Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a medical lnfusion systems
and, m~re particularly, to an improved pump and cassette for use
therein.
A medical infusion system which operates to pump fluid
or semisolids from an upstream portion to a downstream portion is
known. The pump includes upstream and downstream conduit means
and a removable cassette communicates between the two. The
cassette has a window therein and a diaphragm spans the window~
~ Means on the pump engage the diaphragm for varying the volume of
10 the pumping cavity formed by the cassette. The cassette has inlet
and outlet openings valvelessly communicating with the cavity.
Fluid in the conduit is pumped by restricting and opening the
conduit means at upstream and downstream locations and displacing
the contents of the cassette pumping chamber or cavity
i appropriately.
The medical infusion system described hereinabove
provides significant advantages over many prior art constructions.
There are no valves employed in the cassette, thus significantly
improving the reliability and reducing the complexity of
manufacture and therefore the cost. Ir.creased accuracy over
; prior cassette designs is also achieved. By properly controlling
the pinch off of the tubes at the inlet and the outlet of the
~` cassette, good constant flow rates may be achieved, even to very
low rates.
It has been observed that, in the infusion system
described above, the presence of air in the cassette pumping cavity
can detrimentally effect the operation of the device. These eEfects
result from three phenomena. First, at high back pressures, the
fluid level in the drip chamber feeding ~he system
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rises, due to expansion of the compressed air as the
inflow valve opens prlor to filling, which may trigger
an empty bo~tle alarm. 5econdly, flow output decreases
as the back pressure and volume of air increases,
S affecting pumping accuracy. Thirdly, at low back
`~ pressures, which may be caiused by low needle level
~minus 12" to minus 36" belo~7 the casse~te), the
delivered flow rate is higher, due to the expansion of
: the air upon opening of the outflow valve, also
a~fecting accuracy.
The effects of air in the casse~te can be
substantially reduced or eliminated by, in effect,
inverting the cassette so the outlet from the pump
chamber is on the top and the inlet is on the bottom.
In such a position, air bubbles migrate to the outlet
and are pumped out with the expelled fluid or
semisolid. Such a principle is em~loyed in the cassette
described in U.S. Patent No. 4,140,118 issued February
20, 1979. Although successful, such an arrangement may
result in confusion on the part of hospital personnel as
; to which is the inlet. This is because most
conventional and prior art drug infusion systems are
arranged so ~hat the flow is continuously downward from
the bottle to the inlet, which is at the top of the pump.
It is an object of the present invention to
provide an improved cassette and an improved combination
of a pump and cassette for a drug infusion system.
Another, more specific object of the invention
is to provide a drug ~nfusion system utilizing the
combination of a pump and cassette wherein the effect on
accuracy of air in the casiette is substantially
eliminated and wherein the cassette is easy to ins~all
in the pump and is not con~using in setting the system
up for operation.
A further vbject o the invention is to provide
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a casette design of improved construction which ~acilitates use
with a minimum amount of confusion.
The invention comprises a replaceable pump casse.tte,
either alone or in combination with a pump, for a medical infusion
system which pumps fluid or semi-solids from an upstream portion of
the infusion system to a downstream portion thereof. The cassette
includes a rigid enclosure defining a pumpinq cavi-ty and having
inlet and outlet openings and further having a window therein.
' A flexible diaphragm extends across the window and is impermeable
to the passage of fluids or semi-solids therethrough. The
diaphragm is engageable by means on the pump for varying the
volume of the pumping cavity. The cassette is of configuration
such that it is oriented with the inlet and outlet openings both
positioned proximate at the top of the pumping cavity with the
cassette in an operative position in the pump. The pumping cavity
has an internal configuration including interior walls curved to
direct all gas bubbles within the pumping cavity to the outlet
opening with the cassette in the operative position. Either the
pump or the cassette includes means defining a passage
communicating between the outlet opening and a location displaced
from the outlet opening which may be located proximate the lower
portion of the cassette with the cassette in the operative
position.
