A system for delivery of supplemental oxygen

Abstract

An oxygen delivery system (70, 150) includes a mask (72) that is configured to seal around a user's mouth and nose, the mask (72) including a demand valve (20) and an air intake valve (74); a reservoir (30); and a restrictor (28, 156); located upstream of the reservoir (30) in a supply line (76, 152) that provides fluid communication between the demand valve (20) and an end that is connectable to a source of pressurised oxygen. The air intake valve (74) includes a piloting chamber (86) that is in fluid communication with the reservoir (30), the air intake valve (74) being opened and closed in accordance with a pressure in the piloting chamber (86).

Description

[0001] A SYSTEM FOR DELIVERY OF SUPPLEMENTAL OXYGEN

[0002] This invention relates to the field of breathing apparatus and, in particular, to a system to deliver a breathable gas in which ambient air is supplemented with additional oxygen.

[0003] It is known to use a demand valve that opens with the inhalation pressure of a user’s breathing pattern such that the supply of a breathable gas matches the user’s demand. Medical applications include the supply of 100% oxygen gas for resuscitation or for treatment for smoke inhalation. Breathing apparatus regulated by a demand valve, and I or gas regulator, is also commonly used in diving or escape equipment.

[0004] Whilst a demand valve supplying 100% oxygen has its applications, there are many situations in which it is only necessary to supply oxygen in quantities that supplement that which is naturally present in the atmosphere. This may be in the medical field, for example to assist patients with reduced lung function, or in a hypoxic environment such as at altitude. In these situations, it is a mix of oxygen and ambient air that is supplied to the user. It is important in such supplemental oxygen delivery systems to minimise wastage of oxygen. In addition to increasing costs, inefficient use of oxygen limits the portability of a delivery system: either a larger oxygen storage cylinder is required or its more frequent replacement. This may severely impact a patient’s mobility or add further challenges to activities such as high- altitude climbing or parachuting.

[0005] Prior art supplemental oxygen systems use a number of different methods to provide the required mix of gases, each of which will generally address the matter of efficient supply of oxygen in some way. For example, a diluter demand system provides a mix of ambient air and oxygen in a volume that matches a user’s demand. In an approach that is aimed at the parachuting market, the proportion in which the gases are supplied is changed with altitude. This allows the proportion of ambient air in the mix to increase as the parachutist falls, taking advantage of the increase in partial pressure of oxygen in the Earth’s atmosphere at lower altitudes.

[0006] Other systems aim to deliver the additional oxygen in a short period, of around half a second, at the start of inhalation. After this, the oxygen flow is reduced or stopped and subsequent inhalation is primarily of ambient air. It is only gas inhaled at the start of a breath that goes deep into the alveoli and is absorbed by the body. Gas inhaled later in the cycle tends to fill the airways and is then exhaled. It therefore follows that the ambient air that is inhaled is only minimally absorbed and so its sub-optimal oxygen content has little impact. In one arrangement that conserves oxygen in this way, a constant flow of oxygen is supplied to a user’s mask via an inflatable reservoir that provides temporary gas storage. During exhalation, the oxygen supplied fills the reservoir. During inhalation, the user first uses the oxygen stored in the reservoir and then, once this is exhausted, breathes a mixture of ambient air and oxygen from the constant-flow system. In a second arrangement, a pulse delivery system delivers a pulse of oxygen at the start of the breath, with the user supplied with ambient air for the remainder of the inhalation cycle.

[0007] As each system has its own advantages and disadvantages, hybrid approaches in which two or more of the above systems are combined are also known in the prior art. For example, WO 2016 / 185201 describes an oxygen system specifically for use in parachuting in which 100% oxygen is supplied from a demand valve at higher altitudes but, during decent, the system switches automatically to a pulsed delivery system.

[0008] Although the above systems operate some form of oxygen conservation, there remain inefficiencies in each of the approaches adopted and oxygen is wasted to a greater or lesser extent. Moreover, some of the prior art supplemental oxygen systems are not sufficiently flexible in their design to be readily adapted to harsh environments or to the parachute market, which has to satisfy additional requirements. In particular, aeronautical doctors recommend that above 25,000 feet (7,600 m) the breathing gas is 100% oxygen. A pulse delivery system is simply unable to deliver 100% oxygen for the entire breath and so cannot alone meet the needs of a high-altitude parachutist.

[0009] The system developed and described in WO 2016 / 185201 , referenced above, takes a hybrid approach and a pulse delivery system is only used to supply oxygen while the parachutist is at lower altitudes. Although this offers an improvement to efficient delivery of oxygen in parachute systems, it was found that additional problems arise when operating in a harsh environment. A pulsed system requires either electronic or intricate pneumatic circuitry to facilitate the release of gas in pulses and also to set the inter-pulse delay. Cold temperatures however tend to harden elastomeric components within pneumatic circuitry and to prevent the proper functioning of batteries in an electronic circuit. At best, this reduces the performance of a pulsed system and, at worst, may lead to its failure.

[0010] There is accordingly a perceived need for an alternative design of oxygen delivery system that is capable of delivering supplemental oxygen with increased efficiency than is known in the prior art. There is moreover an additional need for an oxygen delivery system that offers the flexibility to be adapted for specific operational environments, without the disadvantages encountered in the hybrid systems of the prior art.

[0011] According to a first aspect of the present invention there is provided an oxygen delivery system including a mask that is configured to seal around a user’s mouth and nose, the mask including a demand valve and an air intake valve; a reservoir; and a restrictor; located upstream of the reservoir in a supply line that provides fluid communication between the demand valve and an end that is connectable to a source of pressurised oxygen, characterised in that the air intake valve includes a piloting chamber that is in fluid communication with the reservoir, the air intake valve being opened and closed in accordance with a pressure in the piloting chamber.

[0012] In this aspect, the present invention is designed to operate with pressurised oxygen to control the breathing gas supplied to the mask at various points in the respiration cycle of its wearer. Oxygen is supplied at a constant rate through the restrictor, the rate being governed by supply pressure and restriction size but is generally insufficient to satisfy the inhalation demand of the user. At the start of inhalation, the demand valve is opened and oxygen from the reservoir is directed into the mask. Once the reservoir is depleted, oxygen flowing through the restrictor cannot match the user’s demand and the air intake valve opens and draws in ambient air. During the exhalation phase, the oxygen flowing through the restrictor is directed to the reservoir, which fills ready to supply oxygen at the start of the next inhalation cycle. The reservoir continues to fill until it reaches supply pressure at which point back pressure in the system shuts off the supply of oxygen. In other words, this present invention supplies 100% oxygen only at the start of the inhalation cycle, where it is most effectively used by the lungs. Later in the cycle, the inhalation gas is primarily ambient air. Oxygen from the source has a restricted flow that, during inhalation, is directed into the mask and, during exhalation, is either directed into the reservoir or is stopped. This therefore offers a degree of oxygen conservation that improves on that provided by the prior art constant flow system with reservoir. In this prior art system, back pressure is not allowed to build and so the restrictor flow is never closed off. This results in a degree of wastage once the reservoir is filled. Moreover, prior art constant flow systems operate at ambient pressure only and the ability to operate at higher pressures, provided by this present invention, permits a smaller reservoir to be used, which makes the system more portable and convenient for a user. In particular, the reservoir may be effectively hidden within the connecting hose(s) of the oxygen delivery system.

[0013] The air intake valve includes a piloting chamber that is in fluid communication with the reservoir, the air intake valve being opened and closed in accordance with a pressure in a piloting chamber. Preferably, the air intake valve is configured such that it is closed in response to a high reservoir pressure, which is communicated to the piloting chamber, and open in response to communication of a low reservoir pressure. This arrangement is advantageous in that it provides improved control of the timings of the opening and closing of the air intake valve. Reservoir pressure changes during the respiration cycle as the reservoir fills and then empties. By linking the opening of the air intake valve to the reservoir emptying, ambient air is admitted to the mask only after the initial dose of 100% oxygen. The air intake valve is then closed when the reservoir is sufficiently refilled, which will ideally be during the exhalation cycle when the user does not require any air. In practice, the air intake valve may also include a biasing means that applies an opening biasing force that is countered by pressure in the piloting chamber.

[0014] Ideally, the air intake valve in this embodiment requires less suction than the demand valve to generate flow. This feature improves the oxygen conservation still further by ensuring that, once the air intake valve is opened, no further flow takes place via the demand valve. Back pressure is therefore built up in the system, which, once the reservoir is full, prevents any further supply of oxygen.

