Apparatus for supplying air and at least one additional gas to a living being

Abstract: An apparatus (2) for supplying air and at least one additional gas to a living being (10) is disclosed. The apparatus (2) comprises a container (4) which comprises an open end (6) for receiving air and is connected to a tubing system (8) for conveying gas to the living being (10). The additional gas is supplied from an additional gas source (20) via a metering system (22) and a supply line (24) to the container (4). As gas is supplied to the living being (10) during inspiration phases by means of a compressor (16), air will flow into the container (4) via the open end (6). At the same time a flow of additional gas is supplied to the container (4) via a point of entry (26). During expiration phases gas will be diverted via a flow divider (28) to flow back to the container (4) via the supply line (24) for the additional gas. Hereby a homogeneous and controllable concentration of additional gas is obtained within the container (4) before each inspiration phase. The apparatus (2) comprises few but robust components making it a low cost apparatus providing for a good control of the concentration of additional gas supplied to the patient.

Description: The present invention relates to an apparatus for supplying air and at least one additional gas to a living being during inspiration phases, comprising a container which is open to surrounding atmosphere at one end for- receiving air, a tubing system connected to the other end of the container and connectable to the living being, a source of an additional gas, a point of entry located between the connection of the tubing system at the other end of the container and the open end in the container for the additional gas to mix with the air to be supplied to the living being, a metering system for supplying the additional gas from the source of additional gas via a supply line and a means for generating a flow of mixed air and additional gas, whereby a predetermined concentration of additional gas is obtained in the mixture of air and additional gas between the point of entry and the tubing system before the onset of each inspiration phase. Advanced ventilators (respirators), capable of providing a plurality of different respiration modes are usually complex to use and also expensive. Normally, they also require reliable power sources and are quite heavy. All together this makes it difficult to use this kind of ventilators in home care equipment or as resuscitation aid for ambulances, air crafts and similar locations. Such equipment should preferably be easy to use and at the same time be reliable. A reliable light weight and low cost ventilator is therefore desirable. Such an apparatus should be able to provide air and at least one additional gas, such as oxygen. An apparatus of this kind is described in DE-1 233 537. The described apparatus comprises a container having an open end towards ambient air and a connection to a tubing system leading to a patient at the other end. Between the container and the patient an additional gas such as oxygen can be provided. The additional gas is supplied with a continuous flow. During spontaneous inhalation the patient will draw gas from the container which then is mixed with the additional gas. During expiration the additional gas will flow towards the container (which is open to ambient atmosphere and thus is unable to generate an overpressure preventing the gas to flow through it in both directions). Due to the continuous supply of oxygen, the first part of the gas supplied to the patient during the initial part of inhalation will be highly enriched with additional gas and may even comprise almost entirely of the additional gas. Depending on the tidal volume inspired by the patient, the amount of the additional gas will be reduced during the remaining part of the inhalation. The reduction will depend on the flow of air from the container and the flow of the supplied additional gas. The respiratory gas flow is normally irregular during an inhalation and the concentration of the additional gas over the entire inhalation phase will thus vary in a high degree. The manner of breathing (few deep breaths or many shallow breaths) will determine the minute volume of the additional gas inhaled by the patient. It is therefore desirable to be able to supply a gas having a homogeneous mixture of air and the additional gas and it is also desirable to be able to select a specific concentration of the additional gas. The advanced ventilators referred to above usually comprise servo controlled valves which can respond quickly and accurately for providing exact mixtures of different gases. It would thus be possible to include an advanced servo controlled valve or similar and a flow meter between the container and the patient in the described known apparatus. By measuring the flow of air to the patient the valve could be controlled to supply an amount of additional gas based on the measured flow, which would result in a desired concentration of additional gas in the air. However, since the flow may vary significantly during an inspiration, and may momentarily reach flow values of several litres per second, the valve must be both very fast and very accurate in order to supply the required amount of additional gas. Although such valves do exist, they are usually very expensive, requires a relatively complex regulation circuit and are also more power demanding than other valves. Further, they usually also require that the additional gas is taken from a high pressure source in order to operate satisfactorily. WO 92/06730 discloses a gas blender for home ventilation equipment. A doubble ended poppet cooperates with two valve seats so that axial motion of the doubble poppet simultaneously opens or closes both valves to maintain a constant flow ratio. One of the valves may be adjustably positioned to determine the initial flow ratio of gases. One gas may be air and the other may be oxygen. It is an object of the present invention to achieve an apparatus according to the preamble which can provide a homogeneous gas mixture containing a defined amount of an additional gas to a patient in a simple but reliable and stable fashion. The object is achieved in accordance with the invention in that the apparatus according to the preamble is arranged so a feedback connection is