Infusion pump

An infusion pump for administering fluid from a fluid source to a patient comprises a base member having an electric motor for driving a fluid pump housed within a cassette detachably mountable on the base and connectable to the motor. The cassette houses a reciprocative piston and cylinder assembly which both pumps fluid to the patient while simultaneously drawing fluid from the fluid source so as to maintain a continuous flow rate of fluid to the patient. The cassette also houses deformably closable pairs of tubes connecting each of the pump's two fluid chambers to the cassette inlet and outlet respectively to provide the necessary valving to produce continuous flow in cooperation with the reciprocative piston and cylinder assembly. The fluid flow rate is adjustably controlled by a microcomputer which regulates the motor by repeatedly initiating electric motor driving pulses at a predetermined time rate, and terminating them in response to the advancement of the motor beyond one of a plurality of predetermined positions so as to maximize accuracy and reliability of flow rate while compatibly maximizing the power efficiency of the motor for portable applications requiring a battery power source.

BACKGROUND OF THE INVENTION 
This invention relates to infusion pumps for administering fluid from a 
fluid source to a patient. More particularly, the invention relates to a 
highly portable, compact, pump having readily disposable and replaceable 
cassette-type pump and value components, and capable of administering 
fluid to a patient at a flow rate which is substantially continuous and 
precisely controlled. 
Previous infusion pumps for supplying fluids to patients can be classified 
generally as syringe type and peristaltic type. Among the syringe type 
infusion pumps are those shown in the following U.S. Pat. Nos. 3,447,479; 
3,701,345; 3,731,679; 3,739,943; 3,858,581; 3,901,231; 3,985,133; and 
4,367,435. These syringe pumps all share the common characteristic of 
employing an electric motor to drive the plunger of a syringe so as to 
expel fluid therefrom at a controlled flow rate for administration to a 
patient. All syringe pumps likewise share the common problem of being 
incapable of providing a substantially continuous flow rate to the patient 
because of the necessity to interrupt delivery of the fluid while the 
plunger is being retracted to refill the syringe after it has been 
emptied. The resultant intermittent interruption of fluid flow to the 
patient during such refilling introduces a troublesome variable into flow 
rate planning, requiring higher than optimum flow rates during delivery of 
the fluid to make up for the intermittent interruptions in flow so that 
the time-averaged flow rate to the patient will be optimal. Unfortunately, 
the necessity for higher than optimal flow rates interspersed with 
interruptions thereof can cause both harmful excessive concentrations of 
infused fluids at some times, and harmful insufficient concentrations at 
other times. The peristaltic type infusion pumps such as those shown in 
U.S. Pat. Nos. 3,736,930, 3,737,251 and 3,841,799, on the other hand, 
although providing substantially continuous flow, do not have the 
necessary accuracy of flow rate control provided by the syringe-type pumps 
and cannot therefore be used where a high degree of precision is required. 
Another problem with prior infusion pump units is that their pumping and 
valving structures, even when provided in easily replaceable cassette 
form, lack the compactness and simplicity to provide a high degree of 
portability and versatility for both hospital and home use. Although some 
units, such as those shown in U.S. Pat. Nos. 3,456,648 and 3,994,294, 
employ simplified valving which utilize tube-deforming devices for 
selectively opening and closing fluid conduits, the means of packaging 
such simplified valving systems in a highly compact, replaceable cassette 
form have not been known. 
Although highly accurate stepper motors have been used to control infusion 
pump flow rates, as exemplified by the aforementioned U.S. Pat. Nos. 
3,736,930 and 3,985,133, the frequency control of pulses driving such 
motors does not provide adequate insurance that the commanded flow rate 
will actually occur, particularly under variable back pressure conditions. 
The same is true of pulsed, nonstepping motors utilized in pumps such as 
those shown in the aforementioned U.S. Pat. Nos. 3,858,581 and 4,367,435, 
where transient load conditions may likewise prevent the motor from moving 
in accordance with the drive pulses. Moreover, the aforementioned pulsed 
electric motors do no have optimal energy efficiency characteristics which 
enable them to maximize the life of a battery power source, which would 
enhance their portability. Usually the drive pulses are of a constant 
duration which is longer than necessary to advance the motor the necessary 
amount against normal back pressures, thereby consuming excess power. 
