Abstract:
A heat and moisture exchanger for both conducting a stream of air produced by a ventilator to a moisturizing medium and internally bypassing the moisturizing medium if aerosolized medication is introduced into the stream includes a housing having a ventilator-side port coupled to an outlet of a ventilator and a source of aerosolized medication. The housing has a patient-side port for coupling to a patient to provide ventilation including either air or air carrying aerosolized medication. A first path conducts air from the ventilator-side port through the moisturizing medium and the patient-side port, and a second path conducts air carrying aerosolized medication from the ventilator-side port directly to the patient-side port. A two-way valve mechanism in the housing selectively couples the ventilator-side port into fluid communication with one or the other of the first and second paths.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. patent application Ser. No. 10/654,797 filed Sep. 4, 2003 entitled “HEAT AND MOISTURE FILTER EXCHANGER AND METHOD”, now U.S. Pat. No. 7,347,203 issued Mar. 25, 2008. That application claims the benefit of prior filed copending U.S. provisional application Ser. No. 60/411,213 filed Sep. 16, 2002 entitled “HEAT AND MOISTURE FILTER EXCHANGER AND METHOD” by Gregory S. Marler and David T. Sladek. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to systems for respiratory therapy, particularly to ventilator systems that includes heat and moisture exchanger (HME) media or heat and moisture exchanger (HME) media in the respiratory path and also provides the additional capability of administering aerosol medication to a patient effectively without interrupting the respiratory path. 
     The closest prior art is believed to be illustrated in  FIG. 1 , in which a conventional heat and moisture exchanger (HME)  1  has a port  2  connected to a port  3  of a bypass device  4 . Bypass device  4  is marketed by DHD Healthcare of Watsonville, N.Y. under the trademark CIRCUVENT. Heat and moisture exchanger  1  has a port  5  connected to port  6  of a Y connector  10  having a connector which is coupled to an endotracheal tube (not shown) in the patient. Bypass device  4  includes another port  7  connected to one end of a flexible bypass tube  8  having its other end connected to another port  9  of Y connector  10 . Bypass device  4  has a port  11  connected by suitable tube to a ventilator (not shown). A rotatable control ring  13  can be adjusted so that gas received through port  11  from the ventilator is selectively routed through either heat and moisture exchanger  1  or bypass tube  8 . If aerosol medication is introduced into the respiratory path upstream from port  11 , then control ring  13  is turned to direct the gas carrying the aerosol medication around heat and moisture exchanger  1  through bypass tube  8 . This prevents the aerosol droplets/particles from impacting on the media of heat and moisture exchanger  1  (and any filter material that may be provided with it). 
     The bypass tube  8  of the assembly shown in  FIG. 1  has a large volume of “dead space” which results in a relatively large amount of previously exhaled air being re-breathed by the patient. This reduces the amount of oxygen received by the patient&#39;s lungs and is always undesirable, and in some instances can be dangerous, especially for a critically ill infant being supported on a ventilator. The assembly shown  FIG. 1  is bulky, relatively heavy, and tends to be leaky. 
     The cost of a typical HME or HMEF element  1  or an HCH element can be in the range from approximately $1.50 to $5.00, and the bypass device  4  can cost from approximately $3.50 to $7.00. 
     Thus, there is an unmet need for a device and method for selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium. 
     There also is an unmet need for such a device and method that reduces the cost of selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium. 
     There also is an unmet need for such a device and method that reduces the cost of selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium, wherein the device and method also reduce the risk of infection to the patient. 
     There also is an unmet need for such a device and method that reduces the cost of selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium, wherein the device and method also reduce the risk to the patient associated with a large volume of a “dead space” in the respiratory path. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a device and method that reduces the cost of selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium. 
     It is another object of the present invention to provide an improved unitary device and a method for selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium. 
     It is another object of the present invention to provide a device and method that reduces the cost of selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium and that also reduces the risk of infection to the patient. 
