Patent Publication Number: US-2023140672-A1

Title: Humidifier for respiratory apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/710,893, filed Sep. 21, 2017, now pending, which is a continuation of U.S. application Ser. No. 11/936,822, now U.S. Pat. No. 9,855,398, which claims priority to U.S. Application 60/955,222, filed Aug. 10, 2007, and to Australian Provisional Application 2006906224, filed Nov. 8, 2006, the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to humidification and heater arrangements used 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. 
     2. Description of Related Art 
     Respiratory apparatus 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, as may occur inadvertently by a leak, 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 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 pressurized 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. 
     The humidified air may cool on its path along the conduit from the humidifier to the patient, leading to the phenomenon of “rain-out”, or condensation, forming on the inside of the conduit. To counter this, it is known to additionally heat the gas being supplied to the patient by means of a heated wire circuit inserted into the patient conduit which supplies the humidified gas from the humidifier to the patient&#39;s mask. Such a system is illustrated in Mosby&#39;s Respiratory Care Equipment (7 th  edition) at page 97. 
     Such a heating method for the patient conduit may only provide poor heat transfer due to the wire locating itself along the conduit wall rather than in the main gas stream. A wire will also only give poor turbulent mixing due to its low profile. As a result heat transfer may be poor and the mixing of water vapor and gas may also be poor. 
     Alternatively the heating wire circuit may be located in the wall of the patient conduit. Such a system is described in U.S. Pat. No. 6,918,389. 
     U.S. Pat. No. 6,918,389 describes a number of humidifier arrangements for supplying low relative humidity, high temperature humidified gas to the patient. Some of these arrangements include pre- or post-heating of the gas to reduce the relative humidity. 
     None of these prior art devices provides an entirely satisfactory solution to the provision of comfortable humidified breathable gas to the patient, nor to ease of construction and hygiene requirements and to energy and patient comfort requirements at startup. 
     SUMMARY OF THE INVENTION 
     Examples of the present invention aim to provide an alternative humidifier arrangement which overcomes or ameliorates the disadvantages of the prior art, or at least provides a useful choice. 
     In one sample embodiment of the invention, a humidifier and/or temperature or other sensing or control apparatus for use with respiratory apparatus comprises a heating filament in thermal contact with the gas and/or water, wherein the filament is in the form of an elongate tape. The tape may be flexible, and may, in a sample embodiment, be passed along the bore of the patient gas conduit, or incorporated into the conduit wall. 
     In another sample embodiment, a humidifier for use with respiratory apparatus comprises a heater in contact with water in the humidifier tub, and which floats or otherwise rises and falls with changes in the water level in the humidifier tub. 
     In a further form, the invention provides a humidifier arrangement for respiratory apparatus, including an elongate filament heater in contact with the air path in the regions before and after the humidification chamber. The filament heater may be further in contact with a body of water in the humidification chamber. 
     Heating of the filament may be divided into two or more separately controllable zones. 
     A further sample embodiment of the invention provides a method of increasing patient comfort during start-up of humidification, the method comprising providing a heating element to thermally contact breathable gas being provided to the patient along a gas flow path and to thermally contact water in a humidifier apparatus; and configuring the heating element to heat the gas in the gas flow path and to heat the water in the humidifier apparatus, such the patient is initially provided with heated gas while the temperature of the water in the humidifier apparatus is being increased to its operating temperature. 
     The heating of the gas in the gas flow path may include heating of a part of the gas flow path upstream of a humidification chamber such that passage of the heated gas through the humidifier apparatus provides an initial degree of humidification. 
     According to a sample embodiment of the invention, a conduit for use in a respiratory apparatus for delivering breathable gas to a patient comprises a tube; a helical rib on an outer surface of the tube; and a plurality of wires supported by the helical rib in contact with the outer surface of the tube. 
     According to another sample embodiment of the invention, the conduit may further comprise a connector block connected to an end of the conduit, wherein the connector block is configured to be connected to a flow generator or a patient interface of the respiratory apparatus. 
     According to a further sample embodiment of the invention, a respiratory apparatus for delivering breathable gas to a patient, comprises a flow generator to generate a supply of pressurised gas to be delivered to the patient; a humidifier to vaporize water and to deliver water vapor to humidify the gas; a first gas flow path leading from the flow generator to the humidifier; and a second gas flow path leading from the humidifier to a patient interface, wherein the first gas flow path comprises a first conduit having a first connector block configured to be connected to the flow generator and the second gas flow path comprises a second conduit having a second connector block configured to be connected to the patient interface. 
     According to still another sample embodiment of the invention, a method of delivering breathable gas to a patient comprises delivering a humidified flow of breathable gas to a patient interface via a conduit; heating the conduit by supplying a DC current at a predetermined duty cycle to a plurality of wires supported by the conduit; sensing a temperature in the conduit during an OFF cycle of the predetermined duty cycle; and controlling the DC current to maintain the temperature in the conduit at a selected temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG.  1   -A is a schematic side sectional view of the patient conduit with a flexible tape heater in an embodiment of the present invention; 
         FIG.  1   -B is an alternative embodiment of  FIG.  1   -A where the flexible tape heater is in a helical configuration; 
         FIG.  1   -C: is an alternative embodiment of  FIG.  1   -A where the flexible tape heater is twisted about its longitudinal axis; 
         FIG.  2    is a schematic perspective view of another embodiment of the flexible tape heater; 
         FIG.  3    is a schematic side sectional view of the humidification chamber with an embodiment of the floating heater; 
         FIGS.  4   -A-D schematically illustrate a number of embodiments that the floating heater may have within the humidification chamber; 
         FIG.  4   -A is a side perspective view of an embodiment of the floating heater, a circular floating plate heater which is secured under a floating plastic support grid; 
         FIG.  4   -B is a side perspective view of another embodiment of a floating heater; 
         FIG.  4   -C is a perspective side view of another embodiment of a floating, helical flexible tape heater; 
         FIG.  4   -D is a plan view of another embodiment of a flexible tape heater wound in a horizontal spiral; 
         FIG.  5    schematically illustrates a humidification heater arrangement comprising multiple zones; 
         FIG.  6   -A is a transverse cross-sectional view of the patient conduit showing the flexible tape heater connected to the conduit wall; 
         FIG.  6   -B is another view of the connector embodiment of  FIG.  6   -A where the connector is disengaged; 
         FIG.  7    illustrates the floating heater plate located in a shallow bath that also floats at the water surface of the body of water; 
         FIG.  8    illustrates a power supply/controller connected to an inlet conduit by a connector according to a sample embodiment of the invention; 
         FIG.  9    illustrates the inlet conduit of  FIG.  8    connected to a flow generator; 
         FIG.  10    illustrates a patient conduit or hose according to a sample embodiment of the invention connected to a patient interface; 
         FIG.  11    illustrates an inlet conduit, including a flow generator connector cuff, connected to a connector according to a sample embodiment of the invention; 
         FIG.  12    illustrates the inlet conduit of  FIG.  11    disconnected from the connector; 
         FIG.  13    illustrates a cross section of the inlet conduit and connector of  FIG.  11   ; 
         FIG.  14    is a rear perspective view of the inlet conduit and portions of the flow generator connector cuff with the terminal clip connected thereto; 
         FIG.  15    is a front perspective view of the inlet conduit, flow generator connector cuff portions, and terminal clip of  FIG.  14   ; 
         FIG.  16    is a top perspective view of the inlet conduit and flow generator connector cuff portions without the terminal clip; 
         FIG.  17    is a perspective view of the terminal clip according to a sample embodiment of the present invention; 
         FIG.  18    is a perspective view of the connector block of the flow generator connector cuff according to a sample embodiment of the invention; 
