Dosing device

Abstract: A dosing device (2) for controlled dosing of a first gas into a second gas, or liquid, is described. The dosing device (2) comprises a membrane (18) which is permeable to the first gas and which separates the first gas from the second gas/liquid. Dosing of the first gas is performed by controlling diffusion. In one embodiment, the size of the active diffusion area is regulated. Here, a barrier means (16) is movingly arranged, in relation to the membrane (18). When the barrier means (16) is moved in relation to the membrane (18), a larger or smaller part of the membrane's (18) diffusion area can be exposed to the second gas/liquid. In alternative embodiments, the membrane's permeability and the partial pressure of the first gas are controlled.

Description: The present invention relates to a dosing device according to the preamble to claim 1. In very small quantities, NO can have a plurality of beneficial effects on pulmonary function. Doses can range from about 1 ppm of NO up to about 50 ppm of NO. However, one problem is that NO is inherently hazardous and contributes to an increase in the conversion of NO into NO 2 on contact with oxygen. NO 2 is a highly toxic gas, even in very low concentrations. A plurality of designs for delivery and monitoring devices have been proposed for minimizing the risk to patients receiving NO. Monitoring is particularly difficult, since no methods are known for rapid and reliable measurement of low concentrations of NO. One object of the invention is to achieve a dosing device for dosing small amounts of gas, NO in particular, into a breathing gas supplied to a patient for medical purposes. One such dosing device is achieved in accordance with the invention in that the dosing device is devised as set forth in the characterizing part to claim 1. The use of a material permeable to oxygen for increasing the oxygen content of a chamber is known. One such device is described in US-A-5, 158,584 and comprises a plurality of tubes arranged in a tube surrounding a chamber. The tubes are made of a material more permeable to oxygen than to nitrogen. The ends of the tubes are open to ambient air. A fan forces air through the tubes. When gas passes the tubes, oxygen diffuses more rapidly than nitrogen through the membrane into the chamber. The amount of oxygen in chamber air is accordingly increased somewhat, compared to ordinary air. Air enriched with oxygen can then be respired by a patient. Similar systems are also used to oxygenate blood in an artificial lung. Blood is then allowed to pass through tubes of similar material, and oxygen is supplied to the exterior of the tubes. The oxygen diffuses into the blood, and carbon dioxide in the blood diffuses out in the opposite direction. This results in a gas exchange like the one occurring in an ordinary lung. One such apparatus is described in EP-A-48 943. Another use for a material permeable to gas is in the dehumidification of gases. A moist gas is fed through a system of tubing made from a material permeable to moisture. Moisture then diffuses into ambient air. The effect can be enhanced if the tubing is enclosed in a container through which a dry and hot gas is passed. Neither of these uses of semipermeable materials sets forth a method for controlled dosing of a first gas into a second gas. The dosing device according to the invention utilizes active control of diffusion. This can be achieved with a plurality of methods. A first method is to vary the active diffusion area, i.e. the area through which the first gas is to diffuse. In one embodiment according to the invention, the membrane is combined with a barrier means. This barrier means is made of a material which is impermeable to the first gas. The membrane and the barrier means are arranged so they can move in relation to each other. A major or minor part of the membrane can then be exposed to diffusion. A second method is to vary the membrane's permeability. In one embodiment of the dosing device according to the invention, the membrane consists of a plurality of coatings with varying permeabilities to the first gas. The coatings can be arranged so one coating at a time serves as the diffusion area, diffusion then depending on the choice of material. Or one or a plurality of coatings can be applied, in whole or part, to the basic coating in order to vary diffusion. A third method is to vary the partial pressure of the first gas, thereby causing more molecules to diffuse when partial pressure rises and fewer molecules to diffuse when partial pressure falls. Additional methods can be obtained by combining the above methods. Additional advantageous embodiments of the dosing device are apparent from the dependent claims to claim 1. Use of a dosing device according to the present invention would eliminate the need for advanced monitoring. Since diffusion through the membrane is physically limited, in relation to the exposure area and relative pressure conditions, dosing can be performed with such inherent safety that the maximum dose is limited. In particular, the concentration of NO in the dosing device can be limited so the patient only receives a harmless amount of NO, even if the entire diffusion area of the membrane is exposed to diffusion into the breathing gas. In principle, monitoring with a concentration meter will then be unnecessary. Embodiments of the dosing device according