     It is another object of the invention to provide a device and method that reduces the cost of selectively conducting a stream of air produced by a ventilator through a moisturizing medium in the device or internally bypassing the moisturizing medium to prevent aerosolized medication that has been introduced into the stream from contacting the moisturizing medium and that also reduces the risk to the patient associated with a large volume of “dead space” in the respiratory path. 
     Briefly described, and in accordance with one embodiment, the present invention provides a heat and moisture exchanger for selectively conducting a stream of air produced by a ventilator through a moisturizing medium or internally bypassing the moisturizing medium if aerosolized medication is introduced into the stream, the device including a housing having a ventilator-side port coupled to a ventilator and a source of aerosolized medication, the housing also having a patient-side port coupled to a patient to provide ventilation including either air or air with aerosolized medication. A first path within the device conducts non-aerosolized air between the ventilator-side port and the patient-side port, and a second path conducts air carrying aerosolized medication between the ventilator-side port and the patient-side port. A two-way valve mechanism is included within the housing for selectively coupling the ventilator-side port into fluid communication with one or the other of the first and second paths. 
     In one embodiment, the heat and moisture exchanger includes a housing having a ventilator-side port ( 21 ) configured to be coupled to an outlet of a ventilator and a source of aerosolized medication, the housing also having a patient-side port ( 25 ) configured to be coupled to a patient to provide ventilation to the patient. The structure within the housing forms a first path for conducting non-aerosolized air from the ventilator-side port through the moisturizing medium to the patient-side port and a second path for conducting air carrying aerosolized medication from the ventilator-side port to the patient-side port by bypassing the moisturizing medium. The two-way valve mechanism in the housing selectively couples the ventilator-side port into fluid communication with one or the other of the first and second paths. An external valve control ( 230 ) extends through the housing to control the two-way valve mechanism. A tube ( 37 ) is supported between the ventilator-side port ( 21 ) and the patient-side port ( 25 ), wherein the second path extends entirely through the tube. The two-way valve mechanism selectively blocks or opens a portion of the second path extending through the tube ( 37 ) in response to the external valve control ( 230 ). The moisturizing medium ( 15 ) is disposed between an outer surface of the tube ( 37 ) and an inner surface of the housing. The first path extends around the tube and through the moisturizing medium. A gap ( 55 ) between a first end of the tube ( 37 ) and the ventilator-side port ( 21 ) forms part of the first path. The two-way valve mechanism includes a butterfly valve coupled to an actuator mechanism. The valve includes a valve disk  74  integral with a cylindrical valve post  78  having a female coupling element  77  at its upper end which mates with a the mail coupling device  73 A. The actuator mechanism includes an actuation knob ( 73 ) external to ventilator-side housing  400 , an actuator stem  73  extending through ventilator-side housing  400  and having the male coupling element  73 A at its lower end. The moisturizing medium ( 15 ) is annular and is disposed around the tube ( 37 ), an inner surface of the moisturizing medium forming a seal with an outer surface of the tube, an outer surface of the moisturizing medium forming a seal with an inner surface of the housing. The housing is cylindrical, and wherein the inner surface and outer surface of the moisturizing medium are cylindrical. The ventilator-side section ( 220 ) includes a plurality of integral support members  54  which support the tube ( 37 ) in axial alignment between the ventilator-side port ( 21 ) and the patient-side port ( 25 ). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view of a prior art assembly including an HME device and a bypass unit. 
         FIG. 2  is a side elevation view of a HME/bypass unit according to the present invention. 
         FIG. 2A  is a block diagram showing a connection of the HME/bypass unit of  FIG. 2  in a ventilator circuit. 
         FIG. 3  is a longitudinal section view showing the interior of the HME/bypass unit of  FIG. 2 . 
         FIG. 4  is a perspective right upper view showing the interior of the ventilator-side section  22  of the HME/bypass unit of  FIGS. 2 and 3 . 
         FIG. 5  is a perspective left view showing the interior of the patient-side section  35  of the HME/bypass unit of  FIGS. 2 and 3 . 
         FIG. 6  is a perspective lower right view of the valve plate  23  of the HME/bypass unit of  FIGS. 2 and 3 . 
         FIG. 7  is an a front upper perspective view of another embodiment of a HME/bypass unit according to the present invention. 