arranged between the tubing system and the supply line and a flow divider is arranged for diverting a flow of air and additional gas to the living being during inspiration phases and for diverting a flow of air and additional gas to the feed back connection during expiration phases, whereby a predetermined concentration of additional gas is obtained in the gas between the point of entry and the tubing system before onset of each inspiration phase. Improvements of the apparatus according to the invention are disclosed in the dependent claims. In one embodiment of the apparatus according to the invention the metering system supplies the additional gas at a constant rate via a supply line and a feed back connection is arranged between the tubing system and the supply line. A flow divider is arranged for diverting a flow of air and additional gas to the living being during inspiration phases and for diverting the flow of air and additional gas to the feed back connection during expiration phases for conveying the air and the additional gas back to the container. If a constant flow is generated in the tubing system, the flow divider can, during inspiration, divert a first variable flow towards the living being and a second variable flow to the feed back connection. The sum of the two flows being equal to the constant flow. During expiration, the entire flow is normally diverted to the feed back connection. This arrangement enhances the mixing of the additional gas and air and improves the homogeneity of the gas mixture to be supplied to the patient. It is advantageous to arrange a flow meter to measure the flow of air and additional gas to the living being. Control over different parts of the apparatus may be utilized with relatively simple regulation means based on the measured flow. In the following the apparatus according to the invention will be described in more detail, referring to the figure which shows which a first embodiment of the apparatus. A first embodiment of the apparatus according to the invention is designated 2 and shown in the figure. The apparatus 2 comprises a container 4 which is open in one end 6 to the surrounding atmosphere. The container 4 preferably has a labyrinthine interior for improving the mixing of gases flowing through it. A tubing system 8 is connected to the other end of the container 4 and conveys a respiratory gas from the container 4 to a patient 10. An expiration valve 12 is connected to an exhalation tube 14 to allow gas to flow from the patient 10 during exhalation. A compressor 16 is arranged in the tubing system 8 for generating a flow of gas towards the patient 10 during inspiration. Hereby a significant breathing support and even breathing control is obtained. The compressor 16 can generate a constant or a variable flow of gas. The compressor 16 can also be replaced by a fan or a pump. The flow of gas supplied to the patient 10 is measured in a flow meter 18, located in the tubing system 8 near the patient 10. An additional· gas to be supplied to the patient 10 is stored in a gas source 20. The additional gas is supplied to the container 4 via a metering system 22 and a supply line 24. A point of entry 26 for the additional gas into the container 4 is arranged between the open end 6 of the container 4 and the tubing system 8. The additional gas is mixed with air in the container 4 for forming the respiratory gas. The volume between the point of entry 26 and the patient 10 should be at least one tidal volume for the patient 10 Preferably, the volume between the point of entry 26 and the compressor 16 (or flow divider 28) comprises this volume. A flow divider 28 is also arranged in the tubing system 8. The flow divider 28 can be operated to lead a flow of gas in two directions. A flow of respiratory gas can be diverted to the patient 10 and to the supply line 24 via a feed back connection 30. The gas flow from the compressor 16 can be partially or completely diverted to either of the two directions. The operation of the apparatus 2 can be described most easily if the compressor 16 is regarded as a constant flow generator of gas, which operates continuously over both inspiration and expiration phases. During inspiration the flow divider 28 is operated to divert a flow of respiratory gas to the patient 10 via the flow meter 18. A variable flow can be generated by varying the proportions of gas flows diverted in the two directions. The flow generated by the compressor 16 should in this case correspond to the highest flow required for the patient 10. At the same time a continuous flow of the additional gas, for instance oxygen, is supplied to the supply line 24 via the metering system 22 and is fed to the container 4, which it enters near the open end 6. Simultaneously with this, air will enter the container 4 via the open end 6. Basically, the same flow which is conducted from the container 4 via the tubing system 8 to the patient 10, will enter the container as the sum of the flow of air via the open end 6 and the flow of additional gas (or mixture of air and additional gas) via the point of entry 26. When the expiration phase commences, the flow divider 28 is changed to divert the entire gas flow via the feed back connection 30 to the supply line 24. The additional gas is still supplied via the metering system 22 with a continuous flow rate and thereby mixes with the gas from the tubing system 8. This gas is made up of air and additional gas, but is not mixed in the desired proportions. As it flows through the supply line 24, it will be enriched with more additional gas and further mixed. This new mixture will enter the container 4. Depending on the volume in the feed back connection 30 and the supply line 24, the gas will circulate one or more times through the system during the expiration phase. However, the volumes of the tubing system 8, container 4, supply line 24 and the feed back connection 30 as well as the constant flow of the additional gas are selected such, that the volume of gas between the point of entry 26 and the compressor 16 (or flow divider 28 or patient 10) is filled with the respiratory gas (i. e. the desired mixture of air and additional gas). During expiration, the flow of gas entering the container 4 at the point of entry 26 via the supply line 24 will be somewhat larger than the flow leaving the container 4 via the tubing system 8 (i. e. the flow