Patent Publication Number: US-2022211965-A1

Title: Pulmonary ventilator with changeable filters

Description:
This application is a divisional of U.S. patent application Ser. No. 16/937,421 filed 23 Jul. 2020, which is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 62/878,170 filed 24 Jul. 2019 the disclosures of which are incorporated by this reference as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field 
     A pulmonary ventilator system has a ventilator to supply blended gas to a patient through an inlet filter to form breathable gas for insertion into the trachea of a patient by a suitable input output structure. The breathable gas is used by and then exhausted by the patient along with moisture and pathogens from the patient to form an exhaust gas with pathogens which exhaust gas is directed to and through an exhaust filter in the exhaust limb. The inlet and exhaust filters have filter media which may be formed to be antibacterial and/or anti viral and are configured so that the filter itself or the filter media of each filter can be changed or cleaned without breaking the patient breathing circuit by, among other options, directing the breathable gas and exhaust gas through one of multiple paths each path having a separate filter or filter media. An HME filter may be included and similarly structured as the inlet and outlet filters. Further, the exhaust filter may be combined into and with a water trap which removes moisture from the exhaust gas. 
     2. The Relevant Technology 
     It is well known to supply a breathable gas to a patient as a medical therapy. A wide variety of pulmonary ventilators are known and commercially available. As an example, the PURITAN BENNETT® machines offered by Coviden Holding, Inc. of Mansfield, Mass. are known and supply breathable gas as or for respiratory or pulmonary therapy. Other pulmonary ventilation machines are known like the LIFE PULSE® machine offered by Bunnell, Inc. of Salt Lake City, Utah. As yet another example, a Servo n® offered by Maquet Critical Care AB Corporation of Solna, Sweden is a pulmonary ventilator machine known to supply breathable gas for small babies. 
     Typical pulmonary ventilation systems such as one illustrated in  FIG. 1  (prior art) include a ventilator  10  that functions to supply blended gas  15  through input filtration  9  that has a supply filter  12  and an optional humidifier  14 . The input filtration  9  receives blended gas  15  from ventilator  10  from an outlet  48  and through a first supply line  40 . The blended gas  15  is filtered and then optionally humidified in the humidifier  14  and then supplied as breathable gas  11  to an input and output device such as endotracheal tube  16  that is inserted in the trachea of a patient  18 . The breathable gas  11  may also be supplied directly into the trachea of the patient  18  through suitable tubing that functions as an input and output device and an opening formed in the trachea by suitable procedures (i.e., a tracheotomy). The filter  12  must be changed from time to time during operation which typically requires one to break the line  41  or otherwise break the supply of breathable gas  11  and thus interrupt the pulmonary therapy. Interrupting the pulmonary therapy even for a short time to effect filter change or replacement can be harmful to the patient. 
     Typically, the patient  18  is a human; but the patient may also be any animal that can be treated with breathable gas. The breathable gas  11  is taken in by the patient  18  through, and then exhausted through, a “Y” connector  7 . The “Y” connector  7  has three legs. One leg is connected to receive breathable gas, another is connected to direct exhaust gas outwardly and a third is connected to an optional HME filter  17  which in turn is connected to the endotracheal tube  16 . After the breathable gas  11  is inspirated into the lungs of the patient  18 , it is thereafter exhausted from the patient  18  becoming exhaust gas  13  that includes pathogens which may have, for example, undesired bacteria or viruses obtained from the patient  18 . The exhaust gas  13  with pathogens may also include water and water vapor from the patient  18 . The exhaust gas  13  proceeds from the endotracheal tube  16  through an exhaust circuit  19  that includes the exhaust line  20  that communicates or directs the exhaust gas  13  to and through exhaust filtration structure  22 . The exhaust filtration structure  22  includes an outlet filter  24  and may also include a water trap  26  to remove moisture from the exhaust gas  13 . 
     The outlet filter  24  functions to remove or filter pathogens in the exhaust gas  13  to form filtered exhaust gas  25 . The filtered exhaust gas  25  is then typically directed to or through an exhaust valve  28  associated with the ventilator  10 . The filtered exhaust gas  25  can be vented to the atmosphere, but venting to the atmosphere is not generally recommended because ventilation processes can be interrupted. 
     The exhaust valve  28  along with a flow control device  30  and a blender  32  are controlled by the control  38  of the ventilator  10  to make sure that the inspiration gas flow is not interrupted. The control  38  has controls to allow an operator to choose or select desired respiration functions (e.g., pressure, respiration rate, gas blend). The ventilator  10  may also have a pressure transducer  33  to detect the pressure via sensor line  33 A of the breathable gas  11  being delivered to the patient  18 . 
     Air  34  and oxygen  36  are the typical gases supplied to the ventilator  10  and blended in the blender  32  to form the blended gas  15 . The amount of air  34  and oxygen  36  supplied is controllable and may be adjusted by the flow control  30  associated with the ventilator so that the blended gas  15  and the breathable gas  11  may vary between essentially all air to air highly enriched with oxygen. The air  34  and the oxygen  36  may be available from central storage in hospitals and other medical facilities. Alternately, the air  34  may be drawn from the environment and compressed within the ventilator. While air and oxygen are the typical gases, other gases may be added or substituted. 
     Filtration of the inspiratory (breathable, inhaled) gas and expiratory (exhaust, exhaled) gas is of critical importance.  Clinical Foundations,  2011, item 0270 (Filtration of Breathing Gases). Patients and caregivers may be exposed to pathogens in the air that come from many sources including other patients. Inspiratory filtration seeks to limit or inhibit the transfer of such pathogens to a patient from the surrounding environment; and expiratory filtration seeks to limit or inhibit the delivery of pathogens from a patient to the surrounding environment including the atmosphere around and near the patient as well as other patients and caregivers. Id. The HME filter when used (e.g., during transport of the patient) is understood to include an HME cartridge that functions to absorb heat and moisture from the exhaust gas provided by the patient and to release or transfer the heat and moisture to the breathable gas being inspirated by the patient. U.S. Pat. No. 7,594,509 (Burk). 
     For patients including especially those patients having a condition in which the exhaust gas has known infectious pathogens that need to be or should be filtered, exhaust filtration (e.g., exhaust filtration structure  22 ) is provided. Operators of the pulmonary ventilation system in use may monitor the operation of the exhaust filtration structure. In turn, when the exhaust filtration structure has a water trap (e.g., water trap  26 ), an operator monitors the water trap and typically empties it on a periodic basis as it starts to fill with water/moisture collected from the exhaust gas. The filter of the system in use (e.g., the filter  24  in the prior art system of  FIG. 1 ) is also typically changed on a regular or periodic basis. The changing may vary from once every few hours to perhaps longer such as once every day or two. 
     An older water trap of the type comparable to those used in today&#39;s pulmonary therapy systems and useful as water trap  26  in  FIG. 1  (prior art) is described in U.S. Pat. No. 3,454,005 (Eubanks, et al). Those skilled in the art will also understand that other commercial water traps are available today including, for example, one from Armstrong Medical Ltd of Coleraine, Northern Ireland. Medtronics also offers a Puritan-Bennett® water trap. 
     Typical filters in the exhaust filtration structure comparable to filter  24  in  FIG. 1  (prior art) useful in respiratory or pulmonary systems can be seen in U.S. Pat. Design D441,449 (Gaskel), in U.S. Pat. No. 6,619,287 (Blackhurst, et. al.) and U.S. Pat. No. 3,782,083 (Rosenberg). It is understood that the CDC (Center for Disease Control) has announced the desired degree of filtration provided by the filter media in the filter and the recommended replacement intervals. 
     For pulmonary ventilation systems with a filter comparable to supply filter  12  to remove contaminants including pathogens from the blended gas  15 , the filter  12  typically has an inlet connected by first supply line  40  to the outlet  48  of the ventilator to receive the blended gas  15  and then filter the blended gas  15  to remove the pathogens and other contaminants found in the air and gas supplied to form the blend. Filtration and optional humidification of the blended gas forms breathable gas  11 . The breathable gas  11  is supplied through an outlet connected to a second supply line  41  that connects to the “Y” connector  7  which is then connected to the endotracheal tube  16 . The humidifier  14 , if included, may be interconnected between the filter  12  and the supply line  41 . An HME filter  17  may also be connected between the “Y” connector  7  and the endotracheal tube particularly when a humidifier is not provided. 
     For patients whose lungs have been compromised or that have not yet developed, it is important to maintain a minimum intra-alveolar pressure to prevent collapse of the alveoli. This residual volume of gas in the lungs during exhalation, termed the Functional Residual Capacity, not only keeps the alveoli open but continues to exchange gases with the blood via diffusion during exhalation. To change the supply filter  12 , the inspiration circuit is opened which temporarily interrupts ventilator therapy. Opening up the inspiration circuit or limb to change a filter and/or to change anything else interrupts that circuit and may lead to a loss of the Functional Residual Capacity, the collapse of the alveoli. Loss of the FRC can mean that steps must be taken to once again recruit these alveoli for breathing by application of opening pressures greater than the surface tension of the tissues. In all, the interruption of therapy can be harmful to the patient. 
     For pulmonary ventilation systems with an exhaust limb or circuit  19  having exhaust filtration structure such as exhaust filtration  22  arrangement to filter or remove pathogens from the exhaust gas, the filter such as outlet filter  24  in the exhaust filtration structure  22  typically has an inlet  20  connected to an exhaust line such as exhaust line  21 . The exhaust filtration arrangement  22  also has an outlet  24 B connected to an exhaust valve such as exhaust valve  28 . To change the outlet filter  24  in the exhaust filtration arrangement  22 , the exhaust circuit or limb  19  must be opened. That is, the exhaust filtration arrangement  22  (or the filter  24  itself inside the exhaust filtration arrangement) is disconnected at the inlet  20  and the outlet  24 B so that the filter  24 , can thereby be removed and discarded or removed and cleaned. In that process, the Functional Residual Capacity also may be lost or reduced impeding or compromising the respiratory therapy. At the same time, the exhaust gas  13  from the patient is unfiltered and discharged into the surrounding atmosphere with the pathogens until the filter is cleaned and replaced or a new filter is reconnected between and to the inlet  20  and outlet  24 B. 
     Filtration is critical in cases where the patient has a disease or disorder that produces pathogens posing a serious health risk (e.g., ebola, measles, pneumonia, COVID 19) to the caregivers and to others in the vicinity. Such pathogens can even pose a risk to others throughout a treatment facility such as a hospital as the pathogens can be circulated by others moving nearby and maybe even be circulated by the building ventilation system. 
