GB2461525A

GB2461525A - Method for gas blending in a respiratory device

Info

Publication number: GB2461525A
Application number: GB0812009A
Authority: GB
Inventors: Frede Jenson
Original assignee: SLE Ltd
Current assignee: SLE Ltd
Priority date: 2008-07-01
Filing date: 2008-07-01
Publication date: 2010-01-06
Anticipated expiration: 2028-07-01
Also published as: GB2461525B; GB0812009D0

Abstract

A blender for mixing a first gas at ambient pressure, generally air, and a second gas, generally oxygen, to obtain a mixed treatment gas with predetermined proportions, generally expressed as an oxygen concentration or percentage. The blender assembly is positioned upstream from a pump (4) in a respiratory device. A first gas inlet valve (2) governs the degree of sub-ambient pressure inside the mixing chamber (3). The pressure inside the mixing chamber (3) is communicated via (8) to the second gas valve (7). The degree of second gas inlet via valve (7) is thereby a function of the position of the first gas valve (2). The position of the first gas valve (2) may be selectively positioned such that its setting predetermines the proportions of first and second gases in the treatment gas mixture.

Description

I

METHOD FOR GAS BLEITDING IN A RESPIRATORY DEVICE

This invention relates to a respiratory device blender for blending a treatment gas used in respiration therapies for human and animal patients, where gas is delivered into the patient's airway through the nose or mouth. In particular this invention relates to a respiratory device where the treatment gas flow and pressure is generated downstream from a blender.

For the present purpose the term "respiratory device" and "respiratory equipment" defines any system that delivers a flow of pressurised gas to a patient's airway, with the intention to augment, supplement or substitute the patient's own respiratory efforts.

A treatment gas is generally an air and oxygen mixture, but it may also contain other gases. The required proportions of the constituent gases in the mixture are determined by the practitioner of a therapy, according to the procedure being performed and the condition of the patient.

Gas flow and pressure is delivered to the patient at a predetermined continuous level or a predetermined cyclic manner involving two or more levels. The blending function must be capable of operating accurately under such continuous or bi-or multi-level conditions.

Conventional solutions for providing the blending function in respiratory devices have a degree of design complexity from the multiplicity of components and multiplicity of control variables, which has an associated cost and demand for technical skills in the device manufacturing and post-manufacturing maintenance/servicing. This complexity can make devices unviable for certain procedures and in certain markets, due to economic constraints and limitations in manufacturing and technical support capabilities.

The present invention is relatively simple in construction, which counters the aforementioned complexity related drawbacks of conventional solutions.

The present invention is a blender for coupling upstream from a pump in a respiratory device comprising an inlet to receive a first gas, generally air, at ambient pressure and a second inlet to receive a second gas, generally oxygen, at above ambient pressure, and where the degree of intake of the second gas is governed by the adjustable degree of inlet of the first gas.

According to the present invention, there is provided a respiratory device blender for coupling upstream from a pump in a respiratory device providing a flow, in use, of pressurised treatment gas that, by time the gas reaches the patient, the gas is mixed in predetermined proportions, said blender comprising a first inlet valve to receive a first gas at ambient pressure and a second inlet valve to receive a second gas at above ambient pressure, and the arrangement being such that the degree of intake of the second gas is governed by the degree of inlet of the first gas.

The invention also extends to a respiratory device incorporating such a blender.

The invention will now be described by way of example and with reference to the accompanying drawings in which: Fig. 1 shows a block diagram of the respiratory device with blender system, Fig. 2 is a graph illustrating the pressure cycle of artificial ventilation, Fig. 3 shows a cross-section of key parts in a simple embodiment, Fig. 4 shows a cross-section of key parts in an alternative embodiment.

In Fig. 1, reference A illustrates a connection by pneumatic conduit, such as a pipe. B illustrates a mechanical connection. C illustrates an electrical connection. When a pump 4 operates to generate a flow of pressurised gas to the patient, it causes a negative, sub-ambient, pressure inside a mixing chamber 3. Ambient air 1, at atmospheric pressure, is thereby drawn into the mixing chamber 3 through an air valve 2. The air inlet 1 and air valve 2 and mixing chamber 3 are coupled by a pneumatic conduit of appropriate cross-sectional area to afford low resistance to air flow. The mixing chamber has a semi-rigid or elastic wall 8, which flexes when pressure inside the mixing chamber 3 differs to that in its ambient environment.

The system uses a second gas source 5, which is generally oxygen compressed to between zero point five and seven bar and received from a bottle or piped services. A pressure regulator 6 reduces the second gas pressure to a non-hazardous level. Activation of an oxygen valve 7 is governed by the mechanical flexing of the elastic wall 8, which is mechanically communicated to the oxygen valve 7. The term "wall" also means any type of a membrane or diaphragm. The relationship is such that the intake of oxygen into the mixing chamber 3 increases as the pressure inside the mixing chamber 3 decreases.

The oxygen valve 7 opening point is adjusted so that when the air valve 2 is fully open, and thereby causes minimal restriction on the flow of ambient air 1, and when the pump 4 simultaneously operates at its maximum level, then the negative pressure inside the mixing chamber 3 is just above the negative threshold for causing the oxygen valve 7 to be opened. Thereby, when the air valve 2 is fully open, there will not under any circumstances be any oxygen intake.

As the air valve 2 closes and thereby chokes the intake of ambient air 1, the negative pressure inside the mixing chamber 3 reduces to a level below the negative threshold for causing the oxygen valve 7 to be opened, which causes oxygen to flow into the mixing chamber 3.

When the air valve 2 is fully closed, only oxygen will flow into the mixing chamber 3.

