Patent Publication Number: US-2015083121-A1

Title: Portable life support apparatus

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a portable life support apparatus and particularly to a respiratory support apparatus adapted to be easily mounted to a stretcher. 
     BACKGROUND OF THE INVENTION 
     When transporting a patient on a stretcher, such as a NATO litter, a large metal bracket called a SMEED is sometimes mounted to the side frame members of the stretcher. The SMEED extends over the patient and serves as a mounting bracket for receiving a plurality of life support devices that function independently of one another. There are several problems associated with the use of the SMEED however. One problem is that the SMEED obstructs access to the patient. Additionally, the SMEED is heavy and cumbersome to use. Loading the SMEED with a variety of different respiratory support and monitoring devices is inefficient from the standpoint of space consumption and weight (the SMEED itself weighs 22 pounds) and does not provide equal optimal access to each of those devices. Accordingly, there is a great need for a portable emergency support device that overcomes the weight, size, positioning, and other portability disadvantages of the SMEED, allows for easy loading of various respiratory support devices in proximity to a subject during the course of emergency transport. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention is directed to a respiratory support apparatus comprising an oxygen generating device including an ambient air inlet, for generating oxygen from ambient air, at least one gas reservoir, a conduit system for handling gas generated by the oxygen generating device and expired gas exhaled by a patient, wherein the conduit system comprises at least one conduit, operatively associated with a one-way valve, that is fluidly connected between a patient airway interface and the gas reservoir for directing expired gas towards the gas reservoir and at least one conduit, operatively associated with a one-way valve, that is fluidly connected between the gas reservoir and the patient airway interface, for directing reservoir gas towards the patient airway interface. A device according to this aspect of the invention is particularly advantageous for portable applications where size of the oxygen generator and its power consumption are of particular importance. 
     In one aspect, the invention is directed to a portable combination ventilator and oxygen generator which integrates the functions of producing oxygen and those pertaining to ventilatory support. The inventors have found that controlling oxygen levels supplied to the patient can be accomplished efficiently with superior oxygen generation, conservation and controls and that a patient can be efficiently ventilated in a variety of different types in emergency settings with vastly enhanced oxygen concentrations relative to ambient air in a single portable, weight and size efficient apparatus. 
     The inventors have determined that a useful arrangement of the gas delivery system is one in which expired gas is collected and re-breathed by the patient, as this potentiates more efficient oxygen output, conserves oxygen already available, and allows the volume and oxygen content of the oxygen generating device to be suited to both ventilate a patient and to be portable i.e. to be of suitable size, weight and power consumption for rapid deployment for a duration suitable in emergency settings. In one respect, since expired gas has a higher concentration of oxygen than ambient air the inventors have found that reuse of oxygen expired by the patient from a previous breath would make generating oxygen feasible within a combination portable unit. Therefore one aspect of the invention provides a portable oxygen generation device that is capable of exploiting both ambient air and expired gas to provide the patients oxygen consumption requirements; the foregoing irrespective of whether the patient is breathing spontaneously or is incapable of breathing spontaneously and is being fully ventilated by an apparatus according to an aspect of the invention. 
     Accordingly in one aspect the invention is directed to portable respiratory support device comprising a ventilator and an oxygen generating device. In a further embodiment the portable respiratory support device further comprises and an oxygen conservation system adapted to utilize both ambient air and air exhaled by the patient to produce the oxygen requirements of the patient. Optionally, the oxygen conservation system comprises a conduit fluidly connected between the patient airway interface (e.g. a mask) and the ventilator for receiving gas exhaled by the patient and a carbon dioxide scrubber fluidly connected therebetween. Optionally, the oxygen generation device is an oxygen concentrator. The oxygen concentrator may be of the type that is set to operate on a pressure swing adsorption or a pressure/vacuum swing cycle. In another embodiment, the portable respiratory support device further comprises a controller that regulates the oxygen output of the oxygen concentrator based on a sensor system that measures the volume of flow and oxygen gas concentration proximal to the patient inspiratory port. 
     An embodiment of the invention enables a combined ventilator/oxygen generating device with an output 1.2 L of 90% oxygen or its equivalent. This output has been determined to be adequate to ventilate a patient with 6 litres of 90% oxygen as opposed using an alternative that supplies the entire 6 L of 90% oxygen. For example, for a 2 hour emergency transport mission, the combined weight of the oxygen generator (and scrubber to remove carbon dioxide from the expired gas) suitable for carrying out aspects of the invention herein may be, for example, no greater than 12 pounds (with battery added 15 lbs—with a combined volume of less than 0.27 cu ft, add 1-2 lbs for housing components) and may obviate the need to carry 5 or 6 bottles of oxygen which occupy a much greater volume and weigh far more. 
     In one embodiment of the invention, the portable life support is adapted to operate in a mode that provides more pleasant ventilation support to a patient capable of breathing spontaneously. Accordingly, optionally, an embodiment of the invention further comprises a by-pass system for by-passing the scrubber. In this connection, the term “by-pass system” or “scrubber-by-pass” is used broadly to refer to any system in which the scrubber is not interposed or in fluid communication between the patient and a gas reservoir on either the inspiratory or expiratory side. It will be appreciated that this can be accomplished with two and three position valves and additional conduits. Optionally, to reduce the size of the apparatus this by-pass system comprises a substitute portion of the breathing circuit, the use of which entails removal of a scrubber unit. Optionally the by-pass system comprises a removable cartridge containing the scrubber and a substitute cartridge comprising a re-breathing circuit, optionally a sequential gas delivery circuit (SGD) which fresh gas is breathed in first and expired gas is available to supply the remainder of the patient&#39;s minute ventilation (separate masks can be purchased (Hi-Ox SR) to operate such an SGD with a scrubber unit, where desired). Optionally, the portable life support apparatus is capable of producing fresh gas flow containing approximately an equivalent of 40% patient oxygen sufficient to make up the effective alveolar ventilation of the patient, for example 5 to 8 litres of fresh gas containing 40% oxygen. Accordingly, in one embodiment the oxygen generator is capable producing approximately 2.0 to 2.2 L of 90% oxygen (for example, 2.2 L of 90% oxygen combined with 5.8 litres of ambient air yields 8 litres of 40% oxygen. In another embodiment, the portable life support apparatus is adapted to operate at reduced pressure, for example the atmospheric pressure corresponding to the altitude at which emergency transport helicopters fly for military emergency patient transport. Optionally, to make up 1.2 L an approximate oxygen generator output of equivalent to 1.8 liters of 90% oxygen is required, and an oxygen generator output of equivalent to 3.0 L of 90% oxygen is required in scrubber by-pass mode to effectively make up 2.2 litres of 90% oxygen. 
     In a further aspect the invention is directed a portable life support apparatus in the form of a portable respiratory support apparatus comprising a ventilator, an oxygen generator and an oxygen conservation system that is capable of exploiting both ambient air and expired gas as oxygen sources with higher oxygen content than ambient air, wherein the oxygen generator and ventilator are arranged (substantially end to end) to provide a longitudinal profile that can thus be compactly secured to a stretcher or other similar emergency transport vehicle. Optionally, the oxygen conservation system is positioned in end to end arrangement with other components. Optionally, the ventilator is positioned between the oxygen generating component and the oxygen conservation system component. Optionally, the oxygen conservation system component comprises at least one of two or more alternative modules (at least a scrubber module which is optionally configured to direct expired gas to the ventilator and optionally a scrubber by-pass which is optionally configured to direct expired gas to an expired gas holding chamber, optionally in the form of an elongated tube and ultimately to atmosphere), for example, in the form of cartridges that have a matching profile to that of the housing the remainder of the apparatus. The apparatus optionally includes a portable power source in the form of rechargeable battery housing unit. Optionally, the portable power source is adapted to minimize the total length of the apparatus and has the same profile as the remainder of the apparatus to make efficient use of profile of the apparatus. Optionally, the placement of the portable power source is at the end of unit opposite end the oxygen conservation system ie. adjacent the oxygen generation device. Optionally, the apparatus further comprises a system for suctioning a patient&#39;s airway. In one embodiment the oxygen generator uses a vacuum pump as part of a pressure swing adsorption system to concentrate oxygen from ambient air and negative pressure generated by this pump can be switched (for example with a two or three position valve) between fluid connection to one or more concentrator sieve beds and a suction port, thereby trimming the weight of the combined apparatus relative to separate devices an additional ten to twelve pounds (the weight of a typical standalone suctioning device typically mounted onto a SMEED for patients that may be in need of this form of respiratory support). 
     In another aspect of the invention, the portable life support apparatus includes a patient monitoring system. The patient monitoring system may display one or more respiratory parameters and optionally displays one or more non-respiratory parameters optionally including ECG, heart rate, continuous or intermittent non-invasive blood pressure, and temperature. The respiratory parameters may be selected from O 2  saturation, expired CO 2  concentration, system CO 2  concentration (particularly immediately upstream of the scrubber) inspired O 2  concentration, airway pressure (particularly, to measure pressure proximal to the patient inspiratory port), respiratory rate, and tidal volume. Optionally, the display also displays one or more device parameters including available battery power and operation mode. 
     Optionally, the patient monitoring system includes a display that is rotatable between a plurality of viewing positions about a display axis that is parallel to the longitudinal axis of the portable life support apparatus. Optionally, display is shaped to a have a compact longitudinal orientation that complements that of the body of the portable life support apparatus. Optionally, the display axis is positioned between the top and bottom of the display to maximize the rotational range of usable reading orientations of the display. Accordingly, in another aspect, the invention is directed to a portable life support apparatus that integrates in a longitudinally arranged profile within a single apparatus a plurality of respiratory support devices selected from the group comprising an oxygen generator, a ventilator, an oxygen conservation system, an airway suctioning system, and further comprises a patient monitoring system including a display rotatable between a plurality of positions (reading orientation positions) about an axis that is parallel to the longitudinal axis of the portable life support apparatus. 
