US 20050247311 A1
The Reduced Oxygen Breathing Device (ROBD2) is an apparatus that dilutes the oxygen present in air to concentrations below 21% by mixing the air with nitrogen. The purpose of this dilution is to simulate the reduced oxygen concentration available as one ascends in altitude. The ROBD2 is unique and different from previous devices that reduce the concentration of oxygen in room air via dilution with nitrogen gas in that it uses sophisticated gas regulating devices known as mass flow controllers. The ROBD also employs a gas extraction device as an independent component of the system that can separate nitrogen gas from air for use in the device.
1. A reduced-oxygen breathing apparatus comprising:
(a) a thermal mass flow controller for regulating the release of nitrogen gas, wherein said nitrogen gas release is for the purpose of contributing to a gas mixture;
(b) a thermal mass flow controller for regulating the release of ambient air, wherein said ambient air release is for the purpose of contributing to said gas mixture;
(c) a nitrogen gas inlet, said inlet being in fluid communication with said nitrogen mass flow controller;
(d) an ambient air inlet, said inlet being in fluid communication with said mass flow controller;
(e) an outlet from said nitrogen mass flow controller, said outlet being in fluid communication with said nitrogen mass flow controller on one end and providing said controlled release of nitrogen gas to a common hose at the opposite end;
(f) an outlet from said ambient air mass flow controller, said outlet being in fluid communication with said ambient air mass flow controller on one end and providing said controlled release of ambient air to said common hose at the opposite end;
(g) a nitrogen gas supply, said nitrogen gas supply being in fluid communication with said nitrogen gas inlet;
(h) an ambient air supply, said ambient air supply being in fluid communication with said ambient air inlet;
(i) a back pressure regulator, said back pressure regulator being in fluid communication with said common hose, wherein said back pressure regulator controls the pressure differential to said mass flow controllers; and
(j) a microprocessor for controlling said releases of said mass flow controllers and thereby regulating the gas component make-up of said gas mixture.
2. The reduced-oxygen breathing device of
3. The reduced oxygen breathing device of
a one-way valve in fluid communication with said common hose and opening towards said subject, and
a one-way valve opening to the ambient environment for exhalation of said controlled gas mixture by said subject.
4. The reduced oxygen breathing device of
5. The reduced-oxygen breathing device of
6. The reduced-oxygen breathing device of
7. The reduced-oxygen breathing device of
8. The reduced-oxygen breathing device of
said oxygen concentration sensor sends a signal to said microprocessor;
said microprocessor manipulates said signal;
said microprocessor provides an output signal to a display panel that will alert an operator if said gas mixture is not within predetermined limits set by said microprocessor.
9. The reduced-oxygen breathing device of
10. The reduced-oxygen breathing device of
11. The reduced-oxygen breathing device of
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20. The reduced-oxygen breathing device of
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24. A reduced-oxygen breathing apparatus comprising:
(n) a thermal mass flow controller for regulating the release of nitrogen gas, wherein said nitrogen gas release is for the purpose of contributing to a gas mixture;
(o) a thermal mass flow controller for regulating the release of ambient air, wherein said ambient air release is for the purpose of contributing to said gas mixture;
(p) a nitrogen gas inlet, said inlet being in fluid communication with said nitrogen mass flow controller;
(q) an ambient air inlet, said inlet being in fluid communication with said mass flow controller;
(r) an outlet from said nitrogen mass flow controller, said outlet being in fluid communication with said nitrogen mass flow controller on one end and providing said controlled release of nitrogen gas to a common hose at the opposite end;
(s) an outlet from said ambient air mass flow controller, said outlet being in fluid communication with said ambient air mass flow controller on one end and providing said controlled release of ambient air to said common hose at the opposite end;
(t) an oxygen concentration sensor, said sensor being in fluid communication with said common hose;
(u) a nitrogen gas supply, said nitrogen gas supply being in fluid communication with said nitrogen gas inlet;
(v) an ambient air supply, said ambient air supply being in fluid communication with said ambient air inlet;
(w) a back pressure regulator, said back pressure regulator being in fluid communication with said common hose, wherein said back pressure regulator controls the pressure to said oxygen concentration sensor and pressure differential to said mass flow controllers;
(x) a microprocessor for controlling said releases of said mass flow controllers and thereby regulating the gas component make-up of said gas mixture;
(y) a back-up system for checking said regulation of said gas component make-up of said gas mixture, wherein:
said oxygen concentration sensor sends a signal to said microprocessor;
said microprocessor manipulates said signal;
said microprocessor provides an output signal to a display panel that will alert an operator if said gas mixture is not within predetermined limits set by said microprocessor; and
(z) a gas extraction system using molecular sieve technology to deliver said nitrogen gas supply and an air compressor in fluid communication with said gas extraction system to deliver said ambient air gas supply.
