Parenteral syringe pump drive system with installation indicator means

Apparatus for fluid flow control in a parenteral administration system, utilizing a syringe pump operated by a motor to repetitively fill and empty a disposable syringe cartridge over a plurality of operational cycles of successive fill and pump stroke periods. The syringe cartridge has no valves, and the apparatus repetitively and sequentially opens and closes, by means of an external pair of tube pinchers, a pair of intake and output I.V. tubes communicating with the inlet and outlet nipples of the syringe cartridge. A reference light source and photoelectric sensor is provided to sense the physical presence of the syringe cartridge, and an appropriate electrical signal is generated whenever the reference light beam is interrupted by one of the syringe nipples, to thereby indicate proper installation of the syringe cartridge for control over pump operation, while another reference light source and photoelectric sensor is provided adjacent one of the syringe nipples as a bubble detector to insure that all of the air has been removed from the syringe and to prevent air delivery to the patient.

BACKGROUND OF THE INVENTION 
This invention relates generally to improvements in syringe pumps and, more 
particularly, to a new and improved drive system and syringe for such 
pumps, wherein a disposible syringe cartridge having no valves is reliably 
and precisely mounted, monitored, and driven through repetitive fill and 
pump strokes. 
The usual medical procedure for the gradual parenteral administration of 
liquids into the human body, such as liquid nutrients, blood or plasma, 
makes use of apparatus which is commonly referred to in the medical arts 
as an intravenous administration set. The intravenous set usually 
comprises a bottle of liquid, normally supported in an inverted position, 
an intravenous feeding tube, typically of clear plastic, and a suitable 
valve mechanism, such as a roll clamp, which allows the liquid to drip out 
of the bottle at a selectively adjustable rate into a transparent drip 
chamber below the bottle. The drip chamber serves the dual function of 
allowing a nurse or other attendant to observe the rate at which the 
liquid drips out of the bottle, and also creates a reservoir for the 
liquid at the lower end of the drip chamber to insure that no air enters 
the main feeding tube leading to the patient. 
While observation of the rate of drop flow via the drip chamber is a simple 
way of controlling the amount of liquid fed to a patient over a period of 
time, its ultimate effectiveness requires that a relatively constant vigil 
be maintained on the drop flow, lest it cease entirely due to exhaustion 
of the liquid supplied or become a continuous stream and perhaps increase 
the rate of liquid introduction to the patient to dangerous levels. 
By way of example, it has been the general practice in hospitals to have 
nurses periodically monitor drop flow rate at each intravenous feeding or 
parenteral infusion station. Such monitoring of drop flow is a tedious, 
and time consuming process, prone to error and associated, possibly 
serious consequences, and resulting in a substantial reduction of the 
available time of qualified medical personnel for other important duties. 
Typically, the nurse monitoring drop flow rate will use a watch to time 
the number of drops flowing in an interval of one or more minutes, and she 
will then mentally perform the mathematics necessary to convert the 
observed data to an appropriate fluid flow rate, e.g., in drops per 
minute. If the calculated flow rate is substantially different than the 
prescribed rate, the nurse must manually adjust the roll clamp for a new 
rate, count drops again, and recalculate to measure the new flow rate. 
Obviously, each of the aforedescribed measurements, calculations and flow 
rate adjustments usually take several minutes time which, when multiplied 
by the number of stations being monitored and the number of times each 
station should be monitored per day, can result in a substantial 
percentage of total personnel time available. In addition, under the 
pressure of a heavy schedule, the observations and calculations performed 
by a harried nurse in measuring and adjusting flow rate may not always 
prove to be reliable and, hence, errors do occur resulting in undesired, 
possibly dangerous infusion flow rates. 
In addition to the aforedescribed difficulties, the parenteral 
administration of medical liquids by gravity induced hydrostatic pressure 
infusion of the liquid from a bottle or other container suspended above 
the patient, is very susceptible to fluid flow rate variation due to 
changes in the liquid level in the bottle, changes in temperature, changes 
in the venous or arterial pressure of the patient, patient movement, and 
drift in the effective setting of the roll clamp or other valve mechanism 
pinching the feeding tube. Moreover, there are a number of situations, 
such as in intensive care, cardiac and pediatric patients, or where rather 
potent drugs are being administered, where the desired drop flow rate must 
be capable of very precise selection. 
It will be apparent, therefore, that some of the most critical problems 
confronting hospital personnel faced with an overwhelming duty schedule 
and limited time availability are the problems of quickly, easily, 
reliably and accurately controlling fluid flow in the parenteral 
administration of medical liquids. 
