Abstract:
The present invention relates generally to a nebulizer, and more particularly but not exclusively to a compact nebulizer that efficiently utilizes medication.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority of U.S. Provisional Applications Nos. 60/891,892 filed on Feb. 27, 2007 and 60/999,755 filed on Aug. 9, 2007, the entire contents of which application are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to a nebulizer, and more particularly but not exclusively to a compact nebulizer that efficiently utilizes medication. 
       BACKGROUND OF THE INVENTION 
       [0003]    The deposition efficiency in the tracheobronchial (TB) and pulmonary regions is highly dependent on particle size. Particle sizes in the range of about 1 to 5 μm, as well as the size range extending from approximately 0.005 to 0.5 μm, have a relatively high rate of deposition within the aforementioned regions. (See William Hinds, Aerosol Technology, p 241 (1999).) Various methods have typically been used to generate these therapeutic fine particles, such as air-blast nebulizers (i.e., compressed air, jet, or venturi nebulizer), pressure nebulizers, ultrasonic nebulizers, a vibrating orifice, a spinning disk, condensation devices, and inkjet technology-based nebulizers. However, despite the variety of methods used to generate therapeutic fine particles, problems remain such as wasted medication that is not dispensed and the swallowing of liquid medication by the user. Currently available nebulizers typically have residual (i.e., waste) medication of 50% or more. This waste is largely due to the fact that existing nebulizers will generate and disperse large and small particles. The large particle dispersion is not well controlled and leads to residual medication in the nebulizer and associated apparatus. Additionally, some nebulizers are relatively bulky, which unfortunately provides considerable surface area for medication deposition within the device which in turn leads to wasted unused medication. Thus, it would be an advance in the state of nebulizer art to more efficiently dispense and utilize liquid medication to reduce waste and increase patient compliance, and to protect the user of the nebulizer from swallowing liquid medication. 
       SUMMARY OF THE INVENTION 
       [0004]    In one of its aspects, the present invention provides a nebulizer comprising an impactor having a curved surface and a nozzle oriented so that outflow from the nozzle engages the curved surface. The nebulizer incorporates a nebulizer tube, which may comprise a single-piece, and that may include a convergent-divergent air mixing nozzle, as well as an integral feed channel for siphoning medication. The nebulizer tube independently provides a first-level (i.e., relatively coarse) nebulization. To obtain the fine particles desired for nebulizers, the output stream from the nebulizer tube is directed towards an impactor having a curved surface at, or proximate, the impact site. When the flow strikes the impactor, very fine particles are generated. The curvature of the impactor promotes two very desirable effects. First, the portion of the flow that is not atomized into very fine particles will drain down the impactor and return to a medication reservoir disposed under the impactor, creating a “waterfall” recycling effect. Second, the impactor curvature also helps to direct the nebulized medication in a preferred direction, in this case toward the user&#39;s mouth. 
         [0005]    In another of its aspects, the present invention also reduces the risk to the user associated with the inadvertent swallowing of unacceptably large quantities of liquid medication present in the nebulizer&#39;s reservoir. This could occur if the patient were to tilt his or her head too far back. To substantially reduce this risk, a semi-permeable membrane or other suitable material that is permeable to mist but sufficiently impermeable to liquid may be deployed to allow delivery of the nebulized mist to the user but prevent the flow of bulk liquid medication. 
         [0006]    The present invention also provides in one of its aspects a reduction in the necessary treatment time through the generation of a dense mist of particles, in part because the particles are in the correct size range for effective deposition in the desired TB or pulmonary regions. The relatively higher density of nebulized particles may be created with the use of multiple jet impactors. Within a single nebulizer assembly, two, three, or more, high velocity jets of liquid-carrying gas may be directed at an impactor surface, creating a relatively higher density of fine droplets. Thus, the patient can inhale the full dose of medicine in a shorter time from which three benefits follow: more rapid treatment in critical situations, a financial benefit for the clinical setting (i.e., less time required from medical staff), and higher patient compliance in the home setting. 
         [0007]    In these regards, the present invention provides a nebulizer for delivering a mist of liquid, comprising a housing and a reservoir disposed internally to the housing for containing liquid to be nebulized by the nebulizer. The nebulizer may include a monolithic nebulizer tube which has a gas channel having a first end for receiving a gas, such as compressed gas, and a second end for expelling the compressed gas and/or liquid. The gas channel may extend from a first end to a second end of the nebulizer tube. The monolithic nebulizer tube may also include a liquid feed channel comprising a first end in fluid communication with the reservoir for receiving liquid from the reservoir. Depending on the application the liquid may desirably be a liquid medication. The feed channel may include a second end in fluid communication with the gas channel. Alternatively, the feed channel may have an annular passageway at a second end of the feed channel with the annular passageway disposed about the second gas channel end. Application of compressed gas to the first end of the gas channel creates a siphon in the liquid feed channel to draw liquid into the feed channel and to expel the liquid and compressed gas from the second end of the nebulizer tube. To direct the flow of nebulized mist to an exit port of the nebulizer, a tortuous passageway may be provided between the second end of the gas channel and an exit port of the nebulizer. The tortuous passageway may be configured to remove nebulized particles larger than a selected therapeutic size from the flow of nebulized mist. 
         [0008]    The nebulizer may further include an impactor disposed proximate the second end of the gas channel to nebulize the expelled liquid when the expelled liquid strikes the impactor. The impactor may be disposed sufficiently close the second end of the gas channel to assist in nebulizing the liquid expelled from the second end of the gas channel. The impactor may comprises a spherical, cylindrical, or mesa-like shape, or may include a ring disposed around the mesa to provide an annular channel between the ring and the mesa. The annular channel may be dimensioned to provide a fundamental resonant frequency of the annular channel tuned to generate particles of a preferred size. 
         [0009]    In another configuration, the present invention provides a nebulizer for delivering a mist of liquid, comprising a housing having an inlet port for receiving compressed gas, such as compressed air for example, and an exit port for delivering a mist of nebulized liquid. A reservoir is disposed internally to the housing for containing liquid to be nebulized by the nebulizer. The nebulizer also includes a nebulizer tube in fluid communication with the liquid having an outlet from which the nebulized mist is provided. The outlet end of the nebulizer tube is disposed internally to the housing. The nebulizer also includes a tortuous passageway disposed within the housing between outlet end of the nebulizer tube and the exit port of the nebulizer for directing the flow of nebulized mist therethrough to the exit port. 