         FIG.  19    is a perspective view of the connector according to a sample of the invention; 
         FIG.  20    is a perspective view of the contacts of the connector of  FIG.  19   ; 
         FIG.  21    is a cross section of the contacts and the connector of  FIG.  20   ; 
         FIG.  22    is a perspective view of the patient conduit or hose and portions of the mask cuff or connector according to a sample embodiment of the invention; 
         FIG.  23    is a cross section of the patient conduit and mask cuff of  FIG.  22    with portions of the cuff removed; 
         FIG.  24    is a cross section of the patient conduit and mask cuff of  FIG.  10   ; 
         FIG.  25    is a top perspective view of the connector block of the mask cuff according to a sample embodiment of the invention; 
         FIG.  26    is a bottom perspective view of the connector block of  FIG.  25   ; 
         FIG.  27    is a top perspective view of the connector block of the mask cuff in connection with the patient conduit and including a printed circuit board of the mask cuff according to a sample embodiment of the invention; 
         FIG.  28    is a side perspective view of the connector block of  FIG.  27    disconnected from the patient conduit; 
         FIG.  29    is a cross section of the patient conduit and connector block of  FIG.  27   ; 
         FIG.  30    is a perspective view of the patient conduit and the connector block of the mask cuff according to a sample embodiment of the invention; 
         FIG.  31    is a perspective view of the patient conduit and mask cuff according to a sample embodiment of the invention; 
         FIG.  32    is a cross section of the patient conduit and mask cuff of  FIG.  31   ; 
         FIG.  33    is a schematic illustration of the temperature sensor and thermal fuse of the circuit of the mask cuff according to a sample embodiment of the invention; 
         FIG.  34    schematically illustrates the circuit of the mask cuff provided on the connector block of the mask cuff; 
         FIG.  35    schematically illustrates power supply/controller according to a sample embodiment of the present invention; 
         FIG.  36    schematically illustrates a three wire heated tube according to a sample embodiment of the invention; 
         FIG.  37   a    schematically illustrates a sample embodiment of the circuits of the power supply/controller; 
         FIGS.  37   b   - 1 - 37 B- 4  schematically illustrate a sample embodiment of the circuit of  FIG.  37     a;    
         FIGS.  38 - 40    are perspective views of overmolded grip portions for the flow generator cuff and/or mask cuff; 
         FIG.  41    illustrates a conduit according to a sample embodiment of the invention; 
         FIG.  42    illustrates a conduit according to a sample embodiment of the invention; and 
         FIG.  43    illustrates a patient conduit and mask cuff according to a sample embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Flexible Tape Heater 
       FIGS.  1   -A to  1 -C illustrate the use of a flexible tape heater  3  within the patient conduit  4  of a respiratory apparatus. The patient conduit  4  is located between the humidification chamber  1  and the patient interface, e.g. mask  5 . The patient conduit  4  conveys the flow of gas from the humidification chamber  1  to the patient mask  5  in respiratory apparatus. The humidification chamber  1  in turn receives pressurized gas from a flow generator  20  ( FIG.  5   ) or blower. 
     The flexible tape heater  3  in the patient conduit  4  is used to heat the flow of gas in the patient conduit  4 . Heating of the gas enables the gas comfort features of temperature and humidity to be attained and maintained for the gas delivered by the respiratory apparatus. 
     The flexible tape heater  3  is electrically coupled to a heater controller  21  ( FIG.  5   ) by a patient conduit connector end  2 . The heater controller  21  may be incorporated in the humidifier or the flow generator  20  or the base unit  22 , or be a separate unit  21 , for example supplying a DC voltage of, for example, 0.1-24V. 
     The patient conduit connector end  2  may connect to the heater controller  21  via another flexible tape heater (partially shown on the left side in  FIG.  1   ) or to the conduit wall  25 , of the patient conduit  4 , via a connector  23 ,  24  shown in  FIGS.  6   -A and  6 -B. The connector may include a male connector element  23  and a female connector element  24  which may make an electrical, communications and/or mechanical connection between the flexible tape heater  3  and the conduit wall  25 . The male connector element  23  and the female connector element  24  may be interchangeable in position. The connector  23 ,  24  locks the flexible tape heater  3  in position on the conduit wall  25 , but may also be disengaged. The connector  23 ,  24  may be used at any location along or around the conduit wall  25 . 
     The patient conduit  4  may be insulated or a heated conduit as in the prior art in order to reduce heat loss and minimize consequent water condensation or “rain-out” within the patient conduit  4 . The insulation could be an outer sleeve or wrapping about the patient conduit  4 . The outer sleeve or wrapping could be foam, fabric or an air space in the case of a double walled conduit. 
     In another embodiment the flexible tape heater  3  may be combined with the wall of the patient conduit  4  in order to provide heating to the wall to prevent condensation, while optionally an additional flexible tape heater  3  within the patient conduit  4  provides the heating to the gas flow. 
     In a further embodiment the patient conduit  4  is formed by making a helix of the flexible tape heater  3  and joining the edges the flexible tape heater  3  to form the patient conduit  4 . 
     The flexible tape heater  3  should be sufficiently flexible so that in use flexing of the patient conduit  4  is not restricted. The flexibility of the flexible tape heater  3  also should be sufficient to enable insertion and removal of the flexible tape heater  3  within the patient conduit  4 , while being sufficiently stiff so that the flexible tape heater  3  can be inserted into the patient conduit  4  and will support itself in a desired position and not collapse against a wall or to one end of the patient conduit  4 . Additionally the stiffness should be sufficient so that the flexible tape heater  3  will not flutter in the gas stream to produce an unwanted audible noise. 
     The thin, flat and extended nature of the flexible tape heater  3  enhances heat transfer with the gas flow while also providing low impedance to the gas flow. The flexible tape heater  3  can be placed in the patient conduit  4  such that it has a helical configuration ( FIG.  1   -B) and/or the flexible tape heater  3  can be twisted or bent about one or more of the flexible tape heater  3  axes. The longitudinal axis twist configuration is illustrated in  FIG.  1   -C. 
     Alternative profiles or geometric structures for the flexible heating tape may include: 
     The transverse cross-section of the flexible tape heater may be rectangular, elliptical or arbitrary; 
     The surface of the flexible tape heater  3  may be rough or smooth or dimpled; and/or 
     One or more surfaces of the flexible tape heater  3  may be rippled. 
     The dimensions of the thickness and width may vary along the length of the flexible tape heater. For example a thicker section of the flexible tape heater  3  in the patient conduit  4  may be provided to give a venturi effect of increasing the gas flow rate so that flow detection may be possible by pressure sensors along the length of the flexible tape heater  3 . 
     The use of these twisted, helical or other configurations described above increases the length of the flexible tape heater  3  in the patient conduit  4  and thus the available surface area for heat transfer between the gas flow and the surface of the flexible tape heater  3 . Additionally these configurations can be used to enhance the turbulent mixing of the water vapor produced in humidification chamber  1  with the gas flow. 
     The various configurations may also be used to provide zones of differing flow, acoustic, humidity or temperature properties along the patient conduit  4  or the apparatus as a whole, as show in  FIG.  5    for example. 
     It may be desirable to modify the acoustic impedance properties of the patient conduit  4  using the flexible tape heater  3 . For example: 
     The generation or reduction in white noise (broad frequency spectrum noise); 
     The damping or filtering of a particular acoustic noise frequency component/s, e.g. structure-borne or air-borne flow generator tonal noise; and/or 
     Enhancement of the propagation of patient respiratory acoustic signals through the patient conduit  4  and to the base unit  22  ( FIG.  5   ) for monitoring and diagnosis. 
     The alteration of acoustic impedance properties using the flexible tape heater  3  may be achieved by the choice of the materials making up the flexible tape heater  3  and the configurations described above of the flexible tape heater  3  in the patient conduit  4 , and additionally as shown in  FIGS.  1   -A to  1 -C. 
       FIG.  2    illustrates one embodiment of the flexible tape heater  3 , in which the heating is by a heating element  6 . 
     In one embodiment, the heating element  6  is formed by printed circuit techniques applied to a surface of a flexible substrate such as KAPTON®, silicone rubber, all-polyimide, PTFE. Included in the printed circuit techniques which may be used are etched foil, printing and vacuum deposition techniques. 