     As noted before, the United States Center for Disease Control (“CDC”) has recommended replacement intervals for filters like supply filter  12  and outlet filter  24 . In some cases, the filter like outlet filter  24  in the exhaust circuit  19  may become partially or fully blocked or clogged. In some cases that blocking or clogging can occur quickly particularly in the outlet filter so that the outlet filter  24  may need to be changed frequently (once every several hours) to once a day. Of course changing the outlet filter  24  at any interval means that the exhaust circuit  19  must be broken open with subsequent risk of reduced or complete loss of the Functional Residual Capacity (FRC) and exhaust gas  13  venting directly to the atmosphere or environment while the filter such as filter  24  is removed and replaced or cleaned. Similarly, changing the supply filter  12  as well as the HME filter  17  means that the lines supplying breathable air  11  must be broken interrupting the ventilation therapy and possibly resulting in exhaust gases from the patient including the pathogens therein exiting through the inspiration line. The more frequent the changing process is performed, the more pathogens are released to the surrounding atmosphere. 
     Systems with input filtration and exhaust filtration that prevents or limits, venting of unfiltered exhaust gas to the atmosphere are not known; and systems that include a bypass and multiple filter configurations are not known. Systems that combine the function of the water trap and the filter to further limit the release of unfiltered exhaust gas to the surrounding atmosphere are also not known. 
     SUMMARY 
     A pulmonary ventilator system and filter as disclosed is configured to provide uninterrupted ventilation therapy to a patient to avoid loss of FRC and prevent contamination of the environment with pathogens when changing filters. The pulmonary ventilation system disclosed is configured to transmit a breathable gas to a patient through an input and output structure like an endotracheal tube configured for introduction of said breathable gas into the trachea of the patient. The breathable gas is inspirated (i.e., breathes in or inhales) and then expirated (i.e., breathes out or exhales) by the patient all on a repetitive basis that correlates to respiration rate. The expirated gas becomes an exhaust gas with pathogens obtained from the patient. 
     The ventilator of the pulmonary ventilator system as disclosed receives and mixes at least two different gases each from an external source to form the breathable gas that is delivered at a ventilator output. A supply line is connected to the ventilator output for receiving the breathable gas and delivering it through input filtration to input output structure for introducing the breathable gas into the trachea of the patient. 
     The pulmonary ventilator system disclosed also has an exhaust line which may also be referred to as an exhaust limb or exhaust circuit. The exhaust line has a first end connectable to the input and output structure for receiving the exhaust gas with the pathogens. The exhaust line has a second end spaced from the first end and connected to exhaust filtration structure that filters the pathogens from the exhaust gas to form filtered exhaust gas. 
     The exhaust filtration structure has an inlet connected to receive the exhaust gas and an outlet configured to supply the filtered exhaust gas from the exhaust filtration structure. A first conduit directs the exhaust gas from the inlet of the exhaust filtration structure (through an optional water trap) to a changeable outlet filter. A second conduit supplies the filtered exhaust gas from the changeable outlet filter to the outlet of the exhaust filtration structure. The changeable outlet filter has a first path directing the exhaust gas through a first filter and a second path directing the exhaust gas through a second filter. 
     The first filter is removable from the first path when the exhaust gas is directed to the second path. The first filter removes pathogens from the exhaust gas having pathogens from the patient to form first filtered exhaust gas. The second filter is also removable and removes pathogens from the exhaust gas with pathogens from the patient to form second filtered exhaust gas. It is configured to be removable from a second path when said exhaust gas is being directed through the first path to the outlet of the exhaust filtration structure. 
     The pulmonary ventilator system also has a discharge line having a first end connectable to the outlet of the exhaust filtration structure to receive the filtered exhaust gas without the pathogens from either the first path and the second path. In effect, a bypass is provided which is configured so that the ventilation of the patient is never interrupted to change the outlet filter. Also, the ventilator does not react to the stopping or loss of flow as the filter is changed and then compensate for the loss of flow by increasing the flow of breathable gas. Further, the fluids/moisture and pathogens from the patient are not introduced into the environment reducing the risk of exposing other patients, caregivers and any others in the surrounding environment. 
     In another configuration, the changeable outlet filter has a filter element holder or housing configured to hold a filter structure such as a cartridge. The filter element holder is configured to receive a first filter structure to be in a first path. When it is desired to change the first filter structure, the first filter structure is moved out of the first path preferably by the second filter structure which is then positioned in the filter element holder in the second path. In the first path and the second path, the change from the first filter structure and second filter structure is made so that in effect the change from the first path to the second path is essentially immediate so the stream of exhaust gas with pathogens continuing to be filtered without any practical interruption of the flow of the stream of exhaust gas with pathogens; and in turn the FRC is not affected. That is, the filter element is moved from a first position in the first path to a second position wherein the first filter element is removed from the first path to form said second path in which the second filter is in the stream of exhaust gas with pathogens. 
     In an alternate arrangement, the changeable filter of the pulmonary ventilator system has a first filter in a first path and a second filter in a second path. The changeable filter includes a valve connected to the first conduit and operable to direct the exhaust gas with said pathogens to either the first path or the second path. In turn, flow of exhaust gas with pathogens is directed from one filter in the first path to a second filter in the second path with virtually no interruption so the FRC is not affected. In turn, the first filter can be changed or cleaned with the flow of the exhaust gas in the second path; and the second filter can be changed or cleaned with the flow of the exhaust gas with the pathogens in the first path. 
     In an alternate arrangement, in a pulmonary ventilator system the exhaust gas includes a water trap to recover moisture in the exhaust gas. The water trap is connected in the first conduit to remove moisture from the exhaust gas before filtration. 
     Notably a filter is disclosed that is structured to filter the flow of a fluid or liquid without effectively interrupting the flow by directing the flow through a first filter in one path while a separate filter is cleaned or readied with the flow changed to a different or separate path through a new and separate filter. In one arrangement, the separate filter is urged into a filter element holder to urge out the first filter with the separate filter. The filter can be structured with filter media to filter pathogens as well as other contaminants. Alternately a valve can be included as part of the filter to direct the flow into one path through a first filter and into another or second path so that the flow can be directed from one to the other with virtually or effectively no interruption of flow. Such a filter can be used as the inlet filter and also as the HME filter in a pulmonary ventilation system. 
     Methods of changing a filter in the exhaust structure are also disclosed along with a kit to provide all that is needed to practice a disclosed method. The methods include steps to bypass a first filter in a first path that has been in use and preferably change to a new or second filter in second path while the used first filter is isolated, removed and replaced with a clean or new filter. The first filter is later put into service while the second filter is isolated, removed and replaced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the advantages and features of the systems and structure herein disclosed, a more particular description is rendered with reference to the appended drawings. It should be understood that the drawings depict only typical embodiments and therefore are not to be considered limiting of the scope of the appended claims. More specifically: 
         FIG. 1  is a block diagram of a prior art pulmonary ventilation system; 
         FIG. 2  is a block diagram depiction of a pulmonary ventilation system having exhaust filtration structure with changeable filters; 
         FIG. 2A  is a block diagram depiction of an input filtration structure as disclosed herein for use in and with a pulmonary ventilation system; 
         FIG. 3  is a perspective of a combined filter and water trap for use in a pulmonary ventilation system; 
         FIG. 4  is a partially exploded perspective of the combined filter and water trap of  FIG. 3 ; 
         FIG. 5  is a cutaway cross sectional view of the combined filter and water trap of  FIG. 3  in a bypass position; 
         FIG. 5A  is a cross sectional view of a valve portion of the combined water trap and filter of  FIG. 3 ; 
         FIG. 5B  is a planar view of a filter for positioning in the valve portion of the combined filter and water trap of  FIG. 5 ; 
         FIG. 6  is a cutaway cross sectional view of the combined filter and water trap of  FIG. 3  in a filter position; 
         FIG. 6A  is a top view of the filter holder of the combined filter and water trap of  FIG. 3 ; 
         FIG. 6B  is a top view of a filter element of the combined filter and water trap of  FIG. 3 ; 
         FIG. 7  is a fully exploded perspective of the combined filter and water trap of  FIG. 3 ; 
         FIG. 8  is a depiction of a dual path changeable filter for use in a pulmonary ventilation system; 
         FIG. 9  is a perspective view of a single path dual filter system for use in a pulmonary ventilation system; 
         FIG. 10  is a cross sectional depiction of the single path dual filter system of  FIG. 9 ; 
         FIG. 11  is a depiction of a dual path changeable filter with partial cross section areas for use in a pulmonary ventilation system; 
         FIG. 12  is a depiction of a check valve useable in the dual path changeable filter of  FIG. 11 ; 
         FIG. 13  is a depiction of another single path dual filter system for use in a pulmonary ventilation system; 
         FIG. 14  is a depiction of a partial cross section of the single path dual filter system of  FIG. 13 ; 
         FIG. 15  is a depiction of a kit containing materials to assemble and operate a dual path changeable filter for use in a pulmonary ventilation system; 
         FIG. 16  is a cross section of a dual path changeable filter for use in a pulmonary ventilation system; 
         FIG. 17  is a perspective of a changeable outlet filter with a one filter element partially removed; 
         FIG. 18  is an enlarged partial cross sectional view of a changeable outlet filter with a locking mechanism; 
         FIG. 19  is a perspective of a filter media for use in a changeable outlet filter; 
         FIG. 20  is a cross sectional view of the filter media of  FIG. 19 ; 
         FIG. 21  is an exploded perspective of an alternate changeable outlet filter; 
         FIG. 22  is a perspective of an alternate changeable outlet filter structure with a housing and cartridge separate; 
         FIG. 23  is a perspective plane view of seal material for use with the changeable outlet filter of  FIG. 22 ; 
         FIG. 24  is a simplified perspective exploded view of a cartridge; 
         FIG. 25  is a simplified exploded perspective of a cartridge similar to the cartridge of  FIG. 24 ; and 
         FIG. 26  is a perspective of an alternate changeable outlet filter with a housing and cartridge separated. 
     
    
    
     DESCRIPTION 
     Hospitals, clinics, infirmaries, immediate or urgent care facilities and even medical offices of doctors and other medical practitioners may have patients visiting such places that carry pathogens exposing the treating medical practitioners and their related staffs (e.g., nurses, nurses aids, orderlies, nurse practitioners, administrators and other care givers) to those pathogens (e.g., a bacterium or bacteria as well as a virus such as COVID 19 or other microorganism that can cause disease). Efforts are being made to reduce the presence and/or spread of such pathogens in all locations using a wide variety of products, practices and procedures (e.g., widespread and frequent cleaning, hand washing, use of face masks, use of surgical gloves and gowns, use of disinfectants and the like). 
