Abstract:
A liquid reservoir for a nebulizer is comprised of a pair of membranes formed of resilient material and sealed about their edges to form a closed chamber between them for containing a liquid to be nebulized. When the chamber is filled with liquid and thereby expanded, the resilient membranes are distended to apply pressure to the liquid in the chamber. A discharge valve controls the discharge of liquid from the reservoir to the nebulizer under the pressure applied by the membranes. The reservoir is mounted on the nebulizer so that one of the membranes abuts a surface of the nebulizer that concavely deforms the membrane to increase the pressure applied to the liquid in the chamber to reduce or eliminate any residual volume of liquid in the chamber at the end of the discharging operation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to nebulizers and more particularly to an improved reservoir arrangement for containing a liquid to be nebulized.  
           [0002]    Nebulizers, or atomizers, are devices that generate a fine spray or aerosol. A particularly useful application for nebulizers is to convert aqueous drug solutions, or suspensions with non-dissolved particles, into an aerosol of small droplets that can thereafter be inhaled to administer the drug to a subject during breathing. Such inhalation treatment is highly effective for conditions effecting the subject&#39;s respiratory organs. Further, since the lungs are close to the heart and the blood circulatory system of the body, drug administration by inhalation provides an effective and rapid delivery system to all organs of the body.  
           [0003]    In many cases, the subject breathes with the aid of a respiratory ventilator. A typical ventilator has a breathing circuit comprising an inhalation limb and an exhalation limb connected to two arms of a Y-connector. The third arm of the Y-connector is connected via a patient limb to a mouth piece, mask, or endotracheal tube for the subject. The ventilator provides a desired degree of assistance to the breathing of the subject during the inhalation phase of the respiratory cycle. The contraction of the subject&#39;s lungs discharges gas through the exhalation limb during exhalation. To achieve the maximum physiological effect for the subject and to avoid wastage of the drug, the nebulizing action of the nebulizer is synchronized with the inspiratory phase of the respiratory cycle. A typical example of a nebulizer arrangement is shown in U.S. patent application Ser. Nos. 09/397,529, filed Sep. 16, 1999; 09/547,523, filed Apr. 12, 2000; and 09/699,049, filed Oct. 30, 2000 and European Patent Applications 311,773.6, filed Dec. 29, 2000 and 311,778.5, filed Dec. 29, 2000 which applications are incorporated herein by reference to the extent permitted. In nebulizers of the type shown in the foregoing U.S. and European patent applications, the liquid is converted to an aerosol by the action of a vibrating element, such as a piezoelectric element. The supply of liquid from a liquid reservoir to the nebulizing element is controlled by a valve. The liquid reservoir is pressurized to cause the liquid to flow through the valve to the element when the valve is open.  
           [0004]    In order to ensure maximum penetration depth of a nebulized drug into the lungs of the subject, the gas volume in the breathing circuit between the nebulizer and the lung should be minimized. To this end, the nebulizer is typically positioned near the patient mouth piece, mask, or endotracheal tube, i.e., in the patient limb of the breathing circuit described above. However, for surgical and intensive care patients, the area around the nose, mouth, neck and upper chest is often critical to the care of the patient and/or crowded with other equipment. The overall size of the nebulizer, including its liquid reservoir, thus becomes very important. A liquid container remote from the nebulizer may be used to reduce the size of the nebulizer. However, if a small volume of drug is to be delivered, such an arrangement can be disadvantageous because of the amount of drug required to fill the liquid supply line between the container and the nebulizer and the residuum of drug left in the supply line. A local liquid reservoir mounted on the nebulizer would thus be advantageous in such circumstances.  
           [0005]    Such a local liquid reservoir for a nebulizer typically comprises two compartments separated by a moving wall. One compartment contains the liquid drug. The other compartment contains a pressurizing gas. The moving wall ensures that the drug is not contaminated by the gas. The liquid compartment is filled with the drug by a syringe through a filling port. A syringe may also be used to pressurize the gas compartment. The reservoir so filled is mounted on the nebulizer to supply liquid to the vibrating element of the nebulizer..  
           [0006]    However, in such a local liquid reservoir, the gas compartment adds to the overall size of the reservoir. As noted above, size is a serious concern for certain uses of the nebulizer. Also, pressurization of the gas compartment is an additional maneuver required when using a nebulizer of this type.  