         [0010]    In yet another configuration, the present invention provides a nebulizer for delivering a mist of liquid, comprising a two-piece housing having separate first and second housing portions, and a reservoir monolithic to the housing for containing liquid to be nebulized by the nebulizer. The nebulizer includes a nebulizer tube monolithic to the housing. The nebulizer tube includes a gas channel having a first end for receiving a gas, such as compressed air for example, and a second for expelling compressed gas and liquid. The gas channel extends from the first end to a second end of the nebulizer tube. The nebulizer tube also includes a liquid feed channel comprising a first end in fluid communication with the reservoir for receiving liquid from the reservoir and comprising a second end in fluid communication with the gas channel. Application of compressed gas to the first end of the gas channel creates a siphon in the liquid feed channel to draw liquid into the feed channel and to expel the liquid along with compressed gas from the second end of the nebulizer tube. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which: 
           [0012]      FIG. 1  schematically illustrates a perspective view of a first exemplary nebulizer of the present invention; 
           [0013]      FIG. 2  schematically illustrates the nebulizer of  FIG. 1 , but without the semi-permeable membrane in place; 
           [0014]      FIG. 3  schematically illustrates a cross-sectional view of the nebulizer of  FIG. 2  taken along the sectioning line  3 - 3 ; 
           [0015]      FIGS. 4A and 4B  schematically illustrate perspective views of exemplary configurations of the lower housing of a nebulizer; 
           [0016]      FIGS. 5A and 5B  schematically illustrate perspective views of exemplary configurations of the lower housing of a nebulizer of the present invention having an enlarged region for receiving liquid medication; 
           [0017]      FIGS. 6 ,  7 A, and  7 B schematically illustrate perspective views of exemplary configurations of the upper housing of the nebulizer of the present invention; 
           [0018]      FIG. 8  schematically illustrates a cross-sectional view of a nebulizer similar to that depicted in  FIG. 3 , but including the lower housing of  FIG. 4B  and the upper housing of  FIG. 7A ; 
           [0019]      FIG. 9  schematically illustrates the cross-sectional view of the nebulizer of  FIG. 3  with the lower housing removed and with the upper housing rotated to show the internal cavity facing upward; 
           [0020]      FIG. 10  schematically illustrates the perspective view of the nebulizer of  FIG. 2  with the lower housing removed and with the upper housing rotated to show the internal cavity facing upward; 
           [0021]      FIGS. 11 and 12  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  12 - 12 , respectively, of a nebulizer tube of the present invention; 
           [0022]      FIG. 13  schematically illustrates a perspective view of a second exemplary nebulizer of the present invention; 
           [0023]      FIG. 14  schematically illustrates a cross-sectional view of the nebulizer of  FIG. 13  taken along the sectioning line  14 - 14 ; 
           [0024]      FIG. 15  schematically illustrates a perspective view of the lower housing of the nebulizer of  FIG. 13 ; 
           [0025]      FIG. 16  schematically illustrates a perspective view of the lower housing of the nebulizer of  FIG. 13  with the nebulizer tube in place; 
           [0026]      FIG. 17  schematically illustrates the nebulizer tube of  FIG. 13  having a key for insertion in the upper housing; 
           [0027]      FIG. 18  schematically illustrates a perspective view of the upper housing of the nebulizer of  FIG. 13  having a keyway for receiving the key of the nebulizer tube; 
           [0028]      FIG. 19  schematically illustrates a perspective view of the upper housing of the nebulizer of  FIG. 13  with the nebulizer tube in place with the key of the nebulizer tube disposed in the keyway of the upper housing; 
           [0029]      FIGS. 20A and 20B  schematically illustrate perspective views of a liquid fill cap; 
           [0030]      FIGS. 21A and 21B  schematically illustrate alternative airfoil shapes for the impactor; 
           [0031]      FIG. 22  schematically illustrates a perspective view of a third exemplary nebulizer of the present invention; 
           [0032]      FIG. 23  schematically illustrates a cross-sectional view of the nebulizer of  FIG. 22  taken along the sectioning line  23 - 23 ; 
           [0033]      FIG. 24  schematically illustrates a perspective view of the lower housing of the nebulizer of  FIG. 22 ; 
           [0034]      FIGS. 25 ,  26 , and  27  schematically illustrate perspective views of the upper housing of the nebulizer of  FIG. 22 ; 
           [0035]      FIG. 28  schematically illustrates a cross-sectional view of the upper housing of  FIG. 26  taken along the sectioning line  28 - 28 , having a three-channel nebulizer tube in place of the single channel nebulizer tube of  FIG. 22 ; 
           [0036]      FIG. 29  schematically illustrates a cross-sectional view of the upper housing of the nebulizer of  FIG. 26  taken along the sectioning line  29 - 29 ; 
           [0037]      FIGS. 30 and 31  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  31 - 31 , respectively, of a nebulizer tube of the present invention having three outlet channels; 
           [0038]      FIGS. 32 and 33  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  33 - 33 , respectively, of a nebulizer tube of the present invention having two outlet channels; 
           [0039]      FIGS. 34 and 35  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  35 - 35 , respectively, of a nebulizer tube of the present invention having one outlet channel; 
           [0040]      FIG. 36  schematically illustrates a perspective view of a lower housing, similar to the housing shown in  FIG. 24 , but having make-up air curtain walls; 
           [0041]      FIG. 37  schematically illustrates a perspective view of an upper housing, similar to the housing shown in  FIG. 25 , but having make-up air curtain walls; 
           [0042]      FIG. 38  schematically illustrates a perspective view of a fourth exemplary nebulizer of the present invention having two parts with an monolithically integrated nebulizer tube; 
           [0043]      FIG. 39  schematically illustrates a perspective view of the nebulizer of  FIG. 38  with the lid open; 
           [0044]      FIG. 40  schematically illustrates a perspective view of the nebulizer similar to that shown in  FIG. 39  but having a two channel nebulizer tube; 
           [0045]      FIG. 41  schematically illustrates a cross-sectional view taken along the sectioning line  41 - 41  of the nebulizer of  FIG. 38 ; 
           [0046]      FIG. 42  schematically illustrates a cross-sectional view taken along the sectioning line  42 - 42  of the nebulizer of  FIG. 38 ; 
           [0047]      FIG. 43  schematically illustrates a perspective view of the upper housing of the nebulizer of  FIG. 38 ; 