In recent years, a number of electrical monitoring systems, drop flow 
controllers and infusion pumps have been developed to accomplish the 
various tasks of sensing and regulating drop flow rates. However, while 
such devices have generally served their purpose, they have not always 
proven entirely satisfactory from the standpoint of cost, complexity, 
stability, reliability or accuracy. In addition, such systems have 
sometimes been subject to drift and substantial flow rate variations due 
to changes in temperature, feeding tube crimps, variations in venous or 
arterial pressure of the patient, or variations in the height of the 
bottle or solution level within the bottle. 
Even positive pressure pumps of the closed-loop peristaltic type only serve 
to maintain accuracy of flow in terms of stabilizing to a preselected drop 
flow rate, rather than delivering a precise preselected volume of fluid, 
e.g., in cubic centimeters per hour. The reason for this is that the 
accuracy of such a system is limited inherently to the accuracy of the 
size of the drops produced by an intravenous administration set, and the 
actual drops produced by the latter apparatus can vary rather 
substantially from its designated drop size, e.g., due to drip chamber 
structural variations, by as much as thirty percent. 
More recently, positive pressure infusion pumps of the syringe type have 
also been provided, wherein a syringe having a very precise displacement 
volume is repeatedly filled and emptied on alternate syringe piston 
strokes during a combined "fill" and "pump" operational cycle, so that 
control of the rate at which the syringe is filled and emptied provides an 
accurate means for precise fluid volume delivery over a prescribed period 
of time. Such syringe pumps are essentially independent of drop flow 
inaccuracies introduced by I.V. administration sets and appear to provide 
the best overall solution to accurate and stable fluid volume delivery 
over long periods of time, at both high and low flow rates. 
At the heart of the syringe pump is the syringe itself. Such syringes must 
be sufficiently rugged and reliable to enable repetitive fill and pump 
strokes over sustained periods of pump operation without leaking, or 
admitting air or pathogens to the interior of the syringe. Where 
disposable syringes are involved, the syringe should preferably be of 
relatively simple and economical construction, easily handled for 
insertion into and removal from the remainder of the pumping apparatus and 
should be mounted in such a fashion as to facilitate removal of air prior 
to start-up. Unfortunately, however, such syringes of the prior art have 
been relatively complex and expensive, have been prone to leakage and have 
been relatively difficult to mount and remove. 
In addition, syringe pumps of the prior art primarily depend on valving 
embodied directly within the syringe itself, for switching from the fill 
mode to the pumping mode. This not only increases the cost and complexity 
of the syringe, particularly where disposable syringes are employed, but 
usually also results in reduced reliability of operation. 
Furthermore, it has been difficult at low flow rates, when the syringe 
piston is moving so slowly that its motion is not visually discernible by 
the operator, to determine whether or not the syringe is being driven at 
all. 
Hence, those concerned with the development and use of parenteral fluid 
administration systems, and particularly those concerned with the design 
of syringe pumps, have long recognized the need for improved, relatively 
simple, economical, reliable, stable and accurate syringes, monitoring and 
drive systems for such syringe pumps. The present invention clearly 
fulfills this need. 
SUMMARY OF THE INVENTION 
Briefly, and in general terms, the present invention provides a new and 
improved means for accurately controlling fluid flow in the parenteral 
administration of medical liquids, wherein a disposable, valveless syringe 
cartridge is easily, reliably and precisely mounted, its state of proper 
insertion into the pumping apparatus being monitored, after which the 
syringe is driven through repetitive fill and pump strokes. Appropriate 
valving is provided within the pumping apparatus external to the syringe 
cartridge, without the need for providing relatively complex, expensive 
and sometimes unreliable valve structures in the syringe itself. 
The syringe cartridge of the present invention is of strong, lightweight, 
durable construction and is constructed to minimize the possibility of 
fluid leakage, enhance the ease and simplicity of mounting and removal 
from the pumping apparatus, facilitate the removal of air prior to 
start-up of the pumping apparatus, and to prevent intake of air or 
pathogens into the interior of the syringe during repetitive pumping 
cycles. A running indicator is provided to indicate visually to the 
operator that the pump is cycling, motion of the indicator being 
observable even at low flow rates where syringe operation may not normally 
be readily discernible by the operator. In addition, a rotation sensor is 
provided to monitor the mechanical output of the motor driving the syringe 
and detect any stalled motor condition. 
More particularly, the present invention provides a new and improved 
syringe pump operated by a motor to repetitively fill and empty a 
disposable syringe cartridge over a plurality of operational cycles of 
successive fill and pump stroke periods. The disposable syringe cartridge 
itself embodies no valving structure, but includes a pair of intake and 
output I.V. tubes communicating with the inlet and outlet nipples, 
respectively, of the syringe. The remainder of the pumping apparatus 
drives the syringe and repetitively and sequentially opens and closes the 
intake and output I.V. tubes by means of a pair of tube pinchers external 
to the syringe cartridge, the I.V. tubes alternating their opened and 
closed states, one tube pincher controlling each I.V. tube. 
