RESPIRATORY MASK AND METHOD FOR ITS MANUFACTURE

Abstract: A method for making respiratory masks comprises contactless determination of the topography of a facial area and shaping material for the mask based on the topography. Also disclosed is a corresponding mask, means for its production, and a database for storing patient topography data obtained by the method.

Description: RESPIRATORY MASK AND METHOD FOR ITS MANUFACTURE FIELD OF THE INVENTION The present invention relates to a method for making respiratory masks, means for use in the method, a corresponding mask, and database for storing data useful in the method and how to use the database. BACKGROUND OF THE INVENTION An important feature of respiratory masks for medical and other applications is their fit. It should be of a kind to make a mask effectively seal against the face of the user when covering the nose and/or mouth. Most often respiratory masks known in the art are manufactured in a number of standard sizes to provide an average fit for the respective group of 'users. A better fit is obtained by forming the mask according to the geometry of the user's face. This may be achieved by directly applying a moldable plastic material to the user' s face and hardening it, either in place or after careful removal. The raw mask may be provided with one or several openings to which conduits are connected for providing the breathing gas and leading away the exhaled air. The mask may also be provided with sealing means, such as a rim of rubber foam, to make it seal at its periphery against the face, and with means for holding it in place. This method may be termed ^direct' molding. Another method consists in making a negative mould of the facial area in question with a suitable material, such as gypsum, which then is used for making a second, positive mould truly reproducing the facial area. The positive mould is used as a form for making a raw mask corresponding to the aforementioned one directly taken from the user, the advantage residing in the lack of time and other constraints, such as the toxicity of certain constituents of the pre-polymers used for making the raw mask, when working with a positive mould. This method may be termed x indirect' molding. A major drawback of indirect molding method is its complexity, and thus considerable cost. Both methods require the person taking the mold of the patient's face to be well skilled in the technique. It is important, for instance, not to apply excessive pressure when applying the mould. This would deform the face and result in a mask not fitting well. Neither of these methods is suited for the industrial production of individually adapted facial masks. The present invention seeks to overcome this important problem. OBJECTS OF THE INVENTION It is an object of the invention to provide a method for making respiratory masks individually fitted to the bearer. It is another object of the invention to provide a means for carrying out the process. It is further object of the invention to provide a corresponding mask. Still another object of the invention is to provide a database comprising data which is used when carrying out the process. Further objects of the invention will become evident from the following description of the invention and preferred embodiments thereof, and of the appended claims. SUMMARY OF THE INVENTION In accordance with the present invention a method of the aforementioned kind comprises the contact-less determination of the topography of a person' s facial area, in particular by optical means, most preferably by laser mean. The topography data (in form of a large number of space points characterized by, for instance, their Cartesian (x,y,z) coordinates thus obtained is storable in a suitable electronic storage medium, such as a hard disc of a computer. The contact-less determination of the topography avoids the face being deformed by excessive pressure. This provides for a perfect fit. In the case of a nasal mask, it is most important to obtain a perfect fit to the nose. Therefore the contact-less determination of the topography of the nose itself is central to the invention. Methods for contact-less determination of topography are known in the art; see, for instance: U.S. Patent No. 3,927,948 (Cox et al.); U.S. Patent No. 5,110,203 (MacCabee); U.S. Patent No. 5,114,226 (Godwin et al . ) ; U.S. Patent No. 4,854,698 (Schmidt). The mask can be produced by suitable ablation machinery, such as an automatic milling cutter known in the art provided with a unit controlled by a microprocessor or similar using suitable software and said topography data. Suitably the mask is produced from a molded blank having roughly the form of the desired product. Suitable polymer materials include polypropene, polystyrene, polycarbonate, poly (methyl methacrylate) and melamine formaldehyde copolymers. Since the outside of the mask is not critical for a good fit, it can be retained from the blank. Only the blank's inside needs to be ablated. The mask milled to the desired form is provided with one or several through bores to which conduits for transport of gas to be inhaled and exhaled gas are connected, for instance by gluing, welding, snap locking means. It is equally possible to provide the blank with the through bores and, possibly, also the conduits prior to the ablation of the material to obtain the desired topography. The mask is also provided with a means for holding it in place, such as one or several straps. According to a particularly preferred