     Another sheet of the substrate material is then laid upon the bottom substrate with the heating element and the two sheets of substrate material adhered or fused together to encapsulate the heating element. The Thermofoil™ range of the type of flexible heaters by Minco of Minneapolis USA, described at www.minco.com, are examples of commercially available strip heaters which may be modified for use in the present invention. 
     An alternative embodiment to produce a flexible tape heater  3  is to use a laminator, such as a twin silicon roller laminator, to encapsulate a heating element  6 , that is in the form of wire or ribbon, within two tapes of polycarbonate film. The resulting tape may for example have dimensions ranging from 1 to 10 mm wide and 0.1 to 1 mm thick. Dimensions of from about 0.2 to 0.5 mm in thickness and about 5 mm wide are usable in the patient conduit  4 . 
     The heating element  6  wire or ribbon may have any suitable transverse cross-section, for example circular, elongate or rectangular. The heating element  6  may for example consist of a resistive conductor. 
     The arrangement of the heating element  6  between the laminating films may be any ordered or disordered arrangement that increases the heat transfer of the flexible tape heater  3  to the surrounding media, be it gas or liquid. The heating element  6  may also have a positive thermal coefficient (PTC) for resistance such that heating decreases as the temperature increases towards a desired temperature. 
     Alternatively the heating element  6  may have a negative thermal coefficient (NTC) to allow sensing of the temperature of the heating element  6  or surrounding media. 
     In other embodiment there may be multiple heating element circuits within the flexible tape heater  3 . The multiple heating elements may be connected in series or parallel. The use of these multiple heating circuits within a flexible tape heater  3  enables additional heating to be applied as required in the operation of the respiratory apparatus. 
     In other embodiments the laminating films may be polyester, polypropylene or any suitable and approved substance for respiratory medicine use. Alternatively, multiple laminating films may be used to create a composite strip having the desired properties while retaining the desired compatibility of the outer film for respiratory medicine use. Other conductors may also be present between each of these multiple layers, for example so as to form multiple heating circuits, such as to allow multiple heating zones along the length of the tape heater. 
     In another embodiment, a sensor  7  for air temperature, such as a thermocouple, platinum resistance thermometer or thermistor with its attendant signal wires  9 , may be included between the two sheets of polycarbonate film. The sensor tip may be flat with a thickness of less than about 2 mm, and may be less than 1 mm. Other circuit components such as surface mount circuit components may be incorporated onto the substrate film for sensing and/or controlling and hence into the flexible tape. Also, the heating element  6  and other circuit components can exist in multiple layers separated by substrate films as described above. 
     For the flexible tape heater  3  the other circuit components all have the common physical feature that they are of a small enough dimension to enable them to be accommodated in the overall profile of the flexible tape heater  3  and collocated with the heating element  6 . 
     In an alternative embodiment the flexible tape may not have a heater element  6 , but instead incorporate one or more other circuit components for sensing and controlling. Thus a respiratory apparatus may contain two or more flexible tapes, one or more undertaking a heating function and one or more undertaking a sensing and/or controlling function. 
     The range of other circuit components that may be used is shown by way of example in the following: 
     Relative and absolute humidity sensors  7   a;    
     Temperature sensors  7   a  with a positive temperature coefficient (PTC) or negative temperature coefficient (NTC) in the form of a thermistor or alternatively the PTC property may be intrinsic to the heating element  6  so that the flexible tape heater  3  is self limiting; 
     Thermocouples, platinum resistance thermometers and the like may be used to produce an actual temperature value signal for control and monitoring; 
     Directional flow sensing of the gas may realized by using at least two independently controlled heating sections spaced along the flexible tape heater each comprising a temperature sensor (e.g. thermistor). The two or more heating sections are controlled and the temperatures sensed to detect the direction of gas flow; 
     Hot wire anemometry for gas flow sensing  7   a;    
     Ambient pressure sensing  7   a , e.g. inspiratory versus expiratory pressures; 
     Controller  7   b  that makes use of the output from a sensor  7   a , such as for temperature, to control, for example, a transistor which regulates the current applied to a heating element  6  used for the heating element(s); 
     Identification-Communication-Memory chips  8  which enable identification and communication of the operating parameters of the flexible tape heater  3  to the base unit  22 , other heaters and components in the respiratory apparatus. For example, the flexible tape heater  3  may communicate regarding itself as well as detect and report regarding other components that are attached to the respiratory apparatus such as the patient mask  5  type or the patient conduit  4  type or an active vent system. The information thus gathered by the flexible tape heater  3  may then be sent to the base unit  22 . The identification-communication-memory system may consist of in part a radio frequency identification chip (RFID) to store the heater  6  and sensor  7   a  identification and operating parameters. The base unit  22  may have a capability to communicate with the RFID chip and adjust its operation accordingly. Such a system has been described in the Australian Patent Application No. 2005907200, titled “Identification System and Method for Mask and Ventilator Components,” the entire contents of which are incorporated herein by reference. The communication may also be used to control an active vent system; 
     Electromagnetic communication protocols via miniature aerials and receivers, e.g. “Bluetooth.”. Aerials for transmitting and receiving information may be located for example in the flexible tape heater  3 , the wall of the patient conduit  4 , or an active vent system, or within the other components of the respiratory apparatus as illustrated in  FIG.  5   . In another embodiment the aerials could be of a dimension as allowed by the length of the flexible tape heater  3  or the patient conduit  4 ; 
     Power supply to the flexible tape heaters may be in a similar manner to the electromagnetic communication described above. In this embodiment the aerials or inductive coils would be adapted for power transmission. 
     These components can be located anywhere along the flexible tape heater  3  as appropriate to their function. For example, a thermocouple may be located on the flexible tape heater  3  at the end adjacent the patient mask  5  to enable closed loop temperature control based on gas temperature delivered to the patient mask  5 . 
     In an alternative embodiment the temperature sensor may be located in or in the vicinity of the patient mask  5  but separated from the flexible tape heater  3 . However the temperature sensor may communicate with the flexible tape heater  3  in the one of the manners described above to enable closed loop control of the temperature of the gas delivered to the patient. 
     The flexible tape heater  3  may also comprise microtubes  26  ( FIG.  2   ) to allow remote sensing away from the flow generator and/or humidification chamber  1 . The microtubes may, for example, provide pressure, noise/snore and/or cardiological signal sensing. For example, the microtubes may be attached to the side of the flexible tape heater  3  and connected back to the flow generator  20  in one of the manners described above. The use of microtubes  26  provides the benefit of avoiding flow noise within the patient conduit  4  and other areas in the respiratory apparatus. 
     The sensing and control methods described above allow closed loop control to be used for improving gas delivery to the patient mask  5  so that it is at the desired temperature and humidity. Alternatively, a simple open loop system may be used where driving voltages or currents for the heating element may be, for example, from 0.1 to 24 V direct current or the power equivalent for alternating current, that may for example be from 0.1 to 50 W. The sensing and control may also control the level of intentional gas leak from an active vent system, depending on the amount of pressure being supplied. For example, as the ventilator pressure increases the active vent system may be controlled to reduce the level of its intentional leak to an acceptable level. 
     Additionally, the sensors  7   a  can be used for compliance or statistical data gathering. 
     Furthermore, the different components of the heater and/or sensing/control system described herein may be used as stand alone components in a respiratory apparatus not employing a humidifier, and such arrangements are within the scope of the invention. 
     A flexible tape heater  3  as thus described would be easily removable from the patient conduit  4  to enable cleaning, maintenance or replacement. The flexible tape heater  3  also offers efficient heating with sensing and control components  7  being easily incorporated into the flexible tape heater  3 . 
     Floating Heater 
     In  FIG.  3    a humidifier arrangement utilizing a floating heater  12  is illustrated. The floating heater  12  floats in the body of water  13  in the humidifier chamber tub  1  such that a substantial portion of the floating heater  12  is immersed but is still adjacent to the water surface  14  so as to heat that part of the water near the surface  14 . 
