Perfusion or enteral/parenteral feeding pump

This pump with a battery-powered drive device comprises a circular elastic diaphragm (1a) and two valves (2b, 10), which has a diameter of 3 to 25 mm and is subjected to a compressive prestress of between 1'104 and 4'104 Pa capable of enabling it to return to its rest position at a maximum working frequency of between 8 and 12 Hz with a travel of between 0.2 and 2 mm, corresponding to a maximum flow rate of 1.5 to 2.5 l/h. The drive device comprises an electromagnet (5) in direct contact with the diaphragm (1a), a standard power supply battery, the available energy of which is from 7000 to 10'000 J, means for analyzing the supply current for the electromagnet and for detecting, at each pumping drive cycle, a minimum defined intensity of the supply current corresponding to the closure of the gap of the electromagnet (5) and means for interrupting the supply current once this minimum intensity has been reached.

This invention relates to an enteral, parenteral or infusion feeding pump with a battery-powered drive mechanism.

The pumps currently found on the market for this type of use are only able to run for a very short time. In most cases they are peristaltic pumps whose overall efficiency is very low, usually not exceeding 2%, sometimes well below 1%. When such a pump is powered by a battery of around 26 000 J and works against a pressure of around 2×104Pa, it can only pump about 3 liters, which corresponds to 1.5 to 3 hours of operation depending on the flow rate. Recharging the battery from a mains adapter takes time and means that much of the time the pump is in use it is connected electrically to a wall socket. This is a serious brake on the spread of the use of pumps to replace drip and gravity infusion.

Peristaltic pumps have the intrinsic disadvantage of wasting a lot of energy due to friction severely reducing the amount of energy that can be used for the controlled delivery of the infusion liquid. Membrane pumps that have been used have large diameters and long strokes, and therefore cannot be used with a motor without mechanical speed reduction, which is itself a substantial source of loss of energy.

The object of the present invention is to substantially increase the amount of pumping that enteral, parenteral or infusion feeding pumps can pump on one battery charge by very significantly increasing the pump's efficiency, while ensuring optimal safety and a high degree of precision.

To this end, the present invention relates to an enteral, parenteral or infusion feeding pump as claimed in claim1.

Not only is such a pump able to pump several tens of times more on one battery charge, but simultaneously it reduces the amount of energy required for its operation, making it possible to run the driving electromagnet on standard commercially available rechargeable 1.2 V AA or LR6 batteries, depending on the standard used. This greatly simplifies and reduces the work and cost of maintenance of these pumps, since these standard batteries are readily available on the market, notably in supermarkets, and at low cost.

Furthermore, the small size both of these pumps and of their drive mechanism makes them easy to use and install. The pump's small size and low energy requirements make it ideal for ambulatory use.

FIG. 1shows a pump, especially a single-use pump, used in the medical field.

As can be seen, this single-use pump is essentially formed by an enclosure made up of three parts1,2,3, two parts1,3forming the wall of the pumping enclosure and one intermediate part2. The wall parts1,3comprise an intake duct6and a delivery duct7, respectively. Wall part1has a thin part forming an annular membrane1asurrounding a thick actuating part1b. The thin annular part1aacts as a pumping membrane while the thick central actuating part1btransmits to the annular membrane the force applied by a pusher in the form of the moving core4of an electromagnet5which drives the pump. The deformation of the membrane1amust of course remain within the limits of elastic deformability of the plastic of which wall part1is made.

The intermediate part2comprises a communication opening2afor allowing selective communication between the upstream and downstream compartments of the pump. This communication opening2ais in front of the thick central part1bof the membrane and a valve2bis situated in front of an opening2cfacing the inward end of the admission duct6formed in wall part1. The opening2ais at the end of a depression, while the thick central actuating part1bforms a projection that engages in the opening2a. The intermediate part2also comprises an annular projection2bextending towards wall part3, the role of which will be explained later.

Wall part3comprises a seat concentric with the delivery duct7, for a valve10which controls the communication opening2aof the intermediate part, which also acts as an anti-drip device, in order to prevent any liquid leaking out when the single-use is not inserted in the pump. This valve10is positioned between this communication opening2aand the delivery duct7of the pump. To ensure that liquid cannot drip from the pump under gravity, the valve10is held against the opening2awith a pressure of 4×104Pa±1×104Pa.

In the rest position, it closes the opening2aand is pressed against it as soon as the pressure difference between the upstream and downstream sides of the communication opening2ais less than 4×104Pa±1×104Pa. It moves away from this opening2aas soon as the pressure difference mentioned above is greater than 4×104Pa±1×104Pa.

Wall part3has an annular seat3afor the valve10. This valve10is retained on this seat3aby the annular projection2dof the intermediate part2. Wall part3also has a projection3badjacent to the control valve2bof the admission duct6to prevent this valve2bpressing against the inside face of the wall3. Given this arrangement, the face of the valve2bnot adjacent to the inward end of the admission duct6of the pump is exposed to the pressure of the compartment of the pump upstream of the communication opening2aof the intermediate part2. This valve2bis thus able to close the inward end of the intake duct6when the pump is in its delivery phase and open it in the suction phase.

In order to give the pump described above a long battery life, a number of conditions must be met at the same time, both as regards the pump itself and its drive mechanism.

First of all, as regards the pump itself, the membrane1amust have a relatively small diameter of between 3 and 25 mm, advantageously around 16 mm, in order to limit its actuating force, which is the product of the pressure P and the area S. Since the object is to move this membrane by means of an energy-saving electromagnet, it must also be small in size and the stroke of the membrane1a, driven by the pusher core4of the electromagnet, is between 0.2 and 2 mm, advantageously around 0.5 mm. Under these conditions the stroke of the membrane1aallows it to be driven directly by the piston core4of the electromagnet and avoids the need for mechanical speed reduction which would significantly reduce the overall efficiency of the pump.

