Abstract:
A spacer assembly for a ventilator or other respiratory equipment for dispensing aerosol drugs from metered dose inhaler (MDI) canisters or nebulized drugs from a nebulizer into a respiratory gas stream delivered from a ventilator or other respiratory equipment connected to a patient. The improvements involve optimizing the shape of the spacer assembly body member and providing an efficient MDI nozzle assembly to allow maximal evaporation of the propellant before the propellant droplets impact the walls of the body member while providing a compact volume for directing the output of an MDI canister or a nebulizer into the gas stream.

Description:
FIELD OF THE INVENTION 
   The invention relates generally to respiratory apparatus and particularly to a device that can dispense a drug from a metered dose inhaler (MDI) canister into a stream of air supplied through the inspiratory path between respiratory equipment and a patient, for example, between a ventilator and an endotracheal tube in the trachea of a patient. The device is also preferably capable of introducing aerosolized medication from a nebulizer into the same air stream. 
   BACKGROUND OF THE INVENTION 
   Drugs dispensed from MDIs usually consist of very finely divided particles, typically in the 1 to 8 micron range. The medication particles are suspended in liquid propellant such as Freon or the like which is under pressure in the MDI canister. Upon actuation, a metered dose of the drug and propellant is ejected through the outlet tube of the canister and, in the prior art, out through one or at most two ports or orifices that are aimed in the longitudinal direction of the air stream to the patient. See, for example, U.S. Pat. No. 5,012,803 for a description of a single orifice nozzle and U.S. Pat. No. 5,474,058 for a two orifice nozzle construction. 
   As the mixture of drug and propellant is ejected out of a nozzle, it is accelerated to a high velocity so that shear forces with the nearly stationary ambient air cause the mixture to break up into many small, rapidly evaporating droplets, each of which contains hundreds to thousands of drug particles. The exit ports of the prior art dispensers typically are about 0.5 mm in diameter for single-orifice dispensers and 0.3 mm in diameter for dual-orifice dispensers. 
   The plume of propellant and agglomerated drug that exits a round orifice nozzle travels several tens of millimeters before the propellant can gain enough heat from the surrounding air to evaporate. The evaporation of the propellant is a phase transition that requires the input of heat to change the propellant from liquid to vapor. The rate at which heat can be transferred from the air to the propellant droplets is the limiting mechanism for their evaporation. 
   A major problem with MDI ventilator dispensers is that the expanding plume, consisting of unevaporated droplets containing drug particles, impinges upon the walls of the ventilator circuit and remains there, forever lost to the patient. One method to minimize this loss of drug is to add a large diameter spacer to the circuit in which the plume may expand, as described, for example, in U.S. Pat. Nos. 5,012,803; 4,484,577; 4,790,305; 4,938,210 and 5,178,138. 
   There are, however, several disadvantages associated with use of large-volume spacers. Their weight tends to pull on the ventilator tubing which is inserted into the patient&#39;s trachea which may cause the patient considerable physical discomfort. They also collect contaminated fluid. The volume of the spacer is also a hindrance to optimal air flow to the patient because the spacer adds needless volume to the circuit. And, in collapsible versions of a large-volume spacer, such as described in U.S. Pat. No. 4,938,210 the spacer may be difficult to open once it has been collapsed. 
   An advantage exists, therefore, for an aerosolized medication delivery device that would enable rapid expansion and evaporation of the medication&#39;s pressurized propellant, thereby resulting in a compact, lightweight device which would efficiently deliver medication yet not cause the patient undue discomfort. 
