Patent Publication Number: US-11642489-B2

Title: Humidifier with a water tub within a pressurized chamber

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 17/707,586, filed Mar. 29, 2022, now allowed, which is a continuation of U.S. application Ser. No. 17/321,616, filed May 17, 2021, now U.S. Pat. No. 11,318,271, which is a continuation of U.S. application Ser. No. 16/223,313, filed Dec. 18, 2018, now U.S. Pat. No. 11,040,166, which is a continuation of U.S. application Ser. No. 15/856,420 filed Dec. 28, 2017, now U.S. Pat. No. 10,195,389, which is a continuation of U.S. application Ser. No. 15/194,634, filed Jun. 28, 2016, now U.S. Pat. No. 10,279,141, which is a continuation of U.S. application Ser. No. 14/157,639, filed Jan. 17, 2014, now U.S. Pat. No. 9,402,970, which is a continuation of U.S. application Ser. No. 12/737,926, filed Mar. 1, 2011, now U.S. Pat. No. 8,631,789, which is the U.S. National Phase of International Application No. PCT/AU2009/001232 filed on Sep. 17, 2009 and which claims priority to U.S. Applications 61/097,765, filed Sep. 17, 2008 and 61/226,134, filed Jul. 16, 2009, each of which is incorporated herein by reference in its entirety. 
     The entire contents of U.S. application Ser. No. 12/397,850, filed Mar. 4, 2009, are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to systems and method to control the humidity of breathable gases used in all forms of respiratory apparatus ventilation systems including invasive and non-invasive ventilation, Continuous Positive Airway Pressure (CPAP), Bi-Level therapy and treatment for sleep disordered breathing (SDB) conditions such as Obstructive Sleep Apnea (OSA), and for various other respiratory disorders and diseases. 
     BACKGROUND OF THE INVENTION 
     Respiratory apparatuses commonly have the ability to alter the humidity of the breathable gas in order to reduce drying of the patient&#39;s airway and consequent patient discomfort and associated complications. The use of a humidifier placed between the flow generator and the patient mask produces humidified gas that minimizes drying of the nasal mucosa and increases patient airway comfort. In addition in cooler climates, warm air applied generally to the face area in and about the mask is more comfortable than cold air. 
     Many humidifier types are available, although the most convenient form is one that is either integrated with or configured to be coupled to the relevant respiratory apparatus. While passive humidifiers can provide some relief, generally a heated humidifier is required to provide sufficient humidity and temperature to the air so that the patient will be comfortable. Humidifiers typically comprise a water tub having a capacity of several hundred milliliters, a heating element for heating the water in the tub, a control to enable the level of humidification to be varied, a gas inlet to receive gas from the flow generator, and a gas outlet adapted to be connected to a patient conduit that delivers the humidified gas to the patient&#39;s mask. 
     Typically, the heating element is incorporated in a heater plate which sits under, and is in thermal contact with, the water tub. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is a respiratory apparatus that comprises a humidifier for humidifying a flow of breathable gas to be delivered to a patient in which a tub of the humidifier is insulated to reduce the temperature of the water and the power consumed by the apparatus. 
     Another aspect of the invention is a humidifier for a respiratory apparatus that includes a chamber that is pressurizable to reduce the pressure on joints of the humidifier tub to reduce leaks. 
     A further aspect of the invention is a humidifier for a respiratory apparatus that includes a chamber that is pressurizable to reduce tolerances for insertion of a tub with respect to seals on an inlet and an outlet tube of the humidifier chamber. 
     A still further aspect of the invention is a humidifier for a respiratory apparatus that directs air over the surface of a supply of water contained in a tub to humidify a flow of breathable gas regardless of the water level. 
     Another aspect of the invention is a humidifier for a respiratory apparatus that includes seals that are not under the supply of water, thus reducing a risk of leakage. 
     A still further aspect of the invention is a humidifier for a respiratory apparatus that prevents water from spilling back into a flow generator, or blower, that generates a flow of breathable gas. 
     Yet another aspect of the invention is a humidifier for a respiratory apparatus that includes a tub that is disposable. 
     Another aspect of the invention is a humidifier for a respiratory apparatus that includes a tub that is cleanable and/or reusable. 
     Still another aspect of the invention is a humidifier for a respiratory apparatus that includes a tub that comprises a water level indicator, for example a water level indicator that indicates a maximum fill level. Yet another aspect of the invention relates to a water level indicator that may be heat from the tub. A still further aspect of the invention relates to a water level indicator in a tub that may be viewed through a window of the humidifier. An even further aspect of the invention relates to a water level indicator that appears to change color as the water level changes, for example appears to be a darker color or mixture of colors. 
     Another aspect of the invention is a humidifier for a respiratory apparatus that is connectable to a heated or non-heated tube for delivery of the humidified flow to a patient. 
     A further aspect of the invention relates to a tub that is removable from the humidifier and is configured to prevent any water flowing out of the tub from flowing back into the flow generator. 
     According to a sample embodiment, a humidifier for humidifying a flow of breathable gas to be delivered to a patient comprises a chamber configured to receive the flow of breathable gas; a tub configured to contain a supply of water, the tub being configured to be inserted into the chamber; a lid provided on the chamber and being movable between an open position and a closed position; and a seal provided on the lid, the seal being configured to seal the chamber such that the flow of breathable gas pressurizes the chamber. 
     According to yet another sample embodiment, a tub for insertion into a humidifier chamber comprises a tub base configured to contain a supply of water; a tub lid; a flow plate; and a seal connected to the flow plate, wherein the flow plate is positioned between the tub base and the tub lid via the engagement of the seal with side wall edges of the tub base and side wall edges of the tub lid. 
