Abstract:
A continuous positive airway pressure (CPAP) apparatus to supply pressurized breathable gas to a patient includes a flow generator having a gas inlet and a gas outlet, a humidifier having a gas inlet coupled to the gas outlet of the flow generator, and a filter operatively positioned between the gas outlet of the flow generator and the gas inlet of the humidifier.

Description:
This application is a divisional of U.S. application Ser. No. 10/872,402, filed Jun. 22, 2004, pending, which is a divisional of U.S. application Ser. No. 10/387,534, now U.S. Pat. No. 6,772,999, filed Mar. 14, 2003, which is a continuation of U.S. application Ser. No. 09/689,775, now U.S. Pat. No. 6,554,260, filed Oct. 13, 2000, which claims priority to Australian Application No. PQ 3390, filed Oct. 13, 1999, each of which is incorporated herein by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to a humidifier. 
   The invention has been developed primarily for use with a breathable gas supply apparatus in Continuous Positive Airway Pressure (CPAP) treatment of, for example, Obstructive Sleep Apnea (OSA) and other ventilatory assistance treatments such as Non Invasive Positive Pressure Ventilation (NIPPV) and will be described hereinafter with reference to these applications. However, it will be appreciated that the invention is not limited to these particular fields of use and also finds application in, for example, assisted respiration, mechanical ventilation and the like. 
   BACKGROUND OF THE INVENTION 
   CPAP treatment is a common ameliorative treatment for breathing disorders including OSA. CPAP treatment, as described in U.S. Pat. No. 4,944,310, provides pressurised air or other breathable gas to the entrance of a patient&#39;s airways at a pressure elevated above atmospheric pressure, typically in the range 4-20 cm H 2 O. 
   It is also known for the level of treatment pressure to vary during a period of treatment in accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment, as described in U.S. Pat. No. 5,245,995. 
   NIPPV is another form of treatment for breathing disorders which can involve a relatively higher pressure of gas being provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. 
   In other NIPPV modes the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment, as disclosed in the applicant&#39;s international PCT patent application No. PCT/AU97/00631. 
   Typically, the ventilatory assistance for CPAP or NIPPV treatment is delivered to the patient by way of a nasal mask. Alternatively, a mouth mask or full face mask or nasal prongs can be used. In this specification any reference to a mask is to be understood as incorporating a reference to a nasal mask, mouth mask, full face mask or nasal prongs. 
   In this specification any reference to CPAP treatment is to be understood as embracing all of the above described forms of ventilatory treatment or assistance. 
   Breathable gas supply apparatus broadly comprise a flow generator constituted by a continuous source of air or other breathable gas generally in the form of a blower or driven by an electric motor. The electric motor driving the blower is typically controlled by a servo-controller under the control of a micro controller unit. A hospital piped supply can also be used. The gas supply is connected to a conduit or tube, which in turn is connected to a patient mask which incorporates, or has in close proximity, an exhaust to atmosphere for venting exhaled gases. 
   In order to prevent drying of the patient&#39;s airways during use of a breathable gas supply apparatus it is known to pass the gas through a humidifier before supplying the gas to the patient. Humidification is achieved by passing the air over a water surface within a humidifier so that the gas absorbs moisture from the water before being delivered to the patient. The two main types of humidifier are passive, where the water is not heated, and active, where the water is heated. 
   A known passive humidifier is the applicant&#39;s Passover (Trade Mark) humidifier. Other passive humidifiers are disclosed in U.S. Pat. Nos. 5,231,979, 5,537,997 and 5,598,837. 
   A known active humidifier is the applicant&#39;s HumidAire (Trade Mark) which heats the water in the humidifier via a thermostatically controlled electric heating element. The temperature of the water is set manually by the patient. The HumidAire humidifier also has a built in safety feature to prevent the heater element reaching excessive temperatures under fault conditions. 
