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Description  |
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BACKGROUND
Intermittent, positive pressure breathing systems represent an important
facet in medical respiratory therapy. In general, these systems respond to
inspiratory impulses to deliver quantities of oxygen and/or other
supportive gases to a patient under a mild positive pressure. Gas flow
communication between the patient and the system is by a mask or
mouthpiece coupled through tubing to a somewhat elaborate control
apparatus serving to regulate gas flow, pressure and the like. Among the
advantages of its use, the therapy has been described as serving to
increase tidal volume and total minute ventilation; to decrease the work
or "cost" of breathing, to facilitate the elimination of carbon dioxide by
increasing alveolar ventilation; to increase arterial and tissue oxygen
tension; to provide mechanical bronchodilation, and to prevent or correct
atelectasis.
To further expand the therapeutic capability of the systems, the common
practice has been to generate medicament carrying aerosols within the
treatment mechanism conducting oxygen to the patient. Thus incorporated,
the system retains an advantageous capability of delivering all
medications used in aerosol therapy, i.e. bronchodilators, mucolytics,
detergents, antibiotics, proteolytics, anti-foaming agents and wetting
agents. For optimum performance in carrying out aerosol therapy it has
been determined that the particle or droplet size distribution of the
aerosol mist should be optimized to achieve requisite introduction of
medicament into the lung. For example the lung is structured having
twenty-three generations of subdivisions, the trachea being the zeroeth
generation, the left and right main branches forming the first generation,
etc. Should the size of the medicament carrying aerosol particles be too
large, it is opined that they would be impacted upon the oral pharynx and
not reach the bronchial tract, thus rendering the therapy substantially
ineffective. On the other hand, some authority suggests that where the
aerosol particles are too fine, i.e. of too small an average diameter,
significant portions of the mist may not be absorbed but will be exhaled.
Accordingly, a most desired medicament carrying aerosol development is one
wherein an optimized distribution of droplet or particle size is achieved.
For example, it is desirable that the particle size distribution be
somewhat monodisperse, the greater number of particles having a diameter
of about 2 microns. Particles of that diametric extent would be suited for
a deposition throughout a sufficient number of generations of the lung
extending toward the alveoli.
Considerations of efficient clinical practice require that the nebulizer
devices which generate the medicament carrying aerosols or "micro mists"
be fabricable at cost levels such that both the nebulizer and connecting
flexible tubing, mouthpieces and the like leading from more complex
control equipment to the patient be disposable after one use. This feature
of disposability permits a clinical assurance of establishing requisite
sterility for all components and as a consequence, minimal opportunity for
human error to occur.
Nebulizer devices currently used or proposed generally fail to meet all of
the above-discussed criteria. For instance, disposable devices typically
in clinical use form the aerosol mist by introducing a stream of
medicament carrying liquid into the gas stream leading to the mouthpiece
or mask. Sometimes identified as the "Bernoulli Effect", a jet of gas
interacts with the liquid stream to shear off droplets. Conventionally
some form of spherical target is positioned downstream from the point of
liquid introduction to achieve a break up of the larger of these air
entrained droplets. Generally, these devices evolve a particulate
distribution of the aerosol having a relatively large number of particles
of larger diameter and mass. These larger particles have only marginal
therapeutic effect upon reaching the lung. Ultrasonic devices have been
proposed but are regarded as too expensive to manufacture for requisite
disposability and, additionally, for typical application, these devices
tend to produce too dense a cloud of aerosol for practical utilization
within the tubular conduits typically provided, in conjunction with lung
ventilating equipment.
SUMMARY
The present invention is addressed to a system, method and apparatus having
a capability for generating micro-mists exhibiting liquid particle size
distribution optimized for aerosol therapy, while remaining fabricable at
costs permitting diposal of the apparatus following a single clinical
usage. Characterized in providing dual stage atomization of medicament
carrying liquid, the inventive approach first develops an aerosol
constituted as having an initial, relatively larger average liquid
particle size. These initial, air entrained particles then are introduced
to a second atomization stage wherein they are subjected to secondary
breakup by aerodynamic forces produced in a rapid expansion sonic
orifice-free-jet flow. By select control over certain of the parameters of
the system, for example initial particle or droplet size and/or free-jet
orifice diameter, a particle size distribution closely conforming to the
precise desires of the operator for individual therapeutic treatment can
be developed.