The disposable syringe cartridge includes a molded plastic cylinder having 
inlet and outlet nipples and defining an interior chamber adapted to 
slidingly receive a plastic piston and piston rod. A rubber sealing cap 
overlies and encases the plastic piston, and defines a conical piston 
face. The sealing cap includes a pair of resilient annular ribs defining 
piston sealing rings, and further includes a limp diaphragm conical 
sealing boot. The dual, spaced apart sealing rings define two point 
contact along the longitudinal axis of the syringe to enhance axial 
alignment and stability of the piston and piston rod as the piston slides 
within the cylinder of the syringe, whereas the sealing boot at the base 
of the cylinder prevents the intake of air or pathogens through the bottom 
of the cylinder during repetitive strokes. All plastic cross-sections of 
syringe cartridge components are selected to provide maximum strength for 
a minimum amount of plastic material. 
The inlet and outlet nipples of the syringe cartridge extend parallel to 
the longitudinal axis of the syringe, on opposite sides of the syringe. 
The interior surface of the cylinder defines, with the piston, a fluid 
chamber, and the cylinder surface above the piston is sloped upwardly 
towards the base of the outlet nipple, so that, when the longitudinal axis 
of the syringe is vertical, gas bubbles will tend to rise to the highest 
point of the cylinder and out through the outlet nipple for easy removal. 
The syringe cartridge and associated mounting means are designed to 
facilitate simple and easy insertion of the cartridge into the pump 
housing, requiring the use of only one hand by the operator. In this 
regard, an integral tab extends from the syringe cylinder and provides an 
operator handle for mounting and removing the syringe from the overall 
pumping apparatus. In addition, the end of the piston rod remote from the 
piston head is partially cut-away and provided with integral, outwardly 
extending mounting bosses. These mounting bosses are adapted to engage and 
be retained by a mounting shoe secured to the leading end of a linear 
drive shaft adapted to be coupled to the piston rod for driving the 
syringe through successive fill and pump strokes. The mounting shoe 
includes a pair of guide slots adapted to engage the piston rod mounting 
bosses so that the syringe cartridge can be inserted into the mounting 
shoe horizontally, be rotated so that its longitudinal axis is vertical, 
and thereby bring the lower, cut-away end of the syringe piston rod into a 
retention slot within the mounting shoe to prevent the syringe cartridge 
from being dislodged, either horizontally by virtue of the retention slot, 
or vertically by means of the lower end of the piston rod and the mounting 
bosses. 
A second pair of outwardly extending mounting bosses, parallel to the first 
set of mounting bosses on the piston rod, are integral with the syringe 
cylinder and are adapted to engage a pair of fixed guide and retaining 
slots provided in opposite walls of a syringe receiving compartment 
defined in the pump housing. The intake and output I.V. tubes from the 
syringe cartridge pass vertically over a pair of tube pincher blades and 
are clamped in position by a suitable tubing compartment access door which 
is appropriately latched. Thus, the syringe cartridge is firmly maintained 
in position during the operational cycles of the pump. The tubing access 
door must be unlatched and opened to enable the syringe cartridge to be 
rotated from the vertical position to a horizontal position for removal 
from the mounting shoe. 
By controlling the initial location of the mounting shoe, relative to the 
guide and retaining slots in the sidewalls of the syringe compartment, the 
pumping apparatus can be conditioned to receive the syringe cartridge only 
if its piston is in a predetermined position within the syringe cylinder, 
i.e., in the top dead center position adapted to initially perform an 
intake stroke to fill the syringe with fluid. The latter is the proper 
state of the syringe for initial start-up of the pumping apparatus. 
A reference light source and photoelectric sensor is provided within the 
syringe compartment to sense the physical presence of the syringe 
cartridge, and an appropriate electrical signal is generated whenever the 
reference light beam is interrupted by one of the syringe nipples, to 
thereby indicate proper installation of the syringe cartridge for control 
over pump operation. Another reference light source and photoelectric 
sensor is provided adjacent one of the syringe nipples as a bubble 
detector to insure that all of the air has been removed from the syringe 
and to prevent air delivery to the patient. 
A motor rotation sensor is provided, the rotation sensor typically being in 
the form of a disc mounted on the motor output shaft for rotation 
therewith, the disc having alternate transparent and opaque sectors. A 
photocell detects light from a reference light source passing through the 
disc, as it rotates, and generates an output electrical signal capable of 
indicating any stalled motor condition. 