Finally, although a number of the prior infusion pump devices include 
occlusion detection systems, such as those shown for example in U.S. Pat. 
Nos. 3,731,679 and 3,985,133, such systems provide insufficient control 
over the likelihood that a partial occlusion, such as a partially 
obstructed or pinched fluid outlet, will disable the system. Accordingly, 
in some cases, disabling occlusions occur with excessive frequency, 
requiring excessive supervision and correction by an attendant. 
SUMMARY OF THE PRESENT INVENTION 
The present invention is directed to an infusion pump having 
mutually-compatible features which overcome all of the foregoing drawbacks 
of the prior art. The pump may be used for intravascular, body cavity, 
enteral and other similar infusions. 
Substantially continuous flow is made compatible with highly accurate 
volumetric flow control by employing a dual chamber piston and cylinder 
assembly with associated valving which pumps fluid to the patient at a 
predetermined volumetric flow rate while simultaneously drawing fluid from 
the fluid source at the same flow rate. Thus no interruptions of the flow 
for refilling are necessary, and the discharge flow rate is thus the 
actual desired optimum flow rate rather than a higher than optimal flow 
rate. These objectives are achieved in a pump housed in a highly compact, 
inexpensive, disposable cassette despite the need for twice as many 
pumping chambers and twice as much input-output valving as is employed in 
prior syringe-type pumps. This is made possible by the utilization of 
pairs of deformably-closable input-output tubes within the cassette 
structure, each pair being connected to a respective pump chamber, with a 
simple tube closure structure movably mounted on the cassette for 
controlling the selective opening or closing of all of the tubes 
simultaneusly. 
Improved reliability with respect to maintaining the desired fluid flow 
rate under variable load conditions, and improved energy efficiency of the 
pumping motor to enhance the battery-powered portability of the pumping 
unit, are achieved in the present invention by a motor system which 
initiates motor driving electrical pulses at an adjustably variable, 
predetermined time rate dependent upon the desired flow rate, but 
terminates each of such pulses not on the basis of time but rather on the 
basis of position attained by the motor in response to the pulse. This 
control system has the advantage of shortening the duration of each 
electrical pulse if light load conditions permit the motor quickly to 
attain a predetermined increment of advancement in response to a pulse, 
thereby saving energy. Alternatively, the system provides longer pulse 
durations if high load conditions, in the form of high back pressure, tend 
to retard the advancement of the motor in response to each pulse. Such 
variable, load-dependent pulse durations increase the likelihood that the 
pump will reliably deliver the required increment of fluid in response to 
each electrical pulse even under conditions of high loading. 
Finally, the occlusion-detection system of the present invention, which 
monitors the average rate of movement of the pump-motor, is accompanied by 
a system for controllably varying the time-averaged electrical current 
driving the pump motor so as to controllably vary the maximum pressure of 
fluid pumped to the patient. This enables the operator to vary the degree 
to which the infusion pump is susceptible to being retarded by back 
pressure, enabling the use of different pumping pressures when appropriate 
to compensate for loading conditions which vary from patient to patient. 
Thus, for example, if a particular patient has a propensity for retarding 
the pump with excessive frequency, the operator has the ability to correct 
this problem by increasing the electrical current to raise the pump's 
output pressure. 
The foregoing and other objectives, features and advantages of the present 
invention will be more readily understood upon consideration of the 
following detailed description of the invention, taken in conjunction with 
the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
General Arrangement 
The exemplary embodiment of the infusion pump of the present invention, 
indicated generally as 10 in FIG. 1, comprises a base member 12 which 
detachably houses an insertable cassette 14, both of which may be of 
impact-resistant plastic construction. The base 12 essentially consists of 
a rectangular housing having major sidewalls 16 and 18 and ends 20 and 22, 
with interior partition 24, 26 and 28 defining battery compartments 30 and 
32, partition 34 and end 22 defining a motor compartment 36, and ribs 38 
and 40 together with end 20 defining a cavity into which the cassette 14 
can be matingly inserted as shown in FIGS. 1-3. When so inserted, the 
major sides of the cassette are engaged by the ribs 40 and held in place 
by opposing pairs of detents 42 mounted in the ribs 40 which engage mating 
depressions in the sides of the cassette 14. The cassette is also 
restrained against movement along its length by the engagement of one of 
its ends with the end 20 of the base 12, and the engagement of its 
opposite end with a lug 38a protruding upwardly from the rib 38 upon which 
the cassette rests, as shown in FIG. 2. 