     According to a further sample embodiment, a respiratory apparatus for providing a humidified flow of breathable gas to a patient comprises a flow generator to generate a flow of breathable gas and a humidifier and/or a tub as described above. 
     According to another sample embodiment, a humidifier for humidifying a flow of breathable gas to be delivered to a patient comprises a chamber configured to receive the flow of breathable gas; a tub configured to contain a supply of water, the tub being configured to be inserted into the chamber; and a lid provided on the chamber and being movable between an open position and a closed position. The tub comprises a tub base configured to contain a supply of water; a tub lid; and a flow plate provided between the tub base and the tub lid, wherein the flow plate comprises a water level indicator configured to indicate a level of the supply of water in the tub base. 
     According to a still further sample embodiment, a tub is configured to contain a supply of water and to be inserted into a chamber of a humidifier. The tub comprises a tub base configured to contain a supply of water; a tub lid; and a flow plate provided between the tub base and the tub lid, wherein the flow plate comprises a water level indicator configured to indicate a level of the supply of water in the tub base. The water level indicator comprises a generally rectangular portion and a generally triangular portion. The generally triangular portion comprises an angled wall that extends at least partially below the flow plate and the angled wall comprises a drain hole and indicia. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG.  1    schematically depicts of a respiratory apparatus including a flow generator and humidifier according to a sample embodiment of the invention; 
         FIG.  2    schematically depicts the humidifier of  FIG.  1    with the lid in the closed position; 
         FIG.  3    schematically depicts the humidifier of  FIG.  1    with the lid in the open position; 
         FIG.  4    schematically depicts a partial exploded assembly view of the humidifier of  FIG.  1   ; 
         FIG.  5    schematically depicts a cradle of the humidifier of  FIG.  4   ; 
         FIG.  6    schematically depicts a lid closure member of the humidifier; 
         FIG.  7    schematically depicts an electrical connector and tube connector of the humidifier of  FIG.  1   ; 
         FIG.  8    schematically depicts the cradle and humidifier bottom of the humidifier of  FIG.  1   ; 
         FIG.  9    schematically depicts the humidifier cradle and the humidifier bottom of  FIG.  8    in an assembled configuration; 
         FIG.  10    schematically depicts an inner plate of the humidifier of  FIG.  1   ; 
         FIG.  11    schematically depicts a latch plate of the humidifier of  FIG.  1   ; 
         FIG.  12    schematically depicts the humidifier of  FIG.  1    including an outlet tube; 
         FIG.  13    schematically depicts a sealing ring for the humidifier outlet tube of  FIG.  12   ; 
         FIG.  14    schematically depicts the outlet tube of the humidifier of  FIG.  12   ; 
         FIG.  15    schematically depicts the humidifier of  FIG.  1    including the inner plate, the outlet tube, and the tube connector; 
         FIG.  16    schematically depicts the lid and the seal of the humidifier of  FIG.  1   ; 
         FIG.  17    schematically depicts the seal of  FIG.  16   ; 
         FIG.  18    schematically depicts a side view cross section of the humidifier of  FIG.  1   ; 
         FIG.  19    schematically depicts a water tub including a tub base and a flow plate of the humidifier of  FIG.  1   ; 
         FIG.  20    schematically depicts a bottom perspective view of the flow plate of  FIG.  19   ; 
         FIG.  21    schematically depicts an exploded assembly of a tub, including the tub base and flow plate of  FIG.  19   , according to one sample embodiment; 
         FIG.  22    schematically depicts the assembled tub of  FIG.  21   ; 
         FIG.  23    schematically depicts a cross section of the tub of  FIG.  22   ; 
         FIG.  24    schematically depicts a section view of the tub of  FIG.  22   ; 
         FIG.  25    schematically depicts a seal between the flow plate and the tub base of the tub of  FIG.  21   ; 
         FIG.  26    schematically depicts a tub according to another sample embodiment; 
         FIG.  27    schematically depicts an exploded assembly view of the tub of  FIG.  26   ; 
         FIG.  28    schematically depicts a plan view of the tub of  FIGS.  26  and  27   ; 
         FIG.  29    schematically depicts a cross section along line  29 - 29 ; 
         FIG.  30    schematically depicts a cross section along line  30 - 30 ; 
         FIG.  31    schematically depicts a bottom perspective of the flow plate and the tub lid in an assembled condition; 
         FIG.  32    schematically depicts a cross section of the flow plate and the tub lid of  FIG.  31   ; 
         FIG.  33    schematically depicts a detailed view of the connection of the flow plate to the tub lid; 
         FIG.  34    schematically depicts a cross section of the tub in the assembled condition, including the tub base; 
         FIG.  35    schematically depicts a connection of the tub base, the flow plate, and the tub lid; 
         FIG.  36    schematically depicts a perspective of the tub in the assembled condition; 
         FIG.  37    schematically depicts a top perspective of the flow plate; 
         FIG.  38    schematically depicts a bottom perspective of the flow plate; 
         FIG.  39    schematically depicts a plan view of the flow plate; 
         FIG.  40    schematically depicts a cross section along line  40 - 40 ; 
         FIG.  41    schematically depicts a bottom view of the flow plate; 
         FIG.  42    schematically depicts an assembly of the flow plate and seal; 
         FIG.  43    schematically depicts a plan view of the flow plate; 
         FIG.  44    schematically depicts a cross section along line  44 - 44 ; 
         FIG.  45    schematically depicts a bottom view of the flow plate; 
         FIG.  46    schematically depicts the maximum water level indicator of the flow plate; 
         FIG.  47    schematically depicts a cross section of the maximum water level indicator on the flow plate; 