Other objects of the invention will become apparent
to those skilled in the art from the following description taken
in connection with the accompanying drawings wherein-:
FI~URE 1 is a schematic view of a medical infusion
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-` system in which the invention ls lncorporated;
FIGURE 2 is a front view of a cassette constructed
in accordance wi~h the invention;
FIGURE 3 is a full section view of the cassette
of FIGURE 2 taken along the line 2-2 of FIGURE 2 with the
invention;
FIGURE 4 is a full section view of the cassette
and a portion of a pump therefor constructed in accordance with
the invention; and
PIGURES 5 and 6 are, respectively, front plan
schematic views of two further embodiments of the invention.
Very generally, the cassette and pump combination of
the invention (FIGURES 1 and 4) operates to pump fluids or
semisolids from an upstream portion 11-12 to a downstream portion
13 of a medical infusion system for a patient 14. The pump 15
supports a cassette 16 (FIGURES 2-3, 5 or 6) comprising a rigid
enclosure 17 defining a pump cavity 18. The rigid enclosure
has an inlet opening 21 located to be proximate the top of the
cassette when the cassette is in an operative position in the
` 20 pump. An outlet opening 23 is also provided in the rigid enclosure,
and the enclosure further has a window 25 therein. A flexible
diaphragm 27 extends across the window and is impermeable to the
passage of fluids or semisolids therethrough. Actuator means 28
; engage the diaphragm to vary the contents of the cavity 18. The
casse~te is of
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a configuration ~or orienting the casset~e with respect
` to the pump such t~at the outlet opening is positioned
; at the top of the pumping cavity when the cassette is in
an operati~e position with respect to the pump~ The
pumping cavity has an internal configuration to cause
gas bubbles to migrate to the outlet opening with the
cassette in the oper~tive position. An outlet passage
29 communicates between the outlet opening and a
location displaced from the outlet opening which loction
is positioned for convenience in settinq up the cassette
and pump for operation. The passage may be located in
the cassette or may be located in a portion of the pump
itself adjacent to the cassette.
Reerring now more particularly to FIGURE 1,
the invention is shown in the 40rm of an intr~venous
delivery system for delivering fluid from a fluid
reservoir or storage means 12 to a patient 14. The
fluid is introduced intravenously through a suitable
catheter 30 attached to the downstream portion 13 of the
delivery system. The catheter is held in place by
adhesive tape 31 on the arm of the patient 14 as is
well-known in the art. The fluid reservoir 12 may be a
conventional intravenous delivery system bottle
suspended on a stand 32. A drip chamber 33 is attached
to the lower portion of the bottle 12 and may be of
conventional construction. An empty bottle alarm, not
shown, of suitble design may be employed beneath or
attached to the drip chamber to signal when the contents
of the bottle 12 have been drained. The contents of the
bottle 12 pass through the upstream conduit portion ll
of the delivery system, the upstream conduit portion
constituting, in the illustrated embodiment, a flexible
hose.
Although the bottle 12 i8 ~hown positioned on
the support 32 ln an elevated condition wlth respe~t to
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the patient 14, as is typical of many intravenous
delivery systems it is not critical in the system of the
invention that the bottle be so elevated inasmuch as the
Pluid is conveyed to the patient by the positive pumping
action of the pump 15. ~he pump 15, shown in FIGURE 1,
may be suitably contained in a housing 34 having control
knobs including a knob 35 thereon. The pump 15 may be
supported on a bedside table 39 or other suitable
structure and is located between the upstream portion 11
and the downstream portion 13 of the delivery system~
Grommets 41 form the entrance and the exit to the
housing 33 for the upstream and downs~ream portions 11
and 13, respectively.
The sys4em of the invention employs a
replaceable cassette 16 in the pump 15. The cassette
utilized in the system of the present invention does not
require any valve~s, vastly simplifying the system and
drasticlly lowering the cost o~ the replaceable portion
thereof. In addition, the system of the present
invention employs a cassette in which a substantial
displacement occurs during each pumping stroke. This
s~roke dIsplacement in the system of the present
invention i5 preferably about at least 0.25 ml and less
than about one ml. In this range, the most acceptable
performance results. Typical volume of the pumping
chamber with the diaphragm in position for maximum
volume is about l.9 ml.
