Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1998-12-29
2001-10-16
Dawson, Glenn K. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204290, C128S201270
Reexamination Certificate
active
06302106
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to diving systems and more particularly to closed circuit and semi-closed circuit rebreathers having two separate gas sources with variable delivery rates for controlling the oxygen partial pressure of the breathing mixture and for maximizing dive and minimizing decompression times.
BACKGROUND OF THE INVENTION
Traditionally, self-contained underwater breathing apparatuses can be viewed as falling into two general categories; open circuit and closed or semi-closed circuit. Open circuit systems are typically recognized by the common term SCUBA and represent the most commonly used form of underwater breathing apparatus. Developed and popularized by Jacques Cousteau, open circuit scuba apparatus generally comprises a high pressure tank filled with compressed air, the tank coupled to a demand regulator which supplies the breathing gas to for example, a diver, at the diver's ambient pressure, thereby allowing the user to breathe the gas with relative ease.
Conventional open circuit self contained diving systems are very well understood in the art and have been developed over the past several years into a wide variety of gas delivery systems, configured for an equally wide variety of applications. For example, compressed air is used as a breathing gas in typical sport diving applications, while one or more artificial mixtures of gasses might comprise the breathing mixture for diving operations at depths greater than approximately 50 meters (150 feet).
While open circuit scuba apparatus is relatively simple, at least in its compressed air form, the equipment required is bulky, heavy and the design itself is inherently inefficient in its use of the breathing gas. Each exhaled breath is expelled to the surrounding environment, thus wasting all the oxygen which was not absorbed by the user during the breath. This inefficiency in breathing gas utilization normally requires a diver to carry a large volume of breathing gas, in order to obtain a reasonable dive time. For example, conventional open circuit scuba gear typically includes compressed air tanks having gas volumes of about 80 cubic feet, and which weigh over 40 lbs.
As a diver descends, the ambient pressure increases approximately one atmosphere for every 30 feet of depth as is well known. Accordingly, gas consumption increases rapidly with depth. As a diver proceeds below approximately 150 feet, the increasing ambient pressure and thus the increasing pressure of the breathing gas, causes serious physiological problems, such as nitrogen narcosis and oxygen toxicity, which may have even deadly effects.
In addition, even short duration dives at depths greater than 100 feet require a certain amount of decompression time which must be pre-calculated in order to ensure a sufficient volume of breathing gas remains after the dive in order to accommodate decompression. Accordingly, while relatively simple and inexpensive, open circuit scuba apparatus imposes a number of practical limitations on both depth and dive time as a consequence of its construction and configuration.
The most common type of open circuit SCUBA apparatus is depicted in FIG.
1
and is of the open circuit demand-type which utilizes compressed air tanks in combination with demand regulator valves which provide air from the tanks on demand from a diver
18
by the inhalation of air. A compressed air supply tank
10
is coupled to a first stage (high pressure) regulator
12
which conventionally including an on-off valve
11
which reduces the pressure of the air within the tank to a generally uniform low-pressure value suitable for use by the rest of the system. Low pressure air (approximately 150 psi) is delivered to a second stage regulator
14
through a demand valve
16
in conventional fashion. Compressed air, at the cylinder pressure, is reduced to the diver's ambient pressure in two stages, with the first stage reducing the pressure below the tank pressure, but above the ambient water pressure, and the second stage reducing the gas pressure to the surrounding ambient or water pressure. The demand valve is typically a diaphragm actuated, lever operated spring-loaded poppet which functions as a one-way valve, opening in the direction of air flow, upon movement of the diaphragm by a diver's inhalation of a breath.
The second form of self contained breathing apparatus is the closed circuit or semi-closed circuit breathing apparatus, commonly termed rebreathers. As the name implies, a rebreather allows a diver to “rebreathe” exhaled gas to thus make nearly total use of the oxygen content in its most efficient form. Since only a small portion of the oxygen a person inhales on each breath is actually used by the body, most of this oxygen is exhaled, along with virtually all of the inert gas content such as nitrogen and a small amount of carbon dioxide which is generated by the diver. Rebreather systems make nearly total use of the oxygen content of the supply gas by removing the generated carbon dioxide and by replenishing the oxygen content of the system to make up for that amount consumed by a diver.
Both types of rebreather systems mentioned above, comprise a certain few essential components; namely, a flow loop with valves to control the flow direction, a counterlung or breathing bag, a scrubber to absorb or remove exhaled CO
2
, and some means to add gas to the counterlung as the ambient pressure increases. Valves maintain gas flow within the flow loop in a constant direction and a diver's lungs provides the motive power.
A typical semi-closed circuit rebreather system is illustrated in FIG.
2
and commonly comprises a compressed gas cylinder
20
conventionally including an on-off value
11
and first stage, high-pressure regulator
12
, containing a specific gas mix having a predetermined fraction of oxygen. The gas is provided to a flow loop
22
, generally implemented by flexible, gas impermeable hoses, which are coupled between the cylinder
20
and a flexible breathing bag
24
, sometimes termed a counterlung. A pair of one-way check valves
26
and
28
are disposed in the flow loop such that the gas flow within the loop is maintained in a single direction (clockwise in the illustration of FIG.
2
). An exhaled breath would thus enter the counterlung, increasing the pressure therein, and pass through one-way check valve
26
and move through some device means to remove excess carbon dioxide from the breathing gas, such as a CO
2
canister
30
, and thereby return to the counterlung through one-way check valve
28
. The check valves thus maintain the gas flow in a constant direction, while the diver's lungs move the gas through the CO
2
canister in the system. The gas mix is introduced into the flow