message
Logger
[0294] The dialysis machine of the present invention has a
technician-activatable "calibration" mode and is programmed to
permit entry of calibration data, dates on which certain
calibrations or adjustments are performed, and dates on which a
particular dialysis center may desire to have certain calibrations
or adjustments performed. Appendix A, pp. Preventive Maintenance
8-9. The machine also automatically logs warning messages that can
be of substantial help to a technician servicing the machine.
[0295] The calibration mode can be activated by turning on an
internal calibration switch, as described in Appendix A, pp.
Preventive Maintenance 7-8. When the calibrations are completed,
the machine is returned to the operational mode by turning off the
internal calibration switch, as described in Appendix A, pp.
Preventive Maintenance 8, and restarting the machine using the
mains power switch. Upon entering the calibration mode, the touch
screen displays tables of various calibrations and makes provision
for the operator to enter data or dates pertaining to any of the
listed calibrations. These tables are illustrated in Appendix A,
pp. Preventive Maintenance 8-9. Representative calibration
instructions, including how to enter data, are provided in Appendix
A, pp. Preventive Maintenance 9-20.
[0296] The machine includes a number of component monitors which
are used by the microprocessor to note and "record" incidents
wherein the respective components experience an operational anomaly
of interest to a machine technician. For example, the "A" and "B"
proportioning pumps 22, 40 (FIG. 1) are each driven with a stepper
motor 90, 114, respectively. The stepper motors 90, 114 utilize 200
"steps" per revolution of the motor shaft. Appendix A, pp. EA 5-EA
6 ("Proportioning Control"). The stepper motors 90, 114 are
provided with optical encoders by which the machine's
microprocessor not only accurately monitors and controls the rate
of concentrate delivery, but also monitors stepper motor operation.
If the stepper motor experiences one full rotation per 190 "steps,"
the microprocessor will "note" and log this anomaly, even if no
adverse effect on dialysate conductivity resulted therefrom. A list
of warning messages is provided below. In the list, system names
above groups of messages are for reference only. Messages having
parentheses indicate software functions. While actual failure of
such functions would not be expected to occur during machine
operation, the messages were useful while debugging the software.
Messages having particular value to the technician, especially for
troubleshooting mechanical malfunctions, are denoted with an
asterisk.
3 BLOOD PUMP SYSTEM "illegal qlen in BP_XMIT" "Blood Pump Low
Speed" * "BP Control Shutdown" * "BP Command Error" * "Blood Pump
Overspeed Alarm" * "Bld Pmp Overspeed Alarm" * "Illegal index in bP
xmit( )" "Illegal index in bP input( )" "long timer error" UF/PROP
SYSTEM "Too much time between EOS signals" * "Early EOS detection"
* "UF SHUTDOWN" * "UF Command Error" * "UF Time scheduled Event
Error" * "Unidentified Error in MISC_ERRFLG" "A Pump Noise" * "A
Pump Missed Steps" * "B Pump Noise" * "B Pump Missed Steps" "C Pump
Noise" * (for three pump system) "C Pump Missed Steps" * "A
temperature probe error" * "B temperature probe error" * IO SYSTEM
"illegal qlen in IO_XMIT" "IO_XMIT: bad stat chnge %d, %d" "Illegal
in io_xmit( ) index" "Illegal index in io_input( )" "Illegal index
in ioport_xmit( )" IOPORT SYSTEM "No 8255... port terminated" *
"Set_pwr state: hw_ver=1" "Set_pwr state: hw_ver=2"
"Set_power_state: Can't power on" * "Set_power_state: Can't power
off" * "Converse: illegal return from uccom( )" "Switch failure in
reset_port( ) function" "Command buffer full in add_cmd( )"
"Unrecognizable command in make_cmd( )" "Illegal number of data
bytes in make_cmd( )" "Illegal number of data bytes in make_cmd(
)"
[0297] Having described and illustrated the principles of our
invention with reference to a preferred embodiment, it will be
apparent that the invention can be modified in arrangement and
detail without departing from such principles. Accordingly, we
claim as our invention all such embodiments as may come within the
scope and spirit of the following claims and equivalents
thereto.
* * * * *