Abstract: An emergency ventilation system ventilates a patient and includes a chamber housing defining a breathing chamber; a piston; and a motor operably connected to the piston. The motor applies an exhalation force to move the piston in an exhalation direction applies an inhalation force to move the piston in an inhalation direction. The piston increases air in the breathing chamber as the exhalation force is applied and decreases air in the breathing chamber as the inhalation force is applied. An exhalation check valve allows airflow from the air source to the breathing chamber and not to allow airflow from the breathing chamber to the air source as the inhalation force is applied. An inhalation check valve allows airflow from the breathing chamber to the air output and not to allow airflow from the air output to the breathing chamber as the exhalation force is applied.

Abstract: The present invention provides an underwater breathing device. The device includes a canister having a pump installed therein, wherein air outside of the canister communicates with the interior of the canister via the pump; a mouthpiece; and an elongate tube interconnecting the interior of the canister and the mouthpiece. Methods of making and using the device are also disclosed.

Abstract: A ventilator includes a bidirectional breath detection airline and a flow outlet airline. The flow outlet airline includes an airline outlet. The flow outlet airline is configured to be connected to an invasive ventilator circuit or a noninvasive ventilator circuit. The breath detection airline includes airline inlet. The airline inlet is separated from the airline outlet of the flow outlet airline. The ventilator further includes a pressure sensor in direct fluid communication with the breath detection airline. The pressure sensor is configured to measure breathing pressure from the user and generate sensor data indicative of breathing by the user. The ventilator further includes a controller in electronic communication with the pressure sensor. The controller is programmed to detect the breathing by the user based on the sensor data received from the pressure sensor.

Abstract: [Object] To provide a compact, high-output actuator device allowing force control. [Solution] An actuator device 1000 includes an electromagnetic coil member 110 provided over a prescribed width on an outer circumference of a cylinder 100, and a movable element 200 slidable as a piston in the cylinder 100. The movable element 200 has a magnetic member 202, and is moved relatively by excitation of the electromagnetic coil member 110. Fluid is supplied to first and second chambers 106a and 106b such that when the movable element 200 is to be moved relatively, the movable element 200 is driven in the same direction.

Abstract: A ventilator that utilizes a cam lever to raise a piston within a cylinder is provided. The weight of the piston can push breathable air out of the cylinder to a patient. A motor assembly provides the only electronic component necessary to operate the ventilator. Adjustments to volume, speed, and pressure can be made by adjusting mechanical components of the ventilator.

Abstract: A device that helps clear a fluid or other material lodged in a person's throat has a barrel with an open proximal end and an opening laden distal end. A plunger is slidably disposed within the barrel such that the plunger, by being manually drawn outwardly, creates suction within the barrel drawing air through the opening. A single or multi-section tube, flexible on at least its distal end, is fluid flow connected to the opening and has a face mask along its length. The distal end of the tube is intubated with a person proximate the fluid or other material so that as the plunger is drawn outwardly through the barrel, the suction created within the barrel causes air to be drawing in through the tube and into the barrel thereby helping draw out and dislodge the fluid or other material. A backflow valve located on the barrel helps clear the barrel of such things as vomit that might have been drawn into the barrel.

Abstract: An air pump apparatus is provided which uses an electric actuator that can electrically operate a pneumatic device such as a suction pad or air chuck. The air pump apparatus includes an air cylinder having a built-in piston, and an electric actuator configured to move the piston linearly and relatively to the air cylinder, using the electric motor as a drive source. Air under negative pressure and/or positive pressure generated by the electric actuator causing the piston of the air cylinder to move linearly is used to operate a pneumatic device.

Abstract: A seal is provided for a chassis assembly of a flow generator configured to provide a flow of breathable gas. The chassis assembly includes an upper chassis and a lower chassis. The seal includes a blower receptacle sealing portion configured to seal a blower receptacle of the chassis assembly configured to receive a blower configured to generate the flow of breathable gas; a flow sensor sealing portion configured to seal a flow sensor provided in the chassis assembly and configured to measure the flow of breathable gas; a blower mount configured to receive a portion of the blower and mount the blower to the seal; and a blower mount suspension configured to connect the blower mount to the blower receptacle sealing portion, wherein in an assembled condition the seal and the chassis assembly define a flow path from an inlet of the chassis assembly to the blower receptacle of the chassis assembly to an outlet of the chassis assembly.