         FIG. 8  is a longitudinal section view showing the interior of the HME/bypass unit of  FIG. 7 . 
         FIG. 9  is a perspective view showing the interior of the ventilator-side section of the HME/bypass unit of  FIG. 7 . 
         FIG. 10  is an elevation view of a butterfly valve assembly included in the ventilator-side section of the HME/bypass unit in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 2 ,  2 A and  3 - 6 , an HME/bypass device  20  includes a ventilator-side section  22  having a ventilator-side port  21 , and a patient-side section  35  having a patient-side port  25 . A knurled, rotatable collar  23 A of a valve plate  23  is used to control a 2-way valve located inside of a complete housing including both ventilator-side section  22  and patient-side section  35 . The outer surface of ventilator-side port  21  is partially knurled, as shown. A CO2 monitoring port  42  is provided as an integral part of a ventilator-side section  22 , and a drainage port  43  is provided as an integral part of patient-side section  35 . 
       FIG. 2A  shows a ventilating system  100  in which HME/bypass device  20  can be connected, wherein a ventilator  101  is coupled by suitable respiratory tubing to one port of an MDI (metered dose inhaler) injection device  103  having an opposite port connected by suitable respiratory tubing to ventilator-side port  21  of HME/bypass device  20 . HME/bypass device  20  includes a patient-side port  25  which is connected to an endotracheal tube  107  that has been intubated into the trachea of a patient. 
     The air pumped by ventilator  101  into ventilator-side port  21  does not carry any aerosolized medication unless an MDI canister  105  is inserted into MDI injection device  103  and depressed so as to open the valve of MDI canister  105 . Knurled collar  23 A is initially set to a position that causes air from ventilator  101  to pass through an optional annular bacterial and viral filter  48  disposed in ventilator side chamber  40 A and through an annular HME element  15  in the patient side chamber  50 A (as shown in  FIG. 3 ) and then through patient-side port  25  and endotracheal tube  107  into the lungs of the patient. If it is desirable to administer aerosolized medication to the patient, then knurled collar  23 A is rotated 90 degrees to a second position which causes air pumped by ventilator  101  to pass directly from ventilator-side port  21  through patient-side port  25  without passing through HME element  15  or the optional bacterial and viral filter element  48 . Then, an MDI canister  105  containing the desired medication is inserted into an injection port of MDI injection device  103  and depressed so as to open a valve of MDI canister  105  and thereby cause a plume of medication droplets/particles to be sprayed into the air stream produced by ventilator  101 . The plume of medication droplets/particles is carried directly through an un-obstructed path through HME/bypass device  20  and endotracheal tube  107  into the lungs of the patient. This prevents medication droplets/particles from being deposited on HME element  15  or the optional bacterial and viral filter element  48 . Alternatively, a device other than an MDI injection device  103 , such as a liquid nebulizer, might be used to introduce aerosolized medication into the stream of air produced by ventilator  101 . 
     Referring to  FIGS. 3-6 , ventilator-side port  21  of HME/bypass device  20  includes a cylindrical passage  21 A that extends into an interior first chamber  40 A bounded by a first chamber wall  40  that is integral with the cylindrical tube that forms/bounds passage  21 A. A portion of passage  21 A extends into first chamber  40 A and forms a cylindrical left cage  30 , the right end of which includes a narrow cylindrical section  31 . Half of the right end of passage  21 A is blocked by two sections of a circular disk  32 , as shown in  FIG. 4 . 
     As shown in both  FIGS. 3 and 4 , the main cylindrical wall of cage  30  has a number of elongated, rectangular, uniformly spaced openings  30 A. 