aspect of the invention, the topography data is used for making a replica of the user' s facial area intended to be covered by the mask, in particular the lower part of the nose and the areas extending in its immediate vicinity laterally and downwardly. The replica is made by, for instance, the aforementioned milling technique using one of the indicated polymers or another suitable polymer, in particular rigid polyurethane foam. By reason of the replica only being a mould for the final product, materials not certified for medical use but having desirable physical properties can be used advantageously. The replica is preferably provided with a platform for air/gas connections, such as a cube or a rectangular parallelepiped the planar surfaces of which (as planar surfaces in general) are particularly suited for attaching said connections. The replica then is used for making the very mask by applying a proper amount of thermoplastic material, such as polypropylene, in se i- liquid form at an appropriate temperature to the replica, cooling it, and removing it for finishing. It is important to use as a replica material one which is not easily deformed at the temperature at which the semi-solid thermoplastic material is applied. In particular, it is preferred that the glass point of a polymer material used for making the replica is higher by at least 20°C than the glass point of a polymer material used to make the mask from a replica made in the polymer material of the replica. It is preferred to carry out the application of the thermoplastic material by vacuum molding (vacuum thermoforming) . What is said above about the outside of the blank is also pertinent to this preferred aspect of the invention. Thereby it is possible to produce more than one mask for a given patient. According to another important preferred aspect of the invention the determination of the topography is carried out at one site, in particular at a health care unit, such as a clinic or a physician's office, the topography data thus obtained then being transferred to a production site housing the automatic milling cutter and other machinery. Transfer of data from one site to the other suitably is effected by electronic means, such as via the Internet or a telephone modem. Thereby it is possible to organize patient data acquisition and mask production in a most economical manner. According to the invention is also disclosed a respiratory mask manufactured by a process comprising contact-less determination of the topography of a person's facial area, in particular by optical means, most preferably laser means. An important advantage of the mask is its small size and weight due to its inherently good fit which allows omission of separate sealing means, if so desired. The simple design provides for easy cleaning and, if needed, sterilization. If an additional circumferential (partial or complete) seal is applied to the inside of the mask according to the invention, it need only be a comparatively thin one. A preferred material for such a seal is soft polyurethane foam. According to the invention a database is established containing facial topographical data acquired by contactless measurement, in particular by optical measurement such as one using laser means. Preferably the data in the database are in Cartesian coordinate or position vector format. One advantage with storing the patient data in a database is their accessibility for production of additional masks at a later time. To store data rather than the physical items produced by reference to them, such as individual moulds, is advantageous from a cost standpoint, the logistics for storing and retrieving a single mould from a large number of moulds being economically disadvantageous. The properties of mould materials - and thus of moulds - may deteriorate during storage whereas data quality will not. According to the invention are also disclosed means for production of a facial respiratory mask comprising optical means for the determination of the topography of a facial area intended for abutment of the mask. The production means may further comprise automated milling machinery controlled by data obtained through the determination of topography. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail by reference to a preferred but not limiting embodiment illustrated in drawings in which Fig. 1 is a rough sketch of a first embodiment of the respiratory mask according to the invention provided with through bores for mounting of gas conduits, in a perspective view; Fig. 2 the mask of Fig. 1, with the conduits mounted and in the same direction of view; Fig. 3 the mask of Figs. 1 and 2 in a mounted position, in a sagittal section and with its abutment area indicated; Fig. 4 a nose area replica for a second embodiment of the respiratory mask according to the invention, in a perspective view; Fig. 5 the respiratory mask made by use of the replica of Fig. 1, in about the same perspective view as that of Fig. 4; Fig. 6 the mask of Fig. 5, in a side view; Fig. 7 the mask of Figs. 5 and 6, in a view corresponding to that of Fig. 3, in section A-A perpendicular to the support (Fig. 4); Fig. 8 a third preferred embodiment of the respiratory mask according to the invention with a removable tube fitting portion, in a side view corresponding to the view of Fig. 6; Fig. 9 the mask of Fig. 8, in a sectional view corresponding to that of Fig. 7; Fig. 10 a schematic block drawing of a preferred embodiment of the method according to the