WO1993023102A1 - Non-wasting respiratory stimulator and high altitude breathing device - Google Patents

Abstract

Disclosed is a non-wasting respiratory stimulator (10) for providing a CO2 enriched fresh air mixture. The respirator comprises a breathing port (16), at least one vent port (18) and a mixing chamber (14). Also disclosed are methods of treating hypocapnia of various etiology, comprising administering a mixture of exhaled CO2 and fresh air, utilizing the non-wasting respiratory stimulator of the present invention.

Description

NON-WASTING RESPIRATORY STIMULATOR AND HIGH ALTITUDE BREATHING DEVICE

Background of the Invention The present invention relates to respiration device and, more particularly, to a simplified non-wasti rebreathing device for ambulatory use.

For more than a century, the role of C0₂ in protecti the 0₂ supply of brain and body has been recognized. F almost as long, investigators have known that C0₂ enriched a permits increased ventilation without hypocapnia. Und ordinary circumstances, each breath contains more than enou 0₂ to meet metabolic needs, as breathing supplies 0₂ and ge rid of C0₂ formed in the body. But contrary to what might expected, respiration is not driven by 0₂ lack but by C excess. In fact, respiration is mediated by C0₂ and t respiratory system is exquisitely sensitive to arterial C levels. Thus, a slight increase in C0₂ level will stimula breathing, and a slight decrease in C0₂ level will depre breathing. These respiratory responses maintain alveolar PC and, hence, arterial PC0₂ at nearly constant values.

A voluntary increase in the rate and depth of breathi causes C0₂ to be exhaled at a faster rate than its rate production by the body's metabolism and results in a drop the amount of C0₂ in the blood, i.e., results in hypocapni If vigorous, rapid breathing is continued for more than a f minutes, increasingly severe hypocapnia will cause cerebr vasoconstriction and unpleasant nervous system symptoms.

An increased rate and depth of breathing, or hyperpne without an appropriate increase in C0₂ production fr metabolism, can be voluntary or caused by a hyperventilati syndrome, anoxic hypoxia, or mechanical ventilation. In a cases, the resultant hypocapnia causes increasingly gra symptoms and is the limiting factor in the amount^' of exce ventilation that can be achieved. In a number of situations - a good example is the anoxic hypoxia that can occur in hi altitude flying — a large increase in ventilation desirable, and C0₂ enriched air makes this possible. Respiratory che oreceptors respond to low arterial P0₂, but this response tends to be sluggish and of low magnitude. However, if alveolar PC0₂ is maintained by breathing C0₂ enriched air, even mild hypoxia is an effective respiratory stimulant. With sudden exposure to severe hypoxia, such as loss of cabin pressure in an airplane at 25,000 feet, the hypoxic stimulus is strong enough to cause hyperpnea. However, this hyperpnea rapidly leads to hypocapnia which limits the respiratory response to a maximum of only about 65% above normal. The hypocapnia also causes cerebral vasoconstriction which further aggravates central nervous system hypoxia. Unless oxygen (or C0₂ enriched air) is immediately available, the severe hypoxia within minutes will cause incapacitation or unconsciousness. An acclimated mountain climber can do heavy physical work at high altitudes because the body can adapt to hypocapnia. This adaptation permits greatly increased ventilation which supplies enough 0₂ not only to prevent hypoxia at rest but also provides enough ventilation for strenuous climbing. However, this adaptive process does not always go smoothly, and acute mountain sickness is a common occurrence. At high altitudes, the alternating stimulation and inhibition of the respiratory center, first by hypoxia and then by hypocapnia, leads to Cheyne-Stokes respiration, which can become quite pronounced during sleep. In the apneic phase, severe hypoxia may potentially cause the subject to slip from sleep into coma, and sometimes from coma into death.

Many physicians, aware of the grave consequences of hypercapnia and C0₂ narcosis, and accustomed to treating the anoxia of respiratory failure with 0₂, are likely to think of 0₂ as life giving and C0₂ as a potentially dangerous exhalation. However, C0₂ is just as essential in the body as 0₂. For example, C0₂ is vitally important to acid base balance, to maintaining cerebral blood flow and, of course, to regulating breathing. During the 1920's, C0₂ mixtures were frequently used to stimulate respiration in carbon monoxide asphyxia, and there was interest in its use in aviation, pilot anoxia being a major source of casualties in World War II.

Although early experiments with C0₂ enriched air ga very encouraging results, technical limitations made dire blood gas data difficult to obtain. Without such informatio the therapeutic use of C0₂ was both unsubstantiated a hazardous. With the coming of aviation 0₂ and pressuriz cabins in the 1940'ε, the problem of anoxia in high altitu flying was largely eliminated. This also eliminated t principle stimulus for the work on C0₂. Recently, however, various works have pointed out t similarity between the symptoms of acute mountain sickne (AMS) and carbon monoxide poisoning. Climbers obtain striking relief from symptoms of AMS with inhalation of 3% C and commentators have suggested that this might be a usef emergency treatment for AMS. Also, over 50 years ago, studi showed that headache and other acute neurological symptoms carbon monoxide poisoning were rapidly relieved by breathi a C0₂ mixture, and that the benefit achieved by this means w greater than that produced by 100% 0₂ alone. Yet, the promise of C0₂ is still largely unfulfilled C0₂ enriched air is essentially unavailable in aviatio mountaineering, and medicine. The probable reason for this that breathing C0₂ mixtures is neither safe nor simple. O cannot just hook up a tank of C0₂ to a breathing apparatus a expect to adjust the flow by monitoring its effect respiration. To do so would be to risk almost instantaneo unconsciousness, potentially soon followed by brain damage death. Producing a smooth flow of accurately mixed C0₂ a air requires a sophisticated mixing device, both delicate a expensive.

Commercially prepared custom mixes of medical grade a and C0₂ are available, but costly, the tanks very heavy, a breathing duration time quite limited. Even a group experienced physician scientist mountain climbers w rediscovered the value of C0₂ in treating acute mounta sickness, although they recommended 3% C0₂ as a usef emergency treatment, did not feel that C0₂ was a practic solution to the hypoxic problems of mountain climbing.

Various attempts to utilize exhaled air, which is high in C0₂, have been made as a substitute for providing prepared custom mixes of C0₂ and air. In fact, generations of emergency room physicians have had patients breathe into simple kraft paper bags to treat hyperventilation that can result from anxiety, fear, or trauma. The paper bag enables a hyperventilating patient to conserve and rebreathe exhaled air, thereby increasing the concentration of C0₂ in the inhaled air. This, in turn, raises the C0₂ content of the blood and relieves symptoms caused by low blood C0₂. A normally ventilating individual who breathes into a paper bag will also experience an increase in blood C0₂ which will markedly stimulate respiration. _ This is the seminal idea behind all of the prior state of the art rebreathing inventions. In one fashion or another they are all designed to duplicate the function of a simple paper bag. However, breathing into a paper bag results in 100% wasted ventilation. Within a relatively short time, the CO_≥ concentrations rise and 0₂ concentrations fall to intolerable levels. In order to achieve a steady state, some fresh air must be added. It should be emphasized that the portion of ventilation that is supplied by the bag does nothing to improve alveolar ventilation and is therefore wasted.