           [0048]      FIG. 44  schematically illustrates a cross-sectional view of the upper housing taken along the sectioning line  44 - 44  of  FIG. 43  with the top cut away; 
           [0049]      FIG. 45  schematically illustrates a perspective view of the lower housing of the nebulizer of  FIG. 38 ; 
           [0050]      FIG. 46  schematically illustrates a cross-sectional view taken along the sectioning line  46 - 46  of the lower housing of  FIG. 45 ; 
           [0051]      FIGS. 47 and 48  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  48 - 48 , respectively, of a nebulizer tube of the present invention having an annular medication delivery port; 
           [0052]      FIGS. 49 and 50  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  50 - 50 , respectively, of an upper housing having a spherical impactor; 
           [0053]      FIG. 51  schematically illustrates a fragmentary cross-sectional view of the upper housing of  FIG. 49  and a lower housing assembled with the nebulizer tube of  FIG. 47  disposed therein; 
           [0054]      FIGS. 52 and 53  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  53 - 53 , respectively, of an upper housing having a cylindrical impactor; 
           [0055]      FIGS. 54 and 55  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  55 - 55 , respectively, of an upper housing having a mesa-shaped impactor; and 
           [0056]      FIGS. 56 and 57  schematically illustrate a perspective and cross-sectional view taken along the sectioning line  57 - 57 , respectively, of an upper housing having a mesa-shaped impactor with a ring disposed about the mesa to provide a resonant annular channel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0057]    Referring now to the figures, wherein like elements are numbered alike throughout,  FIGS. 1 and 2  illustrate an external view of a first configuration of a nebulizer  100  of the present invention. The nebulizer  100  comprises a nebulizer tube  1  disposed within a housing  40  for receiving compressed gas, such as compressed air or nitrogen, for example, and an exit port  10  for delivering a nebulized mist to a user. The housing  40  may comprise an upper housing  2  and a lower housing  3 , which may be registered to one another by cooperation between holes  12  of the lower housing  3  and alignment posts  16  of the upper housing  2 ,  FIGS. 4A ,  6 . The upper housing  2  may include a fill port  30  for introducing a liquid medication into the housing  40 . The fill port  30  may be shaped to readily accept the shape of standard medicine containers, which will facilitate filling of the nebulizer  100  with the correct amount of medication and reduce the possibility of spillage and waste. The fill port  30  may remain open and may also serve as an exit for nebulized liquid, or the fill port  30  may optionally include a separate funnel or duckbill-shaped cap  31  for insertion into the upper housing  2  to direct the liquid medication into the housing  40 ,  FIGS. 1 ,  3 ,  20 A,  20 B. The cap may be located inside the main body of the nebulizer to deter the cap from inadvertently coming loose and being swallowed by the user. Alternatively, the fill port cap  230  may be provided as an integral portion of the upper housing  202 ,  FIGS. 13 ,  14 . The cap  31 ,  230  may be configured so that it deflects to permit liquid to be poured into the nebulizer when a small force applied. For example, the cap  31 ,  230  may deflect when a syringe is inserted for delivering liquid and may close again after the syringe is removed, or the cap  331  may be molded as part of the upper housing  302  and connected thereto via a living hinge  335 ,  FIGS. 22 and 23 . Moreover, the cap  31  may be provided in the form of a one-way duck-bill valve that permits the entry of liquid medication but deters the flow of nebulized mist therethrough. 
         [0058]    To receive a liquid, such as medication, introduced through the fill port  30 , the lower housing  3  includes a reservoir  7  which may include a cylindrical sidewall  33  for containing the liquid medication within a localized region within the lower housing  3 . (While any suitable liquid may be provided in the reservoir, for illustration purposes the devices of the present application are described herein as containing a medication.) 
         [0059]    The reservoir  7  may be dimensioned to hold at least 3 ml of liquid medication, for example. In addition, to further contain the location of the liquid medication, the reservoir  7  may include a hemispherical or other suitably shaped depression  34  into which the liquid medication may pool. Maintaining the liquid medication in a specified location assists in making the medication available to the nebulizer tube  1 , and thus aids in efficient use of the medication. 
         [0060]    The reservoir  7  may include shapes other than cylindrical. For example, the reservoir  7 ″ may have a generally rectangular shape being bounded at the inlet and outlet end of the lower housing  3 ″ by front and rear reservoir walls  13   a ,  13   b ,  FIG. 5A . The reservoir walls  13   a ,  13   b  may be straight, curved  13   a ′, or assume any other suitable shape,  FIGS. 5B ,  16 . In addition, in the event that liquid medication overflows the wall  33 ′ of the reservoir  7 ′, an overflow wall  13  may optionally be provided at the exit port  10  to help deter introduction of liquid medication into the user&#39;s mouth,  FIG. 4B . Furthermore, one or more semi-permeable membranes  4  may be provided at the exit port  10  of the nebulizer  100  to permit mist flow while acting as an effective liquid barrier, thus creating a safety feature that prevents a user from swallowing liquid medication contained in the nebulizer  100 . In one configuration the semi-permeable membranes  4  may be used instead of the front reservoir wall  13   a . Alternatively, or additionally, an absorbent material, such as a sponge, may be incorporated into the nebulizer  100 , for example between the reservoir  7 ′ and overflow wall  13 , to deter the outflow of liquid medication into the exit port  10 . For instance, in the event that the nebulizer is tilted beyond some critical angle during use, the membrane  4  and/or absorbent material will block the flow of medication into the user&#39;s mouth while permitting the nebulized mist to flow through the membrane  4 . 
         [0061]    For example, a foam sponge material may be used as the membrane  4  to permit mist flow while deterring liquid medication flow therethrough. In the nebulizers of the present invention, the flow of small droplets from the nebulizer  100  operates in a very low Reynold&#39;s number flow regime. The Reynold&#39;s number is a dimensionless number, a ratio of the momentum forces acting on a body to that of the viscous forces. In a low Reynold&#39;s number flow, particles tend to follow the path of the gas flow and are not likely to impact upon the solid surfaces that restrain the flow. This holds true even when that flow path is a circuitous one through the pores of a thickness of sponge material. The droplets are carried through with the flowing gas stream, and so the sponge remains dry. 