25. A method of inducing hypoxia in a subject in an isobaric environment to simulate various altitudes comprising:
a. fitting said subject with a delivery unit of a reduced-oxygen breathing device wherein the subject can breathe a controlled gas mixture;
b. choosing a concentration of oxygen to be administered via the control means of a microprocessor, wherein a set point is created by an operator, wherein actual and expected oxygen concentrations are compared at a operator-selectable frequency, and wherein adjustments to said controlled gas mixture are made by way of software in said control means to drive mass flow controllers which release nitrogen and ambient air to said controlled gas mixture in said device.
This application is filed, under 37 CFR 1.53(b), as a continuation-in-part of U.S. application Ser. No. 10/244,003, filed Sep. 16, 2002, herein incorporated by reference. In addition, this application claims priority under 35 USC 119(e) to U.S. Provisional Application No. 60/509,091, filed Oct. 7, 2003 and U.S. Provisional Application No. 60/591,146, filed Jul. 27, 2004, both of which are herein incorporated by reference.
1. Field of the Invention
The present invention relates to a method and apparatus for providing air with a less than ambient concentration of oxygen (reduced-oxygen air) to a human or other subject. More particularly, the invention relates to a method and apparatus for inducing hypoxia in a subject by delivering enriched nitrogen (and, thereby, reduced-oxygen) air to the subject in an isobaric setting to simulate various altitudes above sea level over relatively short periods.
2. Description of Prior Art
Altitude sickness strikes thousands of individuals every year resulting in problems from sleep disorders to pulmonary edemas to death. These individuals are pilots, skiers, mountain climbers, or merely business travelers to high altitude regions. The key to dealing with the altitude sickness is taking advantage of the body's ability to gradually acclimatize through a transition through progressively higher altitudes. Unfortunately, most individuals do not have the time to acclimatize.
The physiology of altitude sickness and the adjustment to altitude is covered in numerous textbooks. An excellent one is “Medicine For Mountaineering” by James Wilkerson, M.D. Copyright 1992, published by The Mountaineers of Seattle, Wash. from which much of the immediately following discussion is derived.
The body adjusts to altitude by increasing respiratory volume, increasing the pulmonary artery pressure, increasing the cardiac output, increasing the number of red blood cells, increasing the oxygen carrying capability of the red blood cells, and even changing body tissues to promote normal function at lower oxygen levels.
For example, at an altitude level of 3,000 feet the body already begins increasing the depth and rate of respiration. As a result of this, more oxygen is delivered to the lungs. In addition, the pulmonary artery pressure is increased which opens up portions of the lung which are normally not used, thus increasing the capacity of the lungs to absorb oxygen. For the first week or so, the cardiac output increases to increase the level of oxygen delivered to the tissues. The body also begins to increase the production of red blood cells. Other changes include the increase of an enzyme (DPG) which, in-turn, facilitates the release of oxygen from the blood and increase the numbers of capillaries within the muscle to better facilitate the exchange of blood with the muscle.