     The floating heater  12  may comprise a length of flexible tape heater of similar construction to that discussed above with reference to  FIGS.  1   -A to  1 -C and  2 . The end of the heater located in the inlet conduit  10  leading from the flow generator  20  may be provided with a connector  11  which enables the floating heater  12  to connect with a flexible tape heater, where that flexible tape heater is connected to the base unit  22  ( FIG.  5   ) of the respiratory apparatus. The floating heater  12  receives its electrical supply via the upstream end connector  11 . Any sensing or controlling signals to or from the floating heater  12  are also received via the upstream end connector  11 . 
     The downstream end  2  of the floating heater, located in the patient conduit  4  leading to the patient interface, may have a further connector for supplying power and any communication with a further portion of flexible tape heater located in the patient conduit  4  (see  FIGS.  1   -A,  1 -B,  1 -C and  2 ). 
     The heater  12  may be adapted to float either by the natural buoyancy of the heater itself, by surface tension effects, or may be supported in a manner which keeps the heater near the water surface regardless of changes in the water level. 
       FIGS.  4   -A-E illustrate a number of embodiments that the floating heater  3 ,  12 ,  16 ,  17  may have within the humidification chamber  1 . The floating heater  3 ,  12 ,  16 ,  17  in each embodiment is formed either from a flexible tape heater of the type previously described or a plate form of the flexible tape heater  3 , the floating plate heater  16 . 
     The construction and use of a floating flexible tape heater  3  and the floating plate heater  16  is the same as described for the flexible tape heater  3  above, except that it is applied to water. This has the significant advantage that the heater for both applications is robust to gas or water immersion, since a floating flexible tape heater  3  or a floating plate heater  16  could be partially immersed in water during the respiratory apparatus&#39; operation, either unintentionally as the body of water increases or decreases in volume or by tilting of the device, or intentionally to maintain the temperature of the water vapor in the gas of the humidification chamber  1 . 
       FIG.  4   -A illustrates a circular floating plate heater  16  which is secured under a floating support grid or plate  15 , for example of a buoyant plastics material. The support grid  15  provides a floating positioning mechanism for the floating plate heater  16  spacing the heater element just below the water surface  14  so that there is sufficient contact with the water to cause vaporization. In an alternative embodiment shown in  FIG.  7   , the floating heater plate is located in a shallow bath that also floats at the water surface  14  of the body of water  13 . In this embodiment the floating plate heater comprises at least one aperture to allow water to fill the bath to cover the heater plate  16 . The small volume of water in the bath is rapidly heated to produce vapor. 
       FIG.  4   -B shows another embodiment where the plate form is rippled or dimpled in a regular or irregular fashion. The rippling and/or dimpling provides valleys which allow pockets of water to accumulate on the upper surface of the floating plate heater  16 . In this embodiment, the floating plate heater  16  is naturally buoyant, so it can float without the need for a support grid or other buoyancy device. 
       FIG.  4   -C illustrates a flexible tape heater  3  which has been wound into a helix. In this embodiment the floating, helical flexible tape heater  17  can intrinsically float such that a sufficient portion of the floating, helical flexible tape heater  17  is immersed in the body of water  13 . In another embodiment the flexible tape heater  3  could be wound in a horizontal spiral,  FIG.  4   -D. For both the  FIGS.  4   -C and  4 -D embodiments a support grid  15  as used in  FIG.  4   -A may be used to position the flexible tape heaters  3 ,  12 ,  17 . 
     The preceding embodiments for the floating heater  3 ,  12 ,  16 ,  17  represent a number of defined configurations whereas in use the floating heater may assume a combination of the defined or undefined configurations. For example a long helix which continues as a spiral, combining  FIGS.  4   -C and  4 -D. 
     In the above embodiments of the floating heater  3 ,  12 ,  16 ,  17  the heater provides effective heat transfer to the water surrounding the heater. In addition, the water adjacent to the water surface is heated for vaporization rather than heating the whole body of water from the bottom up as in the case of a heater being located at the bottom of the body of water  13 . 
     Additionally, the flexible tape heater formation may be spiraled or otherwise formed so as to be partly immersed in the body of water  13  so that it heats both the water near the air and the air near the water to produce a stratified zone of heat to improve water uptake for humidification. Thus, the floating heater  3 ,  12 ,  16 ,  17  may be more power efficient in generating water vapor, and more effective in quickly achieving the desired water surface temperature for humidification at start-up of the apparatus. 
     Multiple Zone Heating 
       FIG.  5    illustrates a respiratory apparatus which makes use of three heaters that are of the same general construction and use as described for the flexible tape heater  3  and the floating plate heater  12 ,  16 ,  17  described above. 
     The heaters may comprise multiple heating circuits, so that each of the three heater zones may be operated independently. 
     A flow generator  20  or blower supplies gas supplied from an ambient temperature supply which may be the air in the room or augmented or replaced by a specific gas supply such as oxygen. A pre-heater  18  is located in the blower coupling  10  leading to the humidifier  1 . The blower coupling may be rigid, flexible or a conduit as required for the operation of the blower coupling  10  or the operation of the pre-heater  18  located within the blower coupling  10 . The pre-heater  18  is connected to the controller/power supply  21 , of the base unit  22 , which supplies power and communication with any sensing or controlling components  7  of the pre-heater  18 , as per the flexible tape heater  3  embodiment. The pre-heater  18  is connected to the floating heater  12 ,  16 ,  17  of the humidification chamber  1  at the blower conduit connector end  11 . The floating heater  12 ,  16 ,  17  receives the controller/power supply  21  power supply and any communication, with the sensing or controlling components  7  of the floating heater  12 ,  16 ,  17 , via the pre-heater  18 . 
     Alternatively the floating heater  12 ,  16 ,  17  may also connect with the controller/power supply  21  via the wall of the blower coupling  10  in the manner described above in relation to  FIGS.  6   -A and  6 -B discussing the patient conduit  4 . 
     The post heater  19  is located in the patient conduit  4 . The patient conduit connector end  2  provides the controller/power supply  21  power supply and communication for the sensing and controlling components  7  of the post heater  19 . The patient conduit connector end  2  may connect to the controller/power supply  21  via floating heater  12 ,  16 ,  17  as shown in  FIG.  5    or via the conduit wall  25 , as shown in  FIGS.  6   -A and  6 -B, and then via the humidification chamber  1  to the controller/power supply  21  in the base unit  22 . 
     In an alternative embodiment one or more of the heaters may not be of the type described above but another suitable heating element. For example, the pre-heater  18  may be formed as a simple wire heater or other conventional heater type rather than as a flexible tape heater of the type described herein. 
     The use of such arrangements may give the advantages of: 
     A single inter-connected heater system which is internal to the blower coupling  10 , humidification chamber  1  and patient conduit  4 ; 
     The complete heater, sensor and control system can be removed simply for cleaning, maintenance or replacement; 
     The interconnection facilitates a high degree of closed loop control for temperature and humidity of the gas delivered to the patient; 
     The ability to sense temperature and humidity at different sections of the patient conduit  4  in order to control the condensation at various sections in the patient conduit  4 ; 
     The different components of the heater and/or sensing/control system may be used in combination or separately within a conventional humidifier. For example the flexible heating tape  3  may also be used to heat the patient conduit  4  together with a conventional humidifier with a heating base plate. Alternatively the floating heater  12 ,  16 ,  17  or flexible tape heater  3  may be used to heat the body of water  13  in the humidification chamber  1  together with a heated or insulated wall patient conduit  4 , as described above; and/or 
     The ability to install multiple heaters in parallel and series at any location of the respiratory apparatus. This may allow, for example, “super heating” during the beginning operation of the respiratory apparatus when the body of water  13  requires time to reach the desired temperature. The temporary extra heating of the air with multiple heater circuits would increase the capacity of the air to take up the cooler water. This may be controlled or profiled in response to the temperature of the water in the body of water  14  to provide the appropriate level of humidity. 