     To reduce the spread of pathogens in locations where patients receive pulmonary respiration or ventilation therapy, the exhaust of the pulmonary ventilation system (e.g., the exhaled breath from the infected patient) may be filtered to reduce the discharge of pathogens from the patient to the atmosphere as recommended by at least the CDC. That is, a filter may be placed in the exhaust limb or exhaust circuit of a pulmonary or respiratory therapy system; and then the filter is changed from time to time consistent with recommendations of agencies such as the CDC. Nevertheless, in known systems, the exhaust gas from the patient is vented directly into the environment of the patient at a location where the pulmonary respiration or ventilation therapy is being administered as the exhaust limb or exhaust circuit or line is opened up to remove and replace or clean the filter in the exhaust limb or exhaust circuit. When the exhaust circuit or limb is opened and the filter in the exhaust circuit or limb is removed, the exhaust gas vents directly to the nearby environment. The amount of exhaust gas that is released to the environment increases with the frequency of filter change (or cleaning) and the amount of time taken to complete the filter change or filter cleaning. 
     As stated hereinbefore, pulmonary ventilation systems are used to provide patients with pulmonary respiration or ventilation therapy in the form of breathable gas. The gas is typically a mixture of air and oxygen. The patient receives the breathable gas typically through an input and output structure such as an endotracheal tube that is inserted through the mouth into the trachea of the patient. The breathable gas may also be inserted using tubing directly inserted into the trachea following a tracheotomy procedure. The input and output structure may also be in the form of an oxygen mask that typically covers the nose and mouth. The breathable gas is inspirated as breathable gas and then expirated through the input and output structure such as the endotracheal tube as exhaust gas with pathogens and also with moisture from the patient entrained. That is, the pulmonary ventilation system has an exhaust limb or circuit to take the exhaust gas away from the patient through exhaust filtration structure to an exhaust valve (associated with a ventilator) which operates in accordance with control input from the ventilator control to maintain a virtually uninterrupted flow of breathable gas and avoid loss of FRC. 
     Also, as hereinbefore stated, the exhaust filtration limbs or circuits typically have a water trap to remove the moisture in the exhaust gas and a filter to remove pathogens from the gas. Water traps typically have a valve associated with them to facilitate removal. However, it is believed that cleaning or replacing the filter involves breaking the exhaust circuit and venting the exhaust gas with any pathogens therein to the atmosphere while the filter is being cleaned or a new or replacement filter or filter element installed. Systems and filter arrangements described hereinafter operate to minimize and preferably eliminate the release of exhaust gas with pathogens and the release of moisture to the atmosphere during the cleaning or changing of the filter and/or filter element in the exhaust limb or circuit. 
     The exhaust filtration structure disclosed herein may also include a filter and water trap combination. That is, a new valve structure includes the combination of a water trap feature and a filter structure along with a valve combined and used in a system to maintain ventilation while servicing the filter or water trap and to preclude or reduce the release of exhaust gas with pathogens to the environment surrounding the patient. Also disclosed is a kit the contents of which are to be used to form an exhaust filter structure for use with a pulmonary ventilation system which reduces the release of exhaust gas with pathogens to the environment. 
     A new pulmonary ventilation system here disclosed in  FIG. 2 , uses some of the components of the pulmonary ventilation system of  FIG. 1  However the pulmonary ventilation system of  FIG. 1  has been modified to include an improved exhaust filtration structure  46  as well as improved input filtration  9 A and an optional HME filter  17 A. That is, the pulmonary ventilator system  35  herein illustrated in  FIG. 2  receives two different gases which are blended to form blended gas  15 . The two different gases are here seen as air  34  and oxygen  36 . Other gases can be added or substituted. Various medicines can also be introduced into the blended gas  15  as desired. For example, Flolan® can be introduced into the inspiration line. See: Multidisciplinary System Critical Care Services, Inhaled Epoprostaol (Flolan®) Guidelines, Rumbaugh, et al, Apr. 9, 2013 (Vanderbilt University Medical Center, Nashville, Tenn.). The ventilator  10  is connected at a ventilator output  48  to first supply line  40  which directs or supplies blended gas  15  to the input of the input filtration structure  9 A which includes filter  12 A and humidifier  14 . The second supply line  41  is connected to an input and output device such as the endotracheal tube  16  to supply breathable gas  11  which has been filtered by filter  12 A and preferably humidified. 
     The new pulmonary ventilation system  35  of  FIG. 2  has an exhaust limb or circuit  19 A that includes exhaust lines  21  and  44  having a first end  50  connected to “Y” connector  7 . The “Y” connector is also connected through another leg to and through HME filter  17 A to the input and output device such as endotracheal tube  16 . The exhaust line  21  receives the exhaust gas  13  and directs the exhaust gas  13  through the line  44  to the second end  52  of the exhaust line  44  with stretch  54  between the first end  50  and the second end  52 . The second end  52  is connected to the inlet  56  of the exhaust filtration structure  46  which filters pathogens from the exhaust gas  13  and supplies filtered exhaust gas  73  and  75  at its outlet  58  as discussed hereinafter. 
     As seen in  FIG. 2 , a first conduit  60  is provided for the exhaust gas  13  to proceed from the inlet  56  to the changeable filter  62 . In  FIG. 2 , an optional water trap  64  is positioned in the first conduit  60  to filter or remove moisture. The changeable filter  62  has a valve  66  to receive the exhaust gas  13  from the first conduit  60  directly or after being dewatered by the optional water trap  64 . The exhaust gas  13  is directed to either a first filter  68  through a first leg  69  or a second filter  70  through a second leg  71 . The exhaust gas  13  is then filtered by the first filter  68  to produce filtered exhaust gas  73  when the valve  66  is positioned in position  84  to direct the exhaust gas  13  through the first filter  68 . Alternately, the exhaust gas  13  is filtered by the second filter  70  to produce filtered exhaust gas  75  when the valve  66  is positioned in position  86  to direct the exhaust gas  13  through the second filter  70 . The second conduit  72  receives and conveys the filtered exhaust gas  73  to the second outlet  58 . Similarly, a third conduit  80  conveys filtered exhaust gas  75  to the second outlet  58  when the valve  66  is in its second position  86 . A discharge line  74  has a first end  76  connected to the second outlet  58  to direct the filtered exhaust gas  73  and  75  from the changeable filter  62  to its second end  78 . The second end  78  may vent to the atmosphere or direct the filtered exhaust gas through an exhaust valve like exhaust valve  28  of ventilator  10 . 
     In operation, it can be seen that the valve  66  is operable between a first position  84  (shown in solid line in  FIG. 2 ) in which the exhaust gas  13  is directed toward the first filter  68 . In that configuration, no exhaust gas  13  is proceeding to or into the second filter  70  which may be removed and replaced with a new second filter. Alternately, the second filter  70  may be removed, cleaned and replaced. With the valve  66  in the first position  84 , filtered exhaust gas  73  from the first filter  68  may be released to the atmosphere through a third conduit  80  when the second filter  70  has been removed. When the new second filter or cleaned second filter is reinstalled, the filtered exhaust gas  73  all proceeds to the outlet  58 . 
     With the valve  66  oriented in the second position (seen in dotted line in  FIG. 2 ), the exhaust gas  13  is directed to the second filter  70 . Because no exhaust gas  13  is being transmitted to the first filter  68 , the first filter  68  may be removed and replaced with a new first filter. Alternately, the first filter  68  may be removed, cleaned and reinstalled. With the valve  66  in the second position, the filtered exhaust gas  75  from the second filter  70  is directed toward the discharge line  74  and may be released to the atmosphere through the third leg or first filter discharge line  82  when and while the first filter  68  is removed. With the valve  66  in either the first position  84  or the second position  86 , only filtered exhaust gas  73  and  75  is released to the atmosphere with the pathogens in the exhaust gas  13  removed by either the first filter  68  or the second filter  70 . And with the water trap  64  in place, the filtered exhaust gas  73  and  75  also has had moisture removed. Suitable check valves may be positioned between filter  68  and the discharge line  82  and between filter  70  and discharge line  80  to prevent back flow through a filter that has been removed for cleaning or replacement comparable to check valves discussed in connection with  FIG. 2A . Suitable check valves include duck valves as well as valves having a thin vane deployed in the flow path. Suitable thin or flap valves may be available from Vernay Laboratories, Inc. of Atlanta, Ga. The check valve selected is of the type to optimally minimize pressure loss through the check valve. 
     As noted, the inlet ventilation system  35  disclosed also has input filtration  9 A that includes changeable inlet filter  450  depicted in  FIG. 2A . It receives the blended gas  15  from a ventilator like ventilator  10  through a first supply line  452  which is comparable to first supply line  40 . The blended gas  15  then proceeds through a first input conduit  454  to valve  456  which has two positions,  458  and  460 . In the first position  458  shown in solid, the blended gas  15  proceeds to filter  1  or a first filter  462  which is configured to remove pathogens (and any other foreign matter) and form first filtered gas  466 . First filter  462  is also configured to be removable so that it can be replaced with a new filter to function as the first filter or Filter  1 . That is, first filter  462  can be disconnected from first conduit  480  and second conduit  482 . The fittings associated with the first conduit  480  and the first filter  462  are typically snug with the first conduit typically being female and frictionally inserted over a fixed male fitting associated with the filter  462 . 
     After the blended gas  15  is filtered in the first filter  462  to remove contaminants including pathogens to produce first filtered gas  466 , the first filtered gas  466  then proceeds to an outlet line  468  through a first check valve  478  discussed hereinafter and then a first filter leg  464 . The outlet line  468  is connected to second supply line  41  for further connection to the input and output structure  42 . A portion of the first filtered gas  466  may also proceed backward (shown in dotted line) through second filter leg  472  toward filter  2  or the second filter  470  when the valve  456  is in the first position  458  and the second filter  470  is removed for disposal and replacement with a new (clean) filter or removed for cleaning if it is of the type or kind that can be cleaned. With the second filter  470  removed, the first filtered gas  466  may exit to the atmosphere directly from the second filter leg  472  if there is no second check valve  476 . If there is a second check valve  476  in the system, it will be configured to stop the flow of first filtered gas  466  therethrough so that all of the first filtered gas  466  proceeds to the outlet  468 . The second check valve  476  is shown in the closed position in solid and an open position in dotted line. 
     When the valve  456  is in the second position  460  shown in dotted line, the blended gas  15  proceeds to the filter  2  or second filter  470  where the blended gas  15  is filtered to remove pathogens and any other unwanted material to form second filtered gas  474  which proceeds to the outlet  468  for further transmission. A portion of the second filtered gas  474  may also proceed as shown in dotted line through the first filter leg  464  when the first filter  462  is removed so it can be replaced or cleaned. Of course to stop the escape of second filtered gas  474  with the first filter  462  removed the first check valve  478  functions to close so that a portion of the second filtered gas  474  cannot escape therepast and all will be directed to the outlet  468 . 