Mounted on the partition 34 within the base 12 are a bidirectional 
pump-motor 44 and a bidirectional valve motor 46. The valve motor 46 is 
preferably a conventional linear actuator stepper motor having high 
reluctance or "cogging" force for holding position without energizing of 
the coils, so as to be capable of maintaining the valve assembly in the 
desired position without consuming battery power. The pump-motor 44, on 
the other hand, is a rotary motor preferably having little or no cogging 
torque. Both motors are powered by four rechargeable batteries which may 
be inserted in battery compartments 30 and 32 or, alternatively, by an 
external DC source. 
Mounted on the drive shaft 44 of the pump-motor 40 is a screw member 48 
threadably engaging the base of a U-shaped drive yoke 50 having a pair of 
spaced-apart legs 50a and 50b which straddle the sides of the cassette 14 
when it is inserted in the base 12 as shown in FIGS. 2 and 3. Turning of 
the pump-motor 44 in one direction moves the yoke 50 away from the motor, 
while turning of the motor in the opposite direction retracts the yoke 50 
toward the motor, the yoke being slidably supported for such reciprocative 
movement on the partition 24. The drive shaft 46a of the linear valve 
motor 46 is attached to an L-shaped valve controller 54, which 
reciprocates with respect to the motor 46 in a direction parallel to the 
direction of reciprocation of the yoke 50. 
The base 12 also includes a control panel 56 attached to the side 18 of the 
base member. The control panel includes an LCD 58 for displaying total 
volume to be infused (cc), volumetric rate of infusion (cc/hr), volume 
currently infused, minimum rate of infusion to keep a vein open following 
total infusion (KVO), and output pressure setting. In addition, the lCD 
displays operating messages which assist the user in the input of new pump 
control settings, interpretation of error conditions, and determination of 
the unit's present operating mode. A key pad 60 permits the user to input 
desired settings by first pressing the "HALT/DATA" key, selecting the 
value to be modified by pressing one of the four "SET" keys, and then 
inputting the setting by depressing the appropriate numeric keys. The key 
pad 60 also provides a key for actuating a "PURGE" mode of the pump for 
the clearing of air from the system by running the pump at high speed 
while connected to the fluid source but not to the patient. 
The electronic control circuitry for the unit, to be explained hereafter, 
is mounted within the control panel 56 and on the interior surface of the 
side wall 18 in the area bounded by the partitions 24 and 34 and the end 
wall 20. 
THE CASSETTE 
As best seen in FIGS. 4-7, the replaceable, disposable cassette 14 has a 
generally rectangular body composed of a bottom portion 62 housing a 
double-acting piston pump assembly, a middle portion 64 housing a valve 
assembly, and an upper portion 66 housing a fluid inlet 68 for connection 
to a source of fluid (not shown) and a fluid outlet 70 for connection to a 
patient. The piston pump assembly comprises a cylindrical bore 72 formed 
in the bottom portion 62 and having a reciprocating piston assembly 74 
therein consisting of two plungers 76 and 78 joined together by a rod 80 
having a transverse pin 82 connected thereto and protruding transversely 
from the bore through respective slots such as 84 formed in both sides of 
the cassette. When the cassette is inserted downwardly into the base 12, 
the ends of the pin 82 are guided by respective V-shaped notches, such as 
50c (FIG. 2) in each leg 50a, 50b of the yoke 50, into a closely mating 
rectangular notch 50d at the bottom of each V-shaped notch. This 
establishes a tight, detachable driving connection between the legs of the 
reciprocative yoke 50 and the piston rod 80 for driving the piston 
assembly 74. 