     The right peripheral edge of ventilator-side section  22  is bounded by a planar, annular surface  34  ( FIG. 4 ) which abuts and slides against a corresponding annular planar surface of annular ring  23 B of valve plate  23 , as shown in  FIG. 6 . An O ring  45 A is disposed in a circumferential O ring grove  45  around the outside surface of chamber wall  40  and performs a seal with the inside surface diameter of knurled collar  23 A. A receiving boss  81  is positioned on the inside diameter of chamber wall  40  to receive a keying post  52  ( FIG. 5 ) to ensure proper alignment of patient-side section  35  with ventilator-side section  22 , annular ring  23 B of valve plate  23  being “sandwiched” between annular planar face  34  of ventilator-side section  22  and annular planar surface  50 B of patient-side section  35 . Keying post  52  also acts as a stop to limit the 90 degree rotation of valve plate  23  in either direction by engaging the portions of spokes  23 C and  23 G between outer ring  23 B ( FIG. 6 ) and middle ring  23 D. 
     The details of valve plate  23  are shown in  FIG. 6 . Knurled collar  23 A surrounds and is rigidly attached to a planar structure including two flat, co-planar, diametrically aligned spokes  23 C and two flat, co-planar, diametrically aligned spokes  23 F which are perpendicular to spokes  23 C. The planar structure also includes three flat, co-planar, concentric, annular rings, including above mentioned outer annular ring  23 B, and also includes middle ring  23 D and inner ring  23 E. Outer ring  23 B is rigidly attached to the inner diameter surface of knurled collar  23 A, and is connected to the outer end of each of spokes  23 C. Middle ring  23 D is attached to a mid portion of each of spokes  23 C. 
     The inner end of each of spokes  23 C is rigidly attached to opposed portions of the outer cylindrical surface of an outer cage  70 . An outer end of each of spokes  23 F is attached to and integral with middle ring  23 D. The inner end of each of spokes  23 F is rigidly attached to opposed portions of the outer cylindrical surface of outer cage  70 . 
     A main cylindrical surface of outer cage  70  ( FIG. 6 ) has therein a plurality of uniformly spaced, elongated openings  70 A that can be selectively aligned with or misaligned with openings  60 A in inner cage  60  ( FIG. 5 ) in order to either (1) allow air from ventilator  101  ( FIG. 2A ) to flow through HME element  15  and openings  60 A or (2) block openings  60 A. The selective alignment or misalignment is achieved by rotating knurled collar  23 A through 90 degrees (relative to the complete chamber wall  40 , 50  with valve plate  23  “sandwiched” between left annular surface  34  and right annular surface  50 B). A semi-circular disk  24  covers half of the inner end of outer cage  70 . Two sectors of circular disk  24  cover part of the inner end of outer cage  70 . 
     Referring to  FIGS. 5 and 6 , the inner surface of outer cage  70  of valve plate  23  can slide over the outer surface of inner cage  60  of a ventilator-side section  22  when it, valve plate  23 , and patient-side section  35  are assembled into the unitary structure shown in  FIGS. 2 and 3 . The annular, planar face  50 B of patient-side section  35  abuts and slides against the front face of outer ring  23 B ( FIG. 4 ), and the keying post  52  attached to the inner surface of right chamber wall  50  of patient-side section  35  extends into the corresponding receiving boss  81  of left chamber wall  40 . 
     A second O ring groove  46  ( FIGS. 3 and 5 ) is circumferentially formed in the outer surface of chamber wall  50 , and a second O ring  46 A is supported in second O ring groove  46 . The first O ring  45 A forms a seal between valve plate  23  and ventilator-side section  22 , and the second O ring  46 A forms a seal between valve plate  23  and patient-side section  35 . 
     Ventilator-side section  22  and patient-side section  35  both will be permanently snapped on to valve plate  23 . Preferably, all of the components of HME/bypass device  20  with the exception of the HME element  15  and the optional bacterial and viral filter are composed of suitable plastic, such as clear ABS plastic, acrylic, polycarbonate, or polypropylene. 
     When valve plate  23  is rotated to a first position such that its two openings  24 A are precisely aligned with the two openings  60 A of ventilator-side section  22 , then semicircular opening  24 A adjacent to disk sectors  24  are also precisely aligned with the openings  32 A adjacent to disk sectors  32 , thereby providing a clear passage from ventilator-side port  21  to patient-side port  25 . At the same time, the solid “vanes”  70 B of outer cage  70  ( FIG. 6 ) are precisely aligned with openings  60 A of inner cage  60 , and thereby prevent air carrying aerosolized medication from passing through HME element  15 , optional bacterial and viral filter  48 , and openings  60 A, so essentially all of the aerosolized medication flows unobstructed through the endotracheal tube  107  into the patient&#39;s bronchial passages and lungs. 