A visual running indicator is also provided, typically in the form of a 
rotating disc having index lines uniformly spaced along its peripheral 
edge, so that pump operation is visually discernible by the operator, even 
at low flow rates where motion of the syringe piston is so slow as to not 
be readily discernible by the eye of the operator. 
The new and improved syringe pump drive system and disposable syringe 
cartridge satisfies a long existing need in the medical arts for improved, 
relatively simple, economical, reliable, stable and accurate syringe 
pumping systems. 
The above and other objects and advantages of the present invention will 
become apparent from the following more detailed description, when taken 
in conjunction with the accompanying drawings of illustrative embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, there is shown a syringe pump system for 
fluid flow control, embodying the features of the present invention. In 
the ensuing description, while reference is made to the term "I.V.", 
normally connoting intravenous administration, it is to be understood that 
this is by way of example only, and the system of the present invention is 
suitable for other forms of parenteral administration as well as 
intravenous administration. 
The system shown in FIG. 1 depicts a syringe pump 20 embodying a disposable 
syringe cartridge 21. The syringe cartridge 21 essentially includes a 
molded plastic cylinder 22 in which a piston 23 is slidably received and 
adapted to be reciprocated back and forth along the axis of the cylinder 
by an integral piston rod 24 which is removably mounted at one end in a 
coupling shoe 26 carried by a linear drive shaft 27 which is advanced and 
retracted by a suitable drive system. The drive system includes a 
reversible motor 29 (typically a d.c. stepping motor) and appropriate 
gearing 31, to advance and retract the shaft 27 which is, in turn, coupled 
to the piston rod 24 of the syringe cartridge 21. The motor 29 is 
energized by a pulse train of motor drive pulses generated by an 
appropriate electrical control system (not shown). 
The displacement volume of the syringe cartridge 21 is determined by the 
volume swept by the piston 23 on each stroke and is identical for the fill 
stroke and for the pump stroke. Therefore, an identical number of discrete 
steps or motor drive pulses from the electrical control system to the 
motor 29 is required for each fill stroke during which the syringe is 
filled with liquid, and for each pump stroke during which the syringe 
delivers its precise volume of liquid under positive pressure to a 
patient. 
The syringe cartridge 21 includes an inlet port 21a and an outlet port 21b. 
The inlet port 21a communicates through a suitable intake I.V. tube 33 
with any appropriate liquid source (not shown), usually an I.V. bottle 
containing appropriate drugs and/or nutrients in liquid form. Typically, 
the intake I.V. tube 33 is part of an I.V. administration set which 
includes a transparent drip chamber in the line between the syringe 
cartridge 21 and the liquid source. 
A similar, output I.V. tube 34 is connected at one end to the outlet port 
21b of the syringe cartridge 21 and conveys fluid from the syringe to a 
patient. 
As best observed in FIGS. 3 and 3A, a pair of syringe pump valves 36, 37, 
external to the syringe cartridge 21, are of the tube pincher type, and 
are selectively opened and closed at appropriate times in the overall 
pumping cycle, under the control of a suitable valve control system 40. 
The valve 36 controls the inlet port 21a and is open during the fill 
stroke to enable fluid to be drawn from the liquid source, through the 
intake line 33, into the syringe cartridge 21, the valve 36 being closed 
during the pump stroke to prevent fluid from exiting the syringe through 
the inlet port. The valve 37 controls the outlet port 21b and is open 
during the pump stroke to enable fluid delivery from the syringe cartridge 
21 to the patient through the output line 34, the valve 37 being closed 
during the fill stroke. 
The valve control system 40 is also driven, through the gearing 31, by the 
same motor 29 as is used to operate the syringe cartridge 21. In addition, 
the valve control system 40 includes means (not shown) for providing 
information to the electrical control system controlling the motor 29, and 
indicating that the syringe cartridge 21 is either in the fill stroke or 
the pump stroke. This latter information, in turn, enables the electrical 
control system to establish the proper direction of rotation of the motor 
29. The electrical control system may be of conventional design for 
electrically energizing the motor 29 and controlling its direction of 
rotation, or the control system may be of the form described in copending 
application, Ser. No. 554,092, entitled Fluid Flow Control System, 
inventor Heinz W. Georgi, filed Feb. 28, 1975, and assigned to the same 
assignee as the present application. 
The motor 29 drives, through the gearing 31 and an output camshaft 41, a 
reversible cam (not shown) in the valve control system 40, which 
cyclically alternates the open and closed positions of the syringe pump 
valves 36, 37. 
