Infusion apparatus

A liquid infuser apparatus includes an elastic sleeve mounted on an elongated member and within a spherical housing to enable it to expand naturally to maintain a constant pressure over the infusion period. An alternate embodiment includes a holding reservoir that may be pre-filled, and a pressure reservoir that is loaded from the holding reservoir preparatory to infusion.

BACKGROUND OF THE INVENTION 
The present invention relates to liquid dispensing apparatus and pertains 
particularly to an improved infuser apparatus for delivering intravenous 
drugs at a controlled rate to a patient. 
It is often necessary to intravenously supply patients with 
pharmaceutically active liquids over a long period of time at a controlled 
rate. It is desirable that this be accomplished while the patient is in an 
ambulatory state. A few devices have been developed in the past for 
accomplishing this purpose. 
The prior art devices typically comprise an elastic bladder forming a 
liquid container mounted in an elongated cylindrical housing, and having a 
flow control valve or device and tubing for supply of the liquid to the 
patient. The elastic walls of the bladder expand along the walls of the 
cylindrical housing when filled with the liquid, and provide the pressure 
for expelling the liquid. These prior art devices are typically filled by 
hand by means of a syringe which often require an inordinate amount of 
force. 
Another drawback to the prior art devices is that the bladder is forced to 
expand into an unnatural elongated configuration along the housing walls 
as the container is filled. As a result of this unnatural configuration, 
the pressure of the bladder and the flow rate of the unit varies widely 
with the volume of liquid therein. Therefore, they do not have a 
reasonably stable pressure and flow rate over the infusion period. 
Most of such devices either have a flow rate that decreases with pressure, 
which decreases with volume, or one that remains roughly constant until 
the end where it surges. Attempts have been made to control pressure and 
flow rates by means of complicated and expensive flow control valves and 
devices. Other approaches have utilized exotic and expensive elastic 
materials in an effort to control the pressures and flow rates. 
In our aforementioned application, we disclose an apparatus for solving the 
aforementioned problems of the prior art. However, one problem remains, 
namely that the materials that provide optimum elasticity do not have 
sufficient chemical inertness for medical application. Similarly, 
materials that are sufficiently chemically inert for medical or 
pharmaceutical use are not sufficiently elastic to serve the function of 
an effective inflatable bladder. 
It is desirable that the bladder of an inflatable bladder infuser be 
chemically inert in order to avoid contamination of the medication, and 
that the pressure and flow rate be reasonably constant over the infusion 
period. 
Accordingly, it is desirable that an improved infuser apparatus be 
available. 
SUMMARY AND OBJECTS OF THE INVENTION 
It is the primary object of the present invention to provide an improved 
liquid infuser apparatus. 
In accordance with a primary aspect of the present invention, a liquid 
infuser apparatus comprises an elastic reservoir mounted within a 
spherical chamber, and comprising an inner inert layer and an outer 
elastic capable of maintaining a substantially constant pressure over the 
range of the infusion cycle.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawings, and particularly to FIGS. 1-2, there is 
illustrated a preferred embodiment of the invention, wherein the infuser 
pump is separate from the charging or filler pump. Moreover, it may be 
filled by any suitable means, such as a syringe or any other pressurizing 
means. As illustrated in FIGS. 1 and 2, an infuser pump, substantially 
like the FIGS. 9-11 embodiments of our prior application, is designated 
generally by the numeral 10 and comprises an outer substantially spherical 
housing of a size to accommodate the necessary volume of intravenous fluid 
to be pumped. 
The housing 12 has a substantially spherical configuration and is provided 
with coaxial, or more particularly aligned bores or ports 14 and 16, in 
which is mounted an inflatable bladder assembly. The housing 12 may be 
made of unitary construction, such as by blow molding, or may be of two 
identical half shells assembled. The ports are formed in axial recesses 18 
and 20. The inflatable bladder assembly comprises a first or inner 
elongated semi-elastic sleeve 22, and a pair of outer elongated latex 
rubber elastic sleeves 24 and 26 mounted on an elongated central 
cylindrical support member 28. The inner sleeve 22 is preferably made of a 
drug compatibility rubber with low leach characteristics that meets USP 
class 6 testing standards. 
A preferred rubber material for the inner sleeve 22 is a class of 
thermoplastic rubber sold under the mark KRATON by Shell Chemical Company 
of Houston, Texas. These materials are available as KRATON D and G 2000 
series rubber, and have FDA status for use in certain applications or 
ingredients of articles for food contact. These materials have less than 
optimum elastic characteristics, and are referred to herein as 
semi-elastic. When stretched, they return to a position of about 75 to 
about 90 percent of original configuration. 