Tissue hypoxia is caused by the body's inability to obtain or utilize an adequate supply of oxygen. Under normal circumstances, there are three main ways by which this can occur. An individual can breathe a gas mixture in which the percentage of oxygen in the inspired air is insufficient to support adequate cellular respiration. This type of hypoxia (hypoxic hypoxia) can be found in situations where gases such as nitrogen or carbon dioxide are present in higher than normal concentrations relative to air at sea level, thereby displacing oxygen in the gas mixture. Breathing a gas mixture that contains approximately the same percentages of gases as found at sea level, but where the total pressure of the gas mixture is reduced causes a second form of hypoxia (hypobaric hypoxia). This is the situation encountered in altitude exposures. Finally, a third form of hypoxia (histiotoxic hypoxia) is caused by certain toxins (e.g. carbon monoxide, cyanide) that interfere with the body's utilization of oxygen at the cellular level.
Physiologically, the response to each of these types of hypoxia is similar as the organism attempts to compensate for the reduced amount of oxygen available for cellular metabolism. The rate and depth of respiration increases and the heart rate also increases. Subjectively, the individual experiences the sensations of shortness of breath and anxiety. If the hypoxia is severe enough, or if compensatory mechanisms cannot be sustained for any reason, other symptoms become apparent. Organs that have a high oxygen demand are affected first. Cognitive processes are impaired, and the subject may experience marked confusion or ataxia. If the hypoxia persists, coma and death result.
Investigators have utilized different mechanisms to study the effects of hypoxia on human physiology. Exposure to hypobaric environments has been the technique most frequently utilized in aviation settings. The military and commercial aviation industry both spend large sums of money annually training aviators to recognize and experience the signs and symptoms of hypoxia. This type of training is accomplished through the use of hypobaric chambers at fixed sites. These chambers have several drawbacks. Because they are expensive to construct and operate, only a limited number of these chambers can be fielded. Despite their relatively large size, however, they are generally too small to incorporate mission simulators into the hypoxic environment. Additionally, any equipment that is placed into the chamber must be extensively tested to ensure that it is compatible with the reduced barometric pressures within the chamber. Some investigators believe that if hypoxia training and flight could be combined, the face validity of the training scenario would be improved, and the overall training benefit would be significantly increased.
Other investigators have utilized mixed-gas hypoxia (i.e., hypoxic hypoxia) for a variety of reasons, most typically to investigate the physiologic effects of breathing gas mixtures containing a reduced percentage of oxygen, and/or an elevated concentration of carbon dioxide. This technique has several drawbacks. Gas mixtures require the ability to accurately blend and compress gases. Premixed gases also require some storage capacity. Typically, several cylinders of gas mixtures are connected in parallel to a manifold, which is in turn connected to the experimental subject. By changing valve settings on the manifold, differing gas mixtures can be administered. Concentrations are, therefore, limited to only those mixtures created before the experiment. Since the gas mixtures are discrete, no intermediate concentrations can be achieved. The gas mixtures can be administered through a conventional breathing apparatus, but the dependence on cylinders of premixed gases outweighs this convenience. However, because these devices also provoke the symptoms of hypoxia, one potentially useful avenue for these devices could be in the simulation of altitude exposure. Experiments have shown that the physical symptoms and performance deficits induced by hypobaric and mixed-gas hypoxia are qualitatively similar.
Certain devices like the present invention have been presented in the literature as being of two fundamental types. The simplest type exhibits a relatively large volume, closed breathing circuit. An experimental subject is connected to the circuit, and breathes off the reservoir, gradually exchanging the gas mixture present in the reservoir with his or her own exhaled gas (re-breathing). Carbon monoxide and water vapor from the subject may or may not be removed from the reservoir, depending on the experimental design. This type of device is limited in several important respects. The rate at which the oxygen in the reservoir is depleted is dependent on the ratio of the subject's minute ventilation volume and the volume of the reservoir. Since this device has no means to replace oxygen in the reservoir, this device cannot maintain a gas mixture at a particular ratio or concentration. The duration of the experiment is therefore limited to the time it takes for oxygen levels in the reservoir to fall to critical levels. Additionally, the concentration of oxygen in the system is constantly changing making interpretation of the results much more challenging.
