Abstract:
A gas and air mixing device receives a pressurised supply of a gas, drawing an air supply from the ambient environment and outputs a pressurised combined mixture of air and said gas. The device includes a turbine with a gases inlet and a gases outlet and a pump with an air inlet and an air outlet. A combined gases outlet receives gases from the gases outlet of the turbine and air from the air outlet of the pump. The combined gases outlet ouputs a combined flow of the gases. The turbine is configured to drive the pump.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to devices for the mixing of air and oxygen in a medical environment.  
           [0003]    2. Summary of the Prior Art  
           [0004]    It is often desirable to supply a patient or person with an air stream enriched in oxygen to a greater concentration than ambient air. For this purpose a supply of oxygen is mixed with a supply of air for breathing by the patient.  
           [0005]    Where a patient is capable of normal breathing, an air entrainer may be added to a breathing intake tube. The air entrainer includes an oxygen inlet nozzle receiving a high pressure oxygen supply from a high pressure oxygen supply source. An air inlet port is provided in the wall of the entrainer adjacent the nozzle outlet. High velocity oxygen flow through the nozzle outlet and into the conduit draws air into the conduit through the air inlet port. This air becomes mixed with the oxygen flow as it passes along the conduit to the patient. The mixing ratio may be adjusted by adjusting the size of the air inlet opening. The passive air entrainer is effective where the conduit has no significant resistance to flow. The passive air entrainer is unable to operate effectively where there is a significant flow resistance.  
           [0006]    For example, where the patient requires positive pressure therapy the air entrainer is ineffective. Positive pressure therapy is presently considered desirable in treatment in a range of respiratory ailments.  
           [0007]    In many situations it is desirable to humidify respiratory gases provided to a patient. Many devices used to humidify such gases unavoidably add significant flow resistance to the breathing intake tube. Air entrainers that operate in the manner described above must therefore be placed between the humidification device and the patient to operate correctly. The consequence of this placement is that the entrained ambient air does not pass through the humidifier and is not humidified.  
           [0008]    To overcome this difficulty an alternative mixed air/oxygen supply apparatus is commonly used in which the supplied gases are drawn from a compressed air supply and a compressed oxygen supply. Each gas is supplied through a regulator valve. The relative flow rate of each gas is thereby adjustable and the flows undergo a simple combination into a supply conduit.  
           [0009]    Alternatively a mixed air/oxygen supply apparatus known as a blender uses partial pressure to provide a pressurised source of air and oxygen, controlling the source pressure of each of the gases to be mixed. Such a device comes with a dial to set the oxygen concentration of the new pressurised source. A blender is usually connected to a regulator valve with which the user can set the desired flow rate of the blended gas.  
           [0010]    Both these systems can provide a high pressure air/oxygen mixture which can be used to provide positive pressure therapy and is suitable to supply gases via a humidifier. The disadvantage of these systems is the need for a compressed air supply in addition to the compressed oxygen supply, and in the case of the blender, considerable cost.  
         SUMMARY OF THE INVENTION  
         [0011]    t is an object of the present invention to provide an air/oxygen mixing device which at least goes some way towards overcoming the above disadvantages or will at least provide health providers with a useful choice.  
           [0012]    In a first aspect the present invention may broadly be said to consist in a gas and air mixing device for receiving a pressurised supply of a gas, drawing an air supply from the ambient environment and outputting a pressurised combined mixture of air and said gas comprising:  
           [0013]    a turbine having a gases inlet and a gases outlet,  
           [0014]    a pump having an air inlet and an air outlet, and  
           [0015]    a combined gases outlet receiving gases from said gases outlet of said turbine and air from said air outlet of said pump and outputting a combined flow,  
           [0016]    said turbine being configured to drive said pump.  
           [0017]    Preferably said turbine comprises:  
           [0018]    a first chamber having an oxygen inlet and an oxygen outlet and a turbine in said first chamber receiving oxygen from said oxygen inlet;  
           [0019]    said pump comprises:  
           [0020]    a second chamber having an air inlet and an air outlet, and  
           [0021]    an impeller in said second chamber receiving air from said air inlet; and  
           [0022]    a drive train connects between said turbine and said impeller.  
