Abstract:
A method of providing a source of breathable humidified oxygen gas. A membrane oxygen humidifier is provided that includes at least one water permeable membrane and an enclosure. The at least one water permeable membrane has a first membrane side and a second membrane side that are in communication through the water permeable membrane. The enclosure extends over the second membrane side and wherein the enclosure has an air inlet port and an air outlet port. A first gas containing oxygen is directed past the first membrane side. The second gas is directed past the second membrane side with a fan. The first gas is humidified by transferring moisture through the at least one water permeable membrane from the second gas to the first gas.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 12/402,288, filed Mar. 11, 2009, and claims priority to U.S. Provisional Applic. No. 61/082,247, filed Jul. 21, 2008, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to methods for providing oxygen to persons. More particularly, the invention relates to a method of providing breathable humidified oxygen gas to a patient. 
     BACKGROUND OF THE INVENTION 
     The method to produce oxygen from oxygen concentrators using pressure swing adsorption is widely known in the art, see Spearman et al., U.S. Pat. No. 7,331,342 and McCombs et al., U.S. Pat. No. 6,558,451. Oxygen concentrators produce a high level of oxygen of approximately 95% at flow rates approximately 1-10 lpm. There are approximately 2 million oxygen concentrators in use in America. 
     Oxygen concentrators despite being able to deliver high levels of oxygen, since they rely on PSA (pressure swing adsorption), dry the oxygen to extremely dry levels. In fact, the oxygen can be so dry to a patient that the patient can suffer bloody noses and dry lungs due to the rapid evaporation of fluid from tissue cells within the nasal passage way and lungs. To combat the problem of dry gas being delivered to the patient, health care providers will do one of two things to deliver humidified gases to their patients, each of which has shortcomings. 
     One technique to humidify the oxygen is to connect the patient oxygen port outside of the concentrator to a water bubbler through which the oxygen bubbles and adsorbs water that is subsequently delivered to the patient at relatively high levels of humidity, approximately 50%-90%. This high level of humidity is beneficial to the patient and provides comfort to the patient. Bacteria however, can grow within the humidifier itself, thereby jeopardizing the patient&#39;s safety. Additionally, the bubblers on a humidifier are recommended to be changed quite frequently by the health care provider. These bubblers are not reimbursed and are paid for out of the health care provider&#39;s pocket. This can be quite costly for a healthcare provider. 
     Another technique to provide humidification is through membrane gas humidifiers. Porous Media&#39;s HUMIDIFLOW membrane gas humidifier, which was the subject of U.S. Pat. No. 7,331,342, provides humidification to the patient without using water bubblers, but rather using a hollow fiber membrane having a high selectivity of water over nitrogen and oxygen. This device is installed on the upstream side of the air compressor in the oxygen concentrator and plumbed to flow atmospheric air from the air compressor across one side of the membranes and oxygen from the downstream side of the molecular sieve beds across the other side to induce a gradient such that the water vapor in the atmosphere on the one side of the fibers transfers to the dry oxygen on the other side of said hollow fiber membrane to a level of humidity that is close to that of the room air. 
     Porous Media teaches installing the HUMIDIFLOW membrane gas humidifier inside the oxygen concentrator: “In one embodiment of the present invention, the membrane device is installed in the oxygen concentrator such that the membrane device engages a stream of ambient air prior to the compression of the ambient air by a compressor while an oxygen-enriched gas engages the membrane device after the oxygen-enriched gas has engaged a regulator and needle valve.” 
     “In an alternative embodiment of the present invention, the membrane device is installed in an oxygen concentrator such that the membrane device engages the stream of ambient air after compression of the ambient air by the compressor while the oxygen-enriched gas engages the membrane device prior to the engagement of the oxygen-enriched gas with the gas regulator” and “More specifically, since membrane devices used in oxygen concentrators are usually installed downstream of the compressor”, and “A second embodiment of the present invention involves installing the membrane device in an oxygen concentrator . . . ” from page 3 of the provisional patent. 
     There are many problems with the prior art inventions created by having to install the device in the inside of an oxygen concentrator. As illustrated from an instructional installation DVD for the HUMIDIFLOW membrane gas humidifier, which was purchased from a publicly available distributor of Porous Media listed on the HUMIDIFLOW website (The Aftermarket Group, OH) the following problems can be observed pertaining to the installation of the HUMIDIFLOW membrane gas humidifier. First is that the health care provider is required to remove the oxygen concentrator cabinet that is generally secured by screws to a frame on the oxygen concentrator. 