     For the respiratory apparatus the placement of the three heaters, and the timing and sequence of their use allows the gas comfort features of temperature and humidity to be managed by allowing the separate, staggered production of: 
     Heating of an ambient gas that has a low absolute humidity; 
     Water vaporization; and/or 
     Heating of the gas that has an increased absolute humidity (after the humidification chamber  1 ). 
     The following example of use illustrates an advantage in the operation of the sample embodiments described herein. 
     Patient respiratory gas requires attention to the comfort features of temperature and humidity, in particular in winter and colder climates. In the embodiments, the aim of the system from a cold start-up is to rapidly deliver warm gas initially and then increase humidity over time as the humidifier warms up. This approach allows the patient to receive comfortable warm air closely followed by an increasing relative humidity, before there is an onset of any adverse symptoms of low humidity respiratory assistance. 
     For a cold start in a winter climate the three heater system may thus operate in the following manner Firstly, the cool ambient temperature gas from the flow generator  20  is warmed by using the pre-heater  18  in the blower coupling  10  with perhaps assistance from the post-heater  19  in the patient conduit  4 . This initially provides warm, dry air to the patient. 
     As the warmed gas flow begins to absorb appreciable water vapor from the unheated water in the humidification chamber  1 , the post-heater  19  in the patient conduit  4  would begin or increase its heating in order to prevent “rain-out” condensation in the patient conduit  4 . The initial warming of the air with the pre-heater  18  has the advantage of immediately commencing a degree of humidification, as a simple “pass-over” operation, while the floating heater  12 ,  16 ,  17  is still warming up the water. The heat for vaporization in the simple “pass-over” operation being provided by the heated air. 
     As the floating heater  12 ,  16 ,  17  begins to warm the water surface and rapidly increase the absolute humidity in the gas passing through the humidification chamber to achieve the desired level of humidification, the post-heater  19  in the patient conduit  4  would adjust its heating to maintain the absolute humidity by preventing condensation in the patient conduit  4 . The post-heater  19  may also serve to maintain the desired gas temperature in the patient conduit  4 . The pre-heater  18  may have a heating profile based on the level of heating of the body of water  13  in the humidification chamber  1 , the heating profile being the rate of heating of the gas flow in a period of time that can be provided by changing the power to the pre-heater  18  or the structural configuration of the pre-heater  18 . It is believed that there may be more effective and control of the humidity by controlling the air temperature as opposed to heating the water. 
     An additional advantage of this sample embodiment is that it allows reduced power consumption at humidification start up so that the respiratory apparatus may be able to be operated by direct current power supply or a portable power supply. Also, satisfactory operation can still be obtained when two or more heaters are multiplexed, one heater is operated at a time but there is cycling in operation between two or more heaters. 
     Inlet Conduit Connection 
     Referring to  FIG.  8   , the power supply/controller  21  may be connected to the inlet conduit/blower coupling  10  by a connector  52 . The connector  52  has a first connector  52   a  connected to the power supply/controller  21  and a second connector end  52   b  connected to the inlet conduit  10 . The inlet conduit  10  has a flow generator cuff or connector  54 . The flow generator cuff  54  has an end  54   a  which is configured for connection with the flow generator  20 . The flow generator cuff  54  also has an overmolded grip or cuff  54   b  which defines a terminal clip  54   c.    
     As shown in  FIG.  9   , the inlet conduit  10  is connected to the flow generator  20  by the flow generator cuff  54 . The connector  52  is connected to the flow generator cuff  54  at the terminal clip  54   c . Although not shown in  FIG.  9   , it should be appreciated that the first end  52   a  of the connector  52  is connected to the power supply/controller  21 . The power supply/controller  21  provides electrical current and signals to the flow generator cuff  54  through the connector  52 . 
     Patient Conduit Connection 
     The patient conduit/air delivery hose  4  is connected to the patient interface  5  by a mask connector or cuff  56 , as shown in  FIG.  10   . The patient conduit  4  includes a tube  4   a , for example of thermoplastic elastomer, and a helical rib  4   b  of very low density polyethylene. Wires  4   c ,  4   d ,  4   e  are supported in the helical rib  4   b  so as to be in contact with the outer surface of the tube  4   a . The wires  4   c ,  4   d ,  4   e  may be used to heat the tube  4   a  and to carry signals to and from the power supply/controller  21 . It should be appreciated that the inlet conduit  10  may have a construction similar to the patient conduit  4 , including a tube  10   a , a helical rib  10   b,  and wires  10   c - 10   e  supported by the helical rib on the tube. 
     Inlet Conduit and Flow Generator Connector Cuff 
     Referring to  FIG.  11   , the flow generator cuff  54  includes a connector block  54   a . A grip or cuff  54   b  is overmolded on the connector block  54   a  to connect the connector block  54   a  to the inlet conduit  10 . The overmolded grip or cuff  54   b  includes grip features  54   d , such as recesses for a user&#39;s fingers, in the outer surface of the overmolded grip or cuff  54   b  to provide a better grip on the connector cuff  54 . 
     As shown in  FIGS.  8 ,  12  and  13   , the flow generator cuff  54  includes a terminal clip  54   c  that receives the second connector end  52   b  of the connector  52 . As shown in  FIG.  13   , the terminal clip  54   c  includes a rib  54   n  that is received in a lead-in  52   e  of the connector  52 . The rib  54 n engages the lead-in  52   e  to secure the connector  52  to the terminal clip  54   c.    
     The terminal clip  54   c  also includes a tooth  54   e  that locates the wires  10   c ,  10   d ,  10   e  of the inlet conduit  10 . The wires  10   c ,  10   d ,  10   e  are placed on the outer surface of the thermoplastic elastomer tube  10   a  and held in place on the outer surface by the helical rib  10   b.    
     A channel  54   j  is provided in the connector block  54   a  to allow the overmolded material  54   b  to flow and bond to the inside of the tube  10   a  to establish the connection between the connector block  54   a  and the inlet conduit  10 . The connector block  54 , the tube  10   a  and the overmolded material  54   b  may be formed of materials that will chemically bond. 
     Referring to  FIG.  14   , the terminal clip  54   c  includes terminal clip pins  54   h  that are received in hinged slots  54   g  of a terminal clip hinge  54   f . The terminal clip hinge  54   f  is provided on the connector block  54   a . The terminal clip  54   c  is snap-fit into the terminal clip hinge  54   f  to ensure connection of the tooth  54   e  with the wires  10   c ,  10   d ,  10   e  of the inlet conduit  10 . As shown in  FIG.  15   , the terminal clip  54   c  may be attached to the connector block  54   a  prior to attachment of the inlet conduit  10  to the connector block  54   a . The terminal clip pins  54   h  are attached in the hinge slots  54   g  and the terminal clip  54   c  is tilted or rotated forward. The inlet conduit  10  is then attached to the connector block  54   a  and the terminal clip  54   c  is then rotated or pivoted back so that the tooth  54   e  contacts the wires  10   c ,  10   d ,  10   e  of the inlet conduit  10 . As shown in  FIGS.  16  and  17   , the connector block  54   a  includes a guide away  54   p  for the helical rib  10   b  of the inlet conduit  10  to position the wires  10   c ,  10   d  and  10   e  for contacting by the tooth  54   e.    
     Referring to  FIG.  17    the terminal clip  54   c  includes an arched portion  54   k  that defines a channel with the guide way  54   p  ( FIG.  16   ) when the terminal clip  54   c  is inserted into the terminal clip hinge  54   f . A groove  54   i  ( FIG.  18   ) is provided in the connector block  54   a  to receive the helical rib  10   b  and the wires  10   c ,  10   d ,  10   e  of the inlet conduit  10 . The groove  54   i  has a smooth surface and wide contact area to prevent or minimize damage to the wires  10   c ,  10   d ,  10   e . As also shown in  FIG.  18   , a void  54   m  is provided adjacent to the channel  54   j  to allow for the passage of any air during the overmolding of the grip or cuff  54   b  to the connector block  54   a.    