   European patent application No. EP 0845277 discloses an active humidifier that includes a thermostatically controlled electric heating plate. Active humidifiers are also disclosed in U.S. Pat. Nos. 4,621,632 and 4,203,027. 
   A disadvantage of known active humidifiers is the expense of the heating elements and associated thermostatic temperature control equipment. 
   A disadvantage of known passive humidifiers is an inability to easily vary the amount of humidification of the gas. 
   It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. 
   SUMMARY OF THE INVENTION 
   Accordingly, in a first aspect, the present invention provides a humidifier for use with a breathable gas supply apparatus, said humidifier comprising: 
   a hollow body adapted for partial filling with water up to a predetermined maximum water level; 
   a gas inlet to the body above the maximum water level; 
   a gas outlet from the body above the maximum water level; and 
   a constant temperature heating element for heating the water. 
   In one embodiment, the heating element is disposed within the body. 
   In another embodiment, the heating element is disposed external the body. 
   In a second aspect, the present invention provides a humidifier for use with a breathable gas supply apparatus, said humidifier comprising: 
   a hollow body adapted for partial filling with water to a predetermined maximum water level; 
   a gas inlet to the body above the maximum water level; 
   a gas outlet from the body above the maximum water level; 
   means to heat the water, in the body; and 
   an adjustable flow divider adapted to divide the interior of the body above the maximum water level into a relatively dry gas region and a relatively wet gas region, wherein the position of the divider is variable so as to vary the relative proportion of the gas flowing from the inlet to the outlet that passes through the relatively dry and relatively wet gas regions to thereby vary the amount of humidification thereof. 
   Preferably, the position of the divider is variable between a first position in which all of the gas is diverted to the relatively wet gas region for maximum humidification, and a second position in which all of the gas is diverted to the relatively dry gas region for minimum humidification. 
   The heating means is preferably a constant temperature heating element, such as a self regulating wire. 
   The humidifier desirably also includes a storage reservoir adapted to replenish the water in the body. 
   The divider preferably also includes baffle plates. The position of the baffle plates can be fixed or adjustable. 
   In one embodiment, the divider is a generally planar plate of substantially complimentary cross section to the interior of the body above the maximum water level. The plate preferably includes a threaded hole adapted to engage a threaded rod, wherein rotation of the rod causes the plate to move between the first and second positions. The exterior of the plate preferably forms a substantially fluid-tight seal with the interior of the body. 
   In another embodiment, the divider includes a first end remote the gas inlet and the gas outlet and a second end adjacent the gas inlet and the gas outlet, wherein the divider is adapted to rotate about or near the first end to cause the second end to move between the first and second positions. 
   In a further embodiment, the divider includes a first and second end adjacent the gas inlet and the gas outlet, wherein the divider is adapted to rotate about or near its centre to cause the first and second ends to move between the first and second positions. 
