Abstract:
An improved therapy for both clearing the blood of unwanted carbon monoxide and anaesthetic chemicals and for rapidly re-oxygenating blood suffering from carbon monoxide poisoning or smoke inhalation. It also includes a therapy delivery device for carbon dioxide and oxygen metering and mixing apparatus for gases under pressure particularly for respirators and medical devices which has a plurality of compressed gas supply lines which are connected to a mixing device for delivery into a demand regulator (respirator or face mask). It includes a gas selection device, an automatic shut off of the carbon dioxide, a purging system, metering of the gases and a mixing chamber to promote a homogeneous mixture of gases and sized for field use by emergency care operators. The therapy is a mixture of carbon dioxide and oxygen for promoting the rapid oxygenation of the patient&#39;s blood supply for cases of carbon monoxide poisoning, smoke inhalation or other cases where the blood oxygen level is low.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application PCT/CA00/00481, filed Apr. 26, 2000, which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a therapy for clearing the blood of unwanted carbon monoxide and anaesthetic chemicals and for rapidly re-oxygenating that has had it&#39;s oxygen level depleted by environmental conditions i.e. carbon monoxide poisoning or smoke inhalation. The invention includes the means of delivering the therapy in a convenient manner whether given in-situ, in an ambulance or other emergency response vehicle, or at the hospital or other care facility, and whether administered by medical professionals or paramedical personnel. The device relates in general to pneumatic/mechanical control of respirator gas supply control devices and in particular to gas selection, automatic shut off of the carbon dioxide, purging, metering and mixing of the therapeutic gases. 
     BACKGROUND OF THE INVENTION 
     Carbon monoxide (CO) is a tasteless, colorless, odourless gas. Thus it is undetectable by potential victims. The blood prefers CO to oxygen by a ratio of 200:1. As a result, relatively small amounts of CO in the air can cause CO poisoning. CO attaches to blood forming carboxyhemoglobin, thus starving the brain and other organs and tissues for oxygen (O 2 ). Carbon monoxide poisoning occurs when carboxyhemoglobin levels are high enough to impair cellular functions. Symptoms of carbon monoxide poisoning include drowsiness, nausea and possibly death. The CO poisoning rate is significant, with over 70,000 hospital visits and 10,000 deaths per year in the U.S. 
     The cellular oxygen starvation from CO poisoning can cause death, or long-term, non-reversible health problems (i.e. to the brain, heart or neurological system). If a CO poisoning victim does not die, the average body will clear carboxyhemoglobin at the following typical rates: 
     Spontaneous breathing−cleansing half-life =220 minutes; Breathing pure O 2 =40 minutes; Hyperbaric chamber=20 minutes. 
     While the best current therapy is placing the patient in a hyperbaric chamber, these chambers are usually unavailable (only about 700 exist world-wide) and are rarely used. Typically these chambers require a “warm-up” time of 2 hours, which largely negates their theoretical usefulness. That is, significant permanent damage may have already occurred before the treatment can be commenced. 
     The current therapy of choice is to administer pure O 2 . As suggested above, pure O 2  would require approximately 2 hours to clear 87.5% of the CO from the bloodstream (e.g. 40 minutes=50% of CO is eliminated; 80 minutes=25%; 120 minutes=12.5%). Breathing pure O 2  has an unfortunate side effect; it lowers the respiratory rate and reduces the exchange of gases in the lungs, thereby prolonging the tissue starvation period. Accordingly, there is a need for a device that would overcome these disadvantages. 
     Typical respirator gas supply control devices, particularly those used for mixing gases under pressure and feed a delivery line of a respirator, or medical device, are too large and bulky to be used in situ or in emergency vehicles. They also require the operation of a skilled, medical practitioner to properly administer. A complete system that can be used by emergency and paramedical should have a gas selection device, an automatic shut off of the carbon monoxide a purging system, metering of the gases and a mixing chamber to promote a homogeneous mixture of gases and sized for in-situ or vehicle as well as hospital emergency room use. It should be able to use a whole range of different gas storage systems for input and demand regulators and facemasks as output. It can not rely on electrical control of the gas flow and mixing as power demand for both in situ or emergency vehicle applications is already greater than is reasonable to expect. Also electrical power at fire and other emergency sites is problematical to provide and higher priority uses get first use of this power. Finally battery power is not acceptable as the system must operate every time demanded regardless of the interval between demand and maintenance of batteries is a low priority item for emergency care providers. 
     For example, U.S. Pat. 3,441,041 allows for either atmospheric or compressed air to be used for a breathing apparatus but the mixture device is not easily portable, and requires adjustment by a trained individual when dealing with a patient to determine if the by-pass should be opened or closed and to adjust the compressed air flow based on respiration demands and the state of the patient&#39;s health. 
     U.S. Pat. 4,535,797 discloses a device that uses flow to keep the by-pass open and the by-pass is required to open the gas flow valve for the first time. Should the CO 2  supply fail, the O 2  supply will shut and the patient&#39;s therapy is terminated. 
     U.S. Pat. 4,549,563 maintains a constant ratio between two gases, G 1  and G 2 , by keeping the pressure of both gases P 1  and P 2  constant and keeps P 1  constant at a set rate of flow through the use of a pressure limiter. 
     The device disclosed in U.S. Pat. 4,549,563 does not provide for automatic shut off of the CO 2  gas stream should the O 2  stream become clogged. This shortcoming would expose the patient to an asphixyant and would not revert to the previously accepted therapy. In U.S. Pat. 4,549,563 the practitioner operates the flush system described in case the patient requires pure O 2  instead of the gas mixer. Such facemasks are commercially available and are not shown in the drawings. Also the system in 4,549,563 has no means of purging, which would mean that the second patient would face an incorrect mixture or if the system selection was changed, for example from O 2  to CO 2  then the patient would have to inhale the incorrect mixture prior to receiving the correct therapeutic gases. 
     U.S. Pat. 4,313,436 mixes O 2  and other medical gases for patients. It requires electronic sensing to determine if the gas mixture is correct and if not then causes a pressure pulse to close the by-pass thereby allowing only pure O 2  to enter the facemask. The use of electronics that have a large demand for power, i.e. 4 sensors and an automatic controller, are not feasible for in-situ on in vehicle use where power demand is already quite high and the most frequent operational problem is dead batteries due to limited maintenance time. Also this device has up to 5 separate valves that need to be adjusted by the medical practitioner to ensure the patient is receiving the proper gas mixture depending on his state. This degree of adjustment is inimical to the use by paramedical and emergency personnel. The system in 4,313,436 lacks a means of purging and only has two selection options, no mixture or mixture. Since there is no intermediary stage the operator is not prompted to purge the system. 
