Abstract:
A portable ventilator for providing an air-recipient with compulsory respiration is provided with an outlet manifold and a single-expansion-chamber muffler configured so that airflow through an inhale outlet port of the muffler is pulse-free and a transmission loss, defined as the ratio of sound power generated by the at least one compressor and incident on the muffler to the sound power transmitted by the muffler, is sufficient to deaden the sound power of the compressor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Application No. 60/351,077, filed Jan. 23, 2002. The contents of the aforesaid U.S. Provisional Application No. 60/351,077 are incorporated by reference herein. 
     
    
     STATEMENT OF GOVERNMENTAL INTEREST  
       [0002] This invention was made with U.S. Government support under a contract with the U.S. Army Medical Research and Material Command, no. DAMD17-99-2-9041. The U.S. Government has certain rights in the invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention generally relates to a battery operated portable apparatus configured to provide respiratory ventilation in the far forward early trauma scene as well as in the clinical setting. Particularly, the invention is directed to a manifold/muffler assembly of a portable ventilator configured to provide smooth, constant airflow to the air recipient and to reduce the noise level associated with the cyclically operated compressor of the ventilator.  
           [0005]    2. Description of Related Art  
           [0006]    Respiration involves the introduction of gases, especially oxygen, to the lung during inspiration and the removal of waste gases, particularly carbon dioxide, during expiration. In healthy individuals respiration is normally effected by spontaneous ventilation or breathing, which results in the introduction of the necessary gases. Unfortunately, intentionally inflicted wounds or physiological and pathological processes may compromise normal pulmonary function leading to the inhibition of effective respiration or total respiratory failure. In such cases respiratory therapy, often involving artificial ventilation to some degree, is required.  
           [0007]    For example, respiratory therapy is often necessary for victims of natural disasters or military actions associated with weapons of mass destruction, as well as for patients undergoing surgery or those suffering disorders and diseases of the pulmonary air passages. Typically, such respiratory therapy involves the use of mechanical ventilators.  
           [0008]    Mechanical ventilators are simply devices that effect ventilation or, in other words, cause airflow into the lungs. More specifically, such devices typically force air into the lungs during the inspiration phase of the breathing cycle but allow a return to ambient pressure during spontaneous exhalation. The forced influx of fresh air by mechanical ventilation facilitates the pulmonary mediated processes that comprise respiration in mammals. One of these processes, the removal of waste gases, is the primary mechanism by which carbon dioxide is excreted from the body. Modern mechanical ventilators are designed to provide ventilation by regulating tidal volume (volume per breath), flow rate, delivery profile and respiratory flow thereby controlling carbon dioxide excretion. Because they can also regulate airway pressure and the concentration of inspired oxygen they offer control over oxygenation as well.  
           [0009]    Numerous makes and models of mechanical ventilators are used today. All of the ventilators used are either volume-controlled ventilators or pressure-controlled ventilators. In the former, the ventilator is designed to deliver a set volume of gas regardless of the airway pressure. Such devices usually have a pressure cutoff to prevent damage to the lungs. In contrast, the pressure-controlled ventilators, based on the selected respiratory rate, the inspiratory gas flow and the peak airway pressure, deliver inspired gas, while monitoring the tidal volume, until the desired pressure is reached. Each of these types of mechanical ventilators incorporates a number of sophisticated features, which allow unparalleled control over the delivery of gases to the lung. In order to meet the diverse needs of patients requiring ventilation therapy, common mechanical ventilators offer several ventilation modes, each having a variety of programmable parameters, offering an almost unlimited versatility. Accordingly, both types of the above-discussed ventilators are highly expensive to manufacture and maintain.  
           [0010]    Exemplifying at least some of the above-discussed principles of operation is U.S. Pat. No. 4,794,922 which discloses a ventilator operating in clinical conditions and configured to have an electronically controlled artificial respiration to a patient. The ventilator, as disclosed, features an air-tight manifold configured to house a system of ducts which provide air communication between the source of gas and the patient. While meeting many structural requirements, the ventilator of U.S. Pat. No. 4,794,922 is powered by an external source and, therefore, is not portable. Further, because of the complexity of the overall structure, the device is difficult to manufacture and is expensive.  