     Then the health care provider is required to re-plumb the original manufacturer&#39;s equipment so that the oxygen tubing is re-routed from the flow meter to the membrane and from the membrane back to the patient. Next, the health care provider must ensure that the membrane is secured to the inside of the concentrator using nylon zip ties that may come loose during transportation or if not installed properly, causing potential rattling of the membrane against other components inside of the concentrator. 
     In one case, the health care provider is instructed to install a custom compressor inlet filter to the inlet of the HUMIDIFLOW membrane gas humidifier. The intake filter of the HUMIDIFLOW membrane gas humidifier kits may become detached from the module and fall onto the compressor cooling fan during patient treatment. If the filter were to come in contact with the fan blades this could stop the fan from operating and cause the concentrator to overheat and interrupt the flow of oxygen to the patient. 
     Further, there are dozens of oxygen concentrator brands and part numbers on the market, each oxygen concentrator brand requiring a HUMIDIFLOW membrane gas humidifier with different tubing lengths and various connectors. One HUMIDIFLOW membrane gas humidifier requires a special mounting bracket that one has to mount to the top of the air compressor to secure the HUMIDIFLOW membrane gas humidifier in place. This process requires removing a portion of the air compressor OEM&#39;s air compressor components to retrofit a particular oxygen concentrator for the HUMIDIFLOW membrane gas humidifier. As one can see, the installation of the HUMIDIFLOW membrane gas humidifier is less than ideal from an operations stand point or ease of use from the patient&#39;s perspective. 
     It is common for an oxygen concentrator dealer to carry multiple brands of oxygen concentrators and if this is the case, the dealer must inventory as many part numbers of HUMIDIFLOW membrane gas humidifiers as there are concentrators. It is conceivable that the healthcare provider would have to inventory up to 15 or more different HUMIDIFLOW membrane gas humidifier part numbers. 
     Every oxygen concentrator on the market requires that the health care provider measure and verify the oxygen concentration performance of the concentrator. This process is generally done with an oxygen sensor and can be easily measured by holding the sensor up to the oxygen flow meter. However, the oxygen sensors will only give an accurate reading of the concentrator&#39;s oxygen level output in the presence of dry gas. 
     Since the prior art must be installed to verify that it is not effecting the oxygen levels, one must now take another step to dry the gas that has been humidified by the membrane. The way this process is accomplished is by purchasing another in line air dryer comprised generally of PVC tubing and a desiccant. The operator must install the in line dryer at the concentrator&#39;s outlet, dry the oxygen using the desiccant dryer and then measure the oxygen concentration of the concentrator. This desiccant dryer can have a very short life and must be either re-charged by putting in an oven, or the operator must purchase another in line dryer. 
     While membrane devices such as the Teijin and HUMIDIFLOW membrane gas humidifier address a need in the marketplace to provide comfortable levels of humidity without requiring liquid water when the ambient humidity is at levels of 25-30% RH, there exists an inherent problem with prior art membranes in their ability to control humidity to the patient in dry weather. As explained in the Teijin patent, the “make up” air is the ambient air that is drawn through the air compressor. 
     The oxygen is plumbed to the Teijin membrane humidifier and picks up the moisture from the “make up” air side of the membrane via diffusion across the membrane. If the room air is 15% RH, for example in the case of many Southwestern states in the winter months, supplemental humidification may be needed. To provide higher levels of humidity to the patient when the room RH is low, the humidifier may need to be installed near the oxygen concentrator. 
     To increase the humidity to the patient in dry weather, one must increase the humidity in the room at the inlet of the air compressor or “make up air” as Teijin refers to this process, using water droplets and water vapor from a room air humidifier. Most compressors installed in oxygen concentrators operate at approximately 100 lpm. Most oxygen concentrators such as Teijin&#39;s have an oxygen flow rate of approximately 5 lpm. 
     Both of the Teijin and Porous Media membrane humidifiers require the plumbing of the oxygen line to a port of the membrane. Both Teijin and the HUMIDIFLOW offer the use of a fan inside the oxygen concentrator to direct the airflow across the membrane. 
     Another membrane humidifier very similar to the Porous Media HUMIDIFLOW is mentioned in the Teijin patent. The oxygen flows on the opposite side of the fibers containing the makeup air. When a supplemental room air humidifier is installed near the inlet of one of these common membrane humidifiers, the small flow of oxygen relative to the makeup air becomes saturated with water and is delivered to the patient. This is good for the patient because much of the oxygen will now be saturated. However, In the case of a conventional membrane such as the above mentioned membranes, much of the compressed air will also be saturated, but now entering the molecular sieve beds due to the fact that only a relatively small amount of water will be removed from the makeup air and put into the oxygen stream. This deficiency in these conventional membranes will lead to reduced sieve life. 
     While the above mentioned membranes are generally effective at increasing the humidity in dry weather to more comfortable levels of approximately 30% RH using a room air humidifier, for the prior art membranes to provide much more humidity than this is extremely difficult without encountering major problems for the oxygen concentrator as well as the patient&#39;s home. 
     In the average US household, each furnace is equipped with a blower ranging from several hundred SCFM to several thousand SCFM. This means that the air exchange in a standard 10 foot×10 foot room can be 50-200 SCFM. To compound the problem, the atmospheric air drawn by the compressor is rushing through the Teijin and HUMIDIFLOW membranes at a rate of approximately 100 lpm from the air compressor compared to the relatively small flow of 5-10 lpm for the dry oxygen plumbed on the opposite side of the fibers. 
     The average room air supplemental humidifier patients purchase at pharmacies and drug stores only put out several liters per minute to several SCFM of saturated humidity, which is obviously not enough to keep up with the air compressor inlet flow rate and the air exchange of the room. 
     This means in order to humidify a 10 foot×10 foot room to levels of high humidity over about 50%, preferably &gt;60-80% one would literally have to line the floors of this room with humidifiers which in turn would coat every square inch of surface area of the room, including the flooring, walls, windows, books, electrical fixtures, etc. with water droplets, ultimately resulting in the growth of mold and spores. 
     As indicated before, the effects of this amount of water on the oxygen concentrator would be overwhelming to the sieve beds and would cause a substantial reduction in sieve life, not to mention rusting the metal and electrical components within the concentrator. 
     The Teijin oxygen concentrator which is subject of U.S. Pat. No. 6,669,956 utilizes a similar operational principal of the Porous Media oxygen concentrator, however it features a NAFION cationic conductive membrane that is coupled to a cathode and an anode. When an electric current is applied to the conductive membrane, it produces a higher level of humidity on the patient outlet end than the atmospheric air or “make up” air as Teijin describes it. This membrane however loses its charge over time and becomes a “passive” membrane just like the Porous Media HUMIDIFLOW membrane gas humidifier. 
     Teijin describes another Japanese membrane that basically accomplishes a similar “passive” humidification means as the membrane gas humidifier in JP Patent No. 2-99113. The indicated benefit of the Teijin design is that for a period of time (albeit very brief), they are able to control the level of humidity to the patient through the use of applying a higher or lower amount of current to their conductive membrane, depending upon the amount of humidity desired at the patient end. 
     The Burioka oxygen concentrator connects a polyimide hollow fiber (from UBE Industries, Ltd, Japan) membrane shell consisting of 4 connection ports to an air compressor and an oxygen source as described in an article entitled “ Efficacy of a Newly Developed Pressure Swing Adsorption Type Oxygen Concentrator with Membrane Humidifier: Comparison with Conventional Oxygen Concentrator with Bubble Water Humidifier.”   
     The air compressor takes compressed air and compresses the atmospheric air to between about 14 psig and 28 psig. The paper shows a chart illustrating that at approximately 20% RH room air humidity. Burioka was able to achieve 50-60% RH in the patient gas and approximately 80% RH in the patient gas when the room was 30% RH. 
     However, the Burioka prototype suffers from several design deficiencies. First is that the membrane must be installed downstream of an air compressor, which is inside the oxygen concentrator. This configuration would be extremely difficult for aftermarket installations. 
     Since some oxygen concentrator air compressors can operate at relatively high temperatures inside the cabinet (nearly 230° F. in some cases) and the compressors can put out an extremely high amount of contamination, this configuration would expose the membrane to conditions of operation that could cause fatigue and contamination of the membranes. 
     Further, the Burioka design of humidification system provides the patient and the health care provider with a level of humidification that could be too high when operated continually at higher levels of room RH and leaves the patient with no choice or control over the level of humidity. 
     U.S. Pat. No. 7,331,342 indicates that humidity in the Burioka product is provided at a higher level than the atmospheric air and mentions two techniques to overcome over humidification by the membrane devices. First, the membrane devices can be used in an environment where the ambient humidity never exceeds an amount that would cause the oxygen-enriched gas to become over humidified. However, since many of these devices are used in a patient&#39;s home under a variety of environmental conditions, the ambient humidity is difficult to control. 
     Second, a shunt can be installed so that a portion of the oxygen-enriched gas bypasses the membrane device, remaining at an extremely low humidity. When the streams of oxygen-enriched gas are later remixed, an optimal humidity can be achieved. This system however, requires adjustment by the user to match ambient conditions as well as requiring additional valves and tubing. 
     Porous Media teaches against being able to control the humidity of the patient gas with the use of the HUMIDIFLOW membrane gas humidifier, and teaches that it is not possible to create higher levels of humidity on the outlet of the HUMIDIFLOW membrane gas humidifier than the atmospheric air, their concern being condensation or “rain out.” Porous Media views condensation as harmful: “However, if the oxygen-enriched air stream exiting membrane device  63  were allowed to cool to ambient temperature to enable a patient to breathe the oxygen-enriched air, harmful condensation can occur.” 
     The Spearman patent indicates that: “ FIG. 4  shows an embodiment of the oxygen concentrator  92  of the present invention. Oxygen concentrator  92  uses a membrane device  63  similar to the membrane device shown in  FIG. 2 , but with the first inlet  44  of the membrane device  63  in fluid communication with the outlet  39  of the inlet filter  37  and the first outlet  45  of the membrane device  63  in fluid communication with the inlet  41  of the compressor  40 .” 
     Thus, the same stream of air is passed through the membrane device  63  from the first inlet  44  to the first outlet  45  as shown in  FIG. 2 , but the stream of air is now at approximately ambient pressure and thus at nominally the same pressure as the oxygen-enriched gas passing from the second inlet  61  to the second outlet  62  of the membrane device  63 . 
     This means that the partial pressure of water in the oxygen-enriched gas exiting at the second outlet  62  of the membrane device  63  should be no greater than the partial pressure of water in the air entering the membrane device  63  at the first inlet  44  of the membrane device  63  and thus no greater than the ambient partial pressure of water. As a result, as the oxygen-enriched gas cools on the way to the patient, condensation is inhibited or eliminated. 
     Thus, there is no need of a bypass valve as in  FIG. 2 . Additionally, the Patent Examiner from U.S. application Ser. No. 10/958,973 reaffirmed that the “invention requires equal pressure at both level of humidification of gas to overcome condensation of gas at the second level of humidification gas . . . ” The provisional patent states “In one embodiment . . . unlike devices in the previous art, the pressure of both the air and the oxygen enriched air streams will be nominally equal to the environmental pressure and thus each other.” 
     From the provisional patent page 3, Porous Media describes the following installation scenarios in which the pressures of oxygen gas and the feed gas are the same: “In this second embodiment the outlet of the compressor is in fluid communication with the inlet of side one of the membrane in the membrane device. The outlet of side one of said membrane device is in fluid communication with the inlet of the oxygen concentration system, which consists of a valve system, adsorption beds, and usually a buffer tank. The outlet of said oxygen concentration system is in fluid communication with side two of the membrane in said membrane device. 
     The outlet of side two of said membrane device is in fluid communication with, in seriatim, the gas pressure regulator, the flow control valve, and the patient. In this second embodiment both the air and the oxygen-enriched stream are at nominally the same pressure which is higher than the ambient pressure. Like the first embodiment, this second embodiment is different from prior art since there is no total pressure gradient across the membrane.” 
     Porous Media establishes the difference between their device that operates at equal pressures and the Burioka device which is at unequal pressures. Further, Porous Media illustrates the importance of their invention operating at equal pressures and teaches away from pressure gradients: “It is sometimes thought by those experienced in the art that a total pressure gradient across the membrane is required to produce flux across the membrane, suggesting that the module would need to be installed as in  FIG. 2  to function, but this is not the case. Since flux across the membrane is caused by a partial pressure gradient of a compound in the respective streams, and the oxygen enriched air enters the membrane device  8  at entrance  10  extremely dry, there is still a partial pressure gradient of water to drive the membrane flux even though the total pressure on the 2 sides of the membrane is nominally equal.” 
     Porous Media indicates in the patent “no matter how the membrane is designed, or how large it is, or how permeable the membrane is to water vapor, the partial pressure of water in the exiting oxygen enriched stream can never be greater than the partial pressure of water in the entering air stream” (to the compressor that is). 
     SUMMARY OF THE INVENTION 
     An embodiment of the invention is directed to a membrane oxygen humidifier that is used in conjunction with a patient breathing circuit. The membrane oxygen humidifier includes a plurality of fibers through which water can permeate to humidify the oxygen being provided to the patient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. 
         FIG. 1  is a perspective view of a membrane oxygen humidifier according to an embodiment of the invention. 
         FIG. 2  is a perspective view of the membrane oxygen humidifier used in conjunction with a patient breathing circuit. 
         FIG. 3  is a perspective view of the membrane oxygen humidifier used adjacent to a room air humidifier. 
         FIG. 4  is a perspective view of caps removable mounted to the membrane oxygen humidifier. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     It is desirable to maintain a static level of atmospheric humidity (or close to static as possible) going into the air compressor while increasing the humidity provided to the patient to preferably high levels of humidity, such as in the range of 40%-65%. This invention can control higher level of humidity to the patient while imputing no deleterious effect to the concentrator. It is also desirous to provide an easy to install membrane humidifier to an oxygen concentrator that does not require altering of manufacturers&#39; equipment as this could lead to problems for the patient, the provider and the OEM of the concentrator. It is also a desire to be able to test the oxygen performance of the machine with the membrane humidifier installed without having to use a secondary filter-dryer. 
     The present invention is novel and accomplishes all of the desired performance characteristics of the prior art yet without having to alter the manufacturer&#39;s equipment, it provides a simple installation procedure that can be performed inside of 30 seconds (even by an elderly patient), increases the safety of the device, provides a much more efficient and economical means for verifying oxygen performance and also allows the patient to have high levels of humidity without damaging their home or oxygen concentrator. 
     The hollow fiber membrane  10  may be selected to permit water vapor to pass there through while other gases such as oxygen and nitrogen are hindered from passing there through. Since the oxygen-enriched gas entering the hollow fiber membrane  10  at inlet  20  is extremely dry, there exists a driving force for water vapor to pass across the selective membrane. Through this process, the humidity of the oxygen-enriched gas is higher when the oxygen-enriched gas exits the hollow fiber membrane  10  at outlet  22  than when the oxygen-enriched gas enters the hollow fiber member  10  at inlet  20 . While the membrane selectivity is high, the oxygen level is changed only by dilution with water vapor. 
     An embodiment of the invention is directed to a membrane oxygen humidifier  8 , as illustrated in the figures. The membrane oxygen humidifier  8  may include at least one hollow fiber membrane  10  within an enclosure  12 . The hollow fiber membrane  10  has an inlet  20  and an outlet  22 . 
     A fan  16  may be used to direct the air across the membranes  10 . It is possible to use other techniques for directing air across the membranes  10 . Examples of such other techniques include a compressor, a vacuum and a component attached to a home ventilation system. 
     To enhance the usable life of the membrane oxygen humidifier  8 , the hollow fiber membrane  10  may be removably mounted in the enclosure  12 . Such a configuration would enable the hollow fiber member  10  to be replaced if the hollow fiber membrane is damaged or contaminated. 
     An electrical plug  14  may be provided to provide power to the fan  16 . Alternatively or additionally, the membrane oxygen humidifier  8  may include a re-chargeable battery for a portable version of the invention so that the patients can connect the device to their portable oxygen tanks. 
     The membrane oxygen humidifier  8  may also include at least one filter  18 . One filter  18  is located at the air inlet of the device and one filter is located at the air outlet of the device. The reason for employing the filters is that most patients on oxygen concentrators are smokers and the smoke from the cigarettes can contaminate and coat the membranes  10 , potentially degrading the performance of the membrane oxygen humidifier  8 . 
     Installation of the novel invention is as easy as connecting the adapting oxygen tubing  30  to an oxygen concentrator  34 , as illustrated in  FIG. 2 . Then an oxygen tube  30  with nasal cannula  32  is connected to the patient. To operate the device, one simply plugs the membrane oxygen humidifier  8  into an electrical outlet and turns the unit “on” using the “on/off” switch  24 . To turn the humidification off, the patient can simply press the “off” button on the “on/off” switch  24 . Once the unit is turned on, the fan  16  blows at a predetermined flow rate that can also be adjusted from about 1 lpm to 100 lpm. 
     The present invention also provides a technique to increase the humidity levels to the patient higher than the inlet ambient air to the compressor by allowing the patient the ability to place a humidifier  50  proximate to the inlet of the fan  16  and adjust the flow rate to be close to the flow rate of the saturated air that has been humidified proximate to the humidifier, as illustrated in  FIG. 3 . 
     To increase the portion of the humidity that is directed from the humidifier  50  to the membrane oxygen humidifier  8 , a hood  52  may be provided on at least one of the humidifier  50  and the membrane oxygen humidifier  8  to contain and direct the humidified air directly into the fan  16  of the membrane oxygen humidifier  8 . 
     The membrane oxygen humidifier  8  may be connected to a long tube of between about 50-100 feet in length and can be located this far from the oxygen concentrator. The membrane oxygen humidifier  8  can be put into a small humidifying chamber that is isolated from the oxygen concentrator. An oxygen tube can then be connected from the humidifier to a patient who can be as far as 50 feet away from the membrane oxygen humidifier. With this means of supplemental humidification, the humidity entering the air compressor will never be substantially higher than ambient, meaning within 10%-20% points. 
     The configuration of the membrane oxygen humidifier  8  enables testing of the oxygen concentrator oxygen performance. To test the oxygen concentrator for oxygen performance with the membrane installed, the patient can attach the caps  60  to the membrane oxygen humidifier  8  that seals the air inlet and the outlet orifices  62 . This process allows the oxygen only to flow through the membrane tubes without blowing air across the membrane  10 , causing inaccurate readings due to the transfer of moisture vapor across the membranes  10 . 
     To simplify the operation of the membrane oxygen humidifier  8 , the caps  60  may be operably connected to the enclosure  12  so that the caps  60  are mechanically moved between open and closed positions. In one configuration, the switch  24  that controls the operation of the fan  16  also controls the movement of the caps  60  between the open and closed positions. Alternatively, a separate switch may be provided to control movement of the caps  60  between the open and closed position. It is also possible to bias the caps  60  to a closed position and then have the force generated by flow of air from the fan  16  to cause the caps  60  to move from the open position to the closed position. 
     As an alternative to controlling the operation of the membrane oxygen humidifier  8  separately from the oxygen concentrator  34 , it is possible to include a gas flow switch that is positioned at least partially in the path of oxygen enriched gas flowing from the oxygen concentrator  34  such as in tube  30 , tube  32  or membrane oxygen humidifier  8 . When the gas flow switch senses movement of gas being generated by the oxygen concentrator  34 , the gas flow switch may activate the fan  16 . Similarly, when the gas flow switch senses cessation of gas from the oxygen concentrator  34 , the gas flow switch may deactivate the fan. 
     The device is novel as well and operates with substantially unequal pressures on either side of the membrane where the oxygen is at approximately 3-6 psig. Generally, the oxygen is operational at around 3-6 psig. The air directed across the membrane is generally at atmospheric pressure. The operating pressures may also be equal to not limit the scope of the invention. 
     Alternatively, a tube can be provided with the invention that is in fluid communication with the inlet of membrane humidifier. The air flow across the membrane is generally provided by a fixed speed or variable fan that generally operates at ambient pressure. In another embodiment, a tube is connected from the inlet of the air compressor to the humidifier whereby a suction is pulled on the humidifier drawing the air from the inlet of the humidifier across the membrane. 
     The humidifier humidifies the oxygen close to the ambient air relative humidity proximate to the inlet of the humidifier which is generally within 10%-20% RH to the ambient air proximate to the humidifier. For example, if the relative humidity proximate to the humidifier is 30%, the RH of the outlet of the humidifier will be around 10%-28%. 
     It is contemplated that features disclosed in this application, as well as those described in the above applications incorporated by reference, can be mixed and matched to suit particular circumstances. Various other modifications and changes will be apparent to those of ordinary skill.