The syringe pump valves 36, 37 typically consist of a pair of pivotal tube 
pinchers 43, 44 which alternately pinch off and open the intake and output 
tubes 33, 34 respectively, of the syringe cartridge 21. One face of each 
of the tube pinchers 43, 44 is shaped to define a pincher blade 43a, 43b, 
respectively, adapted to cooperate with the confronting face of a shoulder 
45a defined on the interior side of a syringe pump tubing access door 45 
to the syringe compartment. Together, the pincher blades 43a, 44a and the 
access door shoulder 45a define a pair of tube clamps between which the 
intake and output I.V. tubes 33, 34 pass. The access door 45 is held shut, 
after the syringe cartridge 21 has been installed, by any suitable latch 
45b (FIG. 1). 
The tube pinchers 43, 44 are spring biased to the tube shut-off position 
and are positively driven open by the valve control system 40, thus 
allowing full tube closure regardless of normal variations in I.V. tubing 
diameter and wall thickness. 
The valves 36, 37 and valve control system 40 may be of conventional design 
or may be of the form described in copending application, Ser. No. 554,091 
entitled Syringe Pump Valving And Motor Direction Control System, inventor 
Wallace L. Knute, filed Feb. 28, 1975 and assigned to the same assignee as 
the present application, now U.S. Pat. No. 3,994,294 issued Nov. 30, 1976. 
Referring now more particularly to FIGS. 7-9 of the drawings, the new and 
improved syringe cartridge 21 of the present invention is of strong, 
lightweight, durable construction and is constructed to minimize the 
possibility of fluid leakage from the interior of the syringe, enhance the 
ease and simplicity of mounting and removal from the syringe compartment 
of the pump, facilitate the removal of air prior to actual operation of 
the pumping apparatus, and to prevent intake of air or pathogens into the 
interior of the syringe during repetitive pumping cycles. 
The disposable syringe cartridge 21 includes the molded plastic cylinder 22 
having inlet and outlet nipples 51, 52, respectively, at the upper end of 
the cylinder (with the longitudinal axis of the syringe in the vertical 
position as is the case following proper installation shown in FIG. 1). 
The cylinder 22 is hollow and thereby defines an interior chamber adapted 
to slidingly receive a plastic piston head 54 which is integral with the 
piston rod 24. The cylinder 22, and combined piston rod 24 and piston head 
54 are typically injection molded of any suitable thermoplastic material, 
such as polypropylene. 
A rubber sealing cap 56 overlies and encases the piston head 54 to define 
the piston 23, the sealing cap providing a conical piston face 23a 
directed towards the inlet and outlet nipples 51, 52, respectively, of the 
syringe. 
The inlet and outlet nipples 51, 52 of the syringe catridge 21, extend 
parallel to the longitudinal axis of the syringe on opposite sides of the 
syringe, diametrically opposed from each other. The interior surface of 
the syringe cylinder 22 defines, with the piston 23, a fluid containing 
chamber, and the uppermost cylinder surface 22a above the piston is sloped 
upwardly, typically at an angle of approximately 10.degree., towards the 
base of the outlet nipple 52. Hence, when the longitudinal axis of the 
syringe is vertical, following installation into the pumping apparatus, 
gas bubbles will tend to rise to the highest point of the syringe cylinder 
22 and pass out through the outlet nipple 52, for easy removal at some 
convenient access point in the output I.V. tube 34. In addition, the 
piston face 23a slopes symmetrically downward from its apex at an angle of 
approximately 10.degree. to the horizontal, matching the slope of the 
interior surface 22a of the cylinder 22, to minimize the residual volume 
of the syringe. 
The sealing cap 56, which is typically fabricated of a natural rubber, also 
includes a pair of resilient, annular ribs 56a, 56b which fit over and are 
supported by corresponding annular flanges 54a, 54b in the piston head 54. 
The sealing cap ribs 56a, 56b provide a pair of axially spaced apart piston 
sealing rings. These dual, spaced apart sealing rings define two point 
contact support along the longitudinal axis of the syringe cartridge 21 to 
provide improved sealing efficiency, and to enhance the axial alignment 
and stability of the piston and piston rod assembly within the cylinder 22 
of the syringe as the piston 23 reciprocates back and forth within the 
cylinder during repetitive pump cycles. Hence, the two point support along 
the longitudinal axis of the system prevents rocking of the piston 23 
which might otherwise cause the system to be prone to leakage and might 
also provide uneven wear on the sealing rings. 
The sealing cap 56 further includes a thin walled conical sealing boot 56c 
integral at its frustrum with the rib 56b and terminating at its base in a 
thickened wall portion defining a bead 56d. The sealing boot 56c provides 
a limp membrane sealing element when the syringe cartridge 21 is 
assembled, to prevent the intake of air or pathogens through the bottom of 
the cylinder 22 as the piston assembly reciprocates through repetitive 
strokes within the cylinder. 