     The use of first check valve  478  and second check valve  476  is preferable for the changeable inlet filter  450  as the flow of breathable gas  11  to the patient will not be interrupted or changed when an inlet filter such as first inlet filter  462  or the second inlet filter  470  is being changed. Thus the FRC remains unaffected. That is, the ventilation therapy is not then interrupted or modified as second filtered gas  474  does not vent or escape. Use of a system such as that illustrated in  FIG. 2A  allows ventilation therapy to remain stable or unchanged while each inlet filter  462  and  470  is being changed because the other remains in operation. In turn the ventilator like ventilator  10  also does not react to vary the breathable gas being supplied in an effort to maintain the breathable gas  11  as desired. The first filtered gas  466  and the second filtered gas  474  may also proceed through a humidifier like humidifier  14  to form breathable gas  11 . 
     In operation, the changeable inlet filter  450  can operate through one filter like first filter  462  with the valve  456  in a first position  458  until first filter  462  becomes contaminated. When the valve  456  is in the first position  458 , the second filter  470  can be removed and replaced with a new and clean filter or cleaned. The valve  456  may then be moved to the other or second position  460  directing the blended gas to the second filter  470  so that the first filter  462  can be removed and replaced with a new filter or cleaned. Inasmuch as the first filter  462  and the second filter  470  are of the same size and type as are the replacements, the supply of breathable gas  11  remains essentially unchanged and of suitable or desired quality. 
     Turning now to  FIGS. 3-7 , a combined water trap and filter  90  is depicted to function in the pulmonary ventilation system of  FIG. 2  as the exhaust filtration structure  46 . That is, the function of the water trap  64  and the function of the changeable filter  62  are combined into one to be the water trap and a filter. 
     As depicted best in the exploded view of  FIG. 7 , the water trap and filter  90  has a receptacle or cup  92  secured to a filter holder  94 . The receptacle or cup  92  has the filter holder  94  securely attached thereto. The attachment may be done by glue, plastic welding or by any other means to effect a water and air tight connection. In some configurations, it may be desired to provide for a threaded connection to provide access to and to allow for changing the filter as hereinafter discussed. But the preferred arrangement has a filter holder  94  glued to the receptacle or cup  92 . The filter holder  94  has a tube  190  with a filter membrane  184  secured thereto. As a result, when the filter holder  94  is removed, the cup  92  and the filter membrane  184  are removed with it and may be disposed of and replaced with a new filter holder  94  and cup  92  with a new filter membrane  184 . 
     The port  100  has an inlet  102  to receive exhaust gas  13  and direct it through the cup  92  and filter membrane  184  to the outlet  104  to supply filtered exhaust gas in a first configuration. In a second configuration, the exhaust gas  13  as received in the inlet  102  is directed straight to the outlet  104 , all as discussed hereinafter. The port  100  has a top  106  and a side  108 . As seen, the side  108  is circular in projection while the top  106  is essentially planar. 
     As best seen in  FIG. 4 , the inlet  102  has a channel  110  (that is shown to be tubular) with an axis  112  oriented at an angle  114  which may vary from a few degrees above the plane  116  of the top  106  to as much as 90 degrees. The angle  114  is preferably from about 30 degrees to about 60 degrees and most preferably about 45 degrees. Similarly, the outlet  104  has channel  118  (that is also shown to be tubular) with an axis  120  oriented at an angle  122  relative to the plane  116  of the top  100 . The angle  122  also may vary from a few degrees (e.g., 5-10 degrees) above the plane  116  of the top to as much as 90 degrees. The angle  122  is preferably from about 30 degrees to about 60 degrees and most preferably about 45 degrees. In the most preferred configurations, the angle  114  and the angle  122  are the same. 
     It may also be noted that the inlet  102  has an outside diameter  124  and an inside diameter  126  both sized to receive typical flexible tubing used in pulmonary ventilation systems. Similarly, the outlet  104  has an outside diameter  125  and an inside diameter  164 . Both the inlet  102  and the outlet  104  are configured to comply with International Standard ISO 5356-1 (4th Ed.: 2015). The typical flexible tubing is 22 millimeters (mm) in diameter for use with adult patients. The inside diameter of the inlet  102  is designed to mate with smaller, 15 mm diameter pediatric tubing sets. Suitable size adapters may also be used to accommodate tubing of different diameters. 
     The inlet  102  has a receiving portion  126  that may be tapered to have a larger outside diameter  128  abutting the collar  130  to allow the tubing to more easily be affixed to abut the collar  130  and effect a secure air tight connection. The receiving portion  126  also has a length  132  to facilitate the desired secure air tight connection. The inlet  102  is constructed as a conical inlet; and the outlet  104  is constructed to be a socket. Both are constructed in accordance with the ISO standard identified hereinbefore. 
     The valve  98  best seen in  FIG. 7  is cylindrical in shape and sized to fit snugly but not entirely into the port  100 . That is, the valve  98  has a thickness  134  slightly more than the thickness  136  of the port  100  to form a gap  144  to allow the port  100  to be rotatable relative to the valve  98 . 
     The valve  98  has a slot  146  which is elongated having a length  148  extending along a center line  152  as better seen in  FIGS. 5 and 5A  to extend from or between the inlet  102  and outlet  104 . That is, the inlet  102  has the channel  110  that extends to an opening  150  in the top  106  to register with one end  154  of the slot  146 . The outlet  104  also has its channel  118  that extends to an opening  156  in the top  106  that registers with the other end  158  of the slot  146 . As best seen in  FIG. 5 , in a first position or position A, the exhaust gas  13  from the input and output device  42  proceeds down the channel  110  of the inlet  102  of port  100  through the opening  150  and into the slot  146 . The exhaust gas  13  then proceeds through the slot  146  to the opening  156  of the outlet and into the channel  118  of the outlet as indicated by flow path arrow  160 . With the port  100  positioned as shown, the exhaust gas  13  proceeds from the inlet  102  to the outlet  104  so that the exhaust gas is unfiltered and proceeding directly to the exhaust valve  28  or to the atmosphere. The filter holder  94  and receptacle or cup  92  may be quickly and easily removed and replaced in a few seconds so that the amount of exhaust gas released is nominal. The pressure in the cup will vary from 0 to about 125 centimeters of water (cmH2O) which is from about 0 to about 1.77 pounds per square inch with the actual pressure in the range of 10 to 80 cm H 2 O leading to a flow rate that can vary from about 2 to about 50 liters of exhaust gas  13  per minute. Alternately, a small section of filter material may be placed in the channel  146  to form a first path to filter the exhaust gas  13  coming in the inlet  102  so that no unfiltered gas is delivered at the outlet  104 . Since the configuration with the exhaust gas  13  passing from the inlet  102  through the channel  146  directly to the outlet  104  would be used for short periods of time, it is expected that the filter material would last for an extended period of time (e.g., weeks) before it would need to be changed. 
     The channel  110  of the inlet  102  is shown to be circular in cross section having an inside diameter  126  and in turn an area comparable to the cross sectional area of the standard 1 inch supply hose that is the exhaust limb or exhaust circuit from the input and output device  42 . The outlet  104  is also circular in cross section having an inside diameter  164  that is here selected to be the same as the inside diameter  126  of the inlet  102 . In turn the cross sectional area of the inlet  102  is the same as the cross sectional area of the outlet  104 . In some applications, the cross sectional area of the outlet  104  may be larger than the cross sectional area of the inlet  102  to avoid constricting the flow of the exhaust gas and creating a back pressure. The discharge may also have a functional larger cross sectional area so that the discharge does not restrict flow. 
     Referring back to  FIGS. 5 and 5A , the slot  146  is semicircular in cross section between one end  154  and the other end  158 . The diameter  166  of the channel or slot  146  is selected so that the area for the passage of the exhaust gas  13  from the one end  154  to the other end  158  is comparable to or slightly larger (e.g. 5% larger) than the area of the inlet channel  110  so that the slot  146  does not function as an orifice and create a construction to restrict the passage of the exhaust gas  13 . As seen in  FIG. 5A , a filter  208  is sized to fit into the slot or channel  146  to filter the exhaust gas when the valve is in the first position. The filter  208  is semicircular with a frame  207  and filter media  210  as seen in  FIG. 5B  that is selected to meet CDC standards. Further, the filter media  210  may be impregnated with anti viral and anti bacterial compounds. 
     As seen in  FIG. 5A , it may also be noted that the slot  146  is rounded  168  at the one end and rounded  170  at the other end  158 . The rounded ends  154  and  158  have a radius  172  and  174  that is comparable to and preferably the same as the radius  166  of the slot  146 . 
     In operation, it can be seen in  FIG. 5  that the port  100  is in a second position in which the inlet  102  and the outlet  104  are aligned. When the port  100  is in the second position, the exhaust gas  13  follows the flow path indicated by the arrow  160 . The valve  98  is urged upward toward the top  106  of the port  100  to effect a frictional seal between the top  106  and the top surface  99  of the valve  98 . In some instances, a sealing lubricant can be used to enhance the seal. Alternately a seal (not shown) made of a suitable seal material like TEFLON® material or a nylon type material may be placed between the top  106  and the top surface  99  of the valve  98  so that the port  100  may rotate relative to the valve  98  and still effect a seal so that the exhaust gas  13  proceeds as desired. 
     As stated, to use the filter and water trap  90 , the port  100  may be rotated to a first position relative to the valve  98  to form a second path and align the inlet  102  and the outlet  104  to register with or mate with valve aperture  176  at the inlet  102  and valve aperture  178  at the outlet  104  as better seen in  FIG. 6 . When the port  100  is positioned relative to the valve  98  as seen in  FIG. 6 , the exhaust gas  13  is directed to flow through the channel  110  of the inlet  102  through the inlet valve aperture  176  and through the inlet aperture  180  of the filter holder  94  into the interior  182  of the receptacle or cup  92 . The exhaust gas collects in the interior  182  and is then directed to and changes direction to pass through filter membrane  184  and then out through the outlet aperture  186  of the filter holder  94  and into the outlet aperture  178  and the channel  118  of the outlet  104 . The flow path from the inlet  102  to the outlet  104  is shown in  FIG. 6  by arrow or line  188 . 
     In other words, the valve  98  can be rotated between a first or filtering position as seen in  FIG. 6  and a bypass or non filtering position as seen in  FIG. 5 . To preclude accidental rotation or misalignment of the valve  98  relative to the port  100 , the valve  98  is provided with two spring loaded balls  105  and  107  that register with corresponding detents (not illustrated) formed in the top  106  of the port  100 . When a cup and filter holder  92  is attached, the ports on the filter holder  180  and  186  mate with the holes  176  and  178  of the valve  98 . Rotating the cup and filter holder  92  to latch it to the full assembly then rotates the valve  98  to the flow-through position or second path. Rotating the cup to remove it rotates the valve to the bypass or first position or first path seen best in  FIG. 5 . 
