Abstract:
A balanced breathing loop for a rebreather is disclosed which includes a system of components that interact to provide substantial safety and alarm awareness benefits over existing methodology in recirculating breathing apparatus loops. The device relies on a specific arrangement of components to create both automatic alternate delivery of gas to replace metabolized oxygen in case of single component failures and breathing characteristic changes that warn the user that a component failure has occurred. The breathing characteristic changes allow the user to identify which specific component has failed, thus allowing for immediate corrective action.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/034,061, U.S. Provisional Application No. 60/034,062, U.S. Provisional Application No. 60/034,063, U.S. Provisional Application No. 60,034,064, U.S. Provisional Application No. 60/034,186, U.S. Provisional Application No. 60/034,570, and U.S. Provisional Application No. 60/035,777, all filed on Jan. 7, 1997. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to rebreathers and particularly to semi-closed circuit breathing apparatuses and components and accessories therefore. 
     2. Description of Related Art 
     Conventional semi-closed rebreathers operate by delivering a premixed gas from a scuba cylinder through a constant flow regulating device, usually by supplying a regulated gas supply to a changeable orifice. Gas is delivered at a preset rate regardless of depth. The gas being breathed is recirculated, and as the oxygen within the mixture is metabolically consumed, it is hopefully being adequately replaced on a continuous basis with a predetermined continuous flow of oxygen enriched gas. 
     Rebreathers consist of a breathing loop from which the diver inhales and into which the diver exhales. As most of the exhaled gas stays in the breathing loop, rebreathers allow for much greater gas efficiency than open circuit systems. This greater gas efficiency allows for longer duration dives as compared to open circuit systems, or, conversely, requires less gas supply for a dive of equal duration. 
     The breathing loop generally includes a relief valve, scrubber, counterlung, depth equalization regulator, continuous injection system, hoses and a mouthpiece. The relief valve is utilized for dumping or venting excess gas in the breathing loop created by the rebreather on ascent and excess gas which is produced with the use of constant (active) addition systems. The scrubber cleanses the exhaled gas of carbon dioxide. The counterlung or breathing bag allows for the retention of the diver&#39;s exhalation gas. The injection system adds fresh gas to the carbon dioxide cleansed gas in the breathing loop. The depth equalization regulator adds supply mix to the loop to keep pace with depth increases. The hoses are utilized to connect the counterlung and scrubber with the mouthpiece. The mouthpiece is connected to the two hoses and is the point on the breathing loop where the diver exhales and inhales. Typically, two conventional one-way valves are incorporated into the mouthpiece. 
     Rebreathers normally include a harness to strap the unit to the diver, with some units also including a protective case for the various above described components. 
     As stated above, rebreathers generally work by recycling most of a diver&#39;s exhaled breath, which travels through the breathing loop through the scrubber, and is returned to the diver during inhalation. The use of a rebreather allows a diver to remain underwater for a relatively long time as compared to the use of open circuit equipment. 
     Accordingly, rebreathers allow exhaled gas to be cleansed of carbon dioxide and replenished with fresh oxygen for further consumption. A traditional fixed flow (active addition) semi-closed rebreather recycles the gas the diver is breathing, removing excess carbon dioxide from the exhaled gas and replacing it with a measured amount of premixed gas to maintain an oxygen partial pressure in the inspired gas that will continue to support metabolism. 
     There are several previously known types of operating systems for semi-closed circuit rebreathers, including fixed discharge ratio, continuous injection and mechanically pulsed. In the 1970&#39;s, as electronically controlled rebreathers were coming into their own, a fixed discharge ratio counterlung (an inner bellows within an outer bellows) was developed for semi-closed use in Europe. This type of rebreather was coined the first “passive” addition or counter mass ratio system. “Passive” means gas is only added as required to replace gas that has been discharged from the breathing loop by the control mechanism. 
