Patent Publication Number: US-2010116270-A1

Title: Medical Ventilator System and Method Using Oxygen Concentrators

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     This application claims the benefit of provisional patent application 61/112,934, filed Nov. 10, 2008 under 35 U.S.C. 119(e). This provisional patent application is incorporated by reference herein as though set forth in full. 
    
    
     FIELD OF THE INVENTION  
     This invention relates to a medical ventilator system, in particular to a ventilator system for improving the fraction of inspired oxygen values by implementing pulse flow of oxygen. 
     BACKGROUND OF THE INVENTION 
     Oxygen is normally supplied to ventilators through the use of high pressure oxygen sources such as compressed gas cylinders or fixed medical oxygen plumbing systems, often operating at pressures of approximately 50 psig/345 kPa. The oxygen is mixed with air within the ventilator to supply a desired fraction of inspired oxygen (FIO 2 ) to the patient so as to efficiently treat a medical condition. When such high pressure sources are unavailable or limited in capacity, low pressure, low flow oxygen supply to ventilators using oxygen concentrators, typically delivering 5-10 LPM oxygen, has been accomplished with the use of a “reservoir” at the inlet of the ventilator. In one prior art example, a reservoir bag is connected to the ventilator compressor inlet or low pressure O 2  port. The concentrator fills the bag volume between breaths, and the bag is emptied into the ventilator as the ventilator begins a breath, thus adding oxygen to the delivered breath. This volume of oxygen, plus the air delivered by the ventilator, combines to make a homogenous mixture which is then delivered to a patient to yield a fraction of inspired oxygen within the patient&#39;s lungs. U.S. Published Patent Application US 2007/0272243 teaches how oxygen can be added to the inspiratory limb of the patient breathing circuit prior to the inspiration cycle. In this implementation, when a breath is delivered by the ventilator, the oxygen-rich gas stored in the inspiratory limb is preferentially delivered to the patient, due to its proximal location in the ventilator circuit resulting in an elevated fraction of inspired oxygen within the alveolar space of the lungs. In all cases, the current state of the art uses only low, continuous flow settings of oxygen from the concentrator or other oxygen delivery device. 
     Portable oxygen concentrators, compressed gas cylinders equipped with oxygen conserving devices, liquid oxygen storage devices are also used to provide supplemental oxygen to respiratory patients via a nasal cannula for the purposes of increasing the fraction of inspired oxygen. In these cases, oxygen delivery is either low, continuous flows or is a pulsed flow triggered on a decrease of pressure in the cannula as the patient inhales. 
     Taken alone, these prior art methods are capable of producing fractions of inspired oxygen for the patient sufficient to treat some medical conditions, yet still low enough so as to not be widely applicable for many medical interventions requiring elevated oxygen levels. In addition, when traditional high pressure sources of oxygen are not available, not economical, or need to be conserved, there is a need for systems and techniques for improving FIO 2  values and conserving oxygen, allowing longer time on battery, in the medical ventilator systems beyond methods that are currently available. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention, a concentrator device similar to concentrators commonly used in conjunction with a nasal cannula to aid breathing of an ambulatory patient is connected to the patient breathing circuit of a ventilator system. The concentrator device is triggered to supply a pulse of oxygen to the breathing circuit at the onset of each ventilator supplied breath. In one embodiment, the concentrator is designed with a ventilator mode where a trigger pressure signal for triggering the concentrator to distribute oxygen to the patient circuit is phase switched 180 degrees, i.e., to flip the trigger signal sign from negative to positive, so that the criteria for triggering is a positive slope with trigger value(s) above zero. In other embodiments, a venturi is placed in the patient circuit to create a negative pressure signal during the inspiration phase and the pressure at the venturi is used to trigger the concentrator to distribute a pulse of oxygen to the patient during inhalation. 
     An additional aspect of the invention involves a method of using a medical ventilator system for at least one of increasing fraction of inspired oxygen delivered to a patient and conserving oxygen, the medical ventilator system including an oxygen source for pulsed delivery of a bolus of oxygen; a medical ventilator; a ventilator circuit for connecting the ventilator to the patient, the ventilator circuit including a location proximal to the patient. The method includes delivering with the ventilator a breath to the patient during an inspiration cycle; and adding a pulsed delivery of a bolus of oxygen from the oxygen source to the breath from the ventilator during the inspiration cycle to the location proximal to the patient of the ventilator circuit for at least one of increasing fraction of inspired oxygen delivered to a patient and conserving oxygen. 
     One or more implementations of the aspect of the invention described immediately above include one or more of the following: delivering a continuous flow rate of oxygen to the ventilator circuit; triggering the oxygen source for pulsed delivery of a bolus of oxygen; triggering the oxygen source includes triggering the oxygen source based upon sensing a positive inspiratory pressure; triggering the oxygen source includes triggering the oxygen source using a venturi at the location proximal to the patient of the ventilator circuit; triggering the oxygen source includes the ventilator sending a signal to the oxygen source for pulsed delivery of a bolus of oxygen; the ventilator circuit includes at least one of a pressure threshold and a flow threshold, and triggering the oxygen source includes triggering the oxygen source when at least one of the pressure threshold and the flow threshold in the ventilator circuit is exceeded; triggering the oxygen source is based upon at least one of a rate of change based on flow of gases in the ventilator circuit and rate of change based on pressure of gases in the ventilator circuit; a triggering event causes the triggering of the oxygen source for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 1 second; a triggering event causes the triggering of the oxygen source for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 600 ms; a triggering event causes the triggering of the oxygen source for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 1 second; a triggering event causes the triggering of the oxygen source for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 600 ms; the location proximal to the patient of the ventilator circuit includes a wye coupled to the oxygen source, and delivering a bolus of oxygen includes delivering a bolus of oxygen from the oxygen source to the wye of the ventilator circuit; the location proximal to the patient of the ventilator circuit includes a ventilation delivery interface selected from the group consisting of one or more intubation tubes, a non-rebreather mask, a partial rebreather mask, a nasal cannula, and a nasal pillow; the patient is at least one of a spontaneously breathing patient and a non-spontaneously breathing patient; the oxygen source supplies oxygen flow up to 30 LPM; the flow rate of a delivered pulse of the bolus of oxygen exceeds 5 LPM for some portion of the pulse; the flow rate of a delivered pulse of the bolus of oxygen exceeds 10 LPM for some portion of the pulse; the method self adjusts for ventilator positive end-expiratory pressure (PEEP); the method is not affected by ventilator bias flow; the method delivers breaths at a respiratory rate of 5-55 BPM; a gas flow standardizing to body temperature and pressure; compensating gas flow for altitude; the oxygen source is a member from the group consisting of an oxygen concentrator, a portable oxygen concentrator, a compressed oxygen gas cylinder, a membrane oxygen generator, and a chemical oxygen generator; using at least one of air liquidfaction and air distillation methods for generating at least one of liquid oxygen and gaseous oxygen; the oxygen source is an oxygen delivery device with both a ventilator mode wherein pulses of oxygen may be triggered when used with the ventilator and a concentrator mode used to provide supplemental oxygen to the patient; and/or delivering a bolus of oxygen includes varying duration of oxygen pulses delivered to the location proximal to the patient of the ventilator circuit to accommodate varying patient inspiratory durations. 
     Another aspect of the invention involves a medical ventilator system for at least one of increasing fraction of inspired oxygen delivered to a patient and conserving oxygen. The medical ventilator system includes an oxygen source; a controllable valve associated with the oxygen source for pulsed delivery of a bolus of oxygen; a medical ventilator for delivering a breath to the patient during an inspiration cycle; a ventilator circuit for connecting the ventilator to the patient, the ventilator circuit including a location proximal to the patient coupled to the controllable valve and the oxygen source; a triggering mechanism for triggering the oxygen source for pulsed delivery of a bolus of oxygen to the breath from the ventilator during the inspiration cycle to the location proximal to the patient of the ventilator circuit for at least one of increasing fraction of inspired oxygen delivered to the patient and conserving oxygen. 
     One or more implementations of the aspect of the invention described immediately above include one or more of the following: the oxygen source delivers a continuous flow rate of oxygen to the ventilator circuit; the triggering mechanism includes a sensor that senses a positive inspiratory pressure; the triggering mechanism includes a venturi at the location proximal to the patient of the ventilator circuit; the ventilator includes the triggering mechanism, and the triggering mechanism sends a signal to the oxygen source for pulsed delivery of a bolus of oxygen; the ventilator circuit includes at least one of a pressure threshold and a flow threshold, and the triggering mechanism triggers the oxygen source when at least one of the pressure threshold and the flow threshold in the ventilator circuit is exceeded; the triggering mechanism triggers the oxygen source based upon at least one of a rate of change based on flow of gases in the ventilator circuit and rate of change based on pressure of gases in the ventilator circuit; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 1 second; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 600 ms; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 1 second; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 600 ms; the location proximal to the patient of the ventilator circuit includes a wye coupled to the oxygen source; the location proximal to the patient of the ventilator circuit includes a ventilation delivery interface selected from the group consisting of one or more intubation tubes, a non-rebreather mask, a partial rebreather mask, a nasal cannula, and a nasal pillow; the oxygen source supplies oxygen flow up to 30 LPM; the oxygen source delivers a pulse of the bolus of oxygen with a flow rate that exceeds 5 LPM for some portion of the pulse; the oxygen delivers a pulse of the bolus of oxygen with a flow rate that exceeds 10 LPM for some portion of the pulse; the system self adjusts for ventilator positive end-expiratory pressure (PEEP); the system delivers breaths at a respiratory rate of 5-55 BPM; the system includes a gas flow standardizing to body temperature and pressure; the system compensates gas flow for altitude; the oxygen source is a member from the group consisting of an oxygen concentrator, a portable oxygen concentrator, a compressed oxygen gas cylinder, a membrane oxygen generator, and a chemical oxygen generator; the oxygen source is at least one of an air liquidfaction oxygen source and an air distillation oxygen source for generating at least one of liquid oxygen and gaseous oxygen; the oxygen source is an oxygen delivery device with both a ventilator mode wherein pulses of oxygen may be triggered when used with the ventilator and a concentrator mode used to provide supplemental oxygen to a patient; and/or the oxygen source varies duration of oxygen pulses delivered to the location proximal to the patient of the ventilator circuit to accommodate varying patient inspiratory durations. 
     Another aspect of the invention involves a system for at least one of increasing fraction of inspired oxygen delivered by a medical ventilator via a ventilator circuit to a patient and conserving oxygen. The ventilator circuit includes a location proximal to the patient. The medical ventilator system includes an oxygen source; a controllable valve associated with the oxygen source for pulsed delivery of a bolus of oxygen; a triggering mechanism for triggering the oxygen source for pulsed delivery of a bolus of oxygen to the breath from the ventilator during an inspiration cycle to the location proximal to the patient of the ventilator circuit for at least one of increasing fraction of inspired oxygen delivered to the patient and conserving oxygen. 
     One or more implementations of the aspect of the invention described immediately above include one or more of the following: the oxygen source delivers a continuous flow rate of oxygen to the ventilator circuit; the triggering mechanism includes a sensor that senses a positive inspiratory pressure; the triggering mechanism includes a venturi at the location proximal to the patient of the ventilator circuit; the ventilator includes the triggering mechanism, and the triggering mechanism sends a signal to the oxygen source for pulsed delivery of a bolus of oxygen; the ventilator circuit includes at least one of a pressure threshold and a flow threshold, and the triggering mechanism triggers the oxygen source when at least one of the pressure threshold and the flow threshold in the ventilator circuit is exceeded; the triggering mechanism triggers the oxygen source based upon at least one of a rate of change based on flow of gases in the ventilator circuit and rate of change based on pressure of gases in the ventilator circuit; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 1 second; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 600 ms; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 1 second; a triggering event causes the triggering mechanism to trigger the oxygen source for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 600 ms; the location proximal to the patient of the ventilator circuit includes a wye coupled to the oxygen source; the location proximal to the patient of the ventilator circuit includes a ventilation delivery interface selected from the group consisting of one or more intubation tubes, a non-rebreather mask, a partial rebreather mask, a nasal cannula, and a nasal pillow; the oxygen source supplies oxygen flow up to 30 LPM; the oxygen source delivers a pulse of the bolus of oxygen with a flow rate that exceeds 5 LPM for some portion of the pulse; the oxygen delivers a pulse of the bolus of oxygen with a flow rate that exceeds 10 LPM for some portion of the pulse; the system self adjusts for ventilator positive end-expiratory pressure (PEEP); the system delivers breaths at a respiratory rate of 5-55 BPM; the system includes a gas flow standardizing to body temperature and pressure; the system compensates gas flow for altitude; the oxygen source is a member from the group consisting of an oxygen concentrator, a portable oxygen concentrator, a compressed oxygen gas cylinder, a membrane oxygen generator, and a chemical oxygen generator; the oxygen source is at least one of an air liquidfaction oxygen source and an air distillation oxygen source for generating at least one of liquid oxygen and gaseous oxygen; the oxygen source is an oxygen delivery device with both a ventilator mode wherein pulses of oxygen may be triggered when used with the ventilator and a concentrator mode used to provide supplemental oxygen to a patient; and/or the oxygen source varies duration of oxygen pulses delivered to the location proximal to the patient of the ventilator circuit to accommodate varying patient inspiratory durations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The details of the present invention, both as to its structure and operation, may be gleaned in part by study of the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