Another feature and object of the invention is to provide a nebulizer
apparatus which is connectable with a source of life-supporting gas
typically available in a hospital environment. The apparatus incorporates
a first atomization stage which is configured to simultaneously
communicate with the source of gas and a source of liquid to form a first
particulate dispersion of the liquid which is entrained within the gas.
These liquid particles may be considered as exhibiting an average particle
diameter, D.sub.I, and a surface tension, S, while the gas may be
considered to exhibit a density, .rho..sub.g. The apparatus further
includes a second atomizer stage communicating with the first stage and
having an input zone which receives the gas-entrained first particulate
dispersion at a stagnation pressure, P.sub.o. The second stage further
incorporates an exit orifice having a diameter, d.sub.o, through which the
dispersion is expelled, the gas being at supersonic velocities. With the
arrangement, the gas and entrained liquid droplets move under flow
conditions according to the expression:
.rho..sub.g u.sub.r.sup.2 .gtoreq.We(S/D.sub.I),
where
u.sub.r is the relative velocity between a given liquid particle and the
velocity of the gas and W.sub.e is a Weber number of value effective to
carry out a stripping mechanism breakdown of the liquid particles. This
Weber number value is equal to or greater than a critical Weber number
value. Additionally, it is preferred that the exit orifice diameter,
d.sub.o, be selected to derive a liquid particle conversion efficiency,
.epsilon., of at least about 50 percent.
Another object of the invention is to provide a method for generating an
aerosol of selected particle size distribution from a liquid source. This
method includes the step of initially atomizing the liquid in the presence
of a gas flow to produce a first particulate dispersion of the liquid
entrained within the gas. Next, the particulate dispersion, under a given
stagnation pressure, is expelled through an orifice to effect a free-jet
transference and impart supersonic velocities to the gas to form a second
particulate dispersion of particles having a smaller average diameter.
According to the method, the liquid particles within the first dispersion
exhibit a characteristic particle oscillation period, .tau., and remain
under the size-breakdown influence of the gas supersonic velocities
subsequent to the free-jet transference for an action time interval,
t.sub.a, equal to or greater than that oscillation period.
A further object of the invention is to provide a lung ventilating system
of a variety wherein life-supporting gas is conveyed under a positive
pressure through conduit means from a pressurized source into the lung of
a patient. The invention provides for the introduction of nebulized liquid
into the conduit using apparatus which includes first and second atomizer
stages arranged in serial fashion, the second stage providing for a
free-jet acceleration transference of a first suspension of particles
through an orifice leading to the conduit, the transference effecting
formation of a fine particulate suspension.
Other objects of the invention will, in part, be obvious and will, in part,
appear hereinafter.
The invention, accordingly, comprises the system, apparatus and method
possessing the construction, combination of elements, arrangements of
parts and steps which are exemplified by the following detailed
disclosure.
For a fuller understanding of the nature and objects of the invention,
reference should be had to the following detailed description taken in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic and pictorial representation of a lung ventilating
system including the nebulizer innovation of the instant invention;
FIG. 2 is a schematic representation of liquid particle breakup, showing
stripping as well as deformation breakup mechanisms;
FIG. 3 is a schematic representation of a free-jet atomization arrangement
for evolving a stripping mechanism liquid droplet breakup,
FIG. 4 illustrates a series of curves for various atomizer devices showing
the development of initial droplet diameter sizes with respect to
stagnation pressure;
FIG. 5 shows a curve comparison of droplet conversion efficiency with
respect to initial stage droplet diameter for two different free-jet
orifice diametric sizes;
FIG. 6 illustrates curves relating secondary drop size diameter with
initial drop size diameter for two values of free-jet orifice diameter;
FIG. 7 illustrates two curves relating relative volume of drop distribution
with drop diameter;
FIG. 8 illustrates two curves relating the number distribution of liquid
drop particles with their corresponding diameters, and
FIG. 9 is an embodiment of a nebulizer arrangement according to the
invention with portions cut away to reveal internal structure.
