WO1996037245A1

WO1996037245A1 - Feedback-controlled liquid delivery device

Info

Publication number: WO1996037245A1
Application number: PCT/IE1996/000029
Authority: WO
Inventors: Joseph Gross
Original assignee: Elan Medical Technologies Limited
Priority date: 1995-05-22
Filing date: 1996-05-13
Publication date: 1996-11-28
Also published as: IE950366A1; ZA963994B; AU5701596A; TW323957B

Abstract

A liquid delivery device (10) for delivering a nutritive liquid (13) to a subject comprises a reservoir (12) for the nutritive liquid connected, in use, to a gas generator (11) for supplying a gas to the reservoir (12) to drive the liquid (13) therefrom. The generator (11) comprises first and second compartments (16, 17), each containing a reactant (19, 20), the compartments (16, 17) being interconnected in a manner which permits the flow, in use, of a reactant (19) from the first compartment (16) to contact the other reactant (20), the reactants in the form of citric acid solution (19) and powdered sodium bicarbonate (20) reacting on contact to generate a gas, wherein an increase in gas pressure within the generator (11) reduces the rate of flow reactant (19) from the first compartment (16), thereby controlling the rate of gas generation by feedback and in turn the rate of liquid delivery. Delivery of liquid from the device (10) can be stopped by clamping a tube (14) leading from the reservoir (12), and the resultant increase in pressure in the reservoir (12) and in the gas generator (11) cuts off the flow of reactant (19) from the first compartment (16) and thereby stops the reaction. Only when the tube (14) is unclamped and there is a resultant decrease in pressure within the reservoir (12) does the flow of reactant recommence. Thus, delivery can be interrupted for periods of 20-30 hours and subsequently recommenced with full effectiveness.

Description

Feedback-controlled liquid delivery device

Technical Field

This invention relates to liquid delivery devices for delivering a liquid to a subject of the type employing gas generators. In particular, it relates to devices in which a gas is generated by means of an effervescent couple.

Background Art

Devices in which the delivery of liquid from a reservoir is effected by the generation of a gas to pressurise the reservoir have a number of advantages over gravity-controlled liquid delivery systems.

Gravity-controlled systems for the delivery of a nutritive fluid or an intravenous liquid, such as a medicament or a saline drip, deliver the liquid at a rate which is controlled by the hydrostatic pressure generated under the force of gravity between the reservoir and the point of administration. Thus, such drips are generally placed on a stand at a point approximately 1 meter or so above the point of administration (e.g. a needle in the arm of a subject). They are therefore more suitable for immobile patients, since an ambulatory patient must carry the stand around, and this is clearly impossible if the patient is frail or unsteady. Furthermore, if a higher rate of delivery is required, it is necessary to suspend the reservoir 2 or 3 metres above the point of administration. This is clearly impractical. Devices employing gas generators are gravity independent and so can be easily carried by a patient without the use of a stand, and are effective to deliver a liquid at any suitable rate.

A liquid delivery device known as the SmartDose Infusion System (SmartDose is a trade mark) is marketed by River Medical Inc., for the intravenous delivery of liquids. It comprises a container which houses a reservoir for the intravenous fluid, the reservoir being separated from a gas generation chamber by a flexible membrane. The gas generation chamber is supplied with a gas generated by the reaction of the components of an effervescent couple.

Before use, the components of the effervescent couple are separated from one another, but are mixed together upon the depression of a start button. Carbon dioxide is generated when the components are mixed together and the pressure within the gas generation chamber increases, thereby forcing the intravenous fluid from the reservoir by means of an outlet (to which there is typically attached a length of flexible tubing leading to a needle for intravenous delivery). The pressure within the gas generation chamber builds up quickly to the desired level, at which stage a pressure release valve opens to vent the gas and prevent the pressure (and hence the delivery rate) from rising above the desired level. When gas is vented, the pressure drops back down to the desired level and the valve closes, reopening again when the gas pressure has built up above the desired level. If for any reason the fluid flow is stopped (e.g. by an accidental tube blockage or a deliberate clamping of the tube when the desired dose has been delivered), the pressure within the gas generation chamber is maintained at the desired level by the venting of the pressure release valve.