         FIG. 1  illustrates one example of a typical prior art medical ventilator system; 
         FIG. 2  illustrates one embodiment of a ventilator system including an oxygen concentrator; 
         FIG. 3  illustrates another embodiment of a ventilator system including an oxygen concentrator; 
         FIG. 4  illustrates one example of a graph identifying the trigger pressure signal for activating a pulse of oxygen in the embodiment of  FIG. 3 ; 
         FIG. 5  illustrates one example of a graph identifying the trigger pressure signal and oxygen pulse flow for the embodiment of  FIG. 2 ; 
         FIG. 6  is an example graph illustrating a method of adjusting the oxygen pulse as a percentage of inspiratory time. 
         FIG. 7  is a block diagram of another embodiment of a portable oxygen concentration system constructed in accordance with an embodiment of the invention; 
         FIG. 8  is a block diagram of a portable oxygen concentration system constructed in accordance with a further embodiment of the invention, and illustrates, in particular, an embodiment of an air separation device; 
         FIG. 9A  is a perspective, cut-away view of an embodiment of a concentrator that may be used with the portable oxygen concentration system. 
         FIG. 9B  is a perspective, exploded view of the concentrator illustrated in  FIG. 9A . 
         FIG. 10  is a top perspective view of an embodiment of a top manifold and multiple adsorption beds that may be used with the concentrator illustrated in  FIGS. 9A and 9B . 
         FIGS. 11A and 11B  are a bottom plan view and a top plan view respectively of an embodiment of a rotary valve shoe that may be used with the concentrator illustrated in  FIGS. 9A and 9B . 
         FIG. 12A  is a top plan view of an embodiment of a valve port plate that may be used with the concentrator illustrated in  FIGS. 9A and 9B . 
         FIG. 12B  is a flow chart of an exemplary process cycle for the concentraotor illustrated in  FIGS. 9A and 9B . 
         FIGS. 13A and 13B  are a top perspective view and a bottom perspective view respectively of an embodiment of a media retention cap that may be used with the concentrator illustrated in  FIGS. 9A and 9B . 
         FIGS. 14A and 14B  are a top perspective, exploded view and a bottom perspective, exploded view respectively of an embodiment of a rotary valve assembly including a centering pin that may be used with the concentrator illustrated in  FIGS. 9A and 9B . 
         FIGS. 15A and 15B  are a bottom perspective, exploded view and a top perspective, exploded view respectively of an embodiment of a rotary valve assembly including a centering ring that may be used with the concentrator illustrated in  FIGS. 9A and 9B . 
         FIG. 16A  is a bottom perspective view of an embodiment of a rotary valve shoe, a motor drive, and a pair of elastic chain links that may be used with the concentrator illustrated in  FIGS. 9A and 9B . 
         FIGS. 16B and 16C  are a top perspective, exploded view and a bottom perspective, exploded view respectively of the rotary valve shoe, motor drive, and pair of elastic chain links illustrated in  FIG. 16A . 
         FIG. 17  is a table of experimental data for a portable oxygen concentration system including the concentrator illustrated in  FIGS. 9A and 9B . 
         FIG. 18  is a schematic illustration of a further embodiment of the portable oxygen concentration system and an embodiment of a cradle for use with the portable oxygen concentration system; 
         FIG. 19  is a block diagram of the one or more sensors that may be used with an embodiment of the portable oxygen concentration system; 
         FIG. 20  is a block diagram of the one or more components that may be controlled by the control unit of the portable oxygen concentration system; 
         FIG. 21  is a block diagram of a portable oxygen concentration system constructed in accordance with additional embodiment of the invention; 
         FIG. 22  is a schematic illustration of another embodiment of a portable oxygen concentration system including a high-pressure reservoir; 
         FIG. 23  is a block diagram illustrating an example computer system that may be used in connection with various embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     After reading this description, it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. Although various embodiments of the present invention are described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention as set forth in the appended claims. 
     A system and method for increasing the fraction of inspired oxygen (FIO 2 ) to a patient or user (e.g., spontaneously breathing patient, non-spontaneously breathing patient) in a ventilator system by using pulse flow rather than continuous flow of oxygen from low pressure oxygen sources such as oxygen concentrators is described. Other sources of oxygen could be used in the same manner. These include portable oxygen concentrators, compressed oxygen tanks, membrane oxygen generators, chemical oxygen generators, and liquid oxygen systems. 
       FIG. 1  illustrates a typical prior art medical ventilator system. The medical ventilator system  10  includes a medical ventilator  80  having controller/control module  60 , an energy source or power source  50 , and a ventilator/breathing circuit  70  for supplying oxygen to a user  40 . The ventilator system  10  also includes an oxygen source  55  such as a high pressure oxygen supply or oxygen concentrator and reservoir coupled to the medical ventilator  80 . 
     Conditions of the medical ventilator  80  such as flow rate, oxygen concentration level, etc. may be constant for the system, may be manually controllable, and/or may be automatically controllable. For example, the medical ventilator  80  may include a user interface that allows the user, provider, doctor, etc. to enter information, e.g., prescription oxygen level, flow rate, etc. to control the oxygen output of the ventilator system  10 . A flow of oxygen mixed with air is distributed from the medical ventilator  80  to the patient during each breath via breathing or user circuit  70  in the inspiration phase, and the flow is discontinued during the exhalation phase. It should be noted that some ventilators have a small flow rate during exhalation phase used to trigger spontaneous breath delivery so in those instances flow is not completely discontinued during the exhalation phase. A small continuous flow rate of oxygen can be added during this phase also. 
     The control module  60  may take any well-known form in the art and includes a central microprocessor or CPU in communication with the components of the ventilator system  10  described herein via one or more interfaces, controllers, or other electrical circuit elements for controlling and managing the medical ventilator  80 . The ventilator system  10  may include a user interface as part of the control module  60  or coupled to the control module  60  for allowing the user, provider, doctor, etc. to enter information, e.g., prescription oxygen level, flow rate, activity level, etc., to control the ventilator system  10 . 
       FIG. 2  illustrates one embodiment of a modified ventilator system  100  including an oxygen source (e.g., oxygen concentrator/conserving device)  20 , a medical ventilator  80  and a breathing circuit  70  between the ventilator  80  and a patient  40 . In one embodiment, the oxygen concentrator  20  includes a controller/control module (e.g., controller that processed one or more modules stored in memory perform the function(s) described herein)  25  that is configured to generate a trigger signal to initiate the distribution of pulses of oxygen (or a pulse bolus of oxygen) from the oxygen concentrator  20 . In some embodiments, a conserving device may be used in conjunction with the oxygen concentrator  20  to control the distribution of oxygen to the breathing circuit  70 . In other embodiments, the conserving device can be independent of the oxygen concentrator  20 . The controller module for generating a trigger signal to initiate the distribution of pulses of oxygen from the oxygen concentrator  20  can be incorporated in the oxygen concentrator  20  and/or the conserving device. The oxygen concentrator  20  may be similar or identical to oxygen concentrators currently used to provide supplemental oxygen to ambulatory patients via a nasal cannula. In one or more embodiments, the oxygen concentrator  20  includes one or more of the features described below with respect to  FIGS. 8-22 . Where the oxygen concentrator  20  is a portable oxygen concentration system, the portable oxygen concentration system preferably weighs 4 to 20 lbs. The oxygen concentrator  20  may be implemented with one or more discrete valve assemblies (or valves), rotary valve assemblies, or other valve assemblies. For example, but not by way of limitation, the oxygen concentrator  20  maybe implemented with two rotary valve assemblies. 
     In one or more embodiments, the oxygen source  20  includes, but is not limited to, an oxygen concentrator, a portable oxygen concentrator, a compressed oxygen gas cylinder, a membrane oxygen generator, and/or a chemical oxygen generator. In one or more further embodiments, the oxygen source  20  an air liquidfaction oxygen source and/or an air distillation oxygen source for generating at least one of liquid oxygen and/or gaseous oxygen. 
     In the embodiment of  FIG. 2 , the distribution of pulses of oxygen by the oxygen concentrator  20  is controlled by the medical ventilator  80  (e.g., triggering the oxygen source includes the ventilator sending a signal to the oxygen source for pulsed delivery of a bolus of oxygen). Thus, the oxygen concentrator  20  can be controlled by the medical ventilator  80  to trigger at the appropriate time  30 , for example, as soon as possible upon the onset of the ventilator&#39;s inspiration cycle. For example, in a preferred embodiment, the time between the triggering event and onset of oxygen bolus delivery  32  is in the range of 0.01 ms to 1 second. In a more preferred embodiment, the time between the triggering event and onset of oxygen bolus delivery  32  is in the range of 0.01 ms to 600 ms. In another preferred embodiment, the time between the triggering event and full oxygen bolus delivery  34  is in the range of 0.01 ms to 1 second. In a more preferred embodiment, the time between the triggering event and full oxygen bolus delivery  34  is in the range of 0.01 ms to 600 ms. In some embodiments, the medical ventilator  80  controls the oxygen concentrator  20  via a serial interface or wireless devices. The controller/control module  25  generates pulse codes that allow the oxygen concentrator  20  to distribute pulses of oxygen to the breathing circuit  70 . 
     The breathing circuit  70  includes a patient WYE  65  having an inhalation portion to receive air from the medical ventilator  80  and an exhalation portion to distribute exhaled gases. The patient WYE  65  also includes a tail portion that leads to the trachea tube which supplies oxygen to the patient or user  40 . The inhalation portion, the exhalation portion and the tail portion all terminate at a junction forming the WYE  65 . The oxygen concentrator  20  has an output  90  which is connected to the patient breathing circuit  70  (e.g., via a special connector or modified WYE) at the WYE  65 , at a location proximal to the patient. The output  90  may be connected elsewhere in the patient breathing circuit in other embodiments. In additional embodiments, the output  90  is connected to the patient breathing circuit  70  at a ventilation delivery interface including, but not limited to, one or more intubation tubes, a non-rebreather mask, a partial rebreather mask, a nasal cannula, and/or a nasal pillow. 
     The controller/control module  25  controls the oxygen concentrator  20  (e.g., by operating/controlling a controllable valve  28 ) to deliver a pulse of oxygen to the breathing circuit during each ventilator supplied breath, so as to increase the fraction of inspired oxygen when the oxygen concentrator  20  is used in conjunction with the medical ventilator  80 , as illustrated in  FIG. 2 . The pulses of oxygen arrive at the patient WYE  65  at the onset of the inspiration cycle/inhalation phase so that the oxygen is delivered when it is needed. 
     In another embodiment, a small continuous low flow of oxygen may also be supplied when a pulse is not being delivered to aid in elevating FIO 2 . 
     In one embodiment, the oxygen concentrator  20  supplies pulse flow to the ventilator to gain higher FIO 2  values, conserve energy, and/or conserve oxygen (relative to continuous flow). The system  100  may include one or more output sensors to sense one or more conditions of the user  40 , environment, etc. to determine the oxygen output needed by the user  40 . The one or more sensors can include a sensor for monitoring the respiration rate of the user, where the ventilator  80  is being used in an assist mode in response to a patient&#39;s spontaneous breathing. Conditions of the medical ventilator  80  such as flow rate, oxygen concentration level, or the like may be constant or vary, and be based on the conditions of the user  40 , environment, etc. determined by the sensors, while the concentrator  20  provides an additional pulse of oxygen to the inspiratory gas flow from the ventilator  80  to the patient  40 . In one or more embodiments, the ventilator circuit  70  includes at least one of a pressure threshold and a flow threshold, and triggering the oxygen source  20  includes triggering the oxygen source  20  when at least one of the pressure threshold and the flow threshold in the ventilator circuit  70  is exceeded. In one or more additional embodiments, triggering the oxygen source  20  is based upon at least one of a rate of change based on flow of gases in the ventilator circuit  70  and rate of change based on pressure of gases in the ventilator circuit  70 . A conserving device may be incorporated into the ventilator system  10  to more efficiently utilize the oxygen produced by the oxygen concentrator  20  and/or the medical ventilator  80 . 
