BREATHING APPARATUS

Abstract: Apparatus for supplying air or oxygen to a patient comprises an on/off valve (16 to 24) located between a gas inlet (10) and a gas outlet (28), the valve including a driving position (42) which is biased to open the valve by means of a spring (44) and to close the valve by the pressure of gas in a reservoir (34) which has a slow vent or bleed and is fed with gas from the inlet/outlet feed line (26) in accordance with the setting of an adjustable throttle (30). thus, cyclic gas supply to the patient is developed, as the valve is opened and closed in accordance with movement of the piston under the combined effect of the opposed spring pressure and gas pressure acting thereon.

Description: Field of invention. This invention relates to breathing apparatus for supplying pulses of breathable gas to a patient. Such apparatus is used for emergency resuscitation and also as a lung ventilator for persons under anaesthesia. Background to the invention. Breathing apparatus of this type is known in a number of different forms. It is a characteristic of the apparatus that the gas feed to the patient is switched on and off at appropriate intervals, and it is known to use the breathable gas to control the valve movement. However, existing apparatus generally requires a considerable number of different components to provide the necessary regulatory function, and consumes an undesirably large proportion of the breathable gas for the purposes of driving the apparatus (see for example US-A-3522 816). The present invention aims to provide a solution to this problem. Summary of the invention. According to the present invention, there is provided breathing apparatus for supplying pulses of breathable gas to a patient, the apparatus having an inlet, an outlet, a feed passage between the inlet and the outlet, and an ON/OFF valve in the feed passage, the valve including a piston working in a cylinder which is biased in one direction by a spring and is biased in an opposite direction by pressure in a pressure reservoir, wherein the apparatus includes a throttle downstream of the valve and the reservoir communicates with the passage between the throttle and the valve and includes a bleed valve to allow the reservoir pressure to decay. The valve is preferably biased by the spring into the "passage open" position. The throttle and/or the bleed valve are preferably adjustable to alter the respective through flow rates. A flow restrictor may be placed between the feed passage and the reservoir, and this flow restrictor may also be adjustable. A one-way valve can be included at the entry to the reservoir. The valve may comprise a hollow, tubular body which moves in a valve housing. Thus, in one arrangement, the inlet enters the valve housing between two spaced O-rings which seal against the tubular valve member, and the tubular valve member has holes through its tubular walls which communicate with the inlet when the holes are between the O-rings and which are shut off from the inlet when the holes are positioned outside the space defined by the O-­ rings. The tubular member may form a piston rod attached to the piston which is biased in one direction by a spring and in an opposite direction by gas pressure. A pressure reducing valve can be entered upstream of the inlet. A preferred arrangement includes a by-pass passage for the valve, said passage including a spring loaded valve biased to close said by-pass passage except when the reservoir pressure lies below the normal residual pressure to which the pressure in the reservoir falls during ON/OFF cycling. Additionally, the apparatus may include a spring loaded vent valve for the reservoir, openable to vent the reservoir and initiate an on-phase of the gas supply if the outlet pressure falls below a given threshold during an off-phase. There may also be provided a by-pass line connecting from the inlet upstream of the valve to the outlet and an ON/OFF switch in said by-pass line which, when switched to the on-position, provides a continuous supply of gas to the outlet via the by-pass line prior to commencement of ON/OFF cycling. Brief description of the drawing. The invention will now be further described, by way of example, with reference to the accompanying drawing in which: Figure 1 is a schematic view of breathing apparatus in accordance with the invention; and Figure 2 shows a detail in enlargement. Description of the preferred embodiment. Breathable gas (either air or oxygen) is introduced into a pipe 10 and passes through a pressure reducing valve 12 to an inlet 14 to the apparatus. The inlet 14 extends into a valve housing 16, into a space bounded by O-rings 18 and 20. A tubular valve member 22 slides through the O-rings such that an inlet chamber is formed between the O-rings around the tubular valve member. The valve member, which is hollow, has openings 24 through its wall so that, when the valve member is in the position shown in the drawing gas can flow through the openings through the tubular member 22, out through the open end of the tubular member and into a feed passage 26. The gas then leaves the apparatus through an outlet 28 which will be connected to a conventional patient valve. A variable throttle 30 is positioned in the feed passage 26 and creates a back pressure causing gas to flow along a branch passage 32 into a reservoir 34. Another variable throttle 36 is provided in the passage 32, and a one-way valve 40 prevents reverse flow of gas through the passage 32. Whilst the valve 16 is open, gas flows through the apparatus to the patient and also flows through the passage 32 into the reservoir 34, to build up the pressure in the reservoir. The reservoir is permanently connected through a control passage 38 to the reverse side of a piston 42 which controls movement of the valve member 22. As the gas continues to flow, the pressure in the reservoir 34 builds up and thus the pressure acting against the piston 42 continually increases. At a certain pressure level, the pressure acting on the piston 42 is sufficient to overcome the biasing force of a coil spring 44, and the piston 40 together with the tubular member 22 is forced to the left. When this happens, the apertures 24 in the wall of the tubular member 22 pass beyond the O-­ ring 18 and are therefore closed off from the inlet 14. Gas therefore ceases to flow through the feed passage 26. In this condition there is no flow of gas through the outlet 28 to the patient, but the pressure in the reservoir 34 gradually decays through a vent 46 which is again adjustable. The pressure in the reservoir 34 thus drops gradually until the spring 44 is able to force the piston 42 to the right, overcoming the gas pressure in the reservoir. The valve then opens again and another pulse of gas is fed to the patient through the outlet 28, with the cycle repeating itself. Because there is only a single pneumatically controlled valve, the apparatus is considerably simpler than previously known apparatus which achieves the same end. There are less components and less moving parts and the apparatus can be contained in a smaller package. A relatively high proportion of the gas introduced to the apparatus reaches the patient for the patients use with only a small proportion being wasted by venting through the vent 46. The adjustable throttles 30 and 36 and the adjustable bleed valve 46 can be geared together so that the size and frequency of the gas pulses can he altered to suit the requirements of the patient. Optionally, as indicated by the dashed lines, spring loaded throttle 17 generates additional back pressure in the system, enabling it to cycle at a lower input pressure. The gas in passage 26 has to attain a minimum threshold pressure to open the seal 18 against the closing action of the spring 19. Most preferably, however, in the illustrated preferred arrangement, the throttle 17 is not employed, but on starting up (reservoir 34 empty), the initiation of cycling is advanced by means of a by-pass for the valve 16 to 24. The by-pass comprises a passage through the piston 42. This passage is normally closed at seal 47 due to the bias applied to the piston by the combined effect of spring 48 and the reservoir pressure. However on starting, when the reservoir pressure lies below even its minimum pressure level during cycling, the spring 44 is able to overcome the combined effect of the spring 48 and the reservoir pressure to allow opening of the valve by-­ pass passage at the seal 47, thereby to allow direct gas flow from the inlet to the reservoir in order rapidly to raise the reservoir pressure to the level at which cycling is initiated. Additionally, at start up, the patient may be given a continuous supply of gas via by-pass line 54, which incorporates a manual ON/OFF switch 55. Line 54 is closed when the ON/OFF gas cycling process begins. Finally, should the patient gasp for breath during an off-­ phase of the cycle, an on-stage may be immediately triggered through line 50 communicating the outlet 28 to the reservoir via valve 49. This valve includes a diaphragm 51 which is biased by a spring 52 to normally close the valve at seal 53. A negative pressure at the outlet (which is generated if a patient gasps for breath), causes the diaphragm 51 to lift, opening valve 49 at the seal 53 to instantly vent the reservoir and initiate an on-stage of the gas supply.