         FIG.  48    schematically depicts a detailed view of a wedge of the bridge of the flow plate; 
         FIG.  49    schematically depicts a detailed view of the maximum water level indicator; 
         FIG.  50    schematically depicts a perspective view of a tub according to another sample embodiment; 
         FIG.  51    schematically depicts another perspective view of the tub of  FIG.  50   ; 
         FIG.  52    schematically depicts a top view of the tub of  FIG.  50   ; 
         FIG.  53    schematically depicts an exploded assembly of the tub of  FIG.  50   ; 
         FIG.  54    schematically depicts an exploded assembly of the tub of  FIG.  50    from another perspective; 
         FIGS.  55   a  and  55   b    schematically depict cross sections of the tub of  FIG.  50   ; 
         FIG.  56    schematically depicts a perspective view of a flow plate of the tub of  FIG.  50   ; 
         FIG.  57    schematically depicts another perspective view of the flow plate of  FIG.  56   ; 
         FIG.  58    schematically depicts a top view of the flow plate of  FIGS.  56  and  57   ; 
         FIG.  59    schematically depicts a bottom view of the flow plate of  FIGS.  56 - 58   ; 
         FIGS.  60   a - 60   c    schematically depict a water level indicator usable with the flow plate of  FIGS.  56 - 59   ; 
         FIG.  61    schematically depicts a perspective view of the flow plate and water level indicator of  FIGS.  56 - 60     c  with the tub lid of the tub of  FIGS.  50 - 55   ; 
         FIG.  62    schematically depicts another perspective view of the flow plate, water level indicator and tub lid of  FIG.  61   ; 
         FIG.  63    schematically depicts an exploded assembly of a tub, including the tub base and flow plate of  FIG.  19   , according to another sample embodiment; 
         FIG.  64    schematically depicts the assembled tub of  FIG.  63   ; 
         FIG.  65    schematically depicts a cross section of the tub of  FIG.  64   ; 
         FIG.  66    schematically depicts a section view of the tub of  FIG.  64   ; 
         FIG.  67    schematically depicts a seal between the flow plate and the tub base of the tub of  FIG.  63   ; 
         FIG.  68    schematically depicts an exploded assembly of a tub according to another sample embodiment; 
         FIG.  69    schematically depicts an exploded assembly of the tub of  FIG.  68    from another perspective; 
         FIG.  70    schematically depicts a perspective view of the tub of  FIGS.  68  and  69   ; 
         FIG.  71    schematically depicts another perspective view of the tub of  FIGS.  68  and  69   ; 
         FIG.  72    schematically depicts a section of the tub of  FIGS.  68 - 71   ; 
         FIG.  73    schematically depicts a heated air delivery hose, tube, or conduit, including a cuff having a humidifier connector; 
         FIGS.  74  and  75    schematically depict the air delivery hose, tube, or conduit of  FIG.  73    including a cuff to connect the hose, tube, or conduit to a patient interface, such as a mask; and 
         FIG.  76    schematically depicts a cross section of the hose, tube, or conduit and cuff of the  FIGS.  56  and  57   . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS 
     Respiratory Apparatus 
     Referring to  FIG.  1   , a respiratory apparatus  10  comprises a flow generator, or blower,  12  and a humidifier  14 . The humidifier  14  comprises a humidifier chamber  16  and a lid  18  which is pivotable between an open and a closed position. A water chamber, or tub,  20  is provided in the humidifier chamber  16  and is covered by the lid  18  when the lid  18  is in the closed position. A seal  19  is provided to the lid  18 , as shown in more detail in  FIG.  15   . The lid  18  includes a window  30  to allow visual inspection of the contents of the humidifier tub  20 . The seal  19  includes an aperture  31  that corresponds to the position of the window  30  of the lid  18 . 
     The tub  20  comprises a tub lid  86  that is configured to direct a flow of breathable gas generated by the flow generator  12  along a channel  90  and through an outlet  92  of the channel  90  into the tub  20 , as described in more detail below. The tub  20  includes an outlet  88  for the humidified flow of breathable gas to a tube configured to deliver the humidified flow to a patient interface, e.g. a mask. 
     Humidifier 
     As shown in  FIG.  2   , the humidifier  14  is connectable to the flow generator  12  by connectors, or latches,  24 . The latches  24  may be, for example, spring biased latches that engage corresponding recesses (not shown) in the flow generator  12 . An electrical connector  26  is provided to electrically connect the flow generator  12  to the humidifier  14 . Electrical power may be provided from the flow generator  12  to the humidifier  14 , although it should be appreciated that the humidifier may be provided with its own power source. Control signals may also be provided from the flow generator  12  to the humidifier  14  through the electrical connector  26 . 
     It should be appreciated that the humidifier  14  may include its own control system, for example, a microprocessor provided on a printed circuit board (PCB). The PCB may be located in the wall of the humidifier chamber  16  and may include a light, e.g. an LED, to illuminate the contents of the tub  20  to permit visual inspection of the water level. Referring to  FIG.  4   , an aperture  35  may be provided in the wall of the humidifier chamber  16  to allow the light on the PCB to illuminate the humidifier chamber  16 . The aperture  35  is covered with a cover  37  to prevent access to the PCB and the light (e.g. LED) from the humidifier chamber  16 . The cover  37  may be transparent or colored to provide a colored light, such as a green light to appear within the humidifier chamber  16 . The light is provided to shine into the humidifier chamber  16  to allow the water level in the water tub  20  to be seen. Alternatively, multiple lights may be located on the PCB to provide different indications regarding the heating of the humidifier, for example an amber light may be provided to indicate that the humidifier is heating up to a required temperature and a blue light may be provided to identify when the humidifier is at the required temperature. 