Abstract: A control system for a high frequency oscillating ventilator (HFOV) includes an oscillator controller and a mean airway pressure (MAP) controller. The HFOV includes a reciprocating piston which is adapted to generate positive and negative pressure waves for delivery to a patient airway. The oscillator controller comprises a pair of closed loop control circuits including an oscillator pressure loop and a centering loop which are collectively adapted to regulate frequency and amplitude of piston reciprocations and centering of the piston. The MAP controller comprises a closed loop control circuit that is adapted for regulating MAP at the patient utilizing feedback in the form of patient circuit pressure. Likewise, the oscillator controller utilizes patient circuit pressure as well as piston displacement feedback in order to regulate movement of the piston.

Abstract: A breathable gas supply apparatus for a patient features a breathable gas supply system and a respiratory mask assembly in communication with the breathable gas supply system. The breathable gas supply system provides a supply of breathable gas to the respiratory mask assembly and removes a supply of exhaled gas from the respiratory mask assembly. The breathable gas supply system includes a housing having an inspiration chamber and an exhalation chamber and a movable structure in communication with the inspiration and exhalation chambers. The movable structure moves in phase with a respiratory cycle of a patient. In one preferred embodiment, the breathable gas supply system includes a second movable structure, which moves in response to a phase of the respiratory cycle of the patient. In another one preferred embodiment, the breathable gas supply system is powered to assist the patient's respiratory effort.

Abstract: A device for treating a patient suffering from obstructive sleep apnea or snoring can include an expiratory valve connected to a manifold. The expiratory valve can include a body portion including a feedback port configured to be connected to an air flow generator. The expiratory valve can include a plunger at least partially disposed in the body portion. The expiratory valve can include a pressurizing chamber positioned between an end of the plunger and an end of the expiratory valve. The pressurizing chamber can be configured to receive air from the air flow generator through the feedback port.

Abstract: An aspiration and resuscitation system which is useable to perform aspiration and/or resuscitation procedures on living beings, particularly small animals, and most particularly newborn small animals such as puppies and kittens. The system includes an aspirator and a resuscitator. Each includes a separable pump and animal interface mask. Further disclosed are aspiration and resuscitation methods using the disclosed apparatus.

Abstract: An adjustable volume control manual resuscitation bag assembly includes a resuscitation bag, a volume control knob, a traction assembly operating in response to adjustment of the control knob, and a follower assembly including a bag compression limiting member and a follower which are moved in response to operation of the traction assembly to adjust and limit the volume of gas delivered by compression of the bag.

Abstract: A control system for a high frequency oscillating ventilator (HFOV) includes an oscillator controller and a mean airway pressure (MAP) controller. The HFOV includes a reciprocating piston which is adapted to generate positive and negative pressure waves for delivery to a patient airway. The oscillator controller comprises a pair of closed loop control circuits including an oscillator pressure loop and a centering loop which are collectively adapted to regulate frequency and amplitude of piston reciprocations and centering of the piston. The MAP controller comprises a closed loop control circuit that is adapted for regulating MAP at the patient utilizing feedback in the form of patient circuit pressure. Likewise, the oscillator controller utilizes patient circuit pressure as well as piston displacement feedback in order to regulate movement of the piston.

Abstract: Double acting respirator pump apparatus including a pump member reciprocable with respect to two pump chambers to deliver air to a patient via a respirator exhalation system, which also facilitates exhalation of the patient. The exhalation system has a pump unit that is operatively connected to an exhalation valve member and configured for selectively generating an air pressure sufficient for pressurizing one side of the valve member for closing the same when said exhalation system is operating in inhalation mode, and may be operated for opening to allow the patient to exhale therethrough.

Abstract: The method and system ventilates a patient's airway during the inspiratory phase and expiratory phase from a source of pressurized gas, typically from a compressor. The system and method supplies, to the patient airway during the inspiratory phase, a plurality of pulses of small volumes of gas from the gas source, and adds, in succession, pulses of small volumes of gas to provide successively greater volumes of gas successively increasing in pulsatile form the pressure of the gas in the patient's airway. This addition of successively greater volumes of gas serves to provide diffusive ventilation to the patient during the inspiratory phase, and, permits the patient to exhale during the expiratory phase.

