Abstract:
A nebulizer providing a moistened breathing mixture of aerosol for inhalation therapy is provided with an improved heater having a single heating element arranged in a heating housing, configured so as to support and heat the liquid in the nebulizer container and to also heat the aerosol discharged from the nebulizer so as to most efficiently utilize the heat energy and to most efficiently transfer heat energy from the heater to the aerosol. Passage of the aerosol through and accumulation in the relatively long annular accumulator that circumscribes the heater collects rain out from the aerosol and re-vaporizes the collected liquid to add further moisture to the aerosol.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to nebulizers for inhalation therapy, and more particularly concerns a nebulizer having an improved arrangement for heating both the container liquid and the aerosol produced by the nebulizer. 
     Nebulizers are commonly used for inhalation therapy to provide moist warm oxygen enriched breathing mixture to the patient. In many types of nebulizer a stream of oxygen is passed through a restrictive nozzle to increase its velocity and provide a venturi effect that sucks liquid from a container connected with a mixing chamber. The high speed stream of oxygen is mixed with ambient pressurized air and entrains water that is drawn up from the container by the low pressure of the venturi effect of the oxygen stream of high velocity. 
     The aerosol breathing mixture reaching the patient must have a temperature not less than ambient room temperature and moreover should have a significant content of water vapor. Various factors tend to lower the aerosol temperature including the relatively long path of aerosol flow through the tubing from the nebulizer to the patient and, in particular, the operation of the air water and oxygen mixing chamber, which often involves a decreased pressure due to at least the venturi action of the high speed jet. In the mixing chamber, expansion of the compressed oxygen will lower its pressure and thus effectively decrease the temperature of the resulting aerosol. 
     Many attempts have been made to heat either the aerosol or the container liquid but these have not been successful. Nebulizer heaters presently available are considered to be unsatisfactory. It is difficult to heat the aerosol directly, because the mixture, which is basically a gas, has low heat transmissivity, and thus efficiency of prior aerosol heaters has been low. Attempts to heat the aerosol by heating the water in the container before it is mixed with the air oxygen mixture also have been unsatisfactory in that it is difficult to transfer sufficient amounts of heat to the aerosol by means of heating the water. Moreover, having raised the temperature of the resulting aerosol by heating the water, the aerosol becomes more susceptible to &#34;rain out&#34;, which means that water vapor in the aerosol tends to condense into larger droplets and to fall from the aerosol into the connecting tubing. The problem of water collecting in the connecting tubing between the nebulizer and the patient is significant, not only because of the fact that the aerosol reaching the patient has less moisture, but because water collecting in the tubing could block the tubing and prevent flow of any inhalation mixture to the patient. 
     Accordingly it is an object of the present invention to provide an aerosol heater that avoids or minimizes above mentioned problems. 
     SUMMARY OF THE INVENTION 
     In carrying out principles of the present invention in accordance with a preferred embodiment thereof, a nebulizer heater is provided having a heat transfer housing that forms a heater mounting chamber having a heater therein, an accumulator and aerosol passage adjacent the chamber, and a container support adjacent the chamber. The liquid container is heated from the heater mounting chamber and aerosol from the nebulizer flows through the aerosol accululator adjacent the heater chamber before being passed on to the patient. In a particular embodiment the aerosol accumulator completely circumscribes the heater chamber, providing a relatively long large diameter passage, and thus a relatively long dwell time for transfer of heat from the heater chamber to the aerosol in the accumulator. The same heated aerosol accumulator collects rain out or water droplets precipitating from the aerosol, heats the water falling from the aerosol and evaporates it for recapture by the flowing stream of aerosol. Thus the heater of the present disclosure provides a number of functions. It provides a support for the entire nebulizer, with the container sitting directly atop the heater chamber. It heats the container liquid. It heats the aerosol over a relatively long flow path and, still further, it collects and re-vaporizes water dropping out of the aerosol. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of a nebulizer and heater embodying principles of the present invention; 
     FIG. 2 is a section taken on lines 2--2 of FIG. 1; 
     FIG. 3 is a section taken on lines 3--3 of FIG. 2; and 
     FIG. 4 is a fragmentary sectional view showing details of the coated plastic that forms structual elements of the heater housing. 
    
    
     DETAILED DESCRIPTION 
     As illustrated in FIG. 1 a nebulizer, generally indicated at 10, includes a container 12 having its lower portion resting upon and generally confined in a base type heater, generally indicated at 14. The nebulizer may be of the type shown in U.S. Pat. No. 4,629,590 to Bagwell, which describes a nebulizer sold by Cimco, assignee of the present application. The nebulizer container 12 confines a body of sterile water and includes an upper portion having secured thereto a mixer 16, which receives oxygen under pressure from an oxygen input conduit 18. By means of a mixing jet (not shown) contained within the mixer 16, liquid is drawn from the bottom of the container 12 for mixing in a mixing chamber with the pressurized oxygen and with ambient air drawn into the mixing chamber through an aperture 20 in the mixer. Thus, the mixer of the nebulizer provides a output stream, via an output fitting 22, of a moisturized mixture of air and oxygen for use in inhalation therapy. Further details of this nebulizer are shown in U.S. Pat. No. 4,629,590. 