     In another aspect, the portable life support apparatus includes a positioning system comprising a clamp assembly adapted to support the apparatus in a horizontal plane parallel to a patient support surface of a portable patient transport apparatus, for example a stretcher. Optionally, the apparatus is supportable proximal to and below the plane of the patient support surface to facilitate access to the patient (first or patient treatment position), as well as above the plane of the patient support surface of the patient transport vehicle (second or patient transport position). Optionally, the positioning system makes the apparatus displaceable between first and second support positions without detachment from the portable patient transport apparatus. Optionally in the second or in a third position the apparatus is partially displaced towards the center of the patient support surface (i.e. at least partially overlying the side support bar of the stretcher or other such vehicle, implicitly to a degree that does not significantly encroach on the side of patient&#39;s body). Optionally, depending on the support and loading system accorded to the portable patient transport apparatus within the carrier transport (helicopter, ambulance, humvee or other automotive vehicle), the transport position may also be below the stretcher displaced partially underneath the stretcher. 
     Accordingly, in another aspect, the invention is directed to a portable life support system comprising a positioning system and a plurality of respiratory support devices integrated in a longitudinal profile into a single apparatus including a patient monitoring system and at least one device selected from the group comprising an oxygen generator, a ventilator and a patient airway suctioning system, the patient monitoring system including a display rotatable between a plurality of viewing positions about an axis that is parallel to the longitudinal axis of the apparatus, the positioning system including a clamp assembly adapted to support the apparatus in a horizontal plane parallel to a patient support surface of a portable patient transport apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described by way of example only with reference to the attached drawings, in which: 
         FIG. 1  is a schematic illustration of a life support system in accordance with an embodiment of the present invention, in a ventilation mode; 
         FIG. 1   a  is an exploded perspective view of some of the components shown in  FIG. 1 ; 
         FIG. 2  is a schematic illustration of the life support system illustration in  FIG. 1 , in a spontaneous breathing mode; 
         FIG. 2   a  is an exploded perspective view of some of the components shown in  FIG. 2 ; 
         FIG. 5  is a perspective view of a portion of a concentrator that is shown in  FIG. 15   a;    
         FIG. 6  is a perspective view of a ventilator assembly that is shown in  FIG. 15 , with a housing element removed and with a bellows shown as transparent for greater clarity; 
         FIG. 7  is a perspective view of a portion of the ventilator assembly shown in  FIG. 6 ; 
         FIG. 8  is a perspective view of an end of the life support system shown in  FIG. 15 , to show in particular a cartridge that is part of the life support system; 
         FIG. 9  is a perspective view of the cartridge shown in  FIG. 8 ; 
         FIG. 10  is an exploded perspective view of the end of the life support system shown in  FIG. 8 ; 
         FIG. 11  is a perspective view of the cartridge shown in  FIG. 8  with a transparent exterior to show the inner components and to illustrate gas flow therethrough; 
         FIG. 12  is a perspective view of the cartridge with a portion of the exterior housing removed; 
         FIG. 13  is a perspective view from another viewpoint of the cartridge components shown in  FIG. 12 ; 
         FIG. 14  is a perspective view of the housing component removed from  FIGS. 12 and 13 ; 
         FIG. 15  is a perspective view of the life support system schematically illustrated in  FIG. 1 ; 
         FIG. 15   a  is a perspective view of the life support system shown in  FIG. 15 , with some housing components removed to show underlying components; 
         FIG. 16  is a perspective view of a portion of the life support system to illustrate some input that the system optionally receives; 
         FIG. 17  is a perspective view of a display assembly shown in  FIG. 15 ; 
         FIG. 18  is a perspective view of a display housing that is part of the display assembly shown in  FIG. 17 ; 
         FIG. 19  is a sectional view of an end of the display housing shown in  FIG. 18 , being supported in an end support; 
         FIG. 19   a  is a plan view of the end support shown in  FIG. 19 ; 
         FIG. 20  is a perspective view of the end support shown in  FIG. 19 ; 
         FIG. 21  is a perspective view of the life support system shown in  FIG. 15 , with a life support device and an optional positioning system, in accordance with another embodiment of the invention; 
         FIGS. 22   a  and  22   b  are perspective views of a patient transport apparatus connector and a strap, which are part of the positioning system shown in  FIG. 21 , wherein the patient transport apparatus connector is in an open position; 
         FIG. 22   c  is a sectional side view of the patient transport apparatus connector and strap shown in  FIGS. 22   a  and  22   b;    
         FIGS. 23   a  and  23   b  are perspective and sectional side views respectively of the patient transport apparatus connector and strap shown in  FIGS. 22   a  and  22   b , wherein the patient transport apparatus connector is shown in a patient transport apparatus-connected, strap-unlocked position; 
         FIGS. 24   a  and  24   b  are perspective and sectional side views respectively of the patient transport apparatus connector and strap shown in  FIGS. 22   a  and  22   b , wherein the patient transport apparatus connector is shown in a patient transport apparatus-connected, strap-locked position; 
         FIG. 25   a  is a side view of a life support device connector shown in  FIG. 21 , wherein the life support device connector is shown in an unconnected state; 
         FIG. 25   b  is a side view of the life support device connector shown in  FIG. 25   a , with the locking element pushed downwardly; 
         FIG. 26  is a sectional side view of the patient transport apparatus connector shown in  FIGS. 22   a  and  22   b  and another life support device connector shown in  FIG. 22   a , wherein the patient transport apparatus connector is shown connected to a patient transport apparatus and wherein the life support device connector is shown connected to the life support device shown in  FIG. 21 ; 
         FIG. 27   a  is an end view of a channel in the housing of the life support device shown in  FIG. 21 ; 
         FIG. 27   b  is a plan view of a channel in the housing of the life support device shown in  FIG. 21 ; 
         FIG. 28   a  is a perspective view from inside a channel on the housing of the life support device shown in  FIG. 21 , showing the initial position of a life support device connector during mounting; and 
         FIG. 28   b  is a perspective view from inside a channel on the housing of the life support device shown in  FIG. 21 , showing the final position of a life support device connector after mounting. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following terms are defined as set forth below: 
     The term “conditioned gas” is used to refer to a gas, optionally conditioned ambient air, having at least one of the following properties: it has a higher content of oxygen than available ambient air, it is less humid than available ambient air, it has a lower nitrogen gas content relative to available ambient air, it comprises exhaled air of a subject that has been scrubbed of carbon dioxide. In a preferred embodiment, the conditioned gas is a gas that has a higher content of oxygen as a result of having been generated by re-breathing circuit and/or an oxygen concentrator and will optionally have been dehumidified and/or scrubbed). 
     The term “conduit” or “conduit segment” is used broadly to refer to a fluidly intact (pneumatically efficient, and optionally, though not necessarily sealably intact) gas pathway and includes without limitation, tubes and channels of any type that conduct air from place to place. 
     The term “configure”, “configured” and variations thereof, when used with reference to the capability of an oxygen generating device to generate oxygen, refers to design criteria, that impact on portability including at least one of size, weight, and power consumption of the device in watts/liter of oxygen generated. The term “output controller” used in relation to a controller that controls the oxygen generating device means a controller that controls at least one of: (a) the flow rate of oxygenated gas leaving the oxygen generating device; (b) the concentration of oxygenated gas leaving the oxygen generating device; and (c) the on-off status of the device whereby it can be turned on and off without detrimentally affecting the operation of the apparatus as a whole. This allow the oxygen generating device to be run intermittently to control oxygen concentration and/or power consumption, optionally based on feedback from a sensor that detects the oxygen concentration of gas in the circuit. 
     The term “conditioned gas outlet” refers to an apparatus outlet or juncture least proximal to the patient that has substantially the final gas composition available for the beginning of the next upcoming patient inspiratory cycle(s). The term “inspiratory gas” is the gas having this composition. 
     The term “towards” when used describe gas flow in a conduit segment (particularly when in operative association with a one way valve) is used to describe unidirectional flow. It will be appreciated that the location of valves including one way valves and points of attachment of conduit segments may often be dictated by convenience or certain advantages which are not necessarily critical to the operation of the structure in which they are incorporated. Accordingly, precise structural linkages may not be material to the operation even if specified in a drawing or descriptions of preferred embodiments of the invention and equivalent arrangements will apparent to persons skilled in art. The term “operative association” and related terms are meant to signify that the precise method of association or location can be variably selected without inventive skill and do not materially affect the operation of some embodiments of the invention. It will also be appreciated that portions of the gas circuit may be left outside the body of the apparatus, particularly disposable, relatively inexpensive, commonly replacable and technologically trivial parts, and connected by the user via a port designated for such connection, in effect making the port equivalent to those portions of the gas circuit, if added after and secondary to the essential features of the apparatus. Persons skilled in the art of working with respiratory apparatus are attuned to assembly of these types of circuit elements and will readily perceive an assembly of parts as the essential apparatus. Examples follow. A scrubber may be introduced into the circuit outside the core apparatus and may be so introduced advantageously on the inspiratory side of the circuit but without very significant effect also on the expiratory side of the circuit. Oxygenated gas leaving the oxygen concentrator may be introduced into the conduit system or directly into the ventilator reservoir. 
     The term “ventilator” includes pressure based ventilators that provide pressure to the airway of the subject to a certain preset level (e.g. 25 cm H2O) or range, and volume based ventilators that control the tidal volume and frequency of the inspiratory flow to the patient. Ventilators of these types could be used for ventilatory assistance of a type that does not require rigorous pressure, volume, frequency controls. A variety of types of ventilatory assistance are known to those skilled in the art including CPAP, BiPAP, pressure controlled, volume controlled, pressure support ventilation, airway pressure release ventilation, inspiratory pause, inspiratory flow profile, proportional assist ventilation, neurally activated ventilatory assistance, assist control ventilation etc. The term “ventilator device” is used broadly to refer to a ventilator and may depending on the context implicitly exclude the gas reservoir component of such a device. 
     The term “oxygenated” means air having an oxygen content higher than ambient air, optionally having a concentration of at least 40% oxygen. 