A more advanced type of re-breathing circuit has been developed that addresses some of the shortcomings of the simple re-breathing loop. In this device, the subject exhales into a mixing loop, and an oxygen sensor monitors the concentration of oxygen in the loop. Computer software compares the actual concentration of oxygen to the expected concentration of oxygen, and oxygen is added to the mixing loop to hold the concentration of oxygen at a preset level. A shortcoming of this system is that carbon dioxide and water vapor must be continuously removed. Volume loss through the absorption of water vapor and carbon dioxide forces the addition of a replacement volume of gas (typically nitrogen) into the circuit. Because this is a re-breathing apparatus, special masks are required for the subject. Masks are connected to the re-breathing loop by two flexible hoses. Because of the weight of the one-way valve system required, and the weight of the hoses, this apparatus is cumbersome to the subject, and is not well suited for operation in small or confined spaces.
Examples of some of these and similar devices are as follows: Gamow (U.S. Pat. No. 5,398,678) discloses a portable chamber to simulate higher altitude conditions by increasing the pressure within the chamber above that of the ambient pressure, whereas the present invention is practiced in isobaric conditions; Lane (U.S. Pat. No. 5,101,819) teaches a method of introducing nitrogen into a flight training hypobaric chamber (not as in the isobaric conditions of the present invention) to simulate the lower oxygen concentrations at higher altitudes for fighter pilots; Kroll (U.S. Pat. No. 5,988,161) teaches a portable re-breathing device using increasing levels of carbon dioxide to displace oxygen and used to acclimate individuals to higher altitudes, whereas the present invention does not employ this use of exhaled gases (re-breathing) to displace the oxygen; Koni, et al. (U.S. Pat. No. 4,345,612) discloses an apparatus for delivery of a regulated flow of anesthetic gases but uses flow rate input data (not direct measurement of the mixed gases as in the present invention) to control release of gases and is not designed to allow for dynamic conditions; Lampotang, et al. (U.S. Pat. No. 6,131,571) also teaches a device for delivery of anesthetic gases but is more concerned with improved mixing of the gases and maintenance of proper pressure (operating as a ventilator) and is fundamentally different from the present invention, again, in both application and operation (pressure differentials, not direct measurement of mixed gases, is the means for computer control and is utilized to maintain proper system volume, not gas concentrations as in the present invention); and, finally, Marshall, et al. (U.S. Pat. No. 6,196,051) teaches an apparatus for determining odor levels in gas streams but utilizes a mass flow sensor at the inlet valve to regulate the flow of gases into the mixing chamber (not by direct measurement of chamber gases as in the present invention).
Each person reacts differently to a loss of oxygen to the brain. Hypoxia, as this condition is termed, can occur at altitudes as low as 8,000 feet, and occurs rapidly at altitudes of 25,000 feet and above. Being able to predict how individuals react to hypoxia is invaluable in preventing aviation fatalities and accidents that occur as a result of lost or impaired consciousness. Employing altitude chambers, military aviation personnel receive periodic hypoxia-familiarization training to mitigate this threat. The Reduced-Oxygen Breathing Device (ROBD) technology was needed to provide an alternative way of determining how an individual will respond under hypoxic conditions, rather than submitting a person to controlled exposure training in an altitude chamber, which has its own drawbacks. Currently, use of an altitude chamber to determine hypoxic response is costly, risky, and inconvenient.
