The invention is more particularly concerned with apparatus for providing breathing gas to patients having respiratory problems.

It is known that patients with respiratory problems can benefit from a gas mixture of oxygen and helium, the latter gas reducing the patient's work of breathing. Helium, however, is relatively scarce and expensive so conventional ventilation techniques where exhaled gas is exhausted to atmosphere are very wasteful and costly. The high cost is such that treatment with helium can only usually be provided to patients with severe respiratory problems.

Various ways are used to supply breathing gas to a patient, such as face masks, nasal masks or mouthpieces. These can be uncomfortable in prolonged use, often causing damage to the skin around the mouth or nose; they usually prevent the patient talking and often make it difficult to wear spectacles. Alternatively, a hood may be used to enclose the entire head. One problem with hoods lies in the difficulty of ensuring that they allow space between the hood and the face for free movement of gas, that the hood does not contact the nose and mouth of the patient and that the hood is light and comfortable to wear.

It is an object of the present invention to provide alternative breathing apparatus.

According to the present invention there is provided breathing apparatus,

characterised in that the apparatus includes a frame member adapted to fit on the user's head and to extend away from the head at least in the region of the nose and mouth, and a hood member more flexible than the frame member adapted to fit over the user's head and the frame member such that the frame member spaces the hood member from the nose and mouth to ensure free gas movement in this region.

The frame member preferably includes a first U-shape member adapted to extend over the crown of the head and down opposite sides in the region of the ears. The frame member may also include a second U-shape member extending forwardly from the first member around and spaced from the front of the face. The frame member preferably includes a third U-shape member extending forwardly from the first member with the second and third members extending below and above the nose and mouth of the user. The hood member may be formed with gas channel means extending from a gas connection to an inlet opening on the interior of the hood member in the region of the front of the face. The inlet opening may be provided by a chamber with a plurality of gas outlet holes. The gas channel means preferably includes a gas outlet opening spaced below the gas inlet opening. The hood member may have a wall formed of two separate layers and the gas channel means may be formed by joining together the two layers to define the gas channel means. The hood member preferably includes means towards its lower end for making a light seal with the user's shoulders. The apparatus preferably includes a gas supply including a source of helium gas and may be a recirculating gas supply.

Breathing apparatus in the form of a frame-supported hood according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation view of the apparatus in use;

Figure 2 is a front view of the apparatus in use;

Figure 3 is a perspective view of the frame of the apparatus without the hood;

and

Figure 4 is a perspective view of the hood of the apparatus before assembly on the frame.

The apparatus comprises a flexible hood 1 supported internally by a substantially rigid or semi-flexible frame 2 and a gas supply 3 by which a breathing gas mixture is supplied to and from the interior of the hood. With reference to Figures 1 , 2 and 4, the hood 1 is moulded or otherwise formed into a closed hollow main portion 10 of substantially oval section slightly larger than the head of the user on which the hood is to be used and with an enlarged shoulder portion 11 at its lower end. The hood 1 is made from two layers 12 and 13 of a flexible, transparent plastics sheet material such as polythene or polyurethane, which are separate from one another over the major part of their surface but are joined together by welding around the shoulder portion 11 and along two weld lines 14 and 15 (Figure 4). The weld lines 14 and 15 are closely spaced from one another to form a narrow gas channel 16 extending vertically from the rear of the shoulder portion 11 where the gas channel is joined to a gas inlet connector 17. The channel 16 extends over the crown 18 of the hood 1 and down the front of the hood a short distance where the weld lines 14 and 15 diverge away from one another to form an enlarged gas inlet chamber 19 of a general laterally-extending oval shape. The gas inlet chamber 19 is located in the region of the forehead of the user, that is, centrally slightly above the eyes of the user. The chamber 19 is perforated with gas outlet holes 20 through the inner layer 13 so that gas supplied to the gas inlet connector 17 flows out of the chamber 19 into the interior of the hood in the upper part of the user's face. The channel 16 continues down from the upper inlet chamber 19 to a similar lower outlet chamber 21 located level with the user's mouth. The channel 16 between the two chambers 19 and 21 is blocked along its length by a weld 22 so that gas cannot flow between the two chambers. The channel 16 continues down from the outlet chamber 21 to a gas outlet connector 23 in the region of the shoulder portion 1 1. The weld lines 14 and 15 could be interrupted to allow a small amount of gas to leak from the channel 16 between the two layers 12 and 13 so as to slightly inflate the hood 1 and help keep it away from the face.