     U.S. Pat. 4,827,965 uses a venturi nozzle to simultaneously meter and mix the two gases in proper proportions. This scheme means that pressure of the two gases varies over the flow demand regime and that the charge may be stratified. Finally the system in 4,827,965 does not have a means to shut off the CO 2  mixture thus potentially exposing the patient to an asphixyant. Nor does it allow selection of different options (i.e. O 2  only, off, mix or off). Nor does it offer a means of purging the system except by drawing off the first amount of improper mixture. 
     Under U.S. Pat. 5,727,545, one embodiment requires electronic sensing of two temperatures and a pressure to control the action of four flow regulators. In a second embodiment, it requires electronic sensing of two temperatures and a pressure to control the action of two flow regulators. The by-pass is driven electronically so that any failure of the electrical system would endanger the patient&#39;s life. Metering and mixing are all electronic and it has no purging means. The use of electronics that have a large demand for power are not feasible for in-situ on in vehicle use where power demand is already quite high and the most frequent operational problem is dead batteries due to limited maintenance time. 
     U.S. Pat. 4,508,143 discloses the use of a cam actuator to open a valve. It opens two poppet valves either automatically or manually. 4,508,143 has no other features that could deliver or control the therapeutic gas delivery. 
     SUMMARY OF THE INVENTION 
     The invention provides a therapy clearing the blood of unwanted carbon monoxide and anaesthetic chemicals and for rapidly re-oxygenating that has had its oxygen level depleted by environmental conditions, i.e. carbon monoxide poisoning or smoke inhalation. The invention includes delivering the therapy in a convenient manner in situ, in an ambulance or other emergency response vehicle, or at the hospital or other care facility. It may be administered by medical professionals or paramedical personnel. The device relates in general to respirator gas supply control devices and in particular to gas selection, automatic shut off of the carbon monoxide, purging, metering and mixing of the therapeutic gases. 
     It is a great improvement on the current therapy, using pure O 2 , in that it is more rapidly clears carboxyhemoglobin from the patient&#39;s blood stream. Also it does not lower the respiratory rate or reduce the exchange of gases in the lungs, thereby prolonging the tissue starvation period. In fact the body&#39;s autonomous responses in the presence of a CO 2  rich environment is to increase the rate of respiration (panting) thus further decreasing the tissue starvation period. While the method of invention and the use of a hyperbaric chamber are both effective, a hyperbaric chamber is impractical for in situ and vehicle applications due to their size, cost, long warm up time and requirement for trained medical practitioner for operation. 
     Cellular oxygen starvation from CO poisoning, or smoke inhalation, can cause death, or long-term, non-reversible health problems (i.e. to the brain, heart or neurological system). In the United States alone there are 70,000 hospital visits and 10,000 deaths per year due to CO poisoning. Thus a new therapy that radically improves the outcomes of patients exposed to CO poisoning is needed. 
     The invention also includes a device for delivering the improved therapy for in situ, in vehicles (i.e. ambulance or fire truck) and institutional (i.e. hospital) locations. It avoids the above-described shortcomings for example where the system requires electric power to properly operate, making it impractical for most emergency applications. It avoids the requirement for a trained medical practitioner to properly operate and adjust the system while monitoring the patient&#39;s state of health. It avoids the requirement to add other required functions to the system with external components. 
     The invention optionally includes all the functions required of an integrated system: selection of therapy; automatic shut-off of CO 2 ; (i.e. automatic use of current therapy pure O 2 ) or in case of O 2  interruption automatic use of atmospheric air; precision metering of both gases; excellent mixing of both gases; and system purging. One embodiment allows for the use of the use of any O 2  and C O 2  supply to accommodate institutional demands (i.e. hospitals). The first embodiment includes a pneumatic control device. The second embodiment includes its own portable CO 2  supply to allow use with existing portable O 2  supplies found in all emergency response vehicles. The second embodiment contains all items required for the therapy except the external O 2  supply. 
     A cam actuator is used to select the choice of gas that the patient receives and is a four-position, rotary, manual switch. It can either be O 2 , off, O 2 /CO 2 , off. The two intermediary “off” positions allow for the patient to breathe atmospheric air and are a reminder to the operator to purge the system prior to moving to the next selection position. 
     Should one of the source gas pressures become too low to maintain a proper therapeutic gas mixture then the CO 2  flow would be halted by the shut-off valve. A CO 2  shutoff is operated by differential pressure between the O 2  and the CO 2  gas mixture; failing a proper supply of O 2 , the CO 2  shut-off closes so that only atmospheric air or O 2  can be inhaled. This is acceptable as the system reverts to the previously acceptable therapy. In case of O 2  flow interruption the CO 2  flow stops and automatically the patient inhales atmospheric air through the facemask by-pass valve. 
     The pressure of one gas G  1  (O 2 ) maintains the flow of the other gas G 2  (CO 2 ), since PI keeps the G 2  flow passage open. Metering is done separately for each gas and is automatic and based on sonic flow of the gases, but accepts sub-sonic flow for either or both gases. Metering keeps the flow proportional regardless of outlet demand, and mixing is done in a separate chamber where the gas path maximises the chance of a homogeneous mixture. 
     The invention relates to an apparatus and method for clearing the blood of unwanted carbon monoxide and/or anaesthetic chemicals and for rapidly re-oxygenating that has had it&#39;s oxygen level depleted, for example by environmental conditions i.e. carbon monoxide poisoning or smoke inhalation. The therapy includes respiration by the patient of a mixture of CO 2  and O 2 . The apparatus for treating preferably involves administering to the subject oxygen from a source of oxygen and carbon dioxide from a source of carbon dioxide, comprises: 
     an oxygen conduit defining an oxygen inlet and an oxygen outlet, the oxygen inlet adapted for fluid communication with the source of oxygen; 
     a carbon dioxide conduit defining a carbon dioxide inlet and a carbon dioxide outlet, the carbon dioxide inlet adapted for fluid communication with the source of carbon dioxide; 
     a means for combining the oxygen and the carbon dioxide, the means downstream from the oxygen outlet and the carbon dioxide outlet; and 
     a means for administering the combined oxygen and carbon dioxide to the subject. 
     The invention also includes a portable kit including the apparatus. The invention also includes a method for removing carbon monoxide and/or anaesthetic chemicals from blood and for rapidly re-oxygenating that has had it&#39;s oxygen level depleted, including administering to a subject an effective amount of combined oxygen and carbon dioxide from the apparatus. The invention also includes the use of the apparatus for removing carbon monoxide and/or anaesthetic chemicals from blood and for rapidly re-oxygenating that has had it&#39;s oxygen level depleted. 