The system can operate continually with one gas source depleted, obstructed or disconnected, whether such condition occurs accidentally or deliberately. The pressurised treatment gas from a pump outlet 13 is carried to the patient through a flexible hose, tube or patient circuit (not shown) In one method of controlling the air valve 2, where the respiratory equipment is required to deliver bi-or multilevel pressures to the patient, a controller 9 uses cycle times and pressure level variables to calculate an average opening position for the air valve 2. A respiration cycle is the total time for performing an inhalation at an elevated pressure level and the subsequent exhalation at base-level. Generally, both pressure levels are above ambient. The graph in Fig. 2 illustrates how the oxygen intake into the mixing chamber 3 varies during the respiratory cycle generated by the pump 4, according to the predetermined position of the air valve 2.

In Fig. 2, the mean oxygen intake 17, 18 and 19 differs according to the air valve 7 position, when the pump pressure setting is the same. If the air valve 2 is, say, three-quarters open, then the mean oxygen intake over one respiratory cycle 17 is relatively high. If the air valve 2 is, say, half-open, then the mean oxygen intake over one respiratory cycle 18 is medium. If the air valve 2 is, say, one-quarter open, then the mean oxygen intake over one respiratory cycle 19 is lower.

In another method of control, the air valve 2 is cycled between its fully opened and fully closed states.

The gas blend is then determined by simple time-division between the two air valve states.

To ensure uniform mixing prior to the treatment gas reaching the patient, the combined internal volume of the mixing chamber 3 and pump 4 is greater than the volume of gas consumed by the patient and any gas leak in the patient system and any sampling gas volume, over one respiratory cycle.

Fig. 3 illustrates an example of mechanical oxygen valve 7 of conventional design, where its adjuster 7d compresses a spring 7c to counter linear travel of a plunger 7b, with a force that sets the plunger 7b to just fully engage its seat 7a. Inward flexing of the mixing chamber wall 8a is communicated via 8b to cause the plunger 7b to disengage from its seat 7a and thereby allow oxygen to flow into the mixing chamber. A mechanical oxygen valve may also be of a conventional tilt member type, instead of a linear travel plunger 7b type. The pressure level inside the mixing chamber is thereby maintained close to the ambient pressure level.

An electric oxygen cell 14 monitors the oxygen concentration inside the mixing chamber.

Fig. 4 illustrates an example where the oxygen inlet is regulated by an electromechanical valve 20. The valve position is controlled by a feedback signal 21 from a pressure sensor, which measures the pressure inside the mining chamber 3. In this example, the pressure sensor substitutes the mechanical communication, and the mixing chamber 3 has all rigid walls.

In Fig. 4, the pump 4 has a secondary outlet 15, which delivers a lesser volume sampling gas for monitoring of the oxygen concentration by an electric oxygen cell 14. The oxygen concentration measurement value from the monitoring system may be used to servo-control or to calibrate the air valve 2 position, or to signal (e.g. with an audio-visual warning) if there is an intolerable discrepancy between the set and delivered oxygen concentration.

The block diagram in Fig. 1 infers feed forward signal links 10 and 11 from the controller 9. One or both of these links 10 and 11 may be substituted with a closed-loop servo control. This has an advantage of programmable calibration.

The pump 4 and valves 2 and 7 are scaleable to meet gas flow and pressure requirements for treatment procedures for patients of different size, such as infant humans, adult humans or animals.

Claims

Cia � ms 1. A respiratory device blender for coupling upstream from a pump in a respiratory device providing a flow, in use, of pressurised treatment gas that, by time the gas reaches the patient, the gas is mixed in predetermined proportions, said blender comprising a first inlet valve to receive a first gas at ambient pressure and a second inlet valve to receive a second gas at above ambient pressure, and the arrangement being such that the degree of intake of the second gas is governed by the degree of inlet of the first gas.
2. A respiratory device blender according to claim 1, in which the first inlet valve position is adjustable so that the degree of opening of the first inlet valve determines the proportions of a first gas and a second gas in a treatment mixture.
3. A respiratory device blender according to claim 1 or 2, in which a control unit is provided to control the delivery of the gas to a patient and to regulate the position of the first inlet valve.
4. A respiratory device blender according to claim 3, wherein the control unit holds a set of user settable operational parameters for directing the control unit.
5. A respiratory device blender according to claim 3, wherein the control unit includes means to determine the first inlet valve position based on a user set parameter by an algorithm or look-up table calculating the average air valve position necessary to cause the predetermined mixture.
6. A respiratory device blender according to claim 3, wherein the control unit includes means to time-cycle the first inlet valve between fully-opened and fully-closed states, where the open and close times are determined from a user set parameter by an algorithm or look-up table calculating the time values necessary to cause the predetermined mixture.
7. A respiratory device blender according to claim 3, wherein the control unit includes means to servo-control the first inlet valve according to a user-set parameter and respiratory device actual output concentration measured by a gas sensor.
8. A respiratory device blender according to any one of the preceding claims, in which the degree of second gas inlet valve flow is regulated by a electromechanical valve, where the second valve is servo-controlled according to a user set parameter and pressure inside a mixing chamber positioned downstream from the first valve and upstream, in use, from the pump.
9. A respiratory device blender according to any one of the preceding claims, wherein said first inlet valve is a valve for air.
10. A respiratory device blender according to any one of the preceding claims, wherein said second inlet valve is a valve for oxygen.
11. A respiratory device blender according to any one of the preceding claims and being coupled to a pump for providing a flow of pressurised treatment gas in a respiratory device.
12. A respiratory device incorporating a blender according to any one of the preceding claims.