   In a third aspect, the present invention provides a humidifier for use with a breathable gas supply apparatus, said humidifier comprising: 
   a hollow body adapted for partial filling with water to a predetermined maximum water level; 
   a gas inlet to the body above the maximum water level; 
   a gas outlet from the body above the maximum water level; 
   a constant temperature heating element for heating the water; and 
   an adjustable flow divider adapted to divide the interior of the body above the maximum water level into a relatively dry gas region and a relatively wet gas region, wherein the position of the divider is variable so as to vary the relative proportion of the gas flowing from the inlet to the outlet that passes through the relatively dry and relatively wet gas regions to thereby vary the amount of humidification thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings in which: 
       FIG. 1  is an exploded perspective view of a humidifier according to a first embodiment of the invention; 
       FIG. 2  is a front view of a humidifier according to a second embodiment of the invention; 
       FIG. 3  is a top view of the humidifier shown in  FIG. 2 ; 
       FIG. 4  is a side view of the humidifier shown in  FIG. 2 ; 
       FIG. 5  is a partial cross sectional view along line  5 , 6 - 5 , 6  of  FIG. 3  of the humidifier shown in  FIG. 2  with the flow dividing plate in a minimum humidification position; 
       FIG. 6  is a partial cross sectional view along line  5 , 6 - 5 , 6  of  FIG. 3  of the humidifier shown in  FIG. 2  with the flow dividing plate in a maximum humidification position; 
       FIG. 7  is a lower perspective view of the flow divider of the humidifier shown in  FIG. 2 ; 
       FIG. 8  is an upper perspective view of the control knob of the humidifier shown in  FIG. 2 ; 
       FIG. 9  is an upper perspective view of an embodiment of a heating element suitable for use with the humidifier shown in  FIG. 2 ; 
       FIG. 10  is an upper perspective view of another embodiment of a heating element; 
       FIG. 11  is a cross sectional view of a humidifier according to a third embodiment of the invention; 
       FIG. 12  is a partial cross sectional view of a humidifier according to a fourth embodiment of the invention; 
       FIG. 13  is a lower perspective view of an embodiment of a flow dividing plate shown; 
       FIG. 14  is a cross sectional view of an embodiment of a heating element assembly; 
       FIG. 15  is a cross sectional view of a humidifier according to a sixth embodiment of the invention; 
       FIG. 16  is a cross sectional view of a humidifier according to a seventh embodiment of the invention with the flow dividing plate in a maximum humidification position; 
       FIG. 17  is a cross sectional view of the humidifier of  FIG. 15  with the flow dividing plate in a minimum humidification position; and 
       FIG. 18  is a cross sectional view of another embodiment of a heating element assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is an exploded view of a breathable gas supply apparatus  20  which comprises a flow generator  22 , a first embodiment of a humidifier  24  according to the invention, an anti-bacterial filter  26  and a heating element  30 . The filter  26  is operatively positioned between the outlet of the flow generator  22  (not shown) and the inlet  28  of the humidifier  24 . In another embodiment (not shown), the filter is operatively positioned between the outlet of the humidifier and the patient. In the latter, the filter reduces the transfer of bacteria from the patient to the humidifier, and vice-versa. 
   The humidifier  24  includes a control knob  32  which can be rotated in order to vary the amount of humidification of the gas flowing through the humidifier between a maximum and minimum amount. The components of the humidifier  24  which permit this adjustable humidification will be more completely described with reference to the embodiments of the invention shown in  FIGS. 2 to 9 ,  11 ,  12 ,  13 ,  14 ,  15 ,  16  and  17 . 
   The heating element  30  is of self regulating, constant temperature type. The heating element  30  advantageously simplifies the humidifier and breathable gas supply apparatus overall by obviating the need for thermostatic temperature control equipment. 
   The heating element  30  is positioned external and under the humidifier. In another embodiment (not shown), the heating element is suitably insulated and/or water proofed and positioned inside the body of the humidifier. 
   A second embodiment of a humidifier  40  is shown in  FIGS. 2 to 9 . As best shown in  FIGS. 2 to 4 , the humidifier  40  includes a hollow body formed from an upper body portion  42  and a lower body portion  44 . A fluid tight seal  46  is disposed between the upper and lower body portions  42  and  44 . 
   The upper body portion  42  includes a gas inlet  48  and a gas outlet  50 . 
   As best shown in  FIG. 5 , the upper body portion  42  also includes an opening  52  through which passes a threaded shaft  54 . The shaft  54  depends from an external control knob  56 . 
   A fluid tight seal  58  is provided around the shaft adjacent the knob  56  and the boss  52 . The upper casing  42  includes substantially parallel internal side walls  60  which are adapted to provide a substantially fluid tight seal with the external edges  61  of a flow dividing plate  62 . However, a fluid tight seal is not critical. 
   The plate  62  includes a central threaded boss  64  which threadably engages the shaft  54 . Rotation of the knob  56  causes the boss  64 , and thus the plate  62 , to travel along the shaft  54  between the lower most position shown in  FIG. 5  and upper most position shown in  FIG. 6 . 