The following devices are all variations on a simple paper bag. U.S. Patent No. 2,304,033 to Shelton for a sanitary rebreathing bag is a paper bag, but modified with tubes attached to the bag. U.S. Patent No. 2,007,330 to Hicks for a self administering carbon dioxide apparatus describes an inflatable nose/mouth mask connected by a tube to an inflatable rubber bag. U.S. Patent No. 3,513,843 to Exler for a respiratory device for rebreathing C0₂ consists of a nose- mouth mask connected to an inflatable sack, of readily variable size to adjust the same to the rebreathing capacity of the user, with an adjustable two-way flow breather valve and a one-way outlet valve. U.S. Patent No. 4,192,301 to Hardwick for a rebreathing apparatus is a disposable, flexibl polymer bag attached to a nose/mouth mask and an air contro valve located between the mask and the disposable bag which i said to adjust the ratio of rebreathed air to fresh ai through a fresh air inlet.

Ventilation can also be wasted and higher CO concentrations achieved by breathing through a long tube Whatever the volume contained in the tube, an equal volume o ventilation will be wasted. In other words, the entire volum of air in the tube must be inhaled before the user can begi to get any fresh air. If the volume of the tube exceeds th vital capacity of the user, then ventilation is completel wasted and the^situation is identical to that of breathin into a closed bag. . The following devices are all variations on a breathin

^' tube. U.S. Patent No. 3,455,294 to Adler is a respirator device to increase the depth and volume of respiration i patients by adding an area of dead space through which th patient rebreathes. The device comprises a multi-walle chamber of about 1 liter volume providing a tortuous pathwa between a mouthpiece and exterior air. Thus, it is th equivalent of breathing into a long tube. The disadvantage o this device is that, during operation, the entire one lite volume in the tortuous pathway is filled with exhaled ai containing C0₂, and is rebreathed by the user without an mixing of fresh air with the exhaled air. The user is able t breath in fresh air only after breathing the entire one lite volume contained in the device, which can only be accomplishe once breathing is stimulated and the user's tidal volum exceeds one liter. Moreover, even when tidal volume exceed one liter, fresh air is never mixed with the exhaled ai within the device; rather, if mixing occurs at all, it occur in the lungs. U.S. Patent Nos. 4,508,116 and 4,628,926, bot to Duncan for a carbon dioxide rebreathing apparatus, are als generally of the same type as Adler, providing air baffles an chambers that provide a long air passage, again the equivalen of breathing through a tube. U.S. Patent No. 4,275,722 to Sorensen discloses a respiratory exerciser and rebreathing device which, through a system of valves, provides for an inhalation chamber and an exhalation chamber, with a sliding mechanism to vary the amount of air rebreathed from the exhalation chamber. This device has a complex network of chambers, valves and mechanisms, all designed to route exhaled air through an exhalation chamber and through an inhalation chamber that removes moisture from the exhaled air before inhaling. The exhalation chamber is widely open to ambient air so that fresh air is available at the bottom. Nevertheless, little or no turbulence and essentially no mixing occurs at the boundary layer'between the exhaled air and ambient air other than by relatively slow diffusion. Although the patent at times refers to the exhalation chamber as a mixing chamber, there is essentially no mixing of ambient air with exhaled air in the device. Thus, this complicated device is essentially another long tube and wastes ventilation. It does nothing to improve alveolar ventilation and could never serve as a substitute for breathing oxygen at high altitudes. In addition, this device is unnecessarily complex and is disadvantageously expensive to manufacture, and in turn would be costly to purchase. A relatively simple low-cost device which mixes and utilizes C0₂-enriched, exhaled air is therefore preferred. Notwithstanding the various efforts in the prior art, there remains a need for a simple rebreathing apparatus that provides an appropriate C0₂/air mixture. Because C0₂/air mixtures are expensive and impractical and generally not readily available, their full medical potential has never been realized. However, the crucial condition that needs to be met is that such an apparatus must do more than just stimulate ventilation, it must also not waste ventilation. In other words, the apparatus must allow an adequate amount of fresh air and exhaled air to be mixed and reach the alveoli, throughout a range of tidal volumes and respirations per minute.

Summary of the Invention The present invention represents a substantia improvement to the prior device as discussed above, an comprises several distinct advantages. The rebreathin apparatus of the present invention provides an endless suppl of C0₂-enriched air which, as will be discussed in mor detail, has various beneficial uses. However, unlike th prior devices, the present invention utilizes an endles supply of exhaled air and fresh air, which are mixed togethe by the process of normal breathing, in which ventilation i not wasted.

The present invention comprises a mixing chamber havin a predetermined volume, and a breathing port located on th chamber through which a user can draw air out of the chambe and exhale into the chamber. The mixing chamber also has a least one -inlet/outlet port through which fresh air can b introduced into the chamber, and through which air within th chamber can exit. The container advantageously comes in variety of different volumes, each having a specific volum which determines the increase in ventilation stimulated by th device.

One of the main advantages of the present invention i that the source of the C0₂ is the user's own exhaled air. Th exhaled air is breathed into the chamber and is mixed wit fresh air and rebreathed by the user. Because there is n fixed apparatus measuring the quantity of C0₂ being supplied there is no possibility of human error or equipment failur which may lead to accidental asphyxiation or C0₂ narcosis.

The present invention also advantageously provides carbo dioxide-enriched air which effects physiological stimulatio akin to exercise. The free mixing of fresh air with exhale air in the chamber makes it possible for the respirator system to maintain a normal alveolar P0₂ and promote increased ventilation comparable to the ventilation produce by exercise. The present invention is particularly well-suited for variety of aviation applications, as C0₂-enriched air ca substitute for oxygen in high altitude flying. The presen invention can also provide C0₂-enriched air which can treat carbon monoxide poisoning more effectively than 100% oxygen. Moreover, the present invention can provide C0₂-enriched air to treat or prevent acute mountain sickness. The present invention is also advantageously simple to produce in a highly affordable form. Various embodiments of the present invention can also be provided to adapt to various uses, i.e., the device can be portably fastened to the user's nose and mouth area, or can be hooked up to an oxygen supply or adapted with a smog filter. The present invention can also be comprised of a collapsible housing to adjustably provide varying volumes for different users. Moreover, the container of the present invention has applications in a number of settings, and should not be considered limited to the specific embodiments shown in the drawings or described herein.

Brief Description of Drawings Figure 1 is a perspective view of a rebreathing device of the present invention.

Figure 2 is a cross-section of a rebreathing device of the present invention with a flexible tube and a mouthpiece. Figure 3 is a schematic of a collapsible rebreathing device of the present invention in its open position.

Figure 4 is a perspective of a portable rebreathing device adaptable for use as a mask with a strap. Figure 5 is a perspective of a portable rebreathing device with a mask, helmet, headphones and a microphone.

Figure 6 is a schematic of a telescoping rebreathing device of the present invention in an intermediate position. Figure 7 is a schematic of a rebreathing device of the present invention with adaptable valves and a smog filter.

Figure 8 is a schematic of a rebreathing device of the present invention with adaptable valves and an oxygen tank.

Detailed Description of Preferred Embodiments

The present - invention represents a substantial improvement to the prior devices discussed above, in that the present invention provides C0₂-enr^"iched air while utilizing an endless supply of exhaled air and fresh air, which are mixed together by the process of normal breathing. The presen invention comprises an air mixing chamber, with two or mor air ports, one through which a user inhales and exhales, an at least one through which excess air is allowed to vent fro 5 the chamber to atmosphere and fresh air is allowed to be draw into the chamber from the atmosphere.

The present invention also advantageously has relatively large mixing chamber whereby fresh air is draw into the chamber and is mixed with exhaled air by th

10 turbulence caused by the introduction of air into the chamber Turbulence is caused by inhaling, where fresh air is raw into the chamber, and by exhaling, where exhaled air enter the chamber through the user's mouth and nose. Unlike th previous respiratory devices which require the user to inhal

15. a volume of strictly exhaled air before any fresh air i breathed in, the present invention substantially mixes fres air and exhaled air within the chamber prior to being inhaled Thus, the user receives a mixture throughout a wide range o tidal volumes. Substantial equalization of exhaled air an

20 fresh air levels is achieved within the chamber after relatively short amount of time as essentially equal amoτ-ϊκ of fresh air and exhaled air enter the chamber with eac breathing cycle.