           [0011]    A battery powered air mover or ventilator is known using “unfiltered” air supplies which generate acoustic noise and are characterized by a pulsatile flow, both of which can be quite disturbing to the air recipient. Mainly, these disadvantages stem from an unsatisfactory design of the gas-conveying and gas-storing components and particularly, the complexity of the internal tubing and the excess of the connectors needed to assemble the known ventilators. Particularly troublesome noise in the known ventilators is generated by a compressor cycled on and off to provide for the inspiration and expiration of the air recipient&#39;s lungs. When turned on, the loud noise produced by the compressor travels through the ventilation circuit tube and is heard by the air recipient. Critically, the configuration of the gas-conveying ducts and accumulators renders airflow entering the air-recipient&#39;s lungs pulsed. In addition, the number of elbows and tee connectors along the air path is characterized by multiple contractions and expansions in the flow area. As a consequence, the connectors creates the flow noise, which in combination with the pulsation, detrimentally affects audible and tactile senses of the patient during breathing.  
           [0012]    Accordingly, a need exists for a light and compact field-portable ventilator configured to provide a constant, smooth flow of air towards a recipient thereof with a reduced level of noise produced by a compressor, as well as by airflow, typically associated with a battery-powered ventilator.  
         SUMMARY OF THE INVENTION  
         [0013]    To meet this need, the present invention provides for a field-portable ventilator configured to reduce the audible noise generated by at least one compressor and to provide a substantially uniform flow of compressed gas towards the air recipient.  
           [0014]    To reduce the noise and flow pulsation, the inventive device includes a patient circuitry including a manifold and a muffler located downstream from the manifold along an output path of compressed air and being in flow communication therewith. Geometry of the manifold and muffler provides for smooth airflow through the outlet path and for decreases in the sound level at the downstream end of the respiratory or patient circuit due to the work of the compressor.  
           [0015]    Further reduction of the audible components is achieved by the inventive device, which, in addition to the muffler in the patient circuitry, is advantageously configured to have another muffler located along an inlet path of air. The muffler positioned along the upstream portion of the flow path is configured to deaden the external noise emitted through the inlet port of the inventive device during actuation of a compressor.  
           [0016]    Provision of the upstream and downstream mufflers, substantially reducing the audible components generated by the power-actuated components, such as compressors, does not amount to the overall enlargement of the inventive device. On the contrary, the device is miniaturized due to a reduced number of connectors needed to assemble the device. Accordingly, large numbers of the device can be easily delivered to the field when a great number of victims may be in need of compulsory respiration. Concomitantly, fewer components substantially lower the cost of the device, if compared to the known portable models of the air mover or ventilator.  
           [0017]    The geometry of the inventive muffler is based on the analysis description provided in the following publication: Beranek, Leo L. (ed.) 1971, “Noise and Vibration Control”, McGraw-Hill, Inc., New York, N.Y. This publication discloses how to design a single-expansion-chamber muffler by evaluating its Transmission Loss (L TL ). The Transmission Loss is defined as the ratio of sound power incident on the muffler to the sound power transmitted by the muffler, given in decibels. The Transmission loss can be calculated in terms of two parameters m and kl calculated according to the following:  
               L   TL     =     10        log        [     1   +       1   4            (     m   -     1   m       )     2          sin   2        k                 l       ]                 (   1   )                               
 
           [0018]    The parameter m is the ratio of the cross-sectional area of the chamber to the cross-sectional area of duct:  
             m   =       S   2       S   1               (   2   )                               
 
           [0019]    The parameter kl is given as a ratio of 2 pi times the length of the muffler divided by the wavelength according to the following:  
               k                 l     =       2                 π                 l     λ             (   3   )                               
 
           [0020]    λ is the wavelength of the sound at the frequency of interest and is calculated in terms of frequency (f) in Hz, and muffler temperature (θ c ) in ° C. or muffler temperature (θ f ) in ° F. according to the following:  
             λ   =       345   f                θ   c     +   273     295                     meters             (   4   )               λ   =       1130   f                θ   f     +   460     530                     feet             (   5   )                               
 
           [0021]    Ideally, the inventive muffler would be less than about 3″×4″ so as to minimize the space it takes up in the ventilator. The sound generated by the compressor inside of the ventilation tube has a frequency of about 200 Hz, with corresponding harmonics. Appendix A shows the Transmission Loss for mufflers having various lengths and diameters close to these ideal values.  