     When valve plate  23  is rotated 90 degrees from the first position to a second position such that its disk sectors  24  are precisely aligned with the openings  32 A of ventilator-side section  22 , then disk sectors  32  adjacent to openings  32 A are also precisely aligned with openings  24 A adjacent to disk sectors  24 , thereby completely blocking passage of the air from ventilator-side port  21  directly to patient-side port  25  and diverting all of such air from passage  21 A through openings  30 A of left cage  30  into the first chamber  40 A through optional bacterial and viral filter  48 , and through the various gaps between rings  23 B,  23 D and  23 E so the air flows into second chamber  50 A, through HME element  15  in second chamber  50 A, and then through the openings  70 A of outer cage  70  and the aligned openings  60 A of inner cage  60  and into passage  25 A. 
     Another embodiment of the HME/bypass device of the present invention is shown in  FIGS. 7-10 . This embodiment has a substantially simpler internal valve structure and an easier-to-use external control for switching between HME operation and bypass operation in which aerosol medication is introduced into the air stream generated by ventilator  101 . Where appropriate, the same or similar reference numerals used in  FIGS. 2-6  are also used in  FIGS. 7-10 , sometimes with an added “0”. Referring to  FIGS. 7-10 , HME/bypass device  200  includes a ventilator-side section  220  and a patient-side section  350  that can be press-fit or snap-fit onto ventilator-side section  220 . Ventilator-side section  220  has a ventilator-side port  21  having an inlet passage  21 A, gas sampling port (not shown, but similar to port  42  of  FIG. 2 ), and two generally cylindrical ventilator hose connecting surfaces, one being the inner surface of ventilator-side port  21  and the other being the outer surface of a smaller-diameter concentric cylindrical tube  21 B. A standard ventilator hose for coupling to intubated adults can be connected to the inner surface of port  21 , and a smaller ventilator hose for coupling to intubated children can be connected to the outer surface of concentric cylindrical tube  21 B. Similarly, a smaller ventilator hose can be coupled to the inner concentric cylindrical tube  25 B on patient-side port  25  for coupling to a ventilator circuit adapted for children. 
     A butterfly valve assembly is mounted axially within the housing formed by ventilator-side housing  400  and patient-side housing  500 . The valve assembly, shown in  FIGS. 8-10 , is supported by six vanes  54  which are integral to the ventilator-side housing  220  and are symmetrically positioned around a gas flow path that is concentric with ventilator-side housing  220 . 
     A cylindrical valve housing  37  is axially supported by the inner edges of the six vanes  54 . One or more of the opposed vanes  54  extends between a pair of axial ribs  58 , which are integral with the valve housing  37  and which are spaced far enough apart to accommodate the vanes  54 . The vanes  54  support valve housing  37  so that the end thereof closest to the wall of ventilator-side housing  220  is spaced from it by a gap  55  through which air from ventilator  101  can flow when the valve is closed, thereby causing the air from ventilator  101  to be diverted around, rather than through the valve housing  37 . 
     A semicircular slot  38  in the upper surface of valve housing  37  is wide enough to allow the planar, semicircular vanes  74  of the butterfly valve and a valve post  78  to which vanes  74  are attached to pass through during assembly. The diameter of the circle formed by the outer edges of the two vanes  74  is slightly less than inside diameter of cylindrical valve housing  37 , in order to allow the butterfly valve to be smoothly opened and closed by rotating an actuation knob  230  attached to the upper end of a valve actuation stem  73  having a lower male coupling element  73 A which engages a female coupling element  77  attached to the top of valve post  78 . 
