GAS FLOW INDICATOR

This invention is concerned with improvements in or relating to gas flow indicators and is specifically concerned with such indicators capable of indicating that not only is there gas flow but that the gas is flowing at an acceptable or desired rate of flow; this is particularly useful for monitoring the rate of flow of oxygen in apparatus for providing respiratory assistance to a patient, whether in the home or in a hospital, for example as part of a respiratory device provided for a patient to assist with breathing, or as an emergency device which may be used by emergency services such as ambulance and air/sea rescue crews. Although not so limited, the present invention finds particular utility in connection with respiratory devices, and will hereinafter be described with particular reference to this application without, however, thereby introducing any limitation to the scope of invention as defined in the following claims.

Oxygen supply apparatus is frequently provided for the purpose of assisting those with respiratory ailments including, for example, lung disorders, so that patients can administer oxygen themselves in the home environment. Such apparatus is usually of a portable nature. Oxygen may be supplied in one of three ways, namely in compressed form in cylinders, from concentrators which extract oxygen from the atmosphere or as liquid oxygen in a Dewar Flask. Such sources are coupled typically via a line to a face mask.

There are two main types of control regulators currently in use for regulating the rate of flow of oxygen in therapeutic respirators, namely the needle-valve

regulator, which comprises an orifice or passage into which penetrates a tapered needle the position of which determines the effective flow cross section of the orifice and thus the rate of flow. The needle may project transversely into the lumen or may lie substantially parallel to the direction of gas flow. Such devices can have associated with them a flow rate indictor of the type comprising a tapered and calibrated transparent tube (typically methyl methacrylate, commonly called perspex) housing a ball which, in use, 'floats' in a rising gas stream within the tube, the height of the ball in the tube indicating the rate of flow of the gas. This device has a number of disadvantages. The flow rate indication is corrupted or even lost if the tube is not positioned exactly vertically, and the build up of static electricity on the Perspex tubes can cause the ball to adhere to the side wall and thus corrupt the flow rate indication.

The other type of flow regulator in common use is the so-called fixed-orifice flow regulator having a number of different calibrated holes in a plate which can be turned to position a selected hole in the part of the gas stream to select a discrete flow rate. Such part of the devices provide an indirect indication of the flow rate by the position of the plate, but this does not confirm that gas is actually flowing. It is important both for self-administration and for third party administration of oxygen to be certain that the gas is actually flowing and monitoring of the rate of flow of oxygen to the patient to ascertain that an acceptable flow rate is being delivered. There is, for example, the possibility that flow of oxygen to a patient may be disrupted due to a fault in the supply line between the oxygen source and the face mask. Thus, although the rate of flow of oxygen to a patient is controlled

by a valve in the supply line via which oxygen is administered to a patient, this valve adjustment is not always indicative of the gas flow rate nor does it confirm that there is a proper oxygen flow to the patient via the face mask, or indeed that oxygen flow is not impeded.

Consequently it is perceived that there is a need for a visual indicator both for the benefit of a patient and nursing or other support staff where appropriate to provide a reliable indicator that flow of oxygen is taking place, especially in apparatus having a fixed-orifice gas flow regulator. Accordingly, in one aspect, the present invention provides a gas flow rate indicator comprising a container having an inlet and an outlet, the container providing internally a passage through which gas under pressure can be directed from the inlet to the outlet, and the container further having indicator means within the passage responsive to the flow of gas therethrough, the container having a viewing port through which response of said indicator means to the flow of gas therethrough can be observed.

In one embodiment of an indicator according to the invention the indicator means comprises a rotor mounted so as to be free to rotate within the container. This rotor may comprise a central hub mounted on a rotatable spindle supported by bearings, with the rotor having one or more vanes or blades arranged in spaced circumferential relationship with respect to an axis of the spindle.

In an alternative embodiment of the invention the rotor may comprise a central hub mounted on a rotatable spindle as referred to above with the rotor further

comprising one or more vanes or blades each of arcuate cross-section when viewed in the direction of the axis of rotation of the spindle and mounted on the hub for rotation about the axis of the spindle when gas flows through the container. Alternatively, the vanes or blades may be of helical form, and indeed, may be in the form of a single helical vane.

In a further alternative embodiment of the present invention, the indicator means may comprise a rotor mounted in 'frictionless' magnetic bearings wherein the rotor includes a magnetised element which is polarised to float between corresponding magnetically polarised members located upstream and downstream relative to the flow of gas to maintain the rotor in the passage, the rotor further comprising a plurality of vanes or blades as in the preceding embodiments.