Simply put, the present invention is a breathin

25 stimulator which makes possible the rebreathing of conserved exhaled carbon dioxide, thus permitting hyperpnea withou hypocapnia. The present invention utilizes a dead spac volume container, which by exhaling can be partially fille with C0₂-enriched exhaled air, and by inhaling can b

30 partially filled with fresh air, as fresh air is introduce into the chamber through an opening to the atmosphere. Th present invention thus comprises a C0₂ trap which makes i difficult for C0₂ to leave, but readily allows fresh air an 0₂ to be drawn into the trap as the user inhales. No costl

35 valves, multiple chambers or other mechanisms are needed. Tla present invention, therefore, not only stimulates ventilation but allows a sufficient and stabilized amount of fresh ai mixed with exhaled air to reach the alveoli.

In accordance with one aspect of the present invention, there is provided a breathing device for mediating a C0₂ enriched air mixture having an unlimited supply of C0₂ and air. Referring to Figure 1, there is disclosed a breathing device 10 which comprises a housing 12 having a mixing chamber 14 therein. Mixing chamber 14 is in gaseous communication with the exterior of the chamber by way of breathing port 16 and at least one vent port 18. Preferably, breathing port 16 is provided with a fitting

20 such as a tubular connector for facilitating breathing. Any of the wide variety of fittings can readily be envisioned by one of ordinary skill in the art, depending upon the intended application of the breathing device 10. Preferably, the breathing fitting 20 is provided with a mouthpiece 22, as seen in Figure 2, which may be in the form of a snorkel type mouthpiece. Alternatively, a breathing mask (not shown) covering the nose and mouth can be attached to the breathing fitting 20, providing a convenient way to use the device of Figures 1 and 2. The fitting 20 can also be mounted directly on the housing 12 with the proximal end of the fitting 24 extending outward. A flexible tubular extension 26, as shown in Figure 2, can also be provided which allows for easy use. However, the residual air volume within any extension 26 will preferably be minimized, as will be apparent from the disclosure herein. A mask 36 can also be fitted over the face and held in place with straps 44 as shown in Figure 4, or other suitable retention structures can be provided.

In reusable embodiments of the breathing device 10, the mouthpiece 22 or fitting 20 may be removably secured to the breathing port 16 of the housing 12, so that a one-time use disposable sterile mouthpiece (not shown) can be connected to the housing for each new user. Alternatively, a protective outer sheath (not shown) or other structure may be provided for removable attachment to the mouthpiece 22.

As will be apparent to one of skill in the art in view of the description contained herein, the volume between the breathing port 16 and the mouth of the user is optimall minimized in typical applications of the present invention Since the volume contained in the fitting 20 is essentially a extension of the tracheal volume of the user, this additiona dead space adds to the wasted volume of the system. Althoug for some applications such as athletic training, it may b desirable to artificially increase the wasted volume in th system, most applications of the present invention ar optimized by minimizing the wasted volume. Similarly, vent 18 preferably comprises an orific without any additional tubular structures such as extensions The vent 18 is preferably of about the same cross sectiona are as the breathing port 16, so that substantially edua flow characteristics are provided by the vent and breathin port. The vent is preferably relatively small so that whe air is drawn into the chamber, a jet of air causing interna turbulence is created. The vent is preferably large enough however, that air will flow freely out as the user exhale into the chamber. Vent 18 can alternatively take the form o a plurality of smaller ports or openings on the housing 12 fo placing the chamber 14 in communication with the atmosphere The vent 18 can be comprised of more than one opening, locate to provide multi-directional turbulence which can facilitat mixing. In another embodiment, the vent 18 is further provide with a mesh or filter 38, with one or more valves 40, as show in Figure 7, for preventing the introduction of unwante airborne debris or atmospheric pollutants into the mixin chamber 14. One or more inlet valves 40 allows incoming ai to pass through the filter 38 and into the chamber 14. Th size and number of inlet valves are not critical, as long a air is permitted to flow freely into the mixing chamber. funnel 62 with a small opening 64, which serves as an inle vent, causes the incoming air to flow into the chamber as jet of air, causing turbulence to facilitate mixing Preferably, an outlet valve 42 allows air to bypass the filte and leave the chamber. Any of the several one-way valves known to those skilled in the art can be provided, including flutter valves, and slit valves. Selection of any particular filtration element is largely dictated by the intended use environment of the breathing device 10, as will be apparent to one of skill in the art. In general, a simple gauze or mesh type filter is preferably used. Typically, the filter 38 will not introduce an unreasonable degree of resistance to air flow, unless resistance to air flow is desired such as in an application for breathing exercises. The porosity of the filter 38 adjustably determines the flow rate of the incoming air so that the size of the inlet valve 40 is not controlling of the flow. .

In another embodiment, as shown in Figure 8, an oxygen supply can be attached -to a two-way valve system 46 which allows pure 0₂ 48 to be drawn in through an inlet valve 50, and excess air to leave through an outlet valve 60. A pressure regulator (not illustrated) will typically be used between the source of pressurized 0₂ and the mixing chamber, as is well known in the art. Pure 0₂ supplies 48 may be desirable in some medical applications.

In any of the single vent port embodiments or the multiple vent port embodiments discussed above, the vent or vents (not shown) can be located in a manner that optimizes mixing within chamber 14. For example, influent vents can be positioned tangentially on the periphery of a cylindrical housing 12 in a manner that induces a venturi flow within the chamber 14, causing a vortex flow circulation in the cylindrical housing. In one embodiment, the cylindrical housing can have a spiral exterior configuration with the vent 18 located on the wall extending along an axis generally parallel to the longitudinal axis of the cylinder. Influent into this spiral will be tangential, causing the flow to swirl around to maximize the mixing within the housing. Alternatively, one or more baffles (not shown) can be installed on the inside of the vent to focus or dissipate the flow of air tangentially into the housing. Preferably, for maximum circulation to occur within the chamber, the breathin port 16 should be substantially on the opposite end of th chamber from the vent 18. In general, however, chamber within the range of from about 1 liter to about 12 liter wil likely exhibit sufficient mixing without regard to ven location.

.The breathing port 16 can also be adapted to caus exhaled air to be introduced into the chamber 14 as a je stream to facilitate mixing. The breathing fitting 20 can b positioned such that it directs exhaled air at a tangent t cause a vortex swirl within the cylindrical housing 12. Indeed, because people tend to exhale more vigorously tha inhale, this process can be even more important to prope mixing. In the embodiment of Figures 3-5, the exhaled ai comes directly from the nose and mouth of the user, whic assumes the function of the breathing port, and the mixing i caused by the direct exhalation into the chamber.

For some applications, such as mechanical ventilatio where the force of ventilation might be insufficient t produce good mixing, the inclusion of a fan (not shown) withi the chamber would be advantageous. A probe (not shown) fo measuring PC0₂ levels may also be included in the chamber 14.

The volume of air in the mixing chamber 14 is preferabl within the range of from about 0.5 to about 20 liters, and, more preferably, within the range of from about 1.5 to abou 10 liters. With a very small trap, such as a 0.5 L trap, th tidal volume is likely to be twice the volume of the trap. With such a small trap, a slight degree of hypercapnia ma result, having an alerting effect which could be useful as a anti-drowsiness device. On the other hand, in a relativel large trap, with good mixing in the trap, the average conten of the air in the trap will approach 50% exhaled air and 50 ambient air, and will substantially stabilize over time.