The middle portion 64 of the cassette contains two pairs of normally open, 
deformably closable, resilient tubes 86a, 86b and 88a, 88b, respectively, 
each pair being interconnected through nipples 87 and conduits 90 and 92, 
respectively, with a respective fluid chamber 94 or 96 of the piston pump 
assembly. Tubes 86a and 88b are both connected to the fluid inlet 68, 
while tubes 86b and 88a are both connected to the fluid outlet 70. Am 
elongate valve control member 98 is slidably mounted within the middle 
portion 64 of the cassette so as to move longitudinally with respect to 
the cassette in a direction parallel to the direction of movement of the 
piston assembly 74. As best seen in FIGS. 6 and 7, the valve control 
member 98 has four apertures 98a, 98b, 98c and 98d formed therein, each 
enclosing a respective one of the deformable tubes. The member 98 also has 
a portion protruding from one end of the cassette which includes an 
upwardly-tapered aperture 100 which, upon insertion of the cassette 14 
into the base 12, engages an upwardly-protruding pin 102 (FIG. 2) on the 
L-shaped valve controller 54. The valve control member 98 has two 
alternative positions as shown in FIGS. 6 and 7, respectively. The 
position of FIG. 6, caused by the stepper motor 46 retracting the valve 
controller 54 in a direction toward the motor 46, deformably closes tubes 
86a and 88a while permitting tubes 86b and 88b to remain open. Tube 88b 
exposes chamber 96 to fluid inlet 68 while tube 86b exposes chamber 94 to 
fluid outlet 70. This position of the valve control member 98 is used when 
motor 44 is retracting the yoke 50 toward itself, so that fluid is drawn 
from the fluid source into chamber 96 while it is pumped to the patient 
from chamber 94 simultaneously and at the same volumetric flow rate. 
Conversely, the other position of the valve control member 98 is that 
shown in FIG. 7, caused by motor 46 extending the valve controller 54. 
This position is used when motor 44 is extending the yoke 50 away from 
itself, since it opens tube 86a to draw fluid from the fluid source into 
chamber 94 while also opening tube 88a to pump fluid to the patient from 
chamber 96, closing the other tubes 86b and 88b. With the directions of 
the motors 46 and 44 properly synchronized such that valve control member 
98 changes position when yoke 50 changes direction, fluid is pumped 
substantially continuously to the patient from the cassette while fluid is 
simultaneously drawn into the cassette from the fluid source substantially 
continuously and at the same volumetric flow rate. 
GENERAL DESCRIPTION OF CONTROLS 
The control circuitry for the infusion pump is based upon a single chip 
microcomputer (MCU) such as the Hitachi Model HD630V1 microcomputer. The 
program within the MCU is started with power-on switching by means of 
switch 106 (FIG. 8) and maintains and controls all pump functions while 
providing for user input and function display through the control panel 
56. The MCU operates normally in the ultralow-power "sleep" mode (FIG. 10) 
but can be awakened by "interrupts" produced by one of several components 
of the control circuitry. First, under normal pump operating conditions, 
the volumetric rate of fluid infusion set by the user is translated by the 
MCU 104 into a time interval between the initiations of discrete pump 
motor drive pulses. This time interval is placed into a timer register, 
which keeps track of elapsed time regardless of the "sleep" condition of 
the MCU. When each time interval is completed, the MCU awakens, provides 
appropriate commands to the pump-motor and visual displays, and goes to 
sleep again. This cycle is repeated throughout the infusion. In addition, 
abnormal conditions can interrupt the sleeping state of the MCU. The 
operator could make changes to the pump control variables (rate, volume to 
infuse, etc.) by touching the "HALT/DATA" key, the appropriate "SET" key 
and the appropriate numeric keys, which interrupts the MCU. The input is 
processed, and the variables modified until the operator requests the 
pumping operation to resume by a second depression of the "HALT/DATA" key. 
Other conditions which interrupt the MCU are error states which may occur. 
These include such conditions as low battery power, external power 
interruption, air in line, etc. 
With reference to FIG. 9, the MCU has a serial I/O port 108 which provides 
for communication with a peripheral computer device or terminal if 
desired. This port could be used by a nurses' station to monitor the 
pump's performance, change settings, record pumping progress, etc., and 
can be used to "gang" several units infusing several fluids 
simultaneously. 