[0015] Advantageously, the demand valve is a negative pressure direct acting demand valve, such as a tilt valve. A valve that is direct acting uses mask pressure directly to control flow through the system. This is in contrast with a valve such as a piloted demand valve whose response depends on a pressure change within a distinct, additional volume. This preferred type of demand valve does not require back pressure to close off flow, which makes it more suited for this application in which oxygen flow is via a restrictor. Moreover, this type of valve will permit flow in response to a negative, or below ambient, pressure within the mask. In theory, a positive pressure demand valve would also work for some embodiments of this invention. This would however be less comfortable for the user as mask pressure would swing from positive to negative within each inhalation. It is accordingly not preferred.

[0016] Preferably, the air intake valve, or inhalation valve, is configured to open when the reservoir is almost depleted. In one embodiment, this is achieved by the air intake valve and demand valve being configured such that the air intake valve requires more suction to generate flow. This ensures that the demand valve is the only inlet valve that is open on the mask until flow through that valve (from reservoir and restrictor) falls below that demanded by the user, at which point the air intake valve opens to admit ambient air.

[0017] The oxygen delivery system may also include a delay feature that is arranged to delay at least one of the opening and closing response of the air intake valve to changing reservoir pressure. The delay feature may be implemented in a number of ways but, essentially, the delay feature, restrictor and reservoir should be adaptable in accordance with the pressure at which oxygen is supplied such that reservoir pressure falls to a value that causes the piloted air intake valve to open during a user’s inhalation cycle and such that reservoir pressure rises to a value that causes the piloted air intake valve to close during exhalation. For example, the delay feature may include a frictional force that is generated by opening and closing the air intake valve. By way of another example, the delay feature may include a pair of magnets respectively secured to a moveable piston and to a fixed wall of the valve. The magnets are configured such that a magnetic force between them must be overcome either on opening or on closing the valve. Alternatively, or in addition, the delay feature may include a delay mechanism located in a path connecting the reservoir and piloting chamber and that is arranged to delay communication of a rising reservoir pressure and / or of a falling reservoir pressure to the piloting chamber. Preferably, the delay mechanism includes first and second channels arranged in parallel, the first channel permitting flow in a direction that communicates rising reservoir pressure to the piloting chamber and the second channel permitting flow in a direction out of the piloting chamber and wherein the first channel includes one of: a sprung non-return valve, a non-sprung non-return valve, a restrictor and a valve that opens and closes in response to a specific gauge pressure; and wherein the second channel includes one of: a sprung non-return valve, a non-sprung non-return valve, and a valve that opens and closes in response to a specific gauge pressure.

[0018] As an alternative, or in addition, to the reservoir being provided by a volume within a hose connecting components of the oxygen delivery system, the reservoir may include a chamber that is in fluid communication with the supply line. This chamber may be inline or not inline with the connecting hose. If it is not inline, then this chamber may be selectively included or excluded from forming part of the reservoir, depending on the circumstances of use.

[0019] In other variations, the restrictor may be a variable restriction, with one or more selectable values. Ideally, one of the selectable values is close to zero restriction such that permitted flow in the delivery system exceeds an anticipated maximum flow that is demanded by a user. This arrangement allows the oxygen delivery system to be used in situations that may demand supply of 100% oxygen throughout the inhalation cycle. That is, as for a standard demand valve. The variable restriction may, for example, include a needle valve or it may, for another example, be a rotatable arrangement of different restrictors, each with a respective restriction size.

[0020] In a further embodiment, the oxygen delivery system may include the restrictor located in a first feed channel, this first feed channel being in parallel with a second feed channel, and the system may additionally include an output selection piston that is switchable between a first position in which gas flowing therein is directed to the first feed channel and a second position in which gas flowing therein is primarily directed to the second feed channel. In this embodiment, a straightforward mechanism is provided by which the oxygen delivery system can be switched between one in which oxygen delivery is via the restrictor and so provided in the early phase of inhalation only and one in which 100% oxygen is delivered in response to a user’s demand. One application of this embodiment is in the parachuting field. As the switching between modes of delivery is required once the parachutist has descended to a certain height, this may be enabled by ensuring that the switching mechanism is responsive to atmospheric pressure, wherein if atmospheric pressure is below a threshold level (i.e. the user is at high altitude) then the output selection piston is in its second position (unrestricted flow) and if the atmospheric pressure is above a threshold level then the output selection piston is in its first position (restricted flow). In order to achieve this, the output selection piston preferably includes: a piston with narrowed portion that is moveable within a bore that is lined with at least three discrete sealing means; a link passage that opens into the bore between the second and third sealing means; a first feed channel that includes the restrictor opens into the bore in one of two positions: either between the second and third sealing means or, if more than three sealing means are present, between the third and fourth sealing means; a second feed channel opens into the bore between the first and second sealing means; biasing means arranged to urge the piston to a configuration in which the narrowed portion is aligned beyond the second sealing means with the link passage in fluid communication with the first feed channel and such that fluid flow from the link passage into the second feed channel is blocked; a control chamber adjacent the piston and in fluid communication via a bleed restrictor with a gas source, in which a build up of gas pressure within the chamber serves to urge the piston to a configuration in which the narrowed portion is aligned with the second sealing means, thereby allowing fluid flow from the link passage into the second feed channel; and wherein the switching mechanism includes a pressure responsive element and a switching valve whereby the switching valve may be either open or closed in response to a state of the pressure responsive element such that when the switching valve is in its low-pressure configuration, fluid flow is directed into the control chamber. Ideally, the pressure responsive element is an aneroid.

[0021] The system may also include an input selection piston that is switchable between a first configuration in which a first input line is placed in fluid communication with the supply line and a second configuration in which a second input line is placed in fluid communication with the supply line and wherein the first input line is connectable to a cylinder fitted with a pressure regulator and the second input line is connectable to a secondary oxygen source. The advantage of this embodiment is that it readily allows the sources of oxygen to be switched. For example, from one cylinder to another or, again for parachuting applications, to a fixed oxygen supply within an aircraft, prior to a jump. Preferably, in order to implement this switch, the input selection piston may include a piston with narrowed portion that is moveable within a bore that is lined with three discrete sealing means; a link passage that opens into the bore between the second and third sealing means; an input cylinder port that opens into the bore between the first and second sealing means; biasing means arranged to urge the piston to a configuration in which the narrowed portion is aligned with the second sealing means, thereby allowing fluid flow from the input cylinder port to the link passage; and wherein on connection of a connector to a supply port, pressure arising from fluid flowing into the input selection piston from the supply port urges the piston towards a configuration in an end of the piston no longer contacts the third sealing means, thereby allowing fluid flow from the supply port to the link passage.

[0022] The invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0023] Figure 1 is a schematic representation of an oxygen delivery system;

[0024] Figure 2 is a graphical representation of the operation of various components of the system of Figure 1 as it responds to an idealised respiration cycle;

[0025] Figures 3a, 3b and 3c are graphical representations of oxygen delivery in respective prior art systems in response to an idealised respiration cycle;

[0026] Figure 4 is a schematic representation of an oxygen delivery system in accordance with a first embodiment of this invention;

[0027] Figure 5a is a cross-section of an inhalation valve, suitable for use within the system of Figure 4;

[0028] Figure 5b is a cross-section of an inhalation valve with magnetic latch, suitable for use within the system of Figure 4;

[0029] Figure 5c is a cross-section of a frictionless inhalation valve, suitable for use within the system of Figure 4;

[0030] Figure 6 is a schematic representation of pneumatic components, for use in the system of Figure 4, that together delay communication of a pressure change in a first direction relative to communication of a pressure change in a reverse direction;

[0031] Figure 7 is a graphical representation of the operation of various components of the system of Figure 4 as it responds to an idealised respiration cycle;

[0032] Figure 8 is a schematic representation of an oxygen delivery system in accordance with a second embodiment of this invention; and

[0033] Figure 9 is a schematic representation of an exemplary manifold that selects the oxygen source and delivery mode, for use in the system of Figure 8.

[0034] With reference to Figure 1 , there is shown an oxygen system 10 that delivers oxygen to a mask 12 that is configured to cover the mouth and nose of a user 14. The mask 12 includes an inhalation, or air intake, valve 16 through which ambient air can be drawn to the inside of the mask 12, an exhalation valve 18 through which gas flows out of the mask 12 and a demand valve 20. As is well known in the art, the demand valve 20 opens in response to a drop in pressure within the mask 12. The inhalation 16 and demand 20 valves are configured such that the threshold pressure drop required to open the demand valve 20 is less than that required to open the inhalation valve 16. A gas supply line 22 extends from the demand valve 20 and is connectable to a cylinder 24 fitted with a pressure regulator 26, or other source of pressurised oxygen. A restrictor 28 is located upstream of a reservoir 30 in the supply line 22 between oxygen source 24, 26 and demand valve 20.