     Oxygen and carbon dioxide therapy using the apparatus and methods of the invention can produce a clearing half-life of about 20 minutes. 
     The invention relates to an improved therapy for clearing the blood of unwanted carbon monoxide and anaesthetic chemicals and for rapidly re-oxygenating that has had it&#39;s oxygen level depleted by environmental conditions i.e. carbon monoxide poisoning or smoke inhalation. The therapy includes respiration by the patient of a mixture of CO 2  and O 2  . The invention includes an apparatus and method for delivering the improved therapy in a convenient manner whether given in-situ, in an ambulance or other emergency response vehicle, or at the hospital or other care facility, and whether administered by medical professionals or paramedical personnel, and does not require the use of electrical power. In one embodiment, the apparatus acts as a pneumatic control device for the therapeutic gas mixture and where O 2  and CO 2  are stored. Preferably, pressure is regulated externally, an external buffer volume is stored externally and/or the demand regulator and facemask are connected to the equipment. 
     The invention also includes a method and apparatus for delivering the improved therapy, in the second embodiment, where all necessary functions are delivery of the therapeutic gas mixture is self-contained, with the sole exception of the O 2  supply. 
     The invention also includes a control system, in the first embodiment, which preferably includes: supplied gas shut-off valves; therapy selector switch; automatic shut-off valve for CO 2  supply to avoid asphyxiating the patient; separate CO 2  and O 2  metering valves; a common gas mixing chamber, outlet ports to the buffer volume; outlet ports to the demand regulator/facemask; a means to purge the system and the buffer volume of previous gas mixtures prior to each new use. This system requires external connections to pressurised CO 2  and O 2 , a buffer volume and the demand regulator/facemask to operate. 
     The invention also includes a portable apparatus and method of delivering the improved therapy, for emergency personnel and first aid care givers at the emergency site, in the second embodiment, which includes: pressure regulation of supplied O 2  ; CO 2  cylinder; pressure regulation of supplied CO 2 ; CO 2  and O 2  gas shut-off valves; therapy selector switch; automatic shut-off valve for CO 2  supply to avoid asphyxiating the patient; separate CO 2  and O 2  metering valves; a common gas mixing chamber; a buffer volume; a demand regulator, hose and facemask; a means to purge the system and the buffer volume of previous gas mixtures prior to each new use. This embodiment only requires connection to an outside, readily available source of pressurised O 2  to operate. The invention also includes alternate methods of providing a suitable gas metering orifice. The invention also includes a member to filter either or both of the therapeutic gases prior to metering. 
     The invention also relates to a gas metering and mixing apparatus for gases under pressure, particularly for respirators and medical devices, comprising a plurality of gas meters, a gas mixer device, a plurality of compressed gas supply lines connected to said gas meters, a plurality of mixed gas delivery lines extending out of said gas mixer device for the discharge of a mixture of gases from said compressed gas supply lines from said gas meters and from said gas mixer device to a demand regulator, hose and facemask and to a buffer storage volume, and a means of selecting which gases, O 2 , mixture or none, are sourced to said metering and mixing device and at least an automatic shutoff valve for one of the therapeutic gases, CO 2 , which could in excess cause patient asphyxiation without said shut-off valve performing its function and with a means of purging the system including the buffer volume of mixed gases (or O 2  as appropriate). The automatic shut-off valve preferably includes means of adjusting said valve to vary the pressure in which it opens. The invention also includes a gas metering and mixing apparatus, wherein said metering can be adjusted to vary the proportions of the two different therapeutic gases. The apparatus preferably includes the use of sonic nozzles to meter said therapeutic gases. The invention also includes alternate devices for metering said therapeutic gases. The gas metering and mixing apparatus includes the ability to add filtration to the system as a means of protecting the sonic nozzles. The invention also includes a gas metering and mixing apparatus which includes the ability to add filtration to the system to protect the alternate metering means. 
     The invention includes an apparatus for treating carbon monoxide poisoning in a subject by administering to the subject oxygen from a source of oxygen and carbon dioxide from a source of carbon dioxide, comprising: 
     an oxygen conduit defining an oxygen inlet and an oxygen outlet, the oxygen inlet adapted for fluid communication with the source of oxygen; 
     a carbon dioxide conduit defining a carbon dioxide inlet and a carbon dioxide outlet, the carbon dioxide inlet adapted for fluid communication with the source of carbon dioxide; 
     a means for combining the oxygen and the carbon dioxide, the means downstream from the oxygen outlet and the carbon dioxide outlet; and 
     a means for administering the combined oxygen and carbon dioxide to the subject. 
     In a variation, apparatus comprises a gas control means associated with the apparatus for controlling the pressure, flow rate and the ratio of the combined oxygen and carbon dioxide. The gas control means optionally comprises an oxygen regulator for controlling oxygen pressure and a carbon dioxide regulator for controlling carbon dioxide pressure, the oxygen regulator located between the oxygen source and the combining means and the carbon dioxide regulator located between the carbon dioxide source and the combining means. The regulators also control nominal flow rate of the oxygen and carbon dioxide. 
     In a variation, the control means further comprises an oxygen sonic nozzle downstream of the oxygen regulator and a carbon dioxide sonic nozzle downstream of the carbon dioxide regulator, the nozzles dispensing the oxygen and the carbon dioxide. The nozzles dispense the oxygen and the carbon dioxide according to a predetermined flow rate. The apparatus preferably also comprises a means for reducing the flow of carbon dioxide when the percentage of carbon dioxide in the combined carbon dioxide and oxygen exceeds about 6.5% by volume. In another embodiment, the reducing means prevents the flow of carbon dioxide. 
     The invention also includes a variation where the means for reducing the flow of carbon dioxide comprises a differential pressure sensor downstream of the carbon dioxide source and/or the oxygen source. 
     Another variation involves the reducing means being located proximate to the conduits and in fluid communication with the oxygen and the carbon dioxide sources. 