invention. DESCRIPTION OF PREFERRED EMBODIMENTS A respiratory nose mask according to invention shown in Figs. 1-3 is shown without securing straps for reason of clarity. Means other than straps may, of course, be used to keep it in place. The mask consists of a polycarbonate body comprising a central portion 1 centered in respect of the bridge 4 of the nose and lateral left 2 and right 3 wings. A section through the central portion 1 is shown in Fig. 3. It will be noted that the mask abuts the about two thirds of the bridge from the nose tip 5 upwards and extends downwardly from the nose tip to a point close to the upper lip 6 to which it also abuts. The mask does however not abut against the nasal septum 7, thereby leaving a space 8 providing communication between the nostrils. Laterally wings 2 and 3 extend to about the respective zygomatic bone. The area of abutment is indicated in Fig. 3 by λ 9' . Through bores 10 (only one shown) communicate with space 8. In Fig. 2 short rigid tubes 11, 12 serving as conduits for breathing air and exhaled air are shown mounted in the bores 10. In use the tubes 11, 12 are connected to respective flexible tubes for gas transport. The straps fastened at the wings 2, 3 for holding the mask in place are not shown. The mask according to the invention is made in the following way. The topography of the nasal and adjacent regions of a patient is determined by contact-less laser measurement of a number of points of the area of interest The point data is stored in x,y,z format in respect to a pre-selected point of origin (x,y, z = 0) disposed on the nasal bridge. The data is transferred to the manufacturing site, for instance by e-mail. Either at the measuring site or the production site the data is converted to CAM-format for control of a precision milling machine for the production of a replica of the portion of the face to which the mask shall be applied. The data for the air (gas) connection platform are also comprised by the CAM-program. The (copying) program has been modified to restrict ablation in front of the nasal septum and the nostrils, thereby providing for the later formation of space 8. Stiff polyurethane foam was used as replica material. The finished replica is mounted in a vacuum molding apparatus in which the desired number of masks can be produced by vacuum molding of a medium MW range polypropylene. The mask is provided with a pair of symmetrically disposed through bores 10 into which tubes 11, 12 of high MW polypropylene are fixed by welding. Their free ends are provided with fittings for easy coupling of flexible polyvinyl chloride tubes (not shown) . The mask is also provided with holding straps (not shown) . Alternatively the air (gas) tube 11, 12 may be used for fixation of the mask to the patient. The second embodiment of the respiratory mask according to the invention shown in Figs. 5-7 has a single straight air (gas) conduit tube 16 with two open ends. It is integrated in the mask at the mask's air (gas) connection platform portion 17 which is a section of the mask formed by the platform 15 of rectangular parallelepipedal shape pertaining to the replica of Fig. 4. The space underneath the platform portion 17 communicates (at 22) with a central portion of conduit tube 16 where part of its wall has been removed (Fig. 7) . This space underneath the platform portion 17 positioned beneath the nose tip portion 23 communicates also with the nostrils of the patient by being disposed in front (downwardly) thereof when the mask is placed on the intended facial area of the patient for which it is designed. Fig. 7 wherein the mask is shown in sagittal section also illustrates the disposition of the upper lip portion 19 and the nose bridge portion 20. In Fig. 6 which is a left side view of the mask is also indicated its lateral left wing 21. The replica 14 (Fig. 4) is mounted on a rectangular support 13 by gluing. It was actually the replica blank that had been mounted on the support 13 on which it was worked by milling according to CAM-instructions . The blank had the form of a cube abutting and glued to the support 13 with its one base. Also indicated is the nose tip portion 18. The replica need not have the lateral extension of the corresponding respiratory mask since it is primarily the nose and areas in the immediate vicinity of the nose which are critical for a good fit. Preferably though, the support 13 and the replica 14 are made from one piece of material in the milling machine. The further preferred embodiment of the mask according to the invention shown in Figs. 8 and 9 differs from that of Figs. 4-7 by a separate portion 60 for fixation of flexible tubes for gas transport. Portion 60 is fastened at the main body of the mask by a snap connection 61. The lumen of the fittings for the flexible tubes is designated 62. This embodiment is advantageous from a manufacturing standpoint as well from considerations of hygiene since the disassembled mask is easier to clean than one with an integrated tube fixation portion. The tube fixation portion 60 and the snap connection 61 can be made to a standard size for use with different masks. A particularly preferred embodiment of the method of the invention is illustrated in Fig. 10 in form of a schematic block diagram. The topography of the nasal and adjacent regions of a patient 25 is determined by contact-less laser measurement at a Contour Determination Site (CDS) such as, for instance, at a specialist physician's office. With the patient in a supine position