     The term “portable life support apparatus” (or interchangeably “portable life support device”) as used herein, generally is used to refer to the apparatus as whole the name contemplating but not implying monitoring functions that are not limited to respiratory parameters. However, this term may be used interchangeably with “portable respiratory support apparatus” and “respiratory support apparatus”, among others, in which the primary functions of respiratory support are highlighted in name. 
     The term “substantially in series” with reference to longitudinal configuration of an apparatus or system according to an embodiment of the invention is not meant to necessarily imply that each component, of each sub-assembly—namely oxygen generator, ventilator mechanism, scrubber unit, battery housing is in a distinct compartment with each compartment arranged in series but rather that the most space consuming part of each sub-assembly is arranged in series in a longitudinal configuration. 
     The term “re-breathing circuit” means any circuit in which exhaled air is captured and remains available for re-breathing during a portion of an inspiratory phase of breathing. The re-breathing circuit may be optionally a sequential gas delivery (“SGD”) circuit. The term sequential gas delivery circuit means a system which includes controls, (for example, valves) that are set to open sequentially, for ensuring that in the first part of an inspiratory cycle the patient receives a gas of a first composition and in the second part of the inspiratory cycle, the patient receives a second different composition (for example the first gas may be oxygen and the second gas may be gas exhaled from a previous inspiratory cycle). The term “a sequential gas delivery valve” means a one way valve set to open to source of expired gas which opens at a higher pressure than a valve set to open to a source of fresh gas and which is typically positioned in parallel to an expiratory valve which allow expired gas to leave to ambient air. A “sequential gas delivery control system”, optionally a valve system, refers to at least two valves that open sequentially to fresh gas and expired gas sources, typically valves that open at different pressures, one at a lower pressure connected to an inspiratory gas source, and one at a higher pressure connected to an expired gas source. 
     The term “fresh gas” generally means gas entering the patient&#39;s breathing circuit that does not contain appreciable amounts of carbon dioxide, and is usually air or oxygen enriched air, although other components may be present as well, such as anesthetic agents or the like. 
     The term “inspiratory relief valve” means a valve that allows gas, usually ambient air, into a portion of the conduit assembly that is available to the patient to breathe on during an inspiratory cycle in which inspiratory gas, usually in the form of a conditioned gas, is temporarily depleted. 
     The term “patient airway interface” means a patient interface such as a mask, nasal tube, endotracheal tube, or tracheotomy tube that is fluidly connected to a patient airway. 
     The term “independently movable” is understood to mean having some degree of independent movement, for example, rotational independence about at least one axis. 
     The term “reading orientation” means the preferred orientation in which a line of data, normally readable in a horizontal orientation (in the case of many languages) from left to right (or right to left), for example a number, is presented horizontally and therefore is most easily readable. By contrast, a “reading position” is any screen position in which substantially all of the data is normally viewable by a user, though not necessarily in a reading orientation. 
     The top and bottom with reference to the display refer to the borders of the display parallel to its reading orientation. 
     The term “intermediate” with reference to a rotational position refers to a position roughly in the middle of its rotational extremes. 
     The term “vertical” with reference to a display position means that the screen axis is roughly parallel to the ground and the display is a plane roughly perpendicular to the ground. 
     The term “airway” includes, without limitation, the mouth, trachea, and nose. 
     The term “processing” with reference to machine intelligence means any handling, merging, sorting or computing of machine readable information using digital or analog circuitry in a way that it is compatible with visual presentation on a screen. 
     The term “reading” is meant to include scanning with a view to interpretation of any visually depicted subject matter (not just letters and numbers), including without limitation, graphs, symbols, heart monitor output, brain waves etc. Optionally the device is considered positionable for reading when the device is anywhere within arms length of the user, so that the user can use the user interface on the display. 
     The term “plane” is used broadly to include a curvilinear profile that is substantially planar. 
     The term “preferred position” means a position with reference to the position of the portable life support device about an axis generally parallel to the axis of rotation of the display that permits use of at least half and preferably substantially more of the range of motion of the display. 
     The term “device positioning interface”, alternately called the “device interface” when referencing the positioning system, is used broadly to refer to any interface that serves as a point of attachment of the support structure of the positioning system including, without limitation, a flat metallic surface for engaging a magnet. 
     The term “holding” with reference to a way of keeping the screen from rotating is understood in its broadest sense to provide resistance to rotation. For example, the apparatus may include a spring-loaded detent that interacts with a plurality of grooves defined by annularly located toothed portion of the screen housing, so that rotation of the screen in one direction or the other successively engages the intermittent grooves defined by those teeth to define a series of intermittently spaced screen positions. 
     As detailed below, and shown in the drawings ( FIGS. 15 and 15   a ), the portable life support system in accordance with an embodiment of the invention  1100  includes a portable life support apparatus  1102  and positioning system  801  optionally including an independently movable display  600  (also termed a readable output display) that maximizes the versatility of the positioning system by enabling the life support device to be positioned in a variety of convenient positions in which the display can be independently positioned to be readable. This positioning system is useful for positioning a variety of emergency treatment/monitoring devices in relation to portable patient ambulatory vehicles such as stretchers and rolling beds used in civilian applications. 
     As detailed below, according to one embodiment of the invention, the portable life support system is a portable respiratory support apparatus that provides treatment in the form of ventilation and oxygen supply and may be used in many emergency and medical transport applications, particularly by the military—for example, in the field or in transit between forward field surgical units and more permanent treatment units (Echelon 3 units); as well as in the civilian market for emergency transport by ambulance and helicopter. This unit optionally includes a facility to suction the airway of a subject. 
     In one aspect, the portable life support system serves to monitor the outcome of respiratory treatment parameters and also serves to monitor non-treatment parameters of importance to attending medical personnel such as the patient&#39;s ECG, heart rate, temperature and blood pressure. Device parameters may also be displayed most notably available battery power and operation modes. Respiratory treatment parameters measured and displayed by the life support system are detailed below. In a general aspect, the portable life support system of the invention contemplates that other forms of treatment and/or monitoring could be provided, measured and/or displayed. 
     The term “treatment” is used broadly to refer to ministrations of any kind, including without limitation provision of respiratory gases, drugs, stimuli, signals etc. 
     A preferred embodiment of the invention will now be described, and relates to a portable respiratory support apparatus and measurement of respiratory physiological parameters for display. 
     The portable respiratory system optionally comprises six main components collectively termed Mobile Oxygen, Ventilation and External Suction system (portable life support apparatus  1102 ) Referring to  FIG. 15   a:    
     A “conditioning section”  8  ( FIG. 1 ) for ambient air, including a source of O2, in one preferred embodiment an oxygen concentrator  20 , optionally including a dehumidification device  25  (optionally in the form of a moisture exchanger); 
     a ventilator  1 ; 
     a patient airway suction system including a suction port  70 , which is used with conventional accessories to clear the patient&#39;s airway; 
     a patient monitoring system, in the form of a display  600 , which monitors and displays a patient&#39;s vital statistics and optionally device parameters, for example remaining battery power, tidal volume (in ventilatory mode); 
     the breathing circuit, which may optionally be a circle circuit, a non-rebreathing circuit, or a partial rebreathing circuit, which controls delivery of gas to the patient and which may optionally operate in either a ventilated or spontaneously breathing mode, and 
     a power system  1500 , which may for example optionally be comprised of rechargeable batteries, or removable, rechargeable batteries, or removable hot swappable batteries, and which may optionally include an AC power supply, or which may optionally including a connector for connecting to an AC power supply. 
     In one aspect of the invention the oxygen content of the system is controlled independently of the minute ventilation of the patient, that is, without reference to the patient&#39;s minute ventilation and the operation of the ventilator. Accordingly, the inventors have discerned that integrating emergency ventilation and oxygen supply functions is simplified and energy efficient according to the invention. In one aspect of the invention, the oxygen supply is controlled in response to the patient&#39;s minute oxygen consumption. This may be done by measurement of oxygen concentration in the system, for example with an oxygen sensor, and turning the oxygen supply on only when the oxygen concentration drops below a set value, and turning the supply off when it reaches a set concentration. 
     For example, when the oxygen concentration reaches 85%, a controller operatively connected to sensor can shut the concentrator off. When the oxygen concentration is sensed to fall to 80%, for example, the oxygen concentrator can be turned on again. This minimizes the amount of oxygen that needs to be produced by the system and hence provides for a more energy efficient and lightweight system. 
     Importantly, at least some embodiments of the invention overcome dismissive perspectives attributable to presumed design constraints on using an oxygen concentrator in place of oxygen tanks, in emergency transport settings, in terms of power consumption, required size and output of O 2 . Importantly, at least some embodiments of the invention contemplate that these constraints can efficiently be obviated in important part by re-circulating a patient&#39;s expired gas in a circle circuit, or partially reusing a patient&#39;s exhaled gas in a partial rebreathing circuit, for example a SGD circuit. In particular, since ambient air traditionally conditioned in concentrators contains 21% O 2  and exhaled gas of patients receiving, for example, 40% O2, contains approximately 33-35% O2, it has been determined according to an embodiment of the invention to be efficient as well as otherwise advantageous, to use an O 2  concentrator in conjunction with a circle or re-breathing circuit and scrubber, to supply oxygen to patients requiring ventilation during emergency transport. Some embodiments of the invention also contemplates that patients not requiring ventilation can also be efficiently supplied with oxygen generated by an oxygen concentrator by providing a reservoir for collecting the patient&#39;s exhaled gas and optionally allowing the patient to use exhaled gas at the end of an inspiratory cycle. 