     In another variation, the reducing means of the apparatus comprises: a shutoff member located proximate to the carbon dioxide conduit having an on position in which the shutoff member permits the carbon dioxide to communicate from the carbon dioxide source to the combining means and an off position in which the shutoff member prevents the carbon dioxide from communicating from the carbon dioxide source to the combining means; an actuating means for actuating the shutoff member from the on position to the off position when the percentage of carbon dioxide in the combined carbon dioxide and oxygen exceeds about 6.5% by volume, the actuating means operably connected to the shutoff member and responsive to differential pressure in the oxygen conduit and the carbon dioxide conduit. Optionally, the actuating means comprises: 
     a piston means in fluid communication with the oxygen conduit, the piston means located proximate to the oxygen conduit and including a first position in which the piston means is biased away from the oxygen conduit and actuates the shutoff member to the on position and a second position in which it is biased towards the oxygen conduit and actuates the shutoff member to the off position; 
     a biasing means for urging the piston toward the second position; 
     the piston means normally biased by oxygen toward the first position against the force of the biasing means, the piston means being urged toward the second position by the biasing means when oxygen pressure decreases in the oxygen conduit. 
     According to another aspect of the invention, the combining means comprises a mixing chamber. 
     In another variation, the administering means of the apparatus comprises a face-mask including a conduit in fluid communication with the combining means, the face-mask adapted for placement over the face of the subject. The face-mask optionally comprises a pressure regulator. 
     The invention also includes the variation where the apparatus further comprises a buffer in fluid communication with the combining means, the buffer including combined oxygen and carbon dioxide. 
     In another variation, the administering means is capable of administering the combined oxygen and carbon dioxide to the subject in an amount effective to increase the breathing rate of the subject. The carbon dioxide is about 3.5 to 6.5 percent by volume of the combined oxygen and carbon dioxide. 
     According to another aspect of the invention, the combined carbon dioxide and oxygen are in a ratio of about 19:1 by volume. 
     In a variation, the combined carbon dioxide and oxygen have a pressure of about 1 atm to 20 psig. 
     The invention also includes the variation where the oxygen conduit and the carbon dioxide conduits are connected to a tubular housing and extend into the housing. 
     In another variation, the conduits of the apparatus are defined by the housing, and are integrally defined by the housing. 
     In a variation the apparatus is portable. Portable means that the apparatus can fit inside an emergency vehicle and is practical for use in an emergency situation (for example, it can preferably be carried by a person). It further comprises optionally a carbon dioxide tank capable of connection to the carbon dioxide conduit. The apparatus is preferably capable of fitting in a briefcase. The subject is a mammal, preferably a human. The apparatus is preferably operable without electric power. It is optionally pneumatically powered. 
     The invention may also include a selector means or device to control the flow of carbon dioxide and oxygen. In one embodiment, the selector means may include a rotary selector  40 . The invention may also include a purging means or device, such as the valve  140  and port  160  for purging carbon dioxide and oxygen. 
     Another embodiment of the invention relates to a portable kit for treating carbon monoxide poisoning, comprising the apparatus of the invention. 
     This invention also includes a method of treating carbon monoxide poisoning, comprising administering to a subject an effective amount of combined oxygen and carbon dioxide from the apparatus disclosed. The invention also includes the use of an apparatus of the invention for treatment of carbon monoxide poisoning. 
     The invention includes an apparatus for treating carbon monoxide poisoning in a subject by administering to the subject oxygen from a source of oxygen and carbon dioxide from a source of carbon dioxide, comprising: 
     an oxygen conduit defining an oxygen inlet and an oxygen outlet, the oxygen inlet adapted for fluid communication with the source of oxygen; 
     a carbon dioxide conduit defining a carbon dioxide inlet and a carbon dioxide outlet, the carbon dioxide inlet adapted for fluid communication with the source of carbon dioxide; 
     a device for combining the oxygen and the carbon dioxide, the device downstream from the oxygen outlet and the carbon dioxide outlet; and 
     a device for administering the combined oxygen and carbon dioxide to the subject. 
     The apparatus optionally further comprises a gas control device associated with the apparatus for controlling the pressure, flow rate and the ratio of the combined oxygen and carbon dioxide. 
     The control device optionally further comprises an oxygen sonic nozzle downstream of the oxygen regulator and a carbon dioxide sonic nozzle downstream of the carbon dioxide regulator, the nozzles dispensing the oxygen and the carbon dioxide. The apparatus optionally further comprises a device for reducing the flow of carbon dioxide when the percentage of carbon dioxide in the combined carbon dioxide and oxygen exceeds about 6.5% by volume. The reducing device may comprise: 
     a shutoff member located proximate to the carbon dioxide conduit having an on position in which the shutoff member permits the carbon dioxide to communicate from the carbon dioxide source to the combining device and an off position in which the shutoff member prevents the carbon dioxide from communicating from the carbon dioxide source to the combining device; 
     an actuating device for actuating the shutoff member from the on position to the off position when the percentage of carbon dioxide in the combined carbon dioxide and oxygen exceeds about 6.5% by volume, the actuating device operably connected to the shutoff member and responsive to differential pressure in the oxygen conduit and the carbon dioxide conduit. The actuating device optionally comprises: 
     a piston device in fluid communication with the oxygen conduit, the piston device located proximate to the oxygen conduit and including a first position in which the piston device is biased away from the oxygen conduit and actuates the shutoff member to the on position and a second position in which it is biased towards the oxygen conduit and actuates the shutoff member to the off position; 
     a biasing device for urging the piston toward the second position; 
     the piston device normally biased by oxygen toward the first position against the force of the biasing device, the piston device being urged toward the second position by the biasing device when oxygen pressure decreases in the oxygen conduit. The device described  20  above may include various means, as described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described by way of example and with reference to the drawings in which: 
     FIG. 1 is a general cross-sectional view of the first embodiment of the present invention; 
     FIG. 2 is a detailed cross-sectional view of the first embodiment of the present invention; 
     FIG. 3 is a cross-sectional view of an alternative orifice arrangement; 
     FIG. 4 is a cross-sectional view of a filtering assembly; 
     FIG. 5 is a general schematic diagram of the second embodiment of the present invention; and 
     FIG. 6 is a detailed schematic diagram of the second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention comprises a pneumatic control assembly for metering and mixing O 2  and CO 2  in prescribed proportions. The system would preferably operate sonically, with sonic nozzle orifice sizes and pressures adjusted so that the gases are delivered in a 95% to 5% ratio by volume (see Marks Standard Handbook for Mechanical Engineers 9th Edition 1987; John B. Heywood, Internal Combustion Engine Fundamentals, McGraw Hill 1988). However, other ratios could readily be used: typically a useful range for carbon monoxide is from about 3.5 to 6.5 percent of the combined volume. The control system can be manually selected to deliver pure oxygen, the O 2 —CO 2  mixture, or in two “pause” positions, no gases. A manual valve would preferably allow system purging by venting all contained gases to atmosphere. When operating, the system preferably monitors the O 2  and CO 2  input pressures. Should the two pressures become significantly different the system would automatically stop the CO 2  flow. This feature is desirable because high concentration or pure CO 2  delivery would cause asphyxiation. 