         [0062]    Thus, in one embodiment of the present invention, the membrane  4  is provided in the form of a layer of sponge material that covers the flow through the exit port  10  and permits the nebulized mist to flow out. The sponge could comprise either a wettable or non-wettable material for the given liquid medication. (The determination of whether a material is “wetting” or “non-wetting” depends on the liquid being used. As used herein, we are most interested in the wettability of materials mainly as it pertains to the use of aqueous solutions.) If the sponge were non-wettable, a sufficiently small pore size would have enough capillary pressure to prevent the liquid medication from progress through the sponge membrane  4 . (A simple, well known equation can be used to calculate the “capillary pressure.” Capillary pressure is the pressure that would be required to force the liquid through a given-sized circular hole in a non-wetting material. The capillary pressure is dependent upon: the contact angle, the surface tension of the liquid, and the diameter of the hole.) However, most readily available sponge materials are comprised of wettable materials. If a wettable sponge material were employed as the membrane  4 , the wettable sponge material should be located so that it is not typically in contact with the bulk liquid medication in the nebulizer  100 . Otherwise, the liquid medication would undesirably be wicked into the sponge and would not be available to be delivered to the user. Nonetheless, a wettable sponge can provide useful functionality when it is strategically located so that, if the nebulizer  100  is tilted too much, the sponge acts as a barrier wicking up the large liquid drops or liquid that has sloshed due to rapid gross motions of the nebulizer  100 . For example, a 2 mm thick layer of polyethylene wettable foam having about 80% open space and pore sizes of about 0.8 mm may be used as the membrane  4 . In addition, a foam layer in the flow exit path proximate the exit port  10  provides an additional feature: a very slight back-pressure in the flow path of the gas and liquid mixture (i.e. the airborne droplets). This slight back-pressure gives the effect of a diffuser by evening out the velocity profile at the nebulizer exit port  10  so that the nebulized mist exits the nebulizer  100  at a slower average velocity and more uniform distribution across the exit port  10 . (The diffuser effect causes the velocity to be more uniform. The slight flow restriction or back pressure, due to the presence of the foam layer, will tend to slow the flow.) 
         [0063]    Further exemplary materials for use as the membrane  4  would include films comprised of fluoropolymers (PTFE, etc.), such as DuPont Teflon® PTFE, having very small pore sizes. Films such as these are currently being produced by W. L. Gore Company under the Gore-Tex® trademark. Teflon® PTFE has a very low surface energy as it is essentially a non-polar molecule. Water is a polar molecule, and liquid water does not “wet” a Teflon® PTFE surface. Instead, liquid water forms “beaded” drops on the surface of the Teflon® PTFE; each drop has a contact angle much greater than 90 degrees. In the case of liquid water and Teflon® PTFE, a very high pressure is required to force water through small holes in the material. However, gases and water mist flow through the pores with little trouble. Gore-Tex® films are specifically created to exploit this phenomena in a number of applications. (One example is a “T” fitting that has one port covered by Gore-Tex® film. This assembly is used in some intravenous tubing, which allows gases to vent out of the tube but prevents the IV fluid from leaking through.) 
         [0064]    The nebulizer tube  1  includes a liquid feed channel  6  having an inlet end  42  disposed in fluid communication with the reservoir  7  to receive liquid medication disposed within the lower housing  3 ,  FIGS. 3 ,  12 . The feed channel  6  communicates with a gas channel  5  of the nebulizer tube  1  to deliver the liquid medication to the gas channel  5  to be nebulized. The gas channel  5  includes an inlet end  41  for connection to a source of compressed air and a throat  43  where the feed channel  6  connects to the gas channel  5 . The gas channel  5  may be provided in the form of a convergent channel  5  that has a cross-sectional dimension that decreases from the inlet end  41  to the throat  43  where the cross-sectional dimension may be a minimum, e.g., 15 to 20 thousandths of an inch. The feed channel  6  may also have a minimum cross-sectional dimension at the throat  43 , e.g., 15 to 20 thousandths of an inch. The nebulizer tube  1  also includes a nozzle  8  disposed in fluid communication with the throat  43  of the gas channel  5 . The nozzle  8  includes a channel cross-sectional dimension that increases away from the throat  43  towards the outlet end  44  of the nebulizer tube  1 . 
         [0065]    The inlet end  41  of the nebulizer tube  1  may include a barb  18  to assist in securing attachment of a compressed air hose to the inlet end  41  of the nebulizer tube  1 ,  FIGS. 11 ,  12 . A flange  19  may also be included to provide a positive stop for the air hose during initial installation. During operation, compressed air, of 25 to 45 psi for example, enters the convergent channel  5  of the nebulizer tube  1 . The air accelerates until it reaches the throat  43  of the convergent channel  5 . By virtue of the Bernoulli effect, as the flow velocity increases, its static pressure will decrease. As a result, the static pressure at the throat  43  of the convergent channel  5  will be below that of the local atmospheric pressure. Since the static pressure of the liquid is higher than the static pressure at the throat  43  of the nebulizer tube  1 , liquid is siphoned upward into the feed channel  6  as a result of a venturi effect. Subsequent to siphoning, the liquid/air mixture is rapidly expanded in the divergent section of the nozzle  8 . This rapid expansion encourages turbulent mixing and creates an effective first-level of nebulization. 
         [0066]    The nozzle  8  is oriented so that the output flow from the nozzle  8  strikes a curved impactor  9 , which may be provided as part of the upper housing  2 . This energetic collision generates the very fine, therapeutic particles required of nebulizers. It has been determined that a sufficiently small spacing is required between the nozzle  8  and impactor  9  to generate a fine mist. A suitable nozzle to impactor spacing is 10 to 20 thousandths of an inch. The location of the nozzle  8  relative to the curved impactor  9  may be specified by an alignment boss  21  provided on the nebulizer tube  1  that mates with a complementary positioning feature  11  of the lower housing  3  to locate the nebulizer tube  1  within the housing  40 . In addition, the nebulizer tube mates with an nozzle capture feature  15  of the upper housing  2  to stabilize the tube  1  within the nebulizer  100 ,  FIGS. 8-10 . Additionally, or alternatively, registration of the nebulizer tube  1  to the impactor  9  may be provided by direct or indirect physical cooperation between the nebulizer tube  1  and impactor  9 . For example, referring to  FIGS. 16-19  (wherein structures similar to those illustrated in  FIGS. 1-12  are similarly numbered with a “200”-series reference numeral), the nebulizer tube  201  may include a registration feature, such as a boss or key  251 , for mating with a complementary structure, such as keyway  252 , on the nebulizer  209 . Engagement between the key  251  and the keyway  252  establishes the relative position between the nozzle  208  and the impactor  209 . 