Abstract: A pneumatic oxygen conserving device for supplying oxygen to a user via a single-tube cannula is described. Inhalation is sensed by negative pressure in an output line 11 which causes a sensing valve 21 to open, thus venting a main control volume 14 via vent line 22. This fall in pressure causes a main control valve 2 to open to supply a pulse of gas. This pressurizes the output line 11 which in turn causes the sensing valve 21 to close, thus preventing further venting. Volume 14 now re-pressurizes via line 15 and restrictor 16 and eventually reaches a level at which valve 2 closes and terminates the pulse of gas supplied to the user. A sensing delay valve 35 is incorporated in the vent line 22 from volume 14 to prevent the volume from venting after the first pulse has been delivered, until after the user has finished inhaling.

Abstract: Fluid flow regulators and fluid conservers are disclosed. An exemplary fluid conserver may be operated in one of an intermittent mode of operation and a continuous mode of operation. Further, the exemplary conserver provides at least two pulses of fluid in response to a first trigger, such as the inhalation of a patient.

Abstract: A process and a device for dosing a pharmaceutical agent, preferably a liquid, are proposed. To achieve an enhanced dosing accuracy, a first component that is produced in batches, such as a shaped seal, is combined with a second component, such as a guide pipe selected from a suitable group guide pipes, wherein the suitable group of second components is selected based on at least one decisively significant value of the respective batch first components and is distinguished by an essential value of the second component which will optimize the sealing between the first and second components.

Abstract: Disclosed are devices, systems, and methods, including an oxygen delivery device that includes an oxygen delivery module to produce at least concentrated oxygen, and a gas moving device to deliver air to the oxygen delivery module. The gas moving device includes at least one piston rotatable inside a first chamber defined in a housing, the rotational movement of the at least one piston inside the first chamber resulting in varying pressure generated in a first portion of the first chamber, and a vane member rigidly coupled to the at least one piston, the vane member being configured to move inside a vane chamber defined in the housing, the piston and the vane rigidly coupled to the piston define the first portion of the first chamber and a second portion of the first chamber.

Abstract: An oxygen concentrator comprises an oxygen reservoir and adsorbent columns that each have an inlet, an outlet, and a bed of adsorbent material. The concentrator also comprises an air inlet, an exhaust outlet, and a vacuum pump for pumping nitrogen rich gas from one of the column inlets to the exhaust outlet. A product control pump pumps oxygen rich gas from one of the column outlets to the oxygen reservoir. A control valve controls flow in and out of the columns by selectively connecting the air inlet to one column inlet, connecting the vacuum pump to another column inlet, and connecting the product control pump to a column outlet. A motor drives the vacuum pump and control valve to produce vacuum swing adsorption (VSA) cycles in which oxygen-rich product gas is separated and accumulated in the reservoir.

Abstract: A method and system of operating a trans-fill device. At least some of the illustrative embodiments are methods comprising generating an enriched gas stream from atmospheric air, and operating an intensifier which, when provided the enriched gas stream, produces a cylinder fill gas stream. The operating continues in the absence of the enriched gas stream being provided to the intensifier.

Abstract: Concentrated oxygen product gas is produced and delivered to a patient. Product gas is produced by (a) introducing ambient air into a first end of a column containing an adsorbent material that preferentially adsorbs nitrogen and removes oxygen-rich product gas out a second end of the column; (b) evacuating the column through the first end to remove adsorbed gas from the column; (c) repressurizing the column by introducing ambient air into the first end of the column until the column is near 1.0 atmosphere; and (d) repeating steps (a)-(c). Product gas is delivered as needed to the patient.

Abstract: A control system for a high frequency oscillating ventilator (HFOV) includes and oscillator controller and a mean airway pressure (MAP) controller. The HFOV includes a reciprocating piston which is adapted to generate positive and negative pressure waves for delivery to a patient airway. The oscillator controller comprises a pair of closed loop control circuits including an oscillator pressure loop and a centering loop which are collectively adapted to regulate frequency and amplitude of piston reciprocations and centering of the piston. The MAP controller comprises a closed loop control circuit that is adapted for regulating MAP at the patient utilizing feedback in the form of patient circuit pressure. Likewise, the oscillator controller utilizes patient circuit pressure as well as piston displacement feedback in order to regulate movement of the piston.