A problem associated with this type of device is that gas generation cannot be stopped once the start button has been activated. The chemical reaction proceeds to completion whether or not it is desired to deliver all of the liquid within the reservoir in a single infusion. The device cannot be used if one wishes to deliver only a portion of the liquid, cease delivery, wait for a few hours, and then recommence delivery, because by this time, the effervescent reaction will have been completed and the desired pressure will not be available for the delivery of the remainder of the liquid. The effective lifetime of the commercially available device is of the order of 1 hour. Although it would be possible to manufacture a device having a longer lifetime, in order to allow delivery to be interrupted for extended periods, this would be highly inefficient as the system would be generating and venting gas continually throughout the period of interruption.

Even when the device is delivering constantly, the feedback system employed requires gas to be generated at a far higher rate than is actually required, because the desired overpressure required to compress the reservoir is only maintained by the continual venting of gas from the system.

The invention seeks to provide an improved controlled-rate gas generator which can be used for extended periods of time and in which the generation of gas can be interrupted for extended periods of time without the premature completion of the chemical reaction. It is a further object of the invention to provide a gas generator employing an effervescent couple, in which given quantities of the components of the couple will allow an extended period of gas generation when compared with prior art devices.

Disclosure of Invention

In accordance with the invention, there is provided a liquid delivery device for delivering a liquid to a subject, comprising a reservoir for the liquid connected, in use, to a gas generator for supplying a gas to the reservoir to drive the liquid therefrom, the generator comprising first and second compartments, each containing a reactant, said compartments being interconnected in a manner which permits the flow, in use, of a reactant from the first compartment to contact the other reactant, the reactpnts reacting on contact to generate a gas, wherein an increase in gas pressure within the generator reduces the rate of flow of reactant from the first compartment, thereby controlling the rate of gas generation by feedback, and in turn the rate of liquid delivery.

It will be appreciated that the use of feedback control in accordance with the present invention confers a number of distinct advantages over prior art devices. Primarily, there is a significant increase in efficiency with the present invention, since delivery can be stopped (e.g. by clamping a tube leading from the reservoir), and the resultant increase in pressure in the reservoir and in the gas generator cuts off the flow of reactant from the first compartment and thereby stops the reaction. Only when the tube is undamped and there is a resultant decrease in pressure within the reservoir (and hence the gas generator) does the flow of reactant recommence. In this way, it has been found that delivery can be interrupted for periods of 20-30 hours and subsequently recommenced with full effectiveness. This would clearly be impossible with the prior art device described above.

An extra degree of safety is added because the feedback pressure control (and hence the delivery rate control) does not depend on mechanical parts such as valves or vents which may be subject to failure or to blockage.

Generally, the compartments are interconnected via a conduit or an aperture.

Suitably, the compartments are separated by a barrier before use and the aperture or conduit is created in use.

Preferably, the first compartment is bounded by a piercible membrane and an interconnection between the first and second compartments is formed by piercing the membrane prior to delivery.

By employing a suitably sized needle, one obtains a suitable hole the size of which determines the rate of flow of reactant therethrough.

Alternatively, the first and second compartments are interconnected by a hollow glass tube extending from the first compartment to the second compartment, one end of the tube being initially closed, which end is broken away from the tube to establish the interconnection prior to delivery. It will be recognised that this arrangement also provides a consistent interconnection through which the rate of flow of reactant can be predictably determined upon manufacture.

Generally, the reactant flows from the first compartment under an applied pressure.

This pressure can be provided by a spring-loaded piston, a stretched membrane, a spring-loaded clip, by gravity, or in any other suitable manner.

In one embodiment of the invention, the first compartment has a boundary which is displaceable under pressure to expand the first compartment, and the rate of flow of reactant from the first compartment is controlled by a valve operatively connected to the displaceable boundary to restrict the rate of flow of reactant therethrough as the boundary is displaced under increasing pressure, the gas pressures in the first and second compartments being equalised by a conduit therebetween.

Suitably, in this embodiment, the reactant flows from the first compartment to the second compartment under the pressure of gravity.

