Abstract:
This disclosure describes systems and methods for ventilating a patient with a gas mixture containing a low molecular weight gas, such as helium. The disclosure describes a novel proportional solenoid valve for controlling a low molecular weight gas mixture in a medical ventilator with reduced leakage.

Description:
INTRODUCTION 
       [0001]    Breathing devices such as medical ventilators and anesthetic apparatuses normally include an inspiratory side for supplying breathing gas toward a subject and an expiratory side for removing breathing gas from the subject. In the inspiratory side, an inspiration gas regulation device is situated to control flow of gas and/or pressure in the inspiratory side. The inspiratory side can also change and/or adjust the gas mixture concentrations sent to a patient during ventilation. The breathing device can receive pressurized gas from a compressor or centralized pressurized air source, such as wall outlet in a hospital. Often times, different gases or gas mixtures have separate sources or lines. Inspiration gas regulation devices can also be utilized to control the concentrations of the different gas sources received by the breathing device. A gas manifold can be utilized to combine the different regulated gases. 
         [0002]    The inspiration gas regulation devices can be valves. Valves can be controlled pneumatically, mechanically or electromechanically. Electromechanical actuators such as solenoids or voice coil motors have been used. 
         [0003]    However, typically utilized solenoid valves have a propensity leak when low density gases such as helium are utilized. This leakage makes it difficult to control the gas mixture delivered to the patient and is wasteful of the expensive, low density gas. 
       SUMMARY 
       [0004]    This disclosure describes systems and methods for ventilating a patient with a gas mixture containing a low molecular weight gas, such as helium. The disclosure describes a novel proportional solenoid valve for controlling a low molecular weight gas mixture in a medical ventilator with reduced leakage. 
         [0005]    This disclosure also describes a medical ventilator system including: a processor; a source of heliox; and a proportional solenoid valve controlled by the processor and adapted to control the flow of the heliox from the heliox source. The proportional solenoid valve further includes: a seat; a poppet; and an elastomeric material adhering to at least one of the seat and the poppet to form an elastomeric seal when the proportional solenoid valve is closed. 
         [0006]    Yet, another aspect of the disclosure describes a pneumatic system. The pneumatic system includes: a processor; a ventilation system including a patient circuit controlled by the processor; a pressure generating system controlled by the processor, the pressure generating system is adapted to generate a flow of breathing gas in the patient circuit; a source of heliox; and a proportional solenoid valve controlled by the processor and adapted to control the amount of the heliox delivered into the patient circuit. The proportional solenoid valve further includes: a seat; a poppet; and an elastomeric material adhering to at least one of the seat and the poppet to form an elastomeric seal when the proportional solenoid valve is closed. 
         [0007]    These and various other features as well as advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features are set forth in the description that follows and, in part, will be apparent from the description, or may be learned by practice of the described embodiments. The benefits and features will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0008]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following drawing figures, which form a part of this application, are illustrative of embodiments systems and methods described below and are not meant to limit the scope of the invention in any manner, which scope shall be based on the claims appended hereto. 
           [0010]      FIG. 1  illustrates an embodiment of a ventilator connected to a human patient. 
           [0011]      FIG. 2  illustrates an embodiment of a proportional solenoid valve for a ventilator. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Although the techniques introduced above and discussed in detail below may be implemented for a variety of medical devices, the present disclosure will discuss the implementation of these techniques in the context of a medical ventilator for use in providing ventilation support to a human patient. The reader will understand that the technology described in the context of a medical ventilator for human patients could be adapted for use with other systems such as ventilators for non-human patients and general gas transport systems in which periodic gas mixture changes may be required. As utilized herein a “gas mixture” includes at least one of a pure gas and a mixture of pure gases. 
         [0013]    Medical ventilators are used to provide a breathing gas to a patient who may otherwise be unable to breathe sufficiently. In modern medical facilities, pressurized air and oxygen sources are often available from wall outlets. Accordingly, ventilators may provide pressure regulating valves (or regulators) connected to centralized sources of pressurized air and pressurized oxygen. The regulating valves function to regulate flow so that respiratory gas having a desired concentration of oxygen and other gases is supplied to the patient at desired pressures and rates. Ventilators capable of operating independently of external sources of pressurized air are also available. 
         [0014]    While operating a ventilator, it can be desirable to add helium, heliox, or other gas mixtures with gas densities less than the density of air and/or oxygen to the breathing gas delivered to a patient. The gas density of helium is approximately 1/7 th  of the density of air. Such gases are typically referred to as “low density” or “low molecular weight” gas mixtures. Low molecular weight gas mixtures are often expensive and used only under special circumstances. 
         [0015]    Low molecular weight gas mixtures have the propensity to leak past most sealing interfaces that would otherwise be sufficiently effective for normal density gas mixtures. With air or oxygen gas, a metal-on-metal seat/poppet arrangement in a proportional solenoid valve is desirable for its clean, repeatable lift-off characteristics while maintaining reasonable leakage performance. For operation with low density gas mixtures, such as helium or heliox (a helium and oxygen gas mixture), however, a different sealing configuration is necessary due to the leakage allowed by a metal-on-metal seat/poppet arrangement. 
         [0016]    Accordingly, a proportional solenoid valve for use with a low molecular weight gas mixture, such as helium or heliox is desirable. In one embodiment, a proportional solenoid valve for use with a low molecular weight gas mixture includes a poppet design with a thin but durable elastomeric material adhering on top of a metal substrate. The metal seat remains unchanged compared the conventional metal-on-metal seat/poppet arrangement. In an alternative embodiment, a proportional solenoid valve for use with low molecular weight gas mixture includes a seat design with a thin but durable elastomeric material adhering on top of a metal substrate. The metal poppet remains unchanged compared the conventional metal-on-metal seat/poppet arrangement. In another embodiment, a proportional solenoid valve for use with low molecular weight gas mixture includes a poppet and seat design both with a thin but durable elastomeric material adhering on top of a metal substrate. 
         [0017]    With a soft material, a portion of the force budget for the valve is diverted from generating the opening for gas flow to sealing and compressing the elastomeric seal. A balance must be achieved in defining the thickness of the elastomeric material, the softness or durometer of the elastomeric material or sealing material, and the reduction in the effective stroke of the valve caused by the addition of the elastomeric material. 
         [0018]      FIG. 1  illustrates an embodiment of a ventilator  20  connected to a human patient  24 . Ventilator  20  includes a pneumatic system  22  (also referred to as a pressure generating system  22 ) for circulating breathing gases to and from patient  24  via the ventilation tubing system  26 , which couples the patient  24  to the pneumatic system  22  via physical patient interface  28  and ventilator circuit  30 . Ventilator circuit  30  could be a two-limb or one-limb circuit  30  for carrying gas mixture to and from the patient  24 . In a two-limb embodiment as shown, a wye fitting  36  may be provided as shown to couple the patient interface  28  to the inspiratory limb  32  and the expiratory limb  34  of the circuit  30 . 
         [0019]    The present systems and methods have proved particularly advantageous in invasive settings, such as with endotracheal tubes. However, the present description contemplates that the patient interface  28  may be invasive or non-invasive, and of any configuration suitable for communicating a flow of breathing gas from the patient circuit  30  to an airway of the patient  24 . Examples of suitable patient interface  28  devices include a nasal mask, nasal/oral mask (which is shown in  FIG. 1 ), nasal prong, full-face mask, tracheal tube, endotracheal tube, nasal pillow, etc. 
         [0020]    Pneumatic system  22  may be configured in a variety of ways. In the present example, system  22  includes an expiratory module  40  coupled with an expiratory limb  34  and an inspiratory module  42  coupled with an inspiratory limb  32 . The inspiratory limb  32  receives a gas mixture from one or more gas sources  48  controlled by one or more gas regulators or gas regulation devices  46 . 
         [0021]    For instance, a helium/heliox gas source  48  and/or another source or sources of pressurized gas mixture (e.g., pressured air and/or oxygen) is controlled through the use of one or more gas regulators or gas regulation devices  46 . In the embodiment shown, the gas regulator  46  includes a proportional solenoid valve for low density gases. As shown in  FIG. 1 , the gas regulator  46  is located within the ventilator  20 . In one embodiment, the gas regulator  46  is located within the pneumatic system  22 . In an alternative embodiment, the gas regulator  46  and/or proportional solenoid valve is a separate component independent of the ventilator  20 . 
         [0022]    In the illustrated embodiment, the gas regulator  46  and/or proportional solenoid valve is controlled by the ventilator  20 . In one embodiment, the gas regulator  46  and/or proportional solenoid valve is controlled by the pneumatic system  22 . In a further embodiment, the gas regulator  46  and/or proportional solenoid valve is controlled by the controller  50 . In an alternative embodiment, the gas regulator  46  and/or proportional solenoid valve is controlled by a processor separate from and independent of the medical ventilator. 
         [0023]    In the embodiment shown, the proportional solenoid valve has an elastomeric seal specific for low density gases. The elastomeric material may be any suitable material for substantially preventing a low molecular weight gas mixture from leaking through the proportional solenoid valve when closed. Accordingly, the processor for controlling the proportional solenoid valve for low density gases includes the information necessary to control the proportional solenoid valve for low density gases differently from the other valves to get accurate gas blends in the accumulator. In one embodiment, the proportional solenoid valve for low density gases includes lookup tables, formulae, logic, and etc. to control the proportional solenoid valve for low density gases differently from the other valves to get accurate gas blends in the accumulator. 
         [0024]    Further, the gas concentrations can be mixed and/or stored in a chamber of a gas accumulator  44  at a high pressure to improve the control of delivery of respiratory gas to the ventilator circuit  30 . The inspiratory module  42  is coupled to the helium/heliox gas source  48  and/or another gas mixture source, the gas regulator  46 , and accumulator  44  to control the gas mixture of pressurized breathing gas for ventilatory support via inspiratory limb  32 . 