DETAILED DESCRIPTION
As used herein, atomization refers to the process of creating an aerosol of
minute droplets. The nebulizer approach of the present invention involves
a secondary breakup in the initially atomized droplets of a medicament
carrying liquid using a supersonic free-jet expansion through a relatively
small orifice. The system of the invention utilizes the basic controls
currently in use in conjunction with current disposable nebulizer devices
deriving atomization through the "Bernoulli Effect" discussed above.
Referring to FIG. 1, a schematic illustration of the disposable components
of a lung ventilation system according to the invention are revealed in
conjunction with representations of conventional life support gas supplies
and lung ventilation control equipment. In the figure, a patient is shown
at 10 receiving aerosol therapy. With this arrangement, the patient orally
retains the mouthpiece 12 of a disposable, positive-negative unit 14 or
apparatus for the controlled reception of oxygen and other optionally
provided support of gases. Unit 14 is configured incorporating an exhaust
valve 16 and a nebulizer device according to the invention at 18. An
upwardly protruding stem 20 terminating in a ball joint component is
provided to secure the device 14 to an overhead support (not shown) to aid
the patient in retaining mouthpiece 12 in proper position. Support gas at
low positive pressure is introduced into device 14 through flexible
discardable tubing 22 from a lung ventilation control apparatus
represented schematically by block 24. The control provided at block 24
serves to respond to patient breathing activity to inflate the lung until
a preset pressure has been reached, at which time the inspiratory phase is
halted and expiration commences. Generally, such devices also can operate
in predetermined automatically timed control fashion as opposed to a
patient respiratory demand procedure. Pressure signaling inputs to control
24 are provided by discardable flexible tubing 26 extending thereto from
exhaust valve 16 within device 14. A supply of life support gas such as
oxygen under pressure is represented at block 28 in communication with
control 24 through a conduit 30. This supporting gas may be provided
through typical gas retaining cylinders, however, it conventionally is
supplied for clinical use from supply conduits emanating from a central
station. The oxygen-rich supporting gas generally is available to controls
as at 24 at a pressure of about 50 p.s.i.g. For purposes of operating the
nebulizer device 18, a gas delivery control feature may be provided as
represented at block 30. Control 33 communicates with the pressurized
supply at block 28 through conduit 32 and supplies gas at this relatively
higher pressure through conduit 34 to nebulizer 18. This supply may be
provided by control 33 in a pulsing manner over a predetermined duty cycle
for the system.
As discussed above, the developement of the optimum mist droplet size
distribution according to the invention involves an initial, larger
droplet formation followed by a secondary atomization thereof.
Accordingly, as a prelude to describing a particular embodiment providing
this secondary atomization, an examination of the theory of the breakup
mechanism may be found helpful. This breakup mechanism involves the
positioning of a liquid droplet of given larger size within a high
velocity stream of gas. If the velocity of the droplet, v.sub.p, is
considerably different than the velocity of the gas surrounding it,
v.sub.g, a breakup mechanism is observed which is commonly referred to as
"secondary atomization". Generally two dominant breakup mechanisms are
considered to be associated with this phenomenon which are commonly
referred to as a "deformation" mechanism and a "stripping" mechanism. In
analyzing these two mechanisms, the following initial flow and droplet
variables are considered:
D.sub.I =initial particle (i.e., droplet) diameter
u.sub.r =relative velocity between the particle and the gas stream (i.e.,
u.sub.r =v.sub.p -v.sub.g)
.rho..sub.g =density of gas
.rho..sub.L =density of liquid droplet
S=surface tension of liquid
These variables can be associated to develop expressions for determining
the presence or absence of secondary atomization. For example, the
variables may be associated to derive the Weber number, W.sub.e, as a
ratio of the ram pressure deformation force that prevails on the windward
face of the droplet with respect to the surface tension force (i.e.,
S/D.sub.I) which holds the droplet together. Set forth as an equation, the
Weber number is represented by the following expression:
##EQU1##
It may readily be opined that larger Weber number values are required to
evoke a fragmentation of droplets. Critical Weber numbers, W.sub.e.sbsb.c
having values within the range of 10-20 have been reported for
fragmentation of liquid droplets, with values thereof from 12-15 being
common for droplet fragmentation of distilled water. In this regard, it
may be observed that the flow condition set forth below as expression (2)
impliedly obtains in the development of secondary atomization.