     According to the present invention a heater assembly 14 is provided to perform a number of different functions. First, the heater assembly provides a support and a base upon which the nebulizer rests. Second, the heater assembly provides direct heat transfer to the bottom and sides of the bottom of the container 12, to directly heat water within the container. Third, the heater assembly provides an elongated aerosol accumulator of high volume and large cross sectional area for heating the aerosol provided by the nebulizer. This aerosol accumulator receives aerosol produced by the nebulizer via a connecting conduit 24, having one end connected to the nebulizer output fitting 22 and the other end connected to an input fitting 26 on the heater assembly. The aerosol accumulator within the heater assembly terminates in an output fitting 28, to which is connected an output conduit 30 that is connected to a patient breathing apparatus (not shown). 
     A fourth function of the described heater assembly is its collection of rain out from the aerosol of the nebulizer as it flows through and is temporarily stored in the aerosol passage. The heater assembly heats precipitated water droplets to revaporize the water so that it will be again entrained within the nebulizer aerosol. 
     The heater assembly comprises a heat transfer housing, illustrated in cross section in FIG. 2, having a circular top support plate 34 and a depending continuous peripheral wall 36 fixed to the outer edges of the plate 34. A second continuous peripheral wall 38, spaced from the inner wall 36 and running parallel thereto, completely encircles the inner wall 36 and is fixedly connected to the bottom of the inner wall 36 by a continuous annular bottom wall 40, fixedly secured to the bottoms of both the inner and outer walls 36 and 38. Walls 36, 38 and 40 preferably are integral with top plate 34. Fixedly connected to and extending across upper edges 42, 44 of inner and outer walls 36 and 38 is a continuous annular top wall 50, which cooperates with the sidewalls 36, 38 and bottom wall 40 to provide a sealed completely closed continuous annular aerosol passage and accumulator 52. 
     As best seen in FIG. 3 tubular input and output fittings 26, 28 are integrally formed with the circular outer wall 38 and a single baffle or partition 54 extends across the aerosol passage, from the inner wall 36 to the outer wall 38, so as to provide a continuous flow passage and temporary storage chamber. Aerosol will flow in through fitting 26, thence in a clockwise direction, as indicated by the arrows, around the aerosol accumulator passage 52, and thence outwardly through output fitting 28. Aerosol remains in the accumulator 52 because of its relatively large volume and because its cross sectional area is made larger than that of the input and output ports and conduits. 
     A relatively short rigid upstanding container support wall 58 is fixed to the outer edge of top plate 34 and to the upper edge of inner wall 36 and extends continuously around the bottom of container 12 to confine the bottom of the container within a heater recess formed by support wall 58 and top plate 34. Top plate 34 and inner wall 36 cooperatively define a downwardly facing heater mounting chamber of generally circular cylindrical form which snugly mounts a circular cylindrical and heat conductive heater housing 60 containing suitable heater elements (not shown). Heater housing 60 may be secured within the heater chamber and to the top plate 34 by means of fastener means such as for example a screw 62. Heater housing 60 includes a heater housing bottom plate 64 of circular configuration and extending along and in heat conductive contact with the full extent of bottom wall 40, to provide maximum heat flow from the heater to the bottom plate. 
     The heat transfer housing and the heater housing 60 are mounted in a heater assembly housing formed of an inter-fitting base 68 and a heater assembly housing top 70. Housing base 68, formed of a suitable rigid plastic, is of a circular configuration, having four mutually spaced and fixed internal supporting posts 74, 76, and others (not shown) projecting upwardly from a bottom 80 of the base 68. Each post has a vertically extending threaded aperture for receiving respective ones of a plurality of screws 82, 84, 86 and 88, (FIG. 3) which extend through the heater housing bottom plate 64 into the apertures in supporting posts 74, 76 etc. The assembly housing top part 70 has a central aperture 90, through which the bottom of the container 12 extends for support by the heater top support plate 34. Inner edges of the apertured top of assembly housing top 70 rest on upper edges of container support wall 58. A peripheral flange 94, outwardly extending from the assembly housing top, cooperates with a pair of oppositely positioned pivoted latches 96 (only one of which is shown) mounted on the assembly housing base 68 to detachably secure the two parts of the assembly housing to one another. A manually operable switch 100, (FIG. 1) mounted on the assembly housing base 68 is provided to control the heater elements which are connected to a suitable source of electrical power by means of an electrical lead and temperature regulating circuitry or the like (not shown), that may be mounted within assembly housing base 68 below the heater housing bottom plate 64. The top and bottom parts of the assembly housing are provided with mating semicircular recesses to form circular apertures (FIG. 3) 104, 106 through which the fittings 26 and 28 extend. 