Altitude chambers are expensive, large, and immobile. Getting personnel to them presents expense and logistical problems. Their use occasionally induces DCS or barotraumas, such as ruptured eardrums, sinus problems, headaches, and toothaches. The ROBD on the other hand, is relatively inexpensive, small, and mobile, and can be integrated with flight simulators. The ROBD can be used anywhere in a normal room at ground level to reliably and systematically produce normoxic (sea-level oxygen levels) and hypoxic conditions equivalent to those at altitudes up to 35,000 feet. Tests indicate the hypoxia experience using the ROBD is “essentially the same” as using an altitude chamber. The same subjective symptoms, decrement in cognitive performance, and type of physiological changes are reported by volunteer test subjects. The ROBD presents a cost effective, reliable, safe, mobile alternative to the conventional altitude chamber.
The parent application, U.S. patent application Ser. No. 10/244,003 (herein referred to a the 003′ application, of which the present invention is a continuation-in-part), addressed the shortcomings in the prior art by using a non-rebreathing circuit coupled with computer-controlled gas adjustments. Ambient air is diluted in the 003′ application with nitrogen on a breath-by-breath basis, providing the experimenter with precise control over the inspired concentration of oxygen on an almost instantaneous basis. Carbon dioxide and water vapor exhaled by the subject are released directly into the environment. Absorption is not necessary in the 003′ application. The small size of the 003′ invention makes fitting the device into cramped simulator environments possible, and multiple units may be incorporated into multi-place aircraft simulators. Maintenance of the mixing loop in the 003′ application is low when compared to re-breathing units, since no consumable items are necessary to absorb water vapor and/or carbon dioxide.
The 003′ ROBD is designed to create a selected static or dynamic gas mixture for breathing and is intended to induce a state of hypoxia in the subject. The 003′ reduced-oxygen breathing apparatus is made up of the following minimum elements: a vessel for gas mixing; an ambient air inlet; an outlet to provide the controlled gas mixture to a subject; an oxygen concentration sensor; a nitrogen gas supply; a nitrogen valve; and a controller for gas mixing, whereby the sensor sends a signal to the controller which manipulates said signal and provides an output signal to the nitrogen valve that adjusts the nitrogen gas supply to the gas mixing vessel in accordance with parameters set by an operator.
During the past three years, the Naval Aerospace Medical Research Laboratory (NAMRL) has continued to develop, test, and evaluate the portable open loop of the 003′ ROBD. The 003′ device is capable of reliably delivering sea level equivalent oxygen concentrations of altitudes up to 35,000 ft. A comparison of the subjective and objective signs and symptoms of hypoxia in 70 volunteers showed no significant difference during exposure to altitude in a hypobaric chamber and the ROBD.
The 003′ ROBD consists of an open gas-mixing chamber, which is constructed of schedule 40 polyvinyl chloride (PVC) pipe in the form of a rectangular loop. A quick-disconnect fitting is located on one end of the loop, such that a standard aviator's oxygen mask can be connected as it would be connected in an aircraft. The other end of the apparatus contains a one-way valve that permits entrance of ambient air into the loop during inspiration. An oxygen sensor is mounted in the mixing loop. At the start of inspiration, ambient air is drawn into the loop. A personal computer, executing a NAMRL developed gas mixture control program is used to control and monitor the concentration of oxygen in the loop just downstream from a mixing fan. The measured percentage of oxygen in the loop is compared to a target level of oxygen. If the loop oxygen concentration exceeds the target value, the software controller actuates a solenoid valve connected to a cylinder of nitrogen gas. When the two values match, the solenoid valve is turned off. Conversely, if the concentration of oxygen in the mixing loop is below that of the target value, a solenoid valve connected to an oxygen cylinder is actuated, until again those values match.