     In  FIG. 6 , it can be seen that the filter holder  94  has a trunk  190  that is ovular in cross section as better seen in  FIG. 6A . The trunk  190  extends into the interior  182  of the receptacle or cup  92  and has the filter membrane  184  secured thereto. The trunk  190  is truncated so that the filter membrane  184  is circular in projection having a diameter  196  that is the same as the diameter  198  of the trunk  190 . The filter membrane  184  preferably has a rim  202  to register with the rim  204  of the trunk  190 . That is, rim  204  of the trunk has a width  200  sized to mate with the rim  202 . The rim  202  may extend beyond the rim  204  of the trunk and is preferably secured thereto by suitable glue or bonding material. 
     The trunk  190  has a height so that when the filter holder  94  is affixed to the receptacle or cup  92 , the trunk extends from the filter holder  94  to the bottom  194  of the receptacle or the cup  92 . The filter  184  has a membrane or filter material  206  having a porosity to filter out pathogens. The filter material  206  may also be impregnated with various substances to attack the pathogens. That is, the filter material is impregnated with anti bacterial and anti viral substances to enhance the filtration. The filter material  206  may also be pleated to increase the surface area of the filter to enhance filtration and reduce back pressure. 
     As also seen in  FIGS. 5 and 6 , the receptacle or cup  92  has an interior  182  that has a volume sufficient to allow moisture or other liquids to condense and collect therein. That is, the change of direction and the changes in pressure experienced by the exhaust gas  13  allows moisture to condense and collect in the volume of the interior  182  of the receptacle or cup  92 . 
     As seen in  FIGS. 3 and 4 , the latching ring  96  has slots  210  and  212  to receive the tongues  214  and  216  of the filter holder  94 . As seen the slots  210  and  212  as well as the tongues  214  and  216  are opposite each other and are sized so the tongues  214  and  216  register with the slots  210  and  212  and may slide in the slots  210  and  212  to effect a locking relationship. The surfaces of the slots  210  and  212  may be inclined so the slots  210  and  212  ramp or incline effect a frictional fit and in turn secure the filter holder  94  to the latching ring  96 . 
     In  FIG. 7 , the latching ring  96  is shown with ledges  222  and  224  (shown in dotted line) on the interior surface  226 . The bottom surface  228  of the valve is inserted into the latching ring  96  to abut the ledges  222  and  224  with the inlet aperture  180  of the filter holder  94  and the outlet aperture  186  of the filter holder  94  registering with the inlet valve aperture  176  and the outlet valve aperture  178  respectively as best seen in  FIGS. 6 and 7 . In some configurations, a ⅛ inch to ¼ inch thick spring like material (not shown) like neoprene may be placed on the ledges  222  and  224  to urge the valve  98  up toward the top  106  of the port  100 . The latching ring  96  is bonded to the valve  98  by any suitable bonding material. 
     Referring again to  FIG. 7 , the receptacle or cup  92  is shown to be cylindrical in shape with a diameter  230  ( FIG. 3 ) that may range from about 1.5 inches to about 2.5 inches with a height  232  from about 1.5 inches to about 2.5 inches with an interior  182  having a volume sufficient to trap moisture and liquids as the exhaust gas passes therethrough. The truncated trunk  190  allows for a circular opening with the filter membrane  184  positioned thereover. The filter membrane  184  seen in  FIG. 6B  is spaced above the bottom  194  a distance of less than ⅛ of an inch to allow liquid to gather without impacting on the area of the filter membrane  184  available to filter the exhaust gas. If the moisture or liquid has a level in the receptacle or cup  92  so that the a portion of the area of the filter membrane  184  affixed to the trunk  190  is covered with liquid, the combined filter holder  186  and receptacle or cup  92  with the filter membrane  184  should be removed and should be placed in a suitable disposal device. That is, the valve  98  and port  100  may be removed from the locking ring  96  so that the filter holder  94  may be rotated out of the slots  210  and  212  for disposal. A new or replacement combination of filter holder  94  with receptacle or cup  92  attached thereto (with a new filter membrane  184 ) may then be assembled to the latching ring  96  for further assembly with the valve  98  and port  100 . 
     In  FIGS. 5 and 6 , it can be seen that the port  100  when assembled over the valve  98  is sized to fit snuggly and rotatably inside the locking ring  96 . As assembled, the port  100  may be rotated between a first position or position A in which the exhaust gas passes through as shown by the flow arrow  160  and a second position or position B in which the exhaust gas passes through the receptacle or cup  92  and through the filter membrane  184  as seen by the flow arrow  188 . 
     Turning now to  FIG. 8 , changeable filter  240  is depicted which may be used as the changeable outlet filter  62  ( FIG. 2 ) in an exhaust filtration structure such as exhaust filtration structure  46 . The changeable filter  240  as depicted may also be used as the changeable inlet filter  450  seen in  FIG. 2A . 
     The changeable filter  240  of  FIG. 8  has a first conduit  242  to receive exhaust gas  13  or blended gas  15  and direct it or supply it to a vane valve  244 . The vane valve  244  is operable between a first position  243  (shown in solid) and a second position  245  (shown in dotted line). In the first position  243 , the exhaust gas  13  or blended gas  15  is supplied or directed to a first disposable filter  246 . When the vane valve  244  is in its second position  245 , the exhaust gas  13  or blended gas  15  is supplied or directed to a second disposable filter  248 . The exhaust gas  13  or blended gas  15  from the first disposable filter  246  is filtered to remove at least pathogens to form first filtered gas  247  which is supplied through a first exit conduit  250  and a first check valve  252  to an outlet  254 . With the vane valve  244  reoriented to the second position  245  (shown in dotted line), the exhaust gas  13  or blended gas is directed to the second disposable filter  248  which functions to remove pathogens from the patient in the exhaust gas  13  to form second filtered gas  249  that is directed to and through a second exit conduit  256  and a second check valve  258  to the outlet  254 . As can be seen, filtered exhaust gas  247  and  249  cannot pass or vent back through either check valve  252  and  258  so that all first filtered gas  247  and second filtered gas  249  must proceed to and through the outlet  254 . The outlet  254  supplies the first filtered gas  247  and second filtered gas  249  to the atmosphere or to an exhaust valve comparable to exhaust valve  28  ( FIG. 1 ) in a ventilation system so that sensors associated with the ventilator such as ventilator  10  can determine pressures and volumes of the first filtered gas  247  and second filtered gas  249 . 
       FIG. 9  is a perspective view and  FIG. 10  is a cross sectional view which illustrate or depict an inline filter arrangement  270  to function as a changeable filter such as changeable filter  62  or changeable inlet filter  450 . The inline filter  270  has a first conduit  272  to receive exhaust gas  13  and supply it through a first path  274  through a first filter  276  which removes pathogens from the exhaust gas  13  and supplies first filtered gas  294  at a second conduit  284 . The exhaust gas  13  may also be supplied through a second path  278  and a second filter  280  which is also configured to remove pathogens to form filtered second filtered gas  296  for transmission through the second conduit  284 . The first conduit  272  and the second conduit  284  are typically force fit with interconnecting hose or lines to receive and transmit gas to and from the filter arrangement  270 . Notably, the inline filter  270  may also function as a changeable filter  450  seen in  FIG. 2A . That is, blended gas  15  is processed in a fashion through either filter  246  and  248  comparable to exhaust gas  13  to produce breathable gas  11 . 
     As seen in  FIGS. 9 and 10 , the first filter  276  and the second filter  280  are each mounted to a filter holder  282  that slides relative to the housing  290  between a first position  286  seen in solid in  FIG. 9  and second position seen in dotted line  288 . In the first position  286 , the first filter  276  is in position to receive exhaust gas  13  or blended gas  15  from the first conduit  272  and filter out the pathogens from the exhaust gas to form first filtered gas  294 . That is, filter holder  282  positions the first filter  276  in the first path  274  and is movable in the housing  290  to a second position  288  shown in dotted line in  FIG. 9 . In the second position  288 , the first filter  276  is removed from the housing  290  where it may be removed and replaced with a new filter. Alternately, the first filter  276  may be cleaned. In the second position the second filter  280  is positioned in the second path  278  to filter pathogens from the exhaust gas  13  or breathable gas  15  to form second filtered gas  296 . The filter holder  282  slides  292  from the second position  288  to the first position  286  so the second filter  280  may be removed and replaced with a new filter or cleaned. 
     As seen in  FIGS. 9 and 10 , the first path  274  and the second path  278  are in effect the same but for the filter  276  and  280  through which the exhaust gas  13  or blended gas  15  passes. The filter holder  282  is snuggly fit in the housing  290  and may be sealed with, for example, lubricants or with other mechanical seal material. As seen, the in line filter  270  may be operated between the first position  286  and the second position  288  without venting or releasing to the atmosphere and surrounding areas exhaust gas  13  and blended gas  15  that has not been filtered and in turn contains pathogens. Further, the transition from that first position  286  and the second position  288  can be completed very quickly so there is virtually no noticeable impact on the flow of breathable gas  11  and/or exhaust gas  13  so that the FRC remains unaffected. 
     Referring now to  FIG. 11 , a changeable filter  300  is shown to be an alternative type of the changeable filter  62  of  FIG. 1 . The changeable filter  300  has a first conduit  302  to receive exhaust gas  13  from an exhaust line  21  and  44 . The exhaust gas  13  and blended gas  15  is directed to either a first valve  304  or a second valve  306 . As depicted, the first valve  304  is a ball valve shown in cross section with an interior ball  308  having a channel  310  that can be rotated in a housing  312  between open position in which the channel  310  is aligned to pass exhaust gas  13  therethrough and a second or closed position in which the ball  308  and in turn the channel  310  is rotated by the handle  314  to inhibit movement of exhaust gas  13  therethrough. 
     The changeable filter  300  as shown to be an alternative type of the changeable inlet filter  450 . The changeable filter  300  has a first conduit  302  to receive blended gas  15  from the ventilator output  48 . The blended gas  15  is then directed to either a first valve  304  or a second valve  306 . As depicted, the first valve  304  is a ball valve shown in cross section with an interior ball  308  having a channel  310  that can be rotated in a housing  312  between open position in which the channel  310  is aligned to pass blended gas therethrough and a second or closed position in which the ball  308  and in turn the channel  310  is rotated by the handle  314  to inhibit movement of blended gas therethrough. 
     The second valve  306  is a depiction of valve that has a housing  316  with a disc  318  operable by a handle  320  to move the disc between closed (shown) and open positions as known to those skilled in the art. A gate valve may also be used in lieu of either or both first valve  304  and second valve  306 . Any other form of valve may be used that functions to stop and permit flow therethrough. 