     The invention relates to an apparatus for treating carbon monoxide poisoning in a subject by administering to the subject oxygen from a source of oxygen and carbon dioxide from a source of carbon dioxide, comprising: 
     an oxygen conduit defining an oxygen inlet and an oxygen outlet, the oxygen inlet adapted for fluid communication with the source of oxygen; 
     a carbon dioxide conduit defining a carbon dioxide inlet and a carbon dioxide outlet, the carbon dioxide inlet adapted for fluid communication with the source of carbon dioxide; 
     a means for combining the oxygen and the carbon dioxide, the means downstream from the oxygen outlet and the carbon dioxide outlet; and a means for administering the combined oxygen and carbon dioxide to the subject. 
     The conduits may be any conduit compatible with safe medical delivery of carbon dioxide and oxygen. In one embodiment of the invention, the conduits include a connecting passage  21  or a flow passage  31  as shown in FIG. 2 The combining means may include a mixing chamber. For example, one embodiment of the invention includes a mixing chamber  110  as shown in FIG.  2 . The invention also includes a means for administering the combined oxygen and carbon dioxide to the subject. The administering means may comprise a facemask including a conduit in fluid communication with the combining means, the face-mask adapted for placement over the face of the subject. 
     The apparatus preferably also includes a gas control means associated with the apparatus for controlling the pressure, flow rate and the ratio of the combined oxygen and carbon dioxide. The gas control means optionally includes a combination regulators (for example a regulator may be proximate to the oxygen or carbon dioxide source or the face mask) and sonic nozzles. 
     The apparatus optionally also includes a means for reducing the flow of carbon dioxide when the percentage of carbon dioxide in the combined carbon dioxide and oxygen exceeds about 6.5% by volume. In one variation, this means includes a carbon dioxide shut off valve  70 . The reducing means optionally includes a shutoff member including on and off positions and an actuating means for actuating the shutoff member from the on position to the off position when the percentage of carbon dioxide in the combined carbon dioxide and oxygen exceeds about 6.5% by volume. The acutating means may include a sensor  80  shown in FIG. 2 having a piston means such as the body  81  and a biasing means such as the spring  86 . Other devices for reducing or preventing carbon dioxide flow will be apparent. 
     According to the first embodiment, the invention preferably comprises a pneumatic control assembly for metering and mixing O 2  and CO 2  in prescribed proportions for applying the invented therapy. According to the second embodiment, the invention comprises a self contained apparatus, except for the O 2  supply, for administering the invented CO poisoning therapy. 
     Referring to FIG. 1, the pneumatic assembly  5  preferably consists of the following major components: body; gas selector; CO 2  valve; O 2  valve; CO 2  shut off valve; differential pressure sensor; CO 2  metering orifice; O 2  metering orifice; and purge valve. The pneumatic assembly S also consists of 5 ports: CO 2  inlet port; Oz inlet port; outlet to demand regulator and facemask; outlet to buffer volume; and purged gas outlet port. It will be apparent that parts of the embodiments of the invention can be omitted or varied. 
     The system receives pure CO 2  and O 2  at inlet ports  20  and  30  respectively. The pressures at ports  20  and  30  may be in the operating range of approximately 3.4 bar (50 psig). The inlet pressures for each gas are pre-set and relatively constant and are supplied from gas sources and pressure regulators not shown. Since the human body does not need precisely 5% CO 2 , the pressures do not have to be exact. For example, if the input pressures fluctuated from 2.8 to 3.8 bar the mass flow rate would only vary by 11.4%, which is acceptable. 
     A rotary selection device  40  has two cam lobes to enable O 2  or CO 2 /O 2  as required. Preferably, the apparatus has four positions, with positive detent stops for each selection. The positions are: OFF; MIXTURE: O 2  ; and OFF. The two off positions remind the operator to purge the system prior to selecting a gas flow position. As shown, in FIGS. 1 and 2 both gases are selected. Accordingly both the CO 2  valve  50  and the O 2  valve  60  are forced open by the cam lobes, enabling flow of both gases. If the CO 2  and O 2  pressures are nearly equal, differential pressure sensor  80  opens the CO 2  shutoff valve  70 , allowing CO 2  to flow to the metering point. Should the CO 2  pressure significantly exceed the O 2  pressure, sensor  80  will retract and thereby shut-off valve  70  will close, and the flow of CO 2  will stop. 
     Metering orifices  90  and  100  meter the CO 2  and O 2  respectively in the correct proportions. Those orifices are preferably sonic. However, downstream backpressure may occasionally rise to the point where the orifices become sub-sonic. That brief condition is allowed since it represents low flow, or very shallow breathing on the patient&#39;s behalf. In this case the volumetric error of the gas mixture is quite low and the therapeutic value of the gas mixture is not appreciably diminished. The output of the two gases is combined in mixing chamber  110 . The two gases collide at an angle to facilitate mixing, as for example 90°, as they enter mixing chamber  112 , creating turbulence, and promoting mixing. The mixed gases pass on to outlet port  120 , which is connected to a conventional demand type regulator and facemask (not shown). When the patient inhales, the demand regulator withdraws the inspiratory volume from the gas-mixture port  120 . When the patient exhales, the demand regulator isolates the facemask from  120  and vents the expiratory gases to atmosphere. The system is assumed to store a quantity of the gas mixture in a buffer volume, to support large instantaneous demands. Outlet port  130  provides a connection between the buffer volume and the regulator port  120 . 
     After usage, depressing purge valve  140  purges the system. That is, all gases stored in the apparatus and in the buffer volume are vented to port  160 . 
     FIG. 5 shows a second embodiment of the invention  200 , which includes the following major components: carry case  210 ; CO 2  supply  220 ; CO 2  regulator  230 ; O 2  regulator  240 ; control system  5 ; buffer volume  250 ; demand regulator  260 ; low pressure hose  270 ; face mask  280 ; purge line  290 . 
     Preferably, the apparatus is enclosed in a portable case  210 , to which all of the components would be mounted. This case is preferably the size of a briefcase. The apparatus includes a medium pressure storage system, for example a conventional cylinder  220  for storage of CO 2 . Preferably the dimensions of the cylinder are 3″ in diameter and 16″ long. As the CO 2  stored pressures might in practice range between 3 and 100 bar, a metal or composite cylinder would preferably be used (such cylinders are commercially available). The stored CO 2  would be connected to a regulator  230 , which reduces pressure to a low, relatively constant pressure (preferably about 3.4 bar). At extreme pressure, accuracy is not required, and a single stage unbalanced regulator would be acceptable (numerous such devices are commercially available). The regulated CO 2  would then be sealably connected to the pneumatic control device  5  described in the first embodiment above. 
