Abstract:
A high-efficiency liquid oxygen, (LOX) storage/delivery system utilizes a portable LOX/delivery apparatus with a portable LOX container. A portable-unit LOX transfer connector is connected to the portable LOX container and is connectable to a main source of LOX in a primary reservoir LOX container. A portable-unit oxygen gas transfer connector is provided for transferring oxygen gas from the portable LOX container to an oxygen gas delivery device for delivering oxygen gas to a patient. An inter-unit oxygen gas transfer connector also is provided for connecting the portable apparatus to a stationary source of oxygen gas in the primary reservoir container, for transferring oxygen gas to the portable apparatus. A portable-unit primary relief valve is connected to the portable LOX container for venting oxygen gas out of the portable LOX container when pressure in the portable LOX container reaches a predetermined level. When the inter-unit oxygen gas transfer connector of the portable container is connected to the stationary source of oxygen in the primary reservoir container, oxygen gas can be transferred to the oxygen gas delivery device for delivery to the patient from the portable LOX container while oxygen gas is transferred to the portable container from the stationary source of gas in the primary reservoir LOX container.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from U.S. provisional patent application Ser. No. 60/162,131, filed Oct. 29, 1999. The disclosure of the above-referenced provisional patent application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a liquid oxygen storage and delivery system. 
     2. Description of the Background Art 
     Therapeutic oxygen is the delivery of relatively pure oxygen to a patient in order to ease pulmonary/respiratory problems. When a patient suffers from breathing problems, inhalation of oxygen may ensure that the patient is getting an adequate level of oxygen into his or her bloodstream. 
     Therapeutic oxygen may be warranted in cases where a patient suffers from a loss of lung capacity for some reason. Some medical conditions that may make oxygen necessary are chronic obstructive pulmonary disease (COPD) including asthma, emphysema, etc., as well as cystic fibrosis, lung cancer, lung injuries, and cardiovascular diseases, for example. 
     Related art practice has been to provide portable oxygen in two ways. In a first approach, compressed oxygen gas is provided in a pressure bottle, and the gas is output through a pressure regulator through a hose to the nostrils of the patient. The bottle is often wheeled so that the patient may be mobile. This is a fairly simple and portable arrangement. 
     The drawback of compressed, gaseous oxygen is that a full charge of a bottle that is portable does not last a desirable amount of time. 
     In order to get around this limitation, in a second approach a related art liquid oxygen (LOX) apparatus has been used wherein LOX is stored in a container and the gaseous oxygen formed from the LOX is inhaled by the patient. 
     The related art LOX apparatus enjoys a longer usable charge than the compressed gas apparatus for any given size and weight, but has its own drawbacks. 
     Related art LOX systems typically include a stationary storage container located in a patient&#39;s home and a portable unit that the patient uses outside the home. The stationary storage container must be periodically refilled with LOX by a distributor. 
     A significant percentage of the cost of having a LOX system is in the cost of frequent recharging trips by the LOX distributor. A distributor may have to make weekly recharge trips to a patient&#39;s home, or even more frequently, to recharge the patient&#39;s LOX system. There thus is a need in the art to cut deliveries or cut costs in other ways. 
     The main drawback of the related art is that considerable waste occurs. One source of waste is that prior art devices provide continuous flow. Also, in the related art, the portable unit may be filled with LOX and used for normal activities and movement. When the patient is done using the related art portable unit, remaining LOX left within the related art portable unit is vented, wasting any remaining oxygen. Because the LOX continues to convert to gaseous oxygen when not being withdrawn, venting is provided for in both the stationary and portable related art units. When the pressure in the related art stationary unit increases beyond a certain point (such as when the related art portable unit is being used), the related art stationary unit must be vented. 
     There remains a need in the art, therefore, for an improved LOX storage and delivery system, with less gas consumption and requiring fewer deliveries of LOX to the patients home. 