Preferably, the reactant in the first compartment is a liquid.

The term "liquid" as used herein includes liquids, solutions, suspensions, flowable gels and similar materials. In suitable circumstances, materials such as flowable powders may be used instead of a liquid.

The choice of reactants for use in accordance with the invention is very wide. Any substances which can be mixed together to produce a gas in a controlled manner can be used. Suitably, the reactants comprise an acid and a base which react to produce a gas. According to a preferred embodiment, the acid is citric acid and the base is sodium bicarbonate.

The invention is clearly not limited to this particular effervescent couple and the skilled person will be aware of a wide range of substances which can be mixed to produce a gas. The acid/base couple can be initially be separated from one another, with one reactant in the first compartment and the other reactant in the second compartment, or they can be initially mixed in solid form, for example, as a powder or tablet mixture and the reactant in the first compartment can be water. When water is added to such a solid mixture, the effervescent reaction is initiated. However, this arrangement may not be appropriate in the case of certain components. For example, where citric acid and sodium bicarbonate are used as a solid mixture, water is produced as a by¬ product of this reaction. Accordingly, if some water is added to a powder or tablet mixture of citric acid and sodium bicarbonate, the reaction is not easily controllable due to the further reaction of components in the presence of the water produced by the initial reaction.

In a preferred embodiment, the reactant in the first compartment is a solution of citric acid and the reactant in the second compartment is sodium bicarbonate in powder or tablet form.

According to a first embodiment of the invention, the reservoir is a rigid bottle having an outlet through which liquid is delivered as gas is fed into the bottle.

Such a rigid bottle may be a bottle of the type conventionally used for the delivery of an intravenous liquid to a subject, or it may be particularly adapted for use with the present invention.

According to a second preferred embodiment, the device is in the form of a container having a flexible internal wall which defines the reservoir on one side thereof and defines a chamber into which gas is supplied on the other side thereof, such that when gas is supplied to the chamber, the chamber expands, the reservoir is compressed by the movement of the flexible wall, and liquid is delivered from the reservoir via an outlet.

The device can be adapted for the delivery of a nutritive liquid or for the delivery of a medicament. Delivery can typically be oral, nasal or intravenous.

Suitably, the liquid is delivered from the reservoir via an outlet which leads to a restrictor which limits the rate of flow of liquid therethrough.

Suitably, the gas generator is removably mounted on the reservoir for the liquid. Thus, the reservoir and the gas generator are separately disposable and replaceable independently of one another. Furthermore, this allows a separately supplied gas generator to be used in conjunction with a conventional reservoir.

Thus, in a further aspect of the invention, there is provided a gas generator adapted for use as part of a device according to the invention.

Brief Description of Drawings

The invention will be further illustrated by the following descriptions of embodiments thereof, as illustrated in the following drawings, in which:

Fig. 1 is a schematic representation of the components of a controlled-rate liquid delivery device according to the invention;

Fig. 2 is an elevation of a liquid delivery device according to the invention, shown partially in section;

Fig. 3 is an elevation of a variation on the device of Fig. 2; Fig. 4 is a sectional elevation illustrating a detail of the device of Fig. 3;

Figs. 5-7 are schematic representations of restrictors for use with the invention;

Fig. 8 is a sectional side elevation of another liquid delivery device according to the invention, before use;

Fig. 9 is a sectional side elevation of the device of Fig. 8, in use;

Fig. 10 is a front elevation of the device of Fig. 8;

Fig. 11 is a perspective view of a nutritive liquid delivery device according to the invention;

Fig. 12 is a schematic representation of a further embodiment of a liquid delivery device according to the invention; and

Fig. 13 is a side elevation of yet another embodiment of a liquid delivery device according to the invention.

Modes for Carrying Out the Invention

In Fig. 1, there is illustrated, generally at 10, a schematic representation of a liquid delivery device. The device 10 comprises a gas generator, indicated generally at 11, and a container 12 for a nutritive liquid 13 which is to be pumped via a tube 14 in the direction of arrow 15 for intranasal delivery to a subject.