           [0022]    In accordance with another aspect of the invention, the ventilator may produce increased flow output, if such is needed. Remarkably, the installation of the two-compressor power unit does not require structural modifications of the original structure, which remains light and space-efficient. While attempts at installing multiple compressors have been made in the past, the use of elbow and tee connectors with longer lengths of tubing, and coupling the compressors in parallel, caused “fighting” to occur between the compressors, due to lack of synchronous timing between the compressors. As a result, the desired output could not be achieved. The inventive system overcomes the “fighting” problem in a three-fold manner. First, the flow-conveying system configured in accordance with the invention, allows for the air to flow in “straight paths”, by not requiring multiple bends to connect the compressors in parallel. This reduction in the numbers of elbow and tee connectors significantly reduces the restrictions seen by the flow through elimination of multiple contractions and expansions in the flow area. Secondly, the connectors used to attach the tubing to the manifold are sized so as to reduce or eliminate for aforementioned changes in the flow area. Thirdly, the tubing lengths are reduced by positioning the compressors in close proximity to the manifold and muffler, thereby reducing long lengths of tubing, which could further restrict the flow.  
           [0023]    Accordingly, the inclusion of the muffler configured in accordance with the inventive field-portable ventilator substantially reduces the noise emitted through inlet and outlet ports of a ventilation circuit during the activation of the compressor. Still another advantage provides for constant, smooth airflow to an air recipient, which otherwise would have a pulsation in the flow detrimental to the air recipient. Yet a further advantage of the inventive device is the reduced complexity of the internal tubing.  
           [0024]    It is, therefore, an object of the invention to provide a portable ventilator characterized by the reduced noise level during operation of its compressor on both the air input and output paths.  
           [0025]    Yet a further object of the invention is to smooth the airflow for a constant output to the air recipient.  
           [0026]    Still another object of the invention is to provide a portable ventilator configured to provide increased airflow from multiple compressors in a linear fashion while featuring a compact, light structure.  
           [0027]    Still yet a further object of the present invention is to provide a kit for providing compulsory respiration to an air recipient, comprising  
           [0028]    a portable ventilator provided with:  
           [0029]    at least one compressor operative to provide airflow towards the at least one air recipient,  
           [0030]    spaced inlet and outlet manifold/muffler assemblies located along an air path and having each a single-chamber muffler and an inlet opening located upstream from and in direct flow communication with a respective single-chamber muffler, wherein the inlet and outlet manifold/muffler assemblies are configured to decrease an acoustic signal generated by the at least one compressor along upstream and downstream ends of the path and to provide smooth constant airflow to the air recipient; and  
           [0031]    a disposable air conveying tubing providing flow communication between the air recipient and the portable ventilator, the disposable air conveying tubing being externally attachable to an outlet port of the single-chamber muffler of the outlet manifold/muffler assembly and traversed by the smooth, constant airflow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    The above and other objects, features and advantages will become more readily apparent from the detailed description of the preferred embodiment accompanied by the following drawings, in which:  
         [0033]    [0033]FIG. 1 is a perspective view of the device assembled in accordance with the present invention;  
         [0034]    [0034]FIG. 2 is a top/side perspective view of the inventive device of FIG. 1 shown without its housing;  
         [0035]    [0035]FIG. 3 is a flow chart illustrating the principle of operation of the device of FIG. 1;  