Abstract: A compressor suitable for use in a portable oxygen concentrator. In one exemplary embodiment, the compressor includes a crankshaft rotatable about a central axis and a plurality of diaphragm assemblies spaced apart around the central axis generally within a plane. The diaphragm assemblies include diaphragms movably mounted to respective housings to at least partially define chambers. A plurality of rods extend between respective diaphragms and the crankshaft. The rods are coupled to the crankshaft such that the rods are offset axially from one another along the central axis and are coupled to the diaphragms for cyclically increasing and decreasing pressure within the chambers as the crankshaft rotates about the central axis.

Abstract: A method of applying total liquid ventilation to a patient according to a ventilation cycle including inspiration and expiration profiles, comprises supplying oxygenated liquid to the patient's lungs, withdrawing liquid from the patient's lungs, and controlling independently supply of oxygenated liquid to the patient's lungs and withdrawal of liquid from the patient's lungs. This supply and withdrawal independent control comprises producing a ventilation cycle having independently controlled inspiration and expiration profiles. To carry out the method, a total liquid ventilator system comprises an inspiration pump for supplying oxygenated liquid to the patient's lungs, and an expiration pump for withdrawing liquid from the patient's lungs. A ventilation cycle control comprises first and second pump controllers connected to the inspiration and expiration pumps, respectively, to produce a ventilation cycle having independently controlled inspiration and expiration profiles.

Abstract: An actuating device for a manually operable medium dispenser includes an energy store for storing an actuating energy necessary to actuate the medium dispenser and a control device for liberating the actuating energy. The control device is being configured for a liberation of the actuating energy when a minimum energy stored in the energy store is exceeded.

Abstract: A gas regulator includes a delivery valve assembly having a delivery outlet and a delivery valve member engageable with the delivery outlet for controlling flow of a gas from a gas source. A timing gas chamber receives gas from the gas source. Gas pressure within the timing gas chamber controls the operation of the delivery valve member. An adjustment system controls the amount of time required for the gas to fill the timing gas chamber so as to control the length of time that the delivery valve assembly is opened to conserve gas. In other embodiments, a capacity adjustment system can adjust the capacity of a gas reservoir system.

Abstract: A removable gas separation cartridge which includes a housing containing three columns, each having an inlet port, an outlet port, and a bed of adsorbent material. The cartridge is removable from an oxygen concentrator which separates oxygen from ambient air by using a vacuum swing absorption process.

Abstract: A mechanical ventilator is provided with a piston-cylinder for performing an air displacement function and a buffer volume and associated output valve for providing an air metering function. The piston-cylinder may comprise a reciprocating arrangement, in which compressed air is supplied to the buffer volume with each stroke of the piston.

Abstract: A method and system of coordinating an intensifier and sieve beds. At least some of the illustrative embodiments are methods comprising coordinating control of an intensifier with cycles of a sieve bed fluidly coupled to the intensifier such that there is at least one low pressure stroke of the intensifier and at least one high pressure stroke of the intensifier during a fill cycle of the sieve bed.

Abstract: An apparatus (1) to assist a patient's respiration by delivering air to a patient through a mask (20), including a ramp module (10) connected to a control unit (2) to provide the control unit with a pressure value PM at mask (20), so that when apparatus (1) starts functioning, the pressure progressively rises until it reaches a treatment pressure PTi, the apparatus further including a comparator connected to ramp module (10), at least one device for detecting the patient's breathing parameters and sending them to the comparator, so that the comparator can determine whether an event (E1, E2 or E3) occurs in patient's breathing and to send the corresponding data to ramp module (10) which provides control unit (2) with a pressure value PM that will speed up with respect of time, so that the pressure rise at patient's mask (20) is accelerated.

Abstract: A respirator is disclosed that includes a respirator housing, a filtration media element disposed adjacent the respirator housing, and a respiration assist pump adjacent the filtration media element. The respiration assist pump assists the flow of gas through the filtration media element. In addition, a filtration module is disclosed and includes a filtration media element having a photocatalytic agent and a photon source and a gas pump coupled to the filtration media element to assist the flow of gas through the filtration media element. Methods of providing a respirator air stream are also disclosed.

Abstract: The present invention relates to a device and method for providing ventilation and perfusion in a patient. The device comprises an airway pressure supply device and a controller for controlling the airway pressure of the airway pressure supply device. In one embodiment, the airway pressure supply device comprises a piston moveably arranged in a cylinder and a motor connected to the piston. Activation of the airway pressure supply device is performed by moving the piston in the cylinder by the motor.