Gas generator 11 comprises an upper compartment 16 and a lower compartment 17 connected by a narrow tube 18.

Upper compartment 16 contains a citric acid solution 19 and the lower compartment 17 contains powdered sodium bicarbonate 20. These substances, when mixed, generate carbon dioxide gas. A piston 21 in compartment 16 is compressed by a spring 22 to force the citric acid solution 19 to flow through tube 18 onto sodium bicarbonate 20. Tube 18 is sufficiently narrow to prevent the citric acid solution 19 from flowing therethrough under gravity, i.e. when a positive pressure is not effected by piston 21. The rate at which citric acid solution 19 flows through tube 18 is dependent, in part, on the dimensions of tube 18 and, in part, on the force exerted by spring 22 on piston 21 and the corresponding hydrostatic pressure of citric acid solution 19. The rate at which citric acid solution 19 is added to sodium bicarbonate 20 determines the rate at which gas is generated by the effervescent reaction. In the illustrated embodiment, the citric acid 19 flows dripwise from tube 18 under normal conditions.

As gas is generated, pressure builds up in the space 23 above bicarbonate 20 in lower compartment 17, and this pressure is partially relieved by equalisation with the pressure within container 12 via a tube 24 through which gas flows in the direction of arrow 25 to a space 26 at the top of container 12. The increased pressure within container 12 causes nutritive liquid 13 to flow out of tube 14.

When the effervescent reaction is underway and the pressure increases within space 23 and space 26, the gas pressure in space 23 tends to counteract the hydrostatic spring-generated pressure which drives solution 19 through tube 18. If the pressure in space 23 becomes sufficiently high, the flow of solution through tube 18 will stop and the rate of gas generation will decrease accordingly and will eventually stop.

Thus, the pressure is controlled by a feedback mechanism whereby, in steady state, the reaction only proceeds at a sufficient rate to generate enough gas at constant pressure to replace the volume of liquid leaving container 12 via tube 14.

If the flow of liquid through tube 14 is cut off (for example, by clamping tube 14), the effervescent reaction will soon stop because the mixing of the components of the effervescent couple 19,20 is cut off by the increased pressure resulting from the effervescent reaction itself. If the flow of liquid through tube 14 is subsequently resumed, the pressure within container 12 drops, as does the pressure in space 23. This allows citric acid solution 19 to resume dropping from tube 18, causing gas generation to recommence at the necessary rate.

Because the arrangement in Fig. 1 gives rise to constant gas pressures in space 23 and in space 26, the rate of flow of liquid via tube 14 under steady state conditions is also constant. The driving pressure for the system is ultimately determined by the force exerted by spring 22 on piston 21. By choosing appropriate spring parameters, this force can be made constant throughout the entire travel of piston 21 as compartment 16 is emptied. A low spring force gives rise to a lower hydrostatic pressure in upper compartment 16, which means that liquid flow can be cut off through tube 18 by a relatively small increase in gas pressure in space 23. Correspondingly, if spring 22 exerts a higher force, a high pressure will exist in compartment 16 and a corresponding high pressure will be required in space 23 to cut off the flow of liquid through tube 18.

In Figs. 2 and 3, two working embodiments of the device illustrated schematically in Fig. 1 are shown in partially sectional elevation. Common features which can be identified from Fig. 1 are shown by the reference numerals used in Fig. 1. Thus, it can be seen that the devices 10 of Figs. 2 and 3 each comprise a container 12 for a liquid 13 to be delivered via a tube 14. Liquid 13 is pumped via a tube 14. Liquid 13 is a nutritive liquid for nasal administration in a hospital situation.

The device 10 is illustrated before use, with container 12 almost full of liquid 13. The embodiments of Figs. 2 and 3 differ only in the details of tube 24 which connects space 23 in gas generator 11 with space 26 at the top of container 12. In Fig. 2, tube 24 extends up above the initial height of liquid 13, thereby directly delivering generated gas to space 26; in Fig. 3, tube 24 only extends a small way into container 12, so that gas travelling from space 23 to space 26 bubbles up through liquid 13. In Fig. 3, tube 24 is provided with a hydrophobic filter 27 which allows gas to travel up from gas generator 11 into container 12 but prevents liquid 13 from travelling back through tube 24 and flooding gas generator 11.