     In one embodiment, the conserving device or oxygen concentrator  20  is triggered by a trigger mechanism  64 , which may be part of and/or separate from the ventilator  80 , to deliver a pulse of oxygen at the onset of each ventilator inspired breath, as described above in connection with  FIG. 2 . In alternative embodiments, other triggering mechanisms  64 /ways of triggering the pulse may be used. As noted above, existing oxygen concentrators and conserving devices used in conjunction with a nasal cannula are triggered by detection of negative pressure in the cannula as the patient inhales. This cannot be used in the system of  FIG. 2 , because the ventilator  80  increases the pressure in the patient or breathing circuit during inspiration rather than lowering it as is the case with venturi  85 . As a result, if a conventional concentrator device is triggered on a negative pressure from the patient WYE  70  of  FIG. 2  (rather than from ventilator  80  as shown) the pulse is delivered during exhalation which does not help increase the FIO 2  significantly. In other words, the pressure signal is 180 degrees out of phase with the inspiration phase of a ventilator supplied breath. Some possible triggering mechanisms  64 /techniques for avoiding this problem are to switch the trigger pressure signal phase 180 degrees, i.e., to flip the trigger signal sign from negative to positive, so that the criteria for triggering is a positive slope with trigger value(s) above zero, as illustrated in the graph of  FIG. 5 . The controller/control module  25  looks for a positive slope from the incoming positive pressure signal, and then causes one or more oxygen gas pulses to be supplied if a positive slope is detected. 
     In an alternative embodiment, a triggering mechanism/ventilator supplied breath detection mechanism  64  (which may be located at the location of pressure sensing, at the controller  25 , or anywhere in between) may modify the trigger signal for the concentrator  20  by switching the sensed positive pressure signal 180 degrees to a negative pressure signal so that existing oxygen concentrators and conserving devices used in conjunction with a nasal cannula that are triggered by detection of negative pressure in the cannula as the patient inhales may used. 
     As described above, in one or more embodiments, the ventilator circuit  70  includes at least one of a pressure threshold and a flow threshold, and the trigger mechanism  64  triggers the oxygen source  20  when at least one of the pressure threshold and the flow threshold in the ventilator circuit  70  is exceeded. In one or more additional embodiments, the trigger mechanism  64  triggers the oxygen source  20  based upon at least one of a rate of change based on flow of gases in the ventilator circuit  70  and rate of change based on pressure of gases in the ventilator circuit  70 . 
     In some embodiments, a triggering mechanism/ventilator supplied breath detection mechanism  64  in the form of a venturi mechanism (such as a venturi tube)  85  can be placed in the patient circuit to create a negative pressure signal during the inspiration phase in order to simulate a patient using a cannula without modifying the trigger signal for the concentrator device  20 .  FIG. 3  illustrates one embodiment of a ventilator system  200  including an oxygen concentrator  20  in conjunction with a venturi device  85  for implementing a pulse flow of oxygen. The system of  FIG. 3  is otherwise identical to  FIG. 2 , and like reference numbers are used as appropriate. In one embodiment, venturi device  85  is a tube with a specially streamlined constriction to minimize energy losses in the fluid flowing through it while maximizing the fall in pressure in the constriction. A signal output from the venturi device  85  is connected to the control or trigger input of the concentrator device  20 . The venturi device  85  is situated in the inspirational limb or coupled to the inhalation portion of the patient or breathing circuit to allow triggering during inspiration and to avoid triggering during exhalation. A negative slope is created at the venturi device  85  during inspiration. This triggers the oxygen concentrator  20  via the trigger pressure line illustrated in  FIG. 3 , and initiates delivery of a pulse of oxygen to the patient WYE  65 . 
       FIG. 4  illustrates one example of a graph identifying the trigger pressure signal for the concentrator  20  in the embodiment of  FIG. 3 . The graph illustrates the pressure signal used to trigger the oxygen concentrator  20 . For explanatory purpose the graph of  FIG. 4  will be described with respect to  FIG. 3  above. The x-axis represents the time in seconds in the patient or breathing circuit and the y-axis represents pressure in cm H2O. In one embodiment, the pressure in the venturi  85  is tracked between breaths by the conserving device or oxygen concentrator  20  to determine when to trigger delivery of a pulsed bolus of oxygen to attain optimum FIO 2 . The pressure between 0 to 2 seconds which is slightly above zero represents the pressure between breaths in the venturi  85 . The trigger is based on this non-zero value. To achieve optimum FIO 2 , delivery of pulsed bolus of oxygen from the oxygen concentrator  20  is triggered as quickly as possible upon detection of a negative slope at venturi  85 , which indicates the onset of inspiration. In one embodiment, a fast response within a short duration and high flow of the bolus of oxygen is appropriate for optimizing the FIO 2 . (Note:  FIG. 4  does not show the O 2  pulse.) 
       FIG. 5  illustrates one example of a graph identifying a positive trigger pressure signal which may be used to trigger the concentrator device  20  in another embodiment, as described above in connection with  FIG. 2 . The graph illustrates the timing of the oxygen pulse relative to the pressure signal used to trigger the oxygen concentrator  20  to distribute a pulse of oxygen in the breathing circuit  70 . The x-axis represents the time in seconds in the patient or breathing circuit and the y-axis represents pressure in cm H 2 O. Medical ventilator  80  increases the pressure in the breathing circuit during inspiration rather than lowering it. 
     As previously described, in order to deliver a pulse flow of oxygen (or a pulsed bolus of oxygen) at the onset of the ventilator supplied breath, the oxygen concentrator  20  can be designed with a “ventilator mode” for use when connected in a ventilator breathing circuit as in  FIG. 2 , and a “cannula mode” when connected to a nasal cannula to provide additional oxygen to an ambulatory patient. In the ventilator mode, the trigger pressure signal phase is switched 180 degrees and/or the criteria for triggering are changed from a negative slope (cannula mode) to a positive slope with trigger value(s) above zero as illustrated in  FIG. 5 . Thus, in the ventilator mode, the delivery of pulse is triggered as quickly as possible upon detection of a positive slope (illustrated by the slope at about the 2.5 second point on the x-axis) in the breathing circuit, instead of a negative slope. This triggers the oxygen concentrator  20  to deliver the pulse at the onset of the ventilator delivering a breath. 
     As indicated above, delivery of pulse is triggered as quickly as possible upon detection of a triggering event. In a preferred embodiment, the triggering event causes the triggering of the oxygen source  20  for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 1 second. In a more preferred embodiment, the triggering event causes the triggering of the oxygen source  20  for oxygen bolus delivery, and a time between the triggering event and onset of oxygen bolus delivery is in the range of 0.01 ms to 600 ms. 
     Further, delivery of a full pulse occurs as quickly as possible upon detection of a triggering event. Thus, in a preferred embodiment, the triggering event causes the triggering of the oxygen source  20  for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 1 second. In a more preferred embodiment, the triggering event causes the triggering of the oxygen source for oxygen bolus delivery, and a time between the triggering event and full oxygen bolus delivery is in the range of 0.01 ms to 600 ms. 
     As described previously, it is important to track the pressure between breaths and use it as the baseline for triggering. The signal between breaths indicated by the pressure between 0 to about 2.5 seconds is not equal to zero and the trigger can be based on a change from this non-zero value. In the ventilator mode, the pressure signal may be much higher than ambient due to lung mechanics and positive end expiratory pressure (PEEP). The PEEP during operation with an oxygen concentrator  20  can cause the triggering of the oxygen concentrator  20  to change or stop. Some oxygen concentrators  20 , for example, the Eclipse Concentrator made by SeQual Technologies of San Diego, Calif., include an “auto zero” startup that sets the zero value of the trigger pressure signal. Any changes such as a PEEP on the medical ventilator  80  may require a restart of the oxygen concentrator  20  by setting an “auto zero.” The concentrator  20  may also “auto zero” continuously and, thus, adjusting for changes in the pressure signal baseline. All ventilator modalities are considered usable in ventilator mode. These include volume and pressure control, mandatory and assist ventilation, PEEP, bias flows and all common ventilator metabolic settings covering pediatric through adult ranges. For example, this method covers 5-55 BPM and up to 1000 ml tidal volumes. The delivered oxygen may be normalized to body temperature and pressure as this is the standard for ventilators. Gas flow may also be compensated for altitude. The medical ventilator system and method are also not affected by ventilator bias flow. 
       FIG. 6  is an example graph illustrating one embodiment of adjustment of the pulse supplied from the concentrator device  20  as a percentage of inspiratory time. Delivering a bolus of oxygen includes varying duration of oxygen pulses delivered to the location proximal to the patient of the ventilator circuit to accommodate varying patient inspiratory durations. For explanatory purpose the graph of  FIG. 6  will be described with respect to  FIGS. 2 and 3  above. Basically the same holds true regardless of the concentrator trigger signal when it comes to delivery of the oxygen pulse. For high FIO 2  values, it is important to provide 1) fast response, 2) short duration, and 3) high flow. In some embodiments, adjustable pulse lengths may be used to accommodate such things as a long inspiratory (I) time. The O 2  pulse length may extend from at or near to the beginning of inspiration up to close to the end of the inspiration. 
     The concentrator device  20  is modified to provide a larger bolus size than is provided in a nasal cannula application. For example, a setting of 6 in a conventional concentrator may supply a 96 ml bolus. In one embodiment, a concentrator device  20  connected to a patient WYE in a ventilator system as illustrated in  FIGS. 2 and 3  is modified to supply a much larger bolus of oxygen. In one example, a setting of 6 in concentrator device  20  may correspond to delivery of a 192 ml bolus. The concentrator  20  may be arranged to provide higher boluses, so as to produce high FIO 2  values, for example the largest supply of bolus of oxygen without exceeding the capacity of the oxygen concentrator  20  for the highest FIO 2  and smaller boluses to provide lower FIO 2 . In some embodiments, two or more pulses of oxygen bolus may be provided rather than a single large bolus to satisfy the bolus size requirement for ventilator mode. In addition, a small flow of oxygen at times a pulse is not being delivered may be supplied. While the standard or typical cannula bolus size would work, the resultant pulse may exceed 100% inspiratory (I) time, thus not delivering two times the standard bolus to the lungs. The appropriate bolus size for supplying an oxygen bolus can be accomplished by using higher flow rates (10-60 LPM). With higher flow rates, the bolus size can be two or more times the standard (cannula) bolus, and still be within a desired percentage of inspiratory time (see pulse A of  FIG. 6 ). For example, for a pulse rate of about 60 LPM, a bolus size of 192 ml can be distributed in 20% of the inspiratory time. Likewise, for a pulse rate of about 10 LPM, a bolus size of 192 ml can be distributed in 90% of inspiratory time (see pulse B in  FIG. 6 ). Other possible pulses of different size and length are also illustrated. The maximum bolus deliverable is based on breath rate and the concentrator capacity as illustrated in the equation below. 
       Maximum bolus (L)=Capacity (LPM)÷BPM (Breaths per minute) 
     For an oxygen concentrator  20 , such as the SeQual Eclipse Concentrator manufactured by SeQual Technologies of San Diego, Calif. with capacity of 3 LPM continuous, the maximum bolus size at 15 BPM is 0.2 liters (200 ml) and 300 ml at 10 BPM. An algorithm determining the bolus size may be used to account for capacity as a function of breath rate. In an embodiment of the oxygen concentrator/source  20 , the oxygen concentrator  20  supplies oxygen flow up to 30 LPM. In a preferred embodiment, the flow rate of a delivered pulse of the bolus of oxygen exceeds 5 LPM for some portion of the pulse. In a more preferred embodiment, the flow rate of a delivered pulse of the bolus of oxygen exceeds 10 LPM for some portion of the pulse. 
     In the case that the concentrator  20  does not sense a breath for some predetermined time, the concentrator  20  can switch to continuous flow for a period and alarm. Once the breathing is detected again, the concentrator  20  delivers pulses and the alarm is silenced. 
     In one or more embodiments, the concentrator device  20  includes one or more of the features shown and described below with respect to sections I to V and  FIGS. 7-22 . In a preferred embodiment, the concentrator device  20  weighs 4 to 20 lbs. 
     I. Portable Oxygen Concentration System 
     With reference to  FIG. 7 , a portable oxygen concentration system, indicated generally by the reference numeral  100 , constructed in accordance with an embodiment of the invention will now be described. The oxygen concentration system  100  includes an air separation device such as an oxygen gas generator  102  that separates concentrated oxygen gas from ambient air, an energy source such as rechargeable battery, battery pack, or fuel cell  104  that powers at least a portion of the oxygen gas generator  102 , one or more output sensors  106  used to sense one or more conditions of the user  108 , environment, etc. to determine the oxygen output needed by the user or required from the system  100 , and a control unit  110  linked to the output sensor  106 , the air separation device  102 , and the energy source  104  to control the operation of the air separation device  102  in response to the one or more conditions sensed by the one or more output sensors  106 . 
     In an alternative embodiment, the system  100  may not include the one or more output sensors  106  coupled to the control unit  110 . In this embodiment, conditions of the system  100  such as flow rate, oxygen concentration level, etc. may be constant for the system or may be manually controllable. For example, the system  100  may include a user interface  111  ( FIG. 20 ) that allows the user, provider, doctor, etc. to enter information, e.g., prescription oxygen level, flow rate, etc. to control the oxygen output of the system  100 . 
     Each element of the system  100  will now be described in more detail. 
     A. Air Separation Device 
     With reference to  FIG. 8 , the air separation device is preferably an oxygen generator  102  generally including a pump such as a compressor  112  and an oxygen concentrator  114  (OC), which may be integrated. 
     The oxygen generator  102  may also include one or more of the elements described below and shown within the segmented boundary line in  FIG. 8 . Ambient air may be drawn through an inlet muffler  116  by the compressor  112 . The compressor  112  may be driven by one or more DC motors  118  (M) that run off of DC electrical current supplied by the rechargeable battery  104  (RB). The motor  118  also preferably drives the cooling fan part of the heat exchanger  120 . A variable-speed controller (VSC) or compressor motor speed controller  119 , which is described in more detail below, may be integral with or separate from the control unit  110  (CU) and is preferably coupled to the motor  118  for conserving electricity consumption. The compressor  112  delivers the air under pressure to the concentrator  114 . 