to the invention will be described below in greater detail referring to the figures in which FIG. 1 shows a first embodiment of the dosing device according to the invention; FIG. 2 shows a second embodiment of the dosing device according to the invention; FIG. 3 shows a third embodiment of the dosing device according to the invention; FIG. 4 shows a fourth embodiment of the dosing device according to the invention; FIG. 5 shows a fifth embodiment of the dosing device according to the invention; FIG. 6 shows a detail in a sixth embodiment of the dosing device according to the invention; FIG. 7 shows a seventh embodiment of the dosing device according to the invention, and FIG. 8 shows a dosing method for dosing NO with the dosing device. FIG. 1 shows a dosing device 2 intended for use in precision dosing of NO to a patient 10. The dosing device 2 is connected to a Y-piece 4 in a ventilator system (not shown). A breathing gas is supplied, via an inspiratory leg 6 in a Y-piece 4, as the arrow 8 indicates. The breathing gas, to which NO has been added, is carried to the patient 10 through a tracheal tube or in some other known fashion. Gas is carried away from the patient via an expiratory leg 12 in the Y-piece 4, as the arrow 14 indicates. The actual dosing device 2 consists of a tube 16 made of a material impermeable to NO, such as stainless steel. The tube 16 then serves as a barrier means. A membrane tube 18 is movingly arranged inside the tube 16. The membrane tube 18 is made of a material permeable to NO, such as Teflon. The membrane tube 18 is suitably provided with support struts, or some other feature, designed to stabilize the tube. The membrane tube 18 can especially be made of a perforated metal tube whose interior is clad with a membrane. This would give the membrane tube 18 a stable structure and reduce the risk of damage to the membrane. With the aid of a handling means 20, the membrane tube 18 can be slid back and forth inside the tube 16, thereby exposing a major or minor part of the membrane tube's 18 diffusion area to breathing gas in the Y-piece 4. At the same time, a source of gas 22 is connected to the interior of the membrane tube 18 by a gas tube 24. The source of gas 22 contains a gas mixture with a specific concentration of NO, e.g. N 2 containing 100 ppm of NO. The source of gas 22 is suitably regulated so constant pressure prevails in the membrane tube 18. This results in a constant partial pressure gradient between NO inside and outside the membrane tube 18. Diffusion, governed only by the diffusion area of the membrane tube 18, from the interior of the membrane tube 18 into the breathing gas is then achieved. Dosing is regulated by exposing an appropriate amount of the total diffusion area. The handling means 20 and membrane tube 18 can also be devised as a single means. The handling means 20 is suitably provided with a scale which designates the active diffusion area, i.e. the amount of NO which diffuses into the breathing gas. If, for example, 1 ppm of NO is desired, the dosing device 2 is set so a corresponding part of the membrane tube's 18 diffusion area is exposed inside the Y-piece's 4 inspiratory arm 6. Breathing gas then picks up NO and conveys it down into the patient's 10 lungs. The end of the membrane tube 18 is fitted with a plug 26 to prevent the leakage of NO when the membrane tube 18 in the dosing device 2 is completed retracted into the tube 16. The plug is made of stainless steel or some other material impermeable to NO. FIG. 2 shows a second embodiment in the form of a dosing device 30. The dosing device 30 comprises a container 32, connected to or integral with a tube 34, for a gas or a liquid. A membrane 36 separates the tube 34 and container 32. A dosing gas in the container 32 can be carried by a gas flowing in the tube 34, as the arrow 38 shows. A plate 40 is slidingly arranged in the container 32, in front of the membrane 36, to regulate the amount of dosing gas diffusing through the membrane 36. The plate 40, which is made of a material impermeable to the gas, can be moved back and forth, as the arrow 42 shows. A larger or smaller part of the membrane's 36 diffusion area is then exposed to the gas in the tube 34. A source of gas 44 is connected to the container 32 by a gas line 46. Constant conditions for the dosing gas in the container 32 can thereby be maintained. As in the preceding embodiment, exact regulation can be achieved by regulating the diffusion area. Regulation can be manual or mechanical. When dosing gases, whose concentrations can be easily measured are used, a feedback regulatory system can be installed for more accurate control of the membrane's 36 diffusion area. The lid 40 is appropriately located inside the container 32 when a gas with a positive pressure in relation to the dosing gas, flows in the tube 34. The membrane is then pressed against the lid 40 and effects a seal. If the opposite is the case, i.e. if a there is a positive pressure in the container 32 in relation to the gas in the tube 34, the lid should be appropriately located on the exterior of the membrane 36 and container 32. In this embodiment, the lid 40 can also be part of the tube 34 to which the container 32 is connected when dosing is to occur. An alternative embodiment is achieved when the lid 40 has openings and channels leading to a pump. The pump can be connected to the container 32. When