     As shown in  FIG. 8 , HME filter  15  has an annular shape and fits snugly over the outer surface of valve cylinder  37 . The outer radial surface of HME filter  15  fits snugly against the inner cylindrical surface of patient-side housing  500 . Therefore, when the butterfly valve is closed so that vanes  74  block the inner cylindrical passage through valve cylinder  37 , air from ventilator  101  passes through an annular gap  55  and through HME filter  15  before then passing through patient-side port passage  25 A and through a suitable ventilator hose to endotracheal tube  107  ( FIG. 2 ). However, if actuation knob  230  is rotated 90 degrees from its closed position so that vanes  74  are parallel to the longitudinal axis of valve cylinder  37 , then air from ventilator  101  containing aerosol medication injected from MDI canister  105  into the airstream by means of MDI injection port  103 , passes freely through the unrestricted valve cylinder  37  and from there into the intubated patient, without loss of any medication particles that would otherwise be removed by HME filter  15 . 
     The structure of the valve assembly including vanes  74  and valve post  78  is shown in  FIG. 10 . A flexible snap-on anchor  78 A is provided at the bottom of valve post  78 , and has an associated slot  78 D provided in the lower end of valve post  78  to allow flexing that allows the bottom end of valve post  73  to be snapped into and retained in a hole  41  in the bottom of valve cylinder  37 . The bottom of female coupling element  77  limits the depth to which vanes  74  can be passed through slot  38  and an upper hole  44  in valve housing  37 . A valve actuator stem  73  extends through O-ring  57  ( FIG. 8 ) and ventilator-side housing  400  with the male coupling element  73 A at its base being press fit into an opening  77 A in female coupling element  77 . O-ring  57  is disposed around actuator stem  73  to provide a rotary seal between stem  73  and the ventilator-side housing  400 , and is housed within knob  230  between the inside surface of a boss on the top of ventilator-side housing  400  and actuator stem  73 . 
     Ramp style detents (not shown) are provided on the outer surface of ventilator-side housing  400  to conveniently index control knob  230  to either its “valve closed” or HME position or its “valve open” or bypass position. Preferably, all of the components of HME/bypass device  200 , with the exception of the HME element  15  and the optional bacterial and viral filter, are composed of suitable plastic, such as clear ABS plastic, acrylic, polycarbonate, or polypropylene. 
     HME/bypass device  200  is easily assembled by first inserting the valve mechanism snap fit element  78 A through hole  44  and semicircular slot  38  in valve housing  37  until the bottom of female coupling element  77  comes into contact with the outside diameter of valve housing  37 . Valve housing  37  is then inserted between the inside edges of the six radial vanes  54  and pressed into position as shown in  FIGS. 8 and 9 . Actuator stem  73  is subsequently fed through the inside diameter of O-ring  57  and hole  47  in ventilator-side housing  400  with male coupling element  73 A being press fit into female coupling element  77 . HME element  15  is then placed between the outside surface of valve housing  37  and the inside surface of ventilator-side housing  400 , as shown in  FIG. 8 . Finally, ventilator-side housing  400  is press fit into patient-side housing  500 , completing the assembly. 
     As is the case for the HME/bypass device  20  of  FIGS. 1-6 , an optional bacterial and viral filter  48  can be provided within HME/bypass device  200 , and a gas sampling port  42  and/or a drainage port  43  as shown in  FIG. 3  also can be provided for HME/bypass device  200 . 
     The described HME/bypass devices have far smaller “dead space” than the bypass tube  8  of the prior art CIRCUVENT device  4  shown in  FIG. 1 . The described HME/bypass devices, especially HME/bypass device  200 , are much smaller, lighter, less expensive, and easier to use than the combination of the prior art CIRCUVENT device with an HME device or HME device connected thereto. The cost of manufacture of HME/bypass device  200  is expected to be only slightly higher than the cost of prior HME devices alone, and much lower than the total cost of the prior art CIRCUVENT device in combination with a conventional HME device connected therein as shown in  FIG. 1 . 
     While the invention has been described with reference to several particular embodiments thereof, those skilled in the art will be able to make the various modifications to the described embodiments of the invention without departing from the true spirit and scope of the invention. It is intended that all elements or steps which are insubstantially different or perform substantially the same function in substantially the same way to achieve the same result as what is claimed are within the scope of the invention.