     In a preferred embodiment, at a maximum speed air is delivered to the concentrator  114  at 7.3 psig nominal and may range from 5.3 to 12.1 psig. At maximum speed, the flow rate of feed is a minimum of 23.8 SLPM at inlet conditions of 14.696 psi absolute, 70 degrees F., 50% relative humidity. 
     A heat exchanger  120  may be located between the compressor  112  and the concentrator  114  to cool or heat the air to a desired temperature before entering the concentrator  114 , a filter (not shown) may be located between the compressor  112  and the concentrator  114  to remove any impurities from the supply air, and a pressure transducer  122  may be located between the compressor  112  and the, concentrator  114  to get a pressure reading of the air flow entering the concentrator  114 . 
     The concentrator  114  separates oxygen gas from air for eventual delivery to the user  108  in a well-known manner. One or more of the following components may be located in a supply line  121  between the concentrator  114  and the user  108 : a pressure sensor  123 , a temperature sensor  125 , a pump  127 , a low-pressure reservoir  129 , a supply valve  160 , a flow and purity sensor  131 , and a conservation device  190 . As used herein, supply line  121  refers to the tubing, connectors, etc. used to connect the components in the line. The pump  127  may be driven by the motor  118 . The oxygen (gas may be stored in the low-pressure reservoir  129  and delivered therefrom via the supply line  121  to the user  108 . The supply valve  160  may be used to control the delivery of oxygen gas from the low-pressure reservoir  129  to the user  108  at atmospheric pressure. 
     Exhaust gas may also be dispelled from the concentrator  114 . In a preferred embodiment of the invention, a vacuum generator  124  (V), which may also be driven by the motor  118  and integrated with the compressor  112 , draws exhaust gas from the concentrator  114  to improve the recovery and productivity of the concentrator  114 . The exhaust gas may exit the system  100  through an exhaust muffler  126 . A pressure transducer  128  may be located between the concentrator  114  and the vacuum generator  124  to get a pressure reading of the exhaust flow from the concentrator  114 . At maximum rated speed and a flow rate of 20.8 SLPM, the pressure at the vacuum side is preferably −5.9 psig nominal and may range from −8.8 to −4.4 psig. 
     1. Compressor/Variable Speed Controller 
     Example of compressor technologies that may be used for the compressor  112  include, but not by way of limitation, rotary vane, linear piston with wrist pin, linear piston without wrist pin, nutating disc, scroll, rolling piston, diaphragm pumps, and acoustic. Preferably the compressor  112  and vacuum generator  124  are integrated with the motor  118  and are oil-less, preventing the possibility of oil or grease from entering the air flow path. 
     The compressor  112  preferably includes, at a minimum, a 3:1 speed ratio, with a low speed of at least 1,000 rpm and a 15,000 hour operating life when run at full speed. Operating temperature surrounding the compressor/motor system is preferably 32 to 122 degrees F. Storage temperature is preferably −4 to 140 degree F. Relative humidity is preferably 5 to 95% RH noncondensing. Voltage for the compressor  112  is preferably 12 V DC or 24V DC and the electrical power requirements are preferably less than 100 W at full speed and rated flow/nominal pressure and less than 40 W at ⅓ speed and ⅓ flow at rated pressure. A shaft mounted fan or blower may be incorporated with the compressor  112  for compressor cooling and possible complete system cooling. Preferably, the maximum sound pressure level of the compressor  112  may be 46 dBA at a maximum rated speed and flow/pressure and 36 dBA at ⅓ rated speed. Preferably the compressor  112  weighs less than 3.5 pounds. 
     It is desirable for the compressor  112  to run at a variety of speeds; provide the required vacuum/pressure levels and flow rates, emit little noise and vibration, emit little heat, be small, not be heavy, and consume little power. 
     The variable-speed controller  119  is important for reducing the power consumption requirements of the compressor  112  on the rechargeable battery  104  or other energy source. With a variable-speed controller, the speed of the compressor  112  may be varied with the activity level of the user, metabolic condition of the user, environmental condition, or other condition indicative of the oxygen needs of the user as determined through the one or more output sensors  106 . 
     For example, the variable-speed controller may decrease the speed of the motor  118  when it is determined that the oxygen requirements of the user  108  are relatively low, e.g., when the user is sitting, sleeping, at lower elevations, etc., and increased when it is determined that the oxygen requirements of the user  108  are relatively high or higher, e.g., when the user stands, when the user is active, when the user is at higher elevations, etc. This helps to conserve the life of the battery  104 , reduce the weight and size of the battery  104 , and reduce the compressor wear rate, improving its reliability. 
     The variable-speed controller  119  allows the compressor  112  to operate at a low average rate, typically the average rate or speed will be between full speed and ⅙ full speed of the compressor  112 , resulting in an increase in battery life, decrease in battery size and weight, and decrease in compressor noise and emitted heat. 
     2. Concentrator 
     In a preferred embodiment, the concentrator  114  is an Advanced Technology Fractionator (ATF) that may be used for medical and industrial applications. The ATF may implement a pressure swing adsorption (PSA) process, a vacuum pressure swing adsorption (VPSA) process, a rapid PSA process, a very rapid PSA process or other process. If a PSA or VPSA process is implemented, the concentrator may include a rotating valve or a non-rotating valve mechanism to control air flow through multiple sieve beds therein. The sieve beds may be tapered so that they have larger diameter where gaseous flow enters the beds and a smaller diameter where gaseous flow exits the beds. Tapering the sieve beds in this manner requires less sieve material and less flow to obtain the same output. 
     Although an ATF concentrator  114  is used in a preferred embodiment, it will be readily apparent to those skilled in the art that other types of concentrators or air-separation devices may be used such as, but not by way of limitation, membrane separation types and electrochemical cells (hot or cold). If other types of concentrators or air-separation devices are used, it will be readily apparent to those skilled in the art that some aspects described herein may change accordingly. For example, if the air-separation device is a membrane separation type, pumps other than a compressor may be used to move air through the system. 
     The ATF preferably used is significantly smaller that ATFs designed in the past. The inventors of the present invention recognized that reducing the size of the ATF concentrator  114  not only made the system  100  smaller and more portable, it also improved the recovery percentage, i.e., the percentage of oxygen gas in air that is recovered or produced by the concentrator  114  and the productivity (liters per minute/lb. of sieve material) of the concentrator  114 . Reducing the size of the ATF decreases the cycle time for the device. As a result, productivity is increased. 
     Further, finer sieve materials increase recovery rates and productivity. The time constant to adsorb unwanted gases is smaller for finer particles because the fluid path is shorter for the gases than for larger particles. Thus, fine sieve materials having small time constants are preferred. An example of a sieve material that may be used in the ATF concentrator  114  is LithiumX Zeolite that allows for a high exchange of Lithium ions. The bead size may, for example, be 0.2-0.6 mm. In an alternative embodiment, the Zeolite may be in the form of a rigid structure such as an extruded monolith or in the form of rolled up paper. In this embodiment, the Zeolite structure would allow for rapid pressure cycling of the material without introducing significant pressure drop between the feed and product streams. 
     The size of the concentrator  114  may vary with the flow rate desired. For example, the concentrator  114  may come in a 1.5 Liter per minute (LPM) size, a 2 LPM size, a 2.5 LPM size, a 3 LPM size, etc. 
     The oxygen gas generator  102  may also include an oxygen source in addition to the concentrator  114  such as, but not by way of limitation, a high-pressure oxygen reservoir, as described in more detail below. 
     An ATF valve controller  133  may be integral with or separate from the control unit  110  and is coupled with valve electronics in the concentrator  114  for controlling the valve(s) of the concentrator  114 . 
     The concentrator may have one or more of the following energy saving modes: a sleep mode, a conserving mode, and an active mode. Selection of these modes may be done manually by the user  108  or automatically such as through the described one or more sensors  106  and control unit  110 . 
     With reference to  FIGS. 9A and 9B , an embodiment of a concentrator  114  that may be used in the oxygen generator  102  will now be described in more detail. Although the concentrator  114  will be described as separating oxygen from air, it should be noted that the concentrator  114  may be used for other applications such as, but not by way of limitation, air separations for the production of nitrogen, hydrogen purification, water removal from air, and argon concentration from air. As used herein, the term “fluids” includes both gases and liquids. 
     The concentrator  114  described below includes numerous improvements over previous concentrators that result in increased recovery of the desired component and increased system productivity. Improved recovery is important since it is a measure of the efficiency of the concentrator. As a concentrator&#39;s recovery increases, the amount of feed gas required to produce a given amount of product decreases. Thus, a concentrator with higher recovery may require a smaller feed compressor (e.g., for oxygen concentration from air) or may be able to more effectively utilize feed gas to recover valuable species (e.g., for hydrogen purification from a reformate stream). Improved productivity is important since an increase in productivity relates directly to the size of the concentrator. Productivity is measured in units of product flow per mass or volume of the concentrator. Thus, a concentrator with higher productivity will be smaller and weigh less than a concentrator that is less productive, resulting in a more attractive product for many applications. Therefore, concentrator improvements in recovery, productivity, or both are advantageous. The specific improvements that lead to improved recovery and productivity are detailed below. 
     The concentrator  114  includes five adsorption beds  300 , each containing a bed of adsorbent material which is selective for a particular molecular species of fluid or contaminant, a rotary valve assembly  310  for selectively transferring fluids through the adsorption beds  300 , an integrated tube-assembly and mainifold “manifold”  320 , a product tank cover  330 , and a valve assembly enclosure  340 . 
     The adsorption beds  300  are preferably straight, elongated, molded, plastic vessels surrounded by the product tank cover  330 , which is made of metal, preferably aluminum. The molded, plastic adsorption beds  300  surrounded by the metal cover  330  make for a low-cost design without the detrimental effects of water influx that occur with prior-art plastic housings or covers. Plastic adsorption beds have the inherent problem of the plastic being permeable to water. This allows water to penetrate into the adsorbent material, decreasing the performance of the adsorbent material. Surrounding the plastic adsorption beds  300  with the aluminum cover  330 , which also may serve as a product accumulation tank, maintains the low cost of the design and does not sacrifice performance. 
     Each adsorption bed  300  includes a product end  350  and a feed end  360 . With reference additionally to  FIG. 10 , the product ends  350  of the beds  300  communicate with incoming product passages  370  of the manifold  320  through product lines  380  for communication with the rotary valve assembly  310 . The feed ends  360  of the beds  300  communicate with outgoing feed passages  390  of the manifold  320  for communication with the rotary valve assembly  310 . 
     The manifold  320  may also include outgoing product passages  400  that communicate the rotary valve assembly  310  with the interior of the product tank  330 , an incoming feed passage  410  that communicates the rotary valve assembly  310  with a feed pressure line  420 , and a vacuum chamber  430  that communicates the rotary valve assembly  310  with a vacuum pressure line  440 . A product delivery line  450 , which may be the same as the supply line  121  described above with respect to  FIG. 8 , communicates with the interior of the product tank  330 . The vacuum pressure line  440  may communicate directly or indirectly with the vacuum generator  124  for drawing exhaust gas from the concentrator  114 . 
     In use, air flows from the compressor  112  to the feed pressure line  420 , through the incoming feed passage  410  of the manifold  320 . From there, air flows to the rotary valve assembly  310  where it is distributed back through outgoing feed passages  390  of the manifold  320 . From there, the feed air flows to the feed ends  360  of the adsorption beds  300 . The adsorption beds  300  include adsorbent media that is appropriate for the species that will be adsorbed. For oxygen concentration, it is desirable to have a packed particulate adsorbent material that preferentially adsorbs nitrogen relative to oxygen in the feed air so that oxygen is produced as the non-adsorbed product gas. An adsorbent such as a highly Lithium exchanged X-type Zeolite may be used. A layered adsorbent bed that contains two or more distinct adsorbent materials may also be used. As an example, for oxygen concentration, a layer of activated alumina or silica gel used for water adsorption may be placed near the feed end  360  of the adsorbent beds  300  with a lithium exchanged X-type zeolite used as the majority of the bed toward the product end  350  to adsorb nitrogen. The combination of materials, used correctly, may be more effective than a single type of adsorbent. In an alternative embodiment, the adsorbent may be a structured material and may incorporate both the water adsorbing and nitrogen adsorbing materials. 
     The resulting product oxygen gas flows towards the products ends  350  of the adsorption beds  300 , through the product lines  380 , through incoming product passages  370  of the manifold  320 , and to the rotary valve assembly  310 , where it is distributed back through the manifold  320  via the outgoing product passage  400  and into the product tank  330 . From the product tank  330 , oxygen gas is supplied to the user  108  through the product delivery line  450  and the supply line  121 . 