     Existing rebreather designs rely on stabilizing the oxygen content of the entire breathing loop, as in FIG. 3, thus requiring higher oxygen fractions to be added and increasing the disparity between oxygen tolerance and decompression restrictions. Prior system have placed all addition functions either upstream of the scrubber or in the counterlung. 
     Furthermore, all prior self-contained systems use supply bottles that are plumbed inside the rebreather. The supply bottles can be mounted inside or outside the rebreather case. Additionally, all existing hose designs utilize continuous runs of highly restrictive bur flexible hose. Some are externally weighted to reduce buoyancy. Previous systems have also utilized absorbent pads or breathing bag drains to manage water entry. No dedicated disinfecting and/or drying system has previously been incorporated into a rebreather. Gas supply bottles have previously been mounted inside or outside on the base of the rebreather itself. The present invention is directed to overcoming the drawbacks of these previous designs. 
     BRIEF SUMMARY OF THE INVENTION 
     One aspect of the present invention is a rebreather design which allows for placement of the counterlung and all gas control and loop overpressure relief functions on the exhalation side of the breathing loop upstream of the carbon dioxide scrubber. The invention also provides for placement of all gas addition functions on the inhalation side of the breathing loop downstream of the carbon dioxide scrubber. The present invention also uses a desensitized demand regulator on the inhalation side of the breathing loop to relieve water ingestion and excess carbon dioxide levels caused by a partially flooded scrubber. The interaction of the components are designed to produce significant breathing characteristic changes in the event of one or more component failures that act as an alarm system. 
     Some of the benefits of the present invention include, but are not limited to, the following: 
     (1) Greatly reduces possibility of single point gas addition failures; 
     (2) Automatically relieves loop breathing resistance caused by scrubber flooding; 
     (3) Automatically relieves loss of scrubber CO 2  absorbent efficiency caused by scrubber flooding; 
     (4) Every component failure produces an unignorable breathing change that serves as an alarm that doesn&#39;t have to be monitored. This eliminates the “task overload” situation that has caused many rebreather diver deaths because various types of “indicating” alarms were either ignored or not even recognized; and 
     (5) Prevents hypoxia through demand gas addition if systemic discharge proportions are not met by the mechanical addition system. 
     Accordingly, it is an object of the present invention to reduce the possibility of single point gas addition failures. 
     It is another object of the present invention to automatically relieve loop breathing resistance caused by scrubber flooding. 
     It is yet another object of the present invention to automatically relieve loss of scrubber CO 2  absorbent efficiency caused by scrubber flooding. 
     It is still another object of the present invention to produce an unignorable breathing change, for any component failure, to serve as an alarm that doesn&#39;t have to be monitored. 
     It is even still another object of the present invention to prevent hypoxia through demand gas addition if systemic discharge proportions are not met by the mechanical addition system. 
     In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention may be better understood by reference to the drawings in which: 
     FIG. 1 is a schematic view of a balanced breathing loop in accordance with the present invention; 
     FIG. 2 is a schematic view of a breathing loop for a rebreather in accordance with the present invention; 
     FIG. 3 is a schematic view of a breathing loop for a rebreather; 
     FIG. 4 is a sectional view of a portion of a compound breathing hose in accordance with the present invention; 
     FIG. 5 is a schematic view of a rebreather water separator and evacuation system in accordance with the present invention; 
     FIG. 6 is a sectional view taken along line A—A of FIG. 5; 
     FIG. 7 is a schematic view of an external semi-closed circuit rebreather control system in accordance with the present invention; 
     FIG. 8 is a schematic view of a rebreather disinfecting and drying system in accordance with the present invention; and 
     FIG. 9 is an isometric exploded view of a removable tank rack for rebreathers. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As seen in FIG. 1 the rebreather design provides for placement of the counterlung and all gas control and loop overpressure relief functions on the exhalation side of the breathing loop upstream of the carbon dioxide scrubber. The invention also provides for placement of all gas addition functions on the inhalation side of the breathing loop downstream of the carbon dioxide scrubber. A desensitized demand regulator is used on the inhalation side of the breathing loop to relieve water ingestion and excess carbon dioxide levels caused by a partially flooded scrubber. The interaction of the components are designed to produce significant breathing characteristic changes in the event of one or more component failures that act as an alarm system. 