     An O 2  input and regulation system  240  would receive unregulated O 2  from an external source via a quick disconnect. Preferably, the O 2  pressure would range from 3.4 to  160  bar. The received O 2  is connected to a regulator (part of  240 ) which reduces its pressure to a low, relatively constant pressure (typically 3.4 bar). At extreme pressure, accuracy is not required, a single stage unbalanced regulator would be acceptable (numerous such devices are commercially available). The regulated O 2  would then be sealably connected to the pneumatic control device S described in the first embodiment above. 
     Depending on the selector position, control device  5  would then deliver no gas, pure O 2 , or the invented therapeutic gas-mixture to both a cylindrical buffer volume  250  and to a demand regulator  260 . The pressure in the buffer volume would normally swing between atmospheric pressure and approximately 20 psig, with its maximum pressure being the regulated pressures (approximately 3.4 bar). Accordingly, the buffer volume is preferably a low cost metal or plastic cylinder, fabricated from tubing (e.g. spherical ends are not required) preferably having dimensions of 4″ in diameter and 8″ long. 
     When the patient inhales, the demand regulator senses the sub-atmospheric pressure at its outlet port and opens its flow valve to restore a slightly positive pressure (about 1 to 1.5 kPa). Thus the inhalation event causes the demand regulator  260  to withdraw gas from the control system  5  and deliver that gas to the facemask  280 . During inhalation, the demand regulator&#39;s valve throttles the flow to match the inspiratory volume demanded. Such demand regulators are commercially available When the patient stops inhaling, the pressure starts to rise above the 1 to 1.5 kPa set pressure and the demand regulator shuts off. A simple valve (preferably a rubber flapper or umbrella valve) in the outlet chamber  260  vents the outlet gases to atmosphere whenever an overpressure exists. Such an overpressure condition exists every time the patient exhales. 
     The outlet of the demand regulator  260  is connected to a conventional facemask  280  by preferably a flexible low-pressure hose  270 . The items  260 ,  270 , and  280  are readily available commercial parts. 
     FIG. 2 shows the control system  5  preferably housed in a non-sparking body  10 , such as brass to prevent inadvertent problems in the presence of the O 2  gas. Regulated CO 2  (having a preferred inlet pressure of approximately 3.4 bar) is received at any suitable inlet port  20 , such as a threaded female port. After entering port  20 , the CO 2  would pass through a connecting passage  21  and enter valve chamber  22 . If the CO 2  valve  50  is open (as shown), the CO 2  passes through the space between the valve seat  23  and the valve seal  55 . If the valve  50  is shut (not shown), gas flow is prevented by seal  55  resting on seat  23 . As shown, CO 2  flows through the annular space between throat area  24  and the actuator tip  45  and into interconnecting passage  25 . Connecting passage  25  is permanently sealed after construction by a conventional ball  11  and plug  12  system. 
     CO 2  then passes through  25  (and around  81   a ) into valve chamber  26 . If the CO 2  shutoff valve  70  is closed (not shown), seal  75  sitting on valve seat  13  blocks CO 2  flow. If valve  70  is open (not shown), the CO 2  passes through the space between the valve seat  13  and the valve seal  75 . CO 2  then passes through the throat area  27  and into connecting passage  28 . From passage  28  the gas turns an angle to facilitate mixing (for example about 90°) as it passes into orifice chamber  29 . All of the flow passages ( 21 ,  25 ,  28 ), flow annuli ( 23 - 45 ,  27 - 81   a ), and valve-seat clearances ( 23 - 55 , 13 - 75 ) are chosen so as to be non-restrictive to flow when compared to the calibrated restriction presented by orifice insert  90 . 
     Orifice insert  90  meters the CO 2  in accordance with the ideal gas law. The insert  90  is comprised of a body  91  with threaded section  92  for retaining the component in bore  14 . An o-ring  93  (or other appropriate seal), seals the outside diameter of insert  90  to the inside diameter of cavity  29  so that all CO 2  flow must pass through the centre of orifice insert  90 . The actual metering section of orifice insert  90  is comprised of a converging inlet section  95 , a straight throat area  96  (which is the metering orifice) and a diverging pressure recovery section  97 . Two holes  94  in the outlet face of orifice insert  90  allow the insert to be tightened by means of a special tool. 
     CO 2  exiting orifice insert  90  enters bore  14 , then turns turns an angle such as to facilitate mixing (for example, about 90°) as it enters connecting passage  110 . This angular turn creates turbulence, which helps to mix the CO 2  and O 2 . Connecting passage  110  intersects mixing chamber  112 , which is in direct communication with outlet port  120 . Preferably port  120  is typically a female port, with threaded section  121 , and is connected to a demand regulator. Gas in chamber  112  is also in communication with outlet port  130 . Preferably, port  130  is typically a female port, with threaded section  131 , and is connected to a buffer volume. 
     Regulated O 2  (having a preferred inlet pressure of approximately 3.4 bar) is received at any suitable inlet port  30 , such as a threaded female port. After entering port  30 , the O 2  would pass through a connecting passage  31  and enter valve chamber  32 . If the O 2  valve  60  is open (as shown), the O 2  passes through the space between the valve seat  33  and the valve seal  65 . If the valve  60  is shut (not shown), gas flow is prevented by seal  65  resting on seat  33 . As shown, O 2  flows through the annular space between throat area  34  and the actuator tip  48  and into interconnecting passage  35 . 
     O 2  then passes through  35  into valve chamber  16 . The O 2  passes through the annular gap between chamber  16  and the “nose”  87   b  of adjuster  87  and on into orifice chamber  37 . Some O 2  may also flow in the annular gap between  16  and spring  86 . All of the flow passages ( 31 ,  35 ,  37 ), flow annuli ( 16 - 87   b,    16 - 86 ), and valve-seat clearance ( 33 - 65 ) are chosen so as to be non-restrictive to flow when compared to the calibrated restriction presented by orifice insert  100 . 
     Orifice insert  100  meters the O 2  in accordance with the ideal gas law. The insert  100  is comprised of a body  101  with threaded section  10   2  for retaining the component in bore  15 . An o-ring  103  (or other appropriate seal), seals the outside diameter of insert  100  to the inside diameter of cavity  37  so that all O 2  flow must pass through the centre of orifice insert  100 . The actual metering section of orifice insert  100  is comprised of a converging inlet section  105 , a straight throat area  106  (which is the metering orifice) and a diverging pressure recovery section  107 . Two holes  104  in the outlet face of orifice insert  100  allow the insert to be tightened by means of a special tool. 