     Referring to  FIGS.  19 - 21   , the second connector end  52   b  has a grip feature  52   c  to permit easier gripping of the second connector end  52   b . Strain relief features  52   d  are also formed in the second connector end  52   b  to increase flexibility. The grip and strain relief features may also be provided to the first connector end  52   a  of the connector  52 . 
     Contacts  52   f ,  52   g ,  52   h  are provided for sending and receiving signals from the wires  10   c ,  10   d ,  10   e  of the inlet conduit  10 . Although the inlet conduit  10  is shown as including three wires and a terminal clip  54   c  is shown as having three terminals for receipt of the three contacts of the second connector end  52   a , it should be appreciated that any number of wires, terminals and contacts may be used for the delivery and receipt of signals from the power supply/controller  21  to the inlet conduit  10 . 
     Patient Conduit and Mask Connector Cuff 
     Referring to  FIGS.  22 - 34   , a mask connector or cuff  56  is provided for the connection of the patient conduit/air delivery hose  4  to the patient interface  5 . The mask connector or cuff  56  includes a connector block  56   a  that is connected to the patient conduit  4  by an overmolded grip or cuff  56   b . The connector block  56   a , the tube  4   a  and the overmolded cuff  56   b  may be formed of materials that will chemically bond. 
     As shown in  FIG.  24   , the connector block  56   a  is connected to an inlet  5   a  of the patient interface  5 . The inlet  5   a  may be, for example, the swivel elbow of a mask. 
     A printed circuit board (PCB)  56   c  is provided around the outer surface of the connector block  56   a . The wires  4   c ,  4   d ,  4   e  of the patient conduit  4  are attached to the PCB  56   c . As shown in  FIGS.  25 ,  27  and  28   , the connector block  56   a  includes snaps or pins  56   i  that engage holes or apertures  56   u  in the PCB  56   c . The PCB  56   c  is thus wrapped around an outer surface of the connector block  56   a  and held in place. A thermal fuse  56   d  and a temperature sensor  56   e , for example a thermistor, are provided on the PCB  56   c . As shown in  FIGS.  23  and  26   , one or more windows  56   j  are provided in the outer surface of the connector block  56   a  where the thermal fuse  56   d  and the temperature sensor  56   e  are provided. The windows  56   j  are covered by the PCB  56   c , as shown in  FIG.  24   . As discussed in more detail below, the PCB  56   c  includes a heater track that is cooled by exposure of the PCB  56   c  to the airflow along the window  56   j.    
     A helical rib  56   f  is provided on the outer surface of the connector block  56   a  to locate the patient conduit  4 , as shown in  FIGS.  22 - 26   . As shown in  FIG.  25   , the outer surface of the connector block  56   a  includes a stepped recess  56   h  to allow the overmold material to flow and bond to the underside of the flexible PCB  56   c . As shown in  FIG.  29   , the connector block  56   a  also includes a channel  56   t  to allow the overmold material to bond with the inside of the tube  4   a  of the patient conduit  4 . Referring back to  FIG.  25   , a void  56   g  is provided adjacent the channel  56   t  to allow for the escape of air during overmolding. As also shown in  FIGS.  28  and  29   , the end of the connector block  56   a  includes a profile  56   n  that minimizes the capacity for debris to collect and to be cleaned if debris does collect. The end of profile  56   n  also minimizes flow impedance of the overmolded material. 
     As shown in  FIGS.  25  and  27   , an access channel  56   m  is provided between the helical rib  56   f  and the end channel  56   t  to allow the overmold material to bond the tube  4   a  to the connector block  56   a . As shown in  FIG.  30   , the tube  4   a  is twisted on to the connector block  56   a  and the wires  4   c ,  4   d ,  4   e  of the patient conduit  4  are soldered to the flexible PCB  56   c  as shown at  56   p.    
     Referring to  FIG.  31   , the overmolded grip or cuff  56   b  may include a molded grip feature  56   q , such as recesses to accommodate a user&#39;s fingers, to improve the gripping ability of the mask cuff or connector  56 . The connector block  56   a  may be formed of a rigid polymer and the overmolded grip or cuff  56  may be formed of a thermoplastic elastomer. As shown in  FIG.  32   , the connector block  56   a  may have a standard  22  mm ISO taper for connection to the patient interface. As also shown in  FIG.  32   , the overmolded material may be blanked off at  56   s  in the region of the thermal fuse  56   d.    
     Referring to  FIGS.  33  and  34   , the circuit on the flexible PCB  56   c  includes the thermal fuse or switch  56   d  and the thermal sensor  56   e . One of the wires, e.g.  4   c , may be used as a temperature sensing wire for sending a temperature signal to the power supply/controller  21 . The other wires, e.g.  4   d ,  4   e , may be used as heater wires to heat the tube  4   a  of the patient conduit  4 . If the temperature exceeds a certain value, the thermal fuse  56   d  is configured to cut off current to the heater wires  4   d ,  4   e.    
     The flexible PCB  56   c  and temperature sensor  56   e  and thermal fuse  56   d  should be provided on the connector block  56   a  as close to the inlet  5   a  of the patient interface  5  and the air path through the patient conduit  4  as possible. The mask connector or cuff  56  should also be formed as small as possible to permit its use with existing breathing apparatus. The use of the overmolded grip or cuff  56   b  is also useful for securing the patient conduit  4  to the connector block  56   a  and to secure the flexible PCB  56   c , including the temperature sensor  56   e  and the thermal fuse  56   d  in place. The use of the overmolded material also helps to reduce or eliminate any locations where bacteria could grow. 
     The mask connector or cuff  56  as described herein is formed of biocompatible materials. The connector block  56   a  also includes an end  56   r  ( FIG.  32   ) that includes a standard  22  mm female ISO taper for use with existing patient interfaces. The use of the overmolded material also eases manufacture and improves reliability of the mask connector or cuff. 
     Power Supply/Controller 
     Referring to  FIG.  35   , the power supply/controller  21  comprises a switch mode power supply  21   a , a switch  21   b , a control unit  21   c , and a plurality of LED&#39;s  21   d . The power supply/controller  21  has an AC power input  21   e , a DC power output  21   f , and a bypass AC power lead  21   g  to the flow generator  20 . The AC power input  21   e  may be, for example, 110-240V AC universal inputs. The switch  21   b  may be a MOSFET switch in series with the heater element controlled by the control unit  21   c . The DC power output  21   f  may be, for example, a 500 mA regulated 5V DC, or a 1.3 A, 24V DC output. At 24V the power output is 30 W. 
     The power input  21   e  is connected to the switch mode power supply  21   a  and the bypass  21   g  is connected to an AC power socket of the flow generator  20 . The power supply/controller  21  is configured to provide power to the inlet conduit  10 , regulate preset temperature levels at the patient interface  5 , and act as an ON/OFF control. 
     The control unit  21   c  is a closed loop temperature control system. The temperature sensor  56   e  located in the mask cuff  56  provides the feedback signal through the wire  4   c  of the patient conduit  4  back to the control unit  21   c . It should be appreciated, however, that the control may not rely on a feedback of a temperature signal. The control unit  21   c  may instead be configured to provide a predetermined amount of power to the output  21   f  without reliance, or dependence, on a temperature sensor signal. 
     The DC power output  21   f  supplies power to the inlet conduit  10  and the switch  21   b  is provided in series with the power output  21   f  and is controlled by the control unit  21   c . The power regulation is based on an ON/OFF control technique. The power regulation has fixed duty cycles at a rate of about 95-99%. The OFF cycle, at a rate of about, for example 1-5%, is used for temperature sensing. 
     The LEDs  21   d  may include a green LED to indicate that power is on and being supplied to the inlet conduit  10 . An amber LED may be provided to indicate that the power output  21   f  is ON, but not provided to the inlet conduit  10 . A red LED may be provided to indicate a fault. Further LEDs may also be provided for indicating and/or controlling the temperature. Manually operable buttons (not shown) may be provided to the power supply/controller to allow control of the temperature by a patient or clinician in response to an indication of temperature by the LED&#39;s. 