     In operation, the diver exhales through mouthpiece  1  or other system interface device. Exhaled gases are prevented from entering inhalation side of breathing loop  4  by non-return valve  3  and directed to exhalation side of loop  5  by non-return valve  2 . The exhaled gases fill the outer portion of the compound counterlung  6  through tube  7 . Simultaneously being drawn inward by suction created by the rising bellows plate  15  and pushed by the positive pressure created on the exhalation side of the loop by the lungs during exhalation, the inner portion of the compound counterlung  8  fills with exhaled gases through tube  9  and non-return valve  10 . Water is prevented from entering the system through tube  11  by non-return valve  13  and elastomeric diaphragm  12  which is pushed against the end of tube  11  by the positive pressure exerted against it by the exhaled gases delivered through tube  14 . Because the diaphragm has several times more area than the opening at the end of tube  11 , a positive seal is obtained via hydraulic advantage. 
     When the diver inhales, gases in the outer portion of compound counterlung  6  are draw out through tube  7  toward the lungs via the inhalation side of the breathing loop  4  and non-return valve  3  and prevented from returning through the exhalation side of the breathing loop  3  by non-return valve  2 . The gases contained within the inner counterlung  8  are prevented from reentering the breathing loop by non-return valve  10  and, pushed by the collapsing outer counterlung  6 , are expelled into the water through non-return valve  13  and tube  11 , which is now open because diaphragm  12  has been pulled away from it by the negative pressure drawn through tube  14 . 
     As gases are drawn into the diver&#39;s lungs through scrubber  16  and the inhalation side of the loop  4 , outer counterlung  6  collapses, driving plate  15  against actuating lever  18  at the end of the inhalation. The lever actuates valve  17 , adding fresh oxygen rich gas to replace the gases discharged overboard during the first part of the inhalation. 
     If valve  17  fails to add all or part of the replacement gas for any reason, a desensitized scuba regulator second stage  21  is actuated by the additional negative pressure at the end of the inhalation and delivers the shortfall. This condition creates an immediately noticeable difference in inhalation resistance but exhalation resistance remains normal, alerting the diver to what has occurred. 
     If water has entered the inner counterlung  8  or the scrubber  16  for any reason, breathing loop resistance will immediately increase on both inhalation and exhalation. The increased inhalation resistance will actuate demand regulator  21  before the compound counterlung has fully collapsed, allowing the diver to draw a full breath. When the diver exhales, there will be too much gas in the loop for the counterlung to accommodate, thus forcing overpressure relief valve  22  against a maximum travel stop  23  and discharging the excess gas. The system will automatically compensate for either type of blockage only to the degree necessary for the diver to receive a full breath, thus providing enough carbon dioxide reduction through increased gas discharge to alleviate hypercapnia problems and enough fresh gas to alleviate hypoxia problems without using any more gas supply than necessary. 
     As seen in FIG. 2, placement of the systemic metabolic replacement gas is disposed in the breathing loop to maximize its usage on the subsequent inhalation by the “active” parts of the lungs, where gas transfer to the blood stream actually takes place. 
     The passive semi-closed circuit breathing loop allows some of the previously exhaled gas (typically 20-25%) to be discharged from the system to ambient  40  by the collapse of the counterlung  35  during the subsequent inhalation. 
     Because part of the previous exhalation will not be available at the last 20-25% of the inhalation, the almost fully collapsed counterlung triggers addition valve  34 , which Baked up the volumetric difference with fresh supply gap. The addition point for the makeup gas  33  is placed so that the entire addition remains in the inhalation part of the breathing loop  30  between the addition point and inhalation non-return valve  36  with the entire addition being as close to valve  36  as possible without going beyond it. 