     O 2  exits the orifice insert  100  and the mixing chamber  112 , which is in direct communication with outlet port  120 . During periods where the mass flow is entering the buffer volume, the O 2  gas stream continues straight through  112 , and collides with the CO 2  gas stream at right angles, thus promoting mixing. The mixed gases then pass from  112  into port  130  for delivery to the buffer volume. During periods where the mass flow is passing to the demand regulator, the O 2  turns 90° in order to pass from mixing chamber  112  into outlet port  120 . The turbulence from turning 90° and from the O 2  and CO 2  impinging one another at 90° promotes mixing. From  112 , the mixed gas (or O 2  only if this operation is selected) enter port and is connected to a demand regulator. 
     The flow diameters seen by the metered and mixed gases ( 14 ,  15 ,  110 ,  112 ) are preferably sized so as to minimize pressure drop at high instantaneous flow rates. The nominal maximum inspiratory flow rate is assumed to  60  standard liters per minute. 
     Preferably, a rotary selector  40  is used to actuate CO 2  and O 2  valves  50  and  60 . Selector  40  has two cam lobes,  42  and  43 , which select CO 2  and O 2  respectively. The lobes are presumed to provide four positions: OFF; MIXTURE; O 2  ; and OFF. This arrangement always allows the user to select the other therapeutic gas stream (than that currently used) or OFF with one click of the selector. Additionally to move from one therapeutic gas stream to another requires two clicks of the selector as a reminder to the operator to purge the system prior to selecting the second therapeutic gas stream. Accordingly, the selector preferably includes a conventional ball-spring-detent system (not shown) so that the selector stops at each position. If the cam lobes are on a single plane (as shown), the selector would rotate through no more than 180°. If continuous 360° rotation were desired, the two cams would be placed on separate planes. 
     As shown in FIG. 2, cam lobe  42  has engaged CO 2  actuator  44  and moved it to its maximum open position. The actuator tip  45  engages a recess  56  in piston  54 , lifting  54  off of valve seat  23 . The end of tip  45  would typically be hemispherical and recess  56  would typically be conical or hemispherical so that the two parts would move freely and smoothly. Actuator  44  slides in bore  17  preferably machined into body  19 , and is sealed to that bore by o-ring  46  (or other appropriate seal). The height of the cam lobe  42 , from the base circle of  41  would typically be such a fraction of sealing diameter of seat  23  such as to ensure that the valve seal  55  does not impact the flow rate when piston  54  is in its open position, for example about 40%. Piston  54  rides in a companion bore in body  51 , with suitable radial clearance. Spring  57  acts to move piston  54  to its closed position when cam lobe  42  is not selecting CO 2 . In that case, the force from spring  57  must overcome the friction from o-ring  46  and provide the force needed to create an effective seal between SS and  23 . As shown, adjuster  58 , sealed by o-ring S 8   a  to body SI, is available to set the pre-load from spring  57 . A special tool engaging the two holes S 9  in its face turns adjuster  58 . The valve body 5.1 is retained in body  10  by thread  52 , and sealed from external leakage by o-ring  53 . A special tool engaging the two holes  51   a  in its face tightens the valve body  51 . 
     As shown in FIG. 2, cam lobe  43  has engaged O 2  actuator  47  and moved to its maximum open position. The actuator tip  48  engages a recess  66  in piston  64 , lifting  64  off of valve seat  33 . The end of tip  48  is preferably hemispherical and recess  66  is preferably conical or hemispherical so that the two parts move freely and smoothly. Actuator  47  slides in bore  18  preferably machined into body  10 , and is sealed to that bore by o-ring  49  (or other appropriate seal). The height of the cam lobe  43 , from the base circle of  41  is preferably at least 40% of sealing diameter of seat  33 . That value ensures that the valve seal  65  does not impact the flow rate when piston  64  is in its open position. Piston  64  rides in a companion bore in body  61 , with suitable radial clearance. Spring  67  acts to move piston  64  to its closed position when cam lobe  43  is not selecting O 2  —In that case, the force from spring  67  must overcome the friction form o-ring  49  and provide the force needed to create an effective seal between  65  and  33 . As shown, adjuster  68 , sealed by o-ring  68   a  (or other appropriate seal) to body  61 , is available to set the pre-load from spring  67 . A special tool engaging the two holes  69  in its face turns adjuster  68 . The valve body  61  is retained in body  10  by thread  62 , and sealed from external leakage by o-ring  63 (or other appropriate seal). A special tool engaging the two holes  61   a  in its face tightens the valve body  61 . 
     Referring to FIG. 2, sensor  80  is comprised of body  81  which slides in bore  19  machined into body  10 , and is sealed to that bore by o-ring  83  (or other appropriate seal). The  35  outer diameter of body  81  is reduced in area Sla so as to minimize the flow restriction in connecting passage  25 . Sensor tip  82  operates against lever  79 , which moves through an arc to raise piston  74  off of valve seat  13 . Specifically, the right end of lever  79  rests against the bottom ledge of groove  79   a,  which is in body  10 , and acts as a pivot point for  79 . Lever  79  passes through slot  78  in piston  74 , with the  78 - 74  contact point serving to raise or lower  74 . The end of tip  82  is preferably hemispherical so that lever  79  will move freely and smoothly. When the pressures in chambers  16  and  27  (O 2  and CO 2 ) are roughly equal, spring  86  acts to move sensor  81  to its fully open position, moving piston  74  off of seat  13 , and enabling CO 2  to flow. Adjusting the pre-load on spring  86  by turning adjuster  87  largely sets the CO 2 —O 2  differential pressure required to close sensor  80 . Adjuster  87  slides in bore  16  and is sealed to that bore by o-ring  88  (or other appropriate seal). A special tool engaging the two holes  89  in its face preferably tightens the adjuster  87 . Its position is retained by thread  87   a.  The fully open position of sensor  80  is controlled by lip  84  on body  81  engaging a seat  85  machined in the end of bore  16 . 
     The fully open position of sensor  81  preferably provides a gap ( 13 - 75 ) such as to ensure that the valve seal does not impact the flow rate when piston  74  is in its open position, as for example, at least 40% of the sealing diameter of seat  13 . Piston  74  rides in a companion bore in body  71 , with suitable radial clearance. Spring  77  acts to move piston  74  to its closed position when sensor  81  retracts to disable CO 2  flow. 