   SUMMARY OF THE INVENTION 
   It is an object of this invention to provide an improved delivery of drug from an MDI to an intubated patient. It is a further object of this invention to provide a spacer of smaller volume to reduce the compressibility effects. It is a further object to provide a spacer of smaller weight to reduce the load applied to the tubing attached to the patient. It is a further object to provide a spacer that efficiently uses all of its internal volume to evaporate more of the propellant before it can impact the walls of the spacer and inhibit drug delivery to the patient. It is a further object to provide a novel nozzle that minimizes the distance that the plume will travel before the propellant is evaporated. It is a further object of this invention to provide a device that can be used for both MDI delivery and the delivery of aerosolized medication from a nebulizer. The present invention provides a spacer assembly suitable for disposition into the respiratory gas stream of a patient, especially an intubated patient attached to a ventilator. The spacer assembly is preferably capable of dispensing mists of aerosolized drugs from an MDI canister as well as nebulized medications from a small volume nebulizer. The spacer assembly preferably comprises a body including an expansion chamber having an inlet and an outlet adapted for connecting the spacer assembly to the air flow tubing of a conventional ventilator or other respiratory equipment operable to deliver a pressurized flow of therapeutic respiratory gas. 
   The expansion chamber preferably includes a first opening for receiving an MDI nozzle assembly and a second opening for receiving a discharge outlet of a conventional nebulizer or the like. The second opening is preferably sealed by a spring-biased valve or the like when the spacer body is disconnected from a nebulizer. According to a preferred embodiment, the MDI nozzle assembly includes multiple, radially arranged channels terminating in outlet ports which collectively function to dispense liquid propellant-borne medication in a diffuse, gentle, generally umbrella shaped mist or plume of finely atomized drops which allows the propellant to rapidly evaporate upon discharge into the expansion chamber. In so doing, the volume of the expansion chamber and, thus, the outer dimensions and weight of the spacer assembly body may be reduced. By virtue of the compact size of the spacer assembly body, the medication is more efficaciously delivered to the patient. More specifically, less medication is wasted by virtue of impingement of unevaporated medication laden droplets on the interior walls of the spacer body. And, surplus compressible volume is eliminated from the breathing circuit. 
   The combined benefits realized by the cooperating structural features of the spacer assembly include, without limitation, superior performance and enhanced patient comfort in a lightweight compact device which may be readily connected to the ventilator tubing or the breathing circuit of any suitable therapeutic respiratory equipment heretofore known in the art. 
   Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become more readily apparent from the following description of preferred embodiments thereof shown, by way of example only, in the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a body member of a ventilator spacer assembly in accordance with the present invention; 
       FIG. 2  is a perspective view of a first portion of the body member of  FIG. 1 ; 
       FIG. 3  is a perspective view of a second portion of the body member of  FIG. 1 ; 
       FIG. 4  is an elevational cross-section view of a n MDI nozzle assembly according to the present invention shown disposed in the body member first portion shown in  FIG. 2 ; 
       FIG. 5A  is a top plan view of a first component of an MDI nozzle assembly according to the present invention; 
       FIG. 5B  is a bottom plan view of the first MDI nozzle assembly component shown in  FIG. 5A ; 
       FIG. 5C  is an elevational cross-section view of a first component of an MDI nozzle assembly according to the present invention taken along line C—C of  FIG. 5A ; 
       FIG. 6  is an elevational cross-section view of an assembled MDI nozzle assembly according to the present invention; 
       FIG. 7  is an elevational cross-section view of an MDI nozzle assembly according to the present invention shown disposed in the body member first portion shown in FIG.  2  and dispensing a plume of aerosolized medication; 
       FIG. 8  is a top plan view of a valve according to the present invention that is suitable for attachment to the second body portion of FIG.  3  and operable to selectively seal the interior of the spacer assembly body member and receive the discharge outlet of a conventional nebulizer; and 
       FIG. 9  is an elevational cross-section view of the valve of  FIG. 8  shown disposed interiorly of the body member first portion shown in FIG.  3  and operatively displaced by the discharge outlet of a conventional nebulizer. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1-4  collectively, there is shown a presently preferred construction of a ventilator spacer body number  10  (FIG.  1 ), including a first portion  12  thereof ( FIG. 2 ) and a second portion  14  thereof (FIG.  3 ), of the ventilator spacer assembly of the present invention. When assembled, the body member  10  defines a bulbous yet compact medicament expansion chamber. Preferably, the central region  16  of body member  10  is at least semi-spheroidal with the first portion  12  defining an outwardly bulging profile and the second portion  14  defining a predominantly flat profile, whereby central region  16  assumes a generally turtle shell shape. First and second portions  12 ,  14  of body member  10  may be fabricated from any suitable rigid to substantially rigid metallic or plastic material. Presently preferred materials include ABS, polycarbonate or the like. To facilitate alignment and assembly of the first and second portions  12 ,  14  one of the first and second body portions is desirably provided with a preferably continuous ridge which is received in a corresponding recess in the other body portion in a tongue-and-groove connection. As shown in  FIG. 3  such ridge is identified by reference numeral  18 , and, in  FIG. 2 , the mating recess is represented by reference numeral  20 . Upon respective attachment to an MDI nozzle assembly and nebulizer valve assembly described in greater detail in connection with the remaining figures, first and second portions  12 ,  14  of body member  10  are preferably fixedly attached to one another by welding, heat bonding, solvent bonding or adhesive bonding or other conventional means or methods that may be appropriate for the materials of fabrication of the first and second portions. 