     As generally shown in  FIGS. 1 ,  2  and  15   a , according to a preferred embodiment of the invention, the concentrator  20 , ventilator  1  and re-breathing sections of the portable life support system are generally arranged end to end, to generate a compact longitudinal profile that matches that of the stretcher (litter) or other similar portable vehicles that support patients in a reclining position. This profile is particularly advantageous in at least the following respects: 
     Litter support stanchions in military helicopters have at least three levels at which litter support hooks or shelf like supports are located so that at least three litters may be occupied and supported one on top of the other during emergency transport from a small surgical field unit (for example a unit that may have only one surgical table, one pre-op area and one post-surgical monitoring area nearest the combat zone—sometimes known as a Forward Resuscitative Surgical Site (FRSS) or Echelon 2 facility) to the next more permanent or Echelon 3 medical facility. The longitudinal profile best enables the portable life support apparatus to be suspended parallel to the litter, off its side, or above it with minimal interference to access to the patient to whom the unit is allocated or any patient above or beneath. 
     The portable life support apparatus can be supported in at least two positions longitudinally displaced from another with individual positioning structures that do not need to support the entire weight of the apparatus and are hence simpler, more versatile, lighter and less bulky. 
     The screen displaying vital statistics may be compactly oriented in a longitudinal orientation parallel of the orientation of the life support apparatus. In this orientation, the display may be adapted to rotate into a variety of planes about an axis parallel to the axis of the apparatus so that it can be rotated into a reading position that accommodates upper, intermediate and lower litter positions. 
     According to one embodiment of the invention, the portable life support apparatus treats both spontaneously breathing patients and ventilated patients and may be operated differently in “spontaneous” mode versus “ventilation” mode, as described below. 
     Referring to  FIGS. 2 and 2   a , with respect to the spontaneous mode of operation, it is first particularly noteworthy that tubes  54 ,  54   a  serve to distance the expiratory outlet  50  contained in cartridge  12  from the patient mask (or other equivalent patient airway interface), which interface does not have an expiratory port, so that oxygen enriched gas is not lost from the mask. 
     Furthermore, as shown in  FIG. 2 , inasmuch as cartridge  12  may include a sequential re-breathing valve  52 , the afore-exemplified mask may be attached to the fresh (also termed “conditioned”) gas output by a length of conduit that stores exhaled gas—for re-breathing in conjunction with a planned requirement for inspiratory relief, prior to the end of an inspiratory cycle, making the oxygen production requirements of the concentrator even more adaptable for portable emergency use. 
     As shown in  FIGS. 1 and 2 , schematically describing embodiments of the “ventilated” and “spontaneously breathing” or “spontaneous” modes, respectively, the system may be modularly constructed to provide a separate ventilator cartridge  10  for attachment to the device for operation in a “ventilator” mode and a different cartridge  12  for operation in the “spontaneous” mode. 
     In both ventilated and spontaneous modes, ambient air enters the portable life support system, through the hydrocarbon filter  14  drawn by the pump  16  and through “conditioning” section generally identified as  8  (oxygenation and optionally dehumidification) of the conduit assembly, as described hereafter. The pump/vacuum  16  (optionally combined) pumps ambient air via conduit section  17  through the inner tubes  82  (shown in  FIG. 3 ) of a dehumidifier, optionally a moisture exchanger  25 , where it encounters lower pressure lower humidity gas being purged from the concentrator  20 . Dehumidified air leaves the moisture exchanger  25  through conduit section  19 . Valve V 5  determines when the dehumidified air is used to pressurize one of the sieves  26  or  28 . During part of the concentrating cycle, for example when valve V 2  is open for one sieve to prime the other (as described below), V 5  directs the air into the concentrator housing to cool the motor  18  and sieves  26  and  28  and other components within first longitudinal section of the device e.g various control boards not shown and air pump  27 ). Valve V 1  determines which sieve is being pressurized and which is being vacuumed. The vacuum head of the pump  16  draws the dry nitrogen-enriched air from the sieve S 1  or S 2  being purged through the valve V 1  and directs it via conduit section  15  through the outer counter flow part  23  of the moisture exchanger  25  around the tubes  82  (see  FIG. 3 ) where it is used to dehumidify the inbound air from conduit section  17 . The vacuumed air exits the device via conduit section  32  and outlet filter  30 . Air intake through hydrocarbon filter  14  is also pumped through conduit section  21  via air pump  27  and then into the inspiratory reservoir  36 , optionally a bellows, via bellows entry port  9010 . Air received via air pump  27  is primarily needed for mixing ambient air with oxygenated air for delivery to spontaneously breathing patients. For example, spontaneously breathing patients may receive eight litres per minute of fresh gas flow composed of a combination of 5.8 litres of ambient air and 2.2 litres of 90% oxygenated air (combined in the conduit  38 ) so that they get fresh gas with 40% oxygen. Although a supplementary volume of air is not needed in the ventilated mode of operation, in some instances, it may be expedient to mix some ambient air into an over-oxygenated air stream. 
     It is generally understood that there are a variety of ways of attenuating the oxygen concentration, in either ventilated or spontaneous mode, depending on the fresh gas flow and oxygen concentration requirements of the patient. These include shutting the concentrator off for a period, blending the oxygenated air with ambient air or changing the oxygen concentration settings (for example, with a controller that controls parameters affecting the performance of the concentrator such as working pressures and length of the cycles). 
     In a circle circuit, the O 2  concentration and rate of the fresh gas flow (“FGF”) are set so as to provide at least the oxygen consumption of the patient, which may be only 200-300 ml of O 2  per minute, at a concentration determined by the needs of the patient. If the FGF has a concentration of 85%, then only 350 ml/minute of FGF is required. However in practice it is common to provide a higher rate FGF, for example, at least 1 L/min to flush out trace gases from the system. By way of example, assume the concentrator is capable of providing 2 L/min of 85% O2, and only 40% O2 is required for a particular patient with an oxygen consumption of 300 ml/min. The minimum FGF for this patient would be 500 ml/min of 40%. If 1 L/min of FGF is required to flush out the system, the 40% concentration may be generated by running the concentrator produce 85% intermittently (for example, the concentrator would be run with a 15% duty cycle to produce 0.3 LPM of 85%) and blending with 0.7 LPM ambient air to achieve 1 LPM at 40% oxygen concentration. Alternatively, the concentrator working pressures may be adjusted to produce 1 L/min of 40% oxygen without blending with ambient air. 
     As shown in  FIG. 1 , the conduit assembly of the portable life support apparatus  1102  may comprise a semi-closed “circle circuit” generally identified by  43  comprising conduit inspiratory sections  38  and  39  and expiratory sections  40 ,  41  and  42 , all fluidly connected to an inspiratory reservoir  36 . As shown in  FIG. 2 , the conduit assembly of the portable life support apparatus  1102  may comprise a partial rebreathing SGD circuit comprising conduit inspiratory sections  38  and  54   a  and expiratory sections fluidly connected to an inspiratory reservoir  36 , and expiratory sections  54 ,  50  leading to ambient air. 
     In one embodiment of the invention, the inspiratory reservoir  36  takes the form of a bellows that is acted on by blower  44  (receiving air through conduit section  48 ) to exert positive inspiratory pressure to ventilate the patient. The bellows  36  contains an expiratory valve  66 , for example a positional valve (see  FIG. 6 ) that only opens when the bellows is fully expanded; when it is fully expanded it may only require a pressure of 1 to 2 cm of H 2 O to maintain the bellows in a position where the valve is positionally open. On the inspiratory side the inspiratory relief valve  68  may also be a positional valve that opens when the bellows is fully contracted and is set to open, at a pressure which ensures that the blower is operating efficiently (working the bellows and not the valve). In the spontaneous mode, it is desirable to have rebreathing valve  52  open when bellows  36  is depleted and the subject is still inspiring, in preference to having inspiratory relief valve  68  open. Thus, the opening pressure of inspiratory relief valve  68  is preferably set higher, and preferably at least 1-3 cm H 2 O higher, than rebreathing valve  52 . A one-way valve  45  (set to open easily—e.g. 0.5 cm of H 2 O) leads from the bellows to the patient, via either the CO 2  scrubber cartridge  10  (shown in  FIGS. 1 ,  9  to  11 , in particular), or the spontaneous breathing cartridge  12 . Conduit section  38  receives a combination of oxygenated air from the concentrator via conduit section  37  and from the bellows  36 . Bellows  36  which is normally filled: a) with exhaled air (in the ventilatory mode) carried to the bellows via conduit sections  40 ,  41  (a scrubber by-pass path directly through the cartridge  12  as shown in  FIGS. 1 ,  9 - 11 ) and  42 ; and b) with ambient air received from air pump  27  via conduit section  35 , primarily in the spontaneous breathing mode (in the spontaneous breathing mode exhaled air enters the atmosphere through a one way valve  50  (set to open easily—e.g. 0.5 cm of H 2 O). 
     In an alternative embodiment, the inspiratory reservoir  36  could comprise some other suitable vessel, such as a bag, instead of a bellows. 
     Conduit  38  leads to the patient via inspiratory hose  39 , optionally an extendable hose, through a Y-piece  34  that connects (in ventilatory mode) to a patient&#39;s endotracheal tube (not shown) through a filter  47  via an elbow connector  49 . 
     On the expiratory side, in ventilatory mode, Y-piece  34  is connected to expiratory conduit sections  42 ,  41  and  40 , and through one-way valve  46  (set to open easily—e.g. 0.5 cm of H 2 O) to the bellows  36 . 
     By contrast, in spontaneous breathing mode, cartridge  12  receives expired air through patient expiratory conduit section  54  which leads to a one-way valve  50  (set to open easily—e.g. 0.5 cm of H 2 O) to atmosphere and sequential rebreathing valve  52  (e.g. set to open at 2.5 cm of H 2 O) which may be planned to open during a planned re-breathing part of the inspiratory cycle and is generally triggered to open during the latter portion of inspiration when the patient&#39;s breathing rate exceeds the rate of fresh gas flow. 
     As described above, expiratory reservoir in the form of optionally extendable expiratory hose  54  one way valve  50  provides a point of venting expired air to atmosphere at a distance from the patient mask, so that much of the 8 litres of 40% oxygen typically generated for a spontaneously breathing patient in need of oxygen, is not otherwise immediately lost to atmosphere via an expiratory vent in the mask. Expiratory hose  54  optionally contains at least 200 ml of volume. 
     The ventilator cartridge contains a CO 2  scrubbing material (e.g. soda lime). Inasmuch as portability may often entail size limitations and hence possibly longitudinal space limitations that reduce the path length through which expired gas can travel for scrubbing (reducing the amount of CO2 that can be removed by the scrubber), a scrubber design containing a helical scrubber material chamber/airflow pathway, as particularly shown in  FIGS. 11 to 13 , can be used to increase the path length and amount of CO2 that can be removed from the patient&#39;s expiratory gas. 
     As described above, ambient air enters the circuit through a hydrocarbon filter  14  and is optionally pumped by pump  16  (having a common motor  18  with vacuum  20 ) directly into the core of moisture removal device  22  which is generally configured like a shell and tube heat exchanger, as shown in  FIG. 3 . 
     In one embodiment, as shown in  FIG. 3 , ambient air is directed through inlet  80  and outlet  86  (Path A) which are fluidly connected to tubes  82 , optionally made of Nafion®, a material known for its moisture (water molecule) permeability properties, and utility in removal of moisture from a current of air, using a counter flow gas of lower humidity. As shown in  FIG. 3 , ambient air flowing through the tubes  82  may be conditioned in the core  84  of the de-humidification device with lower humidity, lower pressure, air traveling around the tubes via path B (inlet  90  to outlet  104 ). The dehumidified gas exits through core outlet  86 . The counter flow or “conditioning air” enters the core through the inlet-sleeve  88  via inlet-aperture  90  in the core wall  96  (also shown in  FIG. 4 ) and travels through a circumferential sleeve-defined pathway  92  around the outside of the core. Pathway  92  is in fluid communication with the counter flow pathways through and around the outside of tubes in the core  84  via air-dispersing, screen-like openings  94  around the periphery of the core wall  96 . Counter flow air exit through openings  98  which are in fluid communication with exit-sleeve pathway  100  defined by exit-sleeve  102  that lead to exit aperture  104 . 
     As shown in  FIGS. 1 and 2 , in one embodiment of the invention, air vacuumed from the sieve beds  26  (S 1 ) and  28  (S 2 ) of the oxygen concentrator  20 , is vacuumed alternatively from sieve bed  26  and  28  through valve V 1 , which is in alternate fluid communication with S 1  and S 2  and exits into atmosphere through valve V 6  and vacuum  16  through outlet conduit  32  past outlet filter  30 . The vacuum  20  purges the sieve beds  26  and  28  in alternating cycles described immediately below. This purged air is enriched in nitrogen gas adsorbed by the zeolite material (e.g. Oxysiv®) in the sieve beds and is at substantially lower pressure than the ambient air pumped through Path A. This purged air is used as the low-pressure, lower humidity, counter flow gas to remove humidity from ambient air. 
     De-humidifiers of the type sold under the name Perma Pure® e.g. FC series handling flow rates of up to 80 slpm, for example 75 slpm, can be used in the present context for gas-gas dehumidification. Optional adaptations of off-the-shelf Perma Pure specifications (e.g. FC-125), include increased Nafion® membrane thickness (e.g. to 0.030 in.) to handle larger pressure differentials between ambient and counter flow gases, and increasing tube number (e.g. to  400  tubes). Parameters impacting on dehumidification include the differences in humidity and pressure between the gas inside and outside the tubes. The combined effect of changes in humidity and pressure differences across the tubes can be routinely approximated using published data and can be readily empirically determined. In one embodiment of the invention, the pressure differential in the tubes is approximately 36 psi. 
     According to one embodiment of the invention, the oxygen concentrator is of the type that operates on a pressure swing adsorption or a pressure/vacuum swing cycle as described by way of background in U.S. Pat. No. 6,478,850 (the &#39;850 patent), the contents of which are hereby incorporated by reference. As described in the &#39;850 patent, the concentrated oxygen is released to the breathing circuit following which some is used to prime the second sieve bed. The sieve bed is then vacuumed to release the nitrogen and purged. This occurs in repeating cycles, with each sieve bed alternately being pressurized, releasing oxygen to the breathing circuit, then being purged. As shown in  FIGS. 1 and 2 , the two sieve beds  26  and  28  (S 1  and S 2 ) may be alternatively pressurized and purged with a valve V 2  between the two sieves permitting recoup of a partially concentrated gas for use in the subsequent pressurization cycle (in the other sieve). Oxygen enriched gas is released from S 1  via valve V 3  and from S 2  via valve V 4 . In one embodiment of the invention, the O 2  concentrator produces at least 2.2 L (at standard pressure) of 90% O 2 . 
     According to one embodiment of the invention, the portable life support system comprises a volume controlled ventilator that provides control of respiratory rate, tidal (breath) volume, and delivered oxygen concentration. As shown in more detail in  FIG. 6 , the ventilator is comprised of a blower  44 , a sealed container  35  that houses the inspiratory reservoir in the form of bellows  36  and a volume measurement device, for example a positional encoder that measures displacement of the bellows via string  9061 . 
     As shown in  FIGS. 6 and 7 , representing a detailed view of the ventilator and positional inspiratory and expiratory relief valves  66  and  68 , respectively, one way inspiratory valve  45  and one way expiratory valve  46  communicate with the interior of the bellows  36 . An oxygen sensor port  9000  (communicating with an oxygen sensor—not shown e.g. MiniOx®) may be used to sample the oxygen concentration in the bellows. The bellows  36  is also in fluid communication with conduit section  35  carrying ambient air propelled by air pump  27 , via bellows entry port  9010 . The bellows may be set to move along a rod  905 , which is positioned via aperture  9030  and  9060  and bellows sleeve  9040 . Pin  9080  on positional expiratory relief valve  68  makes contact to open when the bellows is fully expanded, enabling pin  9080  to contact bulkhead surface  9100 , whereupon sufficient expiratory pressure to maintain pin contact with the bulkhead surface will provide expiratory relief. Similarly, pin  9090  of positional inspiratory relief valve  66  will contact projecting surface  9120  of the bellows floor to open inspiratory relief valve  66  in a ventilated mode of operation which is set to open at a pressure e.g. 5 cm H20 (greater than the inspiratory relief valve—within cartridge  12 —optionally set at 2.5 cm H20). 
     To vary the delivered oxygen concentration ambient air is pulled through the hydrocarbon filter by the air mixing pump and delivered to the patient expiratory tube  40  or to the bellows  36 . This air fills the bellows and is mixed with concentrated product to deliver desired oxygen concentrations (for example, 40% and 85%). 
     During ventilation, the blower produces the pressure that forces the bellows to collapse delivering whatever gas blend is in the circuit to the patient through the scrubber, at the desired tidal volumes and respiratory rates. Correct estimation of the tidal volume requires adjustment for the concentrator generated enriched oxygen flow, that is not simply measured by displacement of the bellows. The blower  44  draws air through the inlet filter  33  and delivers it to the sealed chamber housing the bellows  36 . 
     As shown in  FIG. 1 , during patient exhalation, expired gas travels down the expiratory tube  42 ,  41  and  40  through a one-way valve  46  into the bellows. When the volume in the bellows exceeds maximum volume, excess gas is expelled via the expiratory vent  66  into the bellows chamber, which exits the chamber through the blower. Since expired gas exits through the blower, running the blower during exhalation at a controlled constant rate provides positive end expiratory pressure (PEEP). The PEEP may be controlled, for example to provide varying levels between 0 and 20 cm H 2 O. Additionally, in the breathing circuit, a safety pressure relief valve (not shown) is located with an opening pressure approximately equal to the maximum desired airway pressure, for example, 60 cm H 2 O. Optional ranges for ventilation parameters include: 
     1. inspired O 2  concentrations of 21% to 93%—For increased ease of use, 3 presets may be settable by the user of 21%, 40%, and 85%. Tidal volumes may be settable between 400 ml and 1 litre (e.g in increments of 100 ml), which are useful for adult ventilation. 
     2. Breath Frequency: between 8 and 20 per minute 
     3. PEEP: 0-25 cm H 2 O optionally with settings incremented in 5 cm H 2 O 
     4. Inspiratory: Expiratory ratio between 1:1 AND 1:2—this is typically adjusted automatically based on tidal volume, breath frequency, and blower flow rate. 
     5. End Inspiratory or end expiratory Pause with pressure hold. 
     If the system reaches the maximum airway pressure limit set on the ventilator control, the blower stops blowing and switches into constant PEEP mode as described below. 
     The system is able provide intermittent tracheal suction. A suction kit consisting of a wand, hoses, and suction bucket with optional filter may be attached to the suction port. Activating suction mode energizes valve V 6  which then connects the vacuum head of the pump  16  to the suction port  70 . The vacuumed air is then vented through the outlet filter  30 . Suction is preferably at approximately 100 mm Hg but may be higher or lower is dictated by the patient&#39;s requirements. A suction relief valve (not shown) may be optionally provided in parallel to the suction path and leads to ambient air to ensure the suction does not exceed the maximum desired vacuum level. 
     As shown in detail in  FIG. 6 , the spontaneous breathing cartridge  12  may be attached for the device to operate in spontaneous breathing mode. The cartridge contains an optional patient filter  55  (which can prevent patient secretions from entering the bellows) and may contain two valves  50 , 52  to allow sequential gas delivery, for example as described in WO/2004/073779. Expiratory valve  50  leads to ambient air through port  7420 . When the inspiratory volume of the bellows is depleted, if the patient is still inspiring, valve  52  opens permitting rebreathing of expired gas contained within a length of patient tube  54  (for example six feet). Optionally, an additional exhaled gas reservoir, such as a rebreathing bag, may be connected to port  7420 . 
     In spontaneous breathing mode the concentrator works exactly the same as in ventilated mode. The oxygen produced by the concentrator is fed to the inspiratory limb  37  of the breathing circuit. In ventilated mode, the ventilator and concentrator controls preferably communicate so that oxygen is not released from the concentrator to the breathing circuit during the last portion of inspiration, as this volume would not be accounted for in the tidal volume measurement, as determined for example by the bellows position sensor. 
     As described above with reference to  FIG. 2 , ambient air is delivered to the bellows  36  from the air pump  27 . The air pump draws its air from ambient via the hydrocarbon filter  14 . The rate of ambient air entrainment is approximately 5.8 LPM, which when mixed with 2.2 LPM of 90% O 2  provides 8 LPM of 40% O 2 , sufficient to meet the alveolar ventilation requirements of most patients at rest. The concentration of oxygen that is achievable by the system depends on the capacity of the concentrator and on the ventilation requirements of the patient. For example, if the concentrator can make 2.2 LPM of 90% O 2  and the patient only needs FGF of 6 LPM, then only 3.8 LPM of ambient air is needed for blending, providing 6 LPM of 47% O 2 . 
     In spontaneous breathing mode, it is helpful for ease of use to provide a concentration of 40% O 2 , since most adults require less than 8 LPM of FGF, and providing this concentration requires a concentrator capable of producing 2.2 LPM of 90% O2 which can be made relatively small (&lt;10 lbs.). 
     The patient can breathe at any frequency and with any tidal volume in spontaneous mode. 
     The system can be optionally used in a monitoring mode whereby the ventilator and concentrator are not operative and only patient monitoring is active. The patient may be breathing spontaneously on the circuit with the air pump  27  providing FGF to the circuit. 
     The spontaneous breathing circuit consists of the bellows  36 , the one-way valve  45  from the bellows to the inspiratory limb of the spontaneous cartridge, the cartridge (which contains the optional filter  55 ), an inspiratory hose  54  with a Y-piece  51  connected to a plastic oxygen mask  53  (without holes to prevent dilution), an expiratory hose  54   a , a one-way expiration valve  50  in the cartridge, and a sequential rebreathing valve  52  in parallel to the one-way expiration valve  50 . 
     In spontaneous breathing mode the system does not generally provide assisted ventilation, although it may in some instances. During inhalation gas in the inspiratory limb and bellows is pulled through the optional filter  55  in the cartridge and through the patient inspiratory tube  54  to the mask  53 . The patient exhales through the expiratory tube and out to ambient through the one-way exhalation valve  50 . The sequential rebreathing valve  52  triggers when the patient&#39;s continues to inspire once the bellows  36  is empty, which occurs in general when his breathing rate exceeds the rate of FGF into the circuit. 
     According to one embodiment of the invention, the portable respiratory device operates with battery, DC or AC power. 
     Optionally, the device may house up to two batteries, preferably lithium polymer due to energy density, mounted internally and accessible at the end of the device. Optionally, the device operates on a battery for approximately 1.25 hours (2.5 hours per set). While operating from AC, the device may optionally trickle charge internal batteries. 
     Reference is made to  FIG. 8 , which shows the cartridge  10 , mounted in a seat  300 . The cartridge  10  is configured to be used when the patient is being ventilated. The cartridge  10  is easily removable and replaceable with another cartridge for use when the patient is spontaneously breathing. The cartridge  10  includes a locking tab  900  on two opposing sides. The locking tab  900  engages an aperture  902  through the wall of the seat  300 . To release the cartridge  10  from the seat  300 , the user pushes inwardly on the locking tabs  900  to disengage them from the apertures  902 . To engage the cartridge  10  in the seat  300 , the cartridge  10  is simply pushed into the seat  300  until the locking tabs  900  lock in the apertures  902 . 
     The cartridge  10  includes an inspiratory inlet  215  ( FIG. 9 ), an inspiratory outlet  219  ( FIG. 10 ), an expiratory inlet  235  ( FIG. 10 ) and an expiratory outlet  225  ( FIG. 9 ). When the cartridge  10  is seated, the inspiratory inlet  215  communicates with the one-way valve  45  at the inspiratory outlet, shown at  992 , of the bellows  36 , and the expiratory outlet communicates with the one-way valve  46  at the expiratory inlet, shown at  990 , of the bellows  36 . 
     Referring to  FIG. 11 , the cartridge  10  includes a CO2 scrubber  199  and a pass-through expiratory conduit  41 . As shown in  FIG. 1 , air from conduit section  38  enters the scrubber  199  via the scrubber inlet port  215 . The scrubber  199  includes a housing  205  and an internal structure  207  that together define a two tier helical airflow pathway. The housing  205  includes a first housing element  206   a  and a second housing element  206   b , which are removably connectable together. A first end plate  210  and a second end plate  230  are positioned at opposing longitudinal ends of the scrubber  199  and are part of the first and second housing elements  206   b  and  206   a  respectively. 
     The internal structure  207  includes an internal divider  220  that is generally midway between the first and second end plates  210  and  230 . The plates  210 ,  220  and  230  are all generally perpendicular to the longitudinal axis of the scrubber  199  and of the portable life support apparatus  1102 . 
     The internal structure  207  further includes wall structures  240  and  250  that cooperate with the plate  220  and with the housing  205  to urge the air along the aforementioned generally helical flow path. The interior wall structures  240  and  250  are better shown in  FIGS. 12 and 13  and may be oriented substantially perpendicularly to surfaces  210 ,  220  and  230 .  FIG. 11  also shows scrubber outlet port  200  which is fluidly connected to patient inspiratory tube  39  ( FIG. 1 ). 
     Scrubber material  217  is present through the inspiratory air flow path through the housing  205 . Only a small portion of the total quantity of scrubber material  217  in the scrubber  199  is shown in  FIG. 8 . The scrubber material may be any suitable scrubber material, such as, for example soda lime. 
     Pass-through conduit  41  (also shown in  FIG. 1 ) interconnects conduit sections  40  and  42  and passes right through the scrubber  199  so that air passes through the conduit  41  without contact with the scrubbing material, and includes scrubber expiratory inlet  235  leading from the y-piece ( FIG. 1 ) via conduit section  42  ( FIG. 1 ) and scrubber expiratory outlet  225 . 
     The scrubber housing  205  and internal structure  207  are easily disassemblable for easy replacement of the scrubber material  217  and easy reassembly, as illustrated in the exploded view in FIGS.  11 , 12 . 
     Referring to  FIG. 17 , the portable life support apparatus  1102  includes a display  600  for displaying patient vital statistics including; O 2  saturation, continuous or intermittent non-invasive blood pressure, CO 2 , inspired O 2  concentration, ECG, heart rate, temperature, airway pressure, respiratory rate, and tidal volume. The display  600  may be a vacuum fluorescent display with adjustable brightness and a stealth mode. Additionally, the device  1102  may include one or more alarm lights  1150  (eg. four alarm lights  1150 ) positioned on the exterior. In embodiments wherein there is a plurality of the alarm lights  1150 , the alarm lights  1150  may be dispersed about the perimeter of the device  1102  so as to increase the likelihood that one of them will be visible to a user, with less need to be concerned with the orientation of the device  1102 . 
     As shown in  FIG. 16 , the device  1102  may include input ports which may, for example, be located proximally to the display  600 , which optionally houses a master control board for receiving data from an electrocardiogram (for example, data from a three lead ECG—port  500 ), an oxygen saturation meter (port  510 ), for example, a pulse oximeter (e.g. Nonin brand), a blood pressure cuff, either conventional—device has an air pump (not shown) and cuff inflation port  520 ) or acoustic (with extra microphones and noise cancellation features that are better adapted for helicopter noise cancellation—ports  520  and  525 ), gas sampling (sampling port from position proximal to patient—for example from Y piece  34  shown in FIG.  1 —sampling port  515  leads to oxygen and CO2 monitors, optionally a rapid response infrared CO2 monitor) and temperature (port  530 ); and related parameters may be shown on the display  600 , as shown in  FIG. 17 . 
     Persons skilled in the art will appreciate that a dedicated control board may be allocated for machine intelligence related to ventilator controls (tidal volume, airway pressure and BPM), concentrator control (oxygen concentration %, rate of operation), display controls etc. 
     As shown in  FIG. 17 , the screen  600  controls may set to display (to left to right) tidal volume in ml, BPM (breaths per minute), inspiratory airway pressure  625  in cm H 2 0 in the inspiratory conduit, expiratory airway pressure  627  in cm H20, oxygen concentration, temperature, carbon dioxide concentration (both patient expiratory gas  615  and just upstream from the scrubber  199 —smaller number  5  shown at  616  in  FIG. 17 ), oxygen saturation; bottom left to right—graphic output e.g. ECG, blood pressure—systolic/diastolic and heart rate. Also shown are user interface controls—e.g. membrane switch keys—for activating BP (blood pressure) measurement  620 , setup  630 , suction  650 , screen orientation reversal  660 , ECG (three lead)  640 , soft keys— 610 , screen dimming  680  (including night vision mode), power  690  and alarm silencing  700 . Standard OEM sensing and monitoring modules are well known to those skilled in the art. 
     The display  600  may be part of a display assembly  601  that also includes a housing  603  which may be polymeric. The display assembly  601  may also include a filter suitable to screen output frequency to make the display night vision goggle compatible. The display  600  may utilize membrane switch keys above and below the screen, as exemplified above. 
     The housing  603  permits rotation of the display  600  about a display axis  605  for viewing over a range of angles by a user and can be flipped more than 180° to accommodate various mounting positions of the life support device  1002  in relation to the user. 
     As shown in  FIG. 15   a , the housing  603  is rotatably supported in first and second end supports  1100  and  1102 . Each end support  1100  and  1102  includes a bearing surface  1103  (see  FIG. 19   a ) which supports a shaft portion  1105  ( FIGS. 17 and 18 ) of the housing  603 . Either or both of the end supports  1100  and  1102  may include a detent device  1104  (see  FIG. 19 ) for engaging a plurality of teeth  720  positioned at one or both axial ends of the housing  603 . The detent device  1104  includes a detent  1106  and a biasing member  1108 , which may be, for example, a compression spring  1110 . The detent device  1104  provides a selected amount of resistance to rotation for the display  600  so that the display  600  is less likely to rotate inadvertently when a user is entering input using the membrane switch keys described above. Additionally, the resistance to rotation provided by detent device  1104  is beneficial in that the display is less likely to inadvertently rotate as a result of vibration or other mechanical influence during use, for example, when the patient is being transported by helicopter to a medical facility. 
     Either or both axial ends of the display housing  603  ( FIG. 18 ) may include a first limit surface  1114  and a second limit surface  1116  which engage corresponding limit surfaces  1118  and  1120  ( FIG. 19   a ) in one or both of the end supports  1100  and  1102 . The limit surface pairs, ie.  1114  and  1118 , and  1116  and  1120 , cooperate to limit the range of rotational travel of the display  600 . The range of travel selected for the display  600  may be, for example, about 270 degrees. 
     Reference is made to  FIG. 21  which shows the components of the positioning system  801  in accordance with an embodiment of the present invention. The positioning system  801  may include one or more sets of: patient transport apparatus connectors  800 , one or more straps  802 , one or more life support system connectors  804  and a life support device interface  803 . The life support device interface  803  may be common to all the sets. The patient transport apparatus connectors  800 , one or more straps  802 , one or more life support system connectors  804  make up a positioning structure  805 . 
     The patient transport apparatus connector  800  connects to a patient transport apparatus  806 , such as, for example, a stretcher and more particularly a NATO litter  808 . The patient transport apparatus connector  800  may connect to the patient transport apparatus  806  in any suitable way for supporting the weight of the life support system  1100  (see  FIG. 21 ). For example, the patient transport apparatus connector  800  may connect to one of the frame members, shown at  810 , of the patient transport apparatus  806 . 
     The patient transport apparatus connector  800  may mount releasably to the patient transport apparatus  806 , and more particularly to the frame member  810 . The patient transport apparatus connector  800  may include a clamp assembly  812  that is configured to clamp onto the frame member  810 . The clamp assembly  812  includes a first clamp member  814  and a second clamp member  816 , which cooperate with each other to clamp onto the frame member  810  ( FIG. 21 ). 
     In the embodiment shown in  FIG. 21 , the patient transport apparatus frame member  810  is generally circular in cross-section and the first and second clamp members  814  and  816  (see  FIG. 22   a ) are shaped in a suitable way to grip the circular shape. It will be understood that the cross-sectional shape of the patient transport apparatus frame member  810  may have any suitable shape, such as, for example, circular, elliptical, square or rectangular, for its function as a frame member, and it will be further understood that the clamp members  814  and  816  may have any suitable shape for gripping to the frame member  810 . 
     It will further be understood that the clamp assembly  812  ( FIG. 22   a ) need not only include two clamp members, but could include any suitable number of clamp members. 
     The first and second clamp members  814  and  816  may be pivotally connected to each other about a pivot axis  817 . For example, a shaft  818  may extend through both clamp members  814  and  816 , and may permit one or both of the clamp members  814  and  816  to rotate thereon. 
     The patient transport apparatus connector  800  is movable between an open position, shown in  FIGS. 22   a ,  22   b ,  22   c ,  22   d  and  22   e , a patient transport apparatus-connected, strap-unlocked position, shown in  FIGS. 23   a  and  23   b , and a patient transport apparatus-connected, strap-locked position, shown in  FIGS. 24   a  and  24   b . The clamp assembly  812  includes a biasing member  820  ( FIG. 22   c ), which biases the clamp members  814  and  816  apart, and thus biases the patient transport apparatus connector  800  towards its open position. The biasing member  820  may be any suitable biasing member, such as, for example, a spring, and more particularly a torsional spring, as shown at  822  in  FIG. 22   c.    
     The patient transport apparatus connector  800  further includes an actuation arm  824  that is used to urge the clamp members  814  and  816  towards each other. The actuation arm  824  is pivotally connected to the first clamp member  814  about a pivot axis  825 . A shaft  826  passes through apertures in both the first and second clamp members  814  and  816  and the actuation arm  824 . The aperture in the first clamp member  814  is shown at  828  ( FIG. 22   a ) and is slotted, defining a path along an arc of a circle whose centre is the pivot axis  817  between the first and second clamp members  814  and  816 , and whose function is explained further below. 
     Referring to  FIG. 22   d , the actuation arm  824  includes a clamp member driving cam surface  830 , which is engageable with a receiving surface  832  on the first clamp member  814 . As the actuation member  824  is rotated about the pivot axis  825  by a user, the clamp member driving cam surface  830  engages the receiving surface  832  (see  FIGS. 22   a  and  22   b ) and drives the first clamp member  816  to pivot towards the second clamp member. Because the first clamp member  814  pivots only about the first and second clamp member pivot point  817 , the aperture  830  is slotted to accommodate the pivoting movement of the first clamp member  814 . 
     A biasing member  834  ( FIG. 22   c ) biases the first clamp member  814  and the actuation arm  824  apart. The biasing member  834  may be any suitable biasing member, such as, for example, a spring, and more particularly a torsional spring, as shown at  836  in  FIG. 22   c.    
     Movement of the actuation arm  824  from the position shown in  FIG. 22   c  to the position shown in  FIG. 52   b  moves the first clamp member  814  to its closed position with respect to the second clamp member  816 . 
     The actuation arm  824  further includes a first strap-locking surface  838  which can cooperate with a second strap-locking surface  840  that may be present, for example, on the shaft  818  (see  FIG. 22   c ) to pinch the strap  802  and to therefore lock the patient transport apparatus connector  800  in place on the strap  802 . 
     When the actuation arm  824  is in the position shown in  FIG. 22   c , the first and second strap-locking surfaces  838  and  840  are not engaged, and so the patient transport apparatus connector  800  is free to be slid along the strap  802 . As noted above, the clamp members  814  and  816  are in their open position relative to each other. 
     When the actuation arm is in the position shown in  FIG. 23   b , the first and second strap-locking surfaces  838  and  840  may be closer together than they are when the connector  800  is position as shown in  FIG. 22   c , but they are not engaged, and so the patient transport apparatus connector  800  is free to be slid along the strap  842 . The clamp members  814  and  816 , however, are clamped onto the frame member  810  when in the position shown in  FIG. 23   b.    
     When the actuation arm is in the position shown in  FIG. 22   c , the first and second strap-locking surfaces  838  and  840  cooperate to pinch the strap  802  and therefore lock the patient transport apparatus connector  800  in place on the strap  802 . 
     When the actuation arm  824  is in the position shown in  FIG. 22   c  the biasing member  820  and the biasing member  834  hold the actuation arm  824  generally in the position shown. When it is desired for the actuation arm  824  to be in the position shown in  FIG. 23   b , a retaining member  844  can be employed to hold the actuation arm  824  in the position shown in  FIG. 23   b , against the biasing force of the biasing members  820  and  834 . 
     The retaining member  844  may have any suitable structure for releasably holding the actuation arm  824  in place in the position shown in  FIG. 23   b . The retaining member  844  may be an arm  845  that extends from the first clamp member  814  and that includes a hook portion  846 . The hook portion  846  cooperates with a hook-receiving element  848  on the actuation arm  824  to hold the actuation arm  824  in the position shown in  FIG. 23   b . It will be appreciated that the arm  845  could alternatively be positioned on the actuation arm  824  and the hook-receiving element  848  could be positioned on the first clamp member  814 . 
     The arm  845  may be pivotally movable about a pivot axis  850 . A shaft  852  may extend through the first clamp member  814  and the retaining member  844  along the pivot axis  850  to support such pivoting movement. 
     A biasing member  854  may be provided to bias the retaining member  844  to move in a direction towards hooking an object. The biasing member  854  may, for example, be a torsional spring  856  about the shaft  852 . 
     During movement from the position shown in  FIG. 22   c  to the position shown in  FIG. 23   b , the biasing member  854  biases the retaining member  844  against the actuation arm  824 . The arm  824  moves so that the hook receiving portion sweeps slightly past the hook portion  846  and can then move back slightly along its path for capture by the hook portion  846 . 
     When the actuation arm  824  is held in the position shown in  FIG. 23   b , it can be released from that position and returned to the position shown in  FIG. 22   c  by moving the actuation arm  824  forward slightly along the path (ie. towards the position shown in  FIG. 24   b ). Once the actuation arm  824  has moved out of the bight of the hook portion  846 , the user can move and hold the retaining member  844  out of the path of the actuation arm  824  and the actuation arm  824  can be moved back towards the position shown in  FIG. 22   c.    
     Alternatively, a user could continue moving the actuation arm  824  past the position shown in  FIG. 23   b  towards the position shown in  FIG. 24   b . A retaining member  858  can be employed to hold the actuation arm  824  in the position shown in  FIG. 24   b , against the biasing force of the biasing members  820  and  834 . 
     The retaining member  858  may have any suitable structure for releasably holding the actuation arm  824  in place in the position shown in  FIG. 22   c . The retaining member  858  may be an arm  859  that extends from the first clamp member  814  and that includes a hook portion  860 . The hook portion  860  cooperates with a hook-receiving element  862  on the actuation arm  824  to hold the actuation arm  824  in the position shown in  FIG. 24   b . It will be appreciated that the arm  859  could alternatively be positioned on the actuation arm  824  and the hook-receiving element  862  could be positioned on the first clamp member  814 . 
     The arm  859  may be pivotally movable about a pivot axis  864 . A shaft  866  may extend through the first clamp member  814  and the retaining member  858  along the pivot axis  864  to support such pivoting movement. 
     A biasing member  868  may be provided to bias the retaining member  858  to move in a direction towards hooking an object. The biasing member  868  may, for example, be a torsional spring  869  about the shaft  866 . 
     During movement from the position shown in  FIG. 23   b  to the position shown in  FIG. 24   b , the biasing member  868  biases the retaining member  858  against the actuation arm  824 . The arm  824  moves so that the hook receiving portion sweeps slightly past the hook portion  860  and can then move back slightly along its path for capture by the hook portion  860 . 
     Other structures may alternatively be employed to hold the actuation arm  824  at the positions shown in  FIGS. 23   b  and  24   b . For example, while the embodiment shown in  FIGS. 22   c ,  23   b  and  24   b  has two separate hook receiving portions on the actuation arm  824 , it is alternatively possible to have a single hook receiving portion that is engageable by either of two hooks for holding the actuation arm  824  in the two positions shown in  FIGS. 23   b  and  24   b.    
     When the actuation arm  824  is held in the position shown in  FIG. 24   b , it can be released from that position and returned to the position shown in  FIG. 23   b  by moving the actuation arm  824  forward slightly along its path. Once the actuation arm  824  has moved out of the bight of the hook portion  860 , the user can move and hold the retaining member  858  out of the path of the actuation arm  824  and the actuation arm  824  can be moved back towards the position shown in  FIG. 23   b , either manually, or optionally by the biasing member  834 . 
     It will be understood that the patient transport apparatus connector  800  could alternatively be configured so that the actuation arm  824  drives the second clamp member  816  towards the first clamp member  814 . 
     Reference is made to  FIGS. 25   a  and  25   b , which show the life support device connector  804  and which illustrate its operation. The life support device connector  804  may connect to the life support device in any suitable way. For example, the portable life support apparatus  1102  may include a exterior  1103  with at least one undercut channel  870  thereon, as shown in  FIGS. 27   a  and  27   b . As a result of the undercut, the channel  870  includes overhangs  872  on each side. As best shown in  FIG. 27   b , the overhangs  872  are cut away to form circular cutouts  874  (or any other suitable shape) having a selected spacing from one another. The individual overhang elements that are present between adjacent circular cutouts are shown at  876 . 
     As shown in  FIG. 27   a , the exterior  1103  may include a plurality of channels  870  that extend axially. The channels  870  are spaced at regular intervals about the perimeter of the exterior  1103 . The channels  870  make up the life support device interface  803  referred to above. 
     Referring to  FIG. 54 , the life support device connector  804  includes a body  878 , a movable locking element  880 , a biasing member  882  and a strap connector  884 . The locking element  880  is movable relative to the body and has an enlarged head portion  886  which may be circular (or any other suitable shape). The locking element  880  is biased by the biasing member  882  to drive the head portion  886  towards the body  878 . The biasing member  882  may be any suitable biasing member such as, for example, a coil compression spring. The head portion  886  of the locking element  880  is sized to fit within the circular cutout  874  in the channel  870  on the life support device exterior  1103  (see  FIG. 28   a ). A user may push the locking element  880  downwards, against the biasing force of the biasing element, as shown in  FIG. 25   b.    
     To lock the life support device connector  804  on the exterior  1103 , the body  878  is positioned to rest on a pair of adjacent overhang elements  876 , so that the head portion  886  is aligned with a cutout  874  in the channel  870 , as shown in  FIG. 28   a . The locking element  880  can be pushed inwards by a user, so that the head portion  886  enters the channel  870 . By pushing the head portion  886  down sufficiently into the channel  870 , the life support device connector  804  may be slid along the channel  874  such that the head portion  886  slides underneath the overhang elements  876 . The life support device connector  804  may be slid to a position where the body  878  straddles an overhang element  876  (see  FIG. 28   b ). The biasing member  882  urges the head portion  886  upwards towards the body  878  to clamp the overhang elements  876  that are straddled by the body  878  on either side of the channel  874 . 
     Such a connector is sold by ANCRA (40340-27—Single Stud Track Fitting, and may be used with track 40467-33-144, which is the basis for the shape of the channel  870 ). Other suitable connectors may instead be used. 
     In the embodiment shown in  FIG. 21 , the positioning system  801  includes two sets of positioning structure  805 , wherein each set includes two life support device connectors  804  which are mountable at spaced apart positions about the perimeter of the portable life support apparatus  1102 , a patient transport apparatus connector  800  that is connectable to a patient transport apparatus  806 , and a strap  802  that extends between the two life support device connectors  804  and through the patient transport apparatus connector  800 . 
     Referring to  FIG. 21 , the strap  802  may be adjustable in length. For that purpose, the strap may include any suitable length adjustment mechanism  887 , such as, for example, a length adjustment buckle. 
     Referring to  FIG. 21 , the positioning system  801  permits the portable life support apparatus  1102  to be positioned in a plurality of positions relative to a patient transport apparatus  806 . For example, by extending the strap  802 , the portable life support apparatus  1102  may hang from the patient transport apparatus  806 . By adjusting the position of the life support device connectors  804  about the perimeter of the portable life support apparatus  1102 , and/or by adjusting the position of the patient transport apparatus connector  800  along the strap  802 , the orientation of the portable life support apparatus  1102  can be controlled. 
     The portable life support apparatus  1102  could, for example, be positioned on the patient transport apparatus  806  optionally with the air of an extra strap  897  ( FIG. 30   a ) for entry into a patient transport vehicle, such as a helicopter, and can then be repositioned in a hanging position ( FIG. 30   b ). 
     By shortening the straps  802 , the portable life support apparatus  1102  can be brought into relative close proximity to the patient transport apparatus connector  800 , which reduces the magnitude of any swinging that might take place during use. It is possible that the straps  802  can be shortened sufficiently to bring the portable life support apparatus  1102  into contact with the patient transport apparatus connector  800 , which can effectively create a generally rigid connection between the portable life support apparatus  1102  and the patient transport apparatus  806 . 
     Referring to  FIG. 22   a , a life support device connector  888 , which may be similar to the connector  804 , is optionally integrally joined with the patient transport apparatus connector  800  to form a rigid patient transport apparatus/life support device connector  890  which permits the rigid connection directly between the patient transport apparatus  806  and the portable life support apparatus  1102  (see  FIG. 26 ). 
     Referring to  FIG. 29 , additional straps  892  may be employed to help hold the portable life support apparatus  1102  in a relatively fixed position relative to the patient transport apparatus  806  in cooperation with the rigid patient transport apparatus/life support device connector  890 . It will be also be appreciated that the portable life support apparatus may be suspended above and below a side frame member of a portable patient transport apparatus using the clamps without the aid of any straps by using a track proximal to the bottom and top of the apparatus respectively. When suspended below the side frame member, the weight of the device rotates the device partially under the side frame member towards the center the portable patient transport apparatus. 
     The portable life support apparatus  1102  may include several control boards (eg. five control boards) in the life support apparatus, in addition to any boards that control patient monitors. The control boards are described as follows: 
     User Interface and main bus control—manages display screen and user buttons, communicates with other boards to manage traffic. It sends signals to other boards as to what to do and gets reports back, displays these on screen, handles alarm conditions and warning lights. 
     Main Power—controls battery vs wall power, switching between batteries when discharged, monitoring power etc., including measuring battery temperature for overheating 
     O 2  Controller—controls the oxygen concentrator. Controls MiniOx sensor for measuring O 2  in the bellows as well as sieve pressure sensors used for controlling concentrator valves. Controls the valves on the concentrator. It has a motor controller for controlling the concentrator pump motor. It coordinates with the ventilator control to ensure it does not provide oxygen enriched air to the circuit at the end of inspiration, because at that point it&#39;s impossible to correct the delivered volume for this amount. 
     Ventilator Control—controls the blower motor to provide the required volume and breath frequency, as well as PEEP. This also contains and airway pressure sensor and the bellows position sensor. It also contains a differential pressure sensor which can be used for a flow sensor to measure flow at the patient&#39;s mouth to measure what actually got delivered, as opposed the measuring bellows displacement. Differential pressure divided by the known circuit resistance gives flow). This board controls the mixing pump and measures delivered volume using an estimate of O2 enriched air volume from the concentrator. 
     Sensor Control Board—controls all of the off the shelf patient monitoring devices, some of which have their own boards. Contains/controls the patient CO 2  and O 2  sensors and their sampling pump, pressure sensor for measuring pressure in the sampling line (since this affects the reading of the CO2 and O2 sensors and is preferably corrected for, and it also detects occlusion of the sampling line), contains a barometric pressure sensor for altitude corrections for the sensors. Additionally, knowing the altitude enables “tuning” the concentrator to work at different working pressures based on the altitude (i.e. the set of working pressures that optimizes the concentrator at sea level may not be the same set that optimizes at 8,000 ft.). This board also measures temperature in the housing as well. 
     Patient Monitors—CO 2  and O 2  as above (continuous waveform, calculates inspired and end-tidal from waveform), O 2  saturation and plethysmography (from pulse ox), heart rate (from either pulse ox or ECG or blood pressure cuff), non-invasive blood pressure (NIBP, both acoustic noise cancelling and oscillometric), ECG 3 lead, temperature, airway pressure (see above). 
     Some of the alarm conditions include: 
     Patient parameter out of present range, (eg. O2, CO2, SpO2, HR, BP, T, Airway pressure), system error (occlusion, leak, O2 low, CO2 high, battery low, valve failure, pump failure, ventilator failure and patient monitor failure). 
     The device  1102  may further have sufficient controls to operate in selected failsafe modes. For example, the device  1102  may be configured to operate if there is an O2 failure, in a ‘limpalong’ mode whereby the concentrator is not capable of producing O2 at 85% concentration. It may also ventilate using ambient air. In the event of a ventilator failure, an Ambu bag may be interposed in the breathing circuit for manual ventilation, using the oxygen concentrator and/or mixing pump as its supply. 
     The device  1102  includes optional alarm lights  1150  which may be visible along nearly 180 degrees of viewing angle. The lights may be red to indicate an urgent problem, yellow to indicate a problem that does not require urgent attention, green to indicate that everything is operating within selected ranges and infra-red when operating in stealth mode. 
     The device  1102  may be mounted along the edge of a stretcher or other patient transport device using the positioning system facing either direction, so that preferably the patient connections and tubes are closest to the head. The screen may be rotated and its contents flipped to make reading easier. 
     While the above description constitutes the preferred embodiments, it will be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning of the accompanying claims.