         [0067]    The impactor  9 ,  209  may have a generally cylindrical shape, such as a substantially full cylinder,  FIG. 6 , or a partial cylindrical impactor  17 ,  FIG. 7A . Such impactor shapes will generate a fine mist and will also facilitate the flow of mist toward the user&#39;s mouth. Other curved surfaces may be substituted for the cylindrical impactors  9 ,  209  such as elliptical, or other suitable shape, e.g., an airfoil  60 ,  FIG. 21A . In addition, the curved impactor may have a cross-sectional shape which includes a flat region  62  as well as a curved region  63 , such as the airfoil  61  illustrated in  FIG. 21B , for example. The airfoil impactor  60 ,  61  is oriented within the housing  40 ,  240  so that the tapered portion of the airfoil points in the downstream direction towards the exit port  10 ,  210  of the nebulizer  100 ,  200 . Such an orientation of the airfoil impactor  60 ,  61  would reduce turbulence and backpressure of the air and mist as it moves out the exit port  10 ,  210  of the nebulizer  100 ,  200 . 
         [0068]    In addition to creating a fine mist, the curved impactor  9  also provides at least two other desirable functions: (I) it helps direct the nebulized mist towards the user&#39;s mouth, and (ii) it facilitates a waterfall-like recycling effect. The waterfall effect arises because part of the mixture exiting the nebulizer tube  1  will strike the impactor  9  and simply drain back down into the region containing the pool of liquid, i.e., reservoir  7 . In this regard, the impactor  9  may be positioned above the reservoir  7 . Of course, a significant portion of the air/liquid mixture will exit via port  10  of the nebulizer as a mist directed toward the user&#39;s mouth. An air baffle  20  may be provided on the nebulizer tube  1  proximate the feed channel inlet end  42 , so that the high-velocity mixture striking the impactor  9  does not blow liquid away from the feed channel inlet  42  which could lead to a feed channel starvation condition. In addition, inclusion of the air baffle  20  can deter unwanted formation of large airborne droplets that might result from the surface of the liquid being agitated. 
         [0069]    Additionally, the impactor  9 ,  209  can be shaped to create a scavenging flow within the nebulizer  100 ,  200 . The scavenging flow would be directed throughout the housing interior and would help prevent the accumulation of medication on the internal walls of the nebulizer  100 ,  200 . In addition, curtain walls  261  may be provided in the upper housing  2 ,  202  to redirect any accumulation of liquid on the upper surface of the upper housing  2 ,  202  downward into the reservoir  7 ,  207 . The presence of curtain walls  261  can avoid the situation of liquid running down the interior sidewall of the upper housing  2 ,  202  to encounter and potentially leak out through the seam between the upper housing  2 ,  202  and the lower housing  3 ,  203 . The curtain walls  261  may also be positioned sufficiently close to the impactor  209  to permit fine particles to travel around the impactor  209  to the exit port  210  and to cause larger particles to strike the curtain walls  261  and then drip down into the reservoir  207 . Additionally, a filter-type material may be positioned in the nebulizer  100 ,  200  to give a preferential flow direction for the nebulized mist toward the user&#39;s mouth without creating an excessive flow resistance to inhalation. Furthermore, the housing  40 ,  240  and/or other components of the nebulizer  100 ,  200  may be fabricated from materials that possess surface tension properties characteristic of wetting materials to create a sheeting action that will facilitate the flow of recycled materials to the reservoir  7 ,  207 . For example, the material of the housing  40  may comprise plastics that are non-wetting in their original condition. Polyethylene (PE) and polypropylene (PP) are two examples. If the reservoir  7  is constructed of one of these materials, and has sufficiently steep internal shape, the liquid medication will roll down to the lowest point, which would presumably be the location from which the liquid medication is being siphoned. Many times however, in practical applications, after having been used, a surface that started out as non-wetting, can become fully or partially wetting due to the deposition of a very thin layer of dirt, minerals, or other contaminants on the surface. The surface might then act as a wettable one. For this reason, it is important to design the reservoir  7  to work well as a wettable material to start with. 
         [0070]    The wetting angle of a wettable material is less than 90 degrees. The contact angle can be a very small angle as the edge of a liquid is pulled along a solid surface. Several characteristics of a wettable surface, together with intentional geometric features, can be used to help the functionality of the nebulizer design. An ideal nebulizer would have the capability to utilize every bit of the liquid medication contained therein. Achievement of this goal may be attempted by pulling the liquid medication from a location that is the lowest point in a depression of the reservoir  7 . The inner walls of the reservoir  7  may be sloped as much as possible, because as the liquid medication level goes down, droplets of water can remain stuck in random locations on the walls of a reservoir  7  that is made from a wettable material. These droplets would be counted as wasted medication that the nebulizer  100  is unable to use as residual content. The nebulizer design can cause the air flow to move generally downward along the walls of the reservoir  7 , which is generally a turbulent action. However the shear action downward along the reservoir wall will scrub the liquid down toward the pick up location. 
         [0071]    The geometry of the reservoir walls, together with the wetting characteristics of the reservoir can also help to reduce the amount of residual unused medication. Internal angles or grooves that run in a direction down the side walls of the reservoir  7  can also be included. The dimensions of the angles or grooves can be relatively small as compared with the dimensions of the reservoir  7 , in which case the liquid will “wick” along the angles or grooves. Further, the design can be made to cause the liquid to preferentially move in one direction along the length of these features by gradually changing the size or shape of the groove along its length. For example, if the internal angle of the groove becomes more acute, the liquid will be preferentially pulled in that direction. Another technique for pulling the liquid toward the feed channel inlet  42  of the feed channel  6  is by make the gap between the bottom surface of the reservoir  7  and the feed channel inlet  42  sufficiently small to wick into this gap (if the surfaces are wetting materials). A further aid is to have the gap reduce in size (taper, or converge) as the liquid moves in the flow-wise direction, towards the feed channel inlet  42 . A gap that becomes smaller as it approaches the inlet to the feed channel  42  can encourage the liquid to flow in that direction. 