           [0023]    Preferably each of the components is formed from medical grade plastics, for example by injection moulding. Some forms of turbine in particular may be difficult to form by injection moulding in one piece and may be instead formed as two pieces combined by ultrasonic welding, fasteners, adhesive bonding, integral clipping or other equivalent arrangements. Some other parts may require strength or other properties not obtainable with plastic and may be formed from another material such as aluminium, magnesium or stainless steel.  
           [0024]    Preferably the oxygen inlet is configured for connection with an oxygen wall outlet or a compressed oxygen bottle outlet.  
           [0025]    Preferably said gas inlets and outlets may include adjustable flow dampers.  
           [0026]    Preferably said adjustable flow dampers include a calibration system corresponding with the proportion of air or oxygen in the mixed flow for at least one set oxygen inlet pressure.  
           [0027]    Preferably said first chamber and said second chamber are back to back, said turbine and said impeller are co-axial, and said drive train comprises a shaft, and both said turbine and said impeller are connected to said shaft.  
           [0028]    Preferably said shaft is an integrally formed extension from the centre of said impeller, extending through a dividing wall between said first chamber and said second chamber, into said first chamber, and said turbine is mounted on said extension.  
           [0029]    Preferably said first chamber is formed by a cover member fitted to said dividing wall enclosing said turbine.  
           [0030]    Preferably said second chamber is formed from a cover, fitted to said dividing wall and enclosing said impeller, said second cover including an air inlet at the centre of its main face.  
           [0031]    Alternatively said device is arranged axially, said turbine comprising  
           [0032]    an axial turbine having a gases inlet and gases outlet,  
           [0033]    said pump comprising an axial pump receiving gases from said gases outlet of said turbine and air from a separate air inlet, and  
           [0034]    said combined gases outlet receiving gases from said pump and outputting a combined flow;  
           [0035]    with said turbine and pump being arranged in axial alignment and said turbine being configured to drive said pump.  
           [0036]    Preferably said device includes a housing with a first section and a second section, said first section having said oxygen inlet and said oxygen outlet and housing a rotor of said turbine; and  
           [0037]    said second section having an air inlet, an oxygen inlet and said pump gases outlet, and  
           [0038]    housing an impeller,  
           [0039]    a drive train connecting between said rotor and said impeller.  
           [0040]    Preferably each of the components is formed from medical grade plastics, for example by injection moulding. Some forms of turbine in particular maybe difficult to form by injection moulding in one piece and may be instead formed as two pieces combined by ultrasonic welding, fasteners, adhesive bonding, integral, clipping or other equivalent arrangements. Some other parts may require strength or other properties not obtainable with plastic and may be formed from another material such as aluminium, magnesium or stainless steel.  
           [0041]    Preferably the oxygen inlet of said first section is configured for connection with an oxygen wall outlet or a compressed oxygen bottle outlet.  
           [0042]    Preferably said gas inlets and outlets may include adjustable flow dampers.  
           [0043]    Preferably said adjustable flow dampers include a calibration system corresponding with the proportion of air or oxygen in the mixed flow for at least one set oxygen inlet pressure.  
           [0044]    Preferably said first section and said second section are coaxial and concentric over at least part of their length, said turbine rotor and said impeller are co-axial, and said drive train comprises a shaft, and both said turbine and said impeller are connected to said shaft.  
           [0045]    Preferably said shaft is an integrally formed extension from the centre of said impeller, mounted concentrically within said first and second sections.  
           [0046]    Preferably said first and second sections are connected in a manner which allows unrestricted flow of ambient air into said second section whilst remaining structurally sufficient.  
           [0047]    To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0048]    [0048]FIG. 1 is a cross sectional front elevation through an air oxygen mixer according to the present invention.  
         [0049]    [0049]FIG. 2 is a front elevation of the air/oxygen mixer of FIG. 1.  
         [0050]    [0050]FIG. 3 is a side elevation of the air/oxygen mixer of FIG. 1.  
         [0051]    [0051]FIG. 4 is a perspective exploded view of the air/oxygen mixer of FIG. 1.  
         [0052]    [0052]FIG. 5 is a top view of the mixer of FIG. 1 as connected in use including the combined flow outlet and the oxygen inlet connection.  