   Body member  10  has an inlet  22  and outlet  24  of a size suitable for friction connection to conventional ventilator or other respiratory equipment flexible supply tubing (not shown). Preferably, a horizontal plane through the centers of the inlet  22  and outlet  24  establishes a datum plane between the first and second body members  12 ,  14 . 
   The first body portion  12  is substantially one-half of an ellipsoid or similar spheroid bisected by the datum plane. Body member  10  is preferably nearly symmetrical to symmetrical about a first vertical plane (dot-dash line  26 ,  FIG. 2 ) passing through the centers of inlet  22  and outlet  24 . Similarly, body member  10  is preferably nearly symmetrical to symmetrical about a second vertical plane (dot-dash line  28 ,  FIG. 2 ) extending perpendicular to first vertical plane  26  and disposed at the midpoint of the longitudinal dimension of the body member. 
   The second body portion  14  is preferably generally trayshaped and includes a flat, substantially oval bottom  30  with upwardly turned side walls  32  and  34  which mate with first body portion  12 , preferably at the datum plane. All interior and exterior surfaces of the body member  10  are desirably gently blended and rounded to minimize bulk and weight and to promote efficient respiratory gas flow through the body member. 
   The first body portion  12  includes a first aperture  36  for receiving an MDI nozzle assembly  38  as shown in  FIGS. 4 and 7 . The second body portion  14  also preferably includes a second aperture  40  for cooperating with a valve assembly  42  as shown in  FIGS. 8 and 9 .  FIGS. 5A-5C  provide several views of a first component  44  of MDI nozzle assembly  38  constructed according to the present invention. Like body member  10 , the MDI nozzle assembly  38 , including first component  44  and second component  46  (FIG.  6 ), may be fabricated from any suitable substantially rigid to rigid metal or plastic such as ABS, polycarbonate or the like. First component  44  is a generally cylindrical, receptacle-like member having an open top  48 , a closed bottom  50  and a continuous circumferential wall  52  contiguous with bottom  50 . Circumferential wall  52  is preferably slightly tapered to enable the first nozzle component  44  to snugly receive the correspondingly shaped second MDI nozzle component  46  in the manner shown in FIG.  6 . The upper end of circumferential wall  52  is preferably bounded by a radially outwardly directed annular flange  54  for enabling the MDI nozzle assembly  38  to reside within the first aperture  36  of the first body portion  12  as shown in  FIGS. 4 and 7 . Once seated in the first aperture  36 , the MDI nozzle assembly  38  may be welded or bonded to the first body portion  12  at flange  54  to affix assembly  38  to first body portion  12 . 