Alternatively, housing 12 can be constructed in a manne which provides a selection of chamber volumes. For example as can be seen in Figure 6, housing 12 can be provided with telescope type extension structure 28 wherein a first portio of the housing 30 is slidably concentrically fitted within a second portion 32 and/or third portion 34 of the housing and adapted to be displaced between a first position in which the chamber 14 has a first volume, and at least a second position in which the chamber 14 has a second volume. Alternatively, the housing 12 can be provided with a plurality of pleats 52 so that the chamber volume can be modified in an accordion¬ like fashion, as can be seen in Figure 3. Optionally, a graduated scale (not shown) is provided to provide an indication of the volume of the chamber 14.

The breathing device 10 can be constructed in any of a variety of manners which will be readily understood by one of skill in the art in view of the disclosure contained herein. For example, in a fixed volume chamber 14, the housing 12 can be vacuum- ormed, injected-molded, or produced. in any of a variety of other manners well known in the art of thermoplastic or thermoset forming. Pre-molded plastic parts or plastic sheet stock can also be solvent bonded, heat bonded or bonded with adhesives. Alternatively, the housing 12 can be constructed from cold rolled or other metal sheet stock such as aluminum or stainless steel, to provide a sterilizable reusable breathing device.

Inexpensive disposable breathing devices can also be constructed from paper, cardboard or related materials, such as waxed board or other combinations or composites and layered light weight materials. Material choice and the use of a fixed volume chamber or collapsible housing are largely governed by the intended application of the device, and the available storage space for devices prior to use. The volume of air in the chamber 14 functions as a carbon dioxide trap, in which exhaled air is trapped and mixed with ambient air being drawn in. The chamber 14 conserves and accumulates exhaled C0₂ until the percentage of C0₂ in the container reaches a -level that stimulates respiration, which produces the minute ventilation determined by the volume of the trap. Minute ventilation must^' increase proportionally to the volume of the trap in order to exhale the same volume of C0₂ that was contained in the resting minute ventilation. Because of the increased minute ventilation, the P0₂ of ai inhaled from the trap is virtually the same as that of inhale ambient air. Chamber 14 makes it difficult to get rid of C0 but interferes hardly at all with the uptake of oxygen. I thus provides a safe, simple, lightweight, portable, unlimite supply of C0₂ enriched air.

The following definitions are provided to enhanc understanding of the concepts relating to the physiology o respiration which will clearly show the advantages of th present invention:

Acapnia: A marked diminution in the amount of C0 in the blood.

Apnea: Cessation of respiration. True apnea is th absence of respiratory movements owing to acapnia and th consequent lack of stimulus by C0₂, to the respirator center.

Alveolar Air: Air in the depths of the lungs whic is more or less in contact with the respirator epithelium, and can thus carry out gaseous exchanges wit the blood. It is not the air in the anatomical alveoli, and is a physiological and not an anatomical entity.

Cheyne-Stokes Respiration: A type of breathing i which the respirations gradually increase in depth up t a certain point and then decrease; finally al respiration ceases for half a minute or so and the begins again as before.

Dead Space: The part of the respiratory trac possessing relatively thick walls, that is, from th nostrils to the terminal bronchioles, between which n gaseous blood interchange can take place.

Eucapnia: The presence of C0₂ in normal amount i the blood.

Dyspnea: Shortness of breath. Hypercapnia: The presence of'C0₂ in excess in th blood.

Hyperpnea: A condition in which the respiration i deeper and more rapid than normal.

Hypocapnia: A diminution in the amount of C0₂ in the blood.

Hypoxia: Lack of 0₂, anoxia. Anoxic Hypoxia. Low 0₂ tension in the arterial blood due to interference with the oxygenation of the blood in the lungs, such as may result from a pulmonary abnormality or from a low tension of 0₂ in the atmosphere.

Partial Pressure: The pressure exerted by any one gas in a mixture of gases, equal to the pressure times the fraction of the total amount of gas it represents.

PC0₂: Abbreviation for partial pressure of carbon dioxide.

P0₂: Abbreviation for partial pressure of oxygen. Tidal Volume: The amount of air that enters and leaves the lungs with each cycle of respiration.

Vital Capacity: The greatest amount of air that can be expired after a maximal inspiratory effort. The importance of providing proper mixing of incoming air with exhaled air is demonstrated in Examples I and II below, which qualitively compare the use of two rebreathing devices of the same volume, one ventilation wasting, the other non- wasting.

EXAMPLE I Comparison of 3.87 Liter Wasting Rebreather

With the Present Invention

A 1 gallon or 3.87 liter elongated container measuring

7x7x79 cm, with the vent end of the box open, was compared to a non-wasting rebreather of the same volume and embodying the present invention. The degree of pulmonary ventilation or the level of blood C0₂ was qualitatively estimated by measuring the length of time a breath could be held following use of each device. Short breath holding time is attributable to excessively high C0₂ levels, while the ability to hold breath is promoted by increased alveolar ventilation and eucapnic C0₂ levels.

The following results were obtained. The ventilation wasting device took about three minutes to achieve a stabl maximum breathing rate of 28/min at near maximum tidal volume. At this point there were sensations of shortness of breath, blood pounding in the ears, and a pounding headache synchronous with the pulse. At five minutes there was a feeling of some confusion, and breathing was stopped at the end of an inspiration and breath-holding timed. Breath coul only be held for 12 seconds. This compared to a breath holding time of 25 seconds after a period of quiet breathing. The extremely short breath-holding time produced by the ventilation wasting device is due to high blood C0₂, and this is also the cause of the rapid breathing.

The identical protocol was followed using a non-wasting breathing device in accordance with the present invention. After five minutes of breathing into the non-wasting device, there were no unpleasant sensations. Respiration was 20/min and of moderate tidal volume. Breath-holding was 55 seconds, and this compared to 57 seconds after five breaths of approximately the same depth. The reason for taking five successive breaths was to thoroughly ventilate the lungs but not blow off so much C0₂ as to produce a low blood C0₂ which would markedly prolong breath-holding.

EXAMPLE II Effect of 9.675 Liter Non-Wasting Rebreather in Accordance with the Present Invention

A further comparison was made with a much larger non- wasting device, in accordance with the present invention, having a gas volume of 2^ gallons or 9.675 liters. This device took almost 10 minutes for breathing to reach a maximu rate and stabilize at 34/min with a tidal volume estimated at 4 liters. After 17 minutes there were no adverse symptoms, no sensation of shortness of breath, and no discomfort. Breath- holding was timed at one minute 50 seconds. This compared to only one minute 20 seconds after five similarly deep breaths. Though the device may have produced a slight degree of hyperventilation with lowered blood C0₂ initially, this device produced a pulmonary ventilation of about 126 liters/min, more than 20 times the typical resting rate of 6 liters/min. It is quite impressive that this enormous ventilation caused no discomfort and could have been continued indefinitely.

The discomfort produced by ventilation wasting rebreathing devices should not be underestimated. The 3.87 liter device described above is probably at the upper limit of what can be tolerated in a wasting rebreather. But even much smaller volumes produce a sense of shortness of breath, unease and discomfort. In some individuals they can precipitate a full blown panic attack.