         [0036]    [0036]FIG. 4 is a bottom/side perspective view of the inventive device, as illustrated in FIG. 2;  
         [0037]    [0037]FIG. 5 is a perspective view of a muffler/accumulator assembly of the inventive device;  
         [0038]    [0038]FIG. 6 is an elevated partially broken view of the muffler/accumulator assembly shown in FIG. 5;  
         [0039]    [0039]FIG. 7 is a view of back panel of the inventive device of FIG. 1 provided with an inlet muffler assembly shaped and dimensioned in accordance with the inventive concept;  
         [0040]    [0040]FIG. 8 is a schematic view of a disposable respiratory portion of a kit including, besides the disposable respiratory portion, the inventive device of FIG. 1; and  
         [0041]    [0041]FIGS. 9 and 10 are graphs illustrating power spectral density of sound at the outlet end of the device shown in FIG. 1 with the muffler/accumulator assembly shown in FIG. 4 without and with the assembly, respectively. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]    The inventive portable ventilator  10 , as illustrated in FIGS.  1 - 6 , can be used in the field when a victim/patient, further referred to as an air recipient, requires temporary respiratory relief, as well as in a clinical environment. The insignificant minimal weight of the ventilator of about 4.5-5.5 pounds, its compact structure, and a local source of power  12 , such as, for example, a lithium ion battery  12 , all provide for the easy transportation of a great number of such devices to a scene associated with multiple victims. The battery  12  can power the device for at least about one hour. In addition, the ventilator  10  can be successfully used as a stationary unit coupled to an external source of power such as, for example, a car battery or any other conventional power supply, through hookups  14  located on a front panel  16  (FIG. 1).  
         [0043]    In use, the operator, based on such factors as, for example, the condition, age, body type and gender of the air recipient, manipulates a rotary switch  20  to set the desired volume of compressed air to be delivered and further displaces an on/off switch  18  in an “on” position to provide actuation of at least a first compressor  22  (FIG. 2). Energization of the compressor  22  establishes inflow of outer air through an inlet port  48  (FIGS. 1 and 4), located on a back panel  46  of the device  10 , via a straight inlet conduit  50  (FIG. 2) into a first or inlet manifold  32 . The latter is configured as a tube having a longitudinal axis, which extends substantially perpendicular to the inlet conduit  50 , and provided with at least two outlets. The outlets are in flow communication with opposite chambers of the compressor  22  via substantially straight, uniformly dimensioned conduits  34  that may be configured to have at most one elbow (FIGS. 4 and 6). Following the air path within the device  10 , compressed air is directed along a patient ventilation circuitry including substantially straight uniform conduits  35  (FIGS. 4 and 6) and a second or outlet manifold  30  extending parallel to the inlet manifold  32  and provided with a short outlet duct  36 . The latter is substantially shorter than and extends parallel to conduits  34 ,  35  and  50  and opens into a single expansion chamber muffler or accumulator  38  (FIGS. 4 and 5). Finally, air is advanced from the accumulator  38  via the inhale port  44  located on the front panel  16  (FIG. 1) to the air recipient&#39;s lungs. An electronic controller  52  (FIG. 4) monitors the operator-selected parameters, such as the desired volume of compressed air, during the compressor&#39;s “on” cycle. Switching the compressor  22  between “on” and “off” states generates a strong acoustic signal, which can negatively affect the air recipient, and if produced by multiple ventilators  10  simultaneously, when the help is rendered to many people, becomes more than a nuisance. In accordance with the invention, manifold/muffler assemblies located at opposite upstream (inlet) and downstream (outlet) ends of air path achieve the decrease of the compressor-generated sound and airflow-generated sound. The reduction of the airflow-generated noise is achieved by configuring the conduits  34 ,  35  and  50  substantially free from contractions and expansions and extending parallel to one another, as well as by positioning the compressor  22  and the accumulator  38  in a close spaced relationship.  