           [0007]    Another requirement for a local reservoir for a nebulizer is that it be able to generate the necessary pressure to deliver liquid from the liquid compartment to the nebulizing element, including cases in which the inhalation limb and patient limb are pressurized by the ventilator to provide breathing gases to the subject. It is also desirable that the liquid reservoir be capable of supplying the liquid independently of the position or orientation of the nebulizer. To ensure that a proper drug dosage is administered to the subject and to avoid wastage of drug, it is desirable that the reservoir be capable of being completely emptied. It should be easy to fill the reservoir. At the end of the drug administration, the reservoir should be easy to clean or dispose of. And, as noted above, the reservoir should be as small as possible, commensurate with the volume of liquid to be delivered to the subject.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    It is the object of the present invention to provide an improved local liquid reservoir means for a nebulizer that advantageously meets the foregoing and other requirements.  
           [0009]    Briefly, the present invention contemplates such a liquid reservoir comprised of a pair of membranes formed of a resilient material. The membranes are positioned in an opposing relationship and sealed about their edges to form a closed chamber between them for containing the liquid to be nebulized. The chamber may be filled by a syringe or other appropriate means. Or, the chamber may be filled directly from a container through a check valve using a handle or other means, to draw the membranes apart in which case, the use of a syringe may be eliminated. When the chamber is filled with liquid and thereby expanded, the expansion of the chamber distends the resilient material membranes to apply pressure to liquid in the chamber. A flow control means, such as a valve, communicates with the chamber and controls the discharge of liquid from the reservoir to the nebulizer under the pressure applied to the liquid by the distended membranes.  
           [0010]    The liquid reservoir is mounted on the nebulizer so that one of the membranes abuts a surface of the nebulizer which concavely deforms the membrane to increase the pressure applied to the liquid in the chamber. This pressure increase ensures that the liquid can be discharged from the chamber against any pressures generated in a breathing circuit to which the nebulizer is connected. It further renders the nebulizer insensitive to position as gases from the breathing circuit cannot enter and become trapped in the reservoir. Still further, it reduces or eliminates any residual volume of liquid in the chamber at the end of treatment, thereby ensuring that a patient receives the proper total dosage of a drug and avoiding wastage.  
           [0011]    Inasmuch as the local liquid reservoir of the present invention does not use a pressurizing gas, the overall size of the reservoir can be advantageously reduced due to the absence of a gas chamber.  
           [0012]    The invention will be further understood from the following detailed description, taken in conjunction with the drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0013]    In the drawing:  
         [0014]    [0014]FIG. 1 is a general schematic view of ventilator apparatus containing a nebulizer with a liquid reservoir means according to the present invention;  
         [0015]    [0015]FIG. 2 is a general exploded and schematic cross sectional view of a nebulizer and liquid reservoir means of the present invention;  
         [0016]    [0016]FIG. 3 shows one embodiment of the liquid reservoir of the present invention in the unfilled condition;  
         [0017]    [0017]FIG. 4 is a view showing the reservoir of FIG. 3 in the filled condition;  
         [0018]    [0018]FIG. 5 shows another embodiment of the liquid reservoir of the present invention; and  
         [0019]    [0019]FIG. 6 shows a modification of a filling means for the liquid reservoir. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Nebulizer apparatus  10  of the present invention is typically used in conjunction with breathing circuit  12  and ventilator  14 , as shown in FIG. 1. Nebulizer  10  atomizes liquid solutions or suspensions for delivery to a subject, as for example as a drug treatment for a patient. Breathing circuit  12  includes inhalation limb  16  coupled to ventilator  14 . Exhalation limb  18  is also connected to ventilator  14 . Inhalation limb  16  and exhalation limb  18  are connected to two arms of Y-connector  20 . The third arm of Y-connector  20  is connected to one end of patient limb  22 . The other end of patient limb  22  is connected to a mouthpiece, face mask, or endotracheal tube (not shown) for the subject for supplying respiratory gases to lungs  24  of a subject.  