     On the next inhalation, the lungs  31  first inspire the contents of the pendulum part of the loop, the space bounded by dotted lines Be and  39 . This space consists of the respiratory deadspace contained in the trachea, bronchia, etc. and the deadspace contained in the interface device between the mouth at  2  and non-return valves  36  and  37  Typically, the pendulum deadspace totals approximately 0.35 liter, though the invention is not limited to such amount. 
     Using approximate volumes and based on a  25 discharge/addition, if the respiratory tidal volume is 1 liter, the inspired breath will consist of the 0.35 liter pendulum volume, 0.25 liter fresh gas, and 0.4 liter gas from the unenriched part of the breathing loop, of which 0.35 liters remains in the pendulum deadspace to be the first part of the subsequent exhalation. Thus, approximately 38.5% of the new alveolar gas contact is with fresh gas. The inspired gas is further diluted in the lungs by approximately 1 liter of residual deadspace gas. 
     If the tidal volume is 3 liters, the inspired breath will consist of the 0.35 liter pendulum volume, 0.75 liter fresh gas, and 1.9 liters from the unenriched part of the breathing loop, of which 0.35 liters retains in the pendulum deadspace to be the first part of the subsequent exhalation. Thus, approximately 28.3% of the new alveolar gas contact is with fresh gas. The inspired gas is further diluted in the lungs by approximately 1 liter of residual deadspace gas. The difference in percentage of fresh gas alveolar contact percentage is made up for by the other component of respiratory minute volume, number of breaths per minute. 
     Using standard addition methods, the new alveolar gas contact would be 5-15%, depending on the breathing loop volume. The same amount of oxygen replenishment will be available, but the inspired oxygen fractions will be lower because the fresh gas will have been diluted by all or a large part of the volume of the breathing loop. Some of the benefits include, but are not limited to, the following: 
     (1) Dilution of the higher oxygen partial pressure of the “makeup” or metabolic sustenance gas by the exhaled gases (lower oxygen partial pressure because of metabolic consumption) is minimized; 
     (2) Alveolar contact with the fresh gas addition on each breath is maximized, thus producing a net inspired oxygen fraction that is as close as possible to the supply gas oxygen fraction; 
     (3) The maintenance of e higher inspired oxygen fraction relative to the supply as oxygen fraction reduces the time and depth disparities for oxygen tolerance and decompression requirements between open circuit and semi-closed circuit underwater breathing systems; and 
     (4) In semi-closed underwater breathing systems, the maintenance of an inspired oxygen fraction closer to the supply gas oxygen fraction permits a larger depth range for safe open circuit bailouts using the same supply gas without the occurrence of oxygen toxicity problems. 
     Thus, the invention discloses a method of adding metabolic sustenance gas to a semi-closed circuit breathing loop in such a manner as to avoid diluting the addition with the contents of the “dead” space of the loop and respiratory system, thus assuring maximum alveolar contact with and usage of the added oxygen partial pressure. 
     FIG. 3 shows another breathing loop configuration  41  for a rebreather. As seen in FIG. 4, a compound breathing hose with a water trap for rebreathers is disclosed. The compound hose uses two different types of breathing hose in each hose assembly. Use of a connector between hose types is also provided that traps water away from the diver interface. The hose connector sized and/or weighted to reduce hose assembly buoyancy. 
     In operation, on the inhalation side, breathing gases enter the smooth bore, low flow resistance large diameter semi-flexible elastomeric hose  57  at  59 . The gases proceed to the diver through weighted fitting  51 , while fluid borne caustic scrubber products are trapped by space  53  between hose  57  and fitting extension  52 . 
     Gases are passed to the diver interface through flexible corrugated hose  54 , which is attached to weighted fitting  51  at point  55  and the intake side of the interface at point  56 , and is only long enough to allow diver head movement without placing vertical or side loads on the interface device. Reduction of the length of this hose to the minimum required for free head movement produces a corresponding reaction in internal gas flow resistance and external water flow resistance associated with this type of highly flexible hose. 