Referring additionally to Fig. 4, in which the base of device 10

(as illustrated in Fig. 3) is shown in greater detail, it can be seen that gas generator 11 comprises a housing 28 having upper and lower compartments 16,17. Compartment 16 contains citric acid solution 19 and is bounded below by a membrane 29 and above by a piston 21 pressurised by a loaded spring 22. Compartment 17 is provided with sodium bicarbonate powder 20. In use, a plunger 31 having a needle point at the end thereof is depressed to rupture membrane 29 and create a small aperture through which citric acid solution 19 drips under the pressure of spring 22. When citric acid solution 19 contacts sodium bicarbonate solution 20, carbon dioxide is generated within space 23, and the pressure in space 23 increases. The gas escapes via filter 27 and tube 24 to bubble through liquid 13 which is held within container 12 (shown in dotted outline). As previously described, this causes the pressure in container 12 to increase, thereby forcing liquid 13 out of tube 14. The rate of delivery of liquid increases to a steady state and the rate of gas generation adjusts to provide a steady state pressure in space 23.

An additional feature illustrated in Fig. 4 is a safety valve comprising a floating ball 32 trapped within space 33. When liquid 13 is present within container 12, ball 32 floats within space 33 allowing liquid to flow into tube 14 via aperture 34. As container 12 empties, however, ball 32 drops, thereby cutting off aperture 34 and preventing air or gas from being pumped to the subject via t e 14.

Further additional features which are present in the devices of Figs. 1-4 are a particle filter 35 and a restrictor 36 (Fig.l). A particle filter 35 is fitted at the mouth of tube 14 adjacent to the valve 32,33. Such a filter is desirable where nutritive liquid 13 is liable to contain small particles which might otherwise clog tube 14. A restrictor 36 can be used to control the rate of fluid delivery by providing resistance to the flow of liquid via tube 14. Typically, restrictor 36 will be positioned along the length of tube 14, although it may alternatively be provided at the mouth of tube 14, adjacent to filter 35. The restrictor may have a number of different configurations.

Referring to Figs. 5-7, three examples of restrictor configuration are illustrated schematically. Fig. 5 shows the first configuration, which is a narrow aperture 40 along the length of a tube 41. Fig. 6 shows the second configuration, which is a narrowed section of tubing 42. Fig. 7 shows a third configuration, which is a tube 43 having internal baffles 44. The configurations of Figs. 5 and 6 are roughly equivalent in that they provide a constriction 40,42 which slows the flow of liquid therethrough. Fig. 7 is slightly different in that the resistance to flow is caused by the baffles 44 which force liquid to follow a convoluted path.

Referring now to Figs. 8-10, an alternative embodiment of a liquid delivery device according to the invention is illustrated, generally at 50. Flexible bag 51 has an internal impermeable flexible membrane 52 defining a reservoir 53 on one side thereof and a chamber 54 on the other side thereof. The bag 51 has a pair of external compartments 55,56 one of which 55 contains a citric acid solution 57 and the other of which contains powdered sodium bicarbonate 58.

The compartments 55,56 are interconnected by means of a hollow glass tube 59 which is initially closed at one end 60 thereof, as illustrated in Fig. 8.

As can be seen from Fig. 8, the reservoir 53 is initially full and chamber 54 is almost totally empty. Compartment 55 is in the form of an elastically stretched membrane which pressurises solution 57. In use, the top 60 is broken off tube 59, thereby unblocking the hollow section and allowing liquid to drip therethrough under the pressure exerted by the stretched membrane forming compartment 55. When the citric acid solution 57 contacts sodium bicarbonate powder 58, carbon dioxide gas is generated as a result of the effervescent reaction.

The carbon dioxide gas escapes from compartment 56 through wall 61 which is provided with microscopic holes. Gas begins to fill up chamber 54 thereby exerting a pressure, via membrane 52, onto reservoir 53. A saline solution 62 is held within reservoir 53 and is driven under pressure from reservoir 53 out of bag 51 via outlet tube 63.