         [0021]    Ventilator  14  provides all or a portion of the respiratory gases for the subject by providing inhalation gases in inhalation limb  16 . The inhalation gases pass through Y-connector  20  and into patient limb  22  for supply to the lungs  24  of the subject. On exhalation, the respiratory gases pass through patient limb  22 , Y-connector  20 , and exhalation limb  18  back to ventilator  14 .  
         [0022]    As shown in FIG. 1, nebulizer apparatus  10  is preferably positioned in patient breathing circuit  12  as near the subject as possible to ensure effective delivery of the atomized liquid to lungs  24  of the subject and to minimize the deposition of the liquid on the breathing circuit walls. To this end, nebulizer apparatus  10  may be inserted in the breathing circuit between Y-connector  20  and patient limb  22  as shown in FIG. 1.  
         [0023]    The construction of a nebulizer apparatus suitable for use with the liquid reservoir of the present invention is shown generally in FIG. 2. Nebulizer apparatus  10  includes adapter  30  for connecting the nebulizer apparatus in patient limb  22  of breathing circuit  12 . Housing  32  is mounted in adaptor  30  in a manner to permit the housing and other portions of the nebulizer apparatus to be removed from the adaptor for cleaning, when changing drugs, or for other purposes. Housing  32  contains opening  34  through which nebulized liquid may pass.  
         [0024]    A vibrating element  36 , such as a piezoelectric element, is mounted in housing  32 . The central portion of the vibrating element comprises a mesh plate  38  containing a holes  40 . Holes  40  may be formed in plate  38  by an electro forming process that produces hose having a diameter of preferably approximately 2-15 μm in diameter. Vibrating element  36  may be energized by high frequency alternating voltage provided in conductors  42 .  
         [0025]    Plug member  44  is placed in the cavity defined by housing  32 . Plug member  44  has a central opening  46  through which liquid to be nebulized may pass to mesh plate  38 . Opening  46  may be surrounded by electrode  48  to provide, in conjunction with vibrating element  36 , a capacitive means for determining the amount of liquid provided to mesh plate  38 . Conductor  49  is connected to electrode  48  for this purpose. Plug member  44  also includes electromagnet  50  for operating a valve, hereinafter described. Electromagnet  50  may be energized through conductors  52 . Conductors  42 ,  49 , and  52  are contained in cable  54  connected to nebulizer control unit  56 .  
         [0026]    As shown in FIG. 2, the upper surface  58  of plug member  44  is convexly curved when viewed from the exterior of the plug member.  
         [0027]    [0027]FIG. 3 shows one embodiment of liquid reservoir  60  of the present invention. Reservoir  60  is comprised of a first membrane  62  and a second membrane  64 . As shown in FIG. 3, the membranes are juxtapositioned in a generally opposing relationship. The membranes, which are shown as circular in form in FIG. 3, are joined at their periphery and to form a closed chamber between the membranes. The peripheral edges of membranes  62  and  64  are joined to frame  66  which serves to mount reservoir  60  on plug member  44  as shown in FIG. 2. Bayonet fittings or other suitable means may be provided to fasten the reservoir on plug member  44 . Membranes  62 ,  64  are formed of a resilient material, such as rubber or plastic.  
         [0028]    One of the membranes, for example, membrane  64  contains a means for discharging liquid from reservoir  60 . As shown in FIG. 3, the means may comprise a valve  68  which includes a disc-like plate  70  mounted in membrane  64 . Liquid conveying tube  72  depends from plate  70 . A stopper  74  is placed in tube  72  to rest on valve seat  76  formed in the tube. Spring  78  abuts stopper  74  to bias the stopper onto valve seat  76 . As hereinafter noted, the pressure of the liquid in reservoir  60  may also be used to press stopper  74  against valve seat  76 . Stopper  74  is formed of a ferromagnetic material.  
         [0029]    Membrane  62  contains a means for filling a chamber formed between membranes  62  and  64  with liquid. As shown in FIG. 3, the means may comprise a tube or luer lock fitting  78  suitable for engaging the end of a syringe. Check valve  80  is located in tube  78  to retain the liquid in the chamber. Check valve  80  may be formed of a plastic sealing means that deforms to provide an opening through which liquid may enter the chamber formed between the membranes. Or, the filling means may have a cap for closing the filling means.  