Pump-Motor Control and Occlusion Sensing 
Pump-motor 44 is preferably a noncogging, brushless, permanent magnet 
rotary motor of three-phase, four-pole design having three Hall effect 
sensors for monitoring position of the permanent magnet rotor and 
controlling the solid-state power drive switches (such as Darlington 
pairs) which commutate the three coil phases. Such motors as well-known, 
as evidenced for example by U.S. Pat. Nos. 4,130,769 which is incorporated 
herein by reference. However, in accordance with the special requirements 
of the present invention, the Hall effect sensors cooperate with the MCU 
104 to control the power drive switches in a unique manner. 
FIG. 11 depicts six separate rotor position zones per revolution which the 
three Hall effect sensors are capable of detecting, together with the 
digital signals (for example "011") which the three Hall sensors produce 
when the rotor is anywhere within the corresponding zone. FIG. 12 shows 
the sequence of commutation of the three coil phases A, B, and C as the 
rotor rotates (e.g. "AB" indicates that phase A is connected to positive 
voltage and phase B is connected to ground while phase C is connected to 
neither ). FIG. 13 shows how each of the six rotor position zones is 
correlated to the particular one of the commutations of FIG. 12 which is 
effective to move the rotor to the respective zone (e.g., if the rotor is 
at position "H=011", commutation "AC" will move the rotor to position 
"H=111"; conversely, if the rotor is at position "H=110", the same 
commutation "AC" will move the rotor to position "H=111" by reverse 
rotation). The table of FIG. 14 shows the entire commutation sequence for 
rotation in either a counterclockwise or clockwise direction, representing 
a sequence of six motor-control bytes which are stored in the MCU 104 for 
outputting in sequence at the aforementioned time intervals predetermined 
by the volumetric flow rate selected by the user, each motor-control byte 
initiating a motor-driving electrical pulse. 
With reference to FIG. 15, each motor-driving pulse is initiated by the 
commutation information of the motor-control byte, designated by the bits 
V1, V0, G1, G0, respectively. These are fed to a dual two in--one out 
selector 110, which actuates one of the three switches 111 for connecting 
the appropriate one of the three phases A, B, C to positive voltage, and 
also actuates one of the three switches 113 for connecting the appropriate 
one of the other phases to ground. The motor-control byte thus written is 
the one which corresponds to the position zone immediately adjacent to the 
zone where the rotor is currently located, depending upon the desired 
direction of rotation. While the foregoing drive pulse-initiating portion 
of the motor-control byte is being provided to the selector 110, the 
position command portion of the same byte, designated in FIG. 15 by the 
bits H2, H1, and H0, is being supplied to a four-bit comparator 112. 
Simultaneously, the actual Hall effect position sensor readings from the 
motor 44 are also being supplied to the comparator 112. When the 
motor-control byte is first written and the drive pulse initiated, the 
commanded position and actual position will not be equal, and the 
comparator 112 will emit a low signal on line 114 which is necessary to 
enable the selector 110. However, as soon as the rotor has moved to the 
commanded position as a result of the drive pulse, the commanded position 
and actual position sensed by the comparator 112 will be equal, causing 
the signal in line 114 to go high, thus disabling the selector 110 and 
deactivating the power drive switches 111 and 113. Thus, although the 
motor drive pulses are initiated on a time interval basis, they are 
terminated on a position basis in response to the advancement of the rotor 
beyond a predetermined position (i.e., into a new position zone) after the 
initiation of the pulse. 
Should the rotor, after initiation of a pulse, fail to attain the commanded 
position zone or if, having attained it, the rotor regresses from such 
zone, the output of the comparator 112 on line 114 will be low, enabling 
the selector 110 to drive the motor 44 toward the commanded position zone. 
Thus, the system automatically opposes any regression of the rotor, 
helping to ensure advancement of the motor especially under high load 
conditions. If the rotor cannot attain the commanded position zone, the 
MCU detects this condition by the absence of a high signal from the 
comparator 112 as sensed on line 116, in response to which the MCU, at the 
next pulse initiation time, writes the same motor-control byte previously 
written rather than the next one in the commutation sequence. The MCU 
counts the number of times this error condition occurs per cc of output 
fluid, and transmits an error signal in response to the error count 
exceeding a predetermined number. 