gas is sucked through the openings, a suction effect is created which presses the membrane 36 again the lid 40. When the lid is shifted to a new position, gas is instead pumped out through the openings. The membrane 36 is blown away from the lid 40 which can then easily be moved to a new position. Position changes can accordingly be made without the risk of damage to the membrane caused by adhesion to or friction against the lid surface. A third embodiment is shown in FIG. 3. The dosing device 50 operates according to the same principle as in the two described embodiments, i.e. dosing is controlled by varying the area of a diffusion surface. The dosing device 50 comprises a membrane tube 52 which can be connected to a tube 54 for dosing a gas into a carrier gas inside the tube 54. The carrier gas flows in the direction shown by the arrow 56. The membrane tube 52 is connected by a gas line 58 to a source of gas 60. A constant dosing gas pressure is maintained inside the membrane tube 52. Dosing of the dosing gas can be controlled when a larger or smaller part of the membrane tube is inserted into the tube 54. When necessary, a gaiter 62 is arranged around the gas line with a gas-tight seal at the junction with the tube 54 to prevent leakage into ambient air. A plug 64 is arranged in the end of the membrane tube 52 to prevent diffusion of dosing gas when the membrane tube 52 is retracted back to the wall of the tube 54. FIG. 4 shows a fourth embodiment of the dosing device, designated 70, according to the invention. This dosing device 70 utilizes another principle for controlling dosing. In this instance, diffusion is controlled by varying the rate of diffusion. The dosing device 70 comprises a container 72 connected to a source of gas 74 containing dosing gas. The dosing device 70 is further connected to a tube 78 for dosing gas into a carrier gas in the tube 78. The arrow 80 shows direction of flow of the gas in the tube 78. A first membrane 82 is connected to the container 72 so it separates the interior of the tube 78 from the interior of the container 72. The first membrane 82 is highly permeable to the dosing gas. Inside the first membrane 82, a second membrane 84 is arranged so it can be rolled out in front of the first membrane 82. The second membrane 84 is wound onto a first roller 88, and the second membrane 84 can be rolled back and forth (as shown in the figure) when a first guide pin 94 is actuated. The second membrane 84 can be advantageously arranged so it presses against the first membrane (the distance between the membranes has been exaggerated in the figure to illustrate the structure of the dosing device 70). Diffusion can be controlled by regulating the unrolling of the second membrane 84. The second membrane 84 is somewhat less permeable than the first membrane 82, and dosing accordingly declines as the second membrane 84 is rolled out. In the corresponding manner, a third membrane 86 is arranged on a second roller 90, and a fourth membrane is arranged on a third roller 92. The third membrane 86 is even less permeable to the dosing gas than the second membrane 84. So dosing can be further reduced (successively) by rolling out increasing amounts of the third membrane 86. This is performed with a second guide pin 96. The fourth membrane is appropriately impermeable to the dosing gas and can successively reduce dosing down to zero. A third guide pin 98 is used to regulate the third roller 92 on which the fourth membrane is arranged. A fifth embodiment, designated 100, of the invention is shown in FIG. 5. The dosing device 100 operates according to yet another principle than the previous embodiments. However, the dosing device 100, like the previous embodiments, is connected to a tube 102 for dosing a dosing gas into a carrier gas in the tube 102. The carrier gas travels in the direction shown by the arrow 104. The dosing device 100 comprises a membrane 106 which serves as part of the wall of a tubing system 108. A fan 110 is arranged in the tubing system 108 to push gas through the tubing system 108, causing it to be continuously exchanged at the membrane 106. A first source of gas 112 and a second source of gas 114 are connected to the tubing system 108. The first source of gas 112 contains the dosing gas, and the second source of gas 114 contains a diluent gas. The two sources of gas 112, 114 and the fan 110 are controlled by a control unit 116. The partial pressure of the dosing gas can be regulated by mixing dosing gas from the first source of gas with diluent gas from the second source of gas. Diffusion through the membrane 106 into the carrier gas in the tube 102 is governed by the partial pressure of the dosing gas. Diffusion and, accordingly, dosing are controlled by regulating the partial pressure of the dosing gas in the tubing system 108. A continuous flow of dosing gas, corresponding to the quantity diffused, is supplied to the tubing system 108 from the first source of gas 112. Since dosing gas and diluent gas are circulated in the tubing system 108 by the fan 110, the partial pressure of the dosing gas at the membrane 106 is accordingly maintained at the desired level. Partial pressure can also be quickly changed by changing the amount of dosing gas and/or diluent gas supplied. There are also other ways of controlling diffusion. FIG. 6 shows part of a dosing device which illustrates an additional method