     With reference to  FIGS. 9B ,  11 A,  11 B,  12 A,  14 A, and  14 B, an embodiment of the rotary valve assembly  310  will now be described. The rotary valve assembly  310  includes a rotary valve shoe or disk  500  and a valve port plate or disk  510 . The rotary valve shoe  500  and valve port plate  510  are both preferably circular in construction and made from a durable material such as ceramic, which can be ground to a highly polished flat finish to enable the faces of the valve shoe  500  and port plate  510  to form a fluid-tight seal when pressed together. 
     With reference specifically to  FIG. 11A , the rotary valve shoe  500  has a flat, bottom engagement surface  520  and a smooth cylindrical sidewall  530 . The valve shoe  500  has several symmetrical arcuate passages or channels cut into the engagement surface  520 , all of which have as their center the geometric center of the circular engagement surface  520 . The passages or channels include opposite high-pressure feed channels  540 , equalization channels  550 , opposite low-pressure exhaust passages  560 , circular low-pressure exhaust groove  570  which communicates with exhaust passages  560 , opposite product delivery channels  580 , opposite purge channels  590 , a high-pressure central feed passage  600 , a first annular vent groove  610 , and a second annular vent groove  620 . 
     With reference additionally to  FIG. 11B , a parallel, top, second valve surface  630  of the rotary valve shoe  500  will now be described. The purge channels  590  of the engagement surface  520  communicate with each other through vertical, cylindrical purge passages  640  and a rainbow-shaped purge groove  650  on the top surface  630 . The equalization channels  550  of the engagement surface  520  extend vertically through the valve shoe  500 . Pairs of equalization channels  550  communicate through equalization grooves  660  on the top surface  630 . The equalization grooves  660  are generally U-shaped and extend around receiving holes  670 . Equalization routing via the grooves  660  on the second valve surface  630 , in a plane out of and parallel to a plane defined by the engagement surface  520 , helps to maintain the relatively small size of the rotary valve shoe  500  while at the same time enabling more complex fluid routing through the valve shoe  500 . The equalization grooves allow the secondary valve surface to be used to equalize pressures between adsorption beds  300 . 
     With reference to  FIGS. 9B ,  14 A, and  14 B, a first valve shoe cover  680  is disposed over the second valve surface  630  to isolate the various grooves and passages on the second valve surface  630 . Both the first valve shoe cover  680  and the second valve shoe cover  690  include aligned central holes  691 ,  692 , respectively, for communicating the central feed passage  600  with a high-pressure feed fluid chamber formed around the periphery of a cylindrical base  693  of the second valve shoe cover  690 . The first valve shoe cover  680  also includes a plurality of holes  694  near its periphery for the purpose of maintaining a balance of pressure during operation on either side of the first valve shoe cover  680  between the cylindrical base  693  and the second valve surface  630 . Routing the high-pressure feed fluid into the high-pressure feed fluid chamber on the top or backside of the valve shoe  500  causes pressure balancing on the valve shoe  500  that counteracts the pressure force urging the valve shoe  500  away from the port plate  510 . A spring or other type of passive sealing mechanism (not shown) may be used to hold the rotary valve shoe  500  against the port plate  510  when the concentrator  114  is not operating. 
     With reference to  FIG. 11A , to additionally counteract the pressure force that works to unseat the rotary valve shoe  500  from the port plate  510 , the exhaust groove  570  is sized such that, when the concentrator  114  is operated at nominal feed and purge (vacuum) pressures, the sealing force due to the vacuum in the exhaust groove  570  substantially balances this unseating pressure force. This enables the use of relatively small passive sealing mechanisms, reducing the torque and power required to turn the rotary valve shoe  500  and also reduces the weight and size of the concentrator  114 . 
     With reference to  FIG. 12A , the valve port plate  510  will now be described in greater detail. The valve port plate  510  has a flat engagement surface  700  that engages the flat engagement surface  520  of the rotary valve shoe  500  and a smooth cylindrical sidewall  710 . With reference additionally to  FIG. 9B , an underside of the valve port plate  510  is disposed on a manifold gasket  720 . The valve port plate  510  includes multiple sets of generally symmetric concentrically disposed ports or openings aligned with openings in the manifold gasket  720  to communicate the ports in the plate  510  with the passages in the manifold  320 . The ports extend vertically through the valve port plate  510  in a direction generally perpendicular to the engagement surface  700 . In an alternative embodiment, the ports extend vertically through the valve port plate  510  in an angular direction toward the engagement surface  700 . Preferably, all of the ports of each concentric set have the same configuration. Each concentric set of ports will now be described in turn. 
     A first set of eight circular vacuum ports  730  concentrically disposed at a first radius from the geometric center of the valve port plate  510  communicate with the vacuum chamber  430  of the manifold  320  and the exhaust gas grooves  570  of the valve shoe  500 . In the preferred embodiment, eight ports are used as they allow sufficient gas flow through the valve without significant pressure drop. In an alternative embodiment, a number of ports different from eight could be used. 
     A second set of five round outgoing feed ports  740  concentrically disposed at a second radius from the geometric center of the valve port plate  510  communicate with outgoing feed passages  390  of the manifold  320 , the feed channels  540  of the valve shoe  500 , and the vacuum ports  730  via the exhaust passages  560  of the valve shoe  500 . 
     A third set of five generally elliptical incoming product ports  750  concentrically disposed at a third radius from the geometric center of the valve port plate  510  communicate with the incoming product passages  370  of the manifold  320 , the equalization channels  550  of the valve shoe  500 , the purge channels  590  of the valve shoe  500 , and the product delivery channels  580 . 
     A fourth set of five circular outgoing product ports  760  concentrically disposed at a fourth radius from the geometric center of the valve port plate  510  communicate with the outgoing product passages  400  of the manifold  320  and the incoming product ports  750  via the product delivery channels  580 . 
     A fifth set of three circular port plate alignment holes  731  concentrically disposed at a fifth radius from the geometric center of the valve port plate  510  align with alignment pins  321  ( FIGS. 9B ,  10 ) on the manifold  320 . The alignment holes  731  ensure the port plate  510  will sit in proper alignment with the manifold  320 . In an alternative embodiment, two or more alignment holes located at one or more radiuses from the geometric center of the valve port plate  510  may be aligned with an equal number of alignment pins located at set positions on the manifold  320 . 
     A round central incoming feed port  770  disposed at the geometric center of the valve port plate  510  and the center of rotation of the valve assembly  310  communicates with the incoming feed passage  410  of the manifold  320  and the central feed passage  600  of the rotary valve shoe  500 . 
     In the rotary valve assembly  310  described above, a maximum of 1 PSI pressure drop occurs through any port of the valve assembly  310  when the system is producing 3 LPM of oxygen product. At lesser flows, the pressure drop is negligible. 
     With reference additionally to  FIG. 12B , a single pressure swing adsorption cycle of the concentrator  114  will now be described. During use, the rotary valve shoe  500  rotates with respect to the valve port plate  510  so that the cycle described below is sequentially and continuously established for each adsorption bed  300 . The speed of rotation of the rotary valve shoe  500  with respect to the valve port plate  510  may be varied alone, or in combination with a variable-speed compressor, in order to provide the optimal cycle timing and supply of ambient air for a given production of product. To help the reader gain a better understanding of the invention, the following is a description of what occurs in a single adsorption bed  300  and the rotary valve assembly  310  during a single cycle. It should be noted, with each revolution of the rotary valve shoe  500 , the adsorption beds  300  undergo two complete cycles. For each cycle, the steps include: 1) pre-pressurization  774 , 2) adsorption  776 , 3) first equalization down  778 , 4) second equalization down  780 , 5) co-current blowdown  782 , 6) low-pressure venting  784 , 7) counter-current purge and low-pressure venting  786 , 8) first equalization up  788 , and 9) second equalization up  790 . Each of these steps will be described in turn below for an adsorption bed  300 . 
     In the pre-pressurization step  774 , air flows from the compressor  112  to the feed pressure line  420 , through the incoming feed passage  410  of the manifold  320 . From there, air flows through the central incoming feed port  770  of the port plate  510 , through the central feed passage  600  and out the feed channels  540  of the valve shoe  500 , through the outgoing feed ports  740 , and through outgoing feed passages  390  of the manifold  320 . From there, the feed air flows to the feed ends  360  of the adsorption beds  300 . With reference to  FIG. 11A , because the feed channel  540  is advanced with respect to the product delivery channel  580  (i.e., initially the feed channel  540  is in communication with outgoing feed port  740  and the product delivery channel  580  is blocked, not in communication with the incoming product port  750 ), the feed end  360  of the adsorption bed  300  is pressurized with feed gas, i.e., pressurized, prior to the commencement of product delivery. In alternative embodiments, the product end  350  may be pre-pressurized with product gas, or the product end  350  may be pre-pressurized with product gas and the feed end  360  may be pre-pressurized with feed gas. 
     In the adsorption step  776 , because the product delivery channel  580  is in communication with the incoming product port  750 , adsorption of Nitrogen occurs in the bed  300  and the resulting product oxygen gas flows towards the product ends  350  of the adsorption beds  300 , through the product lines  380 , and through incoming product passages  370  of the manifold  320 . From there, oxygen gas flows through the incoming product port, into and out of the product delivery channel  580 , through outgoing product port  760 , through the outgoing product passage  400 , and into the product tank  330 . From the product tank  330 , oxygen gas is supplied to the user  108  through the product delivery line  450  and the supply line  121 . 
     In the first equalization-down step  778 , the product end  350  of the bed  300 , which is at a high pressure, is equalized with the product end of another bed, which is at a low pressure, to bring the product end  350  of the bed  300  to a lower, intermediate pressure. The product ends  350  communicate through the product lines  380 , the incoming product passages  370 , the incoming product ports  750 , the equalization channels  550 , and the equalization groove  660 . As indicated above, equalization routing via the grooves  660  on the second valve surface  630 , in a plane out of and parallel to a plane defined by the engagement surface  520 , helps to maintain the relatively small size of the rotary valve shoe  500 , in order to keep the torque required to turn the valve shoe  500  as low as possible, while at the same time enabling more complex fluid routing through the valve shoe  500 . In this step  778  and the equalization steps  780 ,  788 ,  790  to be discussed below, the adsorption beds  300  may be equalized at either the feed end  360 , the product end  350 , or a combination of the feed end  360  and the product end  350 . 
     In the second equalization-down step  780 , the product end  350  of the bed  300 , which is at an intermediate pressure, is equalized with the product end of another bed, which is at a lower pressure, to bring the product end  350  of the bed  300  further down to an even lower pressure than in step  778 . Similar to the first equalization-down step  778 , the product ends  350  communicate through the product lines  380 , the incoming product passages  370 , the incoming product ports  750 , the equalization channels  550 , and the equalization groove  660 . 
     In the co-current blowdown (“CCB”) step  782 , oxygen enriched gas produced from the product end  350  of the adsorption bed  300  is used to purge a second adsorption bed  300 . Gas flows from the product side of the adsorption bed  300 , through product line  380 , incoming product passage  370 , and incoming product port  750 . The gas further flows through purge channel  590 , purge passage  640 , through the purge groove  650 , out the purge passage  640  on the opposite side of the valve shoe  500 , through the purge channel  590 , through the incoming product port  750 , through the incoming product passage  370 , through the product line  380 , and into the product end  350  of adsorption bed  300  to serve as a purge stream. In an alternative embodiment, in this step  782  and the following step  784 , co-current blowdown may be replaced with counter-current blowdown. 
     In the low-pressure venting (“LPV”) step  784 , the adsorption bed  300  is vented to low pressure through the feed end  360  of the adsorption bed  300 . The vacuum in the exhaust groove  570  of the rotary valve shoe  500  communicates with the exhaust passage  560  and the feed end  360  of the adsorption bed  300  (via the outgoing feed port  740  and outgoing feed passage  390 ) to draw the regeneration exhaust gas out of the adsorption bed  300 . The low pressure venting step  784  occurs without introduction of oxygen enriched gas because the exhaust passage  560  is in communication with the outgoing feed port  740  and the purge channel  590  is not in communication with the incoming product port  750 . 
     In the counter-current purge and low-pressure venting (“LPV”) step  786 , oxygen enriched gas is introduced into the product end  350  of the adsorption bed  300  in the manner described above in step  782  concurrently with the feed end  360  of the adsorption bed  300  being vented to low pressure as was described in the above step  784 . Counter-current purge is introduced into the product end  350  of the adsorbent bed  300  through fluid communication with the product end  350  of a second adsorption bed  300 . Oxygen enriched gas flows from the product end  350  of the second adsorption bed  300  through the product line  380 , incoming product passage  370 , incoming product port  750 , through purge channel  590 , purge passage  640 , through the purge groove  650 , out the purge passage  640  on the opposite side of the valve shoe  500 , through the purge channel  590 , through the incoming product port  750 , through the incoming product passage  370 , through the product line  380 , and into the product end  350  of adsorption bed  300 . Because the exhaust passage  560  is also in communication with the outgoing feed port  740  during this step  786 , oxygen enriched gas flows from the product end  350  to the feed end  360 , regenerating the adsorption bed  300 . The vacuum in the exhaust groove  570  of the rotary valve shoe  500  communicates with the exhaust passage  560  and the feed end  360  of the adsorption bed  300  (via the outgoing feed port  740  and outgoing feed passage  390 ) to draw the regeneration exhaust gas out of the adsorption bed  300 . From the exhaust passage  560 , the exhaust gas flows through the vacuum ports  730 , into the vacuum chamber  430 , and out the vacuum pressure line  440 . In an alternative embodiment, the vacuum may be replaced with a low-pressure vent that is near atmospheric pressure or another pressure that is low relative to the feed pressure. In another embodiment, product gas from the product tank  330  is used to purge the product end  350  of the adsorbent bed  300 . 