[0035] The regulator 26 is adjustable to set the pressure at which oxygen is supplied from the cylinder 24. This pressure is higher than atmospheric pressure, for example 5 bar (gauge pressure). The maximum flow through the restrictor 26 is determined by the restrictor value and supply pressure. This is termed the “restrictor flow”.

[0036] The response of the oxygen delivery system 10 to respiration of a user is represented graphically in Figure 2. With reference to this Figure, a graph 32 indicates time elapsed since the onset of inhalation (in seconds) along the x-axis 34. Various lines represent changes in the following quantities with time during an exemplary respiration cycle. Inhalation flow demanded by the user is represented by a black solid line 36, with flow rate indicated in litres per minute along the left-hand y-axis 38. Flow rate of oxygen supplied by the system 10 is represented by a dashed line 40, again with flow rate shown on the left-hand y-axis 38; and reservoir pressure is represented by a light solid line 42, with pressure indicated in barg (gauge pressure) along the right-hand y-axis 44.

[0037] In order to demonstrate the performance of the oxygen delivery system 10, the respiration cycle 36 is idealised as a sinusoidal variation with 30 linin'1peak flow (inhalation and exhalation) and a 4 s duration. These values are within the range of a typical human breathing pattern. Supply pressure from the cylinder 24 is regulated to 4 bar and the maximum flow that can be passed by the restrictor 28 at this pressure is 3 Imin-1.

[0038] At the start of an inhalation cycle (0 s), the reservoir 30 is full of oxygen supplied from the cylinder 24 via the restrictor 28 during the latter part of a previous respiration cycle. The mechanism by which this occurs will be explained below. The onset of inhalation causes a reduction in mask pressure, which opens the demand valve 20. Oxygen demanded by the user rapidly exceeds the flow that can be supplied through the restrictor 28 and so is drawn primarily from the reservoir 30. During this period, 100% oxygen is supplied and the dotted line 40 of Figure 2, representing oxygen supplied by the system 10, tracks the black 36 respiration line. Once the reservoir is depleted (indicated at point 46, around 0.5 s), oxygen supplied via the demand valve 20 is limited by the restrictor flow to around 3 Imin-1. The pressure inside the mask 12 decreases, causing the inhalation valve 16 to open and ambient air is admitted. During the latter part of this inhalation cycle, the user is therefore breathing ambient air supplemented by a small flow of oxygen through the restrictor 28.

[0039] At the final stage of inhalation, indicated from point 48, slightly sooner than 2s through the cycle, the inhalation flow demanded by the user falls below that provided via the restrictor 28. From this point 48, any excess oxygen that flows through the restrictor 28 will start to fill the reservoir 30. During the exhalation phase, when no oxygen is demanded by the user, the demand valve 20 closes and all oxygen flowing through the restrictor 28 is directed into the reservoir 30. At point 50, shortly after 3.5 s, pressure in the reservoir 30 reaches supply pressure and oxygen flow ceases. The reservoir 30 is therefore filled with oxygen, ready for use in a subsequent inhalation cycle.

[0040] The demand valve 20 is a direct-acting demand valve that responds directly to negative pressure in the mask 12, rather than a piloted demand valve. A suitable example is described in WO 2006 / 059161 . In this example, a valve member includes a valve head for sealing against a valve seat and a lever, connected to the valve head, that extends through the valve seat. A spring biases the valve to its closed position. Inhalation causes movement of a diaphragm, which pushes the end of the lever such that the valve head is tilted about a pivot point, causing at least a portion of it to move away from the valve seat, thereby allowing flow through the demand valve. This type of valve, in contrast to piloted valves, does not require significant back pressure to close. This requirement potentially makes piloted valves unsuitable for use with a restrictor, where the low flow rate may not allow much back pressure to build.

[0041] Ideally, the reservoir 30 and restrictor 28 are set such that flow into the reservoir 30 at the restrictor flow rate fills the reservoir to supply pressure during the period of the user’s exhalation. For example, a 20 ml volume would be filled in 1 .6 s, which is the scenario illustrated in Figure 2. The system 10 is accordingly able to store an equivalent of 80 ml of oxygen. This quantity is supplied, along with an additional 24 ml through the restrictor 28, during the initial phase of inhalation. If the flow rate is lower, or the reservoir 30 larger, the reservoir 30 would not be filled to supply pressure during exhalation. This has no effect on the initial supply of oxygen to the user, but it does mean that a larger reservoir than necessary has been provided, which unnecessarily increases the size of the system. The 20 ml reservoir volume set out above can be provided either as an internal volume of a connecting hose or hoses between the restrictor 28 and the mask 12 or it may include a separate volume in communication with the hose. The choice may be one of physical convenience: 1 m of 5 mm internal diameter hose would be required to maintain the 20 ml reservoir volume set out in this example.

[0042] As is clear from the above description, the oxygen delivery system 10 is able to supply 100% oxygen during an initial phase of the inhalation cycle and it is this gas that is therefore absorbed by the lungs. During later phases, when the oxygen content of inhaled gas is less important, it is ambient air that is supplied. Little oxygen is supplied during the latter part of inhalation, reducing wastage. All oxygen supplied during exhalation is stored in the reservoir for use during a subsequent inhalation cycle. Oxygen wastage is accordingly kept to a minimum.

[0043] Figures 3a to 3c respectively illustrate in a similar manner to Figure 2 an idealised respiration cycle (black line) and oxygen supplied (dashed line) by one of the prior art systems described above. These helpfully illustrate the advantages that this present system 10 has over various delivery mechanisms known in the prior art.

[0044] Figure 3a illustrates 52 the operation of a diluter demand system. During inhalation, oxygen supplied 54 follows the inhalation pattern but below the level of respiration flow. Ambient air makes up the remainder of the volume required. During exhalation, no oxygen is supplied 56. As is clearly shown in Figure 3a, diluter demand systems do not focus oxygen delivery at the start of inhalation. This is in contrast to the situation shown in figure 2, in which 100% oxygen is delivered during the initial inhalation phase and very little towards the end. This increases blood oxygenation and reduces overall oxygen consumption. Moreover, a diluter system adapted for parachuting has additional problems that affect its efficiency. Inhalation may itself generate a Venturi effect within the mask, which disrupts pressure sensing that is relied on for effective functioning. A high descent rate can cause wind blast, which also changes critical pressures. Additional measures are therefore required to avoid a malfunction. An aneroid is generally used to adjust the mix of oxygen and ambient air as altitude changes. The aneroid however must be finely tuned with both set point and expansion rate, which is difficult to manufacture. This present system 10 avoids the use of an aneroid.

[0045] Figure 3b illustrates 58 the operation of a prior art constant flow system with a reservoir. The reservoir is filled during exhalation and is the primary source of 100% oxygen to satisfy the user’s demand 60 during the initial phase of inhalation. In this way, oxygen delivery is focused at the start of the breath. Similarly, once demand falls below the constant flow that is supplied, excess oxygen is stored in the reservoir and its flow 62 cut off from the user. However, in this prior art system, once the reservoir is full, oxygen continues to flow and the excess is vented through the mask exhalation valve. This is shown in Figure 3b at region 64, from 1.7 to 2 s in the respiration cycle. The system 10 avoids this by supplying oxygen to the mask 12 through a demand valve 20 that remains closed during exhalation. The closed valve 20 prevents flow into the mask 12 and causes back pressure to build within the supply line 22 that reduces flow from the source 26 until it falls to zero. In this way, the system 10 improves on oxygen conservation in comparison with prior art reservoir systems.

[0046] Prior art constant-flow reservoir systems operate at ambient pressure and so require a relatively large volume to store sufficient oxygen for each inhalation, particularly at altitude. For example, 150 ml of gas at ground level requires a storage volume of 300 ml at 18,000 ft, where atmospheric pressure is half of that at ground level. To adapt to operation at different altitudes, these systems generally use an inflatable bag as the reservoir. Even so, the size of the reservoir can be cumbersome and an annoyance for the user. The system 10 requires significantly less volume as the gas within the supply line 22 is maintained at pressure. The same amount of oxygen (150 ml at ground level) needs only 30 ml storage at 5 bar pressure. This allows the system 10 to advantageously make use of space within a connecting hose between oxygen supply 24 and mask 12.