     The humidifier  14  comprises the humidifier chamber  16  and the lid  18  which is pivotally connected to the humidifier chamber  16 . As shown in  FIGS.  3  and  4   , the lid  18  comprises a hinge portion  17  that is hinged to hinge portions  47  provided on the humidifier chamber  16 . Referring to  FIG.  3   , a humidifier bottom  54  is provided to the humidifier chamber  16 , as shown in more detail in  FIG.  8   . An opening member  28  is provided for releasing the lid  18  to allow the lid to be pivoted to the open position as described in more detail below. 
     Referring again to  FIGS.  3  and  4   , the lid  18  comprises catches  15  that are configured to be engaged by the latches  44  to maintain the lid in the closed position. The seal  19  also comprises wedge-shaped protrusions  13  that are configured to engage the water tub  20 , for example the tub lid  86 , when the lid  18  is in the closed position to push the tub  20  in a direction (e.g. laterally) toward an outlet  34  of the humidifier chamber  16  to assist in forming a seal between the water tub outlet  88  and the humidifier chamber outlet  34 . A domed portion  11  is also provided on the seal  19  to push the water tub  20  against a heating plate  36  when the lid  18  is in the closed position. A circular seal section, or sealing ring,  21  is also provided to the seal  19  to seal, when the lid  18  is in the closed position, a tub emptying aperture  89  provided in the tub lid  86 . 
     Referring again to  FIGS.  2  and  4   , the humidifier chamber  16  also includes an air inlet  22  configured to receive the flow of breathable gas generated by the flow generator  12  when the humidifier  14  is connected to the flow generator  12  by the latches  24 . The inlet  22  directs the flow into the channel  90  (see  FIGS.  1 ,  3  and  21 - 24   ) in the tub lid  86  of the water tub  20 . The flow is directed by the channel  90  to the outlet  92  into the water tub  20 . 
     As shown in  FIGS.  4  and  5   , the humidifier chamber  16  comprises a humidifier cradle  32  that includes the air inlet  22 . The humidifier cradle  32  also includes the humidifier chamber outlet  34  to allow the humidified flow to be delivered to a delivery hose, tube, or conduit that is configured to be connected to the humidifier to deliver the humidified flow to a patient. The outlet  34  is provided in a back side of the humidifier cradle  32 . It should be appreciated that the outlet  34  may be provided on a side of the humidifier cradle  32 . Such a modification would also entail modifying the water tub  20  to align the outlet  88  of the tub  20  with the outlet  34  of the humidifier cradle  32 . 
     Referring to  FIG.  4   , the heating plate  36  is provided to heat the water supply contained in the humidifier chamber  16 . A cradle bottom  40  is provided beneath the heating plate  36  and an insulation layer  38  is provided between the heating plate  36  and the cradle bottom  40 . The heating plate  36  may be formed, for example, of a nickel chrome alloy or anodized aluminum that allows the heating plate  36  to be formed thinner than currently available heating plates and with a larger surface area. The heating plate  36  may also include a thermistor that is controlled by a control circuit, for example, provided on the PCB. 
     Referring to  FIGS.  4 - 6   , the humidifier cradle  32  supports a lid closure member  42  that is movable between an open position and a closed position. The lid opening member  28  is provided at an end of the lid closure member  42  as shown in  FIG.  6   . The lid closure member  42  comprises latches  44  that are configured to engage catches  15  of the lid  18  and retain the lid  18  in the closed position. The lid closure member  42  comprises a rod, or post,  48  that supports a spring  46  that biases the lid closure member  42  into the closed position. To open the lid  18 , the opening member  28  is pushed by the user against the bias of the spring  46 , to the right in  FIG.  5   , to move the latches  44 , and the lid closure member  42 , to the open position. When the user releases the lid opening member  28 , the bias of the spring  46  returns the lid closure member  42  and the latches  44  to the closed position. 
     The lid closure member  42  is supported by a front retaining wall  33  of the cradle  32 . The lid closure member  42  includes tabs  45  that engage slots  41  formed in the front retaining wall  33 . The front retaining wall  33  also comprises slots  39  through which the latches  44  protrude. The slots  39 ,  41  accommodate sliding movement of the lid closure member  42  and the latches  44  and the tabs  45 , respectively, engaged with the slots  39 ,  41 . 
     As shown in  FIG.  7   , the electrical connector  26  is connected to a plurality of wires  52 , for example, three wires, that are connected to a tube connector  50  that is shown in  FIG.  15    and described in more detail hereinafter. The tube connector  50  comprises a plurality of contacts  78  that correspond in number to a number of wires  52  and are each connected to a respective wire. Although three wires  52  and three contacts  78  are shown in the drawings, it should be appreciated that a different number of wires and contacts may be provided, for example, two wires and two contacts. The tube connector  50  allows for the connection of a heated tube, for example, such as disclosed in U.S. patent application Ser. No. 11/936,822, filed Nov. 8, 2007, the entire contents of which are incorporated herein by reference. 
     As shown in  FIGS.  8  and  9   , the humidifier cradle  32  is supported by a chamber bottom  54  of the humidifier chamber  16 . The chamber bottom  54  comprises a pair of latches  56  that are configured to engage corresponding catches (not shown) on the back of the humidifier cradle  32  to secure the humidifier cradle  32  to the chamber bottom  54 . The chamber bottom  54  also includes a bottom opening  58  through which the bottom of the humidifier cradle  32  extends. The chamber bottom  54  is configured to cover the wires  52  and the lid closure member  42  when connected to the cradle  32 , as shown in  FIG.  8   . 