.rho..sub.g u.sub.r.sup.2 .gtoreq.W.sub.e.sbsb.c(S/d) (2)
Also considered in the analysis of secondary atomization is the
characteristic droplet oscillation period, .tau.. This characteristic
period is represented by the following expression:
##EQU2##
In determining the probable mechanism of secondary fragmentation of the
droplet, additionally, it is useful to consider a time variable, t.sub.a,
in relation to .tau., the characteristic droplet oscillation period. This
variable, t.sub.a, is referred to as the "action time" and, in general
terms, is the interval during which an initial droplet or liquid particle
is subjected to gas forces reacting upon it under given ram pressure
force. The use of the "action time" provides a means for considering the
droplet dynamics in determining the droplet breakup mechanism, and has
been termed a time constant on the driving force for droplet breakup.
Further discussion of the term is described in: Morrell, G., "Critical
Conditions for Drop and Jet Shattering", NASA-TN-D677 (1961).
Looking to FIG. 2, breakup phenomena for the case of deformation and
stripping mechanism are pictorially revealed. In the figure, a droplet 40
having diameter, D.sub.I, is subjected to a relative gas velocity,
u.sub.r, and consequent ram pressure force represented by the small arrows
adjacent the droplet, defined as .rho..sub.g u.sub.r.sup.2. As labeled in
FIG. 2, with a deformation mechanism, the effect of the ram pressure is to
increasingly flatten the drop with time, as shown at step 42. For
conditions where t.sub.a is greater than or equal to .tau. (i.e. action
time exceeds oscillatory period), a critical time is reached where a hole
is blown in the droplet to form a structure which resembles a bag with a
relatively massive torodial rim and a thin wall, as represented at step
44. Ultimately, the bag-shaped structure bursts producing a shower of much
smaller droplets and the rim, containing a major portion of the initial
mass of the droplet, grows in diameter until it divides into a number of
smaller droplets, as represented at step 46.
For the case of a stripping mechanism, the inertial characteristics of the
droplet cause it to maintain a shape that resembles a planetary ellipsoid,
as represented at step 48. Subsequently, as represented at step 50, liquid
is drawn off in thin sheets from the edge of the droplet and fine
ligaments, the thicknesses of which are of the order of the gas-liquid
boundary layer thicknesses at the thin sheet attachment points, rapidly
disintegrate into very small droplets, hence the term "stripping". Should
the initial Weber number not be sufficiently high or if the time interval
spent at conditions representing a Weber number above critical value not
be sufficiently long, the stripping process will cease and a stable
droplet of smaller size will remain in addition to micro mist. This
condition is represented at step 52 in FIG. 2.
From the foregoing it may be observed that in order to obtain a complete
stripping action, Weber numbers should be large and the characteristic
droplet oscillation period, .tau., should be small. However, the latter
coefficient should have a value sufficient to maintain a continuous
stripping activity with time. The action time should be sufficiently long
to provide for enough of an interval of reaction to completely strip the
droplet and evolve a desired droplet or liquid particle size distribution.
Further, the Weber should be kept high so as to maintain a high driving
force for this stripping mechanism to persist. It has been the observation
of the applicants that the stripping mechanism for secondary droplet
breakup will produce a greater number of smaller diameter droplets. Hence,
high Weber numbers should be produced for time periods of the order of the
characteristic droplet oscillation period in order to provide efficient
secondary atomization. Further, it may be implied that there is no
theoretical limit for preatomized droplet sizes, i.e. droplet diameters
D.sub.I, for the free-jet expansion atomization technique as opposed to
the utilization of a standing shock wave within a nozzle to carry out
droplet breakup.