Examples III and IV will help explain how the carbon dioxide trap works. In both examples, the hypothetical subject is a vigorous male with the following respiratory parameters: Vital capacity , 4.8 liters

Tidal' volume (rest) 0.5 L

Respiratory rate (rest) 12/min

Respiratory minute volume (rest) 6 L/min Anatomical dead space 150 ml Alveolar ventilation (rest) 4.2 L/min

Maximum voluntary ventilation 150 L/min PH₂0 (water vapor) in lungs . 47 mm Hg P0₂ in airway before alveoli 150 mm Hg P0₂ in alveoli 100 mm Hg PC0₂ in alveoli 40 mm Hg

For the sake of simplicity, any increase in oxygen consumption (and C0₂ production) due to the work of increased ventilation will be ignored.

EXAMPLE III The subject breathes into a long tube with a contained volume of 6.5 L. In order to obtain 0.5 L of pulmonary ventilation, he will have to increase his tidal volume to 7.0 L. Clearly, this is impossible since his vital capacity is only 4.8 L. No matter how fast or how deep the subject breathes, he will be unable to obtain any fresh air. If he does not abandon the effort, he will soon suffocate. This is truly wasted ventilation. EXAMPLE IV In this example, the subject now breathes into a 6. liter container which is open to the outside through a smal hole. Inside the container is a fan that rapidly an completely mixes inhaled air with the air in the containe volume. Now the subject will obtain at least some fresh ai with each breath, so the previous reasoning cannot be used t arrive at the new required tidal volume. However, because th minute ventilation is determined by how much carbon dioxid has to be eliminated, then it can be reasoned that the amoun of C0₂ that was contained in 0.5 L will now be contained i 7.0 L (6.5 liters in container plus 0.5 liter tidal volume). Thus/ to eliminate this amount of C0₂, the subject will onc again have to increase his tidal volume to 7.0 L, exactly th same result as with the long tube. Once again, this will b an impossibility. However, the subject will be able t increase his per minute ventilation. Seven liters divided b 0.5 L equals 14, so if his resting ventilation of 6 L/min i multiplied by 14, this new minute ventilation of 84 L/min wil eliminate the same amount of C0₂. A ventilation of 84 L/mi is not much more than half his maximum voluntary ventilation, and he should be able to keep this up indefinitely. Thus, there is a world of difference between breathing into a lon tube and breathing into a well circulating C0₂ trap. In Example IV, a fan insured mixing of the air in th trap. As it turns out, a fan is not required. The turbulenc produced by vigorous breathing adequately mixes new and ol air in the trap. In an actual trial with a large trap, plastic container with a measured volume of 6.8 L was used. Two widely spaced 2 cm diameter holes were drilled in the to of the container. One hole served as a vent, the other wa fitted with a 1.5 cm internal diameter plastic breathing tube. This was used snorkel style in place of a mask.

It would seem probable that if a trap and a C0₂ mixtur both produce the same degree of respiratory stimulation, the would both contain the same percentage of C0₂. If a 6% CO mixture produces a ventilation of about 31.5 L/min and a 2. L trap also produces a ventilation of about 31.5 L/min, then the trap should contain 6% C0₂. Based on this reasoning it was anticipated that breathing into a 6.8 L trap would be quite challenging. It was thought the PC0₂ in the trap would be high enough to cause considerable hypercapnia. Instead, breathing into the trap was surprisingly easy. As the C0₂ concentration gradually built up, respiration became deeper and faster. After about six minutes, respiration stabilized at about 28/min. Tidal volume was very high, estimated at over 3 L. Pulse rate went from a resting level of 50/min to 60/min. Breathing into the trap was continued for over 40 minutes with no change in pulse rate and only minor variations in tidal volume and respiratory rate. At no time were there any symptoms of hypercapnia: no headache, nausea, confusion or change in pulse rate. The subject felt no dyspnea and no fatigue and believed he could have kept breathing into the trap indefinitely. After stopping, there were no symptoms, specifically no onset of headache. All of this was somewhat surprising. On page 532 of the physiology text by Ganong entitled "Review of Medical Physiology," published in 1981 by Lange, there are three graphs showing respiratory minute volume, tidal volume, and respiratory rate plotted against alveolar PC0₂ with various C0₂/air mixtures. The highest C0₂ concentration used was 6%, and this produced a respiratory minute volume of about 31.5 L/min, a tidal volume of about 1.65 L, a respiratory rate of 19/min, and an alveolar PC0₂ of about 50 mm Hg. Of the three graphs, the one showing respiratory rate is the most linear. Extrapolating from this graph to a respiratory rate of 28 gives an alveolar PC0₂ of 74 mm Hg. If this were the case, the subject would have been severely hypercapnic. Some other mechanism must be involved.

There is a fundamental difference between breathing a C0₂ mixture and breathing into a trap. With a C0₂/air mixture the supply of C0₂ is unremitting and inescapable. With a trap, an increase in tidal volume or respiratory rate, immediately lowers the alveolar concentration of C0₂. This may permit the operation of a physiological mechanism that increases ventilation so as to keep alveolar PC0₂ at a constant level. What takes place when breathing into a trap is closer to what actually occurs during exercise: there is a marked increase in ventilation even though alveolar PC0₂ does not rise. This means that a trap is much more physiological than a C0₂ mixture. Traps produce far higher minute ventilation than can be achieved with C0₂/air mixtures. C0₂ produces only moderate stimulation. Mixtures of 2%, 4% and 6% C0₂ and air produce respiratory minute volumes in the range of 9, 16 and 31 L/min respectively. Normal alveolar PC0₂ is 40 mm Hg or 5.3% C0₂. When the percentage of C0₂ in the ambient air exceeds this amount hypercapnia is inevitable. The maximum minute volume ^-that can be produced by C0₂ is about 68 L/min at an alveolar PC0₂ of about 64 mm Hg. Beyond this, respiration begins to fail from impending C0₂ narcosis. It is extremely unpleasant to breath these high concentrations of C0₂, and most people can only tolerate them for a few minutes. Table I illustrates the linear relationship between trap size and required minute ventilation, as well as the improvement in alveolar ventilation that occurs even with small volume traps. The table is not based on data. The values have been calculated on the basis of some assumptions. The assumptions are as follows: (1) resting respiration is 6 L/min with a tidal volume of 0.5 L at a rate of 12/min, resting alveolar ventilation is 4.2 L/min, and dead space is constant at 150 cc; (2) alveolar PC0₂ is maintained at a normal 40 mm Hg? (3) there is good mixing in all traps and the use of average values of partial pressures is justified; (4) there is no increase in metabolism with increasingly energetic breathing. (This is obviously not the case, but because breathing. is so efficient, the increase in C0₂ production is probably negligible with small and medium sized traps. With large traps it is not, but the only effect is to make the trap seem even larger than it is.)

Minute Ventilation Reguired by Trap As described above, the minute volume that a particula trap will produce is determined by the need to blow off specific amount of C0₂ every minute. This is calculated fro the formula: Minute Ventilation = (trap volume + 0.5 L) x 12/min

P0₂ of Inhaled Air The P0₂ of the air inhaled from a trap (the P0₂ in the airway after the PH₂0 has reached 47 mm Hg) is calculated thus. At rest, the P0₂ in 350 ml of alveolar ventilation goes from 150 to 100 mm Hg with each 0.5 L respiration. This 50 m Hg is then spread over an additional 150 cc of dead space air, to make up the tidal volume of 0.5 L. Thus, the ratio 350 cc/500 cc x 50 mm Hg = 35 mm Hg, gives the drop in P0₂ in each 0.5 L of resting tidal volume. In turn, the ratio 0.5 L/(trap volume + 0.5 L) x 35 mm Hg subtracted from 150 mm Hg (the P0 of ambient air after it is saturated with 47 mm Hg of wate vapor) = the P0₂ of the air inhaled from the trap. P0₂ Inhaled Air in mm Hg = 150 mm Hg minus 0.5 L/(trap volume + 0.5L) x 35 mm Hg PC0-, of Inhaled Air

The PC0₂ in the air inhaled from the trap is calculate as follows. The PC0₂ in 350 cc of resting alveolar ventilation goes from 0 to 40 mm Hg. Thus, 350 cc/500 cc x 40 = 28 mm Hg, the PC0₂ in each 0.5 L of resting tidal volume. Thus, 0.5 L/(trap volume + 0.5 L) x 28 mm Hg = PC0₂ of air inhaled from the trap.