     SUMMARY OF THE INVENTION 
     A high-efficiency liquid oxygen (LOX) storage/delivery system is provided according to a first aspect of the invention. The high-efficiency liquid oxygen (LOX) storage/delivery system may include a primary reservoir LOX storage/delivery apparatus comprising a primary reservoir LOX container and a portable LOX/delivery apparatus including a portable LOX container. The primary reservoir LOX apparatus includes a main LOX transfer connector connected to the primary reservoir LOX container for inputting LOX into the primary reservoir LOX container and for outputting LOX from the primary reservoir LOX container to the portable LOX container, and a main-unit oxygen gas transfer connector for transferring oxygen gas from the primary reservoir LOX container. A primary reservoir indicator device may be connected to the primary reservoir LOX container for indicating the LOX contents of the primary reservoir LOX container. A main-unit primary relief valve is connected to the primary reservoir LOX container for venting oxygen gas out of the primary reservoir LOX container when pressure of oxygen gas in the primary reservoir LOX container reaches a predetermined level for the primary reservoir container. The portable LOX apparatus includes a portable-unit LOX transfer connector connected to the portable LOX container and connectable to the main LOX transfer connector for transferring LOX to the portable container from the primary reservoir container, a portable-unit oxygen gas transfer connector for transferring oxygen gas from the portable LOX container to an oxygen gas delivery device for delivering oxygen gas to a patient, an inter-unit oxygen gas transfer connector for connecting the portable apparatus to the main-unit oxygen gas transfer connector for transferring oxygen gas from the primary reservoir container to the portable apparatus, and a portable-unit primary relief valve connected to the portable LOX container for venting oxygen gas out of the portable LOX container when pressure in the portable LOX container reaches a predetermined level for the portable container. When the inter-unit oxygen gas transfer connector of the portable container is connected to the main-unit oxygen transfer connector of the primary reservoir container, oxygen gas can be transferred from the portable container to the oxygen gas delivery device while oxygen gas is transferred to the portable container from the primary reservoir LOX container. 
     A method for utilizing a high-efficiency liquid oxygen (LOX) storage/delivery system is provided according to a second aspect of the invention. One method comprises connecting the inter-unit oxygen gas transfer connector of a portable container to the main-unit oxygen transfer connector of a primary reservoir container, and withdrawing oxygen gas from the portable container through the portable-unit oxygen gas transfer connector while oxygen gas is transferred to the portable apparatus and to the patient from the primary reservoir container through the main-unit oxygen transfer connector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows one embodiment of a high efficiency LOX system of the present invention, and illustrates how the primary reservoir and portable LOX storage/deliver apparatus may be interconnected; 
     FIG. 2 schematically shows detail of one embodiment of the primary reservoir LOX storage/delivery apparatus; 
     FIG. 3 schematically shows detail of one embodiment of the portable LOX storage/delivery apparatus; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows one embodiment of a high efficiency LOX system  100  of the present invention. The LOX system  100  includes a primary reservoir LOX storage/delivery apparatus (primary reservoir apparatus)  120  and a portable LOX storage/delivery apparatus (portable apparatus)  160 . An umbilical conduit  110  may extend between an inter-unit oxygen gas transfer connector  190  of the portable apparatus  160  and a main-unit oxygen gas transfer connector  213  of the primary reservoir apparatus  120 , and may be used to transfer gaseous oxygen therebetween. An oxygen delivery device  90 , such as a mask or nasal tubes or cannulas may be attached to either apparatus in order to deliver gaseous oxygen to a patient. Alternatively, the inter-unit oxygen gas transfer connector  190  may be directly connected to the main-unit oxygen gas transfer connector  213 . 
     Because LOX transforms from a liquid to a gas as heat is added, related art LOX systems have typically relied on venting of excess gaseous pressure to maintain acceptable internal pressure levels. The result is a higher cost for the health care provider. Pressure control of the portable apparatus  160  and the primary reservoir apparatus  120  is of great importance, as keeping pressures down yields a safe, light weight, economical system through the reduction or elimination of venting. The present invention achieves such economy by balancing use of the primary reservoir apparatus  120  and portable apparatus  160  so that internal pressures do not build up to a point where either apparatus must be excessively vented. The LOX system  100  therefore allows usage cycles that make possible efficient LOX use without excessive venting. 
     The primary reservoir apparatus  120  can be of any usable size for storage and delivery of LOX over a desired time period. Suitable units in accordance with the present invention can hold from 20-60 or more liters of LOX. In accordance with one embodiment, a primary reservoir container holding about 36 liters (about 85 pounds) of LOX is provided. In a second embodiment, a primary reservoir container holding about 43 liters (about 110 pounds) of LOX is provided. 