Looking to FIG. 3, the above consideration defining the parameters for
control over a free-jet expansion system are schematically revealed. The
drawing shows an initial atomization stage from which region larger
droplets having an initial diameter, D.sub.I, are introduced along conduit
61 through an access 62 to a droplet containment zone or chamber 64
defined by wall 66. When introduced as entrained within a pressurized gas,
the gas and entrained droplets will exhibit a stagnation pressure P.sub.o
as well as the noted initial droplet diametric size D.sub.I. From chamber
64, the droplets and entraining gas are rapidly expanded through a
free-jet, "knife-edge" orifice 70 formed within wall 66. This rapid
expansion produces supersonic gas velocities very quickly. However, the
droplets cannot be accelerated as rapidly as the gas and a large
gas/particle relative velocity is produced in the barrel shock region
outlined at 72. Accordingly, the above-discussed considerations for
evolving a stripping mechanism mist development are concerned with the
reactions carried out within the zone of supersonic flow outlined at 72.
For example, the action time within the zone should be gauged with respect
to the characteristic droplet oscillation period to achieve the full
stripping action as required. Without appropriate control over the
developmental parameters of the system, excessively large droplet
particles may remain from the stripping action in addition to the desired
mist or aerosol represented at 74. The liquid components exiting from the
supersonic flow region defined by barrel shock boundary 72 may be
considered to represent secondary particles, being the product of the
stripping mechanism as shown at 74 as well as a hypothetical remaining
original or initial particle having been subjected to stripping to reach a
final diameter, D.sub.F. The latter particles may be evaluated by known
analytical techniques with respect to initial diameter to provide a
qualitative efficiency evaluation of the system. It has been determined
that optimized liquid particulate size distributions can be achieved
through a control over the initial atomization at 60 as well as at the
parameters established at the secondary atomization stage commenced within
chamber 64.
Looking to FIG. 4, one aspect of parameter control is revealed through a
comparison of curves generated with a free-jet expansion system utilizing
two different commercially obtained devices for initial atomization, as
described at block 60 in FIG. 3, as well as with a variation of orifice
diameters, d.sub.o, described at 70 in that figure. These curves,
identified at 80, 82 and 84, represent a relative narrow portion of
possible plots, falling within a stagnation pressure, P.sub.o, range of
from about 30 to 60 psig. The curves reveal that initial droplet size,
D.sub.I, is a function of stagnation pressure, P.sub.o, orifice size,
d.sub.o, and the type of atomizer utilized within the initial atomization
stage. Of the curves in FIG. 4, curves 80 and 82 were derived using a
"Soni-mist" atomizer, model no. 900-3, a product of Heat Systems
Ultrasonic, Inc., Plainview, N.Y., curve 80 being generated with an
orifice diameter, d.sub.o, of 0.08 inch, and curve 82 is generated with an
orifice diameter d.sub.o of 0.038 inch. Curve 84 was generated utilizing a
"2-Fluid" device, model no. 15, marketed by the DeVilbiss, Corp. for
initial atomization and in conjunction with an orifice size, d.sub.o, of
0.038 inch. While initial droplet size appears insensitive to stagnation
pressures, P.sub.o, within the noted range, excursions beyond that range
may well evoke more pronounced variation. It may be observed, that the
initial droplet size D.sub.I, is somewhat dependent upon orifice size,
d.sub.o, and particularly, upon the type of commercial first stage
atomizer utilized. Accordingly, the curves would appear to indicate that
the forms of conventional atomizers presently on the market tend to lack a
controlled consistency of droplet development. In deriving the curves of
FIG. 4, distilled water was utilized in conjunction with a confined
chamber into which the liquid particles of the initial atomization
procedure were inserted as entrained within air. All developed droplets,
whether in the initial or secondary stage of atomization, were isolated
from room air to prevent the possibility of dust entry within the region
of measurement for the test system. A Royco particle size analyzer was
employed in the study along with a laser fringe visibility analysis for
examination of the secondary droplet size D.sub.s. Laser fringe visibility
techniques were used to measure the initial atomization stage droplet
sizes as well as final drop size (D.sub.f) after atomization. The Royco
particle analyzer was a model 220 which is produced by Royco Instruments,
Inc., Menlo Park, California.