     In the first equalization-up step  788 , the product end  350  of the bed  300 , which is at a very low pressure, is equalized with the product end of another bed, which is at a high pressure, to bring the adsorption bed  300  to a higher, intermediate pressure. The product ends  350  communicate through the product lines  380 , the incoming product passages  370 , the incoming product ports  750 , the equalization channels  550 , and the equalization groove  660 . 
     In the second equalization-up step  790 , the product end  350  of the bed  300 , which is at an intermediate pressure, is equalized with the product end of another bed, which is at a higher pressure, to bring the product end  350  of the bed  300  further up to an even higher pressure than in step  788 . Similar to the first equalization-down step  778 , the product ends  350  communicate through the product lines  380 , the incoming product passages  370 , the incoming product ports  750 , the equalization channels  550 , and the equalization groove  660 . 
     It should be noted, in a preferred embodiment, the combined duration of feed steps  774 ,  776  may be substantially the same as the combined duration of purge steps  782 ,  784 ,  786 , which may be substantially three times the duration of each equalization step  778 ,  780 ,  788 ,  790 . In an alternative embodiment, the relative duration of the feed steps  774 ,  776 , the purge steps  782 ,  784 ,  786 , and the each equalization step  778 ,  780 ,  788 ,  790  may vary. 
     After the second equalization-up step  790 , a new cycle begins in the adsorption bed  300  starting with the pre-pressurization step  774 . 
     The five-bed concentrator  114  and cycle described above has a number of advantages over other-numbered concentrators and cycles used in the past, some of which are described below. The multiple equalization steps  788 ,  790  at the product ends  350  and the pre-pressurization step  774  contribute to the pre-pressurization of the adsorption beds  300  prior to product delivery. As a result, the beds  300  reach their ultimate pressure (substantially equal to the feed pressure) quickly and thereby allow for maximum utilization of the adsorbent media. Additionally, pre-pressurizing the adsorbent beds  300  allows product to be delivered at substantially the same pressure as the feed, thereby retaining the energy of compression in the stream, which makes the product stream more valuable for use in downstream processes. In an alternative embodiment, pre-pressurizing the beds  300  with product before exposing the feed end  360  of the bed  300  to the feed stream eliminates any pressure drop experienced due to the fluid interaction or fluid communication between two or more adsorbent beds  300  on the feed end  360 . Additionally, compared to systems with greater numbers of beds, the use of a 5-bed system, reduces the duration and number of beds that are in fluid communication with the feed channels  540  at the same time, thereby reducing the propensity for fluid flow between adsorption beds. Since fluid flow between adsorption beds is associated with a reversal of the flow direction in the higher pressure bed (resulting in decreased performance), reduction in this effect is advantageous. 
     A further advantage of a 5-bed system over many systems is that it includes a small number of adsorption beds  300 , allowing the concentrator to be relative small, compact, and light-weight, while delivering sufficient flow and purity and maintaining high oxygen recovery. Other PSA systems, typically those with a small number of adsorption beds, result in deadheading the compressor (resulting in high power use) during a portion of the cycle. Deadheading the compressor eliminates detrimental flow between the feed side  360  of the two or more adsorption beds  300  (as discussed above) but increases system power. The 5-bed system eliminates compressor deadheading and minimizes performance-limiting feed side  360  flow between adsorbent beds  300 . 
     Use of the multiple pressure equalization steps  778 ,  780 ,  788 ,  790  reduces the amount of energy of compression required to operate the concentrator  114 . Equalizing the beds  300  conserves high-pressure gas by moving it to another bed  300  rather than venting it to the atmosphere or to a vacuum pump. Because there is a cost associated with pressurizing a gas, conserving the gas provides a savings and improves recovery. Also, because a bed  300  may contain gas enriched with product, usually at the product end  350  of the bed  300 , allowing this gas to move into another bed  300 , rather than venting it, conserves product and improves recovery. The number of equalizations are preferably between one and four. It should be noted, each equalization represents two equalization steps, an equalization-down step and an equalization-up step. Thus, two equalizations means two down equalizations and two up equalizations, or four total equalizations. The same is true for other-number equalizations. In a preferred embodiment, one to four equalizations (two to eight equalization steps) are used in each cycle. In a more preferred embodiment, one to three equalizations (two to six equalization steps) are used in each cycle. In a most preferred embodiment, two equalizations (four equalization steps) are used in each cycle. 
     In alternative embodiments, the concentrator  114  may have other numbers of adsorption beds  300  based on the concentration of the feed stream, the specific gases to be separated, the pressure swing adsorption cycle, and the operating conditions. For example, but not by way of limitation, there also are advantages to four-bed concentrators and six-bed concentrators. When operating a cycle similar to that described above with a four-bed concentrator, the problem of fluid communication between the feed channels  540  and more than one adsorption bed (at one instant) is completely eliminated. When the feed-end fluid communication is eliminated, the feed steps  774 ,  776  occur in a more desirable fashion resulting in improved recovery of the desired product. The advantages of a six-bed system, compared to a five-bed system, are realized when the pressure-swing cycle described above is modified so that there are three equalization up stages and three equalization down stages instead of two equalization up stages and two equalization down stages. A third equalization is advantageous when the feed gas is available at high pressure. The third equalization conserves compressor energy because it allows the equalized beds to obtain substantially 75% of the feed pressure compared to substantially 67% of the feed pressure when two equalization stages are used. In any PSA cycle, whenever an equalization up occurs, there is a corresponding equalization down. The requirement of matching equalization stages imparts some restrictions on the relative timing of the cycle steps. If, for example, the duration of the feed step is substantially the same as the duration of each equalization step, then a six-bed cycle would provide the required matching of equalization stages. 
     A number of additional inventive aspects related to the concentrator  114  that increase recovery of a desired component and system productivity will now be described. With reference to  FIGS. 9A ,  9 B,  13 A, and  13 B, an embodiment of a media retention cap  800  that reduces dead volume in the adsorption beds  300  will now be described. Each media retention cap  800  is located at the product end  350  of the adsorption bed  300  and supports the adsorbent material above the media retention cap  800 . A spring  810  located within and below the media retention cap  800  urges the media retention cap  800  upwards to hold the packed bed of adsorbent material firmly in place. The media retention cap  800  has a cylindrical base  820  with first and second annular flanges  830 ,  840 . The second annular flange  840  terminates at its top in a circular rim  850 . A top surface  860  of the media retention cap  800  includes a plurality of ribs  870  radiating in a generally sunburst pattern from a central port  880 . Adjacent the central port  880 , gaps  890  create diffusion zones for purge fluid coming out of the central port  880 . The gaps  890  and the radiating ribs  870  cause the purge fluid to be distributed outward from the central port  880 , causing a more uniform, improved regeneration of the adsorbent material during a purging step. The radiating ribs  870  also help to channel product gas towards the central port  880  during a product delivery step. In an alternative embodiment, the media retention cap  800  may have a generally non-cylindrical surface to retain media in a generally non-cylindrical adsorbtion bed  300 . In a further alternative embodiment, the central port  880  may be located away from the geometric center of the either cylindrical or non-cylindrical media retention cap  800 . 
     With reference to  FIG. 13B , on the underside of the media retention cap  800 , the cylindrical base  820  forms an interior chamber in which the spring  810  is disposed. A central port nipple  900  extends from a bottom surface  910  of the media retention cap  800 . An end of the product line  380  connects to the central port nipple  900  for communicating the product end  350  of the adsorption bed  300  with the incoming product passage  370  of the manifold  320 . 
     In the past, media retention caps may be held in place with a spring that fits inside and above the cap so that the spring is in the fluid flow path between the bottom of the adsorbent material and any exit port, at the product end  350  of the bed  300 . The volume in which the spring is housed represents dead volume in the system. As used herein, “dead volume” is system volume that is compressed and purged, but does not contain adsorbent media. The process of filling this volume with compressed feed and then venting that volume represents wasted feed. The improved media retention cap  800  does not add dead volume to the system because the spring  810  is housed outside of the fluid flow path. Elimination of any extra volume within the system results directly in more effective utilization of the feed, and, thus, higher recovery of the desired product. 
     With reference to  FIGS. 14A and 14B , an embodiment of a centering mechanism for maintaining the rotary valve shoe  500  laterally fixed and centered with respect to the valve port plate  510  will now be described. The centering mechanism may include a centering pin  920  having a hollow cylindrical shape and made of a rigid material. When the engagement surface  520  of the rotary valve shoe  500  is engaged with the engagement surface  700  of the valve port plate  510 , the centering pin  920  is partially disposed in the central feed passage  600  of the rotary valve shoe  500  and the central incoming feed port  770  of the valve port plate  510 . In use, the rotary valve shoe  500  rotates around the centering pin  920  and the hollow interior of the centering pin  920  allows high-pressure feed fluid to flow there through. The pin  920  maintains the rotating valve shoe in a fixed position relative to the valve port plate  510 . In the past, the rotary valve shoe was roughly centered with respect to the valve port plate by the motor that drives the rotary valve shoe. If the rotary valve shoe  500  and the valve port plate  510  are off center with respect to each other, the concentrator  114  will not cycle as intended, inhibiting the productivity, recovery, and efficiency of the concentrator. The precision offered by the centering pin  920  is important when the valve assembly  310  is controlling complex cycles or maintaining very small pressure drops. 
     With reference to  FIGS. 15A and 15B , a rotary valve assembly constructed in accordance with another embodiment of the invention includes an alternative centering mechanism to maintain the rotating valve shoe  500  in a fixed position relative to the valve port plate  510 . A circular centering ring  930  fits snugly over the smooth cylindrical sidewall  530  of the rotary valve shoe  500  and the smooth cylindrical sidewall  710  of the stationary valve port plate  510 . The circular ring  930  centers the rotary valve shoe  500  relative to the valve port plate  510  by holding the rotary shoe  500  in a fixed position relative to the port plate  510  while at the same time allowing the rotary valve shoe  500  to rotate. 
     With reference to  FIGS. 16A-16C , an embodiment of an elastic link for coupling the motor  118  to the valve shoe  500  will now be described. A drive mechanism  940  includes a drive shaft  950 , a drive wheel  960 , and three (two shown) elastic chain links  970 . The drive shaft  950  may be connected to the motor  118  for rotating the drive wheel  960 . With reference to  FIG. 16C , a lower side  980  of the drive wheel  960  may include downwardly protruding cylindrical support posts  990 . Similarly, with reference to  FIG. 16B , an upper side  1000  of the second valve shoe cover  690  may include upwardly protruding cylindrical support posts  1010 . The elastic chain links  970  are preferably made of semi-rigid, elastic material (such as silicon rubber) and have a generally wrench-shaped configuration. Each elastic chain link  970  includes cylindrical receiving members  1020  with central cylindrical bores  1030 . The cylindrical receiving members  1020  are joined by a narrow connecting member  1040 . The drive wheel  960  is coupled to the second valve shoe cover  690  through the elastic chain links  970 . One receiving member  1020  of each elastic chain link receives the support post  990  of the drive wheel  960  and the other receiving member  1020  receives the support post  1010  of the second valve shoe cover  690 . In the past, rigid connections were made between the motor and the rotating valve shoe. These rigid connections caused the rotating valve shoe to be affected by vibration or other non-rotational movement of the motor. The elastic chain links  970  absorb the vibration and non-rotational movement of the motor, preventing this detrimental energy from being imparted to the rotating valve shoe  500 . 
       FIG. 17  is a table of experimental data from a concentrator similar to the concentrator  114  shown and described above with respect to  FIGS. 9-16 . As shown by this table, the recovery of oxygen from air with the concentrator  114  is 45-71% at about 90% purity. The ratio of adiabatic power (Watts) to oxygen flow (Liters Per Minute) is in the range of 6.2 W/LPM to 23.0 W/LPM. As defined in Marks&#39; Standard Handbook for Mechanical Engineers, Ninth Edition, by Eugene A. Avallone and Theodore Baumeister, the equation for adiabatic power, taken from the equation from adiabatic work, is as follows: 
     