   The MDI nozzle assembly  38  includes means for discharging a generally annular or, more preferably, generally umbrella shaped plume of medicine-containing propellant. According to a presently preferred construction, the bottom  50  of first nozzle component  44  defines a convex inner surface  56  in which are preferably provided, such as by forming or cutting, a plurality of radial channels  58 . These channels, which are preferably equiangularly arranged and number at least three and preferably at least six or more, may be envisioned as meridians emanating from the north pole of a sphere. Most preferably, channels  58  comprise twelve equiangularly spaced grooves of generally semicircular or U-shaped cross-section. However, it is contemplated that more or less than twelve channels  58  may be provided in the inner surface  56  of the enclosed bottom  50  of the first nozzle component  44  and that such channels may have cross-sectional configurations other than generally semicircular or U-shaped. Each channel  58  terminates at a small port  60  of about 0.10 to about 0.30 mm in size provided in circumferential wall  52 . Additionally, the circumferential wall  52  is preferably somewhat beveled, as indicated by reference numeral  64 , at the mouths of ports  60  to allow the plume of medicine containing propellant to expand without obstruction upon exiting the ports. In the absence of bevels  64 , unevaporated droplets might collect at the mouths of ports  60  thereby wasting medicine and hindering flow of the propellant. 
   Referring to  FIG. 6 , there is shown a fully assembled MDI nozzle assembly  38  constructed in accordance with the present invention. As illustrated, second nozzle component  46  is preferably of a size and shape to be snugly received within the first component  44 . The first and second components  44 ,  46  may be permanently affixed to one another by any suitable bonding means or methods known in the art. Second component  46  includes a central passageway  66  comprising a first portion  68  defining a shoulder  72  against which the discharge stem  76  ( FIG. 7 ) of a conventional MDI canister  80  abuts during operation of the ventilator spacer assembly in an MDI mode of operation. It will be appreciated that the shape and size of stepped portion  68  may be varied to accommodate the discharge stems of any sort of MDI canister. 
   Beneath the stepped portion  68 , central passageway  66  further includes a product delivery portion  82  through which a pressurized flow of medication-containing droplets is conveyed when MDI canister  80  is depressed to activate its internal outlet valve. Product delivery portion  82  of central passageway  66  terminates at a bottom surface  84  of second component  46 . Bottom surface  84  is preferably concave and has a radius of curvature corresponding to or, more preferably, substantially the same as the radius of curvature of convex inner surface  56  of the bottom  50  of first nozzle component  44 . The first and second nozzle components  44 ,  46  are dimensioned such that, when the second component is received in the first, the convex inner face  56  of the first component  44  contacts the concave bottom surface  84  of the second component  46 . 
     FIG. 7  shows the MDI canister  80  in a depressed or activated state wherein it is discharging a stream  88  of medicine-containing liquid into the product delivery portion  82  of the central passageway  66 . Upon exiting product delivery portion  82 , the product stream  88  impinges upon the radially innermost regions of channels  58 . Thereafter, the flow radiates outwardly through the channels  58  and is discharged through ports  60  as a diffuse gentle mist or plume  90 . 
   According to a presently preferred construction, the MDI nozzle assembly  38  preferably includes twelve ports  60  which, by virtue of the curvature of channels  58 , cause plume  90  to assume a general umbrella shape upon discharge from the assembly thus enabling the propellant to rapidly evaporate. As such, the medicine is quickly entrained in the respiratory flow circuit and delivered to the patient. The dispersion and rapid evaporation of the propellant in the plume  90  allows the spacer assembly body member  10  to have a small expansion chamber volume. This coupled with the fact that in a preferred construction the plume  90  is generally umbrella shaped enables the interior space of the body member  10  to be even further reduced and, preferably, mimic the shape of the plume. Reduced interior volume, in a preferred embodiment about 110 cc, translates to reduced exterior dimensions and weight. A ventilator spacer assembly body member of such size and weight, in turn, more effectively conveys medicine to the patient while avoiding much of the patient discomfort associated with the relatively bulky and heavy ventilator spacers heretofore known in the art. 