The thickness of the elastic membrane1ais advantageously between 0.1 and 0.7 mm, preferably around 0.3 mm. These dimensions allow the same thermoplastic to be used for both the membrane1aand wall part1of the pump enclosure. This makes it possible to manufacture the part1and the membrane1ain one and the same injection molding operation. Suitable thermoplastics include PC, PVC, ABS, PP and PE in particular. The choice depends on the cost, precision and stability of the elastic characteristics after sterilization and storage for a maximum period of three years. PC is the material which best meets this specification.

The electromagnet5that forms the reusable driving part of the pump is a cylindrical-pot electromagnet running on 5 volts. It therefore requires a voltage booster between the 1.2 V battery and the 5 V supply of the electromagnet. Its magnetic circuit comprises two air gaps, an inner air gap15and an outer air gap16either side of the coil11housing. In order to keep friction as low as possible, the piston core4, made of hard metal, forming the moving part of the electromagnet5is guided in two lubricating ceramic bearings12,13. The piston core4is connected to the moving armature14of the electromagnet which has practically constant area of reluctance Sp. As can be seen inFIG. 1, in order to reduce the reluctances of the air gaps15,16and maximize the force which they generate, both of them almost completely cover the coil11housing, and as a result the cylindrical pot of the electromagnet5must be made in three parts5a,5b,5c.

The pot of the electromagnet5has a diameter of between 20 and 40 mm, typically 24 mm, and a height of between 15 and 25 mm, typically 20 mm. The fill factor of the housing of the electromagnet5pot by the coil11is around 80%. This coil11has an outside diameter of 18 to 24 mm, typically 21 mm, and a height of 9 to 14 mm, typically 11 mm. The area of reluctance Sp of the moving armature14is between 50 and 120 mm2, typically 70 mm2. The inner air gap15and outer air gap16are between 0.2 and 2 mm, preferably about 0.5 mm. In a preferred embodiment the inner air gap15is 0.5 mm and the outer air gap 0.6 mm.

Achieving a response time of the electromagnet suitable for the transfer times of the pumped liquid (typically 35 ms) giving maximum efficiency requires impedance matching between the source and the load.

To conserve power, the membrane1ais designed to return by itself sufficiently rapidly to its rest position. To this end, this membrane1amust be subjected, in the rest position, to a pressure preload of between 1×104and 4×104Pa, typically 2×104Pa.

Since the only job of the electromagnet is to push the membrane1a, the latter returning of its own accord to its rest position, the drive mechanism comprises means for analyzing the curve of the current supplied to the coil11. This curve is illustrated inFIG. 2and shows that the current passes first through a maximum and then through a minimum, corresponding to the air gaps15,16closing. The current then rises again to reach the value I=U/R where R is the resistance of the coil11.

To conserve energy, the power supply system of the electromagnet5comprises means for analyzing the curve shown inFIG. 2in order to detect the moment at which the curve of the current I passes through a minimum and to then interrupt, in every pumping cycle, the power supply to the electromagnet5. The same analysis can be used to detect a blockage upstream of the duct, which is distinguished by the fact that the membrane fails to return to its rest position and the piston is then lifted back up by a very weak spring17which is only used to lift the piston (the spring17must overcome the forces of friction from the bearings and the weight of the piston, which comes to a total force of about 0.08 N), or downstream of the duct, as illustrated by curves A and B, respectively inFIG. 4, and thus to trigger an alarm.

In the example shown inFIG. 3, the signal is processed digitally but could also be processed by analog means.

The diagram inFIG. 3illustrates the various steps in processing the signal with the changes to the signal as it is processed at each step. As will be seen, by the end of the process the system has detected the presence or absence of falling then rising edges at the end of the normal duration t of travel of the membrane1acorresponding to the half-period of the pumping cycle. If these edges are detected, the pump is working properly and the power supply is interrupted until the end of the pumping cycle, as described earlier. This detection mode thus ensures that the electromagnet has reached the end of its travel, and thus that each volume pumped is precise.

In this example, assuming that the pump is running at a maximum frequency of 10 Hz, if at the end of 50 ms no edge has been detected, this means that the membrane1acould not be moved because of a downstream blockage (curve B inFIG. 4) and the detection device triggers the downstream blockage alarm. If the detection device detects a falling edge in an interval t<0.5 ms, this means that there is an upstream blockage (curve A inFIG. 4) and the detection device triggers the upstream blockage alarm.

In the example described above, the volume pumped in each pumping cycle is 0.058 mL and the maximum pumping frequency is between 8 and 12 Hz, typically 10 Hz. This corresponds to maximum flow rates of between 1.5 and 2.5 L/h, typically 2 liters with an accuracy of around 5%.

With a rechargeable battery holding 7000 to 10 000 J, typically 8600 J, against a pressure of 2×104Pa, the pump of the present invention can deliver 10 to 120 liters, typically 100 liters, on one battery charge. Under the same conditions a peristaltic pump with a rechargeable battery holding 26 000 J can pump 3 liters on one battery charge. This shows the enormous advance achieved by the present invention in the field of enteral, parenteral and infusion feeding pumps.

A comparison of the efficiencies of peristaltic pumps used for feeding, particularly with the pump of the present invention, has shown that the efficiencies are multiplied by a factor of practically 100 in the case of the present invention.