The efficiency, .epsilon., of the breakup mechanism of the inventive system
may be determined by comparing the volume of the droplets of the initial
atomization stage 60 which have been converted to desired small secondary
droplets of diameter D.sub.s, to the volume of particles of initial
diameter, D.sub.I. The former of these values may be represented as the
difference of the cube of the diameter of the particles of initial
atomization, D.sub.I, minus the cubed value of the diameter, D.sub.F, of
those particles following the removal of material therefrom in consequence
of the above-described stripping mechanism. This conversion efficiency may
be expressed as follows:
##EQU3##
Looking now to FIG. 5, values of conversion efficiency, .epsilon., are
plotted with respect to initial atomization stage droplet diameter,
D.sub.I. As represented by curve 86, while efficiencies were very low for
orifice diameters, d.sub.o of 0.038 inch, by increasing the diameter of
the droplets generated in the initial atomization stage, the conversion
efficiency, .epsilon., increases linearly to the order of a fifty percent
efficiency conversion value for initial droplets having diameters of 40
microns. It may be further noted from curve 88 that the conversion
efficiency, .epsilon., for a larger orifice diameter, d.sub.o, of 0.08
inch is relatively high but drops slightly as initial particle diameter
size, D.sub.I, is elevated. In the latter regard, however, the conversion
efficiency remains above about fifty percent through initial diameters of
about 55 microns. The orifice diameter, d.sub.o, utilized in generating
curve 88 was 0.08 inch, and stagnation pressure, P.sub.o, was 50 psig
except where labeled otherwise. The figure additionally serves to show the
advantageous predictability and availability of selecting engineering
parameters for any given clinical requirement. For example, where the
volume of induced lift supportive gases for purposes of nebulization
should be maintained at relatively low levels, an orifice diameter,
d.sub.o, of lesser extent would be selected with some diminishment in
conversion efficiency.
Looking to FIG. 6, the secondary drop size, represented as the secondary
drop diameter, D.sub.S, is plotted as a function of initial diameter size,
D.sub.I. Note from curve 90 derived utilizing an orifice diameter, d.sub.o
of 0.038 inch, as well as curve 92 representig an orifice diameter,
d.sub.o of 0.08 inch, that the secondary drop diameter increases linearly
with initial droplet diameter. This relationship reveals that the size of
the particles evolved through the secondary atomization step can be
produced within any diametric region desired by the operator. The
observation also tends to confirm that the stripping mechanism is most
probably operative with the system, inasmuch as the boundary layer of
thickness of a drop which, as noted above, serves an important roll in the
stripping process, is also related to drop size. The curves of FIGS. 5 and
6 further reveal that excellent conversion efficiencies are possible for
drop ranges which are currently of interest in the field of aerosol
therapy, i.e. in the range of 1-2 microns diameter.
Considered as a whole, the above discourse indicates that a free-jet
atomizer scheme provides a highly advantageous arrangement for generating
an adequate number of droplets of proper size for lung therapy
applications. This observation is amplified where the respirable drop
volume distribution and drop number distribution of the system are
examined as a function of secondary diameter. Curve 94 of FIG. 7 was
developed utilizing the free jet atomization arrangement of the instant
invention, while curve 95 thereof was generated using the above-described
conventionally available "Bernoulli" atomizer device currently in clinical
use. For each of the curves 94 and 96, the droplet volume is given by the
following conventional expression:
##EQU4##
where N.sub.i is the number of drops with diameter D.sub.i and V.sub.i is
the total droplet volume. Curve 94 reveals that the greater portion of
liquid droplet volume, and consequently medicament volume, is provided in
droplets of preferred 2 micron diameter for the free-jet atomizer
technique of the invention. By comparison, the conventional device,
represented at curve 95, reveals that the corresponding greater portion of
droplet volume is present in droplets of larger diameter, i.e. about 4.5
microns. It is generally considered that droplets having a diameter of
about 1-2 microns are more likely to be deposited in the alveoli of the
lungs than droplets of greater than 3 micron diameter. Under the latter
criterion, the free-jet atomizer system of the invention is indicated as
being about twice as effective as the atomizer systems currently in
clinical practice.