     The control unit  21   c  is configured to produce a fixed power switching frequency and duty cycles for the power output  21   f  to heat the inlet conduit  10 . The control unit  21   c  is also configured to sense the temperature via the signal sent by the temperature sensor  56   e  through wire  4   c . Based on the sensed temperature, the control unit  21   c  is configured to regulate the temperature to a preset temperature when ambient temperature changes. The control unit  21   c  is further configured to record the preset temperature when the power control/supply  21  is turned off. 
     The control unit  21   c  may also latch a fault state when a fault is detected, and clear the fault by recycling power. If a fault occurs a fault detection circuit locks into a fault condition to send a fault signal to a driver block ( FIG.  37   a   ) the fault will continue until the power is turned OFF and ON again. The control unit  21   c  may be configured to detect faults, including any discontinuities in the wires  4   c - 4   e  and  10   c - 10   e , any arcing and/or bad connections in the flow generator cuff  54  and/or the mask cuff  56 . The control unit  21   c  may also detect low voltage. 
     The power output  21   f  is maintained in the OFF state by the control unit  21   c  when a fault is detected and is maintained in the OFF state until the power is recycled and the fault state is cleared. 
     The status of the power supply/controller  21  may be indicated through the LEDs  21   d.    
     As shown, for example in  FIGS.  5  and  8   , the power supply/controller  21  may be separate from the flow generator  20  and the humidifier. There is no information exchange between the flow generator  20  and the humidifier and the closed loop control does not include control based on airflow rate, humidity level, and humidifier outlet temperature, for example. It should be appreciated, however, that information may be exchanged, for example through the sensing wire  4   c . The control described above prevents “rain out” in the patient conduit  4  and delivers the humidified air to the patient interface  5 . 
     It should be appreciated that the power supply/controller  21  may be integrated with the flow generator  20  or the humidifier control system. Information may be provided to the integrated power supply/controller regarding the operation of the flow generator, the humidifier, and ambient air. By integrating the power supply/controller with the flow generator  20  or the humidifier, the system will be more able to control the temperature at the patient interface  5 , the humidity levels and “rain out” at a wider range of ambient temperature and humidities. 
     Referring to  FIG.  36   , a three wire heated tube or conduit according to a sample embodiment of the invention is illustrated. The wires  4   d ,  4   e  may be formed , for example, from a 25 m long wire having a diameter of 0.23 mm, and be formed, for example, of copper. The sensing wire  4   c  may be connected to the heating wires  4   d ,  4   e  at a connection point  4   f  that is approximately the middle of the wire forming the wires  4   d ,  4   e  and divides the wire into two resistances Ra, Rb. The total resistance Ra+Rb may be equal to about 15-21Ω, for example about 18Ω, at 20°-26° C., for example about 23° C. The total resistance Ra+Rb is about 18Ω, and about 21Ω, when the wire resistors are heated up to about 33° C. using a 24V DC supply at a power of about 30 W. As discussed above, the DC voltage V+ may be supplied across J 1  and J 3  at a duty cycle of, for example, about 95-99%. The resistances Ra, Rb generate heat during the flow of current through the wires  4   d ,  4   e  to heat the conduit  4 . The sensing voltage Vsen may be determined during the 1-5% OFF cycle. During the OFF cycle, the switch  21   b  is activated by the control unit  21   c  to switch the system into a sensing state and sensing current from J 1  passes resistance Ra and resistance RT 1  of the temperatures sensor  56   e  back to J 2 . The resistance RT 1  of temperature sensor  56   e  may be about 1-50 kΩ and resistance Rb may be about half of Ra+Rb, or about 5-15Ω, for example about 10Ω, so Rb is omitted. 
     Although the sensing wire  4   c  is disclosed as being connected to the temperature sensor  56   e , it should be appreciated that the sensing wire may be connected to a different sensor, such as a pressure sensor, for example in the event that the control is not a feedback control based on the detected temperature. 
     The fuse F 2  of the thermal circuit  56   d  is thermally coupled to the heater track of the PCB  56   c . The PCB  56   c  may be, for example, about 0.05-0.15 mm thick, for example about 0.1 mm thick, have a resistance of about 0.05-0.15Ω, for example about 0.1Ω, and a power output of about 0.12-0.24 W, for example about 0.18 W. As discussed above, one side of the PCB  56   c  faces the open window  56   j  so the PCB  56   c  contacts the air in the patient conduit  4 . The air flowing in the conduit therefore cools the PCB  56   c  to just above the temperature of the air in the conduit. If the flow generator stops, or the air flow through the conduit is blocked, the temperature of the PCB  56   c  will rise and trip the fuse F 2  to protect the patient conduit  4  from damage. The temperature sensor  56   e  and the fuse F 2  of the thermal circuit  56   d  thus provide over air temperature protection, tube over heating protection, and low airflow protection. The thermal circuit  56   d  may include a thermostat, for example a bi-metal strip, instead of the fuse, and an increase in impedance of the thermostat would act to suppress, or stop, an increase in the current. 
     As the patient conduit  4  delivers the humidified air to the patient interface  5 , the power supply/controller  21 , the mask cuff  56  and its components, and the patient conduit  4  should comply with safety standards for temperature regulation, for example, ISO 8185. Under normal operating conditions, the patient or clinician should be able to set the temperature of the air delivered to the patient interface  5  from ambient to about 30° C. If no alarm system or indicator is provided to the system, in accordance with ISO 8185, sections 51.61-51.8, under normal and single fault conditions, the temperature of the air delivered to the patient interface  5  should not exceed about 40°-42° C., for example about 41° C. This maximum temperature (e.g. 41° C.) is under the maximum energy level of 43° C. at 100% RH. The fuse F 2  of the thermal circuit  56   d  may be chosen to trip off at the maximum temperature. 
     Referring again to  FIG.  36   , the three wire ( 4   c - 4   e ) electrical circuit of the patient conduit  4  includes the heating elements Ra, Rb in series with the heater track and fuse F 2  of the PCB  56   c , the wire  4   c  for supplying the sensing voltage Vsen, and the thermal sensor  56   e  including the thermal resistor TR 1  attached to the middle  4   f  of the of the heater wires  4   d ,  4   e . The electrical circuit has two states: ON and OFF. In the ON state, also referred to as the heating state, the wire  4   d  is connected at J 1  to the voltage V+, for example the 24V DC from the power output  21   f . The heating current flows through J 3 , wires  4   d ,  4   e , J 4  and the switch  21   b  and into ground GND. In the ON state, the sensing voltage Vsen at J 2  will not sense the air temperature, but will sense about half of voltage V+, e.g. about 12V. 
     In the OFF state, the switch  21   b  is switched off and the heater wires  4   d ,  4   e  will be pulled up by V+, e.g. about 24V, and the sensing current passes through J 1 , Ra, RT 1  and back to J 2 . 
     The power supply/controller  21  may include circuits for performing numerous functions. These circuits may include: 1) a power switching control circuit; 2) a tube interface and gate drive circuit (driver block); 3) a fault detection and latching circuit (fault detection latch); 4) a temperature preset/control circuit; and 5) a start up and indication circuit. 
     Power Supply/Controller Circuits 
     A sample embodiment of the circuits of the power supply/controller  21  is shown in  FIG.  37   a   . The circuit includes a temperature control circuit configured to control the temperature of the heated conduit(s), a fault detection latch, a sensing circuit and a driver block. The driver block is connected to the switch  21   b , which may be a MOSFET. 
     Referring to  FIGS.  37   b   - 1 - 37   b - 4 , a sample embodiment of the circuit of  FIG.  37   a    may be based on, for example, an UC2843 control IC, available from Texas Instruments. It should be appreciated that other control circuits may be used. The power switching control circuit has chip over-current and over-voltage protections which can be used for error handling. The power switching control circuit may also have an RC clock and under-voltage lockup and a push-pull output driver. By setting the oscillating RC clock such that R 12 =22,000Ω and C 5 =330 nF, the switch frequency may be set at 138 Hz. The time period for such a frequency is determined by T=R 12 ×C 15  (22,000×0.00000033)=7.26 mS. By ratio of R 12  and C 5 , the power switching control circuit provides a 100 μS OFF period, and the duty cycle is thus 100 μS/7.26 mS=1.38%. 