       
         
           
             Power 
             = 
             
               
                 W 
                 t 
               
               = 
               
                 
                   P 
                   1 
                 
                  
                 
                   
                     
                       V 
                       1 
                     
                      
                     
                       ( 
                       
                         k 
                         
                           1 
                           - 
                           k 
                         
                       
                       ) 
                     
                   
                   [ 
                   
                     
                       
                         ( 
                         
                           
                             P 
                             2 
                           
                           
                             P 
                             1 
                           
                         
                         ) 
                       
                       
                         
                           k 
                           - 
                           1 
                         
                         k 
                       
                     
                     - 
                     1 
                   
                   ] 
                 
                  
                 C 
               
             
           
         
       
         
         Power=Adiabatic Power (Watts) 
         W=Adiabatic Work (Joule) 
         t=time (Second) 
         P 1 =Atmospheric Pressure (psia) 
         P 2 =Compressor/Vacuum pressure (psia) 
         k=Ratio of Specific Heats=constant=1.4 (for air) 
         V 1 =Volumetric flow rate at atmospheric pressure (SLPM) 
         C=Conversion Factor, added by authors for clarity=0.114871 Watts/psi/LPM 
       
    
     B. Energy Source 
     With reference additionally to  FIG. 18 , in order to properly function as a lightweight, portable system  100 , the system  100  must be energized by a suitable rechargeable energy source. The energy source preferably includes a rechargeable battery  104  of the lithium-ion type. It will be readily apparent to those skilled in the art that the system  100  may be powered by a portable energy source other than a lithium-ion battery. For example, a rechargeable or renewable fuel cell may be used. Although the system is generally described as being powered by a rechargeable battery  104 , the system  100  may be powered by multiple batteries. Thus, as used herein, the word “battery” includes one or more batteries. Further, the rechargeable battery  104  may be comprised of one or more internal and/or external batteries. The battery  104  or a battery module including the battery  104  is preferably removable from the system  100 . The system  100  may use a standard internal battery, a low-cost battery, an extended-operation internal battery, and an external secondary battery in a clip-on module. 
     The system  100  may have a built-in adapter including battery charging circuitry  130  and one or more plugs  132  configured to allow the system  100  to be powered from a DC power source (e.g., car cigarette lighter adapter) and/or an AC power source (e.g., home or office  110  VAC wall socket) while the battery  104  is simultaneously being charged from the DC or AC power source. The adapter or charger could also be separate accessories. For example, the adapter may be a separate cigarette lighter adapter used to power the system  100  and/or charge the battery  104  in an automobile. A separate AC adapter may be used to convert the AC from an outlet to DC for use by the system  100  and/or charging the battery  104 . Another example of an adapter may be an adapter used with wheel chair batteries or other carts. 
     Alternatively, or in addition, a battery-charging cradle  134  adapted to receive and support the system  100  may have an adapter including battery charging circuitry  130  and a plug  132  that also allow the system  100  to be powered while the battery  104  is simultaneously being charged from a DC and/or AC power source. 
     The system  100  and cradle  134  preferably include corresponding mating sections  138 ,  140  that allow the system  100  to be easily dropped into and onto the cradle  134  for docking the system  100  with the cradle  134 . The mating sections  138 , 140  may include corresponding electrical contacts  142 , 144  for electrically connecting the system  100  to the cradle  134 . 
     The cradle  134  may be used to recharge and/or power the system  100  in the home, office, automobile, etc. The cradle  134  may be considered part of the system  100  or as a separate accessory for the system  100 . The cradle  134  may include one or more additional charging receptacles  146  coupled to the charging circuitry  130  for charging spare battery packs  104 . With a charging receptacle  146  and one or more additional battery packs  104 , the user can always have a supply of additional fresh, charged batteries  104 . 
     In alternative embodiments, the cradle  134  may come in one or more different sizes to accommodate one or more different types of systems  100 . 
     The cradle  134  and/or system  100  may also include a humidifying mechanism  148  for adding moisture to the air flow in the system  100  through appropriate connections  149 . In an alternative embodiment of the invention, the humidifying mechanism  148  may be separate from the system  100  and the cradle  134 . If separate from the system  100  and cradle  134 , the cradle  134  and/or system  100  may include appropriate communication ports for communicating with the separate humidifying mechanism  148 . The cradle  134  may also include a receptacle adapted to receive a separate humidifying mechanism  148  for use with the system  100  when the system  100  is docked at the cradle  134 . 
     The cradle  134  and/or system  100  may also include a telemetry mechanism or modem  151  such as a telephone modem, high-speed cable modem, RF wireless modem or the like for communicating the control unit  110  of the system  100  with one or more remote computers. To this end, the cradle  135  may include a line  153  with a cable adapter or telephone jack plug  155 , or a RF antenna  157 . In an alternative embodiment of the invention, the telemetry mechanism or modem  151  may be separate from the cradle  134  and to this end, the cradle  134  or system  100  may include one or more appropriate communication ports, e.g., a PC port, for directly communicating the telemetry mechanism or modem  151  with the cradle  134  or system  100 . For example, the cradle  134  may be adapted to communicate with a computer (at the location of the cradle) that includes the telemetry mechanism or modem  151 . The computer may include appropriate software for communicating information described below using the telemetry mechanism or modem  151  with the one or more remote computers. 
     The telemetry mechanism or modem  151  may be used to communicate physiological information of the user such as, but not by way of limitation, heart rate, oxygen saturation, respiratory rate, blood pressure, EKG, body temperature, inspiratory/expiratory time ratio (I to E ratio) with one or more remote computers. The telemetry mechanism or modem  151  may be used to communicate other types of information such as, but not by way of limitation, oxygen usage, maintenance schedules on the system  100 , and battery usage with one or more remote computers. 
     A user ideally uses the system  100  in its cradle  134  at home, at the office, in the automobile, etc. A user may decide to have more than one cradle, e.g., one at home, one at the office, one in the automobile, or multiple cradles at home, one in each room of choice. For example, if the user has multiple cradles  134  at home, when the user goes from room to room, e.g., from the family room to the bedroom, the user simply lifts the system  100  out of its cradle  134  in one room, and walks to the other room under battery operation. Dropping the system  100  in a different cradle  134  in the destination room restores the electrical connection between the system  100  and the AC power source. Since the system&#39;s batteries  104  are constantly charging or charged when located in the cradle  134 , excursions outside the home, office, etc. are as simple as going from room to room in the user&#39;s home. 
     Because the system  100  is small and light, the system  100  may simply be lifted from the cradle  134  and readily carried, e.g., with a shoulder strap, by an average user to the destination. If the user is unable to carry the system  100 , the system  100  may be readily transported to the destination using a cart or other transporting apparatus. For an extended time away from home, office, etc., the user may bring one or more cradles  134  for use at the destination. Alternatively, in the embodiment of the system  100  including the built-in adapter, power may be drawn from power sources such as a car cigarette lighter adapter and/or an AC power outlet available at the destination. Further, spare battery Packs  104  may be used for extended periods away from standard power sources. 
     If the battery pack  104  includes multiple batteries, the system  100  may include a battery sequencing mechanism to conserve battery life as is well known in the cell phone and laptop computer arts. 
     C. Output Sensor 
     With reference to  FIGS. 7 ,  8  and  19 , one or more output sensors  106  are used to sense one or more conditions of the user  108 , environment, etc. to determine the oxygen flow rate needs of the user and, hence, the oxygen flow rate output requirements for the system  100 . A control unit  110  is linked to the one or more output sensors  106  and the oxygen gas generator  102  to control the oxygen generator  102  in response to the condition(s) sensed by the one or more output sensors  106 . For example, but not by way of limitation, the output sensor(s)  106  may include at least one of, but not by way of limitation, a pressure sensor  150 , a position sensor  152 , an acceleration sensor  154 , a physiological condition or metabolic sensor  156 , and/or an altitude sensor  158 . 
     The first three sensors  150 ,  152 ,  154  (and, in certain circumstances, the physiological condition sensor  156 ) are activity sensors because these sensors provide a signal representing activity of the user  108 . In the delivery of oxygen with a portable oxygen concentration system, it is important to deliver an amount of oxygen gas proportional to the activity level of the user  108  without delivering too much oxygen. Too much oxygen may be harmful for the user  108  and reduces the life of the battery  104 . The control unit  110  regulates the oxygen gas generator  102  to control the flow rate of oxygen gas to the user  108  based on the one or more signals representative of the activity level of the user produced by the one or more sensors  106 . For example, if the output sensor(s)  106  indicates that the user  108  has gone from an inactive state to an active state, the control unit  110  may cause the oxygen gas generator  102  to increase the flow rate of oxygen gas to the user  108  and/or may provide a burst of oxygen gas to the user  108  from a high-pressure oxygen reservoir to be described. If the output sensor(s)  106  indicates that the user  108  has gone from an active state to an inactive state, the control unit  110  may cause the oxygen gas generator  102  to reduce the flow rate of oxygen gas to the user. 
     In an embodiment of the invention, the amount of oxygen gas supplied is controlled by controlling the speed of the compressor motor  118  via the variable-speed controller  119 . 
     Alternatively, or in addition to the variable-speed controller, the supply of oxygen gas may be controlled by the supply valve  160  located in the supply line  121  between the oxygen gas (generator  102  and the user  108 . For example, the supply valve  160  may be movable between at least a first position and a second position, the second position allowing a greater flow of concentrated gaseous oxygen through than the first position. The control unit  110  may cause the supply valve  160  to move from the first position to the second position when one or more of the activity level sensors  152 ,  154 , 156  senses an active level of activity of the user  108 . For example, the control unit  110  may include a timer, and when an active level is sensed for a time period exceeding a predetermined timed period, the control unit  110  causes the valve  160  to move from the first position to the second position. 
     Examples of pressure sensors  150  include, without limitation, a foot switch that indicates when a user is in a standing position compared to a sedentary position, and a seat switch that indicates when a user is in a seated position compared to a standing position. 
     A pendulum switch is an example of a position sensor  152 . For example, a pendulum switch may include a thigh switch positioned pendulously to indicate one mode when the user is standing, i.e., the switch hangs vertically, and another mode when the user seated, i.e., the thigh switch raised to a more horizontal position. A mercury switch may be used as a position sensor. 
     An acceleration sensor  158  such as an accelerometer is another example of an activity sensor that provides a signal representing activity of the user. 
     The physiological condition or metabolic sensor  156  may also function as an activity sensor. The physiological condition sensor  156  may be used to monitor one or more physiological conditions of the user for controlling the oxygen gas generator  102  or for other purposes. Examples of physiological conditions that may be monitored with the sensor  156  include, but without limitation, blood oxygen level, heart rate, respiration rate, blood pressure, EKG, body temperature, and I to E ratio. An oximeter is an example of a sensor that is preferably used in the system  100 . The oximeter measures the blood oxygen level of the user, upon which oxygen production may be at least partially based. 
     An altitude sensor  158  is an example of an environmental or ambient condition sensor that may sense an environmental or ambient condition upon which control of the supply of oxygen gas to the user may be at least partially based. The altitude sensor  158  may be used alone or in conjunction with any or all of the above sensors, the control unit  110  and the oxygen gas generator  102  to control the supply of oxygen gas to the user in accordance with the sensed altitude or elevation. For example, at higher sensed elevations, where air is less concentrated, the control unit may increase the flow rate of oxygen gas to the user  108  and at lower sensed elevations, where air is more concentrated, the control unit may decrease the flow rate of oxygen gas to the user  108  or maintain it at a control level. 
     It will be readily apparent to those skilled in the art that one or more additional or different sensors may be used to sense a condition upon which control of the supply of oxygen gas to the user may be at least partially based. Further, any or all of the embodiments described above for regulating the amount of oxygen gas supplied to the user  108 , i.e., variable-speed controller  119 , supply valve  160 , (or alternative embodiments) may be used with the one or more sensors and the control unit  110  to control of the supply of oxygen gas to the user  108 . 
     D. Control Unit 
     With reference to  FIG. 20 , the control unit  110  may take any well-known form in the art and includes a central microprocessor or CPU  160  in communication with the components of the system described herein via one or more interfaces, controllers, or other electrical circuit elements for controlling and managing the system. The system  100  may include a user interface ( FIG. 20 ) as part of the control unit  110  or coupled to the control unit  110  for allowing the user, provider, doctor, etc. to enter information, e.g., prescription oxygen level, flow rate, activity level, etc., to control the system  100 . 
     The main elements of an embodiment of the system  100  have been described above. The following sections describe a number of additional features, one or more of which may be incorporated into the embodiments of the invention described above as one or more separate embodiments of the invention. 
     II. Conserving Device 
     With reference to  FIG. 21 , a conserving device or demand device  190  may be incorporated into the system  100  to more efficiently utilize the oxygen produced by the oxygen gas generator  102 . 
     During normal respiration, a user  108  inhales for about one-third of the time of the inhale/exhale cycle and exhales the other two-thirds of the time. Any oxygen flow provided to the user  108  during exhalation is of no use to the user  108  and, consequently, the additional battery power used to effectively provide this extra oxygen flow is wasted. A conserving device  190  may include a sensor that senses the inhale/exhale cycle by sensing pressure changes in the cannula  111  or another part of the system  100 , and supply oxygen only during the inhale portion or a fraction of the inhale portion of the breathing cycle. For example, because the last bit of air inhaled is of no particular use because it is trapped between the nose and the top of the lungs, the conserving device  190  may be configured to stop oxygen flow prior to the end of inhalation, improving the efficiency of the system  100 . Improved efficiency translates into a reduction in the 20 size, weight, cost and power requirements of the system  100 . 