     Referring to  FIGS.  9 - 11   , an inner plate  60  may be secured to the humidifier cradle  32  over the latches  24  and the electrical connection  26 . As shown in  FIG.  10    the inner plate  60  includes a plurality of apertures  62  that are configured to allow the latches  24  to extend therethrough and an aperture  64  configured to allow the electrical connector  26  to extend therethrough. The inner plate  60  also comprises a pair of apertures  66  that are configured to receive fasteners, for example, threaded fasteners  80  ( FIG.  15   ), to secure the inner plate  60  to the humidifier cradle  32 . A boss  68  may also be provided on the inner plate  60  to receive a fastener, for example, a threaded fastener  80  for securing the inner plate  60  to the humidifier cradle  32 . The inner plate  60  provides spillback protection to prevent water spilling back from the humidifier  14  to the flow generator  12 . 
     As shown in  FIG.  11   , the latches  24  are provided on a latch plate  23  that is provided between the humidifier cradle  32  and the inner plate  60 . An end of the latch plate  23  is secured to a plate  25  that is also provided between the humidifier cradle  32  and the inner plate  60 . The plate  25  comprises posts  29  that support springs  27  that are configured to bias the latch plate  23  so that the latches  24  extend through the apertures  62  of the inner plate  60  in the positions shown in  FIG.  9   . When the humidifier  14  is connected to the flow generator  12  the latches  24  engage catches (not shown) provided on the flow generator  12  and the latches  24 , and subsequently the latch plate  23 , are pushed against the bias of the springs  27  (to the right in  FIG.  9   ). Once the latches  24  fully engage the catches, the springs  27  bias the latch plate  23  and the catches  24  back to their starting position shown in  FIG.  9    with the latches  24  engaged with the catches of the flow generator  12 . When the humidifier  14  is connected to the flow generator  12 , the electrical connector  26  connects with a corresponding electrical connector (not shown) in the flow generator  12  to permit the flow generator  12  to provide power and/or control signals to the humidifier  14 . As shown in the figures, the electrical connector  26  may comprise a terminal, or terminals, although it should be appreciated that the electrical connector  26  may comprise a contact, or contacts, that are received in terminals in the flow generator  12 . 
     Referring to  FIGS.  12 - 14   , the humidifier cradle  32  may comprise an outlet tube  70  provided through the outlet  34 . As shown in  FIG.  14   , the outlet tube  70  may comprise a flange  72  that is configured to engage the back wall  55  of the humidifier cradle  32  and a groove  74  that is configured to receive a sealing ring  76  shown in  FIG.  13   . The outlet tube  70  may be removed to allow replacement of all wet area parts of the humidifier, for example, the tub  20  and the outlet tube  70 . The outlet tube  70  may also be made out of a material that can be sterilized. It should be appreciated that the outlet tube  70  may also be disposable. 
     Referring to  FIGS.  15  and  16   , in the closed position the lid  18  provided with the seal  19  allows the humidifier chamber  16  to be sealed and become pressurized by the flow generator  12  when the flow generator generates a flow of air through the inlet  22  of the humidifier  14 . Pressurizing the humidifier chamber  16  reduces the pressure on the joints on the tub  20  to reduce leaks. Pressurizing the humidifier chamber  16  also reduces tolerances for insertion of the tub  20  with respect to seals on the inlet  22  and the outlet tube  70  of the humidifier chamber  16 . The humidifier chamber  16  also insulates the tub  20  to provide enhanced thermal properties and reduce power consumption. Insulating the tub  20  also reduces heat loss to the surroundings. The humidity output of the humidifier is determined directly from the water temperature. As the heat loss from the tub to the surroundings is reduced due to insulating the tub, less power is needed to reach the water temperature corresponding to a desired humidity output. In addition, incoming air is preheated as it passes the outside walls of the tub, before it enters the tub, which also reduces the power required to reach the water temperature corresponding to the desired humidity output. 
     As also shown in  FIG.  15   , the inner plate  60  is secured to the humidifier cradle  32  by the threaded fasteners  80 , although it should be appreciated that other fastening members or methods may be used to secure the inner plate  60  to the humidifier cradle  32 . It should be appreciated that other latching structures and systems may be used to releasably secure the lid. For example, push to close and button to open operation systems may be used. Other examples include, but are not limited to, a rod latching system, a rotating latch or a hooking latch. 
     The outlet tube  70  and the tube connector  50  provide the ability to connect both a standard tube and a heated tube. As shown in  FIG.  15   , the tube connector  50  and the contacts  78  are provided separately from the outlet tube  70 . A heated tube having corresponding electrical connections, e.g. terminals, may be provided in a rotational snap fit with the tube connection  50 . This type of connection provides ease of connection and reduces the tolerance stack of the respiratory apparatus  10 . A heated tube  134  suitable for connection to and use with the humidifier  14  is described in more detail with reference to  FIG.  31   . As shown in  FIG.  15   , a cover  132  may be connected to the back wall of the humidifier to cover the tube connector  50 , and the contacts  78 , when a non-heated tube is connected to the outlet tube  70 . The cover  132  may be formed of a pliable rubber or other suitable flexible material. Alternatively the cover  132  may be a separate component not attached to the humidifier that may be inserted over the connector  50 . 
     Referring to  FIGS.  17  and  18   , the seal  19  comprises a groove  51  configured to receive a corresponding edge, or rim,  57  of the lid  18  to connect the seal  19  to the lid  18 . The wedge-shaped protrusions  13  (see also  FIG.  3   ) are configured to engage the tub lid  86  when the lid  18  is in the closed position to bias the water tub  20  toward the back wall of the humidifier chamber  16  so that the outlet  88  is in sealing engagement with the outlet tube  70 . The seal  19  also comprises a sealing rim  49  that extends around the perimeter of the seal  19  and is configured to seal the perimeter of the lid  18  when the lid is in the closed position. An inner sealing rim  53  is provided around the aperture  31  of the seal  19  to seal around the window  30  of the lid  18 . 