     At normal heating conditions, the power switching control circuit of  FIGS.  37   b   - 1 - 37   b - 4  drives the transistor gate of the switch  21   b  at about 98.62% duty cycles. The ON state of the circuit cannot be interrupted by Vfb signals. At the Vfb critical point, the gate signal can be shown as 50% 69 Hz outputs. 
     The power switching control circuit has enable input through the Vfb pin. When any of the signals through D 3  and D 4  to low, it will disable the output of the switch  21   c . The sensing current Isen is not used for this application as R 10  and R 20  set the sensing voltage Vsen below 1V. 
     Referring again to  FIGS.  37   a  and  37   b   - 1 - 37   b - 4 , the sensing voltage Vsen has two functions: 1) when the heater power is ON, the sensing voltage Vsen detects the heater wires continuity, or any arcing or bad connections by sensing middle voltage V+; and 2) when the heater power is OFF, the sensing voltage Vsen senses the air temperature via the RT 1  and R 13  divider voltages. The Q 2 , Q 3  network provides right logic for sensing operations and MOSFET Q3 provides low impedance (Rdson) for temperature sensing. Q 4  MOSFET gate drives network R 23 , R 25  limiting the maximum gate voltage; R 24  and D 5  together with R 23  control the Q 4  switch off speed. 
     The fault detection circuit operates when heater power is ON. The Vsen signal is fed into a window comparator, for example an ultra-power quad comparator, such as the LP339AM, available from National Semiconductor. U 6 B, U 6 D; R 31 , R 36  and R 43  divider provide a +/−2V window voltage at 12 Volt; the output of window comparator signals will feed into second stage of the comparator U 6 C. 
     The second stage of comparator samples the Q 4  gate signal as a base line and detecting the error signal from window comparator output. When system has no fault detected, window comparator outputs as high impedance, R 34  and R 40  divider has higher voltage out then inverting comparator input R 33  and R 42  divider network, U 6 C will output high. 
     When the system has a fault detected, window comparator outputs low, R 34  and R 40 //R 35  divider has lower voltage then inverting comparator input R 33  and R 42  divider network, U 6 C will output low to U 2 A latch CLR pin. 
     When latch CLR pin  1  receives a low signal the Q pin  5  will output a latched fault signal, it will kill the U 3  output switching signals. The latch may be, for example, a 74HCT74D U 2 A from Fairchild Semiconductor. 
     The temperature sensing operation is only performed during the power OFF period. The air temperature sensor RT 1  and divider base resistor R 13  provides the temperature information Vsen, it directly feed into the comparator U 6 A inverting input, a potentiometer and it&#39;s network does the temperature preset function. The output of this comparator drives D 4  and controls the U 3  switch output. 
     The start up circuit provides a 140 mS delay when system start up and it will reset the latch. After reset, the system will at ON state. The start up circuit may be, for example, an IC U4 TCM809, available from TelCom Semiconductor, Inc. 
     The accuracy of temperature measurement is based on two parts: 1) sensing accuracy; and 2) accuracy of reference. Sensing accuracy depends on NTC thermistor RT 1  and series resistor R 13 . For example, a good NTC sensor RT 1  may have up to a 1-5%, for example about 3%, accuracy tolerance; the series resistor R 13  may have up to a 0.5-1.5% tolerance, for example about a 1% tolerance. The accuracy of the temperature preset circuit is determined when the port is at highest setting (30° C.). The port resistor is 0Ω and the accuracy is dependent on the 1% resistor network. However, when the port is set to the lowest setting, 20% of the port resistor tolerance will be added in. 
     The conduits  4  and  10  will overheat when there is no gas flow in the tubes. The heat can be accumulated in the tube, if the tube is covered, for example under a quilt, and the heater element temperature can rise to 120-150° C. The heat can accrue when the thermal switch is exposed in cold air, but part of the tube was covered, for example under the quilt. For this reason, a no flow or low flow signal from the flow generator should able to trip off the heated tube power supply. 
     A three way connector is provided between thermistor sensor RT 1  and the control unit  21   c . Any bad connection on the contactor will cause increasing impedance on the sensing circuit; for NTC thermistor RT 1  it will lower the temperature readings, and it can cause air temperature rise and may trip the thermal switch  21   b  at the tube. 
     There are two ways to solve fault states in the temperature sensing. A first way is to change the voltage divider logics, as contact resistance is high the air temperature goes low. The other way to protect the sensing contactor is to off-set the sensing wire by changing R 6  and R 31  to 8.2 kΩ. This offset refrence voltage can detect the high impedance connectors. 
     Cuff Configurations 
     As shown in  FIGS.  38 - 40   , the configuration of the inlet conduit connector cuff and/or the patient conduit and mask connector cuff may take various forms. Each of the mask connector or cuff configurations shown and described herein may include grip features, and sufficient strain relief features to improve the flexibility of the connector or cuff. 
     Tube Configurations 
     Referring to  FIG.  41   , the inlet conduit  10  and/or the patient conduit  4  may include an inner tube  4   a ,  10   a , a helical rib  4   b ,  10   b , and an outer tube  4   f ,  10   f . The outer tube  4   f ,  10   f  may be formed of the same material as the inner tube  4   a ,  10   a . The outer tube  4   f ,  10   f  may also be provided with a fleece or flocked material to improve the feel and/or grip of the conduit, and/or to improve the thermal insulation properties of the tube and/or the visual appeal. If the outer tube  4   f ,  10   f  is not provided, the outer surfaces of the inner tube  4   a ,  10   a  and the helical rib  4   b ,  10   b  may be provided with a fleece or flocked material for similar reasons. 
     Referring to  FIG.  42   , the inlet conduit  10  and/or the patient conduit  4  may include an inner tube  4   a ,  10   a  and an outer tube  4   f ,  10   f  spaced by corrugations  4   g ,  10   g . The corrugations  4   g ,  10   g  may extend axially along the conduit  4 ,  10 , or may extend helically along the conduit  4 ,  10 . Wires may be provided within the corrugations  4   g ,  10   g , between the inner tube  4   a ,  10   a  and the outer tube  4   f ,  10   f . The corrugations may also be used to provide a supplemental gas flow along the conduit  4 ,  10 , or to provide a flow of liquid, for example water, to regulate the temperature of the gas flow in the conduit  4 ,  10 . The corrugations may also be used to exhaust gas, for example from the patient&#39;s exhalation, from the patient interface. The outer tube  4   f ,  10   f  may also be covered in fleece or flocked material. 
     Patient Conduit, Mask Connector Cuff, and Flexible Circuit 
     Referring to  FIG.  43   , a patient conduit  400 , mask connector cuff  560  and flexible circuit  570  according to another sample embodiment are illustrated. The patient conduit  400  is connected to the mask cuff  560  by an overmold material  580  that encompasses the flexible circuit  570 . The overmold material  580  is overmolded onto the patient conduit  400  and the mask cuff  560 . The flexible circuit  570  may include the tube wires, sensors, fuses and other components described above in relation to the other sample embodiments. 
     The mask cuff  560  may be formed as a separate part that is connected to the patient conduit  400  through the overmold material  580 . Alternatively, the mask cuff  560  may be formed as a single piece with the overmold material.  580 . 
     Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiments, it is recognized that departures can be made within the scope of the invention, which is not to be limited to the details described herein but is to embrace any and all equivalent assemblies, devices and apparatus. For example, the heating wires may be PTC elements with a voltage regulation to limit the temperature of the wires ad/or the air in the conduit(s). As another example, one or more PTC or NTC wires may be used in conjuction with a resistor to limit the temperature of the wires and the air. As a further example, NTC wires may be used with a current regulator, or a measure resistance, to limit the temperature of the heating wires. The temperature sensing and heating may also be performed using only two wires. 
     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.