     The conserving device  190  may be a stand-alone device in the output line of the system  100 , similar to a regulator for scuba diving, or may be coupled to the control unit  110  for controlling the oxygen generator  102  to supply oxygen only during inhalation by the user  108 . 
     The conserving device  190  may include one or more of the sensors described above. For example, the conserving device may include a sensor for monitoring the respiration rate of the user. 
     The system  100  may also include a special cannula retraction device for retracting the cannula ill when not in use. Further, the cannula  111  may come in different lengths and sizes. 
     III. High-Pressure Reservoir 
     With reference to  FIG. 22 , a high-pressure reservoir  164  may be located in a secondary line  166  for delivering an additional supply of oxygen gas to the user  108  when the oxygen gas generator  102  can not meet the oxygen gas demands of the user  108 . Any of the components described below in the secondary line  166  may be coupled to the control unit  110  or a high-pressure reservoir controller  167  ( FIG. 20 ) for control thereby. Exemplary situations where this additional oxygen gas need may occur are when a user suddenly goes from an inactive state to an active state, e.g., when getting out of a chair, when the system  100  is turned on, or when the system  100  goes from a conserving mode or sleep mode to an active mode. As used herein, secondary line  166  refers to the tubing, connectors, etc. used to connect the components in the line. A valve  168  may be controlled by the control unit  110  to allow gaseous oxygen to flow into the secondary line  166 . The valve  168  may be configured to allow simultaneous flow to both the supply line  121  and the secondary line  166 , flow to only the supply line  121 , or flow to only the secondary line  166 . 
     A pump or compressor  168 , which is preferably powered by the motor  118 , delivers the oxygen gas at a relatively high pressure, e.g., at least approximately 100 psi, to the high-pressure reservoir  164 . 
     An oxygen-producing electrochemical cell  171  may be used in conjunction with or instead of the elements described in the secondary line  166  to supply additional oxygen gas to the user  108 . For example the electrochemical cell  171  may be used to deliver oxygen gas at a relatively high pressure to the high-pressure reservoir  164 . 
     A pressure sensor  172  is in communication with the high-pressure reservoir  164  and the control unit  110  so that when the pressure in the high-pressure reservoir  164  reaches a certain limit, the control unit  110  causes the valve  168  to direct oxygen to the secondary line  166 . 
     A regulator  174  may be used to control flow and reduce pressure of the oxygen gas to the user  108 . 
     A valve  176  may also be controlled by the control unit  110  to allow gaseous oxygen from the high-pressure reservoir  164  to flow into the supply line  121  when the user  108  requires an amount of oxygen gas that cannot be met by the oxygen gas generator  102 . The valve  176  may be configured to allow simultaneous flow from the oxygen gas generator  102  and the high-pressure reservoir  164 , from only the oxygen gas generator  102 , or from only the high-pressure reservoir  164 . 
     The one or more sensors  106  are interrelated with the control unit  110  and the oxygen gas generator  102  so as to supply an amount of oxygen gas equivalent to the oxygen gas needs of the user  108  based at least in part upon one or more conditions sensed by the one or more sensors  106 . When the oxygen gas generator  102  cannot meet the oxygen gas demands of the user  108 , the control unit  110 , based at least in part upon sensing one or more conditions indicative of the oxygen needs of the user, may cause the high-pressure reservoir  164  (via the valve  176 ) to supply the additional oxygen gas needed. 
     In the scenario where the oxygen gas generator  102  is capable of supplying the full oxygen gas needs of the user  108 , but is simply turned off or is in a conserving or sleep mode, the period of time that the high-pressure reservoir  164  supplies the oxygen gas, i.e., the period of time that the valve  176  connects the high-pressure reservoir  164  with the supply line  121 , is at least as long as the time required for the oxygen gas generator  102  to go from an off or inactive condition to an on or active condition. In another scenario, the control unit  110  may cause oxygen gas to be supplied to the user from the high-pressure reservoir  164  when the demand for gaseous oxygen by the user exceeds the maximum oxygen gas output of the oxygen gas generator  102 . Although the high-pressure reservoir  164  is shown and described as being filled by the oxygen gas generator  102 , in an alternative embodiment, the high-pressure reservoir  164  may be filled by a source outside or external to the system. 
     IV. Global Positioning System 
     With reference back to  FIG. 18 , in an alternative embodiment of the invention, the system  100  may include a global positioning system (GPS) receiver  200  for determining the location of the system  100 . The location of the receiver  200  and, hence, the user  108  can be transmitted to a remote computer via the telemetry mechanism or modem  151 . This may be desirable for locating the user  108  in the event the user has a health problem, e.g., heart attack, hits a panic button on the system, an alarm is actuated on the system, or for some other reason. 
     V. Additional Options and Accessories 
     In addition to the cradle  134 , the portable oxygen concentration system  100  may include additional options and accessories. A number of different types of bags and carrying cases such as, but not by way of limitation, a shoulder bag, a backpack, a fanny pack, a front pack, and a split pack in different colors and patterns may be used to transport the system  100  or other system accessories. A cover may be used to shield the system from inclement weather or other environmental damage. The system  100  may also be transported with a rolling trolley/cart, a suit case, or a travel case. The travel case may be designed to carry the system  100  and include enough room to carry the cannula  111 , extra batteries, an adapter, etc. Examples of hooks, straps, holders for holding the system  100  include, but not by way of limitation, hooks for seatbelts in cars, hooks/straps for walkers, hooks/straps, for wheel chairs, hooks/straps for hospital beds, hooks for other medical devices such as ventilators, hooks/straps for a golf bag or golf cart, hooks/straps for a bicycle, and a hanging hook. The system  100  may also include one or more alarm options. An alarm of the system  100  may be actuated if, for example, a sensed physiological condition of the user  108  falls outside a pre-defined range. Further, the alarm may include a panic alarm that may be manually actuated by the user  108 . The alarm may actuate a buzzer or other sounding device on the system  100  and/or cause a communication to be sent via the telemetry mechanism or modem  151  to another entity, e.g., a doctor, a 911 dispatcher, a caregiver, a family member, etc. 
       FIG. 23  is a block diagram illustrating an example computer system  1150  that may be used in connection with the embodiment of the controller/control module  25  and/or the controller/control module  60  described herein. However, other computer systems and/or architectures may be used, as will be clear to those skilled in the art. 
     The computer system  1150  preferably includes one or more processors, such as processor  1152 . Additional processors may be provided, such as an auxiliary processor to manage input/output, an auxiliary processor to perform floating point mathematical operations, a special-purpose microprocessor having an architecture suitable for fast execution of signal processing algorithms (e.g., digital signal processor), a slave processor subordinate to the main processing system (e.g., back-end processor), an additional microprocessor or controller for dual or multiple processor systems, or a coprocessor. Such auxiliary processors may be discrete processors or may be integrated with the processor  1152 . 
     The processor  1152  is preferably connected to a communication bus  1154 . The communication bus  1154  may include a data channel for facilitating information transfer between storage and other peripheral components of the computer system  1150 . The communication bus  1154  further may provide a set of signals used for communication with the processor  1152 , including a data bus, address bus, and control bus (not shown). The communication bus  1154  may comprise any standard or non-standard bus architecture such as, for example, bus architectures compliant with industry standard architecture (“ISA”), extended industry standard architecture (“EISA”), Micro Channel Architecture (“MCA”), peripheral component interconnect (“PCI”) local bus, or standards promulgated by the Institute of Electrical and Electronics Engineers (“IEEE”) including IEEE 488 general-purpose interface bus (“GPIB”), IEEE 696/S-100, and the like. 
     Computer system  1150  preferably includes a main memory  1156  and may also include a secondary memory  1158 . The main memory  1156  provides storage of instructions and data for programs executing on the processor  1152 . The main memory  1156  is typically semiconductor-based memory such as dynamic random access memory (“DRAM”) and/or static random access memory (“SRAM”). Other semiconductor-based memory types include, for example, synchronous dynamic random access memory (“SDRAM”), Rambus dynamic random access memory (“RDRAM”), ferroelectric random access memory (“FRAM”), and the like, including read only memory (“ROM”). 
     The secondary memory  1158  may optionally include a hard disk drive  1160  and/or a removable storage drive  1162 , for example a floppy disk drive, a magnetic tape drive, a compact disc (“CD”) drive, a digital versatile disc (“DVD”) drive, etc. The removable storage drive  1162  reads from and/or writes to a removable storage medium  1164  in a well-known manner. Removable storage medium  1164  may be, for example, a floppy disk, magnetic tape, CD, DVD, etc. 
     The removable storage medium  1164  is preferably a computer readable medium having stored thereon computer executable code (i.e., software) and/or data. The computer software or data stored on the removable storage medium  1164  is read into the computer system  1150  as electrical communication signals  1178 . 
     In alternative embodiments, secondary memory  1158  may include other similar means for allowing computer programs or other data or instructions to be loaded into the computer system  1150 . Such means may include, for example, an external storage medium  1172  and an interface  1170 . Examples of external storage medium  1172  may include an external hard disk drive or an external optical drive, or and external magneto-optical drive. 
     Other examples of secondary memory  1158  may include semiconductor-based memory such as programmable read-only memory (“PROM”), erasable programmable read-only memory (“EPROM”), electrically erasable read-only memory (“EEPROM”), or flash memory (block oriented memory similar to EEPROM). Also included are any other removable storage units  1172  and interfaces  1170 , which allow software and data to be transferred from the removable storage unit  1172  to the computer system  1150 . 
     Computer system  1150  may also include a communication interface  1174 . The communication interface  1174  allows software and data to be transferred between computer system  1150  and external devices (e.g. printers), networks, or information sources. For example, computer software or executable code may be transferred to computer system  1150  from a network server via communication interface  1174 . Examples of communication interface  1174  include a modem, a network interface card (“NIC”), a communications port, a PCMCIA slot and card, an infrared interface, and an IEEE 1394 fire-wire, just to name a few. 
     Communication interface  1174  preferably implements industry promulgated protocol standards, such as Ethernet IEEE 802 standards, Fiber Channel, digital subscriber line (“DSL”), asynchronous digital subscriber line (“ADSL”), frame relay, asynchronous transfer mode (“ATM”), integrated digital services network (“ISDN”), personal communications services (“PCS”), transmission control protocol/Internet protocol (“TCP/IP”), serial line Internet protocol/point to point protocol (“SLIP/PPP”), and so on, but may also implement customized or non-standard interface protocols as well. 
     Software and data transferred via communication interface  1174  are generally in the form of electrical communication signals  1178 . These signals  1178  are preferably provided to communication interface  1174  via a communication channel  1176 . Communication channel  1176  carries signals  1178  and can be implemented using a variety of wired or wireless communication means including wire or cable, fiber optics, conventional phone line, cellular phone link, wireless data communication link, radio frequency (RF) link, or infrared link, just to name a few. 
     Computer executable code (i.e., computer programs or software) is stored in the main memory  1156  and/or the secondary memory  1158 . Computer programs can also be received via communication interface  1174  and stored in the main memory  1156  and/or the secondary memory  1158 . Such computer programs, when executed, enable the computer system  1150  to perform the various functions of the present invention as previously described. 
     In this description, the term “computer readable medium” is used to refer to any media used to provide computer executable code (e.g., software and computer programs) to the computer system  1150 . Examples of these media include main memory  1156 , secondary memory  1158  (including hard disk drive  1160 , removable storage medium  1164 , and external storage medium  1172 ), and any peripheral device communicatively coupled with communication interface  1174  (including a network information server or other network device). These computer readable mediums are means for providing executable code, programming instructions, and software to the computer system  1150 . 
     In an embodiment that is implemented using software, the software may be stored on a computer readable medium and loaded into computer system  1150  by way of removable storage drive  1162 , interface  1170 , or communication interface  1174 . In such an embodiment, the software is loaded into the computer system  1150  in the form of electrical communication signals  1178 . The software, when executed by the processor  1152 , preferably causes the processor  1152  to perform the inventive features and functions previously described herein. 
     Various embodiments may also be implemented primarily in hardware using, for example, components such as application specific integrated circuits (“ASICs”), or field programmable gate arrays (“FPGAs”). Implementation of a hardware state machine capable of performing the functions described herein will also be apparent to those skilled in the relevant art. Various embodiments may also be implemented using a combination of both hardware and software. 
     Furthermore, those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, and method steps described in connection with the above described figures and the embodiments disclosed herein can often be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled persons can implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the invention. In addition, the grouping of functions within a module, block, circuit or step is for ease of description. Specific functions or steps can be moved from one module, block or circuit to another without departing from the invention. 
     Moreover, the various illustrative logical blocks, modules, and methods described in connection with the embodiments disclosed herein can be implemented or performed with a general purpose processor, a digital signal processor (“DSP”), an ASIC, FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     Additionally, the steps of a method or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium including a network storage medium. An exemplary storage medium can be coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can also reside in an ASIC. 
     The above figures may depict exemplary configurations for the invention, which is done to aid in understanding the features and functionality that can be included in the invention. The invention is not restricted to the illustrated architectures or configurations, but can be implemented using a variety of alternative architectures and configurations. Additionally, although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features and functionality described in one or more of the individual embodiments with which they are described, but instead can be applied, alone or in some combination, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus the breadth and scope of the present invention, especially in the following claims, should not be limited by any of the above-described exemplary embodiments. 
     Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as mean “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; and adjectives such as “conventional,” “traditional,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, a group of items linked with the conjunction “and” should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as “and/or” unless expressly stated otherwise. Similarly, a group of items linked with the conjunction “or” should not be read as requiring mutual exclusivity among that group, but rather should also be read as “and/or” unless expressly stated otherwise. Furthermore, although item, elements or components of the disclosure may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated. The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.