The outer sleeves 24 and 26 are preferably made of a natural latex rubber 
with excellent elastic characteristics. A material with good elastic 
characteristics returns from a stretched condition to its original 
un-stressed or stretched condition. A good elastic material also has a 
uniform elastic force over the range stretched. Natural latex rubbers are 
the preferred material for the outer sleeves membranes 24 and 26. 
The central support member 28 is preferably of a generally elongated 
cylindrical configuration, with an annular radially extending retaining 
flange 30 on one end for engaging a shoulder 32 on the housing 12. The 
opposite end of the support member 28 includes a bayonet type coupling 
with a retaining nut 34. The central support member may be constructed of 
any suitable pharmaceutically compatible material, such as metals, 
plastics, glass, etc. 
The coupling comprises a generally rectangular projection 36, with 
shoulders 38 and 40 formed by annular slots in which the retainer nut 
rotates. The retainer nut 34 included a recess 42, with a rectangular 
opening 44 for receiving projection 36 on the end of support member 28. A 
pair of side lips 46 and 48 extend under shoulders 38 and 40 when the nut 
is rotated 90 degrees for retaining the nut in place and the support 
member 28 in the housing bores. The nut 34 rests in annular recess 50 
surrounding recess 20. 
The support member 28 includes an inlet port 52 communicating by means of a 
passage 54, including a one-way valve 56, 59 with the interior of the 
membrane or sleeve 22. Any suitable check valve may be used to permit 
uncoupling of the filling unit without leakage of fluid from the 
pressurized bladder. However, a valve as illustrated in FIGS. 4-6 is 
preferred. The check valve comprises a cross throughbore 56 communicating 
with the end of passage 54, and in which is slip fitted an elastic tube 
58, which may be of a suitable rubber such as silicone. The tube 58 covers 
the end of passage 54 to prevent back flow from inside the bladder formed 
by sleeve 22. The tube 58 collapses, as shown in FIG. 5, in response to 
higher pressure in passage 54 enabling flow of liquid into sleeve 22. 
An outlet passage 60 in support member 28 communicates via an outlet port 
62 and suitable coupling assembly 64, with an outlet or intravenous 
feeding line comprising a two-part tube 66, which includes a filter 68, 
and may include flow control means 70 and a male luer lock adaptor. The 
outlet line may be controlled by a suitable valve assembly (not shown) or 
preferably by the well known type clamp known as a Roberts clamp 76. The 
luer lock has a valve that closes the outlet port when the feeding line is 
uncoupled therefrom. The coupling is effective to open the outlet valve 
when coupled to the outlet fitting. Such luer locks are well known 
off-the-shelf items for I.V. delivery systems. The delivery tubes 66 may 
be selected in size and length to and aid in maintaining a predetermined 
pressure and flow rate. A suitable tube size for the particular 
application is 0.088 inch O.D. by 16.5 inch in length. Orifices or other 
means, such as flow regulating capillary tubes may be also used in 
controlling the flow. 
The elastic sleeves 24 and 26 are mounted over the sleeve 22. Sleeves 24 
and/or 26 may be stretched radially when in position over sleeve 22, e.g. 
24 is stretched radially over 22, with 26 slip fit over the assemblies of 
22 and 24. The outer bladder 26 slips radially over the assembly of 22 and 
24. The composite assembly of 22, 24, 26 is slideably engaged with a slip 
fit over the mandrel or support member 28. Radial stretching of the 
bladder 24 compensates for material 22's less than perfect elasticity. 
More specifically, the wall thickness and amount of stretch of bladder 24 
are selected to just compensate for bladder 22's material less than 
perfect elasticity. The initial strain conditions and bladder wall 
thicknesses are also chosen to minimize the non-linearity exhibited in a 
bladder's stress versus strain. 
It is well known that a single bladder infusion device constrained at both 
ends exhibits a highly non-linear stress versus strain relationship. This 
causes a time varying flow characteristic. The prior art required 
stretching the membrane both axially and radially over a mandrel to reduce 
this non-linear behavior and thus generate a more constant flow versus 
time. We have improved the state of the art by incorporating a chemically 
inert inner bladder and an elastic outer bladder. Further, we have devised 
a structure and method for maintaining constant flow versus time while the 
device is infusing by radially stretching an intermediate bladder over the 
inner bladder. 
The inner semi-elastic drug compatible tube or membrane 22 is mounted on 
the cylindrical support member 28, preferably in a slightly snug but 
un-stretched radial fit, and essentially relaxed elongated or 
non-stretched longitudinal fit. The inner sleeve 22 preferably has what 
shall be called a slip fit on the support member. This slip fit is 
preferably with a clearance of on the order of about one-thousandths of an 
inch of the sleeve on the support. This provides a non-stretched fit, with 
essentially zero volume of the pressure chamber when in the non-stretched 
or totally relaxed state or mode. 