PC0₂ inhaled air in mm Hg = 0.5 L/(trap volume + 0.5 L) x 28 mm Hg

Alveolar PP.. The alveolar P0₂ is calculated as follows. The ratio

.350 L/(trap volume + 0.35 L) x 50 mm Hg = drop in alveola

P0₂. This, subtracted from the previously calculated P0₂ o air inhaled from the trap gives the alveolar P0₂.

Alveolar P0₂ in mm Hg = P0₂ Inhaled Air Minus .35 L/(trap volume + 0.35 I.) x 50 mm Hg.

TABLE I Trap Vol Min Vent P0₂ PC0₂ Alv PC0₂ Alv P0₂

The present invention does not increase the C0₂ content of the blood beyond its eucapnic level and is not applicable for treating hyperventilation syndromes or the specialized application described in U.S. Patent Nos. 4,508,116 and 4,628/926 to Duncan. "However, it should be far superior to the known respiratory exercisers, such as those disclosed in U.S. Patent No. 3,455,294 to Adler and U.S. Patent No. 4,275,722 to Sorensen. It is anticipated that this and other medical uses of the device will probably be just as important as the high altitude applications.

A safe, unlimited supply of carbon dioxide enriched air available from a portable light weight device, such as provided by the present invention, may advantageously be used to solve problems that still exist in the state of the art in a wide variety of fields.

For example, rebreathing devices in accordance with the present invention are particularly well suited for a variety of aviation applications. Oxygen and pressurized cabins have not solved all of the problems posed by hypoxia in aviation. There is a very large fleet of general aviation aircraft and only a small percentage have pressurized cabins. The great majority of the unpressurized aircraft probably fly without oxygen. Although these pilots generally fly below 10,000 feet, occasionally because of strong updrafts or emergency conditions, they may fly at much higher altitudes where hypoxia can become a real hazard. The FAA (FAR Part 9-1.211} dictates that the minimum flight crew must use oxygen on flights of over 30 minutes duration between 12,500 and 14,000 feet of cabin pressure altitude. Above 14,000 feet, the crew must use oxygen at all times, and above 15,000 feet, everyone in the plane must be provided with supplemental oxygen.

However, heavy smokers and many older pilots can become significantly hypoxic and require oxygen at altitudes as low as 10,000 feet.

There is also the problem of low altitude hypoxia. Even at altitudes of 5,000 to 10,000 feet hypoxia can pose a subtle danger. At the very least it adds to the strain and fatigue of flying, but it also interferes with vision, ^•hearing, and cognition. Because of this the FAA recommends the use of oxygen from the ground up for night flying. The accident rate for general aviation aircraft is appallingly high, almost entirely due to pilot error. Otherwise intelligent, reasonably well trained pilots often show poor judgment. How much of this poor judgment is due to the subtle effects of low altitude hypoxia is a matter of conjecture. Airline pilots possibly also experience low altitude hypoxia, since airliners are pressurized at up to 8,000 feet cabin altitude, without any apparent adverse effects. However, airline flying is highly routine and automated - the airplanes literally fly and navigate themselves - and all flights are under instrument flight rules with strict ground control. Even so, many airlines require their pilots to use supplemental oxygen prior to landing to sharpen vision and improve cognitive ability.

Even in airline flying there may be room for improvement particularly in emergency situations. With loss of cabin pressure at high altitude, emergency oxygen masks are automatically deployed. However, the oxygen supply is typically only sufficient to provide time to fly to a lower altitude, but not sufficient to permit sustained flying at higher altitudes. There could be a real safety factor, in terms of avoiding weather or for fuel economy, if the pilot had the option to fly at 20,000 feet instead of lower altitudes .

In a sea level portion of their study, Harvey, et al.» i "Effect of Carbon Dioxide in Acute Mountain Sickness: J Rediscovery," 1988 Lancet, reported that breathing S% oxygen/95% nitrogen rendered subjects unconscious with grossl abnormal changes in the electroencephalogram. The addition o-f 5% C0₂ gas (i.e., 5% C0₂ + 5% 0₂ + 90% N₂) restored- consciousness and returned the EEG to normal. A mixture of 5-^, oxygen has a P0₂ of only 38 mm Hg. Before 1900, Angelo Mossα used C0₂ mixtures at pressures as low as 250 torr (about 8800 in or almost 29,000 feet) in a hypobaric chamber as reported iss "Life of Man on the High Alps," 1898 London. This would. suggest that C0₂ enriched air works almost as well as breathing 100% oxygen. However, since the partial pressure f water vapor in the alveolar air is constant at 47 mm Hg_Λ and. that of C0₂ is normally 40 mm Hg, the very highest the alveolar P0₂ could be at an ambient pressure of 250 mm Hg is- 34 mm Hg (21%[250-87]=34) . Normal EEG or no, it is impossible to believe that a subject would not be severely hypoxic τπan.der these conditions.

The effects of hypoxia are often compared to alcohol intoxication. One may be able to go from being a passed out drunk to a wide awake drunk with the addition of 5% C0₂, but: in either case one should not be flying an airplane. However,. if C0₂ enriched air enabled a pilot to be alert and function at 20,000 feet or so, that would be a significant: contribution. Most light planes rarely fly above 20,000 feet-_* indeed most cannot even climb that high. The availability αf carbon dioxide enriched air could be a valuable backup in case of oxygen system failure, or for emergency conditions in- aircraft without oxygen. It could also be the perfect solution to low altitude hypoxia, and might even give- airliners an added safety factor in case of loss of cabin, pressure. Another application of the present invention is iπ_ mountaineering. For more than half a century, experts have known that inhaled C0₂ might be useful in assisting breathing_/ during climbing to great altitudes. It would be reasonable to expect that unacclimatized climbers would receive the most benefit. The availability of C0₂ enriched air would permit a mountaineer to quickly go from sea level to a high altitude. This would permit unprecedented freedom of movement and scheduling.

C0₂ enriched air should also be of benefit to acclimatized climbers, permitting higher altitudes with less hypoxia. Even if a climber did not wish to wear a mask while climbing, C0₂ enriched air, by abolishing Cheyne-Stokes respiration, should make sleep safer and more restful. The old mountain climbing adage, "climb high, sleep low" would no longer be necessary. For extremely well acclimatized individuals, especially at very high altitudes, C0₂ might be counterproductive. A lower alveolar PC0₂ would permit a higher alveolar P0₂, and hypocapnic hypoxia may be better tolerated than eucapnic hypoxia.

A variety of methods in the field of medicine can be advantageously performed using the non-wasting rebreathing device of the present invention. In the field of medicine, there are a number of clinical situations where a great increase in pulmonary ventilation would be highly beneficial, but at present, because of the unavailability of C0₂ mixtures, this is impossible due to hypocapnia. The following are some examples.

Acute Mountain Sickness (AMS) . AMS can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE) . Both HAPE and HACE are grave medical conditions which continue to cause fatalities. Because C0₂ enriched air may prevent or be used to treat AMS, the ready availability of a C0₂ source could be life saving.