         [0072]    Turning next to  FIG. 22 , an additional configuration of a nebulizer  300  in accordance with the present invention is illustrated, in which the nebulizer is configured to reverse the flow of nebulized medication and then redirect the reversed flow towards the nebulizer exit port  310 . The reversal and redirection of the flow of nebulized medication can serve as a particle size filter, allowing only the smaller sized particles to reach the nebulizer exit port  310 . The three-piece nebulizer  300  includes a nebulizer tube  301 , an upper housing  302 , and a lower housing  303  along with an integral cap  331 . 
         [0073]    Referring to the cross-sectional view of  FIG. 23 , the structure of the nebulizer  300  and mechanism by which the nebulized mist is created may be understood. Compressed air enters the convergent gas channel  305  of the nebulizer tube  301  through an inlet end  341  of the nebulizer tube  301 . A barb  318  may be incorporated into the nebulizer tube  301  to aid in securing an elastomeric air hose through which compressed air is introduced into the nebulizer tube  301 . In addition, a flange  319  may be incorporated to provide a positive stop for the air hose during installation. 
         [0074]    The air accelerates until it reaches the throat  343  (a location of minimum cross-sectional area) of the nebulizer tube  301 . By virtue of the Bernoulli effect, as the flow velocity increases, its static pressure decreases. As a result, the static pressure at the throat  343  of the nebulizer tube  301  is below that of the local atmospheric pressure. An integral liquid feed channel  306  of the nebulizer tube  301  is disposed in communication with the medication located in the reservoir  307  of the lower housing  303 . Since the static pressure of the liquid is higher than the static pressure at the throat  343  of the nebulizer tube  301 , liquid is siphoned upward though the feed channel  306  as a result of this venturi effect. Subsequent to siphoning, the liquid/air mixture is rapidly expanded in the divergent section of the nozzle  314 . This rapid expansion encourages turbulent mixing and creates an effective first-level of nebulization. 
         [0075]    After exiting the nozzle  314 , the mixture strikes an impactor  309  which may be provided as a monolithic part of the upper housing  302 . This energetic collision generates very fine, therapeutic particles. The spacing between the nozzle  314  and the impactor  309  is selected to be sufficiently small, e.g., 20 to 40 thousandths of an inch, to generate a suitably fine mist. The impactor  309  also provides the waterfall-like recycling effect. An air baffle  320  of the nebulizer tube  301  is provided near the bottom of the feed channel  306  so that after the high-velocity mixture strikes the impactor  309  the deflected stream does not disturb the liquid near the feed channel inlet. Without the baffle  320 , it is possible that a feed tube starvation condition could be created due to liquid being blown away from the feed channel  306 . In addition, the surface of the liquid might be agitated to an extent that would produce unwanted formation of large airborne droplets. Note also, that in the event that the nebulizer is tilted forward beyond some critical angle during use, the adjoining walls  313 ,  350  of the upper and lower housings  302 ,  303  block the flow of medication into the user&#39;s mouth. 
         [0076]      FIGS. 24-27  illustrate the lower and upper housings  302 ,  303  from which the structures that contribute to the reversal and redirection of the nebulizer flow through the nebulizer  300  can be seen. Turning first to the lower housing  303  of  FIG. 24 , the reservoir  307  may include a hemispherical or other suitably shaped depression for retaining liquid medication therein. The reservoir  307  may be surrounded by a reservoir wall  313 , such as a U-shaped wall, that is configured to cooperate with corresponding structures in the upper housing  302  to aid in confining and directing the nebulized mist. (Additionally, an alignment feature  311  is provided to position the nebulizer tube  301  within the lower housing  303 , and four holes (of which hole  312  is representative) are provided to align the upper and lower housings  302 ,  303  via the mating posts  316  of the upper housing  302 ,  FIG. 25 .) 
         [0077]    The upper housing  302  includes a nebulization chamber  334  in which the nebulized mist is generated,  FIG. 25 . The nebulization chamber  334  is defined by a chamber wall  350 , which may have a generally cylindrical shape, and which optionally includes a shoulder  351  and an inset chamber wall portion  352  formatting with the lower housing  303  so that the shoulder  351  seats upon the upper surface of the reservoir wall  313  of the lower housing  303  and so that the inset chamber wall portion  352  extends into the cavity of the lower housing  303  defined by the reservoir wall  313 ,  FIGS. 23-25 . Also defining the nebulization chamber  334  is the impactor  309 , which may be provided as a straight wall that spans the cylindrical space defined by the chamber wall  350 . A chamber opening  329  is provided in the nebulization chamber wall  350  through which the nebulizer tube  301 ,  501  extends,  FIGS. 23 ,  26 . (As described more fully below the nebulizer tubes of the present invention can include multiple channels, such as the three-channel nebulizer tube  501  depicted in  FIGS. 26-28 .) As with the nebulizer configurations illustrated in  FIGS. 1-19 , the upper and lower housings  302 ,  303  may include analogous positioning features for registering the nebulizer tube  301 ,  501  relative to the upper and lower housings  302 ,  303 , such as alignment boss  321  and complementary positioning feature  311 , for example. The chamber opening  329  is dimensioned to be sufficiently large so that with the nebulizer tube  301 ,  501  in place a passageway is provided to allow the nebulized mist to exit the nebulization chamber  334  through the chamber opening  329 . This geometry of the upper and lower housings  302 ,  303  is designed to provide a tortuous passageway to reverse and otherwise redirect the flow through the nebulizer  300 ,  FIG. 27 . In this regard, the tortuous passageway may comprise a first section for directing the flow, “F”, of nebulized medication away from the outlet end of the gas channel  305  at nozzle  314  and back towards the direction of the inlet end  341  of the gas channel  305  and may comprise a second section for directing the flow, “F”, of nebulized medication to the exit port  310  of the nebulizer  300 . 