; The cassette is specifically illustrated in
FIGURES 2 and 3. Basically, the cassette is in ony
` 30 three pieces. The main piece is a molded housing 17 of
a suitable medical grade plas~ic. The outline of the
housing is generally circular with an asymetric Plange
40 in the shape of a rectangle plus a contiguous
semicircle. This asymetric shape enables a
corresponding configurat~uon in the pump to permit
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mounting of the cassette only in the proper orientation
as explained below. A socke~ 43 is provided for
connection to the upstream conduit portion o the
infusion system, and a socket 44 (on the lower side of
the housing 17) is provided for connection to the
downstream conduit portion o~ the infusion system.
Unlike many prior art cassettes, the inlet and ou~let
cor.tain no valves. The housing 17 de~ines the pumping
chamber 18 which is generally in the shape of a cylinder
havinq one open side or window 25. An annular recess 45
surrounds the open side of the pumping chamber and
receives the annular lip 47 of the flexible diaphragm
27. The diaphragm 27 is comprised of a suitahle medical
grade flexible material which is impervious to the
fluids or semisolids being pumped ~nd which is capable
of flexing as described below sufficien~ly so as to
enab_e the de~ired displacement, also described in
detail below. ~or the purpose. of holding the flexible
diaphragm in place, a mounting ring 49 seats in and
mates with a projectinq annular lip 51 on the housing 17
and is suitably sealed to the housing, such as by
ultrasonic welding, to form a seal and to hold the
diaphra~m 27 in place spanning ~he open side o~ the
pumping chamber 18.
: 25 Referring ko FIGURE 4, means are employed to
sequentially restrict and open the upstream and
downstream conduit portions 11 and 13, respectively, in
a sequence such as to provide a valve type action to
enable fluid to be pumped from the upstream conduit
portion 11 to the downstream conduit portion of 13 of
the delivery system. Although any suitable means ~or
constricting the conduit portions in the manner
described below may be employed, in the apparatus
illustrated in FI~URE 4, the restricting means are khe
tapered ends of movable rods or bars 63 and 65,
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respectively. The bars are movably supported, by
suitable means not shown, insidP the housing 34 of the
pump lS. The rounded tips of the tapered ends of the
bars 63 and 65 engage the respective upstream conduit
portion 11 and downstream conduit portion 13. The
conduit portions are supported in mating grooves or
channels in a chassis 66 inside the housing 34 of the
pump 15. A boot 53 e~tends across the chassis 66 as
shown to provide a seal between the region of the
cassette 18 and the drive means described below.
For the purpose o expelling the contents of
the pumping chamber 18, ~he rounded end o an elonga'ed
bar 67 is movably mounted in a suitable support, no~
shown, to the chassis 66. The rounded tip of the bar 67
engages the diaphragm 27 over the open side of the
pumping chamber 1~ of the cassette 16. ~hen t~le
cassette is properly mounted~ the ~ctuator means 28
distend the diaphragm 27 sligh~ly inward even at maximum
retraction; thus constantly being in engaqement with the
diaphragm throughout the pumping s~roke. The volume of
the pumping cavity in this maximum retracted position of
~ the bar 67 is at its maximum operating volume. As the
; bar 67 moves inwardly the membrane is distended
. inwardly, thereby reducing the volume of the pumping
chamber 18.
The pump lS includes a hinged door 60 which
opens to allow insertion and removal o the cassette 16
and the regions of the upstream and downstream portions
11 and 13 which are inside the`pump housing 34. As may
be seen in FIGURE 4, when the door 60 is closed, a coil
. spring 55 held in a recess 57 o~ ~he door, the latter
being covered by a plate 59, presses a biasing cup 61
against the cassette hou~ing 17, thus holding tha
housing in position against the chassi~ 66. Pressure
blocks 62 and 64 are provided attached to the door 27 by
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adjusting screws 68. ~he block 62 is positioned on the
- opposite side of the ups~ream conduit portion 11 from
the rod 63. Similarly, the block 64 is positioned on
the opposite side of the downstream conduit portion 13
from the rod 65. By suitably adjusting the position of
the blocks 62 and 64 using the screws 68, the pressure
exerted by the restricting means during ~he operation
described below may be adjusted during manufacture to
insure complete seal off of the tube and thus total
closure, as described.