     On the exhalation side, gases are returned to the rebreather through flexible hose  54 , weighted fitting  55 , and semi-flexible hose  57 . Any water introduced to the gases through interface mismanagement are prevented from returning to the interface by space  53  between fitting extension  52  and semi-flexible hose  57 , Some of the benefits include, but are not limited to, the following: 
     (1) Prevents diver ingestion of caustic scrubber fluids produced during rebreather operation; 
     (2) Prevents water introduced through the diver interface from gurgling against the exhalation valve; 
     (3) Reduces internal gas flow resistance; 
     (4) Reduces external drag on hoses at high propulsion speeds while using a diver propulsion vehicle; and 
     (5) Eliminates strain at the interface caused by hose assembly buoyancy. 
     Thus, a breathing hose is provided which is intended to be used in pairs to connect a recirculating breathing apparatus to a diver interface. Thus breathing hose reduces gas resistance on the inside, water resistance on the outside, and water intrusion to the diver, and hose buoyancy. 
     As seen in FIGS. 5 and 6 a rebreather water separator and evacuation system in accordance with the present invention is illustrated. The system includes a dual chamber water separator that allows breathing gases to continue to the rest of the breathing loop while trapping water. A non-return valve passes the trapped water to a sump and prevents it from returning to the separator. A sump is provided to extend the water holding capacity of the system. A hand operated pump is also provided to evacuate the contents of the sump at any time during the dive. Furthermore, a hand valve is also provided to prevent overboard gas losses between evacuations. 
     Where a diver inadvertently admits water to the breathing loop through mouthpiece  61  while valve  62  is open, water and exhalation gapes enter exhalation hose  63  The gases and water then enter separator  64  through chamber  65 . The gases enter chamber  67  through water dam  66 . Water is prevented from entering chamber  67  by water dam  66 , which traps water even in an inverted position in areas  76  and  77 . The water enters sump  70  through non-return valve  69 , which is located in the part of chamber  65  that is normally lowest when the diver is swimming or working. 
     When valve  71  is opened, sump  70  can be evacuated through outlet  75  to ambient either by repeatedly squeezing elastomeric bulb  73  and alternately operating non-return valves  72  and  74  or utilizing the excess breathing loop pressure produced on ascent. Some of the benefits include, but are not limited to, the following: 
     (1) Traps large amounts of water that would normally flood the scrubber; 
     (2) Permanently removes water from the breathing loop; 
     (3) Can be repeatedly flooded and evacuated during the dive; 
     (4) Can be evacuated during ascents by simply opening the evacuation valve; and 
     (5) Eliminates gurgling noises associated with diver interface mismanagement. 
     Thus, the water separator and evacuation system provides a means for trapping water that is inadvertently admitted to a rebreather breathing loop through diver interface mismanagement, such as dropping the mouthpiece without closing the mouthpiece valve. 
     As seen in FIG. 7, an external semi-closed circuit rebreather control system is illustrated. The control system includes dual internal orifice or regulator supply valves, dual double shutoff quick disconnects mounted  90  degrees apart, and supply valves common to both quick disconnects. An overpressure relief valve common to all components is also provided. Internal supply hoses are routed outside of the rebreather case. The system does not use an internal gas supply. 
     In operation, the diver selects the appropriate gas supply from external Source  91  or  92  and plugs the proper pelf-opening quick disconnect  89  or  90  into socket  88  or  86  with self-opening valves  87  or  85 . The supply gas enters manifold  84  which is common to all adjacent components  81 ,  82 ,  83 ,  85 , and  87 . Either supply valve  81  or  82  can be opened to allow flow through hoses  93  or  94 , or both can be opened if one hose supplies a backup regulator. Either can be closed to stop gas losses from a leaking or free-flowing regulator. If both supply valves  81  and  82  are closed when an external source with creeping regulator pressure is connected, the excess pressure will be vented by overpressure relief valve  83  to prevent the Supply hose(s) from bursting. Some of the benefits include, but are not limited to, the following: 
     (1) No internal high pressure gas leaks that cannot be detected by the diver until he loses his gas supply; 
     (2) Quick disconnects cannot be mistaken for one another; 
     (3) Either of two orifices or regulators can be externally selected; 
     (4) Overpressures from external supply gas regulators are relived if both orifice valves are closed; and 
     (5) Different gas supply mixes can be selected and plugged in during the dive, including decompression gases. Thus, the external semi-closed circuit rebreather control system provides a means for controlling either an active or passive addition system through an external control block and associated valving. 