To improve the visibility of the rotor through the viewing port of the container, it may be desirable to have at least one part of at least one vane or blade of the rotor visually discernible, for example at least partially coloured, so that the rate of rotation of the rotor can be observed and judged by the rate at which the colour changes traverse the window.

hi one form of the invention, the spindle is aligned with the direction of flow of gas through the container. Alternatively the rotor may be mounted for rotation about an axis which is transverse to the flow of gas through the container. Obviously the form of the vanes or blades would be different in each case.

In a still further embodiment of the invention, the means responsive to gas flow may comprise a piezoelectric element mounted within the passage of the container, this element then being arranged to sense change in pressure due to change in flow of gas through the passage, hi such an arrangement the element will then be coupled electrically to a visual indicator mounted in or on the body of the container and arranged to indicate when a correct flow of gas occurs.

hi all embodiments of the invention it is desirable to mount the means for indicating gas flow such that it is adjacent the outlet port of the container thereby indicating that gas flow is taking place close to the target patient.

There now follows a detailed description which is to be read with reference to the accompanying drawings of a gas flow rate indicator according to the present invention; it is to be clearly understood that this indicator has been selected for description to illustrate the invention by way of example only. hi the accompanying drawings :-

Figure 1 is a side view of a gas flow rate indicator according to a preferred embodiment of the present invention;

Figure 2 is a further side view of the gas flow rate indicator shown in Figure 1; and

Figure 3 to 5 are perspective views of a rotor unit for use in an indicator according to the invention.

The gas flow rate indicator illustrated in the accompanying drawings is intended for use in conjunction with an oxygen supply designed for use by a patient whether in the home, in hospital or by deployment by emergency services such as ambulance crews or air/sea rescue teams. Such a supply will typically comprise an oxygen source such as an oxygen cylinder or concentrator which provides a supply of oxygen which can be typically admixed with an air supply to enrich the oxygen content thereof, the gas supply being regulated and supplied to an oxygen mask or the like.

The gas flow indicator illustrated in the Figures comprises a container 10, having an inlet 12 and an outlet 14. The container 10 is a hollow receptacle providing a chamber which defines a passage through which gas under pressure, usually oxygen-enriched air, can be directed from the inlet to the outlet. The container has at least one viewing port or window 15 through which the interior of the container can be viewed by an observer.

Within the container, and more specifically, within the passage defined by the container, is mounted means, in the form of a rotor 16 that rotates in response to flow of gas through the container for providing visual indication of that flow. The rotor 16, shown more clearly in Figures 3 to 5, is mounted on a spindle 18 within the container in a position such that it can be viewed through the viewing window 15.

In the embodiment shown in Figures 3 to 5, the spindle is supported in a housing 20 that is fitted within the container so that the axis of rotation of the spindle is aligned with flow of gas through the container.

(In an alternative embodiment, the means may comprise upper and lower spider supports which provide low-friction bearings that support the spindle.)

The rotor 16 comprises a hub 21 from which extend vanes providing rotor blades 22. The vanes 22 are integral with the hub 21, and extend outwardly from the spindle axis. Each vane or blade is of a substantially arcuate cross section when viewed in a direction along the axis of the spindle. Each vane or blade is joined to the hub along a line that is itself curved along the length of the spindle such that the outermost edge of each vane or blade is of helical shape.

The vanes or blades 22 are arranged in spaced circumferential relationship to each other and extend outwardly of the spindle, hi an alternative embodiment, the vanes or blades may extend radially with respect to the spindle axis.

The blades 22 may be at least partially coloured in any manner such that rotation of the rotor 16 can be readily seen. The colouring of the blades may ideally be by provision of stripes so that not only can rotation of the rotor be observed but also the rate of rotation. Such stripes can be provided by colour being applied to the outermost edges of the blades.

In an alternative embodiment of the invention (not shown), the hub of the rotor may be formed as or include a magnetic element, the hub being mounted between support members which are also magnetic so that the hub 'floats' in the magnetic field provided by the support members. The magnetic element can thus float in balance in a virtually frictionless arrangement.

In yet another embodiment of the invention, the means which is arranged and provided to give indication that gas is flowing through the container to a patient can be provided by a piezoelectric device provided within the container and associated with a light source that can be powered from the device to provide a visual indication of flow through the container.

When fitted in an oxygen supply line to a patient, supply of oxygen is normally controlled by a regulator valve adjustable by the patient, thereby causing a selected rate of flow of gas through the system, including the indicator, and such flow of gas will be such as to cause the rotor to rotate, and the rotation can be readily observed and monitored by an observer. Such open-loop systems are the most common, although a so-called 'conserver' system in which a valve is triggered to open upon inhalation is also known and the flow rate indicator of the present invention can be used with such a system as well.