     Humidifier Tub—Disposable— First Embodiment 
     Referring to  FIGS.  19  and  20   , the water tub  20  comprises a tub base  82  and a flow plate  84 . The flow plate  84  comprises a dividing plate  96  that comprises an inlet  98  that is configured to receive the flow of breathable gas directed by the channel  90  of the tub lid  86 . The outlet  92  of the channel  90  is configured to direct the flow into the inlet  98  of the dividing plate  96  when the tub lid  86  is secured to the tub base  82  as described in more detail below. 
     The flow plate  84  also comprises a frame or tub seal  94  that is configured to seal the perimeter of the tub base  82  when the tub lid  86  is connected to the tub base  82 . The frame seal  94  is connected to the dividing plate  96  by a plurality of supports, or bridges,  100 . A gap  87  is provided between the dividing plate  96  and the frame seal  94  by the bridges  100 . 
     A water level indicator  102  is provided on the dividing plate  96  of the flow plate  84  to provide an indication of the water level. As shown in  FIGS.  18 - 20   , the water level indicator  102  may include a frusto-conical portion. As shown in  FIG.  23   , the water level indicator  102  may be cone shaped. A small drain hole  104  is located in the bottom of the water level indicator  102  to allow the water to fill up the water level indicator  102  and then drain out of the bottom of the water level indicator  102  to the tub base  82  as the water level decreases in the tub base  82 . The water level indicator  102  provides an indication of the water level in the tub  20  by the water level indicator  102  being filled with water once the water level in the tub base  82  reaches the level of the small drain hole  102 , which then allows the water level in the tub base  82  to be filled until the water in the water level indicator  102  reaches the desired level such as that indicated by indicia  103 . Although the water level indicator  102  provides an indication of the water level, as the flow of breathable gas is directed to the surface of the water contained in the tub base  82 , the water level is not critical as the flow is in good contact with the surface of the water. The water level indicator  102  may be provided with indicia  103  to indicate a maximum water level of the water tub  20 . The light emitted from the PCB through the aperture  35  allows the water level in the water level indicator  102  to be seen. 
     Referring to  FIGS.  21 - 25   , according to a sample embodiment of the invention, the water tub  20  is configured to be disposable. The tub  20  comprises the tub base  82  configured to contain a supply of water. The tub lid  86  is provided on the tub base  82 . The tub lid  86  may be secured to the tub base  82  by, for example, welding. The tub  20  may be formed, for example, of plastic material, metal or a combination of metal and plastic. 
     As shown in  FIGS.  23  and  24   , the flow plate  84  is provided on the tub base  82 . The tub lid  86  comprises the channel  90  that receives the flow of breathable gas generated by the flow generator  12  that enters the humidifier  14  through the air inlet  22 . As shown in  FIG.  23   , the channel  90  comprises the channel outlet  92  that is received in the inlet  98  in the dividing plate  96 . The dividing plate  96  ensures that the flow of breathable gas flows across the whole tub as air enters into the center and flows to the outside of the tub and then up through the gap  87  between the walls of the tub base  82  and the dividing plate  96  to the outlet  88  of the tub lid  86 . 
     Referring to  FIG.  25   , the tub base  82  comprises a tub base rim  118  that is engaged by a latch  130  of the tub lid  86  to connect the tub base  82  and the tub lid  86 . The frame seal  94  comprises a seal  112  that is provided between the latch  130  of the tub lid  86  and the rim  118  at the tub base  82 . A wedge  114  is provided on each bridge  100  and connected to the seal  112  to force the seal  112  into a sealing engagement between the rim  118  and a latch  130 . The wedge  114  is engaged by a wedge  116  of the tub lid  86  to force the seal  112  into sealing engagement between the rim  118  and the latch  130 . 
     Humidifier Tub—Disposable—Second Embodiment 
     Referring to  FIGS.  26 - 49   , a humidifier tub that is configured to be disposable according to another sample embodiment is illustrated. The humidifier tub  20  may comprise a tub base  82 , a tub lid  86  having a channel  90 . The tub lid  86  may also comprise a tub outlet  80  for delivering a humidified flow of breathable gas. A tub emptying aperture  89  may also be provided in the tub lid  86 . 
     Referring to  FIG.  27   , the humidifier tub  20  may also comprise a flow plate  84  having a dividing plate  96 . An inlet  98  is provided on the dividing plate  96  that corresponds to the outlet  92  ( FIG.  28   ) of the channel  90  of the tub lid  86 . The dividing plate  96  of the flow plate  84  is connected to a frame seal  94  by a plurality of bridges  100 . A gap  87  is provided between the frame seal  94  and the dividing plate  96 . 
     Referring to  FIGS.  27 ,  29 ,  30 - 32 ,  37 - 41 , and  43 - 49   , the humidifier tub  20  may also include a water level indicator  102 . The water level indicator  102  may be provided on the dividing plate  96  of the flow plate  84 . As shown, for example, in  FIG.  39   , the water level indicator  102  may have a generally polygonal perimeter, including a generally rectangular portion  175  and a generally triangular portion  177 . It should be appreciated, however, that other perimeter shapes may be provided for the water level indicator  102 , including regular polygonal shapes (e.g. square, rectangular, pentagonal), or polygonal shapes that are combinations of regular polygonal shapes, or polygonal shapes combined with curvilinear surfaces. 