In accordance with a further aspect of the present invention, there is provided a method of treating Carbon Monoxide Poisoning._, The treatment objective is to remove carbon monoxide from the blood stream and body as quickly and thoroughly as -possible. However, -the affinity of hemoglobin for carbon monoxide is 210 times its affinity for oxygen. To speed up the otherwise very slow release of carbon monoxide from carboxyhemoglobin, a mass action effect is required. For this reason, hyperbaric oxygen is especially valua-fole. However, for immediate treatment and for treatment during transport to a hyperbaric oxygen facility, C0₂ enriched oxygen or C0₂ enriched air provided by a device in accordance witϊs the present invention, would greatly increase ventilation and accelerate the elimination of carbon monoxide.

Mechanical Ventilation can also potentially be enhanced by a use of a breathing apparatus in accordance with thte present invention. Just as in ordinary breathing, the rate of mechanical ventilation is limited by hypocapnia. CQ>₂ enrichment Would' permit much more flexibility. Greatly increased ventilation might permit the use of lower concentrations -of oxygen and lower positive end expiratory pressure (PEEP) /thereby avoiding possible oxygen toxicity and- complications of'high PEEPs.

There is further provided a method of inducing Breathing Exercise for Patients Unable to Exercise, comprising breathing through a breathing device of the present invention for an exercise inducing period of time. Bedridden patients, or patients with angina pectoriε, pulmonary disease, congestive heart failure, arthritis, and the like, may get little or no exercise. Not only do these patients develop severe deconditioning of their skeletal muscles, but their respiratory muscles are also affected. This has well known adverse consequences when the respiratory system is put under stress, such as with pneumonia or major surgery. In extremely compliant and strongly motivated people, special exercises may theoretically improve respiratory muscle strength and endurance, but as a practical matter it is unlikely these exercises accomplish anything in other patients, and particularly sick elderly patients.

A non-wasting respiratory stimulator, however, can provide very vigorous breathing which, being automatic and involuntary, requires no compliance or motivation. This increased breathing can be continued for one or more preset intervals up to the fatigue limits of the patient.

Furthermore, because breathing is so efficient, even a high ventilatory rate can be sustained at only a small metabolic cost. As an example, a coronary patient who develops angina with moderate walking, could probably sustain a ventilatory rate equivalent to fast running without discomfort. If over a period of time such as several weeks the patient could work up to an hour of this level of breathing a day, there should be substantial improvement in vital capacity and respiratory muscle strength and endurance. This should greatly improve the patient's chances of going through coronary bypass surgery without pulmonary complications. Thus, C0₂ enriched air offers the possibility of substantially improving respiratory , function and well being in a very large group of debilitated patients, something that is completely unobtainable at the present time.

A method of respiratory training of healthy humans, such as in preparation for any of a variety of athletics is also provided in accordance with the present invention. For many athletes, the most difficult, distressing, and performance limiting factor is the extreme dyspnea that develops with maximal effort. This is probably both a physiological and psychological barrier. There is evidence that, with training, athletes can inure themselves to dyspnea.

Although it is difficult to know what measures are available to world class athletes in sophisticated proprietary and government training programs, the great majority of athletes are limited to wind sprints and interval training. These exercises are extremely fatiguing, of short duration, and when overdone can lead to staleness and injury. Thus the amount of respiratory training these athletes receive is really quite limited.

The ability to uncouple respiration from exercise that the non-wasting respiratory stimulator provides, should make it possible to selectively train and condition the respiratory system. The device, especially in combination with mild or moderate exercise, could provide extended periods of severe dyspnea with only a very moderate expenditure of energy.

A number of additional potential uses of carbon dioxide mediated respiration in accordance with the present invention include facilitating smoking cessation, treatment of obesity and resisting drowsiness.

Successfully stopping smoking involves overcoming two addictions, a physiological one and an emotional one. For many heavily addicted smokers the physiological addiction is an insurmountable barrier. However, in the first few days of stopping smoking, a great deal of the often overwhelming urge to smoke, experienced as the intense desire to deeply inhale a cigarette, may simply be a matter of air hunger. Possibly the respiratory center is hypoactive after years of chronic stimulation by nicotine. In any case, the urge for a cigarette can often be dispelled by a few deep breaths. However, for many smokers, this is difficult both to do and to remember. The use of C0₂ enriched air for several days would completely eliminate the air hunger and might be a very useful stop smoking aid for the heavily addicted smoker.

Lack of exercise may be a more important cause of obesity than overeating. Certainly, if everyone walked ten miles a day (or the equivalent) almost everyone could eat to satiety and almost everyone would be thin. However, this is probably ten times more exercise than most people are willing to contemplate much less do, and more than three times as much exercise as most doctors are willing to recommend to their patients.

In all fairness to overweight people, exercise becomes progressively more difficult, uncomfortable and discouraging the older and fatter an individual becomes. For the average middle aged obese person, exercycles and rowing machines are impossible, high impact aerobics out of the question, low impact aerobics the equivalent of no aerobics, and even walking more than a block or two may prove too arduous and painful. Thus, if a person in this predicament could do something to lose weight- that he or she does all the time anyway, such as breathing, it might represent a new and useful alternative.

Even though breathing is extremely efficient, it nevertheless requires work. A small amount of work performed over a long period of time seems just as effective in causing weight loss as a large amount of exercise in a short time. For example, the resting tremor of Parkinson's Disease is very low level exercise, yet because it exists during all waking hours it uses a lot of energy and these patients lose weight. Preliminary estimates suggest that a ventilatory rate that requires the same caloric expenditure as one mile per hour walking would not be unreasonable. An individual would certainly be aware of very heavy breathing, but for most people this should be below the dyspnea threshold. The ideal would be to go to sleep and wake up eight hours later having done the equivalent of eight miles of walking. However, it is doubtful if anyone could fall asleep while breathing that heavily. It .may be possible, however, to fall asleep breathing ambient air through a mask with a controlled valve, which would then switch to connect it to a mixing chamber after a preset time. This device might enable a person to stay asleep while ventilation is increased. Nevertheless, three or four hours of deep breathing every evening would still amount to a great deal of exercise, probably enough exercise for most people to reach an ideal weight.

Many people, perhaps the majority, do not get enough sleep. This can result in daytime drowsiness which can become severe in situations such as driving on long monotonous roads. Every day, drivers of cars, trucks, and buses doze off on the nation's highways. This sometimes results in well publicized tragedies. Preliminary results suggest that it is very difficult to fall asleep breathing C0₂ enriched air. Perhaps the mild hypercapnia that it causes increases cerebral blood flow and sympathetic tone. This suggests that C0₂ enriched air might have an additional use as a method of preventing drowsiness and increasing alertness.

A variety of different models of the breathing stimulator will be apparent to one of skill in the art in view of the disclosure herein, depending on the desired application. All designs incorporate a carbon dioxide trap, which can be integrated in a face mask 36, as shown in Figure 4, or contained in a separate housing 12, as shown in Figure 1. The face mask 36 design can probably accommodate a trap volume of up to 2.5 L, which would multiply resting ventilation by a factor of up to 6. This might be satisfactory for most aviation, mountaineering, and medical applications. For aviation or mountain climbing use, in order to minimize facial injury in case of impact, the mask 36 should be made of soft but fairly firm and durable rubber. The mask 36 can be part of a helmet 54 which would include earphones 56 and a microphone 58 for ease of communication, as can be seen in Figure 5. A clear silicone rubber version might be preferable for other applications, such as for stopping- smoking or as an anti-drowsiness device for drivers. A very light plasticized paper version, which would fold accordion style 52 into a small flat space, might be suitable for one time emergency use on airliners, as can be seen in Figure 3.