     The changeable filter  300  has the first valve  304  in a first leg  322  and the second valve  306  in the second leg  324 . The first leg  322  has a first filter  326  configured to filter pathogens from the exhaust gas  13  or blended gas  15  to form first filtered gas  329  that is directed to and through third valve  330  to a discharge  334 . Similarly, the second leg  324  has a second filter  328  that functions to filter pathogens from the exhaust gas  13  or blended gas  15  and from second filtered gas  331  that is directed to and through a fourth valve  332  to the discharge  334 . 
     The valves  304 ,  306 ,  330  and  332  may be selected to be any one of a ball valve, a gate valve, a disc valve, or other suitable valve as desired by the user. The valves  304 ,  306 ,  330  and  332  are operated between open and closed positions for directing exhaust gas  13  or blended gas  15  to and through the first leg  322  and then the second leg  324  in a manner so that no exhaust gas is vented or released to the surrounding area. So for example, valves  304  and  330  are open when valves  306  and  332  are closed. When valves  306  and  332  are closed, the second filter  328  may be removed from the second leg  324  and replaced with a new filter. Upon the connection of a new filter as the second filter  328 , valves  306  and  332  may be opened following which valves  304  and  330  are closed. With the valves  304  and  330  closed, the first filter  326  may be removed from the first leg  322  and replaced with a new first filter  326 . 
     In  FIG. 12 , a check valve  338  is shown which may function as the third and fourth valves  330  and  332 . The check valve  338  has a disc  340  that swings between a first position in which the valve disc  340  in the housing  342  is urged into the housing and away from inlet  344  to allow second filtered gas  331  therethrough as depicted in  FIG. 12 . With second filtered gas  331  entering the housing  342  from the discharge end  346 , the valve disc  340  is urged against the inlet  344  to block flow to the first filter  326 . The check valve  338  would operate between first and second positions to block flow of the first filtered gas  329  toward the second filter  328  in the same manner. That is, when the valves  304  and  306  are positioned to direct exhaust gas  13  or blended gas  15  through the first leg  322 , the valve  330  as a check valve will open and allow filtered exhaust gas to proceed to the valve  332  which would be urged to a closed position by the filtered exhaust gas. 
     Referring now to  FIGS. 13 and 14 , a filter  350  is shown having two filter elements  352  and  354  that are mounted to a holder  356  that rotates about a pin  358 . The filter elements  352  and  354  are rotatable about the pin (which can be anything that allows rotation such as a nut and bolt with suitable washers)  358  to move between a first position and a second position. In the first position seen in  FIG. 14 , filter element  352  is positioned in housing  360  to be in line to filter exhaust gas  13  or blended gas  15  entering the housing  360  from an inlet  362  to remove pathogens there from to create first filtered gas  396  or breathable gas  11  at the outlet  364 . 
     As better seen in  FIG. 13 , the filter element  352  is circular in projection and secured in first frame  366  which is shown in  FIG. 14  to have gaps  368  from the slot  370  only for illustration purposes. The frame  366  is sized to fit snuggly in the slot  370  with optional use of gasket materials such as a strip of felt material to effect an essentially air tight seal. 
     In  FIGS. 13 and 14 , the second filter element  354  has a second frame  392  that is joined to or unitarily formed with the first frame  366  and with a handle  394 . Then handle  394  can be operated to rotate the first filter element  352  with frame  366  to form its first position in the housing  360  to a second position away from the housing  360  and in turn rotate the second filter element  354  into the housing  360 . In turn the first filter element  352  can be cleaned or replaced while the second filter element  354  is functioning to filter the exhaust gas  13  or blended gas  15  to remove pathogens therefrom and form second filtered gas  398 . Upon rotation of the second filter element  354  from the housing  360 , the first filter element  352  will be reinserted into the housing  360  into its first position. Thus, the second filter element  354  can be cleaned or replaced for use when it is determined that the first filter element is ready to be replaced or cleaned. When the first filter element  352  and the second filter element  354  are rotated in and out of position, the interruption of flow is deemed to be insignificant so that the ventilator will not detect flow problems and automatically take steps to adjust or regulate flow differently to maintain desired flow rate of breathable gas  11 . 
       FIG. 15  depicts a kit  400  having components within a sealed container  402 . The container may be a fixed container but also may be a container with flexible sides like a mailing envelope. The components include all those necessary to form a dual path changeable filter of the type disclosed in  FIG. 2  or in  FIG. 2A . Specifically, the kit  400  contains at least two filters  404  and  406  of the type that can be replaced. Additional filters comparable to filters  404  and  406  can be included or separately packaged. The filters  404  and  406  shown are in line and disposable. 
     The kit  400  of  FIG. 15  also contains conduit or tubing  408 ,  410 ,  412 ,  414 ,  416 ,  418  and  420  each sized and sized to effect connections to form a changeable filter system comparable to the one seen in  FIG. 2 . Additional or fewer tubes may be included depending on the type of changeable filter system to be assembled and operated. 
     The conduit or tubing  408 ,  410 ,  412 ,  414 ,  416 ,  418  and  420  are each configured with suitable connectors  430  and  432  and a suitable stretch  434  in between. The stretch  434  may vary so the user has different sizes available. 
     The kit  400  also contains a suitable water trap  422  and a suitable diversion valve  424  having a handle  426  operable by the user to move it between a first position and a section position to direct exhaust gas into separate legs each with a filter in it like filters  404  and  406 . A separate kit comparable to kit  400  (not shown) may have a humidifier in it and no water trap. 
     The kit  400  may contain other components including latex or surgical gloves (not shown) for use by operators and sterile wipes (not shown) to maintain suitable cleanliness in the area of operation. Vials or tubes of lubricants for use with the conduit or tubing to effect connections may also be included. 
     Turning now to  FIG. 16 , a changeable outlet filter  500  is shown in cross section. The outlet filter  500  has a first filter element  502  and a second filter element  504  installed both of which are removable for cleaning and/or replacement as discussed more fully hereinafter. The changeable outlet filter  500  has an input housing  506  having an inlet  508  that has an outer wall  510  that is cylindrical in shape. The inlet has an inner wall  512  spaced from the outer wall  510  a distance  514  to form an opening selected to receive a conduit like conduit  60  ( FIG. 2 ) to effect a secure connection to the changeable outlet filter  500  and to thereby allow the transmission of exhaust gas  13  with pathogens through inlet channel  516 . The conduit  60  may be standard 22 millimeter (mm) diameter flexible hose used in medical applications to fit over the outer wall  510  or the standard 15 mm diameter tubing or hose to fit over the inner wall  512 . Both walls are tapered and may be said to be conical to meet ISO 5356-1 4th Edition.: 2015. However, different size inlet tubes may be used because the inlet has multiple diameters. Also adapters can be used to accommodate tubing of sizes that are not sized to secure to the inner wall  512  and/or the outer wall  510 . 
     The exhaust gas  13  proceeds through the channel  516  into a valve plenum or chamber  518  which is sized to contain the valve  520  that operates between two positions. In the first position  528  shown, it is blocking the first inlet  522  to prevent the flow of the exhaust gas  13  therethrough into a first path plenum  524  and then into the first filter element  502  as shown by dotted arrow  526 . The valve  520  is operable from the first position  528  blocking the first inlet  508  as shown to a second position  530  shown in dotted line blocking second inlet  532 . When not blocked, the exhaust gas  13  flows as shown by arrow  536  through the second inlet  532  into a second path plenum  534 . With the valve  520  in the second position  530  as shown, the exhaust gas  13  proceeds from the valve plenum  518  through the second inlet  532  into the second path plenum  534  and then into the second filter element  504  as discussed more fully hereinafter. 
     The valve  520  is shown as a simple face or plate that moves between the two positions  528  and  530  upon operation of a lever not shown in  FIG. 16 . But the lever not seen for the changeable outlet filter  500  is comparable to the lever  538  seen in a similar changeable outlet filter  540  shown in  FIG. 17 . That is, the changeable outlet filter  500  and the changeable outlet filter  540  are similar in size shape and function. The outlet changeable filter  540  has a first filter element  542  and a second filter element  544  comparable to the first filter element  502  and the second filter element  504 . The lever  538  may be held in place by suitable friction bumps, ball detent systems, or any other arrangement that holds the lever  538  in place but allows the operator to rotate the lever  538  with suitable force applied by the operator&#39;s hand. 
       FIG. 18  is an enlarged cross sectional view of another changeable outlet filter  550  which is comparable in size, shape and function to the changeable outlet filters  500  and  540 .  FIG. 18  shows a locking mechanism operable to lock the valve  554  in its second position  556  as shown and in a first position  556  shown in dotted line. The valve shaft  558  has a first finger  560  and a second finger  562  each sized to register with a slot  564  formed in the slide  566 . A spring  568  urges the slide  566  to engage the first finger  560  or the second finger  562  into the slot  564  and thereby hold the valve  554  in a closed position blocking the flow of exhaust gas  13  through either the first inlet  567  or the second inlet  570 . With its associated inlet blocked, either the associated first filter element  572  or second filter element  574  may be removed for cleaning or replacement while allowing the flow of exhaust gas  13  through the non blocked inlet and preventing the operator from moving the valve  554  to direct the flow of exhaust gas toward the filter element that has been removed. That is, the second inlet  570  is blocked or closed with the second filter element  574  removed for cleaning or replacement. 
     In  FIG. 18 , the second filter element  574  has a boss  578  having a base  580  with a rim  582  extending away and in a direction to engage the surface  581  as the second filter element  574  is urged inward toward a secure and operational position comparable to the position of the first filter element  572 . As the second filter element  574  moves toward a secure and operational position, the slanted surface  584  of the rim  582  engages and slides on the slanted surface  581  of the slide  566  urging the slide  566  off a finger  560  or  562  so that the valve  554  can be rotated by the operator. When so engaged, the second filter element  574  is in place and ready to function to filter the exhaust gas  13 . As so configured, the operator is not able to direct the flow of exhaust gas to a side or path that does not have or contain a filter like filter  502  or  504 . 
     The first filter element  572  also has a boss  579  which is not shown to engage the locking mechanism. In turn it is not here shown to function to operate the slide  566 . It is presently believed, that the boss  579  may be formed with a rim  583  comparable to rim  582  with surface comparable to slanted surface  584  to engage another slanted surface (not shown) formed on the extension  586  of the slide  566 . In turn, it is believed that the first filter element  572  can be formed to cause the slide  566  to engage and disengage fingers  562  and  564 . 