For moving the bars 63, 65 and 67 in the
desired sequence, the ends of the movable bars 63, 65
and 67 opposite the cassette and conduit portions carry
suitable cam followers 71 biased tby springs, not shown)
against the surface of cams 91, 93 and 95. The cams ~l,
93 and 95 are mounted on a cam shaft 97 which is rotated
by a driving motor 103. The driving motor is a stepping
motor to provide incremental rotation of the shaft and
. therefore incremental movement and control over the
movable bars.
In FIGURE 4, the lower restricting means 65 is
in a position such as to restrict or pinch-off the
downstream flexible conduit portion 13. Dué to the
natural ~low or pressure head of the fluid in the
upstream portion, or to the suction (negative pressure~
created by the retraction of the member 67, the pumping
chamber 13 of the cassette 16 fills. The pumping stroke
occurs when the second restricting means 65 are
retracted to fully open the conduit portion 13 and the
first restricting means 63 have closed to restrict or
occlude the upstream conduit portlon 11. Movement of
the actuator means 67 inwardly reduces the volume o the
~ pumping chamber 18 causing at lea~t ~ome of the contents
`~ to be expelled to the downstream portion of the delivery
system. The distance which the actuator means 67 move
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inwardly determines the displacement volume during the
pumplng strokeO The filling and pumping strokes are
conducted in sequence and repeated according to the
rotation of the cam shaf~ 97 and the co~figuration of
the cams 91, 93 and 95.
: In the embodiment of the cassette of FIGURES 2
and 3, the back wall of the cassette has a vertical
passage 29 bored therein which extends upwardly and
terminates at the upper end of the pump cavity. A
horizontal opening or a hole 23, forming the outlet
opening, extends from the pump cavity 18 adjacent the
periphery thereof to the vertical passage. The
curvature of the interior surface of the pump~ng cavity
assists bubbles of gas in migrating toward the upper end
o~ the pumping cavity. Accordingly, such bubbles
readily pass through the hole 23 and into the upper end
- of ~le passage to be forced out with the flow of fluid
`~ or semisolids during pumping. Accordingly, any air
enterinq the pumping cavity will be forced out and will
` 20 not accumulate therein. ~ecuase air is unable to build
` up in the pumping cavity, the accuracy of the system is
preserved.
Referring now to FIGURE 5, an arrangement is
shown wherein the passage 29 which connects the outlet
" 25 opening 23 to a location proximate to the lower portion
~ of the cassette 16 is formed in the mounting block or
- chassis 66 of the pump itself. The outlet opening,
which is of generally circular cross section, has an
axis which is substantially vertical with the cassette
mounted for operation. The passage 29 provides a loop
which the cassette 16 to a position below the cassette.
; The flexible tubin~ normally connected to the cassette
; and forming the downstream portion of the drug delivery
d' system is pl~ced in this passage by the operator
lnstalling the cassette. The door 60 i5 then closed and
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the dev~ce is ready for operation. An air in line
detector 105 may be provided for warning purposes. The
flexible tubing is occluded by the bars 63 and 65 at 63'
and 65', respectively.
In FIGURE 6, an embodiment is shown in which
the outlet opening 23, which is of generally circular
cross section is on a substantially horizontal axis
when the cassette is positioned or opertion. The
flexible tubing then extends, for at least part of its
; 10 length, horizontally from the outlet opening to exit the
side of the pump.
It may be seen~ therefore, that the invention
provides a replaceable pump and cassette comb nation for
a medical infusion system which is easy to use and which
avoids problems resul~ing from the accumulation of air
in the pumping cavity of the cassette. The device is
easy to instal and maintains the typical configuration
wherein the inlet or upstream portion of the infusion
~; system extends from the top of ~he pump and the
downstream portion extends from ~he bottom.
Various modifications of the invention in
addition to those shown and described herein will become
apparant to those skilled in the art ~rom the foregoing
description and accompanying drawings. Such
modifications are intended to fall within the scope of
the apended claims.
