Pumping arrangement for intravenous supply of fluids

A pumping arrangement including a squeezing device for deforming a length of pliant p.v.c. tubing first in one direction locally to reduce its volume and in another tending to restore its original cross-section and, on either side of squeezing device, inlet and outlet valves which operate by occluding the tubing. The squeezing device and the valves are controlled by a microprocessor control unit such that inlet valve is open and outlet valve shut while the squeezing device is relaxed and thereafter outlet valve is open and inlet valve shut while the squeezing device is operated to deform the tubing, this sequence repeating. Downstream of the output valve is a pressure responsive device providing input to the control unit whereby upon a rise in pressure in the delivery portion of tubing due to a restriction, the squeezing device is disabled and valves are open together to allow excess fluid to pass back towards the fluid source.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to pumping arrangements and in particular to pumping 
arrangements for use in medical applications such as the intravenous 
supply of fluids to a patient. 
This case also relates to the subject matter disclosed is commonly owned 
U.S. applications Ser. No. 07/430,851 filed Nov. 2, 1989, now U.S. Pat. 
Pat. No. 5,151,019 Ser. No. 07/744,350 filed Aug. 13, 1991, now U.S. Pat. 
No. 5,154,700 and Ser. No. 07/775,449 filed Oct. 15, 1991, which are 
hereby incorporated by reference into the present application. 
2. Discussion of Background 
In pumping applications involving intravenous supply of fluids it is common 
for deformable tubing, such as p.v.c. tubing, to be used to deliver the 
required fluid to the point of application. Where the supply rate and 
pressure is required to be carefully controlled, as is generally the case 
in medical applications, a serious problem can arise if the delivery 
tubing is restricted in any way (for example, by a patient rolling over 
onto it). Means can be provided to detect the resultant increase in 
pressure in the delivery tubing and disable the pumping action. However, 
if the restriction is removed (in the example given, by the patient 
rolling over again, off the tubing, or more likely by a nurse responding 
to an alarm also initiated by the means for detecting the increase in 
pressure) an undesirable surge of fluid to the point of application can 
result due to pressure retained in the delivery tubing. 
SUMMARY OF THE INVENTION 
Accordingly, one object of this invention is to provide a new and improved 
pumping arrangement in which the undesirable surge of fluid to the point 
of application, characteristic of the conventional pumping arrangement, is 
mitigated. 
The above object, and others, are achieved according to the present 
invention by providing a novel pumping arrangement including means for 
subjecting fluid to pressure, input and output controllable valve means 
for restricting fluid flow provided on input and output sides of the fluid 
pressure subjecting means, means responsive to fluid pressure in delivery 
tubing connected in operation between the output controllable valve means 
and the point of application of the required fluid for detecting an 
increase in fluid pressure, and means responsive to increases in pressure 
detected by said fluid pressure responsive means for controlling both the 
input and output controllable valve means to open, whereby fluid under 
excess pressure in the delivery tubing is released back towards a source 
of fluid connected in operation to the input controllable valve means. 
Normally means are also provided for disabling the fluid pressure 
subjecting means in response to increases in pressure detected by the 
fluid pressure responsive means. 
Preferably the controllable valve means each includes means operable to 
squeeze the tubing to produce occlusion. 
Preferably the pumping arrangement is also in accordance with the invention 
described in the above cross-referenced copending application Ser. No. 
07/430,851, now U.S. Pat. No. 5,151,019. 
Preferably again the fluid pressure responsive means includes a device as 
described in the above cross-referenced related co-pending application 
Ser. No. 07/744,350 which has issued as U.S. Pat. No. 5,154,700.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawing, a length of standard pliant p.v.c. tubing 1 of 
approximately 4.1 mm outside diameter and 0.5 mm wall thickness is 
connected at one end to a source of fluid 2. From that end, tubing 1 
passes through a pumping device 3 to a point of application 4. The point 
of application in this case is a patient and the fluid is a fluid required 
to be supplied intravenously. The means at the point of application for 
achieving this is not represented, but may be taken to be conventional. 
Between the source of fluid 2 and pumping device 3 the tubing 1 may be 
regarded as supply tubing, whilst between pumping device 3 and the point 
of application 3 the tubing 1 may be regarded as delivery tubing, although 
in this example the length of tubing is continuous. 
Pumping device 3 includes a squeezing device 5 through which tubing 1 
passes. Squeezing device 5 is arranged to deform tubing 1, first in one 
direction locally to reduce its volume and thereafter in another direction 
tending to restore the original cross-sectional shape of the tubing 1. 
On the supply or input side of squeezing device 5 is a controllable input 
valve 6 which is operable to block the passage of fluid between the 
squeezing device 5 and the fluid source 2 by squeezing tubing 1 to produce 
occlusion. 
On the delivery or output side of squeezing device 5 is a controllable 
output valve 7 which is operable to block the passage of fluid between the 
squeezing device 5 and the point of application 4. 
For more detail of the pumping device 3 reference may be made to the 
specification of co-pending application Ser. No. 07/430,851 now U.S. Pat. 
No. 5,151,019. Squeezing device 5 and controllable valves 6 and 7 
described herein corresponding to squeezing device 2 and inlet and outlet 
valves 3 and 4 described in detail in the specification of the co-pending 
application Ser. No. 07/430,851 now U.S. Pat. No. 5,151,019. 