     The primary reservoir apparatus  120  includes the main LOX storage and container. The LOX may be transferred from the primary reservoir apparatus  120  to the portable apparatus  160  as needed to charge the portable apparatus  160  for mobile use. The primary reservoir apparatus  120  is intended to hold a sufficiently large charge so that the primary reservoir apparatus  120  can recharge the portable apparatus  160  on a substantially daily basis for a substantially long period of time, e.g., up to about one month or more. This can reduce recharge costs by up to seventy-five percent or more over the related art. 
     The portable apparatus  160  preferably is about 3.5 pounds fully charged with LOX and about 2.5 pounds empty, is much smaller and lighter than the primary reservoir apparatus  120 , and may provide gaseous oxygen to the patient while being carried by the patient. 
     In use, the primary reservoir apparatus  120  is charged with LOX. The patient may use gaseous oxygen from the primary reservoir apparatus  120  directly via the main-unit oxygen gas transfer connector  213 , or may transfer LOX to the portable apparatus  160  wherein the patient may withdraw gaseous oxygen from the portable apparatus  160 . The portable apparatus  160  allows the patient mobility outside the home, while the umbilical conduit  110 , which may be up to 50-100 feet in length or longer, allows the patient to connect the portable apparatus to the main reservoir container to conserve LOX. 
     The inter-unit oxygen gas transfer connector  190  may be connected to the main-unit oxygen gas transfer connector  213  of the primary reservoir apparatus  120  to allow oxygen gas withdrawal alternatively from either the portable apparatus  160  or the primary reservoir apparatus  120 , or simultaneously from both. 
     FIG. 2 shows detail of one embodiment of the primary reservoir apparatus  120 . The primary reservoir apparatus  120  includes a primary reservoir container assembly  205 , a main LOX transfer connector  209 , a main-unit oxygen gas transfer connector  213 , and a main-unit primary relief valve  257 . In the embodiment shown, a primary indicator device  274  also is included. 
     The primary reservoir container assembly  205  includes an outer container  223 , an inner primary reservoir LOX container  226  spaced apart from the outer container  223 , insulation  229  located between the outer container  223  and the inner container  226 , a molecular sieve  231 , and a vacuum plug  235 . The space between the outer container  223  and the inner container  226  is preferably evacuated to at least a partial vacuum in order to minimize heat transfer to the LOX inside the inner container  226 . 
     The primary reservoir LOX container assembly  205  also includes an outlet port  238 , through which passes a neck conduit  242 . The neck conduit  242  extends a short distance into the inner container  226 , and is employed for gaseous oxygen withdrawal from the primary reservoir LOX container  226 . Inside the neck conduit  242  is a fill conduit  244 , preferably concentric with the neck conduit  242 . The fill conduit  244  may be used to fill the primary reservoir LOX container  226  with LOX. Inside the fill conduit  244  is a liquid withdrawal conduit  247 , preferably concentric with the fill conduit  244 . The liquid withdrawal conduit  247  may be used to withdraw LOX from the primary reservoir LOX container  226 . 
     Above the outlet port  238  of the primary reservoir LOX container  205  the neck conduit  242  splits into two independent conduits. A main-unit vent valve conduit  250  leads to a main-unit vent valve  251  which is openable for filling inner container  226  with LOX through the main LOX transfer connector  209 . When filling inner container  226  with LOX, main unit vent valve  251  is opened until liquid exits valve  251 , indicating that container  226  is filled with LOX. 
     Relief/economizer conduit  255  leads to a main-unit primary relief valve  257  and an economizer valve  261 . The main-unit primary relief valve  257  is provided for relieving excess internal gas pressure from the primary reservoir LOX container  226  if the internal gas pressure exceeds a predetermined limit, e.g., 55 psi. Conduit  255  also leads to a main-unit secondary relief valve  258 , which can be set at the same or a higher level (e.g., 10-20% higher) than the main-unit primary relief valve, and is a back-up thereto in case of failure thereof. 
     Conduit  255  further leads to an economizer valve  261 , the purpose of which will be explained below. 
     Above the neck conduit  242  extends the fill conduit  244 , which extends upward to the main-unit LOX transfer connector  209 . Between the top of the neck conduit  242  and the main-unit LOX transfer connector  209  is a tee  263 , where the liquid withdrawal conduit  247  exits the fill conduit  244 . After exiting the fill conduit  244 , the liquid withdrawal conduit  247  encounters a second tee  264  that joins the liquid withdrawal conduit  247  with an economizer conduit  266  in advance of a warming coil  269 . The economizer conduit  266  connects the economizer valve  261  with warming coil  269 . Gaseous oxygen passes through economizer valve  261  when the economizer valve is open. In order to conserve LOX, the economizer valve  261  can be set at any suitable level below the primary and secondary relief valve settings, so that gaseous oxygen will pass through the economizer valve  261  into the warming coil  269  before such gaseous oxygen is vented through the main-unit primary relief valve  257  or the main-unit secondary relief valve  258 . One suitable setting for the economizer valve  261  is 22 psi. The liquid withdrawal conduit  247  supplies LOX to the warming coil  269 , while the economizer conduit  266  supplies gaseous oxygen withdrawn by way of the relief/economizer conduit  255 . In the warming coil  269  the withdrawn LOX and gaseous oxygen is warmed by exposure to room temperature, speeding the liquid-to-gas transformation. It should be noted that the inside diameter of the warming coil  269  may be greater than the inside diameter of the liquid withdrawal conduit  247 , allowing the LOX to expand as it warms up and transforms from a liquid phase to a gaseous phase. However, the inside diameter of the liquid withdrawal conduit  247  preferably is sized so that when the economizer valve  261  is open, gas flow through line  266  is favored to warming coil  269  over liquid withdrawal through conduit  247 . In the embodiment shown, the warming coil  269  is connected to a pressure regulator  271  which can maintain a desired operating pressure at a main-unit oxygen gas transfer connector  213 . 
     In the embodiment shown, the primary reservoir LOX container  205  includes a primary indicator device  274  that indicates a LOX level in the primary reservoir LOX container  226 . The primary indicator device  274  is connected to a bottom portion of the primary reservoir LOX container  226  via a high pressure sensing conduit  279 . The primary indicator device  274  may be interconnected to a pressure gauge  217 . The pressure gauge  217  gives a visual readout of an internal gas pressure for the primary reservoir LOX container  226 , and may be, for example, a mechanical pressure gauge. The pressure gauge  217  is connected to conduit  255  via a low pressure sensing conduit  277 . 
     In use, LOX may be added to or withdrawn from the primary reservoir LOX container  226  through the main-unit LOX transfer connector  209  and the fill conduit  244 . The main-unit oxygen gas transfer connector  213  may be used to withdraw gaseous oxygen for use. The gaseous oxygen is provided to the main-unit oxygen gas transfer connector  213  from the economizer valve  261  and/or by conversion of LOX to gas through the liquid withdrawal conduit  247 , both through the warming coil  269 . 
     FIG. 3 shows detail of one embodiment of the portable apparatus  160 . The portable apparatus  160  includes a portable LOX container  302 , a portable-unit LOX transfer connector  304 , a portable-unit oxygen gas transfer connector  384 , an inter-unit oxygen gas transfer connector  190 , and a portable-unit primary relief valve  315 . 
     The portable container assembly  302  includes an outer container  318 , an inner portable LOX container  319  spaced apart from the outer container  318 , a fill conduit  322 , a liquid withdrawal conduit  326 , a vacuum plug  328 , and a multi-lumen annular conduit  331 . The space between the outer container  318  and the inner container  319  is preferably evacuated to at least a partial vacuum in order to minimize heat transfer to the LOX inside the inner container  319 . 
     LOX may be introduced into the portable LOX container  319  through the portable-unit LOX transfer connector  304  and the fill conduit  322 . The portable-unit LOX transfer connector  304  may be connected to the main-unit LOX transfer connector  209  of the primary reservoir apparatus  120 , whereby the portable apparatus  160  may be filled with LOX from the primary reservoir apparatus  120 . 
     LOX may be withdrawn via the liquid withdrawal conduit  326 , and gaseous oxygen may be withdrawn via the neck conduit  331 . 
     A manifold  336  is connected to the neck conduit  331 , and splits the neck conduit  331  into a gaseous oxygen withdrawal conduit  339  and a vent conduit  341 . The vent conduit  341  may include a vent valve  344 . The vent valve  344  may be opened during filling of the portable LOX container  302 . When LOX emerges from the vent conduit  341 , it is a visual indication that the portable LOX container  319  is full. 
     In the embodiment shown, the liquid withdrawal conduit  326  passes through the manifold  336  and is connected to a liquid withdrawal warming coil  349  in which the LOX can transform to the gaseous phase. The liquid withdrawal warming coil  349  warms the LOX by exposure to room temperature, speeding the liquid-to-gas transformation. It should be noted that the inside diameter of the liquid withdrawal warming coil  349  may be greater than the inside diameter of the liquid withdrawal conduit  326 , allowing the LOX to expand as it warms up and transforms from a liquid phase to a gaseous phase. 
     The gaseous oxygen withdrawal conduit  339  connects with a gas withdrawal warming coil  352 . The gas withdrawal warming coil  352  warms the gaseous oxygen before delivery to an oxygen user. 
     Connected to the gas withdrawal warming coil  352  is a portable-unit primary relief valve  315 . The portable-unit primary relief valve  315  is capable of opening and relieving a gaseous oxygen pressure in the portable LOX container  319  if the internal gas pressure exceeds a predetermined level, e.g., 27 psi. 
     An economizer valve  356  connects the gas withdrawal warming coil  352  with conduit  380  containing gaseous oxygen from liquid withdrawal warming coil  349 . The portable-unit economizer valve  356  can be set at any suitable level below the portable-unit primary relief valve  315 , such as 22 psi, and allows gaseous oxygen from coil  352  to pass into line  380  when the pressure of the gaseous oxygen in the portable LOX container  319  exceeds the predetermined threshold level, e.g., 22 psi. In preferred embodiments, the inside diameter of the liquid withdrawal conduit  326  is sized so that when the portable-unit economizer valve  356  is open, gas flow through line  339  is favored over liquid flow through conduit  326 . This permits gaseous oxygen from the gaseous head-space in portable container  319  to pass to the patient without the need to waste through the portable-unit primary relief valve  315 . The portable-unit economizer valve  356  thus balances gaseous and liquid oxygen withdrawal from the portable LOX container  319 , and outputs a resulting gaseous oxygen to a conduit  309 . A portable-unit secondary relief valve  382  is provided as a back-up unit to the portable-unit primary relief valve  315 , and can be set at the same or a higher level than the portable-unit primary relief valve, and is a back-up thereto in case of failure thereof. 
     Although the function of the economizer valves of the present invention has been described above with reference to preferred embodiments, other configurations, utilizing operating systems of any suitable pressure, will fall within the scope of the present invention. For example, with systems operating at 20 psig, an economizer valve may be set at any suitable setting such as between 19.5 psig and 22 psig. Alternatively, for systems having operating pressures at about 50 psig, economizer valves having settings, for example, between 48 psig and 55 psig can be utilized. Corresponding primary relief setting for a 20 psig system can, for example, be between 21 psig and 24 psig. Corresponding primary relief settings for a 50 psig system can, for example, be between about 50 psig and 58 psig. However, these configurations are merely exemplary, and other configurations can be utilized in accordance with the present invention. 
     The gaseous oxygen from the conduit  309  may be delivered to a demand flow control device  360 , which also may receive gaseous oxygen from the primary reservoir apparatus  120  via the inter-unit oxygen gas transfer connector  190 . A check valve  363  may be included between the conduit  309  and the inter-unit oxygen gas transfer connector  190  to prevent backflow of gaseous oxygen from the portable apparatus  160  to the primary reservoir apparatus  120 . 
     The demand flow control device  360  is for adjustment of gas flow through a portable-unit oxygen gas transfer connector  384   a  to an oxygen delivery device  90  for delivery of gaseous oxygen to a patient. 
     Gaseous oxygen is provided to the patient through the portable-unit oxygen gas transfer connector  384   a , either from the portable unit, or from the main reservoir unit through connector  190 . 
     In preferred embodiments, the demand flow control device  360  can be connected to a gas conserving device  390 . A known conserving device is disclosed in U.S. Pat. No. 5,360,000. 
     In the embodiment shown, a gas transfer connector system  384   a  and  384   b  is utilized, so that when the patient exhales, flow to the oxygen delivery device  90  is stopped, and gas accumulates in the conserving device  390 . When the patient inhales, a puff (bolus) of oxygen gas is delivered to the patient from conserving device  390 , thereby further preventing waste of gaseous oxygen, followed by an even flow of gaseous oxygen, which then is stopped again when the patient exhales. 
     Use of a conserving device  390  with the portable apparatus of the present invention connected to the primary reservoir apparatus  120  through connector  190  results in tremendous savings and LOX conservation. 
     A method of utilizing the high-efficiency LOX storage/delivery system  100  of the present invention is disclosed. The method uses an umbilical conduit  110  to economize oxygen use by a patient and balance use of the primary reservoir apparatus  120  and portable apparatus  160  so that excess oxygen venting is avoided. 
     The main-unit oxygen gas transfer connector  213  is connected to the inter-unit oxygen gas transfer connector  190 , e.g., by umbilical conduit  110 . The connection allows gaseous oxygen to flow from the primary reservoir apparatus  120  to the portable apparatus  160 . The gaseous oxygen from either the primary reservoir LOX storage delivery apparatus  120  or the portable apparatus  160  may be provided to the patient, depending on which has the higher gas pressure. 
     The umbilical conduit  110  may be a flexible conduit (such as a hose, for example) to give the portable apparatus  160  mobility while yet being connected to the primary reservoir apparatus  120 . In this hookup, the oxygen deliver device  90  is connected to the demand flow control device  360  in order to provide gaseous oxygen to the patient. 
     The method may utilize a filling/using cycle of the portable apparatus  160 . The method of filling/using of the present invention avoids or reduces unnecessary venting of either the portable apparatus  160  or the primary reservoir apparatus  120 . 
     Gaseous oxygen is withdrawn from the primary reservoir  120  for a withdrawal time period, which preferably is at least 5 hours per day, more preferably about 10 hours per day or more. The withdrawal of gaseous oxygen from the primary reservoir apparatus  120  may be through oxygen delivery device  90  either connected directly to-connector  213 , or connected to connector  384  of the portable apparatus with connector  190  of the portable apparatus connected to the main reservoir apparatus. This gaseous withdrawal time period hook-up to the primary reservoir apparatus  120  permits withdrawal of gaseous oxygen from the primary reservoir LOX container without internal pressure in the primary reservoir LOX container reaching excess levels requiring venting. This conserving measure, in conjunction with economizer valve  261  (and economizer valve  356  if the portable unit is hooked-up), enables oxygen withdrawal without wasteful venting. 
     After the above-discussed withdrawal time period, the portable apparatus  160  may be filled with LOX from the primary reservoir apparatus  120  and disconnected, for example, if the patient wishes to go outside the home. 
     In preferred embodiments, the portable LOX container holds about 1 pound of LOX, which, when utilized with the portable LOX/delivery apparatus of the present invention, can last approximately 10 hours at a typical patient use/withdrawal rate of about 2 liters per minute. 
     During withdrawal of gaseous oxygen from the primary reservoir LOX apparatus, oxygen gas pressure in the primary reservoir LOX apparatus is reduced to a level at which the economizer valve is set (e.g., 22 psi) such that after the portable container is filled with LOX and disconnected from the primary reservoir LOX apparatus, pressure may increase within the primary reservoir container for a gas pressurizing period within a range of 5-15 hours per day, e.g., about 10 hours per day, to a pressure of, for example, about 50 psi without LOX or oxygen gas being withdrawn from the primary reservoir container and without oxygen gas being vented from the primary reservoir container during the gas pressurizing period. 
     When the patient returns home prior to complete withdrawal of oxygen gas from the portable LOX container, the inter-unit oxygen gas transfer connector of the portable LOX container is connected to the main-unit oxygen transfer connector of the primary reservoir LOX container, and oxygen gas, may be withdrawn from the portable LOX container or the primary reservoir LOX container while oxygen gas may be transferred to the portable LOX apparatus from the primary reservoir LOX container through the main-unit oxygen transfer connector, depending on the pressure differential between the containers. 
     In accordance with one embodiment, during the withdrawal period, the inter-unit oxygen gas transfer connector of the portable LOX container is connected to the main-unit oxygen transfer connector of the primary reservoir LOX container, and oxygen gas is transferred from the portable container to the oxygen gas delivery device alternately or concurrently with oxygen gas being transferred to the oxygen gas delivery device through, the portable LOX apparatus from the primary reservoir LOX container, thereby lowering gas pressure in the primary reservoir LOX container. 
     The present invention can provide significant savings as compared to. related art systems. For example, at a patient use rate of 2 liters per minute, related art systems utilize about 10 pounds LOX per day. The present invention can provide the same 2 liters per minute utilizing about 2 pounds LOX per day, a savings of up to about 8 pounds LOX per day. 
     While the invention has been described in detail above, and shown in the drawings, the invention is not intended to be limited to the specific embodiments as described and shown.