     As further seen in  FIG. 18 , the boss  578  has a detent  594  in the cylinder portion  592  configured to snuggly receive a ridge  596  formed in a securing ring  598  to hold the filter media  601  of the second filter element thereto. The first filter element  572  is comparably structured. The filter media  600  of the first filter element  572  has a housing  602  that forms a chamber  604  into which the filter media  600  is located. The exhaust gas  13  (with pathogens) passes through the inlet channel  606  and into the valve plenum  608 . The exhaust gas  13  may then pass through inlet  568  or  570  and then through or following a first path or a second path into the interior of the filter media  600  and  601  and then through the filter media into the appropriate chamber  604  or  605 . From the chamber  604  or  605 , the now filtered exhaust gas passes out of the changeable outlet filter  550  through structure not shown but comparable to that of the changeable outlet filter  500  as more fully discussed hereinafter. 
     Returning to  FIG. 16 , the first filter element  502  has a filter media  620  positioned in the chamber  634  while being secured to the boss  622  by a locking ring  624  having a ridge  626  which registers with a detent  628  comparable to that discussed in connection with  FIG. 18 . The exhaust gas  13  passes  630  into the interior  632  of the filter media  620  and through the filter media  620  into the chamber  634 . The exhaust gas  13  thereby becomes filtered exhaust gas  73  that leaves the chamber  634  and proceeds to and through a discharge opening  636  and then through a check valve  638  which is here shown as a duck valve. The check valve  638  has two vanes  640  and  642  that are biased to the closed position as shown. But under pressure from the filtered exhaust gas  73  from the chamber  634 , the vanes  640  and  642  open so the filtered exhaust gas  73  may then pass into a discharge plenum  644  and then through an outlet  646  formed in a fashion similar to the inlet  508 . That is, the outlet  646  is formed as a socket having an inner wall  648  sized to be connected to a 15 mm medical tube and an outer wall  650  sized to connect to a 22 mm medical tube both in accordance with ISO standard 5356-1 4th Ed.: 2015. The outlet  646  is provided to further transport the filtered exhaust gas  73 . In a similar fashion, filtered exhaust gas  75  emanates or exists from the second filter element  504  which is configured comparable to the first filter element  502 . 
     As seen in  FIG. 16 , the filter elements  502  and  504  are secured to frame  660 ; and in  FIG. 17 , filter elements  542  and  544  are secured to the frame  661  by a mechanical locking structure having a lip and slot  663  at one end and tongue  665  to interact with a groove  557  at the other. The inlet housings  506  in  FIG. 16 and 608  in  FIG. 17  are secured by an interlocking ledge structure  662  as best seen in  FIG. 16 . As also seen in  FIG. 16 , the outlet  646  is secured by a ridge and detent arrangement  664 . Other means may be used for locking the inlet  508  and the outlet  646  so long as they effect stable and effectively air tight closures. 
     As better seen in  FIG. 17 , the first filter element  542  is shown removably rotatable  670  relative to the frame  672 . That is, the first filter element  542  has a toe at one end (not shown) that engages the frame  672  proximate the outlet  666 . A latch (not seen) at the other end engages an opening formed in a wing  668  to lock the first filter element  542  in place. The second filter element  544  is structured comparable to the first filter element  542  so that it has a toe and latch comparable to that of the first filter element  542 . The opening in wing  668  is comparable to the opening  670  formed in the wing  672  of the changeable outlet filter  550  seen in  FIG. 18 . In  FIG. 16 , an alternate latching arrangement for securing a filter element is shown. The alternate latching arrangement includes the slot and lip  663  at one end of filter element  502  with a groove  557  formed to receive a tongue  665  to provide for removable connection and securement. 
     A filter media  680  is shown in  FIGS. 19 and 20 . It is formed of a suitable mesh of desired permeability. The material may also be treated with substances to treat any pathogens that may be in the exhaust gas  13 . Antiseptic and anti bacterial materials may be used. The filter media  680  is here shown in cross section in  FIG. 20  to be a rectangle with two hemispheres  684  and  686  on opposite ends  688  and  690 . So in effect, the filter media  680  in cross section is a rectilinear block  692  with a half cylinder  694  and  696  on opposed sides. The front end  698  is open to fit over a boss as hereinbefore discussed. The other end  700  is closed with additional filter material or may be crimped closed. 
       FIG. 21  presents an exploded view of a changeable outlet filter  710  which is similar to the changeable outlet filter  500  of  FIG. 16  but simplified in structure. The changeable outlet filter  710  has an inlet  712 , a valve  714 , a base or frame  716 , check vales  718  and  720 , valve mount  722 , an outlet  724 , a first filter element  726  and a second filter element  728 . The inlet  712  has an inner wall  730  and outer wall  732  assembled to provide a slot or space there between to receive a medical tube. That is, the slot or space  731  is shaped and sized for secure but removable attachment or connection of a suitable conduit or tube functioning as a conduit. A suitable medical tube may also fit over the outer wall  732 . 
     As seen in  FIG. 21 , the circular (in projection) rim  734  of the inlet  712  is sized to fit snuggly over the inlet wall  736  of the frame  716 . The inlet wall  736  has two snap fit “c” shaped mounting brackets  738  and  740  sized to receive and hold the shaft  742  of the valve  714  but still allow it to rotate  739 . The valve  714  is thus free to rotate between a first position to block or close the first inlet aperture  744  and a second position to block or close the second inlet aperture  746 . The valve  714  has a handle  748  for operation by the user. The valve handle  748  can be locked in place by detent structure  750  on the rim  734  which registers with a suitable ball structure (not shown) on the bottom of the handle  748 . The frame  716  has a void space  717  sized to receive the first filter element  726  with another or second void space separated by a spacer plate  719 . The second void space is filled with the second filter element  728 . The sides  717 A and  717 B of the frame  716  are provided to define the void space  717  and provide latching structure to secure the first filter element  726  and second filter element  738  in place. The filter elements  726  and  728  are structured with a boss  729  or similar structure to receive filter material like that seen in  FIG. 19 . Check valves  718  and  720  are each sized to fit thru suitable openings  752  and  754  in the valve mount  722 . The check valves  718  and  720  are shown as duck valves but may be any suitable form of check valve to inhibit back flow and preferably minimize resistance to the flow of filtered exhaust gas therethrough. The outlet  724  is formed similar to the inlet  712  and sized to snuggly receive the valve mount  722  and the outlet wall  732 . The outlet  724  is also formed and shaped to connect to an outlet conduit (not shown). 
     When assembled and connected to operate, the changeable outlet filter  710  receives exhaust gas  13  through the inlet  712 . The exhaust gas  13  then passes through one or the other of the inlet openings  744  and  746  which is not blocked by the valve  714  and more particularly by the valve blade  715 . After passing through one of the inlet openings  744  and  746 , the exhaust gas  13  passes into and through its associated first filter element  726  and second filter element  728 . It then passes through the filter media comparable to that shown in  FIGS. 19 and 20  and into a void space surrounding the filter media comparable to void spaces  604  and  605  seen in  FIG. 18  creating filtered exhaust gas. The filtered exhaust gas then proceeds through one of the valves  720  and  718  and into the outlet  724  for further transmission through the exhaust valve of an associated ventilator. 
       FIG. 22  is a perspective and exploded view of a simplified changeable outlet filter  760  having a housing  762  and a changeable first cartridge  764 . The housing  762  is formed of two virtually identical halves  766  and  768  assembled together. They may be secured to each other by glue, plastic welding or any other means to effect an air tight and rigid seal along the seam  770 . The half  766  has an inlet structure  772  configured to connect to a conduit delivering exhaust gas  13 . The inlet structure  772  is formed consistent with the ISO standard hereinbefore mentioned and has an inner wall  774  and an outer wall  776  each of suitable thickness  778 . The two walls provide suitable connections for different size hoses. For example a slot or opening  780  sized to receive a conduit which could be, for example, a 15 millimeter diameter medical tube made of a suitable synthetic material. When connected, the tube (not shown) delivers exhaust gas  13  into the channel  782 . 
     The half  766  of the housing  762  has a seal material (not shown for clarity) substantially the same as seal material  784  attached or adhered to the wall  786  on the inside  767  of the other half  768  of the assembled housing  762 . The seal material  784  is better seen attached to the wall  786  of the other half  768  and is seen separately in  FIG. 23 . The seal material  784  as here shown has a height  788  of 0.75 inch and has a width  785  that extends between edges  790  and  791  while being spaced inward from the edges  790  and  791  about ½ inch  792  and  793 . As better illustrated in  FIG. 23 , the seal material  794  has a thickness  796  of about 1/16 of an inch with end portions  794  and  795  formed to taper toward their respective out outer edges  798  and  799  to facilitate the movement of the cartridge  764  into the housing  762 . 
     The seal material  784  in this embodiment is EPDM foam tape but may be other suitable material to form an effective seal between the walls  782  and  786  and the cartridge  764  as more fully discussed hereinafter. Openings  797  are formed in the seal material  785  when installed to register with the channel  782  and a similar channel formed in outlet structure  773 . 
     The changeable cartridge  764  also seen in  FIG. 22  is also made of a first half  800  and a second half  802  almost identical to each other. Here, the first half  800  has a tongue  804  on top to register with a groove or inset  806 . While a tongue  804  and a inset  806  are shown on the top  808 , a comparable tongue and inset structure (not shown) may also be formed in the bottom  810 . As seen, the first half  800  and the second half  802  are joined together to form a seam by glue, welding or any other suitable means to join and create an airtight seal between the first half  800  and the second half  802 . 
     When the first half  800  and second half  802  are joined to form the cartridge  764 , they form a void space or an interior  803  that is filled with suitable filter material  812 . That is, filter material may be layered or sandwiched filter material of the type to filter pathogens and known to those of skill in the art and as discussed hereinafter. The filter material may be flat sheets cut to fit and layered. The filter material may also be pleated to increase the surface area; and the filter material may be formed to function as HME filter material to absorb moisture from exhaust gas leaving the patient and humidify breathable air being inspirated by the patient. 
     The cartridge  764  has a length  814  that is less than the length  816  of the housing  762  so that when the cartridge  764  is inserted into the interior or inside  767  of the housing  762  with the back wall  822  of the cartridge  764  is not flush with the edge  790 . A ledge or lip not shown is then formed to allow another cartridge to be lined up ready to push the first cartridge from its operational location installed in the housing  782 . Thus the front wall  824  when installed is set back from the edge  791  of the housing  762  from about ¼ to ¾ of an inch. 
     When installed in the housing  782 , the aperture  818  of the first cartridge formed in the main wall  820  of the first half  800  of the cartridge  764  registers with the channel  782  of the inlet structure  772 . At the same time, a second aperture  826  shown in phantom in the other main wall  828  of the second half  802  of the cartridge  764  registers with the second wall aperture formed in the second wall  786  in communication with a channel (not shown) in the outlet  773  comparable to channel  782  in the inlet structure  772 . It may be noted that when the cartridge  764  is inserted into the interior or volume  767  of the housing  762 , it is secured in place by registering means like a ball and detent arrangement such as balls or bumps  830  and  832  and comparable balls or bumps (not shown) on the side opposite to the top  834  which are positioned to register with corresponding four detents like detent  836  formed in the housing  762 . 