Looking to FIG. 8 curve 96 is a plot of the respirable drop number
distribution with respect to drop diameter for the free-jet atomization
arrangement of the invention, while curve 97 represents the corresponding
drop number distribution for the above-described conventional "Bernoulli"
device. It may be observed that the number distribution represented by
curve 96 falls off quite rapidly with increasing drop size, as compared to
curve 97. In effect, the results represented by curve 96 tend toward a
monodispersed distribution of liquid droplets at the diametric range of
interest.
Now looking to FIG. 9, the device 14 incorporating the system of the
invention is revealed in more enlarged detail. As described earlier,
device 14 includes a mouthpiece 12, exhaust valve assembly and associated
tubing 26, and stem support 20 all communicating with and attached to a
relatively short rigid tube 21. The end of tube 21 opposite mouthpiece 12
is coupled with a disposable flexible tube 22, in turn, leading to a
controlled supply of life supporting gas at relatively low positive
pressure, for instance about one-half p.s.i. The nebulizer 18 of the
invention includes a cylindrical housing 100 within which is integrally
formed an initial atomization chamber 102 and an adjacent, serially
disposed containment chamber 104 for receiving entrained liquid droplets
of initial diameter, D.sub.I. Separating chambers 102 and 104 is a
conical, converging duct formed by an inwardly extending annular component
106 having a concave surface 108 the uppermost edge of which defines a
relatively wide input aperture 110 leading to chamber 104. The lower
surface of chamber 102 is defined by a disc 112 which is configured having
a vertically oriented integrally formed nozzle at 114 extending from the
center thereof. Disc 112 additionally is configured having one or a
plurality of annular passages 116 formed therethrough and communicating in
gas transfer relationship with a cup-like reservoir 118. Nozzle 114 is
formed having a centrally disposed opening 120 extending therethrough and
communicating with a flexible liquid supply tube 122 one end of which is
inserted within a corresponding opening formed within disc 112 and the
opposite end of which extends to the lowermost region of reservoir 118 to
communicate with a medicament conveying liquid represented at 124.
Connection between disc 112 and housing 100 is by a threaded engagement
shown at 126, while the connection of reservoir 118 therewith is
represented by threaded coupling 128. Supporting gas such as oxygen under
a higher pressure, for instance 50 p.s.i.g., is introduced through conduit
34 to reservoir 118 by connection thereof with outwardly extending rigid
tube 130. Tube 130 is shown as integrally formed with the walls of housing
100.
With the arrangement shown, liquid is drawn (Bernoulli effect) through
conduit 122 and thence into nozzle 120 by gas supplied through conduit 34,
tube 130, and passages 116. As this liquid exits from nozzle 120, it is
broken down into the initial droplet size upon encountering and being
entrained by gas passing through passages 116 and into chamber 102. The
size of these droplets may be controlled by adjusting the position of the
tip of nozzle 120 with respect to the converging duct formed by surface
108. The initial, entrained droplets then are introduced to chamber 104 at
the stagnation pressure of the system, whereupon they exit from a
knife-edge orifice 132 formed within tube 21. Secondary atomization takes
place at this point and the secondary liquid particles are entrained by
life supporting gas inserted from tube 22. The gas entrained liquid
particles then are delivered along tube 21 to be administered to the
patient through mouthpiece 12.
All of the components of the device at FIG. 9 may be configured of suitable
polymeric material for fabrication at cost commensurate with the theme of
providing disposability of the device following one clinical utilization.
In the same light, the threaded connections described may be dispensed
with upon the establishing of a desired optimum particulate distribution
for a conventional clinical application. In this regard, the stagnation
pressure, hole size within nozzle 120 and the relative positioning of the
nozzle with respect to conical surface 108 may be pre-established as well
as the size of opening 110. As indicated in detail above, the diameter of
orifice 132 also contributes to the termination of ultimate particulate
distribution.
Since certain changes may be made in the above system, apparatus and method
without departing from the scope of the invention herein involved, it is
intended that all matter contained in the above description or shown in
the accompanying drawings shall be interpreted as illustrative and not in
a limiting sense.
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