The use of the sealing cap to encase the plastic piston head 54 and thereby 
define the outer surface of the piston 23, including the sealing rings 
56a, 56b, enables the piston head 54 and piston rod 24 to be fabricated of 
less expensive materials than would be required if the piston head were in 
direct sliding engagement with the interior walls of the cylinder 22. 
The material from which the sealing cap 56 is fabricated is chosen because 
of its material properties, e.g., wear resistance on the seals, 
compression set resistance so that it will retain its elastic properties, 
resistance to tearing on the boot because of the thin walled membrane, and 
resistance to the temperatures normally encountered in the sterilization 
process. In contrast, the plastic materials from which the cylinder 22, 
piston head 54 and piston rod 24 are fabricated is chosen primarily for 
low cost of material, ease of manufacture, and resistance to sterilization 
temperatures. 
All plastic cross-sections of the various components of the syringe 
cartridge 21 are selected to provide a maximum of strength for a minimum 
amount of plastic material. In this regard, while strength is required, a 
thin walled structure is also desirable in order for plastic molding to be 
most effective. Hence, a maximum degree of rigidity with a minimum amount 
of plastic, in a convenient cross-section, is selected for the syringe 
cartridge 21 of the present invention. In this regard, it will be apparent 
in FIG. 8 that the piston rod 24 is molded in an "H" cross-section, 
defined by a pair of longitudinally extending, parallel flanges 24a, 24b 
joined by an integral, coextensive cross-bar 24c. 
As previously pointed out, the piston head flanges 54a, 54b retain the 
sealing cap 56 and provide adequate support for the piston 23. The 
parallel flanges 54a, 54b are, in turn, supported by four integral ribs 
54c which intersect at the longitudinal axis of the piston head, the 
uppermost ends of these ribs being tapered to provide support for the 
conical face 23a of the sealing cap 56. This prevents the sealing cap 56, 
which is not very rigid, from collapsing. The rib structure defined by the 
four ribs 54c is selected, instead of a solid circular cylindrical 
cross-section, for molding purposes, to provide adequate strength with a 
minimal amount of plastic material required. 
In assembling the cylinder 22, sealing cap 56, and combined piston head 54 
and piston rod 24, (the components of FIG. 9) into the syringe cartridge 
21 of FIG. 7, the sealing cap 56 is simply pressed over the piston head 54 
until the flanges 54a, 54b engage internal slots in the sealing cap 
adjacent the ribs 56a, 56b, which results in the sealing cap and piston 
head snapping together. The resulting assembly of the sealing cap 56 and 
piston head 54 (defining the piston 23) and the piston rod 24, is pushed 
into the opening in the base of the cylinder 22. A suitable lubricant may 
be used to facilitate insertion of the assembly into the cylinder 22, as 
well as subsequent reciprocation within the cylinder. The base of the 
sealing boot 56c is then folded over the open base of the cylinder 22, so 
that the bead 56d, which behaves as an elastic O-ring, grips the outer 
surface of the cylinder and holds the sealing boot 56c in position so that 
it can't be pealed back easily or tear. In this regard, the hoop strength 
of the bead 56d must be sufficient to resist movement once it has been 
positioned to grip the outer surface of the cylinder 22. 
The length of the skirt portion of the sealing boot 56c is such that it is 
not required to stretch at all during any portion of the pumping cycle as 
the piston 23 reciprocates back and forth within the cylinder 22. Hence, 
the boot 56c provides a limp membrane as a seal against admission of air 
or pathogens to the interior of the cylinder 22 during repetitive strokes 
of the syringe. In this regard, since the limp membrane seal provided by 
the sealing boot 56c is essentially unstressed, it is both rugged and 
reliable. In addition, should sufficient air be trapped in the air gap 
between the rib 56b and the sealing boot 56c, during assembly into the 
cylinder 22, the air volume might be compressed during fill strokes of the 
piston 23 when the piston is in its lowermost position. However, the 
combination of the additional volume provided by the unfolding limp 
membrane of the sealing boot 56c, together with the anchoring afforded by 
the bead 56d, resists popping of the sealing boot off the cylinder 22, 
even in the event of ballooning of the boot by any such trapped air. 
After the cylinder 22, sealing cap 56 and combined piston 54 and piston rod 
24 have been assembled in the aforedescribed manner, the intake I.V. tube 
33 and output I.V. tube 34 are appropriately secured to the inlet and 
outlet nipples 51, 52, respectively, to complete the assembly of the 
syringe cartridge 21. 