Squeezing device 5 and inlet and outlet valves 6 and 7 shown in the 
accompanying drawing are controlled by a microprocessor control unit 8 
corresponding to control unit 52 as described in co-pending application 
Ser. No. 07/430,851 now U.S. Pat. No. 5,151,019 to produce pumping action 
as described in detail therein. Briefly, with squeezing device 5 relaxed, 
output valve 7 closed and inlet valve open, fluid passes into the region 
of the tubing encompassed by squeezing means 5. With squeezing means 5 
activated locally to reduce the volume of tubing 1, inlet valve 6 closed 
and outlet valve 7 open, fluid is passed towards the point of application 
4. The process then repeats. Normally, it will be noted, inlet valve 6 is 
shut when outlet valve 7 is open and vice versa. 
Beyond outlet valve 7 is a pressure responsive device 9 which in this 
particular case is an adaptation of the pressure responsive device 
described in detail in the specification of co-pending application Ser. 
No. 07/744,350 now U.S. Pat. No. 5,154,700. Pressure responsive device 9 
is connected to microprocessor control unit 8. When the signal from 
pressure responsive device 9 exceeds a given threshold indicating that the 
pressure in the delivery portion of tubing 1 had risen beyond a 
predetermined value indicative of a restriction caused, for example, by 
the patient rolling over onto the tubing 1, control unit 8 acts to cause 
squeezing device 5 to be disabled and both input and output valves to be 
opened together so as to enable excess fluid in the delivery portion of 
tubing 1 to pass back towards the fluid source 2 and thus relieve the 
excess pressure caused by the restriction. At the same time an alarm is 
caused to be activated to call the attention of a nurse to the 
restriction. 
It will be appreciated that the arrangement may be such that normal 
operation of the pumping device 3 recommences as pressure in the delivery 
portion of tubing reduces. In that case, however, "hunting" may occur 
since a reduction in pressure will occur not only because of a removal of 
the causative restriction, but also by the very opening of valves 6 and 7 
upon device 9 detecting an increase in pressure. 
If "hunting" as described is undesirable, renewed pumping may be subject to 
a reset control, operable by the nurse upon removing the cause of the 
restriction. 
FIGS. 2 and 3 illustrate details of the pressure responsive device 9, as 
disclosed in the noted related U.S. Pat. No. 5,154,700. As shown in FIGS. 
2 and 3, the device 9 includes a hard bed member 11 across the surface of 
which may be positioned a length of the pliant tubing 1. 
Hinged to the bed member 11 by hinge 13 is a main body 14 which has a 
circular cylindrical passage 15 extending orthogonally away from the 
surface of the bed member 11 across which the tubing 1 is positioned. The 
passage 15 exits from main body member 14 towards tubing 1 through a 
tubular projection 16 which, when the main body member 14 is closed up 
towards the bed member 11, flattens the tubing 1 against the surface of 
the bed member 11 over a short length 17 thereof. The extent to which 
tubular projection 16 projects towards bed member 11 is such that when the 
main body member 14 is fully closed up to the bed member 11 (and held by 
means of a suitable catch, not represented) the tubing 1 is flattened 
against the bed member 11 without occlusion occurring and without unduly 
impeding the flow of liquid through the tubing 1. 
Inserted within the passage 15 is a linear voltage displacement transducer 
18 of known form. As know per se transducer 18 has a spring-loaded plunger 
19 and produces an output digital voltage signal which is indicative of 
the extent to which plunger 19 extends beyond the body of the transducer 
18. The output voltage signal of transducer 18 will thus vary with the 
displacement of a surface against which plunger 19 is pressed in the 
direction of action of the plunger 19. 
Transducer 18 is entered into and fixed within the passage 15 to an extent 
such that plunger 19 is spring-biased against the flattened surface of the 
tubing 1 when the main body member 14 is closed up and secured to the bed 
member 11, as previously described. 
In operation, any variation in the pressure of fluid passing through the 
tubing 1 will tend to cause expansions and contractions. It is believed 
that flattening the tubing as above described magnifies the resultant 
displacement of the relatively flat portion of the wall of the tubing with 
which the plunger 9 is in contact, thus enabling the transducer 8 to 
respond to such variations with a higher degree of sensitivity than would 
otherwise be the case. 
FIG. 4 is a schematic block diagram illustrating functional operation of 
the pressure responsive device 9 in conjunction with the microprocessor 8 
of the present invention. 
Referring to FIG. 4 only transducer 18 and plunger 19 of the pressure 
responsive device 9 of FIGS. 2 and 3 are represented. The analog output 
voltage of transducer 18 is arranged to be sampled at the rate of once per 
second by a sampling circuit 20. 
The output of sampling circuit 20 is connected to the input of an 
analog-to-digital converter 21. 
The output of analog-to-digital converter 21 is connected to a 
unidirectional "count down" only shift register 22, where it is stored, 
and in parallel to one input of a comparator circuit 23. A second input 
for comparator circuit 23 is derived from the output of shift register 22 
so that comparator circuit 23 compares the digital signal output of 
analogue-to-digital converter 21 derived from one sample taken by sampling 
circuit 20 with that derived from the sample taken one second before. 
The output of comparator circuit 23 is connected via a positive threshold 
circuit to a suitable visual and/or aural alarm 25. 
For a further understanding of the operation of the arrangement illustrated 
in FIG. 4 reference is made to the above-noted U.S. Pat. No. 5,154,700. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.