[0047] Figure 3c illustrates 66 the operation of a pulse oxygen delivery system. This system delivers a pulse 68 of oxygen at the start of each inhalation. As is clear from the Figure, the oxygen delivered 68 may for a part of the duration of the pulse (in this example, between 0.03 and 0.2 s) exceed demand 36 and may for another part (between 0.2 to 0.33 s) fall short of demand. Initially therefore, excess oxygen is delivered and this is wasted as it leaves the mask 12 via the exhalation valve 18. On the other hand, in the latter phase of the pulse, ambient air is drawn in with the oxygen, resulting in a lower oxygen concentration reaching the alveoli. As the pulse flow rate is pre-determined and that demanded by the user is highly variable, it is virtually guaranteed that for most of the time, one or other of the above situations will occur. In this way, pulse delivery is not ideal and this system has inherent inefficiencies. These inefficiencies are compounded by the fact that pulse delivery systems incorporate a delay mechanism to prevent multiple pulses per breath, effectively introducing a minimum cycle time. If a user breathes faster than this, the delivery pulses will occur later in the inhalation cycle and the system will deliver oxygen at timings that are far from optimal.

[0048] An oxygen delivery system 10 tailors oxygen delivery far better to a user’s demand, and avoids the disadvantages of a delay mechanism. Moreover, it has no requirement for the intricate pneumatic circuitry of the pulse delivery system and so performs more consistently and reliably at cold temperatures.

[0049] Finally, it is noted that in comparison with a prior art 100% demand system, in which oxygen delivery matches demand over the whole of the inhalation cycle, the present system 10 significantly reduces oxygen consumption.

[0050] Figure 4 shows a first embodiment of an oxygen delivery system 70 in accordance with the present invention. Components that are common to the delivery system 10 shown in Figure 1 are similarly referenced. The mask 72 of this system 70 includes a piloted inhalation valve 74 through which ambient air can be drawn, an exhalation valve 18 and a demand valve 20. A gas supply line 76 is connectable to a cylinder 24 fitted with a pressure regulator 26, or other source of pressurised oxygen. When connected, gas flows along the supply line 76 through a restrictor 28 and reservoir 30A, 30B. In this system 70, the reservoir is depicted as first 30A and second 30B connected volumes, the first 30A volume being within the connecting hose 76 and the second volume 30B being external. Downstream of the reservoir 30A, 30B, the supply line 76 has a first branch 76A that connects to the demand valve 20 and a second branch 76B that connects to a piloting chamber (not shown in this Figure) within the inhalation valve 74. Reservoir pressure is therefore communicated to the chamber and is used to pilot the opening and closing of the valve 74. The inhalation valve 74 is configured such that a high reservoir pressure causes it to close and a low reservoir pressure causes it to open and allow flow. The inhalation valve 74 has two further properties. First, a lower suction is required to achieve peak inhalation flow through the valve 74 than is required to open the demand valve 20. Secondly, hysteresis is built into its opening I closing behaviour such that after the inhalation valve opens, it stays open for the remainder of the inhalation cycle. To achieve this, the pressure threshold at which the valve 74 closes in response to rising reservoir pressure is higher than that at which it opens in response to falling reservoir pressure. This may be implemented within the inhalation valve 74 itself, for example by using a sprung inhalation valve with a magnetic latch. Alternatively, it may be a separate delay mechanism 78 that is included in the second branch 76B of the supply line. Or it may be a combination of both. As will be known to those skilled in the art, there are many ways to implement such a delay and that can be incorporated in this system to achieve the objective of delaying closing with increasing reservoir pressure and I or delaying opening with decreasing pressure.

[0051] The external volume 30B section of the reservoir may be fitted with a sealing mechanism (not shown), such that it is bypassed by the oxygen supply. In other words, the total reservoir volume can be configured to be switchable between two different sizes, for example enabling operation at different gas pressures. It will be apparent to one skilled in the art that such a two-part reservoir can be implemented within the other embodiments described herein. It will be further apparent that the external part 30B of the reservoir, or indeed the reservoir 30, if no part of the hose connections are used for this purpose, may be designed to stretch under pressure. This would be similar to the reservoir used in the constant flow prior art system, although it should be of a stiffer material and so able to withstand the higher gas pressures employed with this system. Like the prior art, this would permit an increase in available reservoir volume, for the same size (unstretched) reservoir. In addition however, this feature may also counter some of the effects of low temperature on the system. In low temperatures, rubber tends to harden, which will reduce the available storage volume. The gas itself will also become more dense, leading to an increased cycle time. This can be countered by using a smaller reservoir at lower temperatures.

[0052] A design of inhalation valve 74A suitable for use in this system 70 is shown in Figure 5a. The valve 74A includes a piston 80 with a sealing surface 82 that can be moved towards and away from a valve seat 84. The piston 80 slides within a channel that includes a piloting chamber 86, at the opposite end of the piston 80 from the sealing surface 82. An O-ring 88 fitted to the piston 80 presses against the walls of the channel so as to seal the piloting chamber 86 and prevent leakage of gas within. The piloting chamber 86 is in fluid communication with the reservoir 30A, 30B via the second branch 76B of the delivery system supply line. A spring 90 is fitted within the valve and biased to push the sealing surface 82 away from the valve seat 84 i.e. to keep the valve open. To hold the valve 74A in place, the mask 72 is clamped between valve components.

[0053] If the reservoir 30A, 30B of the delivery system 70 is in the process of filling with oxygen, pressure builds within the chamber 86, which in turn pushes the piston 80 downwards. This movement is resisted by the force of the spring 90. The surface area of the piston 80 and spring 90 are configured such that a high chamber pressure overcomes the resistance of the spring 90 and the sealing surface 82 is pressed downwards to seal the valve seat 84. The valve 74A is therefore closed and no ambient air can be drawn through it into the mask 72. If, on the other hand, reservoir pressure falls as stored oxygen is inhaled by the user, then the spring force becomes larger than the downward force generated by pressure in the chamber 86 and the sealing surface 82 is moved away from the valve seat 84. The valve 74A is now open and ambient air can be drawn into the mask 72. In its open configuration, the valve 74A has low resistance to inhalation flow.

[0054] One way in which hysteresis may be implemented in this valve 74A is if the O-ring 88 provides a frictional resistance to movement. For example, consider the spring 90 configured such that it is biased to an equivalent of 1 bar pressure in chamber 86. If the pressure required to overcome the frictional resistance of the O-ring 88 is 0.5 bar, then valve closing would be delayed until the reservoir pressure reaches 1.5 bar. That is, when chamber pressure is such as to overcome the spring bias (1 bar) plus the O-ring friction (0.5 bar). In order to open, the spring bias must be sufficient to overcome both the chamber pressure and friction required to move the O- ring 88. That is, the valve 74A will open when the chamber pressure reaches 0.5 bar (1 - 0.5 bar). Opening and closing reservoir pressures are therefore separated by 1 bar.

[0055] Figure 5b shows an alternative embodiment of inhalation valve 74B in which the hysteresis is implemented by means of a magnetic latch. This valve 74B is identical in design to that shown in Figure 5a, except for the addition of first 92A and second 92B magnets. The first magnet 92A is fixed to or embedded into a wall of the chamber 86, opposite a leading end of the piston 80 as it moves within the channel. The second magnet 92B is fixed to or embedded in the leading end of the piston 80. The magnets 92A, 92B are oriented to attract when one is brought into the proximity of the other. Consider the situation in which the valve is closed and oxygen is inhaled by the user from the reservoir. As reservoir pressure falls, so too does pressure in the chamber 86. When the force exerted by the spring 90 exceeds the downward force generated by this pressure, the piston 80 moves within the channel to lift the sealing surface 82 away from the valve seat 84. During the opening process, the second magnet 92B is brought nearer to the first 92A and, at some point, the magnetic force causes them to snap together. This facilitates a rapid opening of the valve 74B, allowing a quick switch from oxygen to ambient air. Later in the respiration cycle, during exhalation, the reservoir refills and pressure within the chamber 86 builds. In order to close the valve again, the pressure must overcome the spring force, which biases the piston 80 away from the valve seat 84, as well as the magnetic force that holds the magnets 92A, 92B together. The closing pressure is, therefore, higher than the opening pressure and hysteresis is built into the valve 74B.

[0056] In an alternative arrangement, the magnets 92A, 92B may be repositioned within the inhalation valve 74B such that the magnetic force between them snaps the valve to its closed configuration. Alternatively, two pairs of magnets may be used, each pair arranged to snap open and snap closed respectively.

[0057] The hysteresis required by the system 70 may be realised outside of the valve 74, in a separate pneumatic delay mechanism 78. With this arrangement, one of the above designs of inhalation valve 74A, 74B may be used to provide a further contribution to the total hysteresis but it is also possible to use a frictionless inhalation valve and implement the hysteresis independently of the valve 74. Figure 5c shows an exemplary frictionless inhalation valve 74C that may be included in the system 70 that provide this alternative implementation.