for regulating diffusion. In principle, this method is a combination of some of the above embodiments. A first wheel 120 is mounted on a first hub 122. A first membrane 124, a second membrane 126 and a third membrane 128 are arranged in the first wheel 120. The three membranes 124, 126, 128 have the same shape and size but differing permeabilities to the dosing gas. They are also symmetrically arranged on the first wheel 120. The spaces between the membranes 124, 126, 128 have the same shape as the membranes 124, 126, 128. A second wheel 130 is arranged to form a gas-tight seal against the first wheel 120 via second hub 132. The second wheel 130 is made of a material impermeable to the dosing gas. An opening 134 is arranged in the second wheel 130. The size and shape of the opening 134 correspond to each of the three membranes 124, 126, 128. When the second wheel 130 is rotated in relation to the first wheel 120, an optional amount of any of the membranes 124, 126, 128 can be exposed as a diffusion area for the dosing gas. Rotation can be performed manually or mechanically with a step motor or the like. Mechanical regulation can be controlled by feedback from a dosing gas concentration meter, located on the dosing gas receiver side. An additional design for the dosing device according to the invention is illustrated with a seventh embodiment, designated 136 in FIG. 7. The dosing device 136 comprises a connector tube 138, designed for connection to a flow system for a carrier gas flowing through the connector tube 138, as shown by the arrow 140. A membrane 142 separates the interior of the connector tube 138 from a chamber 144 to which a dosing gas is supplied from a source 146. A valve 148 is arranged near the membrane 142 in the chamber 144. The valve 148 is switched between an open and a closed position by a control unit 150 via a control line 152. When the valve 148 is in the open position, dosing gas comes into contact with the membrane 142 and diffuses through same into the carrier gas in the connector tube 138. When the valve 148 is in the closed position, the dosing gas is prevented from coming into contact with the membrane 142. Diffusion through the membrane 142 can therefore be actively controlled by regulating the valve 148 between the open and closed positions. Even if the valve 148 should fail and stick in the open position, dosing is limited by the membrane's 142 diffusion capacity. This makes the dosing device 136 safer than if the valve 148 were used without the membrane 142. One application for the dosing device 136 is illustrated in FIG. 8 in which the dosing device 136 is assumed to be arranged in the inspiratory part of a ventilator system. The ventilator system generates breathing impulses, FIG. 8 (top) showing a first inspiration 154A, a first expiration 154B, a second inspiration 154C and a second expiration 154D. At the same time as the inspirations 154A, 154C are in progress, a dosing gas, e.g. NO, is supplied in brief pulses 156A-156F. Dosing gas is supplied in such a manner that the control device 150 causes the valve 148 in the dosing device 136 (FIG. 7) to open for a plurality of brief intervals at the start of each inspiration 154A, 154C. Pulsed dosing means that a relatively high concentration of NO (when NO is used) can be supplied in the pulses while the total concentration of NO is kept on a lower level (total dilution in the entire breathing gas). Transformation of NO into NO 2 is simultaneously minimized. Numerous versions of the illustrated embodiments can also be easily achieved. For example, the membrane 36 in FIG. 2 can enclose the entire tube 34, and the disk 40 can be replaced with a tube. A plurality of tubes can be used and moved in different directions to vary the size of the exposure area. The material selected for the membrane depends on the gas to be dosed. For example, Teflon is appropriate for NO. But there are numerous alternatives, since NO has a great diffusion capacity in many materials. The described embodiments can advantageously be combined with each other in different ways. Dosing gas can be dosed into virtually any kind of container, tube or the like. The membrane is made of materials selectively permeable to the dosing gas. In some instances, however, the diffusion of other gases in the "opposite direction" may be permissible. But the most important thing is for dosing gas to diffuse in the "right" direction. Even if only NO is set forth as the specific dosing gas, all medical gases could, in principle, be used. However, the dosing device according to the invention is especially suitable for applications in which the dosing gas and the receiving medium should not come into physical contact (e.g. to prevent over-dosing or to minimize chemical reactions). There are numerous applications in the medical field other than the dosing of NO, e.g. the dosing of other gaseous medication or anesthetic into a breathing gas. The container for the dosing gas does not need to be connected to a source of gas containing the dosing gas. In instances in which the dosing gas is an anesthetic gas, the anesthetic can be in the liquid state in the container, and a constant partial pressure for the anesthetic gas is maintained at the membrane by controlling the liquid anesthetic's temperature. Solid materials which emit a medical gas relatively constantly can advantageously be used as a source of gas.