Although the 003′ ROBD has been used to generate hypoxia in over 100 hundred volunteers in a research laboratory setting, there is a need to further develop and “harden” the system for transitioning to the fleet and also to the public market. Several safety features and system modifications have been identified as necessary to accomplish this transition to a more suitable ROBD. The word suitable implies a new device that overcomes the deficiencies in the prior art as noted above and that is low cost when mass-produced, portable, durable, reliable, simple to operate and maintain, and has low man-hour and monetary maintenance requirements. In general there are four (4) major functional shortcomings, that when properly implemented, will meet the primary objectives of both the military and commercial markets. Four specific improvements needed to overcome the obstacles noted in the prior art of the 003′ application are as follows:
The ROBD2 of the instant invention overcomes the obstacles noted above in the prior art. The ROBD2 is designed to create a programmable gas mixture that can be used for breathing and is intended to induce hypoxia in a test subject. The following is a summary of the major innovations offered by the instant invention:
Accordingly, an object of this invention is to provide a reduced-oxygen breathing device for providing oxygen-reduced (hypoxic)/nitrogen-enriched air (relative to ambient conditions) to a subject.
Another object of the invention is provide a reduced-oxygen breathing device for providing oxygen-reduced/nitrogen-enriched air to a subject and connected to an aircraft flight simulator to provide hypoxia training.
A still further object of the invention is to provide a reduced-oxygen breathing device for providing oxygen-reduced/nitrogen-enriched air to a subject and connected to a treadmill to provide a stress EKG test.
An additional object of this invention is to provide a reduced-oxygen breathing device for providing oxygen-reduced/nitrogen-enriched air to a subject having reduced lung capacity to evaluate the person's fitness for an aircraft flight or travel to a high-altitude location.
A still further object of the invention is to provide a reduced-oxygen breathing device for providing oxygen-reduced/nitrogen enriched air to a subject as a substitute for conventional exercise cardiovascular stress testing. In this model, a patient gradually receives a progressively hypoxic gas mixture, with the intent of increasing cardiac workload while simultaneously reducing the oxygen content of the blood. As the cardiac workload increases, electrocardiographic changes are monitored, as in conventional exercise stress testing. It is anticipated that this methodology will be exceptionally useful in stress testing for patients that are non-ambulatory, or who have orthopedic injuries that preclude the use of conventional exercise testing. It is also felt to be useful in those patients that have contraindications to conventional pharmacologic stress testing.
These and other objects, features and advantages of the present invention are described in or are apparent from the following detailed description of preferred embodiments.
The invention will be described with reference to the drawings, in which like elements have been denoted throughout by like reference numerals. The representation in each of the figures is diagrammatic and no attempt is made to indicate actual scales or precise ratios. Any proportional relationships are shown as approximations.
The present invention is an improvement to the 003′ ROBD which, in part, consisted of the following elements: an open gas-mixing chamber, in the form of a loop; a quick-disconnect fitting located on one end of the loop, allowing fittings such as a standard aviator's oxygen mask; the other end of the apparatus contains a one-way valve for entrance of ambient air into the loop during inspiration; an oxygen sensor is mounted in the mixing loop. In the 003′ ROBD, at the start of inspiration, ambient air is drawn into the loop and a personal computer, executing a NAMRL developed gas mixture control program, was used to control and monitor the concentration of oxygen in the loop just downstream from a mixing fan. The measured percentage of oxygen in the loop of the 003′ invention was compared to a target level of oxygen and operated as follows: if the loop oxygen concentration exceeds the target value, the software controller actuated a solenoid valve connected to a cylinder of nitrogen gas and when the two values match, the solenoid valve is turned off; conversely, if the concentration of oxygen in the mixing loop is below that of the target value, a solenoid valve connected to an oxygen cylinder is actuated, until again those values match.
The instant invention can be thought of as a second generation Reduced Oxygen Breathing Device (ROBD2). ROBD2 is a computerized gas-blending instrument. The system uses Thermal Mass Flow Controllers (MFC) to mix breathing air and nitrogen to produce the sea level equivalent atmospheric oxygen contents for altitudes up to 40,000 feet. The MFCs are calibrated on primary flow standards traceable to the National Institute of Standards and Technology (NIST). NIST is a federal agency whose mission is to develop and promote measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. Several safety features are built into the ROBD2 to prevent over-pressurization of the Pilot's mask and to prevent reduced oxygen contents below those being requested for a particular altitude. The software is Menu driven. The main operator's menu consists of three selections, simplifying the use of the system for the field operator. Built in self-tests verify all system component functionality before the operation of the system can begin. If any self-tests fail, the system will not operate. The system is designed to work with both bottled gases and gases produced by the gas membrane system.