   By way of comparison, the surface area of a typical 0.5 mm diameter orifice or nozzle discharge port as used in the prior art, is approximately 2.5 mm 2 , whereas the sum of the surface areas of the channels  58  in the preferred twelve channel embodiment of MDI nozzle assembly  38  is approximately 23 mm 2 . This is an increase of approximately 900% in wetted area for the present nozzle assembly versus circular single or double port prior art nozzles. The large increase in wetted area adds significant friction to the flow of propellant/drug mixture, slowing its velocity while simultaneously producing great turbulence and shear to cause the exiting mixture to atomize into small droplets. The velocity of the emerging plume  90  is considerably reduced when compared to the exit velocity from one or two round unitary nozzles of the same area. The reduced velocity allows the walls of the body member  10  to be closer to ports  60  without the droplets impacting the walls. The radially emerging plume  90  impinges upon significantly more air as it exits the multiple ports  60  than does a prior art plume. More particularly, plume  90  has much more surface area for mixing with the surrounding air since its geometry is generally umbrella-shaped and inclined downwardly at approximately 300 from horizontal whereby surrounding air contacts both the top and bottom sides of the radially expanding plume. In contrast, a prior art plume that exits a circular orifice is a solid cone with an included angle of about 60° which presents rather limited volume available for contact by the surrounding air. In the current invention, the droplets of propellant in the expanding plume  90  are surrounded by considerably more air and thus heat can be transferred from the air to the propellant droplets more quickly. Hence, the propellant droplets can evaporate more quickly than in plumes generated by prior art spacer devices. The air within a spacer expansion chamber is essentially at rest when compared to the velocity of an expanding plume. Since the umbrella-shaped plume  90  of the present invention has much more volume contacting the air within the expansion chamber, it evaporates faster than prior art plumes. Consequently, accelerated evaporation allows the inner walls of the body member  10  to be closer to the ports  60  in comparison with prior spacer devices. This, in turn, allows the size of the spacer body member  10  of the present invention to be smaller than prior devices, while simultaneously minimizing the amount of drug that is deposited on the inner surfaces of the body member. 
   Although according to a presently preferred embodiment the plume discharging means of MDI nozzle assembly  38  is constructed as a plurality of radially disposed channels  58 , it is contemplated that other means capable of producing the desired plume configuration may be used. For example, rather than at least three channels  58  of substantially uniform cross-sectional area, such means alternatively may be constructed as one or more passageways of radially increasing cross-sectional area suitable for discharging a generally annular and, more preferably, generally umbrella shaped medicament containing plume  90 . 
     FIGS. 8 and 9  reveal a further aspect of the present invention. According to a presently preferred construction, second portion  14  of body member  10  includes the aforementioned aperture for cooperating with a valve  42 . Valve  42 , which is preferably constructed as a gate valve, includes a base  92  that may be adhered or otherwise fastened to the inside face of bottom  30  of second body portion  14 . Integral with and upwardly extending from base  92  is a cylindrical throat  94  having an opening  96  for closely receiving a discharge outlet  98  of a conventional nebulizer (not shown). 
   When disconnected from a nebulizer, valve  42  seals opening  96  from the ambient atmosphere. More particularly, valve  42  further comprises a gate  100  of larger diameter than opening  96  which is connected by one or more, arms  102  to a pivot shaft  104  that, in turn, is rotatably supported in upstanding brackets  106 . Gate  100  is normally biased to a closed position by a torsion spring  108  having a first leg (not illustrated) in contact with the base  92  and a second leg  110  in contact with gate  100 . Preferably, gate  100  further comprises a downwardly depending cam member  112  to promote smooth opening and closing of the gate as the nebulizer discharge outlet  98  is inserted into and withdrawn from body member  10 . When the nebulizer discharge outlet is inserted through aperture  40  and opening  96 , it comes into contact with cam member  112 . Further insertion of nebulizer discharge outlet  98  urges gate  100  from seating contact with throat  94  to the position shown in FIG.  9 . When the nebulizer discharge outlet  98  and gate  100  are so disposed, the patient may inhale the pressurized, medicine-containing air delivered by the nebulizer for as long as desired or necessary. When the therapy is completed, the nebulizer discharge outlet is withdrawn from throat  94  and aperture  40  and gate  100  returns to its seated position against the top of throat  94 . The presence of such nebulizer accommodation structure thus renders the ventilator spacer assembly of the present invention a dual-utility device selectively adaptable to both MDI and nebulizer medication dispensing applications. 
   Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for the purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.