   The lower body portion  44  is adapted to be filled with water to a level approximately 10 mm below the seal  46 . When connected to a breathable gas supply apparatus, the humidifier  40  is positioned directly above a heating element which heats the water and causes water vapour to rise from the upper surface thereof. The upper body portion  42  and lower casing  44  together define the boundaries of the interior  66  of the humidifier  40 . The plate  62  affectively divides the interior  66  above the water surface into a relatively dry gas region  68  above the plate  62  and a relatively wet gas region  70  below the plate  62 . 
   When the knob  56  is rotated to position the plate  62  in the lowermost position shown in  FIG. 5 , the gas (normally air) pumped from the flow generator the inlet  48  of the humidifier  40  passes only through the dry region  68  and therefore undergoes minimal or zero humidification. 
   When the knob  56  is rotated to position the plate  62  in the uppermost position shown in  FIG. 6 , the gas passes only through the wet region  70  and therefore undergoes maximum humidification. 
   When the knob  56  is rotated to position the plate  62  intermediate the lowermost and uppermost position shown in  FIGS. 5 and 6  respectively, then some of the supplied gas passes through the dry gas region  68  (and is not humidified) and some of the gas passes through the wet gas region  70  (and is humidified), which results in partial humidification overall. In this way, the adjustable plate  62  advantageously allows the amount of humidification of the supplied gas to be quickly and easily varied to suit individual user needs, comfort requirements, treatment regimes and changing atmospheric conditions. 
   The plate  62  is shown in isolation in  FIG. 7  in which it can be seen that the boss  64  has a internal thread  72 . The control knob  56  and shaft  54  are shown in isolation in  FIG. 8  and it can be seen that the shaft  54  has an internal groove  74  which engages the thread  72  of the boss  64 . The upper surface of the control knob  56  has two depressions  76  to facilitate gripping of the knob  56  by a user&#39;s fingers. 
     FIG. 9  shows a constant temperature heating element  78  suitable for use with the humidifier  40  shown in  FIGS. 2 to 8 . The heating element  78  comprises a length of self regulating wire  80 , for example LSH-10, manufactured by Letco Products, Inc Texas (USA), which is wound around a core  82 , for example Noryl, manufactured by General Electric. The self regulating wire  80  is able to be connected directly to mains power supply and, as mentioned above, advantageously obviates the need for thermostatic control equipment. 
     FIG. 10  shows another constant temperature heating element  84 . The heating element  84  comprises a self regulating film  85  with power leads  86  and  87 , for example manufactured by ITW, Illinois (USA), which is attached to a plate  88 , for example Noryl. 
     FIG. 11  shows a third embodiment of a humidifier  90 . Like reference numerals to those used in describing the second embodiment will be used to denote like features in the third embodiment. 
   The humidifier  90  has a water storage tank  92  positioned above the humidifier interior  66 . A duct  94  allows water to flow from the tank  92  into the bottom of the interior  66  up to a maximum level indicated by dashed line  96 . An additional advantage of this embodiment is that it can store a relatively large volume of water, to give a longer operational time between refilling, but it has a smaller volume of water adjacent the heating element, which reduces heating time and energy consumption. 
     FIG. 12  shows a fourth embodiment of the humidifier  100  according to the invention. Like reference numerals to those used in describing the second and third embodiments will again be used to denote like features. 
   The humidifier  100  is similar to the humidifier  40  shown in  FIGS. 2 to 8  except it has a flow dividing plate  101  that includes four baffles  102 . The baffles  102  cause the supplied gas to undertake a longer path between the humidifier inlet  48  and the outlet  50 . An additional advantage of this embodiment is that it improves humidification by ensuring the supplied gas does not only flow over the portion of the water directly between the inlet  48  and outlet  50 . A similar plate  101  is shown in  FIG. 13 , except that it includes eight of the baffles  102 . 