With reference now also to Figure 3, the frame 2 is moulded of a substantially rigid or semi-flexible, resilient plastics material, such as polypropylene or polycarbonate and is intended to be reusable. Both the frame 2 and the hood 1 are available in different sizes to fit patients of different builds. The frame 2 is an integral, unitary or one-piece structure having a first, U-shape member 30 with two side legs 31 and 32 and a crown piece 33. The member 30 is fits snugly on the head substantially vertically with the crown piece 33 sitting on the top of the head and with the two side legs 31 and 32 extending down in contact with opposite sides of the head just in front of the ears to a location just below the ears. The lateral spacing between the two legs 31 and 32 is selected to be slightly smaller than the width of the head so that when fitted on the head the legs are splayed resiliently outwardly slightly and the member 30 grips the head lightly to hold the frame 2 securely in position. The frame 2 also includes a lower, chin member 34 of U-shape, which extends forwardly and down at an angle of about 30° to the horizontal from the lower end of the two side legs 31 and 32 to a location forwardly of chin by about 30mm. The frame 2 further includes a second, upper member 35 of U shape extending forwardly from the side legs 31 and 32 from a location just above the ears. The upper member 35 has a common side piece 36 and 37 on each side and is bifurcated into two parallel lateral beams 38 and 39 where the member extends across the front of the face to form a support opening 40 of oval shape. The beams 38 and 39 extend across the face in the region of the forehead and are spaced from the face by a distance of about 30mm.

The gas supply 3 is preferably a helium and oxygen recirculating supply where a mixture of helium and oxygen is provided from compressed gas cylinders to the hood 1 and gas exhausted from the hood is fed back to the supply where it is filtered, carbon dioxide is removed and fresh gas is added as necessary. The gas supply could, instead, be a

conventional air or oxygen supply but the hood of the present invention is particularly suited to recirculating systems with relatively low leakage to reduce waste of expensive gases like helium.

In use, the frame 2 is first fitted on user's head. The hood 1 is then pulled down over the head and frame 2 in the correct orientation so that the upper gas inlet chamber 19 locates in the support opening 40 of the frame 2 and the lower gas outlet chamber 21 locates centrally just above the chin member 34 of the frame. The shoulder portion 1 1 at the lower end of the hood 1 incorporates some means for making a light gas seal with the user's shoulders. This could take the form of an elastic band or an adhesive strip, or, where the user is wearing clothing, a Velcro or similar hooked fabric strip that catches with the threads of the clothing.

The hood inlet connector 17 is then connected to one end of tubing 48 extending to the outlet of the gas supply 3. The hood outlet connector 23 is similarly connected to one end of tubing 49 extending to the inlet of the gas supply 3. The gas supply 3 preferably includes a pump to create a small vacuum in the outlet chamber 21 to help gas flow from the hood 1. The gas supply 3 may be arranged to detect when the patient inhales and exhales and to supply and extract gas from the hood 1 in a cyclical fashion in synchronism with patient breathing.

Gas supplied to the hood 1 enters via the upper chamber 19, which helps disperse the gas over an increased area and also acts as a small gas reservoir to accommodate variation in flow. Because the gas enters the hood 1 towards its upper end it helps push down the stale gas towards the lower chamber 21 where it is extracted from the hood for recycling. The frame 2 helps to keep the material of the hood 1 away from the front of the face, with contact by the hood being confined to the rear of the head where the hair prevents direct skin contact. The design helps minimize the internal effective volume of the hood 1. When the hood 1 becomes soiled it is removed from the frame 2 and disposed of. The frame 2 can be reused to minimize expense. The frame 2 is shaped to distribute pressure over a relatively large area and reduce discomfort while being securely retained.

It will be appreciated that the hood arrangement could include conventional safety valves to vent gas from the hood in the event that pressure rises above an upper threshold level and to allow ambient air to flow into the hood in the event of pressure within the hood falling below a lower threshold level.

The rebreathing arrangement enables the heat and moisture in the exhaled breath to be conserved. It also reduces wastage of gas, which is especially important in the case of helium, which is relatively expensive. The gas supply arrangement within the hood enables efficient removal of stale gases to ensure an ideal patient environment. The hood

arrangement avoids the discomfort and problems often associated with masks.