The present invention, ROBD2, improves on the 003′ ROBD described previously in several ways. The instant invention offers an alternative to the air and nitrogen cylinders with the introduction of an air/nitrogen producing membrane system. The gas-mixing loop of the 003′ ROBD has been replaced in the instant invention by a gas blending system that is based on thermal mass flow controller (MFC) technology. These MFCs have a built in proportional solenoid valve which is controlled via internal electronics. The control of flow in the instant invention is based on the feedback from an internal flow sensor, which uses the thermal conductivity characteristics of gas to determine thermal mass flow. The MFC uses an internal P&ID control loop to achieve consistent, repeatable and stable flow. The strategic layout of plumbing of the instant invention is enough to homogenously mix the gases. This system will produce a gas mixture within 1% of the requested values. The MFC is calibrated on a NIST traceable piston prover primary flow standard, using room air as a source.
The instant invention involves several significant improvements to the 003′ ROBD that can be summarized as follows:
In brief, the reduced-oxygen breathing apparatus of the instant invention has the following elements:
The Reduced Oxygen Breathing Device 2 (ROBD2 or gas mixer system) is an apparatus that dilutes the oxygen present in air to concentrations below 21% by mixing the air with nitrogen. The purpose of this dilution, as stated above, is to simulate the reduced oxygen concentration available as one ascends in altitude. The ROBD2 is unique and different from previous devices that reduce the concentration of oxygen in room air via dilution with nitrogen gas in that it uses sophisticated gas regulating devices known as Mass Flow Controllers (MFC). A MFC is essentially an electronically controlled valve that regulates flow of a given gas based on the size of the gas molecules (molecular weight) and the temperature of the gas. Each valve is engineered for a specific gas and they are highly accurate and are often used to calibrate other gas delivery devices.
The ROBD2 has 1 MFC for regulation of air flow and 1 MFC for regulation of nitrogen gas flow. The primary components of the ROBD2 gas mixer are: 1) 2 MFCs, as noted above; 2) a microprocessor and associated electronics to control the MFCs and run various software driven simulated altitude scenarios; 3) hoses to direct the gas flow from the MFCs to an external port; 4) an oxygen sensor that monitors the oxygen concentration in the system downstream from the MFCs and used to ensure correct functioning and mixing of air and nitrogen by the MFCs; 5) a pulse oximeter that measures and reports the heart rate and oxygen saturation of the subject breathing on the device and; 6) an emergency system that allows 100% oxygen from an external source (not regulated by a MFC) to be delivered to the breathing port and therefore to the subject. The oxygen supply to the ROBD2 is for emergency purposes only and is not required for the primary dilution and altitude simulation function of the ROBD2. Emergency oxygen is supplied by a compressed gas source.
Air and nitrogen passing through the ROBDs mass flow controllers can be supplied by compressed gas cylinders or by a gas extraction system. The gas extraction device is an independent component of the system and can separate nitrogen gas from air. The gas extraction device contains a compressor that entrains room air from the environment, pressurizes the air and delivers it to a molecular sieve. The molecular sieve separates the air into it primary component parts (oxygen and nitrogen) based on the size of the gas molecules. The nitrogen gas is pumped into a cylindrical container that acts as a reservoir for delivery under constant pressure to the gas mixer. The remaining gas, mostly oxygen, is vented to the environment as a “waste gas.” Some bleed air directly from the compressor is also pumped into a container to supply the gas mixer with the necessary air supply. Both the air and nitrogen containers are fitted with pressure gauges for monitoring the pressure within the containers and to control flow to the gas mixer.