     As seen in FIG. 8, a rebreather disinfecting and drying system is illustrated. The system includes an entry port for the introduction of disinfectants and drying air that has a removable cap. Exit ports, having removable caps, are also provided at the end of every non-recirculating passage in the breathing loop. 
     In operation, caps  103 ,  104 , and  108  are removed from inlet port  101  and outlet ports  102  and  107 . Rebreather is rotated until inlet port  101  is the lowest point in the system. Disinfectant is pumped into the breathing loop through inlet port  101 . Outlet ports  102  and  107  are each capped after disinfectant escapes from them. Rebreather is rotated until inlet port  101  is the highest point in the system. Disinfectant flow is stopped and cap  103  is installed on inlet  101 . Rebreather is rotated through three axes and allowed to sit for at least 30 minutes. All ports  101 ,  102 , and  107  are then uncapped. Rebreather is then rotated through three axes until disinfectant has been drained. A low pressure air blower is attached to inlet port  101  and turned on. The blower is allowed to run until breathing loop is dry, then it is removed. Afterwards, all ports  101 ,  102 , and  107  are capped. Some of the benefits include, but are not limited to, the following: 
     (1) Completely eliminates bacterial proliferation in the breathing loop; and 
     (2). Allows for thorough flushing of salt water or other contaminants from the breathing loop. 
     Thus, the rebreather disinfecting and drying system provides a means for more effectively accomplishing disinfecting and drying operations in the breathing loop by eliminating “dead ends.” 
     As seen in FIG. 9, a gas supply bottle frame that sandwiches between the rebreather and backplate or buoyancy control device (whichever incorporates the diver harness) and is held in place by the same attachment components. The gas supply bottle assemblies are preconfigured by mounting the desired components such as bottles  114  and  115  and associated manifolding to removable frame  111 . 
     The required assembly is attached to the rebreather  116  by sliding frame mounting holes  112  and  113  over mounting bolts  117  and  118 , Buoyancy control device  119  is mounted over removable frame  111  by sliding mounting holes  120  and  121  over mounting bolts  117  and  118  Backplate  122  is mounted over buoyancy control device  119  by sliding mounting holes  123  and  124  over mounting bolts  117  and  118 . Nuts  125  and  126  are tightened onto mounting bolts  117  and  11 E, rigidly securing the stacked components. Removal of the gas bottle assembly on rack  111  after the dive is Accomplished in reverse order. The assembly allows depleted bottle configurations to be easily removed as a unit for transport to a gas filling facility, thus eliminating the need to transport the entire rebreather. The assembly also allows rapid change of preconfigured bottle arrangemnents or bottle assemblies with differing oxygen and inert gas fractions. Thus, a removable tank rack for rebreathers is disclosed which provides a means for quickly removing gas supply bottle configurations from rebreathers in order to install another premounted configuration or fill the existing configuration without having to handle the rebreather in the process. 
     Applicant also incorporates by reference the disclosure of its co-pending application entitled Variable Volume Ratio Compound Counterlung which was filed on Jan. 6, 1998, U.S. application Ser. No. 09/003,409. 
     The instant invention has been shown and described herein in what is considered to be the most practical and preferred embodiment. It is recognized, however, that departures may be made therefrom within the scope of the invention and that obvious modifications will occur to a person skilled in the art.