the area of interest is scanned by a laser distance determination probe, such as a PreciMeter® Model CD12030-PH sensor 24 (Preci eter AB, Gδteborg, Sweden) , mounted on a rod assembly (not shown) on which it can be displaced in x, y-increments by two stepped electric motors, respectively, in a plane above the patient's face about parallel to the plane on which the patient rests with his back. Only the motor 69 displacing the sensor 24 in an x-direction is shown in Fig. 10. The contour measurement is based on the principle of laser triangulation. The object to be measured is exposed to a narrow laser beam 26. Some of the light is reflected as 27 (only one reflection shown) . The reflected light is optically focussed on a two dimensional light sensitive device, a CCD (Charge Coupled Device) there producing a video signal. Changes in distance from sensor to object result in displacement of the focus of reflected light along the CCD surface thereby changing the signal which is processed and digitally transmitted through a cable for recording to a personal computer 28. By use of appropriate software the computer 28 also controls the displacement of the sensor 24 by controlling the voltage fed to the stepper motors 69. At the end of a contour measurement session the contour data temporarily stored in the computer 28 is transferred from the CDS site to a Mask Production Site (MPS) situated at substantial distance A from the CDS site, such as typically one kilometer or more. The data can be transferred via a modem pertaining to the PC and a telephone line 29, by Internet, or even wireless. At the MPS site the data is fed into a database 30 and stored for an indefinite time period. When the manufacture of a mask is desired the data is located in the database 30 by a conversion routine and transformed in a CAM microprocessor 31. Via a serial interface the resulting ISO code is fed to an automated milling machine 36. Hard polyurethane foam blanks 33 are fed one-by-one to the milling machine 32 via a conveyor belt 34 from where they are removed by a pick- and-place robot 35 for proper disposal in the milling machine 32. In accordance with the CAD-instructions the blank 33 is ablated by a cutter 37 displaceable in x,y,z- direction to form contours 38, thereby producing a replica 39 of the nose and adjacent areas of the patient 25. The replica 39 is transported on a conveyor 40 to a vacuum molding machine 41. Mask body blanks in form of transparent polycarbonate discs 42 are fed on a conveyor 43 to a heating station 44 in which they are consecutively heated to a temperature sufficient for vacuum molding. From there the hot blanks 45 are fed to the vacuum molding machine 41. One hot blank 45 is placed over the replica 39 at a time. By application of vacuum from a vacuum pump 67 adduced by a vacuum line 68 provided with valve means the hot blank 45 is vacuum molded to the replica 39 forming a raw mask body 46. Upon cooling the raw mask body 46 is lifted off the replica 39 and transported to a machining station 48 via a connecting section 47. Then a second mask body may be produced by use of the same replica 39 from a new hot blank 45, and so on. When the desired number of raw mask bodies 46 have been produced the replica 64 is removed by a pick- and-place robot 65 and placed on a conveyor 66 transporting it to a polyurethane recovery station (not shown) . In the machining station 48 the raw mask body 46 is provided with bores 54,55 for nipples by stationary drills 51,52 with telescoping bits 50,52. At its circumference the raw mask body 46 is trimmed along line 58 to the desired shape by a small cutter 56 displaceably disposed in x, y-direction in a plane above the raw mask body 46. The finished mask body 61 is removed from the machining station by a pick-an-place robot 57 to be placed on a conveyor 62 for transport to an assembly & packaging station 63 where the bores 54,55 are manually provided with nipples for connection of flexible gas tubes, and packed for distribution. The portion 59 cut off from the raw mask body 46 is carried to polycarbonate recovery station (not shown) by a conveyor 60. Any work piece of the method of the invention retains its particular identity through the entire process of manufacture by the process being fully controlled by data from the database 30. For each mask body 61 arriving at the packaging station 63 an identification label is printed by a label printer (not shown) to be affixed to the mask or the box in which it is packed. Thereby the patient is guaranteed to receive his/her own mask. Except for photographic methods, any suitable contact-less method of contour determination can be used in the method of the invention instead of the laser based measurement described in the foregoing. While photographic methods, in principle, might also provide useful topographic information, their application is cumbersome and is not preferred. A further embodiment of the invention comprises the aforementioned method for contact-less determination of the topography a patient's facial area and selection of a mask most closely corresponding to the patient's topography data from a given set of standard masks, such as a set of about 5 masks or more, in particular a set of about 10 masks and more. While only a few embodiments for a nasal respiratory mask and a method for its manufacture have been described the person skilled in the art will have no difficulty in applying the technology masks covering the mouth or the mouth and nose in combination.