Claims: 1. Breathing apparatus for supplying pulses of breathable gas to a patient, comprising an inlet (14), an outlet (28), a feed passage (26) between the inlet and the outlet, and an ON/OFF valve (16) in the feed passage, wherein the valve is operable by a piston (42) working in a cylinder and which is biased in one direction by a spring (44) and is biased in the opposite direction by gas pressure in a pressure reservoir (34), a throttle (30) is provided in the feed passage (26) downstream of the valve, and the reservoir, which has a bleed valve (46) allowing the pressure in the reservoir to decay, communicates with the feed passage between the throttle and the valve. 2. Apparatus according to claim 1, characterised in that the valve piston is spring biased into a position in which the feed passage from inlet to outlet is normally open. 3. Apparatus according to claim 1 or claim 2 characterised in that the throttle and the bleed valve are adjustable for variation of the respective through flow rate. 4. Apparatus according to any of claims 1 to 3, characterised by a flow rate adjustable restrictor located between the feed passage and the reservoir, and a one-way valve at the entry to the reservoir downstream of said flow restrictor. 5. Apparatus according to any of claims 1 to 4, characterised in that the valve comprises a hollow tubular body which is movable in a valve housing to define an inlet chamber around the said valve member, in communication with the inlet, the tubular body having at least one aperture in its cylindical wall through which, in the ON position of the valve, the inlet chamber communicates with the interior of said valve member which thereby in turn communicates with the feed passage. 6. Apparatus according to claim 5, wherein the said tubular body forms a piston rod attached to the piston spring biased in one axial direction by the spring and in the opposite axial direction by the reservoir pressure. 7. Apparatus according to any of claims 1 to 6 characterised by a pressure reducing valve upstream of the valve. 8. Apparatus according to any of claims 1 to 7, characterised by a by-pass passage for the valve, said passage including a spring loaded valve biased to close said by-pass passage except when the reservoir pressure lies below the normal residual pressure to which the pressure in the reservoir falls during ON/OFF cycling. 9. Apparatus according to any of claims 1 to 8, characterised by a spring loaded vent valve for the reservoir, operable to vent the reservoir and initiate an ON-phase of the gas supply if the outlet pressure falls below a given threshold during an OFF-phase. 10. Apparatus according to any of claims 1 to 9, characterised by a by-pass line connecting from the inlet upstream of the valve to the outlet and an ON/OFF switch in said by-pass line which, when switched to the on-­ position, causes a continuous supply of gas to the outlet via the by-pass line prior to commencement of ON/OFF cycling.

Inventors: DEARMAN, PETER THOMAS, HESS, CHRISTOPHER, HESS, RICHARD, KIRK, CHRISTINE ANN, WARDELL, PETER
Applicants: NEOTRONICS MEDICAL LIMITED
Application year: 1986
Main classification: A61M16
IPC codes: A61M16