         [0030]    In use, liquid reservoir  60  is filled with liquid as by connecting a syringe to tube or luer lock  78  and injecting fluid through check valve  80  between membranes  62  and  64 . The injection of the fluid distends resilient membranes  62  and  64 , as shown in FIG. 4, for form chamber  82 . This distention pressurizes the liquid in chamber  82 . The pressure in chamber  82  assists spring  78  in sealing stopper  74  on valve seat  76  to retain the liquid in chamber  82 . FIG. 4 shows liquid reservoir  60  in the filled condition.  
         [0031]    After filling, liquid reservoir  60  is placed on plug  44  to insert tube  72  through electromagnet  50  in plug  44 . Membrane  64  comes into abutment with convex surface  58 . As liquid reservoir  60  is pressed on surface  58 , membrane  64 , as well as membrane  62 , is concavely deformed, as shown in FIG. 2. This further increases the pressure applied by the membranes to the liquid in chamber  82 . Liquid reservoir  60  is secured to nebulizer  10  by a connection between frame  66  and plug member  44 .  
         [0032]    Electromagnet  50  is energized through conductors  52  to lift stopper  74  off valve seat  76  and allow liquid from chamber  82  to flow to mesh plate  38 . Vibrating element  36  is energized through conductors  42  to nebulize the liquid and expel same through holes  40  in mesh plate  38 . The energization provided in conductors  42  and  52  of cable  20  from nebulizer control unit  56  may be synchronized with the respiratory cycle of the subject so that the atomized liquid is carried into lungs  24  of the subject with the breathing gases inhaled during the inspiratory phase of the respiratory cycle. A triggering signal may be provided from ventilator  14  to nebulizer control unit  56  in conductor  84  for this purpose.  
         [0033]    The pertinent portions of plug  44  and liquid reservoir  60  may be formed such that the pressure applied to the liquid in chamber  82  when liquid reservoir  10  is fastened to plug member  44  is sufficient to secure the removal of substantially all of the liquid from chamber  82 , even against the elevated breathing circuit pressure that may be applied to chamber  82  from patient limb  22  through valve  68 . That is, the pressure applied to the liquid in chamber  82  by the membranes forming the chamber can exceed the pressure in patient limb  22 .  
         [0034]    As liquid is discharged from chamber  82 , membrane  62  will approach membrane  64 . The convex surface of plug member  44 , and the resulting concave deformation of membrane  64 , is formed such that membrane  62  progressively contacts membrane  64 , commencing from adjacent frame  66  and extending toward the center of the membranes. This assures that no residual liquid is left in chamber  82 . For this purpose, surface  58  may be formed such that the radius of curvature increases from the edge toward the center.  
         [0035]    The applied pressure also renders nebulizer  10  and liquid reservoir  60  insensitive to position since gas from the breathing circuit will not pass through valve  68  and become trapped in liquid reservoir  60  even if the liquid reservoir is upside down from the orientation shown in FIGS. 2 through 4.  
         [0036]    [0036]FIG. 5 shows a further embodiment of the liquid reservoir of the present invention. In liquid reservoir  60   a , a handle  90  is mounted on membrane  62 . The end of tube  72   a  may be sharpened, and used to penetrate a drug supply container, such as an ampoule. Handle  90  is used to separate, or pull apart, membranes  62  and  64  to create an under pressure between the membranes. This suctions the drug from the drug supply container into the chamber through valve  68  that, in this case also operates as a check valve. The need to use an intermediate device, such as a syringe, to fill chamber  82  is thus avoided although liquid reservoir  60  must be disconnected from nebulizer apparatus  10  to fill chamber  82 . Handle  90  may be removable, if desired, to minimize the size of liquid reservoir  60   a..    
         [0037]    While in the foregoing description, liquid reservoir  60  is placed on plug member  44  after filling, it can also be placed on plug member  44  before filling, if desired. This could occur, for example, if it is necessary to refill chamber  82  to provide an additional dose of a drug to a patient  
         [0038]    Also, while the foregoing has described the filling means  78 ,  80  as mounted in one of the membranes  62 ,  64 , it may also be located elsewhere on liquid reservoir  60 , if desired. For example, it could be mounted on frame  66  as shown in FIG. 6.  
         [0039]    It is recognized that other equivalents, alternatives, and modifications aside from those expressly stated, are possible and within the scope of the appended claims.