[0058] With reference to Figure 5c, a frictionless inhalation valve 74C includes a flexible diaphragm 94 that is attached circumferentially within walls of the valve 74B to separate an upper chamber 96 from a lower chamber 98. The upper chamber 96 is in fluid communication with the reservoir 30A, 30B via inlet 100 and the second branch 76B of the delivery system supply line. A valve seat 102 is located in the lower chamber 98, which is also open to atmosphere. An opening extends from the valve seat 102 and through to the inside of the mask 72. As with the previous example, the mask 72 is clamped between parts of the valve 74C. As shown in Figure 5c, a low pressure is present in the reservoir 30A, 30B and the diaphragm is relaxed. On inhalation, gas is therefore able to flow through the lower chamber 98 and into the mask 72. If the pressure in the reservoir 30A, 30B increases, pressure in the upper chamber 96 expands the diaphragm 94 and pushes it against the valve seat 102, preventing gas flow into the mask 72.

[0059] Figure 6 shows a first example of a delay mechanism 78 suitable for use with this embodiment of the system. In use, the delay mechanism 78 is positioned in the second branch 76B of the delivery system supply line between a first connection 104 to the reservoir 30A, 30B and a second connection 106 to the piloting chamber 86 of the inhalation valve 74. It comprises a first 108 passageway between the two connections 104, 106 that includes a sprung non-return valve 110 that is configured to allow gas flow in one direction only: from the reservoir 30A, 30B to the piloting chamber 86. The delay mechanism 78 further includes a second 112 passageway, in parallel with the first 108, that includes a non-sprung non-return valve 114 that is configured to allow gas flow in an opposite direction to that allowed by the sprung valve 110: from the piloting chamber 86 to the reservoir 30A, 30B.

[0060] The non-sprung non-return valve 114 includes a piston 116a with sealing surface 118a that is slidable in a channel 120a towards and away from a valve seat 122a. A link passage 124a extends through the valve seat 122a and connects to the supply line 76B and piloting chamber 86 of the inhalation valve 74. A chamber 126a is defined within the channel at the opposite end of the piston 116a from the valve seat 122a. The chamber 126a is in fluid communication with the reservoir 30A, 30B of the delivery system. When pressure in the reservoir 30A, 30B is higher than that within the piloting chamber 86, excess pressure in the chamber 126a causes the piston to move in the channel 120a to seal the valve seat 122a. This prevents any flow through the non-return valve. When the reverse situation applies and pressure within the piloting chamber 86 is higher than that within the reservoir 30A, 30B, the piston 116a is moved away from the valve seat 122a and gas is permitted to flow from piloting chamber 86, reducing piloting pressure for the inhalation valve 74.

[0061] The sprung non-return valve 110 has broadly similar components to the non-sprung non-return valve 114: a piston 116b with sealing surface 118b that is slidable in a channel 120b towards and away from a valve seat 122b. This valve 110 additionally includes a spring 128 that biases the piston 116b towards the valve seat 122b. A link passage 124b extends through the valve seat 122b and connects to the supply line 76B and hence the reservoir 30A, 30B of the delivery system. A chamber 126b is defined by the channel at the opposite end of the piston 116b from the valve seat 122b. The chamber 126b is in fluid communication with the supply line 76B and piloting chamber 86 of the inhalation valve 74. When pressure within in the reservoir 30A, 30B is high, it is able to overcome the bias of the spring 128 plus any pressure within the piloting chamber 86 and move the piston 116b away from the valve seat 122b and open the valve 110. Gas flow is therefore permitted from the reservoir 30A, 30B to the piloting chamber 86. Conversely, when pressure within in the reservoir 30A, 30B drops such that it is less than the combined effect of the spring 128 bias and pressure within the piloting chamber 86, excess pressure in the chamber 126b causes the piston to move in the channel 120b to seal the valve seat 122b. This prevents any flow through the sprung valve 110.

[0062] In combination therefore, this arrangement 78 is configured such that the first connection 104 is maintained at reservoir pressure and the second connection 106 is maintained at the pressure within the piloting chamber 86 of the inhalation valve 74. Gas flow is therefore regulated as follows.

[0063] When the first connection 104 is at a higher pressure than the second 106 the non-sprung non-return valve 114 in the second passageway 112 is closed; if the pressure differential is sufficient (i.e. more than the bias of the spring 128), the sprung non-return valve 110 will allow flow from the reservoir 30A, 30B to the piloting chamber 86 via the first passageway 108; if the pressure differential is small, no flow is permitted through either passageway 108, 112.

[0064] When the second connection 106 is at a higher pressure than the first 104 the sprung non-return valve 110 in the first passageway 108 is closed; the non-sprung non-return valve 114 in the second passageway 112 is open and flow is permitted from the piloting chamber 86 to the reservoir 30A, 30B via this passageway 112. The effect of the delay mechanism 78 therefore is to delay the communication of rising reservoir pressure that causes the inhalation valve 74 to close, relative to the communication of falling reservoir pressure that causes the valve 74 to open. In other words, the inhalation valve 74 is closed at a higher reservoir pressure than it is opened.

[0065] It will be apparent to one skilled in the art that the separation between the opening and closing pressures of the inhalation valve 74 may be achieved by including a frictional component in the inhalation valve, such as described in relation to the valve 74A of Figure 5a; by including a magnetic latch within the valve, as shown in Figure 5b and I or by including a delay mechanism 78, for example as described in relation to Figure 6, to delay communication of a pressure change in either an opening or closing response. These mechanisms, and their alternatives, may be implemented separately (for example using the delay mechanism 78 with a frictionless inhalation valve 74C), or in combination, as shown in Figure 4. Using multiple mechanisms may provide greater flexibility for adjusting the degree of separation of opening I closing pressures. Separation is important to control as this, reservoir volume(s) and restrictor flow are the factors that determine the minimum respiration cycle time that can be accommodated by the delivery system. Potentially therefore, with an adaptable system, separation may be adjusted to operate with different system flow rates or to handle a wider range of breathing rates, for example, rest and exercise modes.

[0066] The improvement provided by this embodiment 70 is apparent from consideration of Figure 7, which shows its response to the respiration of a user. This graph 130 uses the same representation as in Figures 2 and 3: an idealised inhalation flow demanded by the user is shown using a black solid line 36, flow rate of oxygen supplied by the system 70 is indicated by a dashed line 132 and reservoir pressure is shown using a light solid line 134. As before, it is assumed that supply pressure is regulated to 4 bar and restrictor flow is set to 3 Imin-1. In this embodiment, there is an additional 1 bar biasing force-equivalent from the spring and the reservoir is larger, with a volume of 40 ml. The inhalation valve 74 is a frictional valve 74A of the type described in relation to Figure 5a. That is, one that opens when the piloting pressure falls to 0.5 bar and that closes when the pressure rises to 1 .5 bar.

[0067] Just prior to the start of inhalation, the reservoir 30A, 30B is full and so at 4 bar (supply) pressure. The pressure in the piloting chamber 86 of the inhalation valve 74A is 3 bar. This is 1 bar less than reservoir pressure as the bias of the spring 128 in the delay mechanism 78 has to be overcome. This pressure in the piloting chamber 86 ensures that the inhalation valve 74A is closed.

[0068] At the onset of inhalation, the pressure inside the mask 72 is reduced and the demand valve 20 opens. Oxygen is supplied primarily from the reservoir 30A, 30B, supplemented by the relatively small restrictor flow. During this phase 136, 100% oxygen is supplied in line with the user’s demand. As the reservoir 30A, 30B depletes, pressure falls and when it reaches 3 bar, to match the pressure in the piloting chamber 86, the nonreturn valve 114 in the delay mechanism 78 starts to open. Flow is controlled by the non-return valve 114 such that the piloting pressure of the inhalation valve 74A falls at the same rate as that of the reservoir 30A, 30B.

[0069] After 0.7 s (point 138 on the graph 130), the reservoir pressure drops below 0.5 bar, which causes the inhalation valve 74A to open. The inhalation valve 74A has a lower resistance than the demand valve 20. Flow into the mask 72 will therefore be solely through the inhalation valve 74A and so of ambient air. This flow of ambient air maintains mask pressure; there is therefore insufficient suction to open the demand valve 20, which accordingly remains closed. That is, for the period in which the inhalation valve 74A is open, the demand valve 20 will be closed. During this phase, oxygen from the cylinder 24 is not supplied to the mask 72.