Claims: A dosing device (2; 30; 50; 70; 100; 136) for controlled delivery of a first gas containing a dosing gas to a second gas in a patient ventilator system, comprising a container (16; 32; 52; 72; 108; 144) for the first gas, characterized by at least one membrane (18; 36; 52; 82, 84, 86; 106; 124, 126, 128; 142) formed of a material selectively permeable to the first gas and arranged to separate the first gas from the second gas, said membrane having an active diffusion area through which the first gas diffuses and the dosing device comprising means adapted to actively control diffusion through the membrane's (18; 36; 52; 82, 84, 86; 106; 124, 126, 128; 142) active diffusion area to achieve a desired dose of the first gas in the second gas. A dosing device according to claim 1, characterized in that means are adapted to vary the size of the membrane's (18; 36; 52; 124, 126, 128) active diffusion area to actively control diffusion. A dosing device according to claim 2, characterized in that the means comprises a barrier (16; 40; 130), impermeable to the first gas, and the barrier (16; 40; 130) and the membrane (18; 36; 124, 126, 128) are movingly arranged in relation to each other, whereby the magnitude of the membrane's (18; 36; 124, 126, 128) active diffusion area is variable. A dosing device according to claim 3, characterized in that the barrier consists of a tube (16) devised to be brought at least partially in contact with the second gas/liquid during dosing, the container is devised as a tubular cylinder (18), slidingly arranged inside the tube (16), and the membrane is devised as at least part of the exterior area of the cylinder (18), whereby the membrane's active diffusion area can be varied when the cylinder (18) is advanced out of the end of the tube (16). A dosing device according to claim 3, characterized in that the barrier is devised as a closure (40; 130) with a variable opening and arranged to cover the membrane (36; 124, 126, 128), whereby the size of the membrane's (36; 124, 126, 128) active diffusion area varies when the opening of the closure (40; 130) varies. A dosing device according to claim 1, characterized in that the means are adapted to vary the membrane's (82, 84, 86; 124, 126, 128) permeability to the first gas, thereby making diffusion actively controllable. A dosing device according to claim 6, characterized in that the means comprises a plurality of coatings (82, 84, 86; 124, 126, 128) with varying permeability to the first gas, said coatings (82, 84, 86; 124, 126, 128) being devised to form, individually or jointly, the active diffusion area. A dosing device according to claim 1, characterized in that the means comprises a valve (148), arranged at the membrane (142) in the container (144) in such a way that the valve (148), in a closed position, prevents dosing gas from coming into contact with the membrane's (142) active diffusion area and, in an open position, allows dosing gas to come into contact with the membrane's (142) active diffusion area, whereby diffusion of the dosing gas through the membrane (142) is regulated by regulating of the time the valve (148) remains in the open position. A dosing device according to any of claims 2 to 8, characterized in that a source of gas (22; 44; 60; 74), containing the first gas, is connected to the container, so a constant partial pressure can be maintained for the first gas in the container. A dosing device according to claim 1, characterized in that the means comprises a gas mixture regulator (112), connected to the container (108), said gas mixture regulator (112) being devised to regulate the partial pressure of the first gas in the container (108) in order to achieve active control of diffusion through the membrane (106).

Inventors: PSAROS GEORGIOS, PSAROS, GEORGIOS
Applicants: SIEMENS ELEMA AB, SIEMENS-ELEMA AB
Application year: 1996
Main classification: A61M16
IPC codes: A61M16