Abstract: A method and system of operating a trans-fill device. At least some of the illustrative embodiments are methods comprising generating an enriched gas stream from atmospheric air, and operating an intensifier which, when provided the enriched gas stream, produces a cylinder fill gas stream. The operating continues in the absence of the enriched gas stream being provided to the intensifier.

Abstract: An oxygen concentrator comprises a vacuum swing adsorption (VSA) gas separation system which includes a cartridge containing a mass of adsorbent material for producing oxygen, a drive which activates the gas separation system, and a power source comprising a mass. A ratio of the mass of the power source to a flow rate of oxygen produced by the oxygen concentrator is between 0.047 and 0.29 kg/LPM·hr.

Abstract: A fluid dispensing device comprising a body defining a cavity and a dispensing nozzle. A fluid discharging device is housed in the cavity. The fluid discharging device has a hollow casing defining a reservoir for containing a volume of fluid and a plunger slidingly engaged within the hollow casing. The plunger has a tubular portion which is arranged to extend from a first end of the hollow casing for co-operation with the dispensing nozzle. A biasing means is interposed between a second end of the hollow casing and an end wall of the cavity to bias the hollow casing towards the dispensing nozzle. A locking means holds the biasing means in a compressed state. Upon release of the locking means, the force stored in the biasing means is applied to the hollow casing thereby causing fluid to be ejected from the reservoir into the dispensing nozzle.

Abstract: A ventilator device and system comprising a rotating compressor, preferably a drag compressor, which, at the beginning of each inspiratory ventilation phase, is accelerated to a sufficient speed to deliver the desired inspiratory gas flow, and is subsequently stopped or decelerated to a basal flow level to permit the expiratory ventilation phase to occur. The ventilator device is small and light weight enough to be utilized in portable applications. The ventilator device is power efficient enough to operate for extended periods of time on internal or external batteries. Also provided is an oxygen blending apparatus which utilizes solenoid valves having specific orifice sizes for blending desired amounts of oxygen into the inspiratory gas flow. Also provided is an exhalation valve having an exhalation flow transducer which incorporates a radio frequency data base to provide an attendant controller with specific calibration information for the exhalation flow transducer.

Abstract: A hand press type rapid positioning first-aid device with cardiopulmonary resuscitation comprises a press device, an air storage device, a control device, a binding device and a sucking disc. The binding device allows the first-aid device being secured to the chest of the patient rapidly and conveniently. An operation process of continuously pressing the pressed part of the patient five times and blowing air one time after the mouth and nose breather masking the mouth and nose of the patient makes the first-aid cardiopulmonary resuscitation more successful and easily to enhance the function of first-aid. The disposal part, which contacts with the patient, in the mouth and nose breather can prevent from possible bacteria infection between patients.

Abstract: A high-frequency oscillator ventilator has a first gas conduit with an opening for gas connection with a patient's airways and a bias gas flow inlet and a bias flow outlet disposed to define therebetween a flow path for a bias gas within the first conduit. An oscillator operable to alternately introduce a volume of additional gas from a source into, and to withdraw at least the same volume of gas from, the first gas conduit, thereby inducing pressure oscillations in gas within the first conduit to move gas along a path intersecting the flow path for a bias gas alternately into and out of the opening at a predetermined high-frequency dependent on the output of a control signal generator.

Abstract: A system controls and manages administration of a therapeutic gas, such as NO, O2, or the like, to a spontaneously breathing, non-ventilated patient such that concentrated NO is as low as reasonably possible while delivering the desired amount of NO to the distal portions of the lungs. The system includes an entrainment cell that provides remote, turbulent mixing with low temporal latency and can be used with a nasal cannula or a mask. The entrainment cell uses room air to dilute the therapeutic gas; however, supplementary gases can also be used. A baffle can be included to promote mixing and a flow sensor can also be used if desired. Multiple ports can be included in the entrainment cell. An equalizing valve is also disclosed.

Abstract: An apparatus and process for supplying low pressure oxygen-enriched gas to a patient and at a moderate pressure to a radial compressor, whereupon it is compressed and fed to a high pressure storage tank. The oxygen-enriched gas is prioritized so that it is continuously supplied via a patient flow line to the patient.