[0070] When the demand valve 20 is closed, oxygen flowing through the restrictor 28 is directed to the reservoir 30A, 30B, which accordingly starts to refill at the restrictor flow rate. Both non-return valves 110, 114 in the delay mechanism 78 are closed, maintaining the pressure in the piloting chamber 86 of the inhalation valve at 0.5 bar. This situation continues as the pressure in the reservoir rises through 1 .5 bar, around 1 .55 s into the respiration cycle 36. At this point 140, the pressure differential is sufficient to overcome the spring bias in the sprung non-return valve 110, oxygen will start to flow through this valve 110 and pressure builds in the piloting chamber 86. This will not yet affect the status of the inhalation valve 74A, as the valve 74A is a frictional valve with a higher closing than opening pressure.

[0071] About 2 s into the respiration cycle, exhalation begins and excess gas leaves the mask 72 through the exhalation valve 18. At around 2.4 s into the cycle, the pressure in the piloting chamber 86 reaches 1.5 bar (2.5 bar reservoir pressure). This causes the inhalation valve 74A to close. At this point 142, the system is ready for the next inhalation, when the demand valve 20 will open in response to a drop in mask pressure. However, the user is still exhaling and so there is no suction to draw flow through the demand valve 20. The oxygen flowing through the restrictor 28 therefore continues to fill the reservoir 30A, 30B. After around 3.55 s, at point 144, the pressure in the reservoir 30A, 30B reaches supply pressure (4 bar) and so the restrictor flow is also stopped. At this point, the oxygen delivery system 70 has the inhalation valve 74A closed, the reservoir 30A, 30B full and the demand valve 20 ready to open in response to the next inhalation.

[0072] A comparison of Figure 7 with Figure 2, clearly shows the improved oxygen regulation provided by the system 70 shown in Figure 4. The two arrangements 10, 70 draw the same amount of oxygen from the source but, for the second system 70, flow is directed to the reservoir 30A, 30B earlier in the cycle. At this point, the oxygen delivered to the mask 72 falls to zero and remains at zero until the next inhalation. By way of contrast, in the first system 10, the restrictor flow of oxygen continues to be supplied to the mask 12 through the majority of the inhalation cycle and so cannot be collected by the reservoir 30. The consequence of this is that the reservoir 30A, 30B in the system 70 has a greater volume and so dispenses 100% oxygen for slightly longer at the start of the inhalation cycle (0.7 s, as opposed to 0.5 s). This is in contrast to the system 10 of Figure 1 in which mask supply persists in particular, towards the end of the cycle when oxygen is not efficiently absorbed.

[0073] Although the above description uses exemplary values to illustrate the mechanisms behind operation of this oxygen delivery system 70, there is of course no such restriction on operation and various parameters are adjustable to suit the circumstances and application. One important requirement however is that the piloted closure of the inhalation valve should be delayed until after the inhalation part of the respiration cycle is complete. Otherwise, the user would be supplied with 100% oxygen when it is not necessary. This is achieved, in this example, by a combination of the hysteresis set within the inhalation valve 74A itself and that provided by the delay mechanism 78. Relative contributions made by these components may be adjusted, as appropriate. For example, if a stiffer spring 128 is used in the sprung non-return valve 110, the point 140 at which this valve 110 opens to allow pressure to build in the piloting chamber 86 of the inhalation valve 74A would occur later in the cycle shown in Figure 7. If this point 140 is pushed into the exhalation part of the user’s respiration cycle 36, then an inhalation valve 74 with smaller differential between opening and closing pressure thresholds could be used, for example the frictionless valve 74C shown in Figure 5c.

[0074] It will be apparent to one skilled in the art that other mechanisms may be used to control pressure in the piloting chamber 86 such that there is a difference between reservoir pressures that open and close the inhalation valve. It is advantageous to have a rapid opening when the reservoir is close to being depleted and a non-sprung non-return valve provides a straightforward way to empty the piloting chamber 86 quickly. It is though possible to use sprung non-return valves in both passageways 108, 112, although these springs should both be weaker than in the single-spring configuration, otherwise the separation between closing and opening pressures of the inhalation valve 74 would be too great and, consequently, the time delay too long. This arrangement should also be implemented with a higher spring force for the spring 90 in the inhalation valve 74A to reduce the risk of the inhalation valve 74A failing to open. An alternative mechanism to delay closing is to include a restrictor in place of the sprung non-return valve 110 in the first passageway 108 of the delay mechanism 78. As reservoir pressure rises, gas flow is blocked by the valve in the second passageway 112 and so must be routed through the restrictor. The restrictor slows the rate of pressure increase in the piloting chamber 86 so as to create a delay between the rise in reservoir pressure and corresponding control of the inhalation valve 74.

[0075] In a further variation, the opening and I or closing of the inhalation valve is achieved in a graduated manner. This may be used to enable a mix of pure oxygen I ambient air to be given for a portion of the breath.

[0076] It is further possible to replace the restrictor 28 with a variable restriction, such as an adjustable needle valve, or with a switchable bank of restrictors of different values that can be selected either manually or automatically. This gives flexibility to the system, allowing it to be implemented with different reservoir sizes (for example if the external reservoir volume 30B is added in or removed) and I or oxygen is supplied to a different pressure. This may be particularly useful in a parachuting application in which the requirement for supplemental oxygen reduces as the parachutist falls. By additionally restricting the flow at lower altitudes, the oxygen supply may be further conserved. Further applications include mountaineering when a user may want to switch between exercise and rest modes and in the medical field, when oxygen content may need to be adjusted to suit the needs of different patients. Moreover, one of the selectable settings may be largely unrestricted, which would allow the system to be used as a 100% demand valve.

[0077] In summary, with this arrangement, regardless of the details of its implementation, the pressure in the reservoir controls operation of the inhalation valve such that it opens at low reservoir pressure, once a required volume of 100% oxygen has been dispensed, and closes during the exhalation cycle, prior to a subsequent inhalation.

[0078] Figure 8 is a schematic illustration of a second embodiment 150 of this invention, in which the oxygen delivery system 70 described above is adapted more specifically for a parachuting application. This new embodiment includes all components of the delivery system 70 described with reference to Figure 4, and these components are similarly referenced.

[0079] The mask 72 accordingly includes a piloted inhalation valve 74 through which ambient air can be drawn, an exhalation valve 18 and a demand valve 20. The system 150 further includes a reservoir 30 that is connected, via a first branch 152A of a supply line 152 to the demand valve 20 and to a piloting chamber (not shown) within the inhalation valve 74 via a second branch 152B. Reservoir pressure is therefore communicated to the chamber and, as with the previous embodiment, controls opening and closing of the valve 74. The inhalation valve 74 is configured such that a high reservoir pressure causes it to close and a low reservoir pressure causes it to open. The inhalation valve 74 has lower resistance to flow than the demand valve 20 and exhibits hysteresis in its opening I closing threshold pressures. A delay mechanism 78 is included in the second branch 152B of the supply line, which delays communication of reservoir pressure changes to the piloting chamber in one or both directions (rising and I or falling pressure).

[0080] It is upstream of the reservoir 30 that this arrangement 150 differs from that of the previous embodiment 70. In particular, the supply line 152 includes first 154A and second 154B feed channels arranged in parallel and that link an upstream part of the supply line 152 with the reservoir 30. The first feed 154A channel contains a restrictor 156; the second 154B bypasses the restrictor. The system 150 also includes an output selection piston 158 that is switchable between a first configuration in which the first feed channel 154A is selected and a second configuration in which the second feed channel 154B is selected. Upstream of the output selection piston 158 is an input selection piston 160. This piston 160 is switchable between a first configuration in which a first input line 162A is placed in fluid communication with the supply line 152 and a second configuration in which a second input line 162B is placed in fluid communication with the supply line 152. The first input line 162A is connectable to a cylinder 24 fitted with a pressure regulator 26, or other portable source of pressurised oxygen. The second input line 162B is connectable to a console 164, which is a non-portable supply of oxygen, for example an aircraft oxygen supply.

[0081] An oxygen system for use in high-altitude parachuting is ideally able to facilitate three different breathing regimes. This first is on the aircraft, prior to a jump. In preparation for the jump, the pressure in the aircraft cabin is reduced to match that of the altitude at which the jump is to be made. Such depressurisation however carries a risk of decompression sickness. In order to prevent decompression sickness, nitrogen should be flushed from the bloodstream prior to the reduction in atmospheric pressure. This is typically achieved by “pre-breathing” 100% oxygen for a period of 30 - 45 minutes before cabin depressurisation and the jump. As the parachutist will be static during this pre-breathing, it is preferable that oxygen is drawn from a fixed aircraft supply, to conserve oxygen in the cylinder that will be used during the jump. When the user is about to jump, the aircraft supply is disconnected and breathing continues from the cylinder oxygen supply. During the descent, ambient pressure and air oxygen content increase. While the parachutist will therefore need to be provided with a 100% oxygen breathing gas at altitudes above around 25,000 feet, the requirement for supplemental oxygen diminishes during the course of the jump. Below 25,000 feet, efficient use of cylinder oxygen means that the parachutist should now be breathing a mixture of oxygen and ambient air, ideally with a continuous reduction in the percentage of oxygen supplied.