         [0078]    Specifically, with reference to  FIG. 27 , the reverse flow geometry functions as follows. The mixture containing air and medication is directed through the nebulizer tube  301 ,  501  and exits the nebulizer tube  301 ,  501  striking the impactor  309 . Since there is no immediate forward path toward the exit port  10  within the nebulization chamber  334 , the nebulized mist is redirected out of the nebulization chamber  334  through the chamber opening  329  towards the rear of the nebulizer  300 . By reversing the direction of the flow, particle size filtering occurs. Smaller particles that are able to quickly change direction will successfully exit the nebulization chamber  334 . However, larger particles will impact upon the internal surface of the nebulization chamber  334  and will be recycled. The larger particles may then run down the internal surface of the chamber wall  350  to be deposited in the reservoir  307  so as to create a scavenging flow to minimize medication residuals. Upon exiting the chamber opening  329 , since there is no exit port at the rear of the nebulizer  300 , the flow of mist must again reverse direction in the direction of the exit port  310  to be emitted from the nebulizer  300 . The redirection effectively serves as a particle size filter to ensure that therapeutic particles are emitted from the nebulizer  300 . Additionally, to assist in diffusion of the nebulized flow as it exits the nebulizer  300 , a taper  330  may be provided on the exterior of the nebulization chamber  334  in the form of an airfoil to diffuse the flow as the flow nears the exit port  310 . The taper  330  also reduces the velocity, turbulence, and backpressure of the air and mist as it exits the nebulizer  300 . 
         [0079]    To further assist in directing airflow through the nebulizer to the patient, upper and lower housings  402 ,  403  may be provided which have a geometry that includes a flow path for external air to be drawn in by the patient,  FIGS. 36 ,  37 . In this regard, the upper and lower housings  402 ,  403  may be open at the end  412  opposite that of the exit port  410 , and make-up air curtain walls  470 ,  474  may be included in the upper and lower housings  402 ,  403  provide make-up (or bypass) air passageways  472 ,  476  through the body of the housings  402 ,  403 , allowing air to be drawn directly from the inlet end  412  through to the exit port  410 . 
         [0080]    Each of the nebulizer configurations discussed so far may also utilize multi-channel nebulizer tubes  401 ,  501 , rather than a single channel nebulizer tube  1 ,  201 ,  301 , to reduce the treatment time. For example, as shown in  FIGS. 26-33 , the nebulizer  300  may utilize a two- or three-channel nebulizer tube  401 ,  501  instead of the single-channel nebulizer tube  301 . The inlet gas channel  405 ,  505  may be split downstream into two or three outlets  427 ,  527 . Each of the outlet  527  may be fed by a separate liquid feed channel  506 ,  FIG. 29 . Experiments have shown that a multi-channel nebulizer tube configuration can decrease the time required to nebulize a given volume of liquid, thus minimizing the time needed to treat a patient. 
         [0081]    In addition, still further configurations of nebulizers and nebulizer tubes are provided by the present invention. For instance, with reference to  FIGS. 47-48 , a nebulizer tube  801  is provided, that may include similar structures to those of the nebulizer tube  1  of  FIGS. 11-12 , such as, an air baffle  20 , an alignment boss  821 , a barb  818 , and a flange  819 . In addition, the nebulizer tube  801  includes a gas channel  805  that may be provided in the form of a convergent channel  805  that has a cross-sectional dimension that decreases from the air inlet end  841  towards the opposing outlet end  842  which terminates at outlet nozzle  811 . However, the nebulizer tube  801  includes an annular medication exit port  808  disposed in liquid communication with the liquid feed channel  806  through which liquid medication may be provided to the output end  842  of the nebulizer tube  801 . The liquid feed channel  806  may have a generally rectangular or circular cross-sectional shape and have a cross-sectional dimension of 30-90 mils. The nebulizer tube  801  is disposed within the housing which may have upper and lower housing portions  802 ,  803  and which includes an impactor  809  proximate the outlet nozzle  811  and a reservoir  807  disposed in fluid communication with the feed channel  806 ,  FIGS. 49-51 . 
         [0082]    In operation, a high pressure gas (typically air) enters the nebulizer tube  801  through the inlet end  841  and is accelerated to sonic velocity. The air expands as it leaves the nozzle  811 . Since the feed channel  806  is in communication with a reservoir  811  of liquid (typically medication), under the proper conditions, liquid medication is siphoned through the feed channel  806  and exits the nebulizer tube  801  via annular medication exit port  808 . Whether siphoning occurs depends on the spacing between the exterior face of the nozzle  811  and the impactor  809 . Provided that the spacing between the exterior face of the nozzle  811  and the impactor  809  is sufficiently small (for example, 20 to 80 mils, with 30 mils representing a preferred spacing), a low-pressure air zone will be formed proximal to the annular medication exit port  808 . This creates a pressure differential across the liquid that will siphon fluid from the reservoir  807  and direct it towards the impactor  809 . The energy imparted to the liquid from the gas, as well as the impaction on the impactor  809 , generates fine particles from the liquid. 
         [0083]    Further, alternative impactor structures in addition to the spherical impactor  809  of  FIGS. 49-51  may be used in the present invention. For example, a cylindrical impactor  819  provided as part of an upper housing  812 ,  FIGS. 52-53 , or a mesa-shaped impactor  829  provided as part of an upper housing  822 ,  FIGS. 54-55 , may be used to increase the efficiency of the nebulization process. The mesa-shaped impactor  829  has been demonstrated to yield a relatively-high nebulization efficiency. It is believed that the turbulence that is generated as the air flow detaches from the circular edge of the mesa enhances efficiency. The flat surface of the mesa may be roughened to further enhance nebulization. Additionally, it is observed that the impaction surface of the mesa may be flat, convex, concave, or some other non-planar structure. The edges of the mesa may incorporate jagged features to further enhance efficiency. In addition, a ring feature  840  may be added about a mesa  839  to facilitate the creation of a resonant annular channel  841  in the housing  832 ,  FIGS. 56-57 . The fundamental resonant frequency of the annular channel  841  may be tuned to help generate particles of a preferred size. Also, the ring  840  can create more turbulence to increase efficiencies. Moreover, each of the impactor configurations illustrated in  FIGS. 49-57  may be used with any of the other nebulizer and/or nebulizer tube configurations described herein. 