The logic flow diagram by which the MCU 104 starts and controls the 
pump-motor 44 is shown in FIG. 16. To start the motor, the aforementioned 
error count is initialized to zero, and the present position of the motor 
is determined in the following manner. Starting at the top of the 
motor-control byte table of FIG. 14, the commutation information in the 
byte is masked off and the byte is then written. Since all commutation 
information is now zero, no power or ground can be connected to any phase. 
The Hall effect sensors feed actual rotor position to the comparator 112 
where it is compared with the position command information in the 
motor-control byte. If they are unequal, the next motor-control byte in 
the table is written, and so forth until comparator 112 senses equality, 
at which time the signal in line 116 goes high establishing the starting 
point for the commutation sequence. Motor direction is determined by the 
location of the valve controller 54, as sensed by the closure of one of 
two limit switches 118 and 120 (FIGS. 2 and 15) or, alternatively, by Hall 
effect sensors (not shown) within the linear actuator valve motor 46. This 
information determines in which direction to initiate the commutation 
sequence. The next motor-control byte in the appropriate direction is 
written to initiate a motor-drive pulse and rotate the motor. When such 
drive pulse is terminated depends on whether the rotor has attained the 
commanded position zone as determined by the comparator 112 in accordance 
with the previous discussion. 
At the end of an interval of time predetermined by the operator's selection 
of volumetric flow rate, the MCU reads the comparator's output signal on 
line 116 to determine whether or not the rotor has moved to the commanded 
position zone. If the signal on line 116 is low, indicating that the 
commanded position was not attained, the MCU increments the error count 
and determines whether the count has reached a predetermined maximum 
count. If not, the same motor-control byte previously written is rewritten 
at the end of the next time interval. But, if the maximum count has been 
reached, the MCU transmits an error signal which indicates that the 
average rate of movement of the motor 44 has been to slow. The error 
signal may disable the pump and/or actuate an alarm (not shown) mounted in 
the base 12, and/or write a message to a remote monitor which may be 
connected to the MCU. 
Conversely, if a high signal on line 116 indicates that the commanded 
position zone has been attained, variables are updated to track progress 
of the infusion, and the next motor-control byte in the sequence is 
written. One of the updated variables is the cc-step count which signals 
the completion of each cc infused. After the infusion of each cc, the 
error count is cleared so that it can begin again. This feature makes the 
error count dependent upon the volume of fluid infused, providing a 
constant error tolerance per cc, as opposed to a variable error tolerance 
dependent upon motor speed. 
When the yoke 50 reaches the end of its stroke in either direction, as 
indicated by its engagement with one of a pair of limit switches 122 and 
124 (FIGS. 2 and 15), the MCU senses closure of the respective switch and 
actuates valve motor 46 through switch 126 to move the valve control 
member 98 rapidly it its opposite position for the return stroke of the 
piston assembly 74. The fluid is thus pumped continuously until the preset 
total volume to be pumped is reached, or until some error condition 
interrupts pumping. 
Variably controllable output pressure of the pump is made possible by an 
amplifier 128 inserted in the main power line to the motor drive switches 
111. The amplifier 128 variably regulates the time-averaged electrical 
current in response to a conventional digital-to-analog converter 130 
which receives commands from the MCU 104 in response to the pressure 
setting entered by the user on the control panel 56, as previously 
described. The output torque of the pump-motor 44, and thus the output 
pressure of the fluid, is directly proportional to the time-averaged drive 
current as thus controlled, permitting adjustment of the fluid output 
pressure by the operator to compensate for excessive error counts due to 
external loading variables. 
The bit indicated as "Hor" in FIG. 15 is a rotor position override, or 
"masking," bit capable of preventing the comparator 112 from outputting a 
high signal disabling the dual selector 110, regardless of rotor position. 
This bit can be used in high-speed applications, such as purging air from 
the system, where disabling of the selector 110 to terminate drive pulses 
is undesirable. 
The terms and expressions which have been employed in the foregoing 
specification are used therein as terms of description and not of 
limitation, and there is no intention, in the use of such terms and 
expressions, of excluding equivalents of the features shown and described 
or portions thereof, it being recognized that the scope of the invention 
is defined and limited only by the claims which follow.