[0082] These three different breathing regimes may be facilitated by the apparatus shown in Figure 8, as follows. When the console 164 is connected to the second input line 162B, oxygen pressure forces the input selection piston 160 into its second configuration and oxygen from the console 164 supplies the system 150. The console 164 also mechanically forces the output selection piston 158 into its second configuration. The oxygen supplied is therefore directed into the second feed channel 154B and so bypasses the restrictor 156. With no restriction on the flow of oxygen, high pressure (of the aircraft supply) is permanently in the supply line 152. This pressure is communicated to the piloting chamber 86 of the inhalation valve 74, which ensures that this valve 74 remains closed. The reservoir 30 will be permanently full. The user therefore breathes 100% oxygen from the fixed supply via the demand valve 20.

[0083] In order to select oxygen input from the cylinder 24, via the first input line 162A, the input selection piston 160 adopts its first configuration. The output selection piston 158 is no longer constrained by the console supply and, instead, its configuration is dependent on atmospheric pressure I altitude. At altitudes above 25,000 feet, the system responds to the low ambient pressure by causing the output selection piston 158 to adopt its second configuration. As before, this configuration directs the source oxygen to the second feed channel 154B, bypassing the restrictor 156. The user is therefore able to breathe 100% oxygen, via the demand valve 20. As the parachutist descends, ambient pressure increases and the output selection piston 158 is switched to its first configuration. In this configuration, the source oxygen is directed to the first feed channel 154A, which includes the restrictor. The oxygen delivery system 150 then operates in exactly the same manner as described in relation to the embodiment 70 of Figure 4: an initial volume of oxygen is supplied from the reservoir, with the remainder of the inhaled volume being ambient air drawn through the inhalation valve 74. During the time period in which the demand valve 20 is closed, the reservoir refills from the restrictor flow, in preparation for the subsequent inhalation.

[0084] The system described above is ideally suited for delivering oxygen as necessary during the course of a high-altitude parachute jump. It will provide a mixture of oxygen with ambient air at altitudes below 25,000 feet (or other set point) and pure oxygen at altitudes above this and for pre-breathing in the aircraft prior to the jump. It will further be clear to one skilled in the art that, in another embodiment, the oxygen delivery system 10 of Figure 1 may be adapted as shown in Figure 8, with selection pistons 158, 160, to enable connection to both a fixed 164 and portable 24,26 oxygen source and to provide selective delivery of both 100% oxygen and diluted oxygen.

[0085] In an alternative arrangement, the portable oxygen source 24, 26 may be connected directly to the output selection piston 158 i.e. the input selection piston 160 is removed. This provides a system that is able to deliver either 100% oxygen or diluted oxygen from a single source. This may find application in a medical field, for example adapting to a patient’s worsening or improving lung condition, or in mountaineering should a user need the option of breathing 100% oxygen. It will further be apparent that the input selection piston 160 may be used without the output selection piston 158, with the result that either a fixed 164 or portable 24, 26 oxygen source may be selected to provide supplemental oxygen to a user.

[0086] Exemplary input 160 and output 158 selection pistons that are capable of performing as set out above are illustrated in Figure 9. In this figure, the input selection piston 160 and output selection piston 158 are connected by a link passage 170, which forms part of the supply line 152. This manifold system is based on that described in WO 2016 / 185201 , with adaptation to enable use with the oxygen delivery system 10, 70 described herein.

[0087] The input selection piston 160 comprises an input piston 172 that runs in a bore 174 lined with a series of three O-rings 176 (for example). The piston 172 has a narrowed section 178 but otherwise is sized so as to form a seal with the O-rings 176. An inlet 180 from the first input line 162A, connectable to the oxygen cylinder 24, is located in the bore 174 intermediate first and second O-rings. The link passage 170 extends from the bore 174, intermediate the second and third O-rings. A spring 182 biases the input piston 172 to the position shown in Figure 9, with the narrowed section 178 of the input piston 172 aligned with the second O-ring. There is accordingly no seal made between piston 172 and O-ring 176 at this position and gas entering the inlet 180 is able to flow through the bore 174 to the link passage 170. In this configuration therefore, oxygen for the delivery system is sourced from the oxygen cylinder 24. If, on the other hand, a connector 184, for example from the console 164 of an aircraft oxygen supply, is attached to connection port 186 of the input selection piston 160, pressure from the supply is exerted on the input piston 172. This counters the bias of the spring 182 and moves the piston 172 to the left (in Figure 9). This causes the narrowed section 178 of the piston 172 to align with the portable gas supply inlet 180. The piston 172 therefore forms seals with the first and second O-rings, sealing this input 180 from the link passage 170. With the piston 172 in this position, its end no longer seals against the third O-ring and the link passage 170 is now in fluid communication with the connector 184. Oxygen passed to the delivery system is therefore sourced from the fixed aircraft supply.

[0088] The output selection piston 158 comprises an output piston 186 that runs in a bore 188 lined with a series of four O-rings 190 (for example). The piston 186 has a narrowed section 192 but otherwise is sized so as to form a seal with the O-rings 190. The four O-rings therefore form distinct sealable sections of the bore, each of which contains a connection to a channel as follows. From left to right in the Figure, the second feed channel 154B is connected to the bore between the first and second O-rings; the link passage 170 is connected between the second and third O-rings and the first feed channel 154A, with restrictor 156, is connected between the third and fourth O-rings. It therefore follows that if the narrowed section 192 is aligned with the second O-ring, the link passage 170 is in fluid connection with the second feed channel 154B, which puts the system into a mode supplying 100% oxygen on demand. If, on the other hand, the narrowed section 192 is aligned with the third O-ring (as shown in Figure 9), the link passage 170 is in fluid communication with the first feed channel 154A and restrictor 156. This causes the oxygen delivery system 10, 70, 150 to deliver a mix of oxygen and ambient air, as previously described.

[0089] A spring 194 biases the output piston 186 towards the right of the figure, such that the third O-ring is aligned with the narrowed section 192 and an oxygen I air mix is delivered. Movement of the output piston 186 away from this position is facilitated by one of two mechanisms. First, if the connector 184 is attached to connection port 186 of the input selection piston 160, a descending lug 196 on the connector 184 contacts a protruding end 198 of the output piston 186, forcing it to move leftwards in the bore 188. This aligns the narrowed section 192 with the second O-ring and physically forces the system into delivery of 100% oxygen. The system therefore delivers in the correct mode for pre-breathing. The second control system is provided by pressure that is built up or released in a chamber 200 formed between a seal on the head of the output piston 186 and the first O-ring. Gas is fed to this chamber 200 from a connector 202 to the oxygen source via a bleed restrictor 204. Alternatively, gas from the bleed restrictor 204 flows to a valve 206. If the valve 206 is open, pressure in the chamber 200 is released; the bias of the spring 194 pushes the piston 186 to the right and the system delivers a mix of ambient air and oxygen. If the valve 206 is closed, pressure in the chamber 200 builds up, which forces the piston 186 to the left, against the bias of the spring, and the system delivers 100% oxygen. At high altitudes, an aneroid 208 expands to move a sealing surface 210 towards the valve 206. The valve is therefore sealed when there is insufficient oxygen in the atmosphere and 100% oxygen is needed. As a parachutist falls, the aneroid 208 contracts until, at a predetermined set point, the valve 206 is opened and the system switches to deliver a mix of air and oxygen at lower altitudes.

[0090] With this arrangement, the same oxygen delivery system can be used both before and during a high-altitude parachute jump. In order to conserve oxygen further, the restrictor 156 may be replaced with a variable restriction. This can be adjusted during the descent such that the amount of oxygen supplied gradually decreases.

[0091] In a variation of this arrangement, the output selection piston 158 may incorporate only three O-rings 190 in the bore 188. Both the link passage 170 and the first feed channel 154A, with restrictor 156, are connected between the second and third O-rings. As with the previous embodiment, the second feed channel 154B is connected between the first and second O- rings. This provides a safety-critical feature that guards against the output piston 186 ever occupying a mid-position that provides no output flow. If there is flow into the output selection piston 158 then there will always be flow out. The proportion that flows through the restrictor 156 will however be relatively small if the output piston 186 is moved to the left of Figure 9 and the second, unrestricted feed channel 154B is also in fluid communication with the link passage 170.