     As shown in  FIGS.  31 ,  37 ,  39 ,  41 ,  43 ,  45 ,  46  and  49   , the water level indicator  102  comprises a drain hole  104  to allow the water to drain out of the bottom of the water level indicator  102  to the tub base  82 . As shown, for example, in  FIG.  49   , the drain hole  104  is not provided at the bottom of the water level indicator  2 , but is located at an intermediate position between the bottom and the top of the water level indicator  102  to allow any pooled water to drain away from the intermediate position. In this embodiment the water level indicator  102  is not filled with water but the water level is indicated against the sloping surface of the water level indicator as described in more detail below. As shown in  FIG.  37   , the drain hole  104  is located at a position generally corresponding to the plane of the dividing plate  96  of the flow plate  84 . As also shown in  FIG.  37   , and  FIGS.  31 ,  38 ,  39 ,  41 ,  43 ,  45  and  46   , the water level indicator  102  may include indicia  103  that indicates a maximum fill level of the humidifier tub  20 . As shown in the figures, the indicia  103  may be provided at the same level of the water level indicator  102  as the drain hole  104 . 
     Referring to  FIG.  49   , the generally triangular portion of the water level indicator  102  extends below the frame seal  94  into the tub base  82  when the tub is in the assembled condition and includes a first angled wall  109  and a second angled wall  111 . As the water level of the tub base  82  increases during fill up, the water level will initially contact the bottom of the water level indicator  102 . As the water level continues to increase, the second angled wall  111  directs the water level toward the drain hole  104  and the indicia  103  which are provided in the angled wall  111  between the frame seal  94  and the dividing plate  96  of the flow plate. As the water level continues to increase and approaches the drain hole  104 , the visibility of the water level relative to the indicia  103  increases. As the indicia  103  is provided at the same level as the drain hole  104 , the maximum fill level of the tub  20  is detected when the water level reaches the level of the drain hole  104  and the indicia  103 . 
     Referring to  FIGS.  33 ,  35 ,  42  and  48   , the seal  112  may be provided on the periphery of the wedge  114  of the bridge  100 . The wedge  116  of the tub lid  86  is configured to engage the wedge  114  of the dividing plate  96  of the flow plate  84  to force the seal  112  between the rim  118  of the tub base  82  and the latch  130  of the tub lid  86 . As shown in  FIG.  48   , the wedge  114  may comprise a flange  105  around its perimeter that includes a slot  107  that is configured to receive a portion of the seal  112 , as shown, for example, in  FIG.  33   . 
     Humidifier Tub—Disposable—Third Embodiment 
     Referring to  FIGS.  50 - 62   , a humidifier water tub  20  is configured to be disposable according to still another sample embodiment as illustrated. The humidifier tub  20  comprises a tub base  82  and a tub lid  86 . The tub lid  86  includes an oval opening  300  and a sump region  340  that surrounds the outlet  92  of the channel  90  that is formed in the tub lid  86  to direct the flow of air from the flow generator to the water contained in the tub  20 . The sump region  340  facilitates filling the tub  20  by providing a larger area for entry of water than the outlet  92  of the flow channel  90 . 
     The tub lid  86  also comprises a cover portion  301  that covers the section of the flow channel  90  from the flow generator  12  to the inlet  98  of the tub  20  that is angled down towards the flow generator  12 . The cover portion  301  prevents any water from flowing back into the flow generator  12  if the tub  20  was filled with water while still connected to the flow generator  12  as water may only be poured into the tub in the region provided by the opening  300  which is designed to channel the water down towards the outlet  92 . 
     As shown in  FIGS.  53 - 62   , a water level indicator  320  may be provided to the humidifier tub  20  that is visible through the window  30  of the lid  18 . The water level indicator  320  may comprise a base portion  307  and an angled portion  303  extending from the base portion  307 . The angled portion  303  may include markings  304  to indicate various water levels. The angled portion  303  may also include indicia  311  to indicate a maximum water fill level. 
     The water level indicator  320  may be removably connected to the dividing plate  96  of the flow plate  84  by posts  305 . The posts  305  may be inserted into apertures  309  in the dividing plate  96  of the flow plate  84 . As shown in  FIGS.  60   a - 60   c   , the posts  305  may include latches  313  that are resiliently moveable with respect to the remaining portions of the posts  305 . The latches  313  may be provided at the ends of leg portions  315  which are attached to the base  307  of the water level indicator  320 . The leg portions  315  may be connected by a cross member  317 , as shown in  FIGS.  59 ,  60     b  and  61 . 
     The water level indicator  320 , for example, the angled portion  303 , may be formed of a colored plastic material, for example yellow. The water level indicator  320  may be, for example, translucent. When the tub  20  is filled with water, the water level indicator  320  may appear to change color, for example appearing slightly darker or a greenish-yellowish color as the water level rises. 
     As shown in the figures, the water level indicator  320  may be a rounded D-shape, although it should be appreciated that other shapes may be used. It should also be appreciated that the water level indicator  320  may be attached to the dividing plate  96  of the flow plate  84  by structures other than the post  305  as shown and described in the drawings. For example, the water level indicator  320  may be adhered to the dividing plate  96 , or the water level indicator  320  may be integrally formed, for example molded, with the dividing plate  96  of the flow plate  84 . 
     Humidifier Tub—Reusable and Cleanable—First Embodiment 
     Referring to  FIGS.  63 - 67   , a tub  20  according to another embodiment of the invention is configured to be reusable, and cleanable. The tub base  82  comprises a plurality of clips  106  that are configured to engage and retain the tub lid  86  in connection with the tub base  82 . A clip  108  is also provided and comprises an aperture  110  to accommodate the outlet  88  of the flow plate, as shown in  FIG.  63   . 