The syringe cartridge 21 is constructed to cooperate with associated 
mounting means within the syringe compartment of the pump housing to 
facilitate simple and easy insertion of the cartridge into the pump 
housing while requiring the use of only one hand by the operator. In this 
regard, an integral tab 58 projects from the outer surface of the syringe 
cylinder 22 near the upper end of the cylinder, and thereby provides an 
operator handle for mounting and removing the syringe cartridge 21 from 
the pump housing in the manner to be hereinafter described in further 
detail. 
At the end of the piston rod 24 remote from the piston head 54, the 
longitudinal flanges 24a, 24b are partially cut-away to define surfaces 
24d and in order to provide clearance for insertion into the coupling shoe 
26. In addition, this same end of the piston rod 24 is provided with a 
pair of integral, outwardly and oppositely extending, cylindrical m 
mounting bosses 59, one boss projecting perpendicularly outward from the 
outside face of the flange 24a, the other boss likewise projecting outward 
from the flange 24b. 
A second pair of outwardly extending mounting bosses 61, parallel to the 
first set of mounting bosses 59 on the piston rod 24, are integral with 
the syringe cylinder 22 near the upper end of the cylinder. 
As best observed in FIGS. 3, 5 and 6, the piston rod mounting bosses 59 are 
adapted to engage and be retained by the mounting and coupling shoe 26 
which is secured to the leading end of the linear drive shaft 27 adapted 
to be coupled to the piston rod 24 for driving the syringe cartridge 21 
through successive fill and pump strokes. The coupling shoe 26 includes a 
pair of confronting, wide mouth guide slots 63 in upstanding flanges 62, 
disposed on opposite sides of the coupling shoe, and adapted to engage and 
guide the mounting bosses 59 so that the syringe cartridge 21 can be 
inserted into the coupling shoe horizontally. 
Hence, during the cartridge installation procedure, the tab 58 of the 
syringe cartridge 21 is gripped by two fingers of one hand of the operator 
and, with the longitudinal axis of the syringe cartridge held 
horizontally, the piston rod 24 and mounting bosses 59 are inserted 
horizontally into the guide slots 63 of the coupling shoe 26 (with the 
cutaway surfaces 24d of the piston rod directed downward) and moved to the 
rear of the coupling shoe which essentially defines a mounting yoke for 
the bosses 59. The syringe cartridge 21 is then rotated upwardly, about an 
axis of rotation through the mounting bosses 59 in the coupling shoe 26, 
so that the longitudinal axis of the syringe cartridge is brought into a 
vertical position, as illustrated by the solid lines in FIG. 3. The latter 
procedure brings the cut-away, lower end of the piston rod 24 into a 
retention channel 64 within the coupling shoe 26. In this regard, the 
cut-away surfaces 24d of the piston rod are rotated into abutment with a 
ledge 64a of the retention channel 64. 
When the syringe cartridge 21 has been thus installed, the mounting bosses 
59 in the guide slots 63 prevent the syringe cartridge from being 
dislodged vertically, whereas the cut-away surfaces 24d in the retention 
channel of the coupling shoe 26 prevent the cartridge from being dislodged 
horizontally. 
As best observed in FIGS. 1 and 3, the mounting bosses 61 of the syringe 
cylinder 22 are adapted to engage a pair of fixed guide and retaining 
slots 66 provided in opposite walls of the syringe receiving compartment 
of the pump housing. By controlling the initial location of the coupling 
shoe 26, relative to the curved, wide mouth guide and retaining slots 66, 
the pumping apparatus can be conditioned to receive the syringe cartridge 
21 only if its piston 23 is in a predetermined position within the syringe 
cylinder 22, i.e., in the top dead center position adapted to initially 
perform an intake stroke to fill the syringe with liquid. The latter is 
the proper state of the syringe for initial start-up of the pumping 
apparatus. 
The intake and output I.V. tubes, 33, 34, respectively, from the syringe 
cartridge 21, are then passed vertically over the tube pincher blades 43a, 
44a and are clamped in position by the closing of the tubing compartment 
access door 45 which is then latched shut by the latch 45b to firmly 
anchor and maintain the syringe cartridge in position during the 
operational cycles of the pump. The tubing access door 45 must be 
unlatched and opened to enable the syringe cartridge 21 to be rotated from 
the vertical position to a horizontal position for removal from the 
coupling shoe 26, whenever it is desired to replace the cartridge. 
The coupling shoe 26 is, as previously indicated, secured to the upper end 
of the linear drive shaft 27 which advances and retracts the coupling shoe 
and thereby advances and retracts the piston rod 24 and piston 23 within 
the cylinder 22 for repetitive fill and pump strokes. As best observed in 
FIGS. 3 and 4, the linear drive shaft 27 is of non-circular cross-section 
and, in the preferred embodiment shown, is of rectangular cross-section. 