[0092] In comparison with the prior art, this embodiment 150 provides a number of additional benefits. Neither the constant flow system nor the pulse system of the prior art are capable of delivering 100% oxygen and so cannot be used in high-altitude applications. Hybrid systems have been developed that, for example, combine a 100% demand system with a pulse system or other dilution system. Employing two different systems effectively doubles the complexity. With this present arrangement however, the demand valve that is needed for high altitude is reused in the low-altitude restricted-flow system. This saves on parts and complexity making this a more reliable and less costly alternative to these hybrid systems.

Claims

CLAIMS1. An oxygen delivery system (70, 150) including:• a mask (72) that is configured to seal around a user’s mouth and nose, the mask (72) including a demand valve (20) and an air intake valve (74);• a reservoir (30); and• a restrictor (28, 156); located upstream of the reservoir (30) in a supply line (76, 152) that provides fluid communication between the demand valve (20) and an end that is connectable to a source of pressurised oxygen, characterised in that the air intake valve (74) includes a piloting chamber (86) that is in fluid communication with the reservoir (30), the air intake valve (74) being opened and closed in accordance with a pressure in the piloting chamber (86).

2. An oxygen delivery system (70, 150) in accordance with claim 1 , wherein the demand valve (20) is a negative pressure direct acting demand valve.

3. An oxygen delivery system (70, 150) according to claim 1 or 2, wherein the pressure in the reservoir (30) is maintained at 1 bar above atmospheric pressure for at least part of its operating cycle.

4. An oxygen delivery system (70, 150) according to claim 3, wherein the pressure in the reservoir (30) is maintained at 2.5 bar above atmospheric pressure for at least part of its operating cycle.

5. An oxygen delivery system (70, 150) in accordance with anypreceding claim, wherein the air intake valve (74) is configured such that it is closed in response to a high reservoir pressure and open in response to a low reservoir pressure.

6. An oxygen delivery system (70, 150) in accordance with claim 5, wherein the air intake valve (74) includes a biasing means (90) that applies an opening biasing force that is countered by pressure in the piloting chamber (86).

7. An oxygen delivery system (70, 150) in accordance with any preceding claim, wherein the system includes a delay feature (78, 88, 92A, 92B) that is arranged to delay at least one of the opening and closing response of the air intake valve (74) to changing reservoir pressure.

8. An oxygen delivery system in accordance with claim 7, wherein the delay feature includes a delay mechanism (78) that is arranged to delay communication of a rising reservoir pressure and / or of a falling reservoir pressure to the piloting chamber (86).

9. An oxygen delivery system (70, 150) in accordance with claim 7 or 8, wherein the delay feature includes a frictional force that is generated by opening and closing the air intake valve (74).

10. An oxygen delivery system (70, 150) in accordance with any one of claims 7 to 9, wherein the delay feature includes a pair of magnets (92A, 92B) respectively secured to a moveable piston (80) and to a fixed wall of the valve (74) and configured such that a magnetic force between the pair of magnets (92A, 92B) must be overcome either to close or to open the valve (74).

11. An oxygen delivery system (70, 150) in accordance with claim 8, wherein the delay mechanism (78) includes first (108) and second (112)channels arranged in parallel, the first channel (108) permitting flow in a direction that communicates rising reservoir pressure to the piloting chamber (86) and the second channel (112) permitting flow in a direction out of the piloting chamber (86) and wherein the first channel (108) includes one of: a sprung non-return valve (110), a non-sprung non-return valve, a restrictor and a valve that opens and closes in response to a specific gauge pressure; and wherein the second channel (112) includes one of: a sprung non-return valve, a non-sprung non-return valve (114), and a valve that opens and closes in response to a specific gauge pressure.

12. An oxygen delivery system (70, 150) in accordance with any one of claims 7 to 11 , wherein the delay feature (78, 88, 92A, 92B), restrictor (156) and reservoir (30) are adaptable to supply pressure such that reservoir pressure falls to a value that causes the piloted air intake valve (74) to open during a user’s inhalation cycle and such that reservoir pressure rises to a value that causes the piloted air intake valve (74) to close during exhalation by a user.

13. An oxygen delivery system in accordance with any preceding claim, wherein the air intake valve (74) and demand valve (20) are configured such that the air intake valve (74) requires less suction to generate flow.

14. An oxygen delivery system (70, 150) in accordance with any preceding claim, wherein the reservoir (30, 30A) includes a volume within a hose connecting components of the oxygen delivery system.

15. An oxygen delivery system (70, 150) in accordance with any preceding claim, wherein the reservoir (30, 30B) includes a chamber that is in fluid communication with the supply line.

16. An oxygen delivery system (70, 150) in accordance with any preceding claim, wherein the restrictor (28, 156) is a variable restriction, withone or more selectable values.

17. An oxygen delivery system (70, 150) in accordance with claim 16, wherein one of the selectable values is close to zero restriction such that permitted flow in the delivery system exceeds an anticipated maximum flow that is demanded by a user.

18. An oxygen delivery system (70, 150) in accordance with claim 16 or 17, wherein the variable restriction is a rotatable arrangement of different restrictors, each with a respective restriction size.

19. An oxygen delivery system (150) in accordance with any one of claims 1 to 17, wherein the restrictor (156) is located in a first feed channel 154A that is arranged in parallel with a second feed channel (154B), and the system additionally includes an output selection piston (158) that is switchable between a first position in which gas flowing therein is directed to the first feed channel (154A) and a second position in which gas flowing therein is directed to the second feed channel (154B).

20. An oxygen delivery system (150) in accordance with claim 19, wherein when the output selection piston (158) is in its second position, gas is directed to the second feed channel (154B) in addition to the first feed channel (154A).

21. An oxygen delivery system (150) in accordance with claim 19 or 20, that also includes a switching mechanism responsive to atmospheric pressure, wherein if atmospheric pressure is below a threshold level then the output selection piston (158) is in its second position and if the atmospheric pressure is above a threshold level then the output selection piston (158) is in its first position.

22. An oxygen delivery system (150) in accordance with claim 21wherein the output selection piston (158) includes a piston (186) with narrowed portion (192) that is moveable within a bore (188) that is lined with at least three discrete sealing means (190); a link passage (170) that opens into the bore (188) between a second and third sealing means; a first feed channel (154A) that includes the restrictor (156) opens into the bore (188) between the second and final sealing means; a second feed channel (154B) opens into the bore (188) between the first and second sealing means; biasing means (194) arranged to urge the piston (186) to a first configuration and a control chamber (200) adjacent the piston (186) and in fluid communication via a bleed restrictor (204) with a gas source, in which a build up of gas pressure within the chamber (200) serves to urge the piston (186) to a second configuration.

23. An oxygen delivery system (150) in accordance with claim 22, wherein the first configuration of the piston (186) is one in which the narrowed portion (192) is aligned beyond the second sealing means with the link passage in fluid communication with the first feed channel (154A) and such that fluid flow from the link passage into the second feed channel (154B) is blocked; and the second configuration of the piston (186) is one in which in which the narrowed portion (192) is aligned with the second sealing means, thereby allowing fluid flow from the link passage into the second feed channel (154B); and the switching mechanism includes a pressure responsive element (208) and a switching valve (206) whereby the switching valve (206) may be either open or closed in response to a state of the pressure responsive element (208) such that when the switching valve (206) is in its low-pressure configuration, fluid flow is directed into the control chamber (200).

24. An oxygen delivery system (150) in accordance with claim 23, wherein the pressure responsive element (208) is an aneroid.

25. An oxygen delivery system (150) in accordance with anypreceding claim, wherein the system includes an input selection piston (160) that is switchable between a first configuration in which a first input line (162A) is placed in fluid communication with the supply line (152, 170) and a second configuration in which a second input line (162B) is placed in fluid communication with the supply line (152, 170) and wherein the first input line (162A) is connectable to a cylinder (24) fitted with a pressure regulator (26) and the second input line (162B) is connectable to a secondary oxygen source (164).

26. An oxygen delivery system (150) in accordance with claim 25 wherein the input selection piston (160) includes a piston (172) with narrowed portion (178) that is moveable within a bore (174) that is lined with three discrete sealing means (176b); a link passage (170) that opens into the bore (174) between the second and third sealing means; an input cylinder port (180) that opens into the bore (174) between the first and second sealing means; biasing means (182) arranged to urge the piston (172) to a configuration in which the narrowed portion (178) is aligned with the second sealing means, thereby allowing fluid flow from the input cylinder port (180) to the link passage (170); and wherein on connection of a connector (184) to a supply port (186), pressure arising from fluid flowing into the input selection piston (160) from the supply port (186) urges the piston (172) towards a configuration in which an end of the piston (172) no longer contacts the third sealing means, thereby allowing fluid flow from the supply port (186) to the link passage (170).

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