In brief, air and nitrogen either from compressed gas cylinders (tanks) or from the gas extraction component are supplied to the gas mixer via hoses from the source gas to quick disconnect fittings on the back of the gas mixer. Oxygen from a compressed gas cylinder source only is also supplied via a hose to a quick disconnect fitting on the back of the gas mixer solely as an emergency 100% oxygen breathing supply in case of a medical emergency. Once the air and nitrogen enter the gas mixing system, they are routed to their respective MFC. The amount of flow permitted through each MFC controller is determined by the operator who inputs a specific altitude or series of altitude changes into the microprocessor by a keypad and LED interface on the front of the gas mixer. The altitudes inputted are associated with a particular reduced oxygen concentration and the microprocessor software and the electronic control hardware direct the appropriate flow through the air and nitrogen MFC to produce the desired altitudes and their respective oxygen concentrations.
Output from the air and nitrogen MFCs is funneled into a common hose where the oxygen content is double checked by the oxygen sensor noted above and then the gas is routed to a port on the face plate of the gas mixer. A hose with a standard military aviation facemask is connected to this port for delivery of the gas to the test subject.
Example of One Preferred Embodiment of the Instant Invention
The device consists of 2 separate modules that can be linked together or work independently. Module 1, the ‘ROBD2’, is the gas mixture delivery and test control device and consists of the actual gas mixing and delivery device with embedded micro-controller. Module 2 contains the gas extraction system.
Module 1 is capable of independent operation when removed from module 2. Module 1 contains the LCD display, keypad, and RS-232C interface. The embedded micro-controller firmware for module 2 is completely upgradeable. A device driver is provided to allow for configuration and/or monitoring of the module 1 micro-controller using National Instruments, Inc. “LabVIEW” software. A common RS-232C connection allows interface with the micro-controller, the pulse oximeter, and the oxygen analyzer. A dedicated ‘Oxygen Dump’ key/button on Module 1 is provided to immediately override the currently running program and deliver 100% oxygen within the breathing loop within 5 seconds.
Each module fits within a watertight crushproof case. The modules can be an integral part of the transport case or the module can be removed for use. Each module meets NEMA 12 standards when closed.
Both the ROBD2 and the gas extraction system are capable of operating from an input power of either 100 to 240 V/50 to 60 Hz AC. Each module requires a single power cord to supply power to all components of the module.
The gas extractor module is capable of supplying medical grade breathing gases and has external quick disconnect metal connections for attaching the oxygen and nitrogen hoses to the ROBD2 unit.
Each module has been designed to be essentially free of safety hazards that could injure operators, users or maintenance personnel during operation. These safety hazards include but are not limited to sudden, uncontrolled changes in loop pressure, flow rate and reduction in oxygen content below preset value, non-standard wiring or any non-standard electrical or mechanical practice.
The ROBD2 is expandable, that is, control panels can be added or reconfigured, control input devices changed, display devices can be upgraded to higher resolution devices, microprocessor code can be changed/upgraded and uses industry standard components when appropriate. The ROBD is also supportable throughout the systems projected life. Hardware components are generally commercial-off-the-shelf (COTS) products whenever possible to ensure supportability throughout the life cycle. There have been no modifications to any COTS hardware or software that will require special support or will cause incompatibility issues with new releases of the hardware or software product. This allows the ROBD2 to be maintenance friendly with a mean time to replace consumable items such as the oxygen sensor of 5 minutes or less and a repair goal of less than 30 minutes for all replaceable components.
The following are some of the performance characteristics of this preferred embodiment:
The design and implementation of the gas mixing subsystem and the mask pressure subsystem is accomplished so that gas usage is minimized over the entire operating altitude range. A dynamic, on-demand, and real time control system approach has been utilized.
A. The ROBD2 has these, among other, capabilities:
The inventors contemplate the following as some of the potential applications for the present invention:
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.