         [0084]    In yet another aspect of the present invention, a nebulizer configuration is provided in which the nebulizer body comprises only two parts, with the nebulizer tube  601  monolithically formed as a part of either the upper or the lower housing  602 ,  603 ,  FIG. 38 . Specifically, with reference to  FIGS. 38-46  a nebulizer configuration in accordance with the present invention is shown in which the nebulizer tube  601  is formed as a part of the upper housing  602 . As such, the nebulizer  600  may desirably include only two parts, the upper housing  602  and lower housing  603 . However, as with the various nebulizer configurations  100 ,  200 ,  300  described above, one or more semi-permeable membranes (or filters) may additionally be provided at the exit port  610  to permit mist flow while acting as an effective liquid barrier to create a safety feature that prevents the user from swallowing liquid medication contained in the nebulizer  600 . A sponge-like (or other absorbent) material may be incorporated into the nebulizer  600  as an alternative manner to obtain this feature. In the event that the nebulizer  600  is tilted beyond a critical angle during use, the membrane will block the flow of medication into the user&#39;s mouth. 
         [0085]    The upper housing  602  may include a “living hinge”  622  that allows the impactor half of the upper housing  602  to open as a lid  620  to permit the introduction of liquid medication into a reservoir  607  of the lower housing  603 ,  FIG. 39 .  FIG. 43  shows the upper housing  602  after the living hinge  622  is flexed into its closed functioning orientation. To assist in maintaining the liquid medication in the reservoir  607 , a medication retention flange  614  that extends over the reservoir  607  proximate the exit port  610  is provided as a part of the lower housing  603  to prevent medication from flowing out of the reservoir  607  and into the user&#39;s mouth,  FIGS. 45 ,  46 . The medication retention flange  614  allows the user to be inclined in bed or reclining while using this device. The reservoir  607  may be shaped to make the liquid medication available to the inlet end of the feed tube  606  of the nebulizer tube  601 . For example, the reservoir  607  may be generally V-shaped and may include a trough  611  into which the liquid medication can pool and over which the inlet end of the feed tube  606  may be positioned to receive the pooled medication,  FIG. 41 . The lower end of the feed tube  606  may meet with the geometry of the reservoir  607  in the lower housing  603  such that medication in the reservoir  607  is wicked to the bottom of the feed tube  606  so that nearly all the medication can be siphoned into the air stream. (The feed tube  606  is the only feature that requires “side-action” to form the geometry.) The flat sloping walls that form the reservoir  607  allow the medication to be fully consumed even when the user is reclined at a significant angle. 
         [0086]    The integral nebulizer tube  601  may also include a convergent channel  605  through which compressed air is introduced to the nebulizer  600 . The air accelerates until it reaches the throat  643  (minimum cross-sectional area) of the tube. By virtue of the Bernoulli effect, as the flow velocity increases, its static pressure will decrease. As a result, the static pressure at the throat  643  of the nebulizer tube  601  is below that of the local atmospheric pressure. Since the static pressure of the liquid is higher than the static pressure at the throat  643  of the nebulizer tube  601 , liquid is siphoned upward as a result of this Venturi effect. Subsequent to siphoning, the liquid/air mixture is rapidly expanded in the divergent section of a nozzle  608  of the nebulizer tube  601 . This rapid expansion encourages turbulent mixing and creates an effective first-level of nebulization. After exiting the nozzle  608 , the mixture strikes an impactor  609  which is also monolithic to the upper housing  602 ,  FIGS. 41 ,  42 ,  44 . This energetic collision generates the very fine, therapeutic particles required of nebulizers. Because the nozzle  608  and impactor  609  are both monolithic to the upper housing  602  through the living hinge  622 , the spacing between the nozzle  608  and the impactor  609  is very repeatable,  FIGS. 42 ,  44 . A sufficiently small spacing between the nozzle  608  and the impactor  609  is required for fine mist generation, which may be, for example, about 30 thousandths of an inch. 
         [0087]    As with the nebulizer configuration of  FIG. 22 , the nebulizer  600  may also include the “reverse flow” feature. Referring to  FIG. 42 , the reverse flow feature is illustrated where the mixture of air and nebulized medication (indicated by the lines with arrowheads), after hitting the impactor  609 , is forced to flow back away from the exit port  610 , then change direction to exit the nebulizer  600  at the exit port  610 . In this regard, as with the nebulizer  300 , the nebulizer  600  includes a nebulization chamber  634  defined and surrounded by chamber walls  650  that assist in defining the flow path of the mixture of air and nebulized medication. The change of flow direction acts as a filter, removing large droplets of medication from the air stream. The desired small airborne particles change direction with the air stream, while the larger particles with significantly more inertia do not readily change direction and impact the chamber walls or fall out of the air stream to head downward into the reservoir  607  to be reused. 
         [0088]    In addition, the nebulizer  600  may also include one or more make-up air channels  672 , which may be provided as a monolithic part of the upper housing  602 ,  FIGS. 42 ,  43 . The make-up air channels  672  allow the user to inhale or even exhale while using the nebulizer  600 . The end  674  of the channel  672  inside the nebulizer  600  is positioned in the air stream such that the natural flow of the air stream will draw air into the nebulizer  600  rather than allowing nebulized medication to exit the make-up air channels  672  to the room. Furthermore, as with the various nebulizer configurations discussed above, the two-piece nebulizer  600  may make use of a nebulizer tube  701  that has more than one convergent/divergent gas channel and nozzle  708 ,  FIG. 40 . The inclusion of more than one gas channel can be achieved without significantly increasing the complexity of the mold tooling, which may be desirable because multiple gas channels can significantly reduce the time required to nebulize a certain amount of medication by drawing more medication through multiple feed tubes for mixing with high velocity air in multiple divergent nozzles  708 . 
         [0089]    The various nebulizer configurations presented above may have a compact size permitting the nebulizers to substantially fit within the user&#39;s mouth which contributes to minimizing the amount of residual medication. The compact size is not just a matter of design choice—it has an effect on all other aspects of the nebulizer&#39;s functionality. A higher nebulization rate, within a small volume, can have negative aspects. For example, there can be interaction between the multiple jets leading to an increased probability of particle agglomeration to a size larger than that desired for effective patient treatment. However, there can be substantial benefits of making the nebulizer very compact, such as high efficiency use of the medication, which is partially dependent upon having a compact nebulizer. A compact nebulizer has a smaller wettable surface area. Thus, the inner surfaces of the nebulizer will hold less residual medicine. The location and geometry of the liquid reservoir and intake, together with the gas flow path, are also important factors affecting the amount of residual. Thus, the designs strike a balance between nebulization rate and compactness. 
         [0090]    These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims.