OXYGEN CONCENTRATOR WITH MOISTURE MANAGEMENT

An oxygen concentrator (100) may have a moisture conditioning system. In some implementations, the concentrator includes a compressor to induce feed gas into the concentrator. A first pathway may receive the feed gas from the compression system. The first pathway may be configured to draw moisture to produce moisture reduced feed gas. The first pathway may lead the moisture reduced feed gas to sieve bed(s) which produce oxygen enriched air with the moisture reduced feed gas. An accumulator may be configured to receive the produced oxygen enriched air from the sieve bed(s). A second pathway from the accumulator may apply the drawn-out moisture to the produced enriched air to produce humidified enriched air. A third pathway may transfer the drawn-out moisture from the first pathway to the second pathway. An outlet coupled with the second pathway may release the humidified enriched air from the concentrator for a user.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims priority from Singapore Patent Application Serial No. 10202003154R, filed on 6 Apr. 2020, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The present technology relates generally to methods and apparatus for treating respiratory disorders, such as those involving gas adsorption or controlled pressure and/or vacuum swing adsorption. Such methods and apparatus may be implemented in an oxygen concentrator including one or more components to provide oxygen enriched air conditioned with moisture.

BACKGROUND

The Human Respiratory System and its Disorders

A range of respiratory disorders exist. Examples of respiratory disorders include respiratory failure, Obesity Hyperventilation Syndrome (OHS), Chronic Obstructive Pulmonary Disease (COPD), Neuromuscular Disease (NMD) and Chest wall disorders.

Respiratory failure is an umbrella term for respiratory disorders in which the lungs are unable to inspire sufficient oxygen or exhale sufficient CO2to meet the patient's needs. Respiratory failure may encompass some or all of the following disorders.

A patient with respiratory insufficiency (a form of respiratory failure) may experience abnormal shortness of breath on exercise.

Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a group of lower airway diseases that have certain characteristics in common. These include increased resistance to air movement, extended expiratory phase of respiration, and loss of the normal elasticity of the lung. Examples of COPD are emphysema and chronic bronchitis. COPD is caused by chronic tobacco smoking (primary risk factor), occupational exposures, air pollution and genetic factors. Symptoms include: dyspnea on exertion, chronic cough and sputum production.

Neuromuscular Disease (NMD) is a broad term that encompasses many diseases and ailments that impair the functioning of the muscles either directly via intrinsic muscle pathology, or indirectly via nerve pathology. Some NMD patients are characterised by progressive muscular impairment leading to loss of ambulation, being wheelchair-bound, swallowing difficulties, respiratory muscle weakness and, eventually, death from respiratory failure. Neuromuscular disorders can be divided into rapidly progressive and slowly progressive: (i) Rapidly progressive disorders: Characterised by muscle impairment that worsens over months and results in death within a few years (e.g. Amyotrophic lateral sclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers); (ii) Variable or slowly progressive disorders: Characterised by muscle impairment that worsens over years and only mildly reduces life expectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic muscular dystrophy). Symptoms of respiratory failure in NMD include: increasing generalised weakness, dysphagia, dyspnea on exertion and at rest, fatigue, sleepiness, morning headache, and difficulties with concentration and mood changes.

Chest wall disorders are a group of thoracic deformities that result in inefficient coupling between the respiratory muscles and the thoracic cage. The disorders are usually characterised by a restrictive defect and share the potential of long term hypercapnic respiratory failure. Scoliosis and/or kyphoscoliosis may cause severe respiratory failure. Symptoms of respiratory failure include: dyspnea on exertion, peripheral oedema, orthopnea, repeated chest infections, morning headaches, fatigue, poor sleep quality and loss of appetite.

Therapies

Various respiratory therapies have been used to treat one or more of the above respiratory disorders.

Respiratory Pressure Therapies

Respiratory pressure therapy is the application of a supply of air to an entrance to the airways at a controlled target pressure that is nominally positive with respect to atmosphere throughout the patient's breathing cycle (in contrast to negative pressure therapies such as the tank ventilator or cuirass).

Non-invasive ventilation (NIV) provides ventilatory support to a patient through the upper airways to assist the patient breathing and/or maintain adequate oxygen levels in the body by doing some or all of the work of breathing. The ventilatory support is provided via a non-invasive patient interface. NIV has been used to treat respiratory failure, in forms such as OHS, COPD, NMD and Chest Wall disorders. In some forms, the comfort and effectiveness of these therapies may be improved.

Invasive ventilation (IV) provides ventilatory support to patients that are no longer able to effectively breathe themselves and may be provided using a tracheostomy tube. In some forms, the comfort and effectiveness of these therapies may be improved.

Flow Therapies

Not all respiratory therapies aim to deliver a prescribed therapeutic pressure. Some respiratory therapies aim to deliver a prescribed respiratory volume, by delivering an inspiratory flow rate profile over a targeted duration, possibly superimposed on a positive baseline pressure. In other cases, the interface to the patient's airways is ‘open’ (unsealed) and the respiratory therapy may only supplement the patient's own spontaneous breathing with a flow of conditioned or enriched air. In one example, High Flow therapy (HFT) is the provision of a continuous, heated, humidified flow of air to an entrance to the airway through an unsealed or open patient interface at a “treatment flow rate” that is held approximately constant throughout the respiratory cycle. The treatment flow rate is nominally set to exceed the patient's peak inspiratory flow rate. HFT has been used to treat respiratory failure, COPD, and other respiratory disorders. One mechanism of action is that the high flow rate of air at the airway entrance improves ventilation efficiency by flushing, or washing out, expired CO2from the patient's anatomical deadspace. Hence, HFT is thus sometimes referred to as a deadspace therapy (DST). Other benefits may include the elevated warmth and humidification (possibly of benefit in secretion management) and the potential for modest elevation of airway pressures. As an alternative to constant flow rate, the treatment flow rate may follow a profile that varies over the respiratory cycle.

Another form of flow therapy is long-term oxygen therapy (LTOT) or supplemental oxygen therapy. Doctors may prescribe a continuous flow of oxygen enriched air at a specified oxygen concentration (from 21%, the oxygen fraction in ambient air, to 100%) at a specified flow rate (e.g., 1 litre per minute (LPM), 2 LPM, 3 LPM, etc.) to be delivered to the patient's airway.

Respiratory Therapy Systems

These respiratory therapies may be provided by a respiratory therapy system or device. Such systems and devices may also be used to screen, diagnose, or monitor a condition without treating it.

A respiratory therapy system may comprise an oxygen source, an air circuit, and a patient interface.

Patient Interface

A patient interface may be used to interface respiratory equipment to its wearer, for example by providing a flow of air to an entrance to the airways. The flow of air may be provided via a mask to the nose and/or mouth, a tube to the mouth or a tracheostomy tube to the trachea of a patient. Depending upon the therapy to be applied, the patient interface may form a seal, e.g., with a region of the patient's face, to facilitate the delivery of gas at a pressure at sufficient variance with ambient pressure to effect therapy, e.g., at a positive pressure of about 10 cmH2O relative to ambient pressure. For other forms of therapy, such as the delivery of oxygen, the patient interface may not include a seal sufficient to facilitate delivery to the airways of a supply of gas at a positive pressure of about 10 cmH2O. For flow therapies such as nasal LTOT, the patient interface is configured to insufflate the nares but specifically to avoid a complete seal. One example of such a patient interface is a nasal cannula.

An oxygen concentrator may control oxygen enriched air release in a pulsed or demand mode. This may be achieved by delivering the oxygen as a series of pulses, where each pulse or “bolus” may be timed to coincide with inspiration. Such a mode is typically controlled by actuating a pneumatic valve that releases oxygen enriched air for a fixed time. The fixed time is calibrated to be associated with a desired or target bolus volume. However, as such a fixed-time bolus release process does not always achieve the target bolus volume (e.g., due to system characteristics such as compressor variability, as well as aspects of the adsorption process such as the PSA cycle, sieve bed condition, air filter condition etc.), the pneumatic valve may also be operated in a variable manner to regulate the delivered bolus volume more closely to the target volume.

Air Circuit

An air circuit is a conduit or a tube constructed and arranged to allow, in use, a flow of breathable gas to travel between two components of a respiratory therapy system such as the oxygen source and the patient interface. In some cases, there may be separate limbs of the air circuit for inhalation and exhalation. In other cases, a single limb air circuit is used for both inhalation and exhalation.

Oxygen Source

Experts in this field have recognized that exercise for respiratory failure patients provides long term benefits that slow the progression of the disease, improve quality of life and extend patient longevity. Most stationary forms of exercise like tread mills and stationary bicycles, however, are too strenuous for these patients. As a result, the need for mobility has long been recognized. Until recently, this mobility has been facilitated by the use of small compressed oxygen tanks or cylinders mounted on a cart with dolly wheels. The disadvantage of these tanks is that they contain a finite amount of oxygen and are heavy, weighing about 50 pounds when mounted.

Oxygen concentrators have been in use for about 50 years to supply oxygen for respiratory therapy. Traditional oxygen concentrators have been bulky and heavy making ordinary ambulatory activities with them difficult and impractical. Recently, companies that manufacture large stationary oxygen concentrators began developing portable oxygen concentrators (POCs). The advantage of POCs is that they can produce a theoretically endless supply of oxygen. In order to make these devices small for mobility, the various systems necessary for the production of oxygen enriched air are condensed. POCs seek to utilize their produced oxygen as efficiently as possible, in order to minimise weight, size, and power consumption. This may be achieved by delivering the oxygen as series of pulses or “boluses,” each bolus timed to coincide with the onset of inhalation. Such a mode of operation may be implemented with a conserver. The therapy mode is known as pulsed oxygen delivery (POD) or demand mode, in contrast with traditional continuous flow delivery more suited to stationary oxygen concentrators.

Oxygen concentrators may implement processes such as vacuum swing adsorption (VSA), pressure swing adsorption (PSA), or vacuum pressure swing adsorption (VPSA). For example, oxygen concentrators, e.g., POCs, may work based on depressurization (e.g., vacuum operation) and/or pressurization (e.g., compressor operation) in a swing adsorption process (e.g., Vacuum Swing Adsorption VSA, Pressure Swing Adsorption PSA or Vacuum Pressure Swing Adsorption VPSA, each of which are referred to herein as a “swing adsorption process”). For example, an oxygen concentrator may control a process of pressure swing adsorption (PSA). Pressure swing adsorption involves using a compressor to increase gas pressure inside a canister that contains particles of a gas separation adsorbent that attracts nitrogen more strongly than it does oxygen. Such a canister when containing a mass of gas separation adsorbent such as a layer of gas separation adsorbent may serve as a sieve bed. As the pressure increases, certain molecules in the gas may become adsorbed onto the gas separation adsorbent. Removal of a portion of the gas in the canister under the pressurized conditions allows separation of the non-adsorbed molecules from the adsorbed molecules. The adsorbed molecules may then be desorbed by venting the sieve beds. Further details regarding oxygen concentrators may be found, for example, in U.S. Published Patent Application No. 2009-0065007, published Mar. 12, 2009, and entitled “Oxygen Concentrator Apparatus and Method”, which is incorporated herein by reference.

Ambient air usually includes approximately 78% nitrogen and 21% oxygen with the balance comprised of argon, carbon dioxide, water vapor and other trace gases. If a feed gas mixture such as air, for example, is passed under pressure through a canister containing a gas separation adsorbent that attracts nitrogen more strongly than it does oxygen, part or all of the nitrogen will stay in the canister, and the gas coming out of the canister will be enriched in oxygen. When the sieve bed reaches the end of its capacity to adsorb nitrogen, it can be regenerated by reducing the pressure, thereby releasing the adsorbed nitrogen. It is then ready for another “PSA cycle” of producing oxygen enriched air. By alternating pressurization cycles of the canisters in a two-canister system, one canister can be concentrating oxygen (the so-called “adsorption phase”) while the other canister is being purged (the “purge phase”). This alternation results in a near-continuous separation of the oxygen from the nitrogen. In this manner, oxygen can be continuously concentrated out of the air for a variety of uses include providing LTOT to users.

Vacuum swing adsorption (VSA) provides an alternative gas separation technique. VSA typically draws the gas through the separation process of the sieve beds using a vacuum such as a compressor configured to create a vacuum within the sieve beds. Vacuum Pressure Swing Adsorption (VPSA) may be understood to be a hybrid system using a combined vacuum and pressurization technique. For example, a VPSA system may pressurize the sieve beds for the separation process and also apply a vacuum for depressurizing the sieve beds.

Even if the sieve beds are alternated according to the PSA, VSA, or VPSA processes discussed above, they will ultimately retain some of the adsorbed nitrogen after every cycle. As a result, the overall capacity of a sieve bed to adsorb nitrogen will decrease with use, eventually requiring the sieve beds to be replaced.

A typical adsorbent material used in air separation is called zeolite. For medical oxygen generators (such as portable oxygen concentrators), a common type of zeolite is Li-LSX, a low silica high lithium exchanged zeolite, which has a high affinity for Nitrogen (N2). However, the high polarity of the Li-LSX zeolite also increases its affinity for polar molecules, such as water. The water may be in the form of a gas such as water vapor and/or a liquid such as moisture or condensed water vapor. As zeolite adsorbs water, its affinity for nitrogen significantly decreases, since its adsorption sites will be occupied by moisture.

A standard practice to tackle this problem is to dry the air prior to feeding it into the sieve bed. This can be achieved by utilizing a guard layer which adsorbs the water. With a correct material choice, effective sizing of the guard layer and PSA/VPSA cycle tuning, water ingress into the sieve bed can be managed.

Thus, moisture (or water) management within a portable oxygen generator (POC) is important. In particular, the presence of moisture can deactivate the sieve beds in the POC. As such, it is advantageous to minimize moisture in the air that enters the sieve beds. Furthermore, when oxygen enriched air is delivered to a patient, the flow of oxygen enriched air may cause drying of airways, thereby causing discomfort. As such, it may be advantageous to humidify the flow of oxygen enriched air to minimize drying of the nasal mucosa and increase patient airway comfort.

SUMMARY OF THE TECHNOLOGY

Examples of the present technology may provide an apparatus for an oxygen concentrator, such as a portable oxygen concentrator (POC). In particular, the technology provides methods and apparatus for a portable oxygen concentrator having one or more components to manage moisture within the apparatus.

Thus, some implementations of the present technology may relate to a moisture management system for a POC. Generally, the moisture management system may include any one or more of (i) a moisture separation sub-system (MS) or separator; (ii) a moisture transport sub-system (MT) or aqueduct; and (iii) a moisture containment module (MC) or reservoir.

The aforementioned sub-systems may be integrated into an existing POC100system. In some implementations, the moisture management system may be implemented to recycle moisture, such that moisture is removed from the intake air or feed gas, using the separator or MS. Advantageously, the sieve beds which otherwise may be deactivated by moisture may have a longer shelf life because of the relatively dry air that enters the sieve beds as a result of the moisture separation. The dried air may be passed through the oxygen generation sub-system (which typically includes the gas separation adsorbent serving as part of the sieve beds). Subsequently, the previously removed moisture may be transferred, such as via an aqueduct or MT, to a reservoir or MC. Such a reservoir or MC may be configured to return previously captured moisture to the product gas (i.e. oxygen enriched air) for patient use. Thus, oxygen enriched air that is produced from the sieve beds may be hydrated or humidified prior to release of the oxygen enriched air to the patient or user of the oxygen concentrator.

Some example implementations of the present technology may include an oxygen concentrator. The oxygen concentrator may include a compression system, which may include a motor operated compressor, configured to induce a flow of a feed gas into the oxygen concentrator. The oxygen concentrator may include one or more sieve beds coupled with the compression system. The oxygen concentrator may include a first pathway from the compression system. The first pathway may be configured to receive the feed gas from the compression system. The first pathway may be configured to draw out moisture from the feed gas to produce moisture reduced feed gas. The first pathway may be further configured to lead the moisture reduced feed gas to the one or more sieve beds. The one or more sieve beds may be configured to produce oxygen enriched air with the moisture reduced feed gas. The oxygen concentrator may include an accumulator configured to receive the produced oxygen enriched air from the one or more sieve beds. The oxygen concentrator may include a second pathway from the accumulator. The second pathway may be configured to apply the drawn-out moisture to the produced oxygen enriched air to produce humidified oxygen enriched air. The oxygen concentrator may include a third pathway configured to transfer the drawn-out moisture from the first pathway to the second pathway. The oxygen concentrator may include an outlet coupled with the second pathway and may be configured to release the humidified oxygen enriched air from the oxygen concentrator for a user.

In some implementations, the first pathway may be configured to induce a centrifugal flow of the feed gas received from the compression system to separate moisture from the feed gas. The first pathway may include a helical flow path. The first pathway may include one or more of (a) a spin inducer, (b) one or more flow directors, and (c) a volute. The first pathway may include a tapered vortex. The first pathway may include a moisture wick to draw out moisture from the feed gas. The first pathway may include a surface of a water vapor permeable membrane. The first pathway may include a condenser. The condenser may include a condensing material. The condenser may include a condensing coil. The oxygen concentrator may include a circulator to circulate a fluid within the condensing coil. The second pathway may include a containment tank configured as a pass over humidifier. The third pathway may be configured to transfer the drawn-out moisture to the containment tank. The third pathway further may include one or more liquid transport components. The one or more liquid transport components may include one or more of (a) a valve; (b) a conduit, and (c) a pump. The one or more liquid transport components may be configured to induce the transfer of the drawn-out moisture to the containment tank. The third pathway may include one or more conduits.

In some implementations, the first pathway may be formed as a concentric helix may include a plurality of layers. A first layer of the plurality of layers may include a condenser material. A second layer of the plurality of layers may include a wicking material. The plurality of layers may include an inner layer and an outer layer. The plurality of layers may further include a water vapor permeable membrane. An inner surface of the water vapor permeable membrane may form a cylindrical surface around the plurality of layers of the concentric helix. An outer surface of the water vapor permeable membrane may form a collector in the second pathway.

In some implementations, an oxygen concentrator may be configured to remove moisture from a feed gas that may be then applied to a gas adsorption process of the oxygen concentrator and to reapply the removed moisture to an oxygen enriched air that may be accumulated from the gas adsorption process.

In some implementations, a portable oxygen concentrator apparatus may include means for gas separation. The portable oxygen concentrator apparatus may include means for feeding a feed gas into the means for gas separation. The portable oxygen concentrator apparatus may include accumulation means for receiving oxygen enriched air from the means for gas separation. The portable oxygen concentrator apparatus may include dehumidifying means for removing moisture from the feed gas. The portable oxygen concentrator apparatus may include humidifying means for recycling the removed moisture to humidify the oxygen enriched air. The portable oxygen concentrator apparatus may include outlet means for providing the humidified oxygen enriched air to a user.

DETAILED DESCRIPTION OF THE IMPLEMENTATIONS

An example adsorption device of the present technology involving an oxygen concentrator may be considered in relation to the examples of the figures. The examples of the present technology may be implemented with any of the following structures and operations.

Outer Housing

FIG.1depicts an implementation of an outer housing170of an oxygen concentrator100. In some implementations, outer housing170may be comprised of a light-weight plastic. Outer housing includes compression system inlets105, cooling system passive inlet101and outlet173at each end of outer housing170, outlet port174, and control panel600. Inlet101and outlet173allow cooling air to enter the housing, flow through the housing, and exit the interior of housing170to aid in cooling of the oxygen concentrator100. Compression system inlets105allow air to enter the compression system. Outlet port174is used to attach a conduit to provide oxygen enriched air produced by the oxygen concentrator100to a user.

Schematic

FIG.2illustrates a schematic diagram of an oxygen concentrator100, according to an implementation. Oxygen concentrator100may concentrate oxygen within an air stream to provide oxygen enriched air to a user.

Oxygen concentrator100may be a portable oxygen concentrator. For example, oxygen concentrator100may have a weight and size that allows the oxygen concentrator to be carried by hand and/or in a carrying case. In one implementation, oxygen concentrator100has a weight of less than about 20 pounds, less than about 15 pounds, less than about 10 pounds, or less than about 5 pounds. In an implementation, oxygen concentrator100has a volume of less than about 1000 cubic inches, less than about 750 cubic inches, less than about 500 cubic inches, less than about 250 cubic inches, or less than about 200 cubic inches.

Oxygen enriched air may be produced from ambient air by pressurising ambient air in canisters302and304, which contain a gas separation adsorbent and are therefore referred to as sieve beds. Gas separation adsorbents useful in an oxygen concentrator are capable of separating at least nitrogen from an air stream to produce oxygen enriched air. Examples of gas separation adsorbents include molecular sieves that are capable of separating nitrogen from an air stream. Examples of adsorbents that may be used in an oxygen concentrator include, but are not limited to, zeolites (natural) or synthetic crystalline aluminosilicates that separate nitrogen from an air stream under elevated pressure. Examples of synthetic crystalline aluminosilicates that may be used include, but are not limited to: OXYSIV adsorbents available from UOP LLC, Des Plaines, Iowa; SYLOBEAD adsorbents available from W. R. Grace & Co, Columbia, Md.; SILIPORITE adsorbents available from CECA S.A. of Paris, France; ZEOCHEM adsorbents available from Zeochem AG, Uetikon, Switzerland; and AgLiLSX adsorbent available from Air Products and Chemicals, Inc., Allentown, Pa.

As shown inFIG.2, air may enter the oxygen concentrator through air inlet105. Air may be drawn into air inlet105by compression system200. Compression system200may draw in air from the surroundings of the oxygen concentrator and compress the air, forcing the compressed air into one or both canisters302and304. In an implementation, an inlet muffler108may be coupled to air inlet105to reduce sound produced by air being pulled into the oxygen concentrator by compression system200. In an implementation, inlet muffler108may have a contaminant filter, moisture filter and/or sound reducing muffler. Thus, such the air inlet105may be implemented with a contaminant filter to remove contaminants from the intake air (or feed gas). In some implementations, a water adsorbent material (such as a polymer water absorbent material or a zeolite material) may be used to both adsorb water from the incoming air and to reduce the sound of the air passing into the air inlet105. Alternatively, as discussed in more detail herein, the water may be separated with separator1704. Such a separator may optionally be upstream or downstream of the compressor but will typically be in the path of the inlet stream of the POC that is upstream of the sieve beds. As illustrated inFIG.2, such a component of the system is shown proximate to an outlet of the compression system200.

Compression system200may include one or more compressors configured to compress air. Pressurized air, produced by compression system200, may be forced into one or both of the canisters302and304. In some implementations, the ambient air may be pressurized in the canisters to a pressure approximately in a range of 13-20 pounds per square inch gauge pressure (psig). Other pressures may also be used, depending on the type of gas separation adsorbent disposed in the canisters.

Coupled to each canister302/304are inlet valves122/124and outlet valves132/134. As shown inFIG.2, inlet valve122is coupled to canister302and inlet valve124is coupled to canister304. Outlet valve132is coupled to canister302and outlet valve134is coupled to canister304. Inlet valves122/124are used to control the passage of air from compression system200to the respective canisters. Outlet valves132/134are used to release gas from the respective canisters during a venting process. In some implementations, inlet valves122/124and outlet valves132/134may be silicon plunger solenoid valves. Other types of valves, however, may be used. Plunger valves offer advantages over other kinds of valves by being quiet and having low slippage.

In some implementations, a two-step valve actuation voltage may be used to control inlet valves122/124and outlet valves132/134. For example, a high voltage (e.g., 24 V) may be applied to an inlet valve to open the inlet valve. The voltage may then be reduced (e.g., to 7 V) to keep the inlet valve open. Using less voltage to keep a valve open may use less power (Power=Voltage*Current). This reduction in voltage minimizes heat buildup and power consumption to extend run time from the power supply180(described below). When the power is cut off to the valve, it closes by spring action. In some implementations, the voltage may be applied as a function of time that is not necessarily a stepped response (e.g., a curved downward voltage between an initial 24 V and a final 7 V).

In an implementation, pressurized air is sent into one of canisters302or304while the other canister is being vented. For example, during use, inlet valve122is opened while inlet valve124is closed. Pressurized air from compression system200is forced into canister302, while being inhibited from entering canister304by inlet valve124. In an implementation, a controller400is electrically coupled to valves122,124,132, and134. Controller400includes one or more processors410operable to execute program instructions stored in memory420. The program instructions configure the controller to perform various predefined methods that are used to operate the oxygen concentrator, such as the methods described in more detail herein. The program instructions may include program instructions for operating inlet valves122and124out of phase with each other, i.e., when one of inlet valves122or124is opened, the other valve is closed. During pressurization of canister302, outlet valve132is closed and outlet valve134is opened Similar to the inlet valves, outlet valves132and134are operated out of phase with each other. In some implementations, the voltages and the durations of the voltages used to open the input and output valves may be controlled by controller400.

The controller400may include a transceiver430that may communicate with external devices to transmit data collected by the processor410or receive instructions from an external computing device for the processor410.

Check valves142and144are coupled to canisters302and304, respectively. Check valves142and144may be one-way valves that are passively operated by the pressure differentials that occur as the canisters are pressurized and vented, or may be active valves. Check valves142and144are coupled to the canisters to allow oxygen enriched air produced during pressurization of each canister to flow out of the canister, and to inhibit back flow of oxygen enriched air or any other gases into the canister. In this manner, check valves142and144act as one-way valves allowing oxygen enriched air to exit the respective canisters during pressurization.

The term “check valve,” as used herein, refers to a valve that allows flow of a fluid (gas or liquid) in one direction and inhibits back flow of the fluid. Examples of check valves that are suitable for use include, but are not limited to: a ball check valve; a diaphragm check valve; a butterfly check valve; a swing check valve; a duckbill valve; an umbrella valve; and a lift check valve. Under pressure, nitrogen molecules in the pressurized ambient air are adsorbed by the gas separation adsorbent in the pressurized canister. As the pressure increases, more nitrogen is adsorbed until the gas in the canister is enriched in oxygen. The nonadsorbed gas molecules (mainly oxygen) flow out of the pressurized canister when the pressure reaches a point sufficient to overcome the resistance of the check valve coupled to the canister. In one implementation, the pressure drop of the check valve in the forward direction is less than 1 psig. The break pressure in the reverse direction is greater than 100 psig. It should be understood, however, that modification of one or more components would alter the operating parameters of these valves. If the forward flow pressure is increased, there is, generally, a reduction in oxygen enriched air production. If the break pressure for reverse flow is reduced or set too low, there is, generally, a reduction in oxygen enriched air pressure.

In an exemplary implementation, canister302is pressurized by compressed air produced in compression system200and passed into canister302. During pressurization of canister302inlet valve122is open, outlet valve132is closed, inlet valve124is closed and outlet valve134is open. Outlet valve134is opened when outlet valve132is closed to allow substantially simultaneous venting of canister304to atmosphere while canister302is being pressurized. Canister302is pressurized until the pressure in canister is sufficient to open check valve142. Oxygen enriched air produced in canister302exits through check valve and, in one implementation, is collected in accumulator106. As discussed in more detail herein, an outlet of the accumulator106may lead to a reservoir1710that is configured to apply moisture to the product gas released from the accumulator106. As illustrated inFIG.6, in addition to this downstream arrangement with respect to the accumulator, the reservoir1710may also optionally be downstream of various additional components (such as when present) of the oxygen concentrator including any one or more of supply valve160, expansion chamber162, flow restrictor175, flow rate sensor185and/or particulate filter187. Such an arrangement permits a storage of drier gas and can thereby reduce negative effects of the presence of moisture on such upstream system components. The reservoir1710may include moisture, such as moisture previously removed by the separator1704, and the moisture may optionally be heated, such as with a heating element or coil, to warm the oxygen enriched product gas for a more comfortable user experience for a user.

After some time, the gas separation adsorbent will become saturated with nitrogen and will be unable to separate significant amounts of nitrogen from incoming air. This point is usually reached after a predetermined time of oxygen enriched air production. In the implementation described above, when the gas separation adsorbent in canister302reaches this saturation point, the inflow of compressed air is stopped and canister302is vented to remove nitrogen. During venting, inlet valve122is closed, and outlet valve132is opened. While canister302is being vented, canister304is pressurized to produce oxygen enriched air in the same manner described above. Pressurization of canister304is achieved by closing outlet valve134and opening inlet valve124. The oxygen enriched air exits canister304through check valve144.

During venting of canister302, outlet valve132is opened allowing pressurized gas (mainly nitrogen) to exit the canister to atmosphere through concentrator outlet130. In an implementation, the vented gases may be directed through muffler133to reduce the noise produced by releasing the pressurized gas from the canister. As gas is released from canister302, the pressure in the canister302drops, allowing the nitrogen to become desorbed from the gas separation adsorbent. The released nitrogen exits the canister through outlet130, resetting the canister to a state that allows renewed separation of nitrogen from an air stream. Muffler133may include open cell foam (or another material) to muffle the sound of the gas leaving the oxygen concentrator. In some implementations, the combined muffling components/techniques for the input of air and the output of oxygen enriched air may provide for oxygen concentrator operation at a sound level below 50 decibels.

During venting of the canisters, it is advantageous that at least a majority of the nitrogen is removed. In an implementation, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 98%, or substantially all of the nitrogen in a canister is removed before the canister is re-used to separate nitrogen from air. In some implementations, a canister may be further purged of nitrogen using an oxygen enriched air stream that is introduced into the canister from the other canister.

In an exemplary implementation, a portion of the oxygen enriched air may be transferred from canister302to canister304when canister304is being vented of nitrogen. Transfer of oxygen enriched air from canister302to304during venting of canister304, helps to further purge nitrogen (and other gases) from the canister. In an implementation, oxygen enriched air may travel through flow restrictors151,153, and155between the two canisters. Flow restrictor151may be a trickle flow restrictor. Flow restrictor151, for example, may be a 0.009D flow restrictor (e.g., the flow restrictor has a radius 0.009″ which is less than the diameter of the tube it is inside). Flow restrictors153and155may be 0.013D flow restrictors. Other flow restrictor types and sizes are also contemplated and may be used depending on the specific configuration and tubing used to couple the canisters. In some implementations, the flow restrictors may be press fit flow restrictors that restrict air flow by introducing a narrower diameter in their respective tube. In some implementations, the press fit flow restrictors may be made of sapphire, metal or plastic (other materials are also contemplated).

Flow of oxygen enriched air between the canisters is also controlled by use of valve152and valve154. Valves152and154may be opened for a short duration during the venting process (and may be closed otherwise) to prevent excessive oxygen loss out of the purging canister. Other durations are also contemplated. In an exemplary implementation, canister302is being vented and it is desirable to purge canister302by passing a portion of the oxygen enriched air being produced in canister304into canister302. A portion of oxygen enriched air, upon pressurization of canister304, will pass through flow restrictor151into canister302during venting of canister302. Additional oxygen enriched air is passed into canister302, from canister304, through valve154and flow restrictor155. Valve152may remain closed during the transfer process, or may be opened if additional oxygen enriched air is needed. The selection of appropriate flow restrictors151and155, coupled with controlled opening of valve154allows a controlled amount of oxygen enriched air to be sent from canister304to canister302. In an implementation, the controlled amount of oxygen enriched air is an amount sufficient to purge canister302and minimize the loss of oxygen enriched air through venting valve132of canister302. While this implementation describes venting of canister302, it should be understood that the same process can be used to vent canister304using flow restrictor151, valve152and flow restrictor153.

The pair of equalization/vent valves152/154work with flow restrictors153and155to optimize the gas flow balance between the two canisters. This may allow for better flow control for venting one of the canisters with oxygen enriched air from the other of the canisters. It may also provide better flow direction between the two canisters. It has been found that, while flow valves152/154may be operated as bi-directional valves, the flow rate through such valves varies depending on the direction of fluid flowing through the valve. For example, oxygen enriched air flowing from canister304toward canister302has a flow rate faster through valve152than the flow rate of oxygen enriched air flowing from canister302toward canister304through valve152. If a single valve was to be used, eventually either too much or too little oxygen enriched air would be sent between the canisters and the canisters would, over time, begin to produce different amounts of oxygen enriched air. Use of opposing valves and flow restrictors on parallel air pathways may equalize the flow pattern of the oxygen enriched air between the two canisters. Equalising the flow may allow for a steady amount of oxygen enriched air to be available to the user over multiple cycles and also may allow a predictable volume of oxygen enriched air to purge the other of the canisters. In some implementations, the air pathway may not have restrictors but may instead have a valve with a built-in resistance or the air pathway itself may have a narrow radius to provide resistance.

At times, oxygen concentrator may be shut down for a period of time. When an oxygen concentrator is shut down, the temperature inside the canisters may drop as a result of the loss of adiabatic heat from the compression system. As the temperature drops, the volume occupied by the gases inside the canisters will drop. Cooling of the canisters may lead to a negative pressure in the canisters. Valves (e.g., valves122,124,132, and134) leading to and from the canisters are dynamically sealed rather than hermetically sealed. Thus, outside air may enter the canisters after shutdown to accommodate the pressure differential. When outside air enters the canisters, moisture from the outside air may be adsorbed by the gas separation adsorbent. Adsorption of water inside the canisters may lead to gradual degradation of the gas separation adsorbents, steadily reducing ability of the gas separation adsorbents to produce oxygen enriched air.

In an implementation, outside air may be inhibited from entering canisters after the oxygen concentrator is shut down by pressurising both canisters prior to shutdown. By storing the canisters under a positive pressure, the valves may be forced into a hermetically closed position by the internal pressure of the air in the canisters. In an implementation, the pressure in the canisters, at shutdown, should be at least greater than ambient pressure. As used herein the term “ambient pressure” refers to the pressure of the surroundings in which the oxygen concentrator is located (e.g. the pressure inside a room, outside, in a plane, etc.). In an implementation, the pressure in the canisters, at shutdown, is at least greater than standard atmospheric pressure (i.e., greater than 760 mmHg (Ton), 1 atm, 101,325 Pa). In an implementation, the pressure in the canisters, at shutdown, is at least about 1.1 times greater than ambient pressure; is at least about 1.5 times greater than ambient pressure; or is at least about 2 times greater than ambient pressure.

In an implementation, pressurization of the canisters may be achieved by directing pressurized air into each canister from the compression system and closing all valves to trap the pressurized air in the canisters. In an exemplary implementation, when a shutdown sequence is initiated, inlet valves122and124are opened and outlet valves132and134are closed. Because inlet valves122and124are joined together by a common conduit, both canisters302and304may become pressurized as air and/or oxygen enriched air from one canister may be transferred to the other canister. This situation may occur when the pathway between the compression system and the two inlet valves allows such transfer. Because the oxygen concentrator operates in an alternating pressurize/venting mode, at least one of the canisters should be in a pressurized state at any given time. In an alternate implementation, the pressure may be increased in each canister by operation of compression system200. When inlet valves122and124are opened, pressure between canisters302and304will equalize, however, the equalized pressure in either canister may not be sufficient to inhibit air from entering the canisters during shutdown. In order to ensure that air is inhibited from entering the canisters, compression system200may be operated for a time sufficient to increase the pressure inside both canisters to a level at least greater than ambient pressure. Regardless of the method of pressurization of the canisters, once the canisters are pressurized, inlet valves122and124are closed, trapping the pressurized air inside the canisters, which inhibits air from entering the canisters during the shutdown period.

Referring toFIG.3, an implementation of an oxygen concentrator100is depicted. Oxygen concentrator100includes a compression system200, a canister system300, and a power supply180disposed within an outer housing170. Inlets101are located in outer housing170to allow air from the environment to enter oxygen concentrator100. Inlets101may allow air to flow into the compartment to assist with cooling of the components in the compartment. Power supply180provides a source of power for the oxygen concentrator100. Compression system200draws air in through the inlet105and muffler108. Muffler108may reduce noise of air being drawn in by the compression system and also may include a desiccant material to remove water from the incoming air. Oxygen concentrator100may further include fan172used to vent air and other gases from the oxygen concentrator via outlet173.

Compression System

In some implementations, compression system200includes one or more compressors. In another implementation, compression system200includes a single compressor, coupled to all of the canisters of canister system300. Turning toFIGS.4and5, a compression system200is depicted that includes compressor210and motor220. Motor220is coupled to compressor210and provides an operating force to the compressor to operate the compression mechanism. For example, motor220may be a motor providing a rotating component that causes cyclical motion of a component of the compressor that compresses air. When compressor210is a piston type compressor, motor220provides an operating force which causes the piston of compressor210to be reciprocated. Reciprocation of the piston causes compressed air to be produced by compressor210. The pressure of the compressed air is, in part, estimated by the speed at which the compressor is operated (e.g., how fast the piston is reciprocated). Motor220, therefore, may be a variable speed motor that is operable at various speeds to dynamically control the pressure of air produced by compressor210.

In one implementation, compressor210includes a single head wobble type compressor having a piston. Other types of compressors may be used such as diaphragm compressors and other types of piston compressors. Motor220may be a DC or AC motor and provides the operating power to the compressing component of compressor210. Motor220, in an implementation, may be a brushless DC motor. Motor220may be a variable speed motor configured to operate the compressing component of compressor210at variable speeds. Motor220may be coupled to controller400, as depicted inFIG.2, which sends operating signals to the motor to control the operation of the motor. For example, controller400may send signals to motor220to: turn the motor on, turn the motor off, and set the operating speed of the motor. Thus, as illustrated inFIG.2, the compression system200may include a speed sensor201. The speed sensor may be a motor speed transducer used to determine a rotational velocity of the motor220and/or other reciprocating operation of the compression system200. For example, a motor speed signal from the motor speed transducer may be provided to the controller400. The speed sensor or motor speed transducer may, for example, be a Hall effect sensor. The controller400may operate the compression system200via the motor220based on the speed signal and/or any other sensor signal of the oxygen concentrator, such as a pressure sensor (e.g., accumulator pressure sensor107). Thus, as illustrated inFIG.2, the controller400receives sensor signals, such as a speed signal from the speed sensor201and accumulator pressure signal from the accumulator pressure sensor107. With such signal(s), the controller may implement one or more control loops (e.g., feedback control) for operation of the compression system based on sensor signals such as accumulator pressure and/or motor speed as described in more detail herein.

Compression system200inherently creates substantial heat. Heat is caused by the consumption of power by motor220and the conversion of power into mechanical motion. Compressor210generates heat due to the increased resistance to movement of the compressor components by the air being compressed. Heat is also inherently generated due to adiabatic compression of the air by compressor210. Thus, the continual pressurization of air produces heat in the enclosure. Additionally, power supply180may produce heat as power is supplied to compression system200. Furthermore, users of the oxygen concentrator may operate the device in unconditioned environments (e.g., outdoors) at potentially higher ambient temperatures than indoors, thus the incoming air will already be in a heated state.

Heat produced inside oxygen concentrator100can be problematic. Lithium ion batteries are generally employed as power supplies for oxygen concentrators due to their long life and light weight. Lithium ion battery packs, however, are dangerous at elevated temperatures and safety controls are employed in oxygen concentrator100to shut down the system if dangerously high power supply temperatures are detected. Additionally, as the internal temperature of oxygen concentrator100increases, the amount of oxygen generated by the concentrator may decrease. This is due, in part, to the decreasing amount of oxygen in a given volume of air at higher temperatures. If the amount of produced oxygen drops below a predetermined amount, the oxygen concentrator100may automatically shut down.

Because of the compact nature of oxygen concentrators, dissipation of heat can be difficult. Solutions typically involve the use of one or more fans to create a flow of cooling air through the enclosure. Such solutions, however, require additional power from the power supply180and thus shorten the portable usage time of the oxygen concentrator. In an implementation, a passive cooling system may be used that takes advantage of the mechanical power produced by motor220. Referring toFIGS.4and5, compression system200includes motor220having an external rotating armature230. Specifically, armature230of motor220(e.g. a DC motor) is wrapped around the stationary field that is driving the armature. Since motor220is a large contributor of heat to the overall system it is helpful to transfer heat off the motor and sweep it out of the enclosure. With the external high speed rotation, the relative velocity of the major component of the motor and the air in which it exists is very high. The surface area of the armature is larger if externally mounted than if it is internally mounted. Since the rate of heat exchange is proportional to the surface area and the square of the velocity, using a larger surface area armature mounted externally increases the ability of heat to be dissipated from motor220. The gain in cooling efficiency by mounting the armature externally, allows the elimination of one or more cooling fans, thus reducing the weight and power consumption while maintaining the interior of the oxygen concentrator within the appropriate temperature range. Additionally, the rotation of the externally mounted armature creates movement of air proximate to the motor to create additional cooling.

Moreover, an external rotating armature may help the efficiency of the motor, allowing less heat to be generated. A motor having an external armature operates similar to the way a flywheel works in an internal combustion engine. When the motor is driving the compressor, the resistance to rotation is low at low pressures. When the pressure of the compressed air is higher, the resistance to rotation of the motor is higher. As a result, the motor does not maintain consistent ideal rotational stability, but instead surges and slows down depending on the pressure demands of the compressor. This tendency of the motor to surge and then slow down is inefficient and therefore generates heat. Use of an external armature adds greater angular momentum to the motor which helps to compensate for the variable resistance experienced by the motor. Since the motor does not have to work as hard, the heat produced by the motor may be reduced.

In an implementation, cooling efficiency may be further increased by coupling an air transfer device240to external rotating armature230. In an implementation, air transfer device240is coupled to the external armature230such that rotation of the external armature230causes the air transfer device240to create an air flow that passes over at least a portion of the motor. In an implementation, the air transfer device240includes one or more fan blades coupled to the external armature230. In an implementation, a plurality of fan blades may be arranged in an annular ring such that the air transfer device240acts as an impeller that is rotated by movement of the external rotating armature230. As depicted inFIGS.4and5, air transfer device240may be mounted to an outer surface of the external armature230, in alignment with the motor220. The mounting of the air transfer device240to the armature230allows air flow to be directed toward the main portion of the external rotating armature230, providing a cooling effect during use. In an implementation, the air transfer device240directs air flow such that a majority of the external rotating armature230is in the air flow path.

Further, referring toFIGS.4and5, air pressurized by compressor210exits compressor210at compressor outlet212. A compressor outlet conduit250is coupled to compressor outlet212to transfer the compressed air to canister system300. As noted previously, compression of air causes an increase in the temperature of the air. This increase in temperature can be detrimental to the efficiency of the oxygen concentrator. In order to reduce the temperature of the pressurized air, compressor outlet conduit250is placed in the air flow path produced by air transfer device240. At least a portion of compressor outlet conduit250may be positioned proximate to motor220. Thus, air flow, created by air transfer device240, may contact both motor220and compressor outlet conduit250. In one implementation, a majority of compressor outlet conduit250is positioned proximate to motor220. In an implementation, the compressor outlet conduit250is coiled around motor220, as depicted inFIG.5.

In an implementation, the compressor outlet conduit250is composed of a heat exchange metal. Heat exchange metals include, but are not limited to, aluminum, carbon steel, stainless steel, titanium, copper, copper-nickel alloys or other alloys formed from combinations of these metals. Thus, compressor outlet conduit250can act as a heat exchanger to remove heat that is inherently caused by compression of the air. By removing heat from the compressed air, the number of molecules in a given volume at a given pressure is increased. As a result, the amount of oxygen enriched air that can be generated by each canister during each pressure swing cycle may be increased.

The heat dissipation mechanisms described herein are either passive or make use of elements required for the oxygen concentrator100. Thus, for example, dissipation of heat may be increased without using systems that require additional power. By not requiring additional power, the run-time of the battery packs may be increased and the size and weight of the oxygen concentrator may be minimized. Likewise, use of an additional box fan or cooling unit may be eliminated. Eliminating such additional features reduces the weight and power consumption of the oxygen concentrator.

As discussed above, adiabatic compression of air causes the air temperature to increase. During venting of a canister in canister system300, the pressure of the gas being released from the canisters decreases. The adiabatic decompression of the gas in the canister causes the temperature of the gas to drop as it is vented. In an implementation, the cooled vented gases327from canister system300are directed toward power supply180and toward compression system200. In an implementation, base315of canister system300receives the vented gases from the canisters. The vented gases327are directed through base315toward outlet325of the base315and toward power supply180. The vented gases, as noted, are cooled due to decompression of the gases and therefore passively provide cooling to the power supply. When the compression system200is operated, the air transfer device240will gather the cooled vented gases and direct the gases toward the motor220of compression system200. Fan172may also assist in directing the vented gas across compression system200and out of the housing170. In this manner, additional cooling may be obtained without requiring any further power requirements from the battery.

Canister System

Oxygen concentrator100may include at least two canisters, each canister including a gas separation adsorbent. Examples may be considered in relation to the version shown inFIGS.9-13, which show a canister assembly that is generally integrated into a housing of a POC and typically requires a service technician and tools to install and remove. An alternative version is shown inFIG.15as a removable canister assembly that may be easily inserted and removed from the POC as illustrated inFIGS.16A-16C.

The canisters of oxygen concentrator100may be disposed in or formed from a molded housing. In an implementation, canister system300includes two housing components310and510, as depicted inFIG.9. In various implementations, the housing components310and510of the oxygen concentrator100may form a two-part molded plastic frame that defines two canisters302and304and accumulator106. The housing components310and510may be formed separately and then coupled together. In some implementations, housing components310and510may be injection molded or compression molded. Housing components310and510may be made from a thermoplastic polymer such as polycarbonate, methylene carbide, polystyrene, acrylonitrile butadiene styrene (ABS), polypropylene, polyethylene, or polyvinyl chloride. In another implementation, housing components310and510may be made of a thermoset plastic or metal (such as stainless steel or a lightweight aluminum alloy). Lightweight materials may be used to reduce the weight of the oxygen concentrator100. In some implementations, the two housings310and510may be fastened together using screws or bolts. Alternatively, housing components310and510may be solvent welded together. Installation of the canister assembly300ofFIG.9into or out of the housing of POC shown inFIG.1generally requires removal of the outer housing170of the POC100and the use of tools, such that its replacement is typically performed by technician.

As shown inFIGS.9-13, valve seats322,324,332, and334and air pathways of conduit330and346may be integrated into the housing component310to reduce the number of sealed connections needed throughout the air flow of the oxygen concentrator100.

Air pathways/tubing between different sections in housing components310and510may take the form of molded conduits. Conduits in the form of molded channels for air pathways may occupy multiple planes in housing components310and510. For example, the molded air conduits may be formed at different depths and at different x,y,z positions in housing components310and510. In some implementations, a majority or substantially all of the conduits may be integrated into the housing components310and510to reduce potential leak points.

In some implementations, prior to coupling housing components310and510together, O-rings may be placed between various points of housing components310and510to ensure that the housing components are properly sealed. In some implementations, components may be integrated and/or coupled separately to housing components310and510. For example, tubing, flow restrictors (e.g., press fit flow restrictors), oxygen sensors, gas separation adsorbents, check valves, plugs, processors, power supplies, etc. may be coupled to housing components310and510before and/or after the housing components are coupled together.

In some implementations, apertures337leading to the exterior of housing components310and510may be used to insert devices such as flow restrictors. Apertures may also be used for increased moldability. One or more of the apertures may be plugged after molding (e.g., with a plastic plug). In some implementations, flow restrictors may be inserted into passages prior to inserting plugs to seal the passages. Press fit flow restrictors may have diameters that may allow a friction fit between the press fit flow restrictors and their respective apertures. In some implementations, an adhesive may be added to the exterior of the press fit flow restrictors to hold the press fit flow restrictors in place once inserted. In some implementations, the plugs may have a friction fit with their respective tubes (or may have an adhesive applied to their outer surface). The press fit flow restrictors and/or other components may be inserted and pressed into their respective apertures using a narrow tip tool or rod (e.g., with a diameter less than the diameter of the respective aperture). In some implementations, the press fit flow restrictors may be inserted into their respective tubes until they abut a feature in the tube to halt their insertion. For example, the feature may include a reduction in radius. Other features are also contemplated (e.g., a bump in the side of the tubing, threads, etc.). In some implementations, press fit flow restrictors may be molded into the housing components (e.g., as narrow tube segments).

In some implementations, spring baffle139may be placed into respective canister receiving portions of housing components310and510with the spring side of the baffle139facing the exit of the canister. Spring baffle139may apply force to gas separation adsorbent in the canister while also assisting in preventing gas separation adsorbent from entering the exit apertures. Use of a spring baffle139may keep the gas separation adsorbent compact while also allowing for expansion (e.g., thermal expansion). Keeping the gas separation adsorbent compact may prevent the gas separation adsorbent from breaking during movement of the oxygen concentrator100.

In some implementations, filter129may be placed into respective canister receiving portions of housing components310and510facing the inlet of the respective canisters. The filter129removes particles from the feed gas stream entering the canisters.

In some implementations, pressurized air from the compression system200may enter air inlet306. Air inlet306is coupled to inlet conduit330. Air enters housing component310through inlet306and travels through conduit330, and then to valve seats322and324.FIG.10andFIG.11depict an end view of housing310.FIG.10depicts an end view of housing310prior to fitting valves to housing310.FIG.11depicts an end view of housing310with the valves fitted to the housing310. Valve seats322and324are configured to receive inlet valves122and124respectively. Inlet valve122is coupled to canister302and inlet valve124is coupled to canister304. Housing310also includes valve seats332and334configured to receive outlet valves132and134respectively. Outlet valve132is coupled to canister302and outlet valve134is coupled to canister304. Inlet valves122/124are used to control the passage of air from conduit330to the respective canisters.

In an implementation, pressurized air is sent into one of canisters302or304while the other canister is being vented. For example, during use, inlet valve122is opened while inlet valve124is closed. Pressurized air from compression system200is forced into canister302, while being inhibited from entering canister304by inlet valve124. During pressurization of canister302, outlet valve132is closed and outlet valve134is opened. Similar to the inlet valves, outlet valves132and134are operated out of phase with each other. Valve seat322includes an opening323that passes through housing310into canister302. Similarly valve seat324includes an opening375that passes through housing310into canister302. Air from conduit330passes through openings323or375if the respective valves322and324are open, and enters a canister.

Check valves142and144(SeeFIG.9) are coupled to canisters302and304, respectively. Check valves142and144are one way valves that may be passively operated by the pressure differentials that occur as the canisters are pressurized and vented. Oxygen enriched air produced in canisters302and304passes from the canisters into openings542and544of housing component510. A passage (not shown) links openings542and544to conduits342and344, respectively. Oxygen enriched air produced in canister302passes from the canister though opening542and into conduit342when the pressure in the canister is sufficient to open check valve142. When check valve142is open, oxygen enriched air flows through conduit342toward the end of housing310. Similarly, oxygen enriched air produced in canister304passes from the canister through opening544and into conduit344when the pressure in the canister is sufficient to open check valve144. When check valve144is open, oxygen enriched air flows through conduit344toward the end of housing310.

Oxygen enriched air from either canister travels through conduit342or344and enters conduit346formed in housing310. Conduit346includes openings that couple the conduit to conduit342, conduit344and accumulator106. Thus, oxygen enriched air, produced in canister302or304, travels to conduit346and passes into accumulator106. As illustrated inFIG.2, gas pressure within the accumulator106may be measured by a sensor, such as with an accumulator pressure sensor107. (See alsoFIG.6.) Thus, the accumulator pressure sensor provides a signal representing the pressure of the accumulated oxygen enriched air. An example of a suitable pressure transducer is a sensor from the HONEYWELL ASDX series. An alternative suitable pressure transducer is a sensor from the NPA Series from GENERAL ELECTRIC. In some implementations, the pressure sensor may alternatively measure pressure of the gas outside of the accumulator106, such as in an output path between the accumulator106and a valve (e.g., supply valve160) that gates the release of the oxygen enriched air for delivery to a user in a bolus.

After some time, the gas separation adsorbent will become saturated with nitrogen and will be unable to separate significant amounts of nitrogen from incoming air. When the gas separation adsorbent in a canister reaches this saturation point, the inflow of compressed air is stopped and the canister is vented to remove nitrogen. Canister302is vented by closing inlet valve122and opening outlet valve132. Outlet valve132releases the vented gas from canister302into the volume defined by the end of housing310. Foam material may cover the end of housing310to reduce the sound made by release of gases from the canisters. Similarly, canister304is vented by closing inlet valve124and opening outlet valve134. Outlet valve134releases the vented gas from canister304into the volume defined by the end of housing310.

While canister302is being vented, canister304is pressurized to produce oxygen enriched air in the same manner described above. Pressurization of canister304is achieved by closing outlet valve134and opening inlet valve124. The oxygen enriched air exits canister304through check valve144.

In an exemplary implementation, a portion of the oxygen enriched air may be transferred from canister302to canister304when canister304is being vented of nitrogen. Transfer of oxygen enriched air from canister302to canister304, during venting of canister304, helps to further purge nitrogen (and other gases) from the canister. Flow of oxygen enriched air between the canisters is controlled using flow restrictors and valves, as depicted inFIG.2. Three conduits are formed in housing component510for use in transferring oxygen enriched air between canisters. As shown inFIG.12, conduit530couples canister302to canister304. Flow restrictor151(not shown) is disposed in conduit530, between canister302and canister304to restrict flow of oxygen enriched air during use. Conduit532also couples canister302to304. Conduit532is coupled to valve seat552which receives valve152, as shown inFIG.13. Flow restrictor153(not shown) is disposed in conduit532, between canister302and304. Conduit534also couples canister302to304. Conduit534is coupled to valve seat554which receives valve154, as shown inFIG.13. Flow restrictor155(not shown) is disposed in conduit534, between canister302and304. The pair of equalization/vent valves152/154work with flow restrictors153and155to optimize the air flow balance between the two canisters.

Oxygen enriched air in accumulator106passes through supply valve160into expansion chamber162which is formed in housing component510. An opening (not shown) in housing component510couples accumulator106to supply valve160. In an implementation, expansion chamber162may include one or more devices configured to estimate an oxygen concentration of gas passing through the chamber.

Removable Canister Assembly (FIGS.15-16)

In some implementations, to facilitate removability by its user, the canisters of oxygen concentrator100may be formed as shown inFIG.15. Such canisters are similar in relation to the pressurization and depressurization operations to the canisters described in relation toFIGS.9-13but are otherwise structured to facilitate easy replacement and removal from the POC. As illustrated in the example ofFIG.15, canister assembly700includes canisters702and704. Each canister provides a separately pressurizable container for a sieve bed comparable to the sieve bed previously described.

The canister assembly700may have a container portion1504, which may define one or more container volumes for the sieve bed(s). The canister assembly700may also include one or more cap portions1508. The container portion1504may include one or more mounting flanges1510for mounting or joining the cap portion(s)1508onto the container portion(s)1504to form each or both canisters of the canister assembly700. Thus, the cap portion1508may similarly include a flange portion1511corresponding with the flanges1510such that they may optionally be joined by various joining means (e.g., welding or fasteners such as screws, bolts or rivets).

Each canister702,704includes an inlet (or air inlet) and an outlet (or air outlet). For example, as shown in the example ofFIG.15, a first canister (canister702) includes an inlet706and an outlet710that provide gas access to the sieve bed of the first canister. A second canister (canister704) includes an inlet708and an outlet712that provide gas access to the sieve bed of the second canister. As illustrated, any or all of the inlets and/or outlets may be formed as projections or nipples for respective insertion within a coupler or port/orifice of a sieve bed compartment of the POC when inserted into the POC outer housing for use. Such inlets and outlets may have a channel (e.g., cylindrical) within each so that each serves as a path for the gas transfer involved in pressure swing and/or vacuum swing operations of the respective sieve bed of the canister. Each inlet may have an inlet seal respectively, such as a flexible rubber O-ring to create a sealed connection with the oxygen concentrator100for pressurized operations. The outlets710,712may similarly include outlet seals.

While the terms “inlet” and “outlet” are generally used herein to assist with an explanation of features of the canister, such terms are not intended to require only a single direction of gas transfer since it will be recognized that the PSA or VSA process can involve ingress and egress of gas at a common end of the canister depending on the cycle of the process. However, in the example ofFIG.15, the POC may be configured so that the outlets are associated with an output of a product gas (e.g., oxygen enriched air) whereas the inlets may be associated with an introduction of ambient gas (e.g., air) to the sieve bed for the adsorption process. Nevertheless, it will be understood that such functions of these inlets and outlets may be reversed depending on the implementation of the controlled flow path of the POC (i.e., operation of its valves and manifolds) in which the canister assembly700is inserted.

As previously mentioned, the removable canister assembly700may be easily inserted and removed from the POC. This is illustrated byFIG.16A, which shows canister assembly700installed into a compartment1602(seeFIG.16B) of oxygen concentrator100, within the outer housing170. The compartment1602is adapted to contain the canister assembly700. As shown in the cutout view ofFIG.16B, compartment1602may be accessed by removing a portion of the outer housing170, such as a lid (or canister cover or canister panel), for removing and/or inserting of the canister assembly700via a portal1604, such as at a side, of the outer housing170of the oxygen concentrator100. Such a lid1666is shown inFIG.16C. Thus, insertion or removal of the canister assembly700may be achieved without disassembling or removing the entire outer housing170but may be achieved by removing the lid (shown inFIG.16C) of the outer housing170. As illustrated inFIGS.16A and16B, such insertion of the canister assembly700may involve engaging the ports of the inlets and/or outlets of the canister assembly700with a coupling of one or more manifolds adjacent to the compartment1602and within the outer housing170of the oxygen concentrator100. Each outlet of the canister assembly700may have a nipple for joining to a coupling of a manifold. For example, as illustrated inFIG.16B, the outlets of the canister assembly700may be coupled to manifold1606(e.g., an outlet manifold) at the couplings1608-1,1608-2(e.g., outlet couplings) of the manifold1606, which may permit pneumatic sealing of the outlets of the canister assembly700. Such couplings (e.g., outlet couplings1608-1,1608-2) may have a pneumatically sealable structure to complement a reciprocal structure (or complementary structure) of the outlet of the canister assembly700. For example, such couplings (e.g., outlet couplings1608-1,1608-2) may be configured as orifices to receive nipples of the outlets of the canister assembly700within channels of the orifices. The manifold1606may be generally affixed within the oxygen concentrator100as a stationary component. The manifold1606may also include one or more valves, such as any of valves (or control valves)152,154when the manifold1606is an outlet manifold, or valves122,132,124,134if the manifold1606is an inlet manifold.

Similarly, as illustrated inFIGS.16A and16B, the inlets of the canister assembly700may be coupled to manifold804(e.g., an inlet manifold) with additional couplings1609-1,1609-2(e.g., inlet couplings) (seeFIG.16B), which may permit pneumatic sealing of the inlets of the canister assembly700. Such couplings (e.g., couplings1609-1,1609-2) may have a suitable pneumatically sealable structure to complement a reciprocal structure (or complementary structure) of the inlet of the canister assembly700. The manifold804may be generally affixed within the oxygen concentrator100as a traversing or moveable component as discussed in more detail herein.

The oxygen concentrator100of the example ofFIGS.16A,16B, and16Cis similar to those described above. As illustrated inFIG.16A, the oxygen concentrator may have a battery compartment1665within the outer housing, separate from, and beneath the removable canister assembly700. An optional battery compartment lid1667may be removable for accessing the battery. The outer housing may have a button1669to indicate to a user that the adjacent conduit is for attachment to an airway delivery device, e.g. a cannula for receiving enriched air. The outer housing may also include a first and second sets of cooling system outlets1671-1and1671-2. The outer housing may also include a charging port1673for supplying power to the oxygen concentrator for operations and/or for charging the battery. The outer housing may also have a removable panel1675, such as with vent apertures. The removable panel1675may serve as an air filter and a single opening for feed gas to go in and move to the compressor inlet. The outer housing may have a set of cooling system inlets1677.

Moreover, as shown inFIGS.16A and16B, the oxygen concentrator may also include a securing mechanism800that may permit removably engaging of the manifold804with the air inlets706and708. The securing mechanism800may also secure canister assembly700within oxygen concentrator100. Advantageously, the canister assembly700may be secured in position during operation of the oxygen concentrator100, such as at a relatively high pressure. The securing mechanism800is configured such that it is movable between a closed position and an open position. Thus, operation of the securing mechanism800may be utilized to achieve securement of the canister assembly700as well as pneumatic sealing with the canister assembly700, such as when in operation. Securing mechanism800may be manipulated by a user for easy removal and insertion of the canister assembly700.

Outlet System

An outlet system, coupled to one or more of the canisters, includes one or more conduits for providing oxygen enriched air to a user. In an implementation, oxygen enriched air produced in either of canisters302and304is collected in accumulator106through check valves142and144, respectively, as depicted schematically inFIG.6. The oxygen enriched air leaving the canisters may be collected in the accumulator106prior to being provided to a user. In some implementations, a tube may be coupled to the accumulator106to provide the oxygen enriched air to the user. Oxygen enriched air may be provided to the user through an airway delivery device that transfers the oxygen enriched air to the user's mouth and/or nose. In an implementation, an outlet may include a tube that directs the oxygen toward a user's nose and/or mouth that may not be directly coupled to the user's nose.

Turning toFIG.6, a schematic diagram of an implementation of an outlet system for an oxygen concentrator is shown. A supply valve160may be coupled to an outlet tube to control the release of the oxygen enriched air from accumulator106to the user. In an implementation, supply valve160is an electromagnetically actuated plunger valve. Supply valve160is actuated by controller400to control the delivery of oxygen enriched air to a user. Actuation of supply valve160is not timed or synchronized to the pressure swing adsorption process. Instead, actuation is synchronized to the user's breathing as described below. In some implementations, supply valve160may have continuously-valued actuation to establish a clinically effective amplitude profile for providing oxygen enriched air.

Oxygen enriched air in accumulator106passes through supply valve160into expansion chamber162as depicted inFIG.6. In an implementation, expansion chamber162may include one or more devices configured to estimate an oxygen concentration of gas passing through the expansion chamber162. Oxygen enriched air in expansion chamber162builds briefly, through release of gas from accumulator106by supply valve160, and then is bled through a small orifice flow restrictor175to a flow rate sensor185and then to particulate filter187. Flow restrictor175may be a 0.025 D flow restrictor. Other flow restrictor types and sizes may be used. In some implementations, the diameter of the air pathway in the housing may be restricted to create restricted gas flow. Optional flow rate sensor185may be any sensor configured to generate a signal representing the rate of gas flowing through the conduit. Optional particulate filter187may be used to filter bacteria, dust, granule particles, etc., prior to delivery of the oxygen enriched air to the user. The oxygen enriched air passes through filter187(when present) and through the reservoir1710(when present) to connector190which sends the oxygen enriched air to the user via delivery conduit192and to pressure sensor194.

The fluid dynamics of the outlet pathway, coupled with the programmed actuations of supply valve160, may result in a bolus of oxygen being provided at the correct time and with an amplitude profile that assures rapid delivery into the user's lungs without excessive waste.

Expansion chamber162may include one or more oxygen sensors adapted to determine an oxygen concentration of gas passing through the chamber. In an implementation, the oxygen concentration of gas passing through expansion chamber162is estimated using an oxygen sensor165. An oxygen sensor is a device configured to measure oxygen concentration in a gas. Examples of oxygen sensors include, but are not limited to, ultrasonic oxygen sensors, electrical oxygen sensors, chemical oxygen sensors, and optical oxygen sensors. In one implementation, oxygen sensor165is an ultrasonic oxygen sensor that includes an ultrasonic emitter166and an ultrasonic receiver168. In some implementations, ultrasonic emitter166may include multiple ultrasonic emitters and ultrasonic receiver168may include multiple ultrasonic receivers. In implementations having multiple emitters/receivers, the multiple ultrasonic emitters and multiple ultrasonic receivers may be axially aligned (e.g., across the gas flow path which may be perpendicular to the axial alignment).

In use, an ultrasonic sound wave from emitter166may be directed through oxygen enriched air disposed in chamber162to receiver168. The ultrasonic oxygen sensor165may be configured to detect the speed of sound through the oxygen enriched air to determine the composition of the oxygen enriched air. The speed of sound is different in nitrogen and oxygen, and in a mixture of the two gases, the speed of sound through the mixture may be an intermediate value proportional to the relative amounts of each gas in the mixture. In use, the sound at the receiver168is slightly out of phase with the sound sent from emitter166. This phase shift is due to the relatively slow velocity of sound through a gas medium as compared with the relatively fast speed of the electronic pulse through wire. The phase shift, then, is proportional to the distance between the emitter and the receiver and inversely proportional to the speed of sound through the expansion chamber162. The density of the gas in the chamber affects the speed of sound through the expansion chamber and the density is proportional to the ratio of oxygen to nitrogen in the expansion chamber. Therefore, the phase shift can be used to measure the concentration of oxygen in the expansion chamber. In this manner the relative concentration of oxygen in the accumulator may be estimated as a function of one or more properties of a detected sound wave traveling through the accumulator.

In some implementations, multiple emitters166and receivers168may be used. The readings from the emitters166and receivers168may be averaged to reduce errors that may be inherent in turbulent flow systems. In some implementations, the presence of other gases may also be detected by measuring the transit time and comparing the measured transit time to predetermined transit times for other gases and/or mixtures of gases.

The sensitivity of the ultrasonic sensor system may be increased by increasing the distance between the emitter166and receiver168, for example to allow several sound wave cycles to occur between emitter166and the receiver168. In some implementations, if at least two sound cycles are present, the influence of structural changes of the transducer may be reduced by measuring the phase shift relative to a fixed reference at two points in time. If the earlier phase shift is subtracted from the later phase shift, the shift caused by thermal expansion of expansion chamber162may be reduced or cancelled. The shift caused by a change of the distance between the emitter166and receiver168may be approximately the same at the measuring intervals, whereas a change owing to a change in oxygen concentration may be cumulative. In some implementations, the shift measured at a later time may be multiplied by the number of intervening cycles and compared to the shift between two adjacent cycles. Further details regarding sensing of oxygen in the expansion chamber may be found, for example, in U.S. Published Patent Application No. 2009-0065007, published Mar. 12, 2009, and entitled “Oxygen Concentrator Apparatus and Method”, which is incorporated herein by reference.

Flow rate sensor185may be used to determine the flow rate of gas flowing through the outlet system. Flow rate sensors that may be used include, but are not limited to: diaphragm/bellows flow meters; rotary flow meters (e.g. Hall effect flow meters); turbine flow meters; orifice flow meters; and ultrasonic flow meters. Flow rate sensor185may be coupled to controller400. The rate of gas flowing through the outlet system may be an indication of the breathing volume of the user. Changes in the flow rate of gas flowing through the outlet system may also be used to determine a breathing rate of the user. Controller400may generate a control signal or trigger signal to control actuation of supply valve160. Such control of actuation of the supply valve may be based on the breathing rate and/or breathing volume of the user, as estimated by flow rate sensor185.

In some implementations, ultrasonic sensor165and, for example, flow rate sensor185may provide a measurement of an actual amount of oxygen being provided. For example, flow rate sensor185may measure a volume of gas (based on flow rate) provided and ultrasonic sensor165may provide the concentration of oxygen of the gas provided. These two measurements together may be used by controller400to determine an approximation of the actual amount of oxygen provided to the user.

Oxygen enriched air passes through flow rate sensor185to filter187. Filter187removes bacteria, dust, granule particles, etc. prior to providing the oxygen enriched air to the user. The filtered oxygen enriched air passes through filter187to connector190. Connector190may be a “Y” connector coupling the outlet of filter187to pressure sensor194and delivery conduit192. Pressure sensor194may be used to monitor the pressure of the gas passing through conduit192to the user. In some implementations, pressure sensor194is configured to generate a signal that is proportional to the amount of positive or negative pressure applied to a sensing surface. Changes in pressure, sensed by pressure sensor194, may be used to determine a breathing rate of a user, as well as the onset of inhalation (also referred to as the trigger instant) as described below. Controller400may control actuation of supply valve160based on the breathing rate and/or onset of inhalation of the user. In an implementation, controller400may control actuation of supply valve160based on information provided by either or both of the flow rate sensor185and the pressure sensor194.

Oxygen enriched air may be provided to a user through conduit192. In an implementation, conduit192may be a silicone tube. Conduit192may be coupled to a user using an airway delivery device196, as depicted inFIGS.7and8. Airway delivery device196may be any device capable of providing the oxygen enriched air to nasal cavities or oral cavities. Examples of airway delivery devices include, but are not limited to: nasal masks, nasal pillows, nasal prongs, nasal cannulas, and mouthpieces. A nasal cannula airway delivery device196is depicted inFIG.7. Airway delivery device196is positioned proximate to a user's airway (e.g., proximate to the user's mouth and or nose) to allow delivery of the oxygen enriched air to the user while allowing the user to breathe air from the surroundings.

In an alternate implementation, a mouthpiece may be used to provide oxygen enriched air to the user. As shown inFIG.8, a mouthpiece198may be coupled to oxygen concentrator100. Mouthpiece198may be the only device used to provide oxygen enriched air to the user, or a mouthpiece may be used in combination with a nasal airway delivery device196(e.g., a nasal cannula). As depicted inFIG.8, oxygen enriched air may be provided to a user through both a nasal airway delivery device196and a mouthpiece198.

Mouthpiece198is removably positionable in a user's mouth. In one implementation, mouthpiece198is removably couplable to one or more teeth in a user's mouth. During use, oxygen enriched air is directed into the user's mouth via the mouthpiece. Mouthpiece198may be a night guard mouthpiece which is molded to conform to the user's teeth. Alternatively, mouthpiece may be a mandibular repositioning device. In an implementation, at least a majority of the mouthpiece is positioned in a user's mouth during use.

During use, oxygen enriched air may be directed to mouthpiece198when a change in pressure is detected proximate to the mouthpiece. In one implementation, mouthpiece198may be coupled to a pressure sensor194. When a user inhales air through the user's mouth, pressure sensor194may detect a drop in pressure proximate to the mouthpiece. Controller400of oxygen concentrator100may control release of a bolus of oxygen enriched air to the user at the onset of inhalation.

During typical breathing of an individual, inhalation may occur through the nose, through the mouth or through both the nose and the mouth. Furthermore, breathing may change from one passageway to another depending on a variety of factors. For example, during more active activities, a user may switch from breathing through their nose to breathing through their mouth, or breathing through their mouth and nose. A system that relies on a single mode of delivery (either nasal or oral), may not function properly if breathing through the monitored pathway is stopped. For example, if a nasal cannula is used to provide oxygen enriched air to the user, an inhalation sensor (e.g., a pressure sensor or flow rate sensor) is coupled to the nasal cannula to determine the onset of inhalation. If the user stops breathing through their nose, and switches to breathing through their mouth, the oxygen concentrator100may not know when to provide the oxygen enriched air since there is no feedback from the nasal cannula. Under such circumstances, oxygen concentrator100may increase the flow rate and/or increase the frequency of providing oxygen enriched air until the inhalation sensor detects an inhalation by the user. If the user switches between breathing modes often, the default mode of providing oxygen enriched air may cause the oxygen concentrator100to work harder, limiting the portable usage time of the system.

In an implementation, a mouthpiece198is used in combination with a nasal airway delivery device196(e.g., a nasal cannula) to provide oxygen enriched air to a user, as depicted inFIG.8. Both mouthpiece198and nasal airway delivery device196are coupled to an inhalation sensor. In one implementation, mouthpiece198and nasal airway delivery device196are coupled to the same inhalation sensor. In an alternate implementation, mouthpiece198and nasal airway delivery device196are coupled to different inhalation sensors. In either implementation, the inhalation sensor(s) may detect the onset of inhalation from either the mouth or the nose. Oxygen concentrator100may be configured to provide oxygen enriched air to the delivery device (i.e. mouthpiece198or nasal airway delivery device196) proximate to which the onset of inhalation was detected. Alternatively, oxygen enriched air may be provided to both mouthpiece198and nasal airway delivery device196if onset of inhalation is detected proximate either delivery device. The use of a dual delivery system, such as depicted inFIG.8may be particularly useful for users when they are sleeping and may switch between nose breathing and mouth breathing without conscious effort.

Controller System

Operation of oxygen concentrator100may be performed automatically using an internal controller400coupled to various components of the oxygen concentrator100, as described herein. Controller400includes one or more processors410and internal memory420, as depicted inFIG.2. Methods used to operate and monitor oxygen concentrator100may be implemented by program instructions stored in internal memory420or an external memory medium coupled to controller400, and executed by one or more processors410. A memory medium may include any of various types of memory devices or storage devices. The term “memory medium” is intended to include an installation medium, e.g., a Compact Disc Read Only Memory (CD-ROM), floppy disks, or tape device; a computer system memory or random access memory such as Dynamic Random Access Memory (DRAM), Double Data Rate Random Access Memory (DDR RAM), Static Random Access Memory (SRAM), Extended Data Out Random Access Memory (EDO RAM), Random Access Memory (RAM), etc.; or a non-volatile memory such as a magnetic medium, e.g., a hard drive, or optical storage. The memory medium may comprise other types of memory as well, or combinations thereof. In addition, the memory medium may be located proximate to the controller400by which the programs are executed, or may be located in an external computing device that connects to the controller400over a network, such as the Internet. In the latter instance, the external computing device may provide program instructions to the controller400for execution. The term “memory medium” may include two or more memory media that may reside in different locations, e.g., in different computing devices that are connected over a network.

In some implementations, controller400includes processor410that includes, for example, one or more field programmable gate arrays (FPGAs), microcontrollers, etc. included on a circuit board disposed in oxygen concentrator100. Processor410is configured to execute programming instructions stored in memory420. In some implementations, programming instructions may be built into processor410such that a memory external to the processor410may not be separately accessed (i.e., the memory420may be internal to the processor410).

Processor410may be coupled to various components and sub-systems of oxygen concentrator100(e.g., sub-systems associated with1704,1706,1708ofFIG.17), including, but not limited to compression system200, one or more of the pumps or valves used to control moisture and/or fluid flow through the system (e.g., valves122,124,132,134,152,154,160), oxygen sensor165, pressure sensor194, flow rate sensor185, temperature sensors (not shown), fan172, and any other component that may be electrically controlled. In some implementations, a separate processor (and/or memory) may be coupled to one or more of the components.

Controller400is configured (e.g., programmed by program instructions) to operate oxygen concentrator100and is further configured to monitor the oxygen concentrator100such as for malfunction states or other process information. For example, in one implementation, controller400is programmed to trigger an alarm if the system is operating and no breathing is detected by the user for a predetermined amount of time. For example, if controller400does not detect a breath for a period of 75 seconds, an alarm LED may be lit and/or an audible alarm may be sounded. If the user has truly stopped breathing, for example, during a sleep apnea episode, the alarm may be sufficient to awaken the user, causing the user to resume breathing. The action of breathing may be sufficient for controller400to reset this alarm function. Alternatively, if the system is accidentally left on when delivery conduit192is removed from the user, the alarm may serve as a reminder for the user to turn oxygen concentrator100off.

Controller400is further coupled to oxygen sensor165, and may be programmed for continuous or periodic monitoring of the oxygen concentration of the oxygen enriched air passing through expansion chamber162. A minimum oxygen concentration threshold may be programmed into controller400, such that the controller lights an LED visual alarm and/or an audible alarm to warn the user of the low concentration of oxygen.

Controller400is also coupled to internal power supply180and may be configured to monitor the level of charge of the internal power supply. A minimum voltage and/or current threshold may be programmed into controller400, such that the controller lights an LED visual alarm and/or an audible alarm to warn the user of low power condition. The alarms may be activated intermittently and at an increasing frequency as the battery approaches zero usable charge.

The controller of the POC may implement compressor control to regulate pressure in the system. Thus, the POC may be equipped with a pressure sensor such as in the accumulator downstream of the sieve beds. The controller400in the POC100can control adjusting of the speed of the compressor using signals from the pressure sensor as well as a motor speed sensor such as in one or more modes. In this regard, the controller may implement dual control modes, designated a coarse pressure regulation mode and a fine pressure regulation mode. The coarse pressure regulation mode may be implemented for changing between the different flow rate settings (or “flow settings”) of the POC and for starting/initial activation. The fine pressure regulation mode may then take over upon completion of each operation of the coarse pressure regulation mode.

Additionally, the controller of the POC may be configured to implement bolus control to regulate bolus size in the system, which may optionally be implemented without use of a flow rate sensor of the POC. For example, the POC may be equipped with a pressure sensor, such as in the accumulator downstream of the sieve beds, and regulate bolus size, generated by the POC, as a function of pressure. Such regulation of bolus size may be a function of pressure and valve timing.

Control Panel

Control panel600serves as an interface between a user and controller400to allow the user to initiate predetermined operation modes of the oxygen concentrator100and to monitor the status of the system.FIG.14depicts an implementation of control panel600. Charging input port605, for charging the internal power supply180, may be disposed in control panel600.

In some implementations, control panel600may include buttons to activate various operation modes for the oxygen concentrator100. For example, control panel may include power button610, flow rate setting buttons620to626, active mode button630, sleep mode button635, altitude button640, and a battery check button650. In some implementations, one or more of the buttons may have a respective LED that may illuminate when the respective button is pressed, and may power off when the respective button is pressed again. Power button610may power the system on or off. If the power button is activated to turn the system off, controller400may initiate a shutdown sequence to place the system in a shutdown state (e.g., a state in which both canisters are pressurized). Flow rate setting buttons620,622,624, and626allow a flow rate of oxygen enriched air to be selected (e.g., 0.2 LPM by button620, 0.4 LPM by button622, 0.6 LPM by button624, and 0.8 LPM by button626). Altitude button640may be activated when a user is going to be in a location at a higher elevation than the oxygen concentrator100is regularly used by the user.

Battery check button650initiates a battery check routine in the oxygen concentrator100which results in a relative battery power remaining LED655being illuminated on control panel600.

A user may have a low breathing rate or depth if relatively inactive (e.g., asleep, sitting, etc.) as estimated by comparing the detected breathing rate or depth to a threshold. The user may have a high breathing rate or depth if relatively active (e.g., walking, exercising, etc.). An active/sleep mode may be estimated automatically and/or the user may manually indicate active mode or sleep mode by pressing button630for active mode or button635for sleep mode.

Moisture Management Systems

As previously mentioned, the POC100may implement a moisture management system with one or more components for managing moisture (or moisture conditioning). Such a system may be implemented to remove moisture from incoming ambient air (i.e. feed gas) and re-introduce such moisture to outgoing oxygen-enriched air for breathing by a user. Such a system may be considered in relation to the gas flow diagram ofFIG.17. As illustrated, ambient air AA may contain moisture due to ambient humidity. Consequently, humid ambient air HAA may be drawn into the POC100system by a compressor of the compression system200(not shown inFIG.17) so as to become a flow of pressurized humid ambient air PHAA. Optionally, the feed gas may be applied to a contaminant filtration module1702(e.g., a filter) as previously described so as to remove one or more airborne contaminants from the incoming ambient air. For example, the contaminant filtration module1702may be configured to remove dust and/or allergen particles from the humid ambient air HAA prior to the humid ambient air HAA entering the compressor of the compression system200. Subsequently, the resultant cleaned humid ambient air HAA which becomes pressurized humid ambient air PHAA may be applied to a pathway of a moisture separation sub-system1704(e.g., a separator). The pathway of the separator1704may be configured to remove moisture M from the pressurized humid ambient air PHAA so as to produce a drier ambient air DAA. As previously described, such drier ambient air DAA may then serve as the feed gas for the gas adsorption processes (e.g., PSA cycles) in the sieve bed(s) as previously described in the concentration sub-system1708of the POC100. Thus, the concentration sub-system1708may produce a dried oxygen enriched air DOEA. The removed moisture M may optionally be applied to a pathway of a moisture transport sub-system1706(e.g., an aqueduct) so that the moisture M may be transferred to a location suitable for re-application of the removed moisture M into the product gas produced by the concentration sub-system1708. The pathway of the aqueduct1706may transport the moisture M to a moisture containment module1710(e.g., a reservoir such as a containment tank) or other location where the moisture M may be collected. Such a reservoir1710may include a pathway for re-applying the moisture M of the reservoir1710(or collector1710) to the dried oxygen enriched air DOEA. Thus, the reservoir1710may humidify the dried oxygen enriched air DOEA to produce a humidified oxygen enriched air HOEA. The humidified oxygen enriched air HOEA may then be released from the POC100at an outlet port174. Consequently, oxygen enriched air with moisture OEAM may be released to the patient or user of the POC100.

The separator1704may have various configurations for drawing moisture out of the humid ambient air. For example, the separator1704may include a pathway with a wicking material or other porous or hydrophilic material, or water vapor permeable membrane, to promote water separation from air. In some implementations, the wicking material or membrane of the separator1704, or a conduit pathway of the separator1704, may be formed of a Nafion™ polymer, which is a copolymer of tetrafluoroethylene (Teflon®) and perfluoro-3,6-dioxa-4-methyl-7-octene-sulfonic acid. The separator1704may optionally include a condenser, such as a condenser coil and/or material. Portions of the condenser may be in the pathway of the separator1704to provide a level of cooling of the feed gas in the separator1704. For example, such a condenser may serve as a circulator of a cooling fluid so that the condenser may have a relatively cool temperature when compared to the feed gas. Thus, the condenser may optionally include a pump or compressor for moving a cooling fluid/gas through the condenser via a coil portion. Such components may be operated or controlled by one or more control signals generated by controller400of the POC100, so as to maintain a desired temperature set point in the separator1704. Thus, the separator1704may optionally include a temperature sensor (not shown) to generate a temperature signal associated with the temperature in the separator1704for the controller400so that the controller may implement a temperature control loop with the condenser and temperature sensor.

In some implementations, the pathway of the separator1704may be circuitous. Such a pathway may help to maximize contact surface area between the feed gas and the moisture wicking material or membrane of the pathway. In some implementations, the pathway of the separator1704may also be configured as a centrifuge. Thus, the pathway may be configured to induce the feed gas into a centrifugal flow within the separator1704. Such a centrifugal flow may thereby force the feed gas to circulate so as to promote a radial directional force within the separator1704. Such forced circulation may increase the interaction between the feed gas and an outer structure or material, such as a cylindrical membrane and/or wicking material, of the separator1704so that it attracts moisture from the feed gas. In some implementations, the separator1704may include various elements to induce such a centrifugal flow. For example, the pathway of the separator1704may include a helical and/or spiral flow path to induce the centrifugal flow. Optionally, the pathway may include a spin inducer or other flow director(s) such as fin(s) or other similar structure to guide such a flow. Optionally, the pathway may also be formed with a volute or be formed as a coil.

Examples of components of such systems for moisture conditioning may be considered in more detail in relation to the illustrated implementations shown inFIGS.18to21. In the cross-sectional illustration of the example ofFIG.18, a separator1704includes flow directors1820to implement a helical flow path1822. The flow directors1820induce a centrifugal flow CF within the separator1704. Such flow directors may be formed as a helical ring about an inner chamber surface or conduit surface of the separator1704. Such flow directors may optionally be formed of a material of a conduit of the separator1704or other material described in more detail herein. Moisture from the pressurized humid ambient air PHAA may form in the helical flow path and wick into a wicking or hydrophilic surface1830. The wicking or hydrophilic material such as at the surface1830may be configured as an inner cylindrical surface of the separator that encompasses the helical flow path1822. Moisture M may be absorbed by such a wicking surface as the pressurized humid ambient air PHAA rotates along the pathway of the separator1704. Such pressurized state within the separator may also assist the outward wicking of the moisture.

Moisture M wicked or absorbed at the surface1830may be transferred to a reservoir1710shown as a tank or other container which may be configured as a pass over humidifier. The reservoir1710may include a pathway through which the dried oxygen enriched air DOEA from the accumulator106of the POC100becomes humidified oxygen enriched air HOEA. Along such a pathway, the dried oxygen enriched air DOEA may wick moisture from the contained moisture of the reservoir1710. In the implementation ofFIG.18, collected moisture from the surface1830is transported via an aqueduct1706. Such an aqueduct may optionally include one or more conduits (e.g., tubing), one or more valves (e.g., gate valves) and/or one or more pumps to induce the moisture to collect in the reservoir1710. Such valve components may be moisture resistant. Optionally, such moisture may gravitate through the aqueduct as a result of a relatively lower position of the reservoir1710. In some implementations, pressure from the compression system may be applied (e.g., periodically) via a conduit and a valve controlled by the controller to periodically induce transport of the moisture to the reservoir1710via the aqueduct1706. In some implementations, the reservoir1710may include a heating element1860, such as a heating coil, to warm the collected moisture to improve wicking by the product gas. The product gas may be released in a bolus or otherwise from the accumulator106by operation of the supply valve160(not shown inFIG.18) as previously described (seeFIG.6), to the pathway of the reservoir1710. The heating element1860may also serve to warm the product gas in the reservoir1710for user comfort. With such a system, the moisture drawn from the feed gas in the separator is effectively recycled back to the product gas via the pathways of the system. Optionally, such a reservoir1710may additionally include a water inlet (not shown) such as for adding water to the reservoir from a water supply external to the POC100. For example, a user may pour water into an aperture of the housing of the POC100to add additional water to the reservoir1710.

FIG.19shows another implementation of a moisture conditioning system similar to the example ofFIG.18. However, the implementation ofFIG.19additionally implements a condenser, such as a condensor as previously described. A condenser coil1940may be applied to the helical flow path1822to lower gas temperature within the separator1704. Such a lowering of temperature can increase moisture condensation within the separator1704. Such a condenser coil may helically encircle a conduit of the separator1704. Optionally, the condenser coil may be located at the surface1830, and may follow the helical pathway. When at the surface1830it may more directly assist in lowering the temperature of the wicking material/structure of the surface1830and thereby promote condensation at the material of the surface1830.

FIG.20shows another implementation of a moisture conditioning system similar to the example ofFIG.19. However, the implementation ofFIG.20more directly integrates its reservoir1710and separator1704. In this implementation, an extended aqueduct1706is not required due to the proximity of the separator1704and reservoir1710. In such an implementation, the moisture collects inside the reservoir1710at an outer, opposing side surface of the wicking material surface1830. Thus, moisture transfers through the wicking material from the inner surface side of the wicking material surface1830that is inside the separator to thereby arrive in the reservoir1710. As such, the moisture transport sub-system1706may be a material, such as the material through which the moisture moves including the wicking material surface1830. In such an implementation, conduits, valves and/or pumps are not required for the aqueduct1706. Movement of dried oxygen enriched air DOEA through reservoir1710wicks moisture from the outer, opposing side surface of the material surface1830. Such recycling of the moisture from the material of the surface1830and back into the product gas (i.e., dried oxygen enriched air DOEA) increases the performance of the wicking material at the surface1830as the wicking material dries on the reservoir side so as to promote further wicking of moisture from the feed gas within the separator1704ofFIG.20as the wicking material acts to achieve a wetted equilibrium.

Another example moisture conditioning system is illustrated inFIGS.21A and21B, as well asFIG.22. The figures illustrate an implementation of the present technology that is similar toFIG.20which includes a more directly proximate relationship between the separator1704and reservoir1710. As illustrated, the separator1704is configured with a concentric helical formation utilizing multiple layers, such as two or more of an inner layer2152, an outer layer2150and an outer membrane2154. In this configuration, the two or more of the layers of the separator1704may serve as flow directors to form a helical pathway that induces the centrifugal flow as previously described. The moisture transport sub-system1706may then be made up of one or more layers of material(s), which may be different materials, that serve as a pathway for moisture to move through any two or more of the inner layer2152, the outer layer2150and the outer membrane2154. As such, the moisture transport sub-system1706may form part of the separator1704. In some implementations, the inner layer2152may be directly adjacent to the outer layer2150. In some implementations, the outer membrane2154may be directly adjacent to the outer layer2150. In some implementations, an inner layer2152of the concentric helix may be formed with a condensing material (e.g., a circulator coil). Moreover, an outer layer2150of the concentric helix may be formed of a wicking material. In some implementations, the sequence of the inner layer2152and the outer layer2150may be interchanged such that the inner layer2152is an outer layer and the outer layer2150is an inner layer. The concentric helix may have a further outer membrane2154structure. For example, the separator1704may include a water vapor permeable membrane. The membrane may form a cylindrical structure that may serve as an outer boundary for the pathway of the separator1704. For example, an inner surface of the water vapor permeable membrane may form a cylindrical surface around the plurality of layers of the concentric helix that form the pathway of the separator1704. Moreover, an outer surface of the water vapor permeable membrane may form a cylindrical inner surface of a pathway of the reservoir1710. Thus, the porous material of membrane2154may serve as one or more ducts to transfer moisture from the separator1704to the reservoir1710. Thus, the pathway of the reservoir1710ofFIG.21A, like that ofFIG.20, permits wicking of moisture from an outside surface of the membrane2154into the product gas moving through the reservoir1710. Although the pathway of the reservoir1710is shown as a generally direct path (e.g., non-circuitous), in some implementations, the pathway through the reservoir may optionally be implemented with one or more flow directors to induce a less direct flow (e.g., helical flow) through the reservoir. Such flow directors may form a helical path through the reservoir1710to increase the interaction (surface contact) between product gas and the collected moisture of the reservoir1710. Such a modification may similarly be implemented with the moisture conditioning systems illustrated in remaining figures described herein (e.g.,FIGS.18-20).

In the illustrated example ofFIG.21A, the gas flow direction (arrow DOEA) through the pathway of the reservoir1710is illustrated in a generally opposing direction to that of the gas flow pathway (arrows PHAA) through the separator1704. However, in some implementations, such directions may be reversed. Moreover, in some implementations, the flows of both may move in a generally common direction.

As previously mentioned, the example moisture conditioning system shown in inFIG.22is similar to the implementation ofFIG.21A. Thus, the separator1704is configured with a concentric helical formation utilizing multiple layers such that the layers serve as flow directors to form a helical pathway for inducing the centrifugal flow as previously described. However, unlike the implementation ofFIG.21A, the separator1704ofFIG.22has a helical shape formed with a tapered end. The tapering thereby forms a vortex structure (e.g., a conic structure or a cone) such that the flow path spirals inward toward a central area as the flow path helically advances through the separator. In such an example, a first end FE of the separator1704may have an outer diameter (OD1) such as a diameter associated with an inner side surface of the membrane2154. Moreover, a second end SE of the separator1704may have another outer diameter (OD2) such as another diameter associated with an inner side surface of the membrane2154. For example, the diameters (OD1and OD2) may extend across a cavity within a conic surface of the separator1704that is formed by the inner surface side of the membrane2154. Thus, each diameter may extend from the inner surface side on one side of the cavity to an inner surface side on an opposing side of the cavity. Each diameter may then pass through an imaginary central axis CA that is a central axis of the conic surface of the separator1704that passes through the cavity of the conic surface. In order to form such a vortex structure, the outer diameter (OD1) associated with a first end of the separator may be larger than the outer diameter (OD2) associated with a second end of the separator. Such a structure may assist with encouraging moisture collection of condensed moisture toward a lower portion of the structure.

Methods of Operating the POC

The methods of operating and monitoring the POC100described below may be executed by the one or more processors, such as the one or more processors410of the controller400, configured by program instructions, such as including, as previously described, the one or more functions and/or associated data corresponding thereto, stored in a memory such as the memory420of the POC100. Alternatively, some or all of the steps of the described methods may be similarly executed by one or more processors of an external computing device to which the controller is connected via the transceiver430. In this latter implementation, the processors410may be configured by program instructions stored in the memory420of the POC100to transmit to the external computing device the measurements and parameters necessary for the performance of those steps that are to be carried out at the external computing device.

The main use of an oxygen concentrator100is to provide supplemental oxygen to a user. One or more flow rate settings may be selected on a control panel600of the oxygen concentrator100, which then will control operations to achieve production of the oxygen enriched air according to the selected flow rate setting. In some implementations, a plurality of flow rate settings may be implemented (e.g., five flow rate settings). As described in more detail herein, the controller may implement a POD (pulsed oxygen delivery) or demand mode of operation to regulate size of one or more released boluses to achieve delivery of the oxygen enriched air according to the selected flow rate setting.

In order to maximise the effect of the delivered oxygen enriched air, controller400may be programmed to synchronise release of each bolus of the oxygen enriched air with the user's inhalations. Releasing a bolus of oxygen enriched air to the user as the user inhales may prevent wastage of oxygen by not releasing oxygen, for example, when the user is exhaling. For concentrators that operate in POD mode, the flow rate settings on the control panel600may correspond to minute volumes (bolus volume multiplied by breathing rate per minute) of delivered oxygen, e.g. 0.2 LPM, 0.4 LPM, 0.6 LPM, 0.8 LPM, 1.1 LPM.

Oxygen enriched air produced by oxygen concentrator100is stored in an oxygen accumulator106and, in POD mode, released to the user as the user inhales. The amount of oxygen enriched air provided by the oxygen concentrator100is controlled, in part, by supply valve160. In an implementation, supply valve160is opened for a sufficient amount of time to provide the appropriate amount of oxygen enriched air, as estimated by controller400, to the user. In order to minimize the wastage of oxygen, the oxygen enriched air may be provided as a bolus soon after the onset of a user's inhalation is detected. For example, the bolus of oxygen enriched air may be provided in the first few milliseconds of a user's inhalation.

In an implementation, pressure sensor194may be used to determine the onset of inhalation by the user. For example, the user's inhalation may be detected by using pressure sensor194. In use, conduit192for providing oxygen enriched air is coupled to a user's nose and/or mouth through the nasal airway delivery device196and/or mouthpiece198. The pressure in conduit192is therefore representative of the user's airway pressure and therefore indicative of user respiration. At the onset of an inhalation, the user begins to draw air into their body through the nose and/or mouth. As the air is drawn in, a negative pressure is generated at the end of the conduit192, due, in part, to the venturi action of the air being drawn across the end of the conduit. Controller400analyses the pressure signal from the pressure sensor194to detect a drop in pressure indicating the onset of inhalation. Upon detection of the onset of inhalation, supply valve160is opened to release a bolus of oxygen enriched air from the accumulator106. A positive change or rise in the pressure indicates an exhalation by the user, upon which the release of oxygen enriched air is discontinued. In one implementation, when a positive pressure change is sensed, supply valve160is closed until the next onset of inhalation is detected. Alternatively, supply valve160may be closed after a predetermined interval known as the bolus duration. By measuring the intervals between adjacent onsets of inhalation, the user's breathing rate may be estimated. By measuring the intervals between onsets of inhalation and the subsequent onsets of exhalation, the user's inspiratory time may be estimated. Thus, the user's breathing rate or respiration rate may be detected with a signal from the pressure sensor and/or a flow rate sensor.

In other implementations, the pressure sensor194may be located in a sensing conduit that is in pneumatic communication with the user's airway, but separate from the delivery conduit192. In such implementations the pressure signal from the pressure sensor194is therefore also representative of the user's airway pressure.

In some implementations, the sensitivity of the pressure sensor194may be affected by the physical distance of the pressure sensor194from the user, especially if the pressure sensor194is located in oxygen concentrator100and the pressure difference is detected through the conduit192coupling the oxygen concentrator100to the user. In some implementations, the pressure sensor194may be placed in the airway delivery device196used to provide the oxygen enriched air to the user. A signal from the pressure sensor194may be provided to controller400in the oxygen concentrator100electronically via a wire or through telemetry such as through Bluetooth™ or other wireless technology.

In some implementations, if the user's current activity level, such as that estimated using the detected user's breathing rate, exceeds a predetermined threshold, controller400may implement an alarm (e.g., visual and/or audio) to warn the user that the current breathing rate is exceeding the delivery capacity of the oxygen concentrator100. For example, the threshold may be set at 40 breaths per minute (BPM).

Glossary

Air: In certain forms of the present technology, air may be taken to mean atmospheric air, consisting of 78% nitrogen (N2), 21% oxygen (02), and 1% water vapour, carbon dioxide (CO2), argon (Ar), and other trace gases.

Oxygen enriched air: Air with a concentration of oxygen greater than that of atmospheric air (21%), for example at least about 50% oxygen, at least about 60% oxygen, at least about 70% oxygen, at least about 80% oxygen, at least about 90% oxygen, at least about 95% oxygen, at least about 98% oxygen, or at least about 99% oxygen. “Oxygen enriched air” is sometimes shortened to “oxygen”.

Medical Oxygen: Medical oxygen is defined as oxygen enriched air with an oxygen concentration of 80% or greater.

Ambient: In certain forms of the present technology, the term ambient will be taken to mean (i) external of the treatment system or user, and (ii) immediately surrounding the treatment system or user.

Flow rate: The volume (or mass) of air delivered per unit time. Flow rate may refer to an instantaneous quantity. In some cases, a reference to flow rate will be a reference to a scalar quantity, namely a quantity having magnitude only. In other cases, a reference to flow rate will be a reference to a vector quantity, namely a quantity having both magnitude and direction. Flow rate may be given the symbol Q. ‘Flow rate’ is sometimes shortened to simply ‘flow’ or ‘airflow’.

Patient: A person, whether or not they are suffering from a respiratory disorder.

Pressure: Force per unit area. Pressure may be expressed in a range of units, including cmH2O, g-f/cm2 and hectopascal. 1 cmH2O is equal to 1 g-f/cm2 and is approximately 0.98 hectopascal (1 hectopascal=100 Pa=100 N/m2=1 millibar˜0.001 atm). In this specification, unless otherwise stated, pressure is given in units of cmH2O.

General Remarks

The term “coupled” as used herein means either a direct connection or an indirect connection (e.g., one or more intervening connections) between one or more objects or components. The phrase “connected” means a direct connection between objects or components such that the objects or components are connected directly to each other. As used herein the phrase “obtaining” a device means that the device is either purchased or constructed.

Other Remarks

When a particular material is identified as being used to construct a component, obvious alternative materials with similar properties may be used as a substitute. Furthermore, unless specified to the contrary, any and all components herein described are understood to be capable of being manufactured and, as such, may be manufactured together or separately. It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include their plural equivalents, unless the context clearly dictates otherwise.

It is therefore to be understood that numerous modifications may be made to the illustrative examples and that other arrangements may be devised without departing from the spirit and scope of the technology. Further modifications and alternative implementations of various aspects of the present technology may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the technology. It is to be understood that the forms of the technology shown and described herein are to be taken as implementations. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the technology may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the technology. Changes may be made in the elements described herein without departing from the spirit and scope of the technology as described in the appended claims.

LABEL LIST