         [0044]    A downstream manifold/muffler assembly  26 , in addition to minimizing the compressor-generated and air-connector generated sound, is configured to smooth airflow entering the air recipient and eliminate the pulsations therein. Configured of the manifold  30 , duct  36  and the single-expansion chamber muffler  38 , the assembly is most effective when structured in accordance with the principles summarized in Beranek&#39;s paper.  
         [0045]    Structurally, the muffler/accumulator assembly  26  is a single expansion chamber structure enclosed in a housing  42  (FIGS. 4 and 5) juxtaposed with the compressor  22  and sealingly coupled to the front panel  16  of the ventilator  10 . The manifold  30  is configured as an elongated tube, which is provided with numerous ports receiving the conduits  35  (FIGS. 4 and 5) traversed by compressed air, and the duct  36  provided with a manifold outlet  40  opening into the single expansion chamber of the muffler  38 . The shape of the muffler  38  can be either cylindrical or rectangular depending on the configuration of the device  10 . The dimensions of the muffler vary as a function of size and the amount of reductions achieved for a specified volume when using the equations as disclosed in Beranek&#39;s paper. The rectangular muffler  38 , as illustrated in FIGS.  2 - 6 , is advantageously about 3-4″ long, about 3.5″ wide and about 1.25″ thick. Mufflers of such dimensions were found to almost completely eliminate the loud compressor sound from the tubing. Alternatively, instead of the rectangular muffler, the cylindrical muffler, having substantially the same volume as the rectangular one and dimensioned to have a diameter of about 2.5″ and a length of about 3-4″, produces equally satisfactory sound-deadening effects. The sound at the downstream end of the air output path circuit was recorded with and without the muffler  38 . FIGS. 9 and 10 show the power spectral density of these sound recordings. FIG. 9 illustrates the plot corresponding to the sound with no muffler present, whereas FIG. 10 shows the drastically reduced magnitude of the compressor-generated sound upon installation of the inventive manifold/muffler assembly  26 .  
         [0046]    According to Beranek&#39;s publication, the Transmission Loss of the sound is greatest when the m parameter is 100 or higher. Since ¼ in tubing is used before and after the muffler, it was decided to design the cylindrical muffler to have a diameter of about 2.5 in. This gives an m parameter value of about 100. Advantageously, based on experiments, the m parameter varies between about 100 and about 200. Empirical data shows that choosing m=140 allows to lessen the volume needed for the muffler to 12 cubic inches. Furthermore, selection of transmission loss of about 21 dB eliminates the pulsations. The manifold/muffler assembly  26  is designed to have a maximum amount of transmission loss at a wide range of frequencies below and above 200 Hz. To accomplish this, advantageously the kl parameter varies from about 0.1 to about 0.4 and, thus, fits the requirement of less than 0.8 corresponding to a transmission loss of around 19 to 24 dB.  
         [0047]    Referring to FIGS. 2 and 7, further reduction of the sound signal is achieved by providing the upstream or inlet manifold/muffler assembly  60  formed in the back panel  46  of the device  10 . The back panel  46  is formed with a muffler  62  configured as a chamber of a sufficient depth. Although the geometry of the chamber can vary, one of its configurations includes a U-shape peninsula  64  having an upstream duct  66 , which is in flow communication with the air inlet  48  (FIG. 2). Ambient air, forced through the air inlet  48  in response to the actuation of the compressor  22 , flows through the upstream duct  66  into the muffler  62  and, further, through an outlet duct  68  towards the patient ventilation circuit. The upstream duct  66  and the chamber of the muffler  62  are shaped and directed to meet the requirements of Beranek&#39;s publication. Preferably, the outlet duct  68  is configured similarly to the inlet duct  66 .  