The elastic sleeves 24 and 26 are respectively stretch fit and snug fit 
radially over the inner semi-elastic sleeve 22. The intermediate sleeve 24 
is radially stretched up to about five percent over the inner sleeve 22 
for compressing it. The outer sleeve 26 is slip fitted over the 
intermediate sleeve 24. All of these sleeves 22, 24, and 26 are fitted 
over the support member 28 and clamped at the ends by means of a pair of 
O-rings 76 and 78. These O-rings 76 and 78 bias the ends of the multiple 
sleeves into annular grooves 80 and 82 in the outer surface of the member 
28. The O-rings 76 and 78 are held in place by the walls of the housing 
forming the recesses 18 and 20. The multiple sleeves when being filled 
tend to elongate and roll over the ends thereof as shown in FIG. 2. The 
support member 28 is of a fixed length and holds the ends of the sleeves 
at a fixed position. The multiple thin sleeves easily roll over the ends 
thereof as the bladder made up of the multiple sleeves fills and expands. 
The pressure applied by the pressure chamber, formed by the multiple 
sleeves, will be substantially a function of the thickness of the wall of 
the elastic sleeve or sleeves. For example, a typical two to three (2-3) 
psi may be obtained by a wall thickness of about eighteen to 
twenty-thousandths (0.018-0.020) of an inch. In order to obtain higher 
pressure with superior uniformity, a multi-layered sleeve configuration as 
described hereinabove has been found to be preferred. 
As illustrated in FIG. 1, a plurality of sleeves (three illustrated) 22, 23 
and 24 are slip fitted (non-stretched) on the support member. The inner 
sleeve 22 is slip fitted on the support member 28, and a second sleeve 24 
is slightly stretch fitted over the first sleeve 22. Thereafter, a third 
sleeve 26 is slip fitted over the intermediate sleeve 24. These are shown 
in the fully deflated position in FIG. 1 and in the fully inflated 
condition in FIG. 2, showing the fold or roll over the ends. These 
multiple layers have been found to be superior to the use of thicker 
membranes or sleeves to obtain higher and uniform pressures. The use of 
multiple layers also enables the use of a semi-elastic substantially 
chemically (medically) inert inner membrane or sleeve for contact with the 
infusible liquid. The multiple sleeves will roll or fold over at the ends, 
as illustrated in FIG. 2. Thus, to increase the pressure, additional 
sleeves of substantially the same thickness are used. 
When being filled, the elastic multi sleeve membrane has a tendency to 
elongate, but expands into a spherical configuration (FIGS. 10 and 11 of 
our prior application). The sleeve is shown in the partially filled 
position in FIG. 10 and in the fully filled position in phantom. 
The elongation is accommodated in this pump configuration by an accordion 
effect at the ends of the bladder, as shown in FIG. 2, wherein the bladder 
rolls over the ends thereof and outward along the support member 28 as it 
expands outward to fill the housing 12. The accommodation of the elastic 
membrane in the spherical configuration enables it to expand and contract 
in its natural fashion, and to maintain a substantially constant pressure 
and thereby flow rate over the intravenous injection period. 
The layered or multiple sleeve configuration has been found to better 
accommodate the accordion fold and maintain a more uniform pressure than a 
thicker sleeve. The tubular elastic sleeve membranes are selected and 
mounted on the support member in a manner that enables them to roll or 
fold over at the ends when being filled. 
In operation, an assembled infuser pump unit is selected, and the inlet 
port 52 is secured to a source of fluid under pressure. As fluid is being 
introduced into the inlet, the valve 58 collapses in FIG. 5 as fluid flows 
into the inner sleeve or membrane 22. As the reservoir or bladder formed 
by the sleeves begins to fill, it expands and attempts to elongate. The 
ends of the sleeves begin to fold and roll over the ends thereof as in 
FIG. 2. The bladder forms a substantially spherical shape as its natural 
form of expansion. The roll at the ends accommodates this expansion and 
aids in maintaining a substantially constant pressure over the range of 
infusion. 
As the bladder deflates, the outer elastic membranes force the inner 
semi-elastic membrane back to substantially its original position. This 
helps to evacuate the entire volume of fluid. It also will be appreciated 
that any form of pressurized filling apparatus may be used. For example, 
the squeeze fill embodiment of FIG. 1 of our prior application could be 
utilized with this infusion pump. 
While we have illustrated and described our invention by means of specific 
embodiments, it is to be understood that numerous changes and 
modifications may be made therein without departing from the spirit and 
scope of the invention as defined in the appended claims.