generated by the compressor 16) due to addition of the constant flow of additional gas in the supply line 24. Therefore, no air will enter the container 4 via the open end 6. By selecting the volume between the open end 6 and the point of entry 26 in an appropriate manner, the loss of additional gas to the surrounding atmosphere can be minimized, even at high levels of concentration of the additional gas, i. e. at relatively high constant flows of the additional gas. The constant flow of the additional gas is selected based on the desired concentration of the additional gas and the total minute volume of respiratory gas to be supplied to the patient. If the required minute volume is 10 litres and the respiratory gas shall contain 10% of additional gas, 1 litre of additional gas should be supplied each minute. Hence, the constant flow of additional gas corresponds to the required minute volume of the additional gas, in other words 1 litre/minute. Since no additional gas will escape from the system and the supplied minute volume can be controlled via the flow meter and the compressor, the apparatus will operate in a very satisfactory manner. It should be noted that for many additional gases, such as oxygen, laughing gas or similar, a variance in the selected concentration of ± 1-2%. (i. e. with a selected concentration of 10% additional gas, the mixture supplied to the patient can contain 8-12%) is not serious for this kind of apparatus 2. The control of the compressor 16 is indicated by a control line 32 from the flow meter 18. The compressor 16 (or a similar flow generating device) can thus be operated to supply a variable flow to the patient 10. The operation of the apparatus 2 is basically the same even if a variable flow is used. The difference is that the flow of air entering the container 4 will vary more. The feed back system of air and additional gas will, however, ensure that a homogeneous and desired mixture is obtained. As already stated above, the variable flow can also be achieved by means of the flow divider 28. However, with a variable flow generated by the compressor 16, the flow divider 28 can operate as (or even be replaced with) a switch and divert the entire gas flow either to the patient 10 or to the feed back connection 30. It is of course also possible to use a switch instead of the flow divider 28 when a constant flow of gas is generated by the compressor 16. It is not even necessary to supply a continuous flow of the additional gas. It is sufficient to supply the required minute volume only. This can therefore be supplied with a variable flow to further enhance the mixing of the gases, such that a higher flow of additional gas is supplied during the inspiration phases, when a higher flow of air from the surrounding atmosphere may enter the container 4 via the open end 6 and a reduced flow of additional gas is supplied during the expiration phases, when the mixture of air and additional gas in the container 4 only needs to be further enriched with the additional gas for obtaining the final mixture to be supplied to the patient 10. Other controls in the apparatus 2 can also be exercised based on measured flow. For instance, the metering system 22 can be controlled based on the measured flow via a control line 34 and the flow divider 28 may also be controlled based on the flow measured by flow meter 18, indicated by a control line 36. The flow meter 18 comprises in these instances the required regulation components. Since regulation can be based on known regulation systems, these need not be further described here. The supply of the additional gas may also be controlled via the compressor 16 directly, as indicated by control line 38. The point of entry can basically be located everywhere between the open end of the container and the connection to the tubing system, provided that the volume of gas between the point of entry and the patient (or compressor/fan/pump) comprises at least one tidal volume.

Claims: Apparatus (2) for supplying air and at least one additional gas to a living being (10) during inspiration phases, comprising a container (4) which is open to surrounding atmosphere at one end (6) for receiving air, a tubing system (8) connected to the other end of the container (4) and connectable to the living being (10), a source (20) of an additional gas, a point of entry (26) located between the connection of the tubing system (8) at the other end of the container (4) and the open end in the container (4) for the additional gas to mix with the air to be supplied to the living being (10), a metering system (22) for supplying the additional gas from the source (20) of additional gas via a supply line (24) and a means (16) for generating a flow of mixed air and additional gas, characterized in that a feed back connection (30) is arranged between the tubing system (8) and the supply line (24) and a flow divider (28) is arranged for diverting a flow of air and additional gas to the living being (10) during inspiration phases and for diverting a flow of air and additinal gas to the feed back connection (30) during expiration phases whereby a predetermined concentration of additional gas is obtained in the mixture of air and additional gas between the point of entry (26) and the tubing system (8) before the onset of each inspiration phase. Apparatus according to claim 1, characterized in that the means for generating a gas flow is a compressor (16). Apparatus according to claim 1, characterized in that the means for generating a gas flow is a fan. Apparatus according to claim 1, characterized in that the means for generating a gas flow is a pump, preferably a positive displacement pump. Apparatus according to any of the above claims, characterized by a flow meter (18), arranged to measure a flow of air and additional gas supplied to the living being (10). Apparatus according to claim 5, characterized in that the metering system (22) is controlled based on the measured flow. Apparatus according to claim 5 or 6, characterized in that the means (16) for generating a gas flow is controlled based on the measured flow. Apparatus according to claim 5, 6 or 7, characterized in that the flow divider (28) is controlled based on the measured flow.

Inventors: BAUM MARCEL, BAUM, MARCEL
Applicants: SIEMENS ELEMA AB, SIEMENS-ELEMA AB
Application year: 1997
Main classification: A61M16
IPC codes: A61M16