         [0053]    [0053]FIG. 6 is a perspective view of the air inlet portion of a second chamber housing according to a preferred embodiment of the present invention with partial cutaway.  
         [0054]    [0054]FIG. 7 is a perspective exploded view of an air/oxygen mixer according to another embodiment of the present invention.  
         [0055]    [0055]FIG. 8 is a cross sectional exploded view of the air/oxygen mixer of FIG. 7.  
         [0056]    [0056]FIG. 9 is a perspective view of the assembled air/oxygen mixer of FIG. 7. 
     
    
     DETAILED DESCRIPTION  
       [0057]    One preferred embodiment of the present invention is disclosed in the Figures. It will be appreciated that significant variations may be applied to this preferred embodiment without departing from the scope of the present invention.  
         [0058]    Referring in particular to FIGS. 1, 2 and  5  the oxygen mixing device according to the preferred embodiment includes a first chamber  1  enclosing a turbine rotor  2  and a second chamber  3  enclosing an impeller  4 . A shaft  5  extends from the impeller  4  into the first chamber  1 . The turbine rotor  2  is mounted on the shaft  5 .  
         [0059]    In one preferred form, the turbine is of a Pelton wheel type, and the rotor  2  includes a plurality of peripheral cups formed as depressions  8  in its annular face  9 . Compressed oxygen is supplied through an oxygen inlet  6 . The compressed oxygen leaves the oxygen inlet  6  as a jet and impacts the cups of turbine rotor  2 , driving rotation of turbine rotor  2 . The air exits the turbine enclosure  1  through an oxygen outlet  10 . Rotation of the rotor  2  rotates shaft  5  and impeller  4 . The impeller  4  is a centrifugal air pump impeller. Rotation of impeller  4  draws air through an air inlet  13  adjacent the centre of impeller  4 . The air is spun outwards between the impeller blades to a peripheral exit zone  14  and exits by exit  15 .  
         [0060]    A flow combining connector is connected with the oxygen outlet  10  and the air outlet  15 . The flow combining connector comprises for example a flexible tube Y-piece  16  with a first end  17  fitted over oxygen outlet  10  and a second end  18  fitted over air outlet  15 , the flows combining through a third leg  19 .  
         [0061]    In the preferred embodiment of the invention the first chamber  1  is formed between a first cover  30  and a dividing wall member  32  and the second chamber  3  is enclosed between a second cover  34  and the dividing wall member  32 . The dividing wall member  32  is a substantially circular disk and includes an annular flange  38  extending from one face to support the rim of cover  30  and an annular flange  36  extending from its other face to support the rim of cover  34 . The dividing member  32  includes a central aperture  40  receiving the shaft  5  therethrough. An annular flange  42  surrounding aperture  40  extends from the air chamber surface of dividing member  32 , and a similar annular flange  44  extends from the oxygen chamber face of member  32 . The flanges provide additional bearing support for the shaft  5  and thrust bearing surfaces for the impeller  4  and rotor  2 . Additional bearings may be used between the flanges  42  and  44  and the shaft  5  to provide a longer life product. The air chamber cover  34  includes air inlet  13  as an open short tube  50  extending from the centre of its main face. The oxygen chamber cover  30  includes oxygen outlet  6  as an open short tube  52  extending from the centre of its main face.  
         [0062]    Accordingly, in the preferred embodiment of the present invention the device is comprised of six components—the first cover  30 , the second cover  34 , the dividing wall member  32 , the impeller (with integral shaft  5 ), the turbine  2  and the flow combining connector  16 .  
         [0063]    It should be appreciated that substantial variation in the actual construction is possible without departing from the scope of the invention, and advantageous variations may include integrating the flow combining connector  16  with the covers  30  and  34  (for example by providing the outlet passages  10  and  15  as a combination of the cover  30  or  34  respectively and the dividing wall  32 , and leading to a common location to combine as a single outlet connector). Other variations may include using other forms of turbine for extracting energy from the high pressure oxygen flow, and/or other forms of impeller for creating the air flow.  