     The flow plate  84  is configured to be removable from the tub base  82  and it is not permanently secured to the tub base  82 . As shown in  FIGS.  65  and  67   , the bridges  100  of the flow plate  84  include a wedge  114  that is connected to a seal  112 . The seal  112  is forced into sealing engagement between a rim  120  of the tub lid  86  and the rim  118  of the tub base  82 . The clip  106  is provided to clip the tub lid  86  to the tub base  82  with the seal  112  secured in between in sealing engagement. A first portion  124  of the clip  106  engages the tub base  82  up to the rim  118  and a second portion  126  of the clip  106  is configured to engage a projection  128  of the tub lid  86  to secure the tub lid  86  and the tub base  82  in engagement. 
     The humidifier  14  does not include any seals that are provided under the water supply of the tub base  82 . The lid  18  comprises the seal  19  to allow for pressurizing of the humidifier chamber  16  with the flow provided by the flow generator  12  to reduce the pressure on the tub joints, including the disposable tub and the reusable, cleanable tub, thus reducing leaks. Pressurizing the humidifier chamber also reduces tolerances for insertion of the water tub with respect to seals on the inlet of the humidifier and the outlet tube  70  of the humidifier  14 . The sealing ring  76  provided to the outlet tube  70  is provided on an outer surface of the humidifier cradle  32  and not provided under the water of the supply contained in the tub base  82 . 
     Humidifier Tub—Reusable and Cleanable—Second Embodiment 
     Referring to  FIGS.  68 - 72   , a water tub  20  according to another sample embodiment is configured to be reusable and cleanable. The tub  20  may have a water level indicator  320  similar to the water level indicator described with respect to the previous embodiments. It should be appreciated that the tub  20  may be provided with any of the water level indicators described herein. 
     The tub lid  86  may include the cover portion  301  to cover the inlet region of the flow channel  90  adjacent to the inlet  22  of the humidifier  14  that is connected to the flow generator  12 . 
     As shown in  FIGS.  68 - 72   , the tub lid  86  may be secured to the tub base  82  by a plurality of clips  106 ,  108 . The clip  108  may have an aperture configured to accommodate the outlet  88  of the tub  20 . The tub lid  86  may include projections  128  that are received in apertures  129  in the clips  106 . The tub lid  86  may also include projections  152  that are received in apertures  151  provided in the clip  108 . 
     As also shown in  FIGS.  68 - 72   , the tub lid  86  may include recesses  330  to accommodate the fingers of a user of the tub  20  to provide a space between the tub lid  86  and the clips  106  as the user inserts the tub lid  86  on to the tub base  82  so that the projections  128  are received in the apertures  129 . The recesses  330  may also accommodate the fingers during removal of the lid  86  from the base  82 , for example to allow the parts of the tub  20  to be disassembled and cleaned. 
     It should be appreciated that the reusable and cleanable tubs may include a water level indicator as discussed above with respect to the embodiments of the disposable tub. It should also be appreciated that the reusable and cleanable tubs may include more than one water level indicator as discussed above with respect to the embodiments discussed above. It should further be appreciated that the water level indicator, or indicators, or the tub may not include indicia to include a maximum water level. 
     Heated Tube 
     Referring to  FIG.  73   , a heated tube  134  is connectable to the outlet tube  70  of the humidifier  14 . The heated tube  134  comprises a cuff  136  that includes a humidifier connector  138  that is configured to be connected to the tube connector  50  of the humidifier  14 . The humidifier connector  138  comprises terminals  140  that are configured to receive the contacts  78  of the tube connector  50  when the humidifier connector  138  and the tube connector  50  are connected. The cuff  136  may be formed as described, for example, in U.S. application Ser. No. 11/936,822, the entire contents of which are incorporated herein by reference. The heated tube may include, for example, two or three wires and may transmit and receive signals to and from a controller in the humidifier and/or the flow generator as described in U.S. application Ser. No. 11/936,822. The end of the humidifier connector  138  that is configured for insertion into the tube connector  50  of  FIG.  15    may include an angle  200  to facilitate insertion of the connector  138  into the tube connector  50 . The angle  200  may be between about 15°-35°. 
     Referring to  FIGS.  74 - 76   , the heated tube  134  may be connected to a patient interface, e.g. a mask, by a cuff  142  provided at the end of the heated tube  134 . An aerofoil fixture  144  is provided in the cuff  142  and includes a thermistor  148 , as shown in  FIG.  75   . The shape of the aerofoil fixture  144  provides a smooth flow around the aerofoil fixture  144  so that the thermistor  148  provides a good reading of the temperature of the flow of breathable gas in the tube  134 . The cuff  142  may be formed by, for example, overmolding on a pre-block  146 , or any method disclosed, for example, in U.S. application Ser. No. 11/936,822. The thermistor  148  is connected to the wires in the heated tube  134  by lead frames  150 . The temperature sensed by the thermistor  148  may be provided as a signal from the thermistor  148  through the lead frames  150  and the wires to a controller located in the humidifier and/or the flow generator. 
     The tube  134  may have a 15 mm internal diameter. The tube  134  may be heated using wires as described in U.S. application Ser. No. 11/936,822. A non-heated 15 mm air delivery tube my also be used. The 15 mm internal diameter tube may be connected to the tube connector  50  and the patient interface using a 22 mm isotaper connection. 
     While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. Furthermore, each individual component of any given assembly, one or more portions of an individual component of any given assembly, and various combinations of components from one or more embodiments may include one or more ornamental design features. In addition, while the invention has particular application to patients who suffer from OSA, it is to be appreciated that patients who suffer from other illnesses (e.g., congestive heart failure, diabetes, morbid obesity, stroke, barriatric surgery, etc.) can derive benefit from the above teachings. Moreover, the above teachings have applicability with patients and non-patients alike in non-medical applications. 
     In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise,” “comprised” and “comprises” where they appear. 
     It will further be understood that any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates.