Abstract:
A ventilatory system for providing ventilatory support to a patient without the need for an external source of pressurized drive gas. The ventilatory system comprises a drive pump and a controller such that the drive pump collects ambient air and may pressurize it to a pressure determined by the controller. The controller may signal to the drive pump to pressurize the collected ambient air to a first pressure for delivering ventilatory support to a patient and a second pressure for providing PEEP support to a patient. The controller may signal to the drive pump to deliver a targeted flow and/or volume of collected ambient air to the bellows to provide volumetric ventilatory support during inhalation and a PEEP support during exhalation.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The disclosure is directed towards mechanical ventilators for providing a patient with respiratory support including the delivery of anesthesia as well as ventilatory support. Specifically, the disclosure is directed towards a mechanical ventilator with increased mobility. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    Patients that have respiratory difficulties often must be placed on a mechanical ventilator. These respiratory difficulties may be pathological in nature or may be due to the fact that the patient is too weak or sedated to independently perform respiration functions. Often, the patient may be spontaneously attempting to breathe but is not able to complete a full respiratory cycle. In these cases, mechanically assisted ventilation is provided. In some mechanically assisted ventilation platforms, a combination of pressure and/or flow sensors detect a patient&#39;s breath attempt. Detection of a breath attempt triggers the mechanical delivery of a breath. The breath is provided by the delivery of medical gases under a pressure that is sufficient to overcome the system resistance and the patient&#39;s airway resistance to fill the lungs in an inspiratory phase. When the pressure of the medical gas is reduced, the natural elasticity of the patient&#39;s chest wall forces the delivered breath out of the patient in an expiratory phase. 
         [0003]    The medical gases supplied to the patient may comprise air, oxygen, helium, nitric oxide, anesthetic agent, drug aerosol, or any other gas breathed by the patient. Air is referred to as the drive gas for the ventilator system and any other medical gases are referred to as supplemental gases to the air. 
         [0004]    The healthcare industry faces the challenge of providing higher quality care, while reducing the cost of providing that care. One aspect of the challenge to reduce cost is to reduce the fundamental costs that are associated with the provision of healthcare. Fundamental costs are the costs that are associated with the infrastructure needed to provide medical care to patients, for example, the costs of medical gas used to provide ventilatory support. Additionally, a need exists for an improved quality of care provided in remote locations such as military field hospitals, third world countries, and rescue or emergency situations. One aspect that is common to meeting these challenges is to provide equipment that is mobile. The mobility of a piece of equipment includes reducing the equipment&#39;s need for external components, such as tanks of medical gas, or an external medical gas supply. The increased mobility of a piece of equipment allows for it to be moved around a hospital to the area where it is currently needed and allows for a piece of equipment to be transported to a remote location where other less portable equipment is not available. 
         [0005]    There are currently a wide variety of systems available to provide ventilatory support to a patient, or to provide anesthesia delivery to a patient. There are systems that combine both of these functionalities, as disclosed in U.S. Pat. No. 5,315,989, which is incorporated in its entirety herein; however, these systems require a supply of pressurized medical gas in order to provide the respiratory support to the patient. Medical gas is often supplied from pressurized supply tanks, or medical gas may be delivered to the ventilator via gas connections in the wall of a room in the hospital. Dependence upon fixed-location gas connections severely limits the portability of a ventilatory system as the system can only be used in those rooms that have been outfitted with medical gas supply lines, tapping into a centralized supply of medical gas. Furthermore, dependence upon medical gas supply lines increases the cost of adding additional rooms to a hospital facility since each of these new rooms must be connected to the centralized supply of medical gas and outfitted with the medical gas supply lines. Alternatively, smaller and thus more portable medical gas supply tanks may be used by an individual ventilatory system. However, these tanks are more expensive and, while mobile, are still cumbersome to transport. 
         [0006]    A third type of ventilatory system currently available reduces the need for a supply of medical gas, where the medical gas to be used is air, by integrating a pump with the ventilatory system such that the pump pressurizes the ambient air to the pressure required by the ventilatory system. Ventilatory systems integrated with a high pressure pump for pressurizing ambient air suffer from limitations inherent with high pressure pumps. In general, high pressure pumps suffer from the fact that they are relatively large and heavy which thus reduces the portability of systems using these pumps. The weight of the pump is counter-productive as the implementation of a ventilatory system with a pump is generally for the purpose of making the ventilatory system a mobile one. Alternatively, non-high pressure pump systems (e.g., blower or turbine systems) generally have a slow response time for delivering the proper supply of medical gas to the patient at the proper time. To compensate for this, non-high pressure pump systems are used with complicated valves and circuitry, thus increasing the amount of power used to operate the ventilator system. This too is not desirable in a mobile ventilatory support system. 
         [0007]    Therefore, a patient respiratory support system that can provide sufficient medical gas pressure to ensure proper patient ventilation, provide a fast response time to continually adjust the pressure delivered in conjunction with the patient&#39;s respiratory cycle, provide low power consumption, and reduced system size and weight is desirable. A patient&#39;s respiratory support system that uses a pump that combines these qualities would greatly increase the mobility of a patient respiratory support system, thus allowing greater flexibility in the locations where the patient may receive respiratory support. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    Embodiments provide a patient respiratory support system that is mobile, has a fast response time, and conserves electrical power when compared to high pressure compressor pump systems. The patient respiratory support system of the present invention utilizes a drive pump to control the delivery of the medical gas to the patient. The drive pump provides a dependable source of high flow rate and energy efficient drive gas supply for the ventilatory system of the present invention. Thus, a ventilatory system comprising a drive pump provides a solution to hospitals with budgetary needs due to the fact that the drive pump can provide the needed pressurized medical gas to a ventilatory system capable of providing either ventilatory support or anesthesia delivery support to a patient. Because of the mobile nature of the present invention, the present invention may be moved about the medical facility to provide respiratory support to a patient that needs it, thus increasing the scalability of a brick and mortar medical care facility. 
         [0009]    A further embodiment, utilizes an oscillating pump as the drive pump for producing a flow of ambient air. 
         [0010]    In another embodiment, the drive pump is capable of pressurizing the ventilatory system to provide positive end expiratory pressure (PEEP) support. 
         [0011]    In a still further embodiment, the ventilatory system comprises a sound dampening device to reduce the noise exterior to the drive pump. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The drawings illustrate the best mode presently contemplated of carrying out the invention. In the drawings: 
           [0013]      FIG. 1  is a schematic diagram of the pneumatic system of a prior art ventilatory system; 
           [0014]      FIG. 2  is a schematic diagram of the pneumatic system of an embodiment; 
           [0015]      FIG. 3  is an overhead view of the general physical structure of the linear oscillating pump; 
           [0016]      FIG. 4  is a side view of the motor core and windings cut along line  4 - 4 ; 
           [0017]      FIG. 5  is a schematic diagram of the electrical signals used to drive the linear oscillating pump; 
           [0018]      FIG. 6A  is a graph depicting the output pressure of the linear pump before receiving pressure damping; and 
           [0019]      FIG. 6B  is a graph of the output pressure of the linear oscillating pump after receiving pressure damping: 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  depicts a schematic diagram of a ventilatory system  10  known in the art. A ventilator of this system is described in U.S. Pat. No. 5,315,989 to Tobia, which is herein incorporated in its entirety by reference. In ventilatory system  10 , a pressurized source of medical gas  12  is connected to a regulator  14  and a gas inlet valve  16 . The pressurized medical gas serves as the drive gas for operating the ventilatory system  10 . The pressurized gas flows from the inlet valve  16  to an inspiratory flow control valve  18 . Typically, the inspiratory flow control valve  18  is a proportional flow solenoid valve, but many other suitable types of valves exist, including single or multiple pulse-width modulated (PWM) two-position valves. The inspiratory flow control valve  18  is controlled by CPU  20  via line  22 . The CPU  20  directs the inspiratory flow control valve  18  to open and close according to the pressure that is desired to be in a first inspiratory conduit  24 . The pressure in inspiratory conduit  24  is measured by manifold pressure sensor  26  which sends a pressure signal via line  28  back to the CPU  20 . 
         [0021]    Inspiratory flow control valve  18  opens and closes upon direction by CPU  20  such that the constant supply of pressurized medical gas from the gas source  12  is controlled to produce varying pressures within the first inspiratory conduit  24 . Medical gas in the first inspiratory conduit  24  flows through a check valve  30  into conduit  32 . Check valve  30  typically requires a threshold pressure in inspiratory conduit  24  in order to open, allowing medical gas to flow into the second inspiratory conduit  32 . In an embodiment, the check valve  30  may require pressure greater than 3.5 cmH 2 O in the first inspiratory conduit  24 . Second inspiratory conduit  32  further comprises a mechanical overpressure valve  34 . The mechanical overpressure valve  34  maintains safety of the patient receiving mechanical ventilation by venting any excess pressure in and above a threshold amount, typically about 110 cmH 2 O within the second inspiratory conduit  32  and venting it to the ambient air. Thus, the pressure in the second inspiratory conduit  32  is maintained at a pressure safe for the patient. 
         [0022]    The drive gas in second inspiratory conduit  32  is directed to bellows chamber  42  of the bellows assembly  36 . The drive gas pressurizes the bellows chamber  42  and compresses the bellows  40 . A free breathing check valve  38  is also disposed within the second inspiratory conduit  32 . If the patient receiving mechanical ventilation begins to spontaneously breathe the bellows assembly  36  must have a source of gas to deflate the bellows  40  independently of the drive gas. Therefore, the presence of a negative pressure in the bellows  40  relative to the pressure in the bellows chamber  42  will result in the opening of the free breathing check valve  38  such that ambient air is drawn into the second inspiratory conduit  32  and directed to bellows chamber  42  such that the bellows  40  may be compressed and the patient can take a spontaneous breath. The compression of the bellows  40  directs the gas within the bellows  40  to a conduit  44 . The conduit  44  is disposed for connection to a patient interface (not depicted) that delivers the medical gas to the patient. The drive gas in the bellows chamber  42  is released through expiratory conduit  46  to an exhalation valve  48 . The exhalation valve  48  controls any positive end expiratory pressure (PEEP) that is to be provided to the patient. 
         [0023]    PEEP is a type of ventilatory therapy wherein upon patient exhalation, the patient&#39;s airway is not returned to the ambient pressure, but instead is held at a pressure above ambient that is determined by the clinician. The PEEP pressure serves to keep the patient&#39;s lungs partially inflated and open thereby reducing the patient&#39;s airway resistance, increasing lung compliance, and preventing alveolar collapse, or atelectasis. The effect is akin to a rubber balloon which is easier to inflate once it is started by a small inflationary pressure. Keeping the patient lungs partially inflated at the end of expiration also results in the exposure of more of the delivered medical gas to the alveoli that perform the gas exchange within the patient&#39;s lungs, thus making the gas exchange more efficient and the ventilation of the patient more effective. 
         [0024]    A system for providing PEEP control for a ventilatory system is described in U.S. Pat. No. 5,651,360 to Tobia, which is herein incorporated in its entirety by reference. During exhalation, the exhalation valve  48  controls the pressure of the air in the bellows and correspondingly the pressure of the air in the patient&#39;s lungs. The pressure in pressure control conduit  50  controls the pressure restriction provided by the pneumatic exhalation valve  48 . Pressure control conduit  50  is pressurized to the same pressure as first inspiratory conduit  24  as the pressure control conduit  50  and the first inspiratory conduit  24  are fluidly connected. During exhalation, check valve  30  is sealed because pressure in the bellows chamber  42  plus the bias pressure required to open the check valve  30  is greater than the pressure in the inspiratory conduit  24 . The flow therefore bleeds out of bleed resistor  56 . Increased pressure in the inspiratory conduit  24 , and correspondingly in pressure control conduit  50  results in a greater PEEP pressure in the bellows  40  and the patient&#39;s lungs. This has the effect of allowing PEEP control from the control of the inspiratory flow control valve  18 . Typically, CPU  20  will vary the opening of the inspiratory flow control valve  18  between a first inspiratory flow and a second expiratory PEEP flow. 
         [0025]    A pop-off valve  52  is connected to the bellows  40  such that if the pressure generated during patient exhalation exceeds that of the combination pop-off valve  52  and the pressure conduit  46 , the valve opens such that a portion of the gas from bellows  40  will be diverted to the exhalation valve  48 . Exhalation valve  48  directs any gas from the pop-off valve  52  and the drive gas in expiratory conduit  46  to a scavenging unit. The scavenging unit removes any medical gases that may be harmful to the clinicians or others in the room with the patient if these gases were allowed to exhaust into the room. If concentrations of some medical gases are allowed to build up on the room, clinicians may be harmed in the form of liver sclerosis or other health effects. The scavenging unit normally vents the medical gases out of the hospital or care facility and exhausts it outside where it will be diluted to non-harmful concentrations in the environment. 
         [0026]      FIG. 2 , is a schematic diagram of an embodiment of a ventilatory system  110  wherein much of the schematic diagram performs similar functions as the prior art described in  FIG. 1 . Common or unchanged elements from  FIG. 1  are depicted in  FIG. 2  with a similar one hundred&#39;s ( 100 &#39;s) level reference number. 
         [0027]    A drive pump  160  takes in ambient air and drives a flow of the ambient air into a first inspiratory conduit  124 , causing the pressure in the first inspiratory conduit  124  to increase such that the ambient air can be used as the drive gas for the ventilatory system  110 . CPU  120  measures the pressure in the first inspiratory conduit  124  via the pressure sensor  126  and controls the drive pump  160  to achieve a specified pressure in the first inspiratory conduit  124 . It is understood that the CPU  120  may comprise a variety of elements capable of performing control operations of the ventilatory system  110 . In embodiments, CPU  120  may comprise one or more microprocessors or microcontrollers capable of performing parallel processing, or a desktop or laptop personal computer. The CPU  120  receives input from pressure sensor  126  via line  128  as well as other sources of patient ventilatory input (not pictured). The other ventilatory inputs processed by the CPU  120  may include, but shall not be limited to, measured pressures within conduits of the ventilatory system  110 , patient airway pressures and gas flows, clinician input data such as respiration rates, I:E ratio, the addition of supplemental gases into the medical gas delivered to the patient. Ventilatory inputs such as those previously described as well as others may be used by CPU  120  in adjusting the controls of the ventilatory system  110 . 
         [0028]    The CPU  120  directs the drive pump  160  to deliver a commanded flow into inspiratory conduit  124  causing the pressure of the air in the inspiratory conduit  124  to rise to a desired pressure. Thus, the need for a separate pressurized gas source  12 , gas regulator  14 , gas inlet valve  16 , as well as the inspiratory flow control valve  18  as depicted in  FIG. 1 , is eliminated by the use of the drive pump  160 . By eliminating the need for these elements from the prior art, the drive pump  160  increases the mobility of the ventilatory system  110 . 
         [0029]    Once the ambient air enters the drive pump  160  through an intake filter  162  it is directed to an oscillating pump  164 . The oscillating pump  164  receives, from CPU  120 , a power signal indicative of the pump flow to drive the pressure in the inspiratory conduit  124  to the desired level. A suitable oscillating pump  164  that may be used is the one disclosed in pending patent application Ser. No. 11/461,792, the complete disclosure of which is herein incorporated by reference. The oscillating pump  164  is advantageous for implementation in this embodiment as the oscillating pump presents the advantages of having a fast response time such that precise control of the pressure of the drive gas can be achieved. It is understood, however, that any suitable drive pump that exhibits a fast response time could be used in the place of the oscillating pump  164 . In a further embodiment, oscillating pump  164  is a linear oscillating pump comprising two diaphragms such that a plug of gas is pressurized at each stroke of the linear oscillating pump. A linear oscillating pump may deliver a continuous gas flow. Furthermore, the linear oscillating pump may generate compressed gas flow without frictional mechanical moving parts which reduces wear. It is further understood that other oscillating, piston, or rotary pumps may be used in place of the oscillating pump  164  herein described. 
         [0030]    A sound isolation enclosure  166  surrounds the oscillating pump  164  to—attenuate the noise and vibration that is created by the operation of the oscillating pump  164  in the ventilatory system  110 . In a clinical setting, excessive noise is undesirable as clear communication between clinician, patients, and patient monitoring systems is desirable for providing quality health care. While the sound isolation enclosure  166  would necessarily need to surround the drive pump  164 , embodiments of the present invention may comprise a sound isolation enclosure  166  that also surrounds the intake filter  162  and/or the damping system  168 , as depicted. However, in an embodiment comprising a drive pump  160  that does not generate excessive noise, the sound isolation enclosure  166  may not be needed. Finally, the flow of air from the oscillating pump  164  is sent to a damping system  168 . The damping system  168  directs the flow of air through a series of baffles (not depicted) to reduce or eliminate the oscillating component of the drive gas flow that is produced as an inherent characteristic of the oscillating pump  164 . The damping system  168  further reduces the noise of the pressurized drive gas before it is directed to the inspiratory conduit  124 . 
         [0031]    The operation of the ventilatory system  110  as depicted in  FIG. 2  is now herein described. A patient is receiving mechanical ventilation via ventilatory system  110 . The CPU  120  directs the oscillating pump  164  to take ambient air via intake filter  162 . This air will be pressurized within the system to be the drive gas for the system. The oscillating pump  164  produces a flow of air into the first inspiratory conduit  124 . The flow of air travels to the first inspiratory conduit  124  through the damping system  168  where a substantial portion of the oscillatory frequency content of the drive gas is removed. Next, the drive gas is directed to the first inspiratory conduit  124  to achieve a first target pressure. Upon achieving a minimum pressure difference between the inspiratory conduit  124  and the bellows chamber  142  to open the check valve  130 , the drive gas flow is directed through the check valve  130  into the conduit  132 . The check valve  130  may typically require about 3.5 cmH 2 O of pressure in order to open initially, and also prevents the back flow of drive gas from the second inspiratory conduit  132  back into the first inspiratory conduit  124 . The second inspiratory conduit  132  directs the drive gas into the bellows chamber  142  of the bellows assembly  136 . The pressure in the first inspiratory conduit  124  is monitored by pressure transducer  126 . 
         [0032]    A buildup of pressure within the bellows chamber  142  compresses the bellows  140  forcing the medical gas within the bellows  140  into conduit  144 . The patient connection conduit  144  directs the medical gas to the patient through a patient interface (not depicted) to provide the patient respiratory support. It is also recognized that the flow rate of medical gas delivered to the patient is equal to the drive gas flow delivered by the pump  164  reduced by losses in gas volume due to gas leakage and compliance of the breathing system. The respiratory support can be in the form of pressure or gas volume generated by controlling the drive gas flow out of the drive pump  160  as directed by the CPU  120 . A series of ventilatory components (not pictured) may be disposed along the patient connection conduit  144  to provide further respiratory support to the patient. The ventilatory components may comprise, but are not limited to, supplemental medical gas, a nebulizer, a carbon dioxide absorber canister, or a humidifier. 
         [0033]    Upon completion of the inspiratory phase of the mechanical ventilation the ventilator cycles to the expiratory phase. The exhaled breath from the patient is directed back to the bellows  140  through the patient connection conduit  144 . When the ventilator cycles to the expiratory phase, the CPU  120  directs the oscillating pump  164  to produce a lower flow of drive gas thus achieving a second, lower target pressure in the first inspiratory conduit  124 , the conduit  132 , and the bellows chamber  142 . As the expired breath from the patient is directed to the bellows  140 , the bellows  140  begins to expand within the bellows assembly. The displaced drive gas from the bellows chamber  142  is directed through an expiratory conduit  146  to an exhalation valve  148 . 
         [0034]    During exhalation, the check valve  130  is nominally closed and the exhalation valve  148 , a pressure control conduit  150 , and a pop-off valve  152  control the pressure of the medical gas in the bellows chamber  142  and in the bellows  140 . The exhalation valve  148  is connected to a pressure control conduit  150  that is in fluid connection with the first inspiratory conduit  124 . Therefore, the pressure in the inspiratory conduit  124  created by the flow generated by the oscillating pump  164  is used to control the pressure in the bellows chamber  142 . As such, when the patient is in the expiratory phase, the pressure in the bellows  140  is controlled by the pressure to overcome the pop-off valve  152 , the pressure in the first inspiratory conduit  124 , and the pressure required to maintain the minimal pressure differential across the check valve  130  to keep the check valve  130  closed. The pressure in the bellows  140  is the PEEP pressure delivered to the patient. As such, the patient&#39;s exhalation reaches a pressure equilibrium within the bellows  140  at the PEEP pressure, thus maintaining that airway pressure within the patient&#39;s lungs. 
         [0035]    Pressure transducer  126  is disposed in fluid connection with the first inspiratory conduit  124  such that it provides a signal indicative of the pressure in first inspiratory conduit  124  to the CPU  120 . CPU  120  uses the pressure detected by pressure sensor  126  in a feedback loop to accurately determine the power signal needed to drive the oscillating pump  164  to produce the desired drive gas flow to produce the desired pressure in the first inspiratory conduit  124 . To prevent a buildup of excess pressure within the first inspiratory conduit  124 , a constant bleed of gas is vented to the ambient air by bleed valve  156 . 
         [0036]    In another embodiment, one or more flow sensors (not shown) may be disposed in the gas passage between the bellows  140  and the patient, such as in conduit  144 , to measure the medical gas flow or volume breathed by the patient. The flow sensor may provide a signal to the CPU  120  in a feedback loop to accurately determine the power signal needed to control the oscillating pump  164  to drive the bellows and deliver the desired volume of medical gases to the patient. 
         [0037]    The oscillating pump  164  is advantageous for implementation in this embodiment as the oscillating pump presents the advantages of having a fast response time such that precise control of the pressure of the drive gas can be achieved. It is understood, however, that any suitable drive pump that exhibits a fast response time could be used in the place of the oscillating pump  164 . In a further embodiment, oscillating pump  164  is a linear oscillating pump comprising two diaphragms such that a plug of gas is pressurized at each stroke of the linear oscillating pump. 
         [0038]      FIG. 3  is an overhead view of the general physical structure of an embodiment of the linear oscillating pump  164  as depicted in  FIG. 2 . As depicted in  FIG. 4 , which is a cutaway view of the pump along line  4 - 4 , the linear oscillating pump  164  comprises a stator, comprising two annular ferromagnetic laminated motor cores  250  and a plurality of motor windings  253 . Referring back to  FIG. 3 , the pump  164  also comprises a rotor  251 . In an embodiment the rotor  251  is a linearly moving rotor  251 , however it is understood that it is within the scope of the oscillating pump devices that may produce alternative directions of rotor movement. The rotor  251  comprises two magnets  252 , one disposed at either end of the rotor  251 . 
         [0039]    When an electrical current is applied to the motor windings  253  via leads  271 , a magnetic field is produced within the motor cores in the exemplary direction of magnetic field lines  254 . These fields push both magnets  252  in the rotor  251  in the same direction, thereby moving one end of the rotor  251  towards the outside of the linear oscillating pump  164  and the other magnet towards the center line  255  of the linear oscillating pump  164 . 
         [0040]    A pump assembly  256  is disposed on either side of the linear oscillating pump  164  in coaxial relationship to both the motor cores  250  and the magnets  52 . Each pump assembly  256  comprises a rubber diaphragm  258 , defining a pump chamber  257 , an “in” one-way valve  260 , and an “out” one-way valve  262 . 
         [0041]    As the magnetic field  254  through the motor cores  250  forces the rotor  251  towards the outside of the linear oscillating pump  164 , this electrical force  264  pushes the rubber diaphragm  258  outwards thereby forcing the air in the pump chamber  257  out through the “out” one-way valve  262  into inspiratory conduit  124 . On the other side of the linear oscillating pump  164 , the position of rotor  251  proximal to the centerline  255  of the pump  164  produces a mechanical force  266  pulling the rubber diaphragm  258  towards the center of the pump which pulls ambient air through the “in” one-way valve  260  to be stored in the pump chamber  257 . 
         [0042]    When the direction of current flowing through windings  252  is reversed, the magnetic fields depicted by magnetic field lines  254  reverse forcing the magnets  252  in the opposite direction. As such, the air in the full pump assembly  256  is forced out through the “out” one-way valve  262  and into the inspiratory conduit  124  while the other pump assembly  256  that had been previously emptied now begins to fill with ambient air through the “in” one-way valve  260 . This cycle of charges on the motor cores  250  produces the desired output of pressurized gas into the inspiratory conduit  124 . 
         [0043]      FIG. 5  depicts a schematic diagram of the electrical signals that are sent via leads  271  to the motor windings  253  of the linear oscillating pump  164 . Part or all of which signals may be provided to the linear oscillating pump  164  by CPU  120  via line  122 . As an embodiment the motor windings  253  are controlled using an H-bridge inverter  268 . It is understood that there are a variety of other DC to AC inversion methods for motor controllers that could be used. The H-bridge inverter  268  comprises four MOSFETs  270 . These MOSFETs  270  receive signals from either a first AND gate  272 , a second AND gate  274 , and from square wave signal  282  or  284 . Both the first  272  and second  274  AND gates receive a signal from a comparator  276  which compares a triangular wave  278  with the flow control signal  244  which may be received from the CPU  120 . The product from the triangle wave  278  and the flow control signal  244  sent to the comparator  276  produces a comparator signal  280  that is indicative of the desired duty cycle for the operation of the linear oscillating pump  164 . A first square wave signal  282  is provided as the second input to the first AND gate  272  and a second square wave signal  284  that is the same frequency as, but 180 degrees out of phase with, the first square wave signal  282  is provided to the second AND gate  274 . 
         [0044]    In an embodiment, the duty cycle of these two square waves is slightly less than 50% to create a dead time between switching voltage polarity of the pump. The creation of dead time prevents shoot through, the case when two MOSFETs on the same side of the H-Bridge are active and the positive voltage is therefore shorted to ground. First square wave  282  and second square wave  284  operate at a frequency that is equal to that of the motor AC operating frequency. The triangular wave  278  operates at a frequency much greater than the motor operating frequency to implement PWM voltage magnitude control. In an embodiment, the motor drive signal is a 24 V 60 Hz pulse width modified square wave with the effective voltage magnitude of the wave being defined by the output signal  280  of the comparator  276 . However, it is understood that any control signal capable of producing an oscillating motion in the oscillating pump may alternatively be used. 
         [0045]    The linear motor driven diaphragm  258  displaces air at a rate dependent on rotor position, thus causing the flow output to oscillate over each individual stroke of the rotor. This flow oscillation resembles a sine wave of a frequency that is twice the motor&#39;s electrical frequency. Such flow rate oscillation is depicted in  FIG. 6A . Therefore, before the inspiratory flow is delivered to the patient, mechanical damping is applied to the pressurized gas to remove much of the oscillatory characteristic, as depicted in  FIG. 6B , making the delivered gas flow more suitable for delivery to the patient. 
         [0046]    In an embodiment, the oscillating pump is not limited to the pump described above. Embodiments may use an oscillating pump to produce non-linear motion by a rotor. This type of oscillating pump may produce rotational rotor movement or exert an alternative force on an alternative rotor such as a spring. Further embodiments of the oscillating pump may comprise a single diaphragm. 
         [0047]    The present invention presents the advantage of having very low average power consumption. The linear oscillating pump is efficient at producing low flow rates, but the power efficiency of the pump decreases as the flow rate increases. However, the majority of flow rates required to supplement an average breathing cycle are in the range of 0 to 40 liters per minute. These flow rates are well within the range where the pump efficiency is very high. As an example of the efficiency of an embodiment of a linear oscillating pump, a laboratory test found that for a respiratory support system driven by a flow diverting rotary pump, the rotary pump consumed an average of 84W, while for a similarly performing respiratory support system utilizing a linear oscillating pump, the linear oscillating pump averaged only 2.9W of power consumption over the same time period. 
         [0048]    The electrical characteristics of an embodiment of the linear oscillating pump that may be used in an embodiment presents the advantage of a rapid response time to reach a designated target output pressure. During the acceleration of the linear oscillating pump, there are no large starting currents, low starting torque problems, nor are there any complex combinations of input voltage and electrical frequency necessary to start the motor as is often necessary in rotary devices. The linear oscillating pump takes approximately one full cycle of operation to accelerate to peak output and requires no special controls. As an example, at an electrical frequency of 60 Hz, the linear pump requires approximately 20 ms to accelerate to full flow output. This fast flow acceleration creates desirable response times for reaching target pressures. This facilitates delivering medical gas to the patient in conjunction with the patient entering the inspiratory phase of the respiration cycle. 
         [0049]    Embodiments also present the additional benefit of added maintenance efficiency. Stock linear oscillating pumps have a long MTBF (mean time between failure) thereby running efficiently for a long time without need for replacement. This is directly related to the simple design of the linear oscillating pump and the absence of frictional moving parts. Therefore, embodiments have the additional benefit of requiring relatively low maintenance compared to current designs. 
         [0050]    Embodiments offer the advantage of mobility, as embodiments eliminate a dependency upon pressurized drive gas tanks for a source of drive gas. The need is eliminated whether the tanks are smaller portable tanks connected directly to the ventilator or larger tanks that are connected to a room of a medical facility. This mobility makes the embodiments useful for the remote provision of medical care such as in third world countries, military field hospitals, or in rescue situations. Advanced medical care facilities to be deployed at these locations require devices that are portable as well as energy efficient as compared to existing compressor based drive gas supply systems as typically the electricity must be generated on-site. 
         [0051]    Further embodiments exhibit the advantage of being energy efficient as the drive pump  160  replaces the inspiratory flow control valve, gas inlet valve, and a compressor type high pressure drive gas source of the prior art. The compressor type high pressure drive gas source exhibits high energy demands because it must be constantly generating pressurized gas to provide the highest flow rate needed by the ventilatory system. The inspiratory flow control valve then must continuously operate to control the flow of the drive gas from the drive gas source. Therefore, by eliminating these components of the ventilatory system of the prior art, a more energy efficient system is created. 
         [0052]    In a further advantage of embodiments, the oscillating pump provides the advantage of being a low maintenance type of pump with a long mean time between failure (MTBF). The oscillating pump generally has few moving parts, resulting in easier maintenance and fewer parts that may fail or malfunction, requiring replacement. 
         [0053]    Furthermore, embodiments comprise drive pumps that exhibit a fast response time, thus making the drive pumps suitable choices for replacement of both the pressurized gas source and the inspiratory flow control valve of the prior art. One example of such a drive pump is an oscillating drive pump; however, it is understood that any other pump configuration that exhibits a fast response time such to be able to match the transfer characteristics of the inspiratory flow control valve would be a suitable drive pump for use with the present invention. 
         [0054]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
         [0055]    Various alternatives and embodiments are contemplated as being with in the scope of the following claims, particularly pointing out and distinctly claiming the subject matter regarded as the invention.