Claims: C l a i m s 1. A method for making respiratory masks, comprising making a contact-less determination of the topography of a facial area, shaping material for the mask based on the topography. 2. The method of claim 1, wherein said determination comprises the use of optical means. 3. The method of claim 2, wherein the optical means comprise laser means. 4. The method of any of claim 1, wherein the topography is determined for a number of selected points. 5. The method of claim 4, wherein the data for each point is obtained in form of Cartesian coordinates or position vectors. 6. The method of claim 5, wherein the point data is stored in a medium for electronic storage. 7. The method of claim 4, wherein the point data is transferred from a topography measurement site where the determination is made to a mask production site where the material is shaped. 8. The method of claim 7, wherein the shaping comprises producing a mask body of the topography by computer controlled ablation of a polymer material. 9. The method of claim 8, comprising producing the mask body with through bores at which means for coupling of flexible gas tubes are mountable. 10. The method of claim 7, wherein the shaping comprises producing a replica of the topography by computer controlled ablation of a polymer material. 11. The method of claim 10, wherein the shaping comprises producing a mask body from the replica. 12. The method of claim 11, wherein the glass point of a polymer material used to make the replica is higher by at least 20°C than the glass point a polymer material used to make the mask from a replica made in said polymer material. 13. The method of claim 1 or 2, wherein the optical means comprise photometric means. 14. A respiratory mask manufactured by a process comprising contact-less determination of the topography of a portion of a person's facial area. 15. The respiratory mask of claim 14, wherein the contact-less means comprise optical means selected from the group consisting of laser means and photometric means. 16. A respiratory mask produced by use of a nose area replica mechanically shaped by use of predetermined data for an air (gas) connection platform combined with nose area topographical data. 17. A method for making respiratory masks comprising the use of a database containing facial topographical data acquired by contact-less determination. 18. The method of claim 17, wherein the determination is by an optical method selected from laser means and photometric means. 19. The method of claim 17, comprising acquisition of data for an air (gas) connection platform separately from said contact-less determination. 20. The method of any of claims 17-19, wherein the data is in Cartesian coordinate or position vector format. 21. Means for production of a facial respiratory mask comprising contact-less means for the determination of the topography of a facial area intended for abutment of the mask. 22. The means of claim 21, comprising optical means selected from laser means and photometric means. 23. The means of claim 21 or 22, further comprising automated milling machinery controlled by data obtained through said determination of topography and data obtained or selected independently thereof. 24. A database containing facial topographical data acquired by contact-less determination intended for use in making respiratory masks. 25. The database of claim 24, wherein determination comprises the use of laser means. 26. A respiratory mask made by use of the database of claim 24 or 25. 27. A standard set of masks produced according the method of any of claims 1-13.

Inventors: EKLUND OVE, EKLUND, OVE
Applicants: BREAS MEDICAL AB, EKLUND OVE, EKLUND, OVE
Application year: 2000
Main classification: A61M16
IPC codes: A61M16, A62B18