The drive shaft 27 passes through and is in sliding engagement with an 
anti-rotation bearing 68 having an opening of complimentary cross-section, 
and enabling the drive shaft to move along its longitudinal axis while 
being keyed against rotation about that axis. 
A lead screw 70 is integral with, or otherwise appropriately secured to, 
the drive shaft 27 and is advanced and retracted along its longitudinal 
axis, to thereby advance and retract the drive shaft 27, by an internally 
threaded gear 72 in the gear train 31 driven by the motor 29. The gear 72 
is appropriately supported for rotation in a pair of stationary gear 
carriers or thrust bearings 73, 74. 
As best observed in FIGS. 1 and 3, a visual running indicator is provided 
in the form of a rotating disc 76 having a plurality of visually 
observable, preferably uniformly spaced, vertical index lines 77 located 
along its entire peripheral edge. The disc 76 is secured to a central 
bushing 78 (through which the lead screw 70 passes freely) and is 
journaled for rotation in the upper gear carrier 73. The bushing 78 and 
disc 76 are driven by the output shaft 29a of the motor 29 via a belt 
drive in the form of a simple O-ring 79 which passes around the output 
shaft of the motor and around the bushing 78 to provide a simple friction 
drive. 
The peripheral index lines 77 are readily observable through a window 81 in 
the pump housing. Hence, when the pumping apparatus is operating at a very 
low pumping rate, so that no movement of the coupling shoe 26 or piston 
rod 24 is visually discernible by the operator, the rotation of the 
running indicator disc 76 will be apparent through the window 81 to assure 
the operator that the system is in operation. 
Referring now more specifically to FIGS. 1 and 2, a motor rotation sensor 
83 is provided to insure proper detection of a stalled motor 29 so that, 
in cooperation with the electrical control system, an alarm condition can 
be appropriately generated. Such motor stalling has a greater probability 
of occurring when the pump is used with a downstream filter which may clog 
and induce high back pressure on the pumping system. 
The rotation sensor 83 comprises a disc 84 mounted on the output shaft 29a 
of the motor 29 for rotation therewith, the disc having alternate 
transparent and opaque sectors 85, 86, respectively. A photocell 87 
detects light passing through the disc 84 from a reference light source 
88, as the disc rotates, and generates electrical pulses which are 
appropriately directed to the electrical control system for monitoring and 
alarm functions. Hence, the rotation sensor 83 is capable of indicating 
any stalled motor condition. 
As best observed in FIGS. 10 and 11, the pumping system, including the 
syringe cartridge 21, may embody appropriate means for indicating proper 
installation of the syringe cartridge and for detecting the presence of 
gas bubbles. In this regard, the inlet nipple 51 of the syringe cartridge 
21 is surrounded by an integrally molded, transparent flag member 89. A 
fixed light source 91 and photoelectric sensor 92, both located in fixed 
positions within the syringe compartment of the pump housing, provide a 
reference light beam which is selectively interrupted by the flag member 
89 whenever the syringe cartridge 21 has been properly positioned in the 
syringe compartment of the pump housing. In this regard, the flag 89 
prevents the reference light beam from reaching the sensor 92 by 
interposing a totally reflecting surface 89a in the path of the light beam 
to deflect the light beam away from the sensor. 
In addition, bubble detection is accomplished in the arrangement of FIG. 11 
by providing a fixed light source 94 and photoelectric sensor 95 on 
opposite sides of the inlet nipple 51, so that gas bubbles passing through 
the nipple will interrupt the light beam and generate an appropriate 
electrical signal. The latter signal is appropriately transmitted to the 
electrical control system to bring about the generation of an alarm state. 
Hence, the bubble detection system insures no air bubbles are entering the 
syringe through the inlet nipple 51. 
An alternative embodiment of a suitable system for monitoring the proper 
insertion of the syringe cartridge 21 within the syringe compartment is 
shown in FIG. 12. In this embodiment, a syringe nipple 151 is 
appropriately provided with an opaque, typically black, outer coating 151a 
so that, when the cartridge has been properly installed, a reference light 
beam from a fixed light source 191 in the pump housing is interrupted. 
This causes an appropriate electrical signal to be generated by a fixed 
photosensor 192 located in the pump housing on the opposite side of the 
nipple 151. 
The new and improved syringe pump drive system and disposable syringe 
cartridge of the present invention satisfies a long existing need in the 
medical arts for improved, relatively simple, economical, reliable, stable 
and accurate syringe pumping systems. 
It will be apparent from the foregoing that, while particular forms of the 
invention have been illustrated and described, various modifications can 
be made without departing from the spirit and scope of the invention. 
Accordingly, it is not intended that the invention be limited, except as 
by the appended claims.