   In the embodiments shown in  FIGS. 12 and 13  the position of the baffles  102  are fixed. However, in other embodiments (not shown) the position of the baffles can be adjusted and/or individual baffles can be removed. 
     FIG. 14  shows an embodiment of a heating element assembly  110  also suitable for use with humidifiers. The assembly  110  includes a heating element  112 , which is similar to that shown in  FIG. 9 , and a heating plate  114 . In use, the plate  114  is positioned between the upper surface of the heating element  112  and the lower surface or underside of a humidifier. The heating plate  114  is separated from a base  116  by springs  118 . 
   When a humidifier filled with a predetermined volume (and thus weight) of water is placed on the heating plate  114 , it compresses the springs  118  such that the plate  114  makes contact with the heating element  112  for heating. If there is insufficient water in the humidifier, or if the humidifier is removed from the assembly  110 , the springs  118  lift the heating plate  114  away from the heating element  112 . This creates an air gap  119  between the heating element  112  and the hot plate  114  which advantageously reduces further heating of the heating plate  114 . This reduces the risk of the assembly  110  burning a user or starting a fire or the like if operated incorrectly. 
     FIG. 15  shows a humidifier  120  according to a sixth embodiment of the invention and like reference numerals will again be used to denote like features to earlier embodiments. The humidifier  120  is similar to the humidifier  90  shown in  FIG. 11  in that it has a water storage tank  92  mounted above the humidification interior  66 . However, in this embodiment, the flow dividing plate  62  pivots at one end about axis  122 , as indicated by arrow  123 , between maximum and minimum humidification positions. The humidifier  120  also includes a plug  124  to allow filling of the water storage tank  92 . The humidifier  120  is shown mounted above a heating element assembly  126  which comprises a heating element  128  within an outer casing  129 . 
     FIGS. 16 and 17  show a seventh embodiment of a humidifier  130  similar to the embodiment shown in  FIG. 15 . However, in this embodiment, the flow dividing plate  62  rotates about a substantially central axis  132  between the maximum humidification position shown in  FIG. 16  and the minimum humidification position shown in  FIG. 17 . The path taken by the supplied gas from the inlet  48  to the outlet  50  is indicated by arrows  134 . The water level is indicated by broken line  136 . 
     FIG. 18  shows another embodiment of a heating element assembly  140  similar to that shown in  FIG. 14 . The assembly  140  includes a heating element  142 , which is similar to that shown in  FIG. 10 , a conducting plate  144  and a heating plate  146 . The heating plate  146  is separated from a base  148  by springs  150 . The assembly  140  functions similar to the assembly  110  shown in  FIG. 13 . 
   Another advantage of the preferred embodiments of the invention stems from the ability to control humidification levels substantially independently of temperature. Different temperatures inhibit the growth of, or kill, different bacteria. For example, in chlorinated drinking water (0.2 mg/L) with a pH of 7.6, a temperature of 32 degrees C. will kill 99.9% of  Legionella pneumophilia  in 30 minutes (VanDemark &amp; Batzing (1987), The Microbes, Benjamin/Cummings Publishing Company, Inc.). Accordingly, once a particular desired temperature has been identified, for example to effect a particular bacteria, a heating element can be manufactured to achieve that temperature. The desired effect will be achieved whenever the humidifier is operated with that element. The desired amount of humidification can be selected by adjusting the position of the flow dividing plate. 
   In contrast, with a thermostatically controlled humidifier, the above effect on bacteria could only be achieved by setting a minimum temperature in the thermostat. However, in the absence of other means to control the humidity, this limits the available range of humidification. For example, if the temperature could not be reduced below 40 degrees C., then a low range of humidification could not be achieved, unlike embodiments of the present invention. 
   Although the invention has been described with reference to specific examples, it is appreciated by those skilled in the art that the invention may be embodied in many other forms.