Abstract: A constant pressure generator has a variable volume fluid reservoir formed by a container having fixed walls which cooperate to define a cross-sectional area of the container perpendicular to an axis that varies with location along the axis and an end wall arranged for movement along the axis to vary the volume of the reservoir and which is adapted to conform substantially to the fixed walls of the container to provide the region of variable area substantially that defined by the fixed walls. A force generator is engageable with the variable area region to exert a variable force thereon and the walls are shaped such that the area of the region varies interdependently with the exerted force as the volume varies to maintain the communicated pressure constant.

Abstract: A ventilator device and system comprising a rotating compressor, preferably a drag compressor, which, at the beginning of each inspiratory ventilation phase, is accelerated to a sufficient speed to deliver the desired inspiratory gas flow, and is subsequently stopped or decelerated to a basal flow level to permit the expiratory ventilation phase to occur. The ventilator device is small and light weight enough to be utilized in portable applications. The ventilator device is power efficient enough to operate for extended periods of time on internal or external batteries. Also provided is an oxygen blending apparatus which utilizes solenoid valves having specific orifice sizes for blending desired amounts of oxygen into the inspiratory gas flow. Also provided is an exhalation valve having an exhalation flow transducer which incorporates a radio frequency data base to provide an attendant controller with specific calibration information for the exhalation flow transducer.

Abstract: An automatic transfer regulator for automatically switching between a primary (hose line) breathing air source and a secondary source (escape cylinder). A pressure sensing system detects the line pressure of the primary source using a spring loaded poppet connected to one side of a transfer poppet valve, with the other side connected to the output of a reducer. The pressure sensing system is fed by the primary source through an orifice. When the sensor detects loss of hose line pressure, the system pressure is released to ambient. This bleeds the pressure from the system side of the transfer poppet valve, allowing the reducer output to force the poppet back, thus actuating the secondary source. A check valve prevents reducer output from escaping through the primary source inlet.

Abstract: An apparatus and process for supplying low pressure oxygen-enriched gas to a patient and at a moderate pressure to a radial compressor, whereupon it is compressed and fed to a high pressure storage tank. The oxygen-enriched gas is prioritized so that it is continuously supplied via a patient flow line to the patient.

Abstract: A respirator includes a hollow body defining therein a fresh air body and an exhaust air body. The fresh air body includes a fresh air inlet and a first breathing pipe. The exhaust air chamber includes an exhaust air pipe and a second breathing pipe. A first piston is reciprocally received in the fresh air chamber and a second piston is reciprocally received in the exhaust air chamber so that fresh air is able to be forced to the mask and exhaust from the mask is able to be drawn from the mask and into the exhaust air chamber. A patient unable to breathe independently is forced to breathe by using the respirator.

Abstract: A process and system are provided for controlling a respirator with a breathing circuit (2), an inspiration branch (10) and an expiration branch (12), in which the gas components needed for the respiration are fed in by a fresh gas metering device (20) via a fresh gas line (9), as a result of which at least the amount of breathing gas consumed can be replenished. A breathing gas delivery unit (1) is provided in the inspiration branch (10) and with a volume flow sensor (13) in the expiration branch (12). The fresh gas utilization of the respirator is improved and the process and system reduces the resistances in the breathing circuit (2) for the patient (3) by the breathing gas delivery unit (1) being returned during the phase of expiration at a speed that depends on the volume flow that is measured by the volume flow sensor (13).

Abstract: A gas forwarding apparatus for respiration and narcosis devices including a radial compressor and a drive apparatus which produces a magnetic rotary field, with the radial compressor including a housing within which a compressor wheel and a rotor which is connected thereto are arranged, with the drive apparatus being arranged outside the housing and with the drive apparatus and the rotor being designed to be mutually matched and arranged in such a manner that the rotor can be driven by the drive apparatus.

Abstract: The gas mixing apparatus provides the components of a breathing gas for mixing at approximately ambient atmospheric pressure, and regulates the pressure of a selected gas to approximately ambient atmospheric pressure for mixing with air at ambient atmospheric pressure. The gas mixing apparatus includes a piston disposed within a pump chamber. A flow limiting inlet controls introduction of a first selected gas such as oxygen for mixing with a second selected gas such as air. The pressure of the first selected gas is limited to an acceptable maximum pressure, so that even if a valve for admitting the first selected gas for mixing at ambient pressure fails, breathing gas will not be provided at an excessive pressure.