         [0048]    Structural integrity of the device  10  is achieved by utilizing a mounting plate  70  (FIG. 2) configured to support the electronic controller  52  and the first compressor  22 . Configuration of the device allows for an auxiliary compressor  72  coupled in parallel to the first compressor  22  to be mounted to the mounting plate  70  without taking on an additional space. The compressors  22  and  72  can be switched on simultaneously by the electronic controller  52  if the desired volume, set by the operator, exceeds a given reference value. Due to the geometry of the air conveying manifold/muffler assemblies  26  and  60  including relatively short air-paths, which are practically free from elbows, contractions and expansions, no “fighting” between the compressors  22  and  72  has been observed. To provide flow communication between the second compressor  72  and the manifold/muffler assembly  26 , the device  10  features additional two inlet conduits  39  and two outlet conduits  37  (FIG. 6). The former two convey incoming air from the inlet manifold  32  into the mixing chambers of the compressor  72 , whereas the outlet conduits  37  convey compressed air from the compressor&#39;s expansion chambers towards the outlet manifold  30  of the manifold/muffler assembly  26 .  
         [0049]    The compressors, which are actuated during the inhale stroke of the air recipient, are turned off automatically based on the desired volume of compressed air delivered into the air-recipient&#39;s lungs. Turning to FIGS.  1 - 3  and  8 , a disposable air conveying system  80  (FIG. 8) delivers the compressed air to the air recipient through a first flexible tube  82  coupled to the inhale port  44  (FIG. 2). As the compressor completes its “on” mode of operation, the electronic controller  52  (FIG. 2) actuates a micro air pump  84  (FIG. 3) opening a one-way pneumatic exhalation valve  86  to allow for the exhale stroke of the air recipient during which wasted gases are vented to atmosphere through the exhalation valve  86 . Structurally, as seen in FIG. 5, the side of the manifold/muffler  26  has a channel  90  leading from the micro air pump  84  to the exhalation valve  86  through a conduit  92  formed in the rear wall of the panel  16 . Actuation of the micro pump generates pressure sufficient to open the exhalation valve  86  allowing wasted gases to escape into the atmosphere. Exhalation continues until an airflow sensor  88  (FIG. 1) located on the front panel  16  senses airflow. Zeroing out of the flow rate triggers actuation of the compressor(s)  22 , and a duty cycle corresponding to the inhale stroke is repeated. To prevent overpressurization of the air recipient&#39;s lungs, a safety valve  94  (FIGS. 1 and 2) provided on the front panel  16 , opens immediately if a reference value has been exceeded (FIGS. 1 and 5). Specific locations of the inhale port  44  is illustrated in FIGS.  1 - 6  for purely illustrative purposes and can be changed. One of the possibilities is to form the inhale port in alignment with the manifold outlet  40  of the outlet manifold/muffler assembly  26 .  
         [0050]    The device  10  can be used for a prolonged period of time by recharging the battery  12  or by providing external power. For this purpose, as shown in FIG. 4, the back panel  46  is provided with an adapter  96  (FIG. 4) allowing coupling of the device to an external charging source. If the device  10  is used in contaminated atmosphere, the air inlet  48  can be provided with a removably connectable to filter  98 , as illustrated in FIG. 2. Reduction in vibration can be achieved by implementing vibration mounts  100  (FIG. 2) coupling the front  16  and back  46  panels to the mount plate  70 . To assure that the malfunction of the inventive device does not go undetected, a sound generator (not shown) can be removably mounted on the back panel  46  and coupled to the electronic controller  52  and the rechargeable battery  12 .  
         [0051]    The inventive device  10  has a simple, cost-efficient and substantially noise-free structure providing the air recipient with smooth, uniform airflow. The ventilator can be distributed as part of a kit including, besides the ventilator itself, the filter  10 , the disposable conveying system  80  providing flow communication between the ventilator and the air-recipient and a sound source. While the invention has been disclosed with respect to preferred embodiments, various changes can be made without departing from the scope of the invention as defined by the appending claims.