     The mixed gas in chamber  112  is communicated to the input of purge valve  140  by passage  111 . Valve  140  includes a plunger  153  attached to seat  151  by thread  152 . Seat  151  is normally closed against the protruding seal profile  150  of elastomeric seal  149  (or other suitable sealing material), preventing the flow of gases into the purge port  161 . This normally closed state is maintained by spring  155  acting against purge body  141  and pushbutton  156 , to maintain a closing force on the  150 - 151  seal interface. Plunger  153  slides in bore  147  of body  141  and is sealed to that bore by o-ring  154  (or other suitable sealing means). Body  141  is retained in body  10  by thread  142  and sealed from external leakage by o-ring  143  (or other suitable sealing means). Body  141  is preferably tightened by a special tool, which engages the two holes  144  on the rear face of  141 . When pushbutton  156  is depressed, seat  151  moves away from seal  150  admitting purge gas into the annular space between throat  157  and plunger pin  158 . The purge gas then passes into the annular space between bore  147  and pin  158 . The outside diameter of body  141  has an annular relief  145 , which is intersected by four through holes  146 . The  145 - 146  system allows purge gas in the  147 - 158  cavity to pass first into connecting chamber  159  and then into the purge port  160 . Port  160  is typically a female port with thread  161 . 
     As shown in FIG. 6, a briefcase-sized system  200  would include all of the items needed to provide the therapeutic gas mixture, except for O 2  storage. As ambulances, emergency vehicles, fire trucks and hospitals, or other health institutions, already have O 2  storage available, there is no benefit to including the O 2  storage system in such a device. 
     The apparatus preferably includes a suitcase type of enclosure  210 , which would house and mount all of the equipment. The largest item is most likely the CO 2  storage system  220 . System  220  preferably includes a CO 2  source  221 , capable of operating at least  100  bar. The outlet of  221  accommodates a cylinder valve  222 , with a manual shut-off valve  223  for switching CO 2  sources, an outlet port  224 , and a quick connect  225 . Quick connect  225  would be permanently attached to a line  226 , which delivers the unregulated CO 2  to the pressure regulator  230 . Preferably, a full CO 2  cylinder would preferably contain enough CO 2  to handle two therapy events of 30 minutes each, at 60 liters per minute inspiratory flow at 5% CO 2  by volume. The CO 2  cylinders  221  would be replaced routinely (and after each use) and re-filled as an unrelated activity. 
     The CO 2  regulator  230  includes an inlet  232 , a main regulator section  231 , and an outlet  233 . The regulating section  231  preferably comprises a single stage, non-balanced conventional pressure regulator. The output of the regulator would be permanently connected to the inlet port  20  of control device  5  (previously described). 
     The O 2  is preferably sourced externally. The O 2  circuit  240  includes a portal  241  in the suitcase  210  through which a quick-connect  242  passes. Quick connect  242  is connected to line  243  which routes the input O 2  to pressure regulator  244 . The O 2  regulator  244  includes an inlet  245  and an outlet  246 . The regulating section  244  preferably comprises a single stage, non-balanced pressure regulator. Commercial devices are readily available. The output of the regulator is permanently connected to the inlet port  30  of control device  5  (previously described). 
     Control device  5  includes a selector  40 , to choose O 2 , Mixture, or no gases. A button  153  would be used to purge the system after use, with purge gases being vented to port  160 . Purged gases would be plumbed through line  291  to a terminal vent fitting (or quick connect)  292 , passing through a portal  293  in the carrying case. 
     The gas output of control device  5  would appear at ports  120  and  130 . Port  130  would be permanently connected to a buffer volume  250 . As buffer  250  typically sees only 20 psig, it would preferably be of inexpensive construction, such as from thin wall metal pipe with simple end caps. Preferably, the dimensions of the buffer volume are 4″ diameter by 8″ in length. 
     Port  120  is connected to a demand-type regulator  260  (previously described). At a minimum, regulator  260  would include an inlet  261 , a main regulator section  262 , an over pressure relief valve  263 , and an outlet  264 . Regulator  260  is connected to a conventional facemask  280  by a conventional flexible hose  270 . 
     For example, FIG. 3 shows an alternative orifice arrangement. Certain combinations of design criteria (buffer volume, CO 2  and O 2  pressure, and maximum and minimum respiratory rates) can require very small orifice sizes. In such cases, the design format shown for orifices  90  and  100  may be impractical to machine. For example, orifice size could be as small as 0.003″, which is very difficult to mechanically machine using conventional methods. Accordingly, an alternative orifice arrangement is provided, as shown in FIG. 3, orifice insert  170  includes an outer body  171 , machined conventionally. Body  171  has a similar o-ring sealing diameter  171 , and the same o-ring ( 203 ) as inserts  90  and  100 . Body  171  includes a conventional o-ring gland  173 . A similar body outside diameter  174  would be used, along with the same thread  10   2 , as seen in  90  and  100 . Body  171  includes a converging inlet section  178 , terminating at face  177 , with a relatively large terminal outside diameter  179 . A preferably thin, circular, flat orifice plate  180  would be inserted from the rear of body  171  and is seated against the face  177 . The orifice plate preferably comprises metal substrate with a small through hole  181 . Electron discharge machining, laser drilling, mechanical micro machining, and chemical micro-machining means can reliably produce such small holes. The hole  181  would be the actual metering orifice, and the thickness of the plate  180  would provide the desired throat depth. Plate  180  is held in body  171  by a plug  190 . Plug  190  threads into  171  via thread  192 , and would seal to  180  and  171  by seal  182 . Plug  190  creates a chamfer type o-ring gland via surface  197  and sits against the orifice with surface  196 . Where practical, plug  190  may preferably have a second throat section  195  and a diverging pressure recovery section  194 . Plug  190  is preferably tightened into body  171  via a special tool engaging two holes  193  in its rear face. A commercially available thread sealant would lock plug  190  to orifice insert  170  so that it would function as an integral piece and could be installed and removed from body  10  without the two pieces separating. 
     A filtration means is optionally provided to keep the orifices clean. In the case of very small orifices, there could be a concern about foreign particles lodging in and blocking the metering orifices. In such a case, a filter element could be included in each orifice. As shown in FIG. 4, filter element  199  could be press fitted into a recess  198  in insert  170 . Such filter elements are commercially available and could include a wire screen, a sintered (porous) brass or porous fabric. 
     It will be appreciated that the above description relates to the preferred embodiments by way of example only. Many variations on the apparatus for delivering the invention will be obvious to those knowledgeable in the field, and such obvious variations are within the scope of the invention as described and claimed, whether or not expressly described. 
     All patents, patent applications (including Canadian application no.  2,269,890),  and publications referred to in this paper are incorporated by reference in their entirety.