     The entire heater assembly is supported on four legs, of which three, indicated at 110, 112, and 114 are shown, which are formed integrally with and depend from the bottom 80 of the bottom part of the heater assembly base 68. 
     Heater housing 60 and its bottom plate 64 are made of a suitable metal having high heat conductivity such as for example aluminum, whereas the heat transfer housing is made of a light weight plastic having improved heat transfer and cleaning characteristics provided by a heavy metal coating. Thus, as illustrated in FIG. 4, the heat transfer housing including top support plate 34, walls 36, 38, and 40, (but not walls 50 and 58) are formed of a plastic material 120 coated on both sides with heavy, thick coatings 122, 124 of suitable metal. Presently preferred for such coatings are combinations of electroless copper, electroless nickel and chromium, formed in layers, one upon the other and deposited upon both sides of the interposed plastic 120. By this means the plastic is provided with good heat transfer characteristics and a smooth easily cleaned surface, and the parts are still readily manufactured of inexpensive and readily formed plastic. The entire heat transfer housing is readily removable for sterilization. Walls 50, 58 are made of the same plastic as the other walls, but need not be coated with metal. 
     In operation of the device, oxygen under pressure is fed to the mixer 16 via oxygen input conduit 18 and mixed with fine water droplets or vapor derived from water contained in the container 12 to provide an aerosol discharge via fitting 22 and connecting the conduit 24. The aerosol flows from the conduit 24 through heater assembly input fitting 26 and thence in a substantially 360 degree path through the aerosol accumulator and passage 52 which closely encircles the heater chamber that contains the heater housing 60. Aerosol remains in the accumulator for a relatively increased time. Aerosol then flows through the output port 28 to connecting tubing 30. The container 12, which is resting upon heat transfer housing plate 34 and confined within the circular container support wall 58, has its contents heated by transfer of heat from the heater through the plate 34. Temperature of the aerosol is raised by using water heated in the container by the heater and also by temporarily retaining the aerosol in the accumulator adjacent the very same heater that heats the container. The flow of aerosol through and time of storage within the passage or accumulator 52 is of sufficiently long duration to enable liquid collecting in the bottom of the passage, due to rain out from the aerosol, to be heated, vaporized and recombined with the flowing aerosol. Thus the described heater is effective not only to heat the aerosol provided from the apparatus but also significantly improves its moisture content. 
     The entire apparatus is readily disassembled for cleaning and sterilization. To disassemble the apparatus, latches 96 are disengaged and the hoses are disconnected. Container 12 is removed from the heater assembly and the the assembly housing top 70 is removed from the base 68. The heat transfer housing, comprising the walls 36, 38, top support plate 34, bottom plate 40, and walls 50 and 58 are readily removed as an integral unit from the heater housing 60 which remains fixably secured to the assembly housing base 68 by means of the screws 82 through 88. The heat transfer housing may then be readily cleaned and sterilized. The chromium plated surfaces of the aerosol passage and of the heat transfer housing top plate 34 are smooth and readily cleaned and sterilized. 
     The described heater assembly is easily adapted for use with nebulizers of different types and different configurations. It is only necessary to change the configuration of the container receiving recess defined by the top support plate 34 and support wall 58, and also the size of opening 90, to enable the heater to receive, support and operate upon a nebulizer having a container of different size, shape or configuration. 
     The assembly housing provides protection for the heating unit and the heat transfer housing. It prevents heat loss and also protects the controls and electric elements from accidental spillage of water. The housing serves as an insulator and also prevents accidental contact with electrical elements within the assembly housing base. 
     As mentioned above, a significant aspect of the described construction and configuration of the heater is the fact that the aerosol accumulator or passage not only has a relatively large volume but also has a large cross sectional area. In a presently preferred embodiment the cross sectional area of the annular aerosol passage 52 is approximately twice the cross sectional area of either of the conduits 24 or 30, which are of a size normally employed in devices of this kind. The increased volume and area of the aerosol passage provides a number of advantages. The large volume causes the annular passage to act as an accumulator or reservoir so that aerosol produced by and discharged from the mixer 16 is effectively stored in the passage 52 for a period of time before it is discharged through the relatively small cross sectional area output port 28. Thus, because the formed aerosol is stored for a short period of time within the accumulator or chamber 52, there is more time for large water droplets to be precipitated from the aerosol and, importantly, there is more time for the accumulated water already precipitated in the accumulator chamber to be vaporized and re-introduced into the aerosol within the accumulator chamber. Another advantage of the relatively large cross sectional area of the accumulator 52 is the fact that it has a larger surface area to provide a much greater area of contact between its heated wall and the aerosol that is temporarily stored therein. 
     There has been described an improved nebulizer heater assembly which employs but a single heating unit to heat both the liquid in the nebulizer container and the aerosol produced by the nebulizer, while at the same time collecting rain out from the produced aerosol and reintroducing the collected rain out as water vapor into the aerosol.