     The changeable outlet filter  760  of  FIG. 22  with a cartridge comparable to cartridge  764  may be connected in a pulmonary ventilation system like the system seen in  FIG. 2  as the changeable outlet filter  62 . That is, the cartridge  764  can be deemed to function as filter  68 . When connected, the exhaust gas  13  is introduced via conduit  52  ( FIG. 2 ) into the channel  782  in the inlet  772  ( FIG. 22 ) and then into and through the aperture  771  in wall  786  and the aperture  818  of the cartridge  764  and then into the filter media  812  which functions to filter pathogens out of the exhaust gas  13  to form filtered exhaust gas  73 . As stated before, the filter material may be flat sheets of filter material cut to fit and layered. The filter material may also be pleated to increase the surface area; and it may be formed to function as an HME filter material to absorb moisture from exhaust gas leaving the patient and humidify breathable air being inspirated by the patient. The filtered exhaust gas  73  proceeds through aperture  826  and aperture  797  through the outlet  783  which is connectable to discharge the filtered exhaust gas  73  to the atmosphere or to the exhaust valve  28 . 
     A second cartridge  850  is then provided comparable or identical in structure and function to cartridge  764 . Thus the number  850  is assigned to the same illustration for cartridge  764  to show they are identical. The second cartridge  850  is then pushed or urged toward the interior or volume  767  of the housing  762  in alignment with or to register with the cartridge  764  in place in the housing  762  and to in turn contact rear wall  802  of cartridge  764 . By advancing cartridge  850  into the housing  762 , one is at the same time advancing the cartridge  764  through and outwardly of the housing  762  with the walls  820  and  828  of the exiting cartridge  764  and then the walls  820  and  828  of the entering cartridge  850  functioning as valve  66  first closing or blocking flow of exhaust gas  13  into the exiting cartridge  764  and then opening as the apertures  818  and  826  come into alignment with the inlet channel  782  in the housing  762  as well as the outlet channel (not shown) in the outlet  783 . The cartridge  850  thus functions as filter  70  supplying filtered exhaust gas  75  though the outlet aperture  826  to the outlet channel in the outlet structure  773  and then to atmosphere or to the exhaust valve  28  in the ventilator  10  ( FIG. 2 ). It can be seen that the process of changing the cartridges  764  with cartridge  850  can be completed very quickly. Practically, the change can be effected in a few seconds or less so the ventilation therapy has not effectively been interrupted and the FRC is not affected. Further, exhaust gas  13  has not been released to the surrounding environment. Additional cartridges can be provided so that the change can be completed at whatever interval desired. 
     Turning to  FIG. 24 , a changeable filter structure  900  is shown similar to that of  FIG. 22 . That is, the filter structure  900  has a housing  902 , a first cartridge  903  and second cartridge  904  which is sized and shaped for insertion into the housing  902  in a manner similar to that of the filter shown in  FIG. 22 . The housing  902  is formed of two identical halves  906  and  908  joined together at seam  910  by glue, welding or any process to fixedly secure the two halves  906  and  908 . Alternately, the housing may be formed or molded as one piece. 
     As shown in  FIG. 24 , the housing  902  has an inlet  912  and outlet  914 . The inlet  902  has an inner wall  916  and an outer wall  918  each having a diameter selected to connect with standard medical tubing as hereinbefore discussed. The inlet  912  is attached to the inlet wall  922  with the channel  920  in alignment with an inlet wall aperture  926  to communicate exhaust gas  13  therethrough into the volume  928  of the housing  902  formed by the two halves  906  and  908 . 
     The outlet  914  is a socket similar to the inlet  912  both having an inner wall (not shown) and an outer wall  930  The inlet  912  and outlet  914  are both formed in accordance with international standards as stated herein to fit with standard 22 mm and 15 mm medical tubing. In addition to the inlet wall  922  and outlet wall  924 , the housing  902  has a plurality of sides at its top  932  and its bottom  934  to form the volume or inside  928 . As shown, the top  932  has a top slot  936  and the bottom  934  has the bottom slot  938 . The bottom slot  938  has a depth  940  and a width  942  and extends the length  944  of the housing  902 . The top slot  936  is identical except that it has an opening  946  positioned centrally along the length  944  having a width  948  and a length  950  sized to register with raised portions  952  on the ridge  954  of the cartridge  904  as hereinafter discussed. 
     The second cartridge  904  seen in  FIG. 24  is essentially identical to the first cartridge  903 . The second cartridge  904  is formed of two identical halves  954  and  956 . The upper half  956  has an inlet aperture  958  formed in the cartridge inlet wall  960 . A screen or grid  959  is positioned in the inlet aperture  958  to retain the filter media within the cartridge  904 . An outlet aperture (not shown) is identically formed in the outlet wall  962 . The first cartridge  903  and the second cartridge  904  each have a plurality of sides to form an enclosed volume that includes the filter media. 
     As illustrated in a simplified exploded view of a cartridge  964  in  FIG. 25 , it has a top half  966  and a bottom half  968  with filter media  970  for insertion into the volume  972  formed when the two halves  966  and  968  are joined together. A suitable filter media useful here and for other filter media herein identified is Technostat® 150 Plus available from Superior Felt &amp; Filtration, LLC of McHenry, Ill. The filter material may be several flat sheets cut to fit and layered. The filter material may also be pleated to increase the surface area; and it may be formed to function as an HME filter material to absorb moisture from exhaust gas leaving the patient and humidify breathable air being inspirated by the patient. The top half  966  has an inlet wall  974  with an inlet aperture  976  comparable to inlet aperture  958 . The bottom half  968  has an outlet wall  978  having an outlet aperture  980  formed therein. 
     Returning to  FIG. 24 , the second cartridge  904  has a top flange or rim  982  and a bottom flange or rim  984  that are sized and shaped to register with the top slot  936  and the bottom slot  938  of the housing  902 . A seal material  986  surrounds the cartridge  904  with an inlet aperture  988  in registration with the inlet aperture  958  in the inlet wall  960 . The seal material  986  has an outlet aperture in registration with the cartridge outlet wall aperture (similar to the outlet aperture  980  in  FIG. 25 ) and with an outlet aperture (not shown) in the outlet wall of the housing  902 . The seal material  986  is placed on the cartridge  904  rather than on the interior of the housing  902 . The seal material  986  is elastic and is stretched to fit tightly about the cartridge  904 . 
     Similar to the filter arrangement of  FIG. 22 , the filter  900  of  FIG. 24  has a first cartridge  903  in the housing with the apertures of its inlet wall, outlet wall, and sealing material in alignment forming a first path by which exhaust gas with pathogens like exhaust gas  13  enters channel  920  and proceeds through the cartridge  903  with the pathogens being filtered out to form filtered exhaust gas like exhaust gas  73 . When it is desired to remove or replace the first cartridge  903 , the second cartridge  904  is presented to the housing  902  with the top ridge  982  and the bottom ridge  984  aligned with top slot  936  and bottom slot  938 . Notably, the cartridge  904  is otherwise suitably dimensioned to fit into the volume  928  of the housing  902  and effect a seal between the front face  990  of the second cartridge  904  and the back face of the first cartridge  903  comparable to the back face  992  of the second cartridge  904 . The seal material  986  also effects a seal between the inlet wall  922  of the housing  902  and the inlet wall  960  of the second cartridge as well as between the outlet wall  924  of the housing  902  and the bottom  962  of the second cartridge  904 . To effect removal of the first cartridge  903 , the raised portion  947  formed in its rim extending into the opening  946  in the top slot of the housing is pressed with the fingers to deflect inward as the second cartridge  904  is urged into the volume  928  of the housing  902 . That is, rim  982  has a number of raised bumps  952  sized in length and width to register with the opening  946  in the top slot  936  of the housing so the second cartridge is correctly positioned to create the second path when the raised bumps  952  are in registration with the opening  946 . In effect the top and bottom walls of the first cartridge and the second cartridge  904  with seal material function as valves closing the first path and opening to form a second path. That is the second path is formed whereby the exhaust gas  13  passes through channel  920  and through inlet wall aperture  926 , seal aperture  988 , inlet cartridge wall aperture  958  and then into the media within the cartridge  904  to the cartridge wall aperture (like cartridge outlet wall aperture  980  in  FIG. 25 ) and then through an outlet aperture in the seal material  986  to and through the outlet wall aperture of the outlet wall  962  to the channel in the outlet  914  to become filtered exhaust gas comparable to filtered exhaust gas  75 . 
     It should be noted that in some configurations, the first cartridge  903  and the second cartridge  904  of the filter  900  may also have connectors to attach one to the other so that the first cartridge cannot be removed before the second cartridge is properly in place. A train coupling arrangement as hereinbefore discussed is a suitable connector. Other connectors may be used that inhibit detachment of the first cartridge  903  from the second cartridge  904  until the second cartridge  904  is positioned and formed the second path. 
     In another configuration seen in  FIG. 26 , a housing  997  similar to housing  902  may be formed with a series of evenly spaced holes  996  along the length  995  of its upper rim as seen in  FIG. 26 . The first cartridge  998  similar to the second cartridge  904  may be formed to have a flexible pawl  999  positioned on its rim  993  to engage the spaced holes  996  when the second cartridge is inserted into the housing  997  to form a changeable filter structure comparable to changeable filter structure  900 . In operation, the pawl  999  can engage the slots  996 . The pawl  999  allows the first cartridge  998  to be urged out of the housing  997  by the second cartridge like second cartridge  904  while preventing removal of the first cartridge  998  before insertion of the second cartridge. In short the second cartridge needs to be urged in to push out the first cartridge. Connectors  1000  and  1002  are also depicted on the cartridge  998  to illustrate a coupling arrangement which functions to couple a first cartridge to a second cartridge so that the first cartridge cannot be removed before the second cartridge is in place. 
     It may be noted that filters herein disclosed may be used as the inlet filter  12  as well as the changeable outlet filter  46 . The filter structures particularly illustrated in  FIGS. 22, 24 and 25  are particularly suitable for use as the HME filter  17  seen in  FIG. 1  with filter media known to those skilled in the art as suitable for HME use. See, for example, HME filter material as disclosed in U.S. Pat. No. 7,594,509 (Burk) at Col3, line 36-54. 
     Those skilled in the art will recognize disclosed structures and methods may be practiced using materials that may be different from those identified hereinabove without departing from the principles as disclosed. Only specific embodiments have been disclosed to illustrate the structures and methods as defined by the appended claims.