         [0025]    The pneumatic system  22  may include a variety of other components, including other sources for pressurized air and/or oxygen, mixing modules, valves, sensors, tubing, filters, etc. Controller  50  is operatively coupled with pneumatic system  22 , signal measurement and acquisition systems, and an operator interface  52  may be provided to enable an operator to interact with the ventilator  20  (e.g., change ventilator settings, select operational modes, view monitored parameters, etc.). Controller  50  may include memory  54 , one or more processors  56 , storage  58 , and/or other components of the type commonly found in command and control computing devices. 
         [0026]    The memory  54  is computer-readable storage media that stores software that is executed by the processor  56  and which controls the operation of the ventilator  20 . In an embodiment, the memory  54  comprises one or more solid-state storage devices such as flash memory chips. In an alternative embodiment, the memory  54  may be mass storage connected to the processor  56  through a mass storage controller (not shown) and a communications bus (not shown). Although the description of computer-readable media contained herein refers to a solid-state storage, it should be appreciated by those skilled in the art that computer-readable storage media can be any available media that can be accessed by the processor  56 . Computer-readable storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. Computer-readable storage media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, DVD, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the processor  56 . 
         [0027]    The controller  50  issues commands to pneumatic system  22  in order to control the breathing assistance provided to the patient  24  by the ventilator  20 . The specific commands may be based on inputs received from patient  24 , pneumatic system  22  and sensors, operator interface  52  and/or other components of the ventilator  20 . In the depicted example, operator interface  52  includes a display  59  that is touch-sensitive, enabling the display  59  to serve both as an input user interface and an output device. The display  59  can display any type of ventilation information, such as sensor readings, parameters, commands, alarms, warnings, and smart prompts (i.e., ventilator determined operator suggestions). 
         [0028]      FIG. 2 , illustrates an embodiment of a proportional solenoid valve  200  for low molecular weight gas mixture, such as in a ventilator  20  described above. The proportional solenoid valve  200  has an inlet  210  and an outlet  212  for breathing gas. 
         [0029]    A valve seat  204  and a poppet  202  are arranged in the valve  200  to interact with each other for control of a valve opening, i.e. distance between valve seat  204  and poppet  202 . In the embodiment shown, an elastomeric material  206  is adhered to the poppet  202 . In an alternative embodiment, the elastomeric material  206  is adhered to the seat  204  of the proportional solenoid valve  200 . In another embodiment, the elastomeric material  206  is adhered to both the seat  204  and the poppet  202  of the proportional solenoid valve  200 . 
         [0030]    The elastomeric material  206  may be any suitable material for preventing a low molecular weight gas mixture from substantially leaking through the proportional solenoid valve  200  when closed. In one embodiment, the elastomeric material  206  is selected from the group of silicone, viton, buna-N (Nitrile), ethylene propylene, and neoprene. In another embodiment, the elastomeric material  206  is selected from the group of butyl rubber, fluorocarbon, and polyurethane. 
         [0031]    An actuator  208  controls the force exercised on the valve stem to move the poppet  202  away from the valve seat  204  depending on the control signal from a controller  50  ( FIG. 1 ). As the poppet  202  moves away from the seat  204  the inlet  210  is opened allowing the gas mixture to flow into the proportional solenoid valve  200  and out of the proportional solenoid valve  200  through the outlet  212 . By altering the force from the actuator  208 , the flow in the inspiration tube from the gas source to the patient circuit can be controlled. 
         [0032]    The actuator  208  also controls the force exercised on the poppet  202  to move it towards the valve seat  204  depending on the control signal from a controller  50  ( FIG. 1 ) for compressing the elastomeric material  206  to seal the gas inlet  210 . Further, depending upon the embodiment, such as the adhering of the elastomeric material  206  to the seat  204 , poppet  202 , and/or both, the thickness and the softness or the durometer of the elastomeric material  206  is specifically chosen to reduce and/or prevent a gas mixture with a molecular weight of less than air and/or oxygen from leaking through the proportional solenoid valve  200 . Further, the addition of the elastomeric material  206  causes a reduction in the effective stroke of the proportional solenoid valve  200 . As used herein “the effective stroke” of the proportional solenoid valve  200  is the distance the poppet  202  can move when acted upon by the actuator  208 . In order to produce a proportional solenoid valve  200  that substantially reduces any leaking of a low molecular weight gas mixture, such as helium or heliox, a balance must be achieved in defining the thickness of the elastomeric material  206 , the softness or durometer of the elastomeric material  206 , and the reduction in the effective stroke of the proportional solenoid valve  200 . As used herein, “substantially reduces any leaking” of the proportional solenoid valve  200  is when the amount of gas mixture leaked through the gas inlet  210  is less than or equal to about 0.010 standard liters per minute as measured with air under normal operating conditions. Air is utilized as the reference gas because flow sensors with helium calibration were not readily available. 
         [0033]    Unless otherwise indicated, all numbers expressing quantities, properties, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. 
         [0034]    Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure and as defined in the appended claims. While various embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure and as defined in the appended claims.