As explained above in relation to the device of Figs. 1-4, an increase in pressure within chamber 54 causes a corresponding increase within compartment 56. This increased gas pressure in compartment 56 counteracts the driving pressure exerted by the membrane forming compartment 55. Thus, the flow of liquid through tube 59 can be slowed and stopped by a sufficient increase in pressure in chamber 54. In this way, a feedback effect acts to control the rate of mixing of the reactants. If outlet tube 63 is clamped, the reaction will stop.

The driving pressure exerted by the flexible membrane forming compartment 55 can be replaced by a spring-loaded clip which can be used to compress compartment 55.

Fig. 11 shows a perspective view of a preferred embodiment of a nutrition delivery device similar to the type illustrated in Figs. 1-4. The device, indicated generally at 70, comprises a reservoir container 71 for a nutritive liquid. Container 71 is formed of translucent plastic allowing the level of liquid held therein to be visually checked. A gas generator is provided in the base 72. A start button 73 is provided on the external surface of the base. This button actuates a mechanism to pierce a membrane in a citric acid compartment (not shown) allowing citric acid solution to drip onto a sodium bicarbonate tablet thereby generating a gas. The operation of the device can be verified by a transparent window 74 which allows a visual check that citric acid solution 75 is, in fact, dripping at a controlled rate. The reservoir within the reservoir container 71 communicates with an outlet 76 and a delivery tube 77 can be plugged into this outlet. Delivery tube 77 leads to a restrictor (not shown) which provides a control on the rate of liquid delivery.

The device 70 can be placed on a bedside table or can be suspended from a hook 78.

In Fig. 12, there is illustrated, generally at 80, an alternative embodiment of a liquid delivery device, similar in many respects to that illustrated in Fig. 1. In this further embodiment, the device 80 is distinguished by the gas generator, indicated generally at 81.

Generator 81 comprises first and second compartments 82,83, separated by a boundary wall 84 having an aperture 85 which allows a solution of citric acid 86 to drip onto a mass of powdered sodium bicarbonate 87, as previously described. The thus generated gas is fed to a reservoir 88 by means of a connecting tube 89.

A conduit 90 leading from connecting tube 89 to first compartment 82 ensures that the gas pressures in the first and second compartments 82,83 are equal at all times. Thus, an increase in gas pressure within the second compartment 83 gives rise to a corresponding increase in gas pressure within first compartment 82.

Aperture 85 defines a valve seat which can be sealed by a valve member 91. In Fig. 12, the valve defined by aperture 85 and valve member 91 is shown in an open position allowing citric acid solution 86 to drip therethrough. A rod 92 connects valve member 91 to roof 93 of first compartment 82. Roof 93 comprises an elastomeric section which imparts a degree of flexibility such that an increase in gas pressure within first compartment 82 causes a section of roof 93 to be expanded upwards. When this occurs, connecting rod 92 moves valve member 91 upwards to shut off the flow of liquid through aperture 85. Thus, it will be appreciated that as gas is generated by the reaction of citric acid solution 86 and sodium bicarbonate 87, the pressure within the gas generator 81 rises (i.e both in first compartment 82 and second compartment 83). The increasing pressure causes a section of roof 93 to be expanded upwards and causes the flow of liquid to be restricted by the closing of the valve defined by aperture 85 and member 91. This in turn leads to a decrease in the rate of gas generation and accordingly gives rise to a feedback effect of the type previously discussed.

Fig. 13 is a schematic illustration of a further aspect of the invention, showing a gas generator which can be made and sold separately from a liquid reservoir. A flexible bag 100 is divided by an impermeable membrane 101 into a gas chamber 102 and a liquid reservoir 103. An expansion of gas chamber 102 causes the contraction of reservoir 103 and the consequent ejection of the liquid contained therein through an outlet 104. Gas chamber 102 is provided with an inlet 105 through which pressurised gas can be fed in order to effect delivery of liquid through outlet 104.