         [0064]    Another modification may include the provision of an inlet air damper on air inlet  13 . An example of an appropriate adapter is depicted in FIG. 6 where air inlet tube  13  is partially enclosed by covering face end  62 . A cap  64  is fitted over the inlet tube  50 , and retained in place by channel  55  fitting over protrusions  68  from the cylindrical surface of inlet tube  50 . The cap  64  includes a cylindrical body and an enclosed end  69 . The enclosed end  69  includes a tapering aperture  70  with a graduated scale marked around its outer perimeter.  
         [0065]    In use the orientation of the cap  64  on the inlet tube  50  determines the size of the inlet opening by the intersection between the aperture  70  and the uncovered portion of the end of tube  50 . The graduated scale of aperture  70  may be calibrated for a set oxygen inlet pressure with a scale corresponding to the proportion of air resulting in the air/oxygen mix. The indicator relative to the scale maybe the edge  72  of the covered in portion  62  of the end of tube  50 . The cap  64  is rotatable on the tube  50  by sliding of protrusions  68  within channel  65  to vary the amount of opening of the air inlet.  
         [0066]    The device is illustrated in use in FIG. 5. A compressed oxygen supply tube  82  is connected with the short oxygen supply tube of housing  30  via a connector  80 . The flow combining connector  16  is connected with a breathing tube  20 . When the compressed oxygen supply is started this spins turbine rotor  2  in its passage through the first chamber to outlet  10 . Rotor  2  spins impeller  4  causing the impeller  4  to draw air into the second chamber  3  through inlet  50  and expel the air through outlet  15 . The outlet flows combine in connector  16  and exit to breathing conduit  20  under pressure.  
         [0067]    A second preferred embodiment of the present invention is disclosed in FIGS. 7, 8 and  9 . It will be appreciated that significant variations maybe also be applied to this second preferred embodiment without departing from the scope of the present invention.  
         [0068]    The second embodiment is an axial arrangement. It includes an axial flow turbine and an axial flow pump. The axial flow turbine and pump are arranged end to end. The turbine includes a rotor or impeller  97 , and the pump includes an impeller  98 , with the turbine rotor  97  arranged to drive the pump impeller  98 .  
         [0069]    The turbine impeller  97  and the pump impeller  98  are located on a common shaft. A first housing surrounds the turbine impeller  97 . The first housing includes an oxygen inlet  90  and an oxygen outlet  92 . A second housing is coaxial with the first housing, and is concentric with the first housing over a part of their length where the two housings overlap. The second housing is greater diameter than the first housing at this overlap. The second housing thus has, centrally, an inlet for oxygen that has passed through the turbine, and an annular air inlet  100  surrounding the outlet end of the first housing.  
         [0070]    The shaft  96  is supported so as not to impede flow either side of the impellers. Struts  92  protuding from the inner surface of the oxygen inlet casing support the shaft at the turbine end and similar struts  93  at the fan end. These struts can be shaped aerodynamically to reduce resistance to flow past them and to have positive effects on flow characteristics either side of the impellers.  
         [0071]    High pressure oxygen flowing through the oxygen inlet must pass by the axial turbine impeller  97  thereby imparting a force that will rotate the shaft. This forced rotation is transmitted to the axial fan impeller  98 . The rotation of the fan impeller, which is larger diameter than the outlet end of the first housing, sucks ambient air through the air inlet  100  where it becomes mixed with oxygen that has passed through both the turbine and fan blades. The mixture of gases is then driven through gases outlet  99  by the pressure created by the fan impeller  98 .  
         [0072]    So for example the device may receive an oxygen supply at 50 psi above ambient pressure and an air supply at ambient pressure, receiving approximately 20 litres of oxygen per minute and extracting energy from the oxygen flow to drive the air pump. In turn the air pump sucks in the ambient air and supplies it at its outlet at for example 2 psi above ambient pressure and at a flow of 20 litres per minute, providing a combined flow from outlet connector  99  of 40 litres per minute at 2 psi static pressure at approximately 60% Oxygen.  
         [0073]    It will therefore be appreciated that the oxygen supply side remains under pressure from its supply source and the air supply side is positively driven by the pump impeller. This makes the device less susceptible to circuit back pressures than a passive air entrainer, while eliminating the need for a compressed air supply.