A tank version 10 (as shown in Figure 1) of the breathing stimulator would be useful for higher volume traps, such as might be necessary for athletic training, weight loss, treatment of carbon monoxide poisoning, and very high altitude applications. The tank 10, connected by tube 20 (as short as possible) to a face mask (not shown) , can be of telescoping design 28, as can be seen in Figure 6, thereby allowing great flexibility in the choice of trap volume and consequent respiratory stimulation. For specialized applications certain additional features can be incorporated. At low altitudes in urban s oggy areas, anyone who breathes at many times the resting rate for a prolonged period would be subjecting the respiratory system to a high load of atmospheric pollutants. Thus, for this type of application a special smog filter 38 with valves 40, 42 may be used as shown in Figure 7. To use the trap with oxygen, simple flutter valves 46 would be required as shown in Figure 8. For use with mechanical ventilation, a fan (not shown) may be required in the mixing chamber to ensure adequate mixing of inhaled and exhaled air in the chamber.

The breathing stimulator does everything that C0₂/air mixture can do. However, it has enormous advantages over C0₂ mixtures. In probable order of importance these are as follows:

The breathing stimulator is safe to use. Because the source of the C0₂ is the user's own respiration, there is no possibility of human error or equipment failure leading to accidental asphyxiation or C0₂ narcosis. As long as the physiological mechanism stimulates respiration to maintain alveolar PC0₂ within normal limits, there should be no complications from hypercapnia. This would mean that the breathing stimulator could be used for prolonged periods (24 hours or more) without loss of sensitivity and responsiveness to stimulation and with no fear of developing pulmonary hypertension.

Physiological stimulation is also provided. The breathing stimulator provides physiological stimulation, akin to exercise, and therefore, has major advantages over C0₂ mixtures. It provides stimulation without adverse effects right up to maximum voluntary respiration and thus provides complete uncoupling or disassociation of ventilation from exercise, which should make it a useful ergogenic training device.

The stimulator also provides an unlimited supply of C0₂ because the source is the user's own respiration. The concentration of C0₂ in the trap is also controlled automatically and involuntarily by the user's respiratory system.

The breathing stimulator also has complete portability, and can be designed to weigh only a few ounces, and can be used under all conceivable conditions. The breathing stimulator will also be only a fraction of the cost of any possible method for delivering a C0₂/air mixture.

Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the invention. Accordingly, the scope of the invention is intended to be defined only by reference to the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A non-wasting respiratory stimulator for providing a user with a C0₂ enriched fresh air mixture, comprising: a housing, having a chamber therein; a breathing port on said housing for providing communication between a user of the non-wasting respiratory stimulator and the chamber; and at least one vent on said housing for providing communication between the chamber and the atmosphere; wherein air is drawn into the chamber through said vent as the user draws air out of said chamber through said breathing port, and wherein the chamber is configured so that substantially all of the air drawn into the chamber through the vent is mixed with the contents of the chamber. -

2. The respiratory stimulator of Claim 1, wherein said chamber is configured so that substantially all of the exhaled air introduced into said chamber through said breathing port is mixed with the contents remaining in said chamber.

3. The respiratory stimulator of Claim 1, further comprising a mouthpiece in gaseous communication with the breathing port.

4. The respiratory stimulator of Claim 1, wherein a mask dimensioned to fit over a user's nose and mouth is in gaseous communication with said breathing port.

5. The respiratory stimulator of Claim 1, wherein said breathing port is dimensioned to fit over said user's nose and mouth.

6. The respiratory stimulator of Claim 5, further comprising a means to secure said housing to said user's face.

7. The respiratory stimulator of Claim 1, wherein said breathing port further comprises a breathing tube.

8. The respiratory stimulator of Claim 7, wherein said tube is flexible.

9. The respiratory stimulator of Claim 1, wherein said housing comprises at least one movable wall for adjusting the volume of the chamber by moving the wall from a first position to a second position.

10. The respiratory stimulator of Claim 1, wherein the volume of the chamber is within the range of from about 100% to about 4,000% of the resting tidal volume of the user.

11. A respiration stimulation device, comprising: a container having a mixing chamber therein; a vent on said container for providing communication between the chamber and the atmosphere; and a breathing port through which a user may inhale from and exhale into said chamber, wherein substantially all of the air drawn into the chamber through said vent is mixed with the contents of the chamber.

12. The device of Claim 11, wherein substantially all of the air exhaled into said chamber is mixed with the contents of said chamber.

13. The device of Claim 11, wherein the volume of said chamber is greater than the vital capacity of said user.

14. The device of Claim 11, further comprising at least one movable wall, wherein said container can be expanded from a first relatively compact storage configuration to a second ready for use configuration.

15. The device of Claim 11, wherein said breathing port is further provided with a mouthpiece.

16. The device of Claim 11, wherein said breathing port is provided with a mask dimensioned to fit over a user's nose and mouth.

17. The device of Claim 11, wherein said container is collapsible.

18. The device of Claim 11, wherein said vent and said breathing port are positioned substantially at opposite ends of said container.

19. The device of Claim 11, wherein said container is cylindrical.

20. The device of Claim 19, wherein said vent is adapted such that air flowing through said vent is directed tangentially to the surface of said container.

21. The device of Claim 11, wherein a fan is located in said container to facilitate mixing within.

22. A method of stimulating respiration, comprising: providing a respiratory stimulator having a chamber with a predetermined volume, said stimulator having a 5 vent and a breathing port in communication with the chamber; exhaling through the breathing port and into said chamber, thereby forcing a portion of air in said chamber out of said chamber through said vent port; and 10 inhaling a mixture of exhaled air and fresh air through the breathing port.

23. A method of providing a mixture of exhaled air and fresh air, comprising: ^» providing a container having a substantially •'15 . constant volume; exhaling carbon dioxide enriched air into said container through a breathing port therein; and inhaling a sufficient volume from the container through the breathing port so that an equal volume of 20 fresh inhaled air is drawn into the container through a vent.

24. A method for mixing air, comprising: providing a mixing container having a cavity with a substantially fixed volume; 25 introducing exhaled air through a first aperture on the mixing container and into said cavity such that said exhaled air is mixed with air in said container and excess air exits through a second aperture; inhaling through said first aperture on said 30 container, whereby fresh air is drawn into said container through said second aperture, such that said fresh air is mixed with exhaled air in said container; and repeating said inhaling and exhaling steps to provide continuous mixing of said exhaled air containing 35 carbon dioxide with said fresh air from outside of said container.

25. The method of Claim 24, including mixing said fresh air with said exhaled air with a fan located in said container.

26. The method of Claim 25, including providing a probe for measuring the partial pressure of carbon dioxide in said cavity.

27. A method of minimizing the effect of hyperpnea by providing an endless supply of carbon dioxide enriched air, said method comprising: providing a chamber having a predetermined volume; exhaling into said chamber through a breathing port to fill said chamber or a portion thereof with exhaled air containing carbon dioxide; inhaling air from said chamber through said breathing port, wherein fresh air is drawn into said , chamber through an aperture, wherein exhaled air in said chamber mixes with said fresh air, providing said user with an endless mixture of fresh air and carbon dioxide enriched air.

28. A method for reducing the effects of hypocapnia, by providing C0₂ enriched air, said method comprising: breathing C0₂ enriched exhaled air into a mixing chamber; permitting excess air in said chamber to leave said mixing chamber; inhaling C0₂ enriched exhaled air from said mixing chamber; and drawing in fresh air through an aperture into said mixing chamber as said user inhales, wherein said air in said chamber is mixed with said fresh air being drawn into said mixing chamber.