A delivery unit, indicated generally at 106, comprises an outlet tube 107 adapted to be attached to outlet 104, and a gas generator 108, adapted to be attached to inlet 105. Gas generator 108 is the feedback type of gas generator according to the invention, as previously described. Accordingly, gas generator 108 ensures that the rate of delivery of liquid through delivery tube 107 remains constant.

Claims

Claims :-

1. A liquid delivery device for delivering a liquid to a subject, comprising a reservoir for the liquid connected, in use, to a gas generator for supplying a gas to the reservoir to drive the liquid therefrom, the generator comprising first and second compartments, each containing a reactant, said compartments being interconnected in a manner which permits the flow, in use, of a reactant from the first compartment to contact the other reactant, the reactants reacting on contact to generate a gas, wherein an increase in gas pressure within the generator reduces the rate of flow of reactant from the first compartment, thereby controlling the rate of gas generation by feedback, and in turn the rate of liquid delivery.

2. A device according to Claim 1, wherein the compartments are interconnected via a conduit or an aperture.

3. A device according to Claim 2, wherein the compartments are separated by a barrier before use and the aperture or conduit is created in use.

4. A device according to Claim 2 or 3, wherein the first compartment is bounded by a piercible membrane and an interconnection between the first and second compartments is formed by piercing the membrane prior to delivery.

5. A device according to Claim 2 or 3, wherein the first and second compartments are interconnected by a hollow glass tube extending from the first compartment to the second compartment, one end of the tube being initially closed, which end is broken away from the tube to establish the interconnection prior to delivery.

6. A device according to any preceding claim, wherein the reactant flows from the first compartment under an applied pressure.

7. A device according to Claim 6, wherein the applied pressure is provided by a spring-loaded piston.

8. A device according to Claim 6, wherein the applied pressure is provided by a stretched membrane.

9. A device according to Claim 6, wherein the applied pressure is provided by a spring-loaded clip.

10. A device according to Claim 6, wherein the applied pressure is provided by gravity.

11. A device according to Claim 1, wherein the first compartment has a boundary which is displaceable under pressure to expand the first compartment, and wherein the rate of flow of reactant from the first compartment is controlled by a valve operatively connected to the displaceable boundary to restrict the rate of flow of reactant therethrough as the boundary is displaced under increasing pressure, the gas pressures in the first and second compartment being equalised by a conduit therebetween.

12. A device according to Claim 11, wherein the reactant flows from the first compartment to the second compartment under the pressure of gravity.

13. A device according to any preceding claim, wherein the reactant in the first compartment is a liquid.

14. A device according to any preceding claim, wherein the reactants comprise an acid and a base which react to produce a gas.

15. A device according to Claim 14, wherein the acid is citric acid and the base is sodium bicarbonate.

16. A device according to Claim 15, wherein the reactant in the first compartment is a solution of citric acid and the reactant in the second compartment is sodium bicarbonate in powder or tablet form.

17. A device according to any preceding claim, wherein the reservoir is a rigid bottle having an outlet through which liquid is delivered when the gas is fed into the bottle.

18. A device according to any one of Claims 1-16, when in the form of a container having a flexible internal wall which defines the reservoir on one side thereof and defines a chamber into which gas is supplied on the other side thereof, such that when gas is supplied to the chamber, the chamber expands, the reservoir is compressed by the movement of the flexible wall, and liquid is delivered from the reservoir via an outlet.

19. A device according to any preceding claim, when adapted for the delivery of a nutritive liquid.

20. A device according to any preceding claim, when adapted for the delivery of a medicament.

21. A device according to any preceding claim, wherein the liquid is delivered from the reservoir via an outlet which leads to a restrictor which limits the rate of flow of liquid therethrough.

22. A device according to any preceding claim, wherein the gas generator is removably mounted on the reservoir for the liquid.

23. A gas generator adapted for use as part of a device according to any one of Claims 1-22.

24. A liquid delivery device according to Claim 1, substantially as hereinbefore defined, with reference to and as illustrated in Figs. 1-4, 8-10, 11, 12 or 13 of the drawings.

25. A gas generator according to Claim 21, substantially as hereinbefore defined, with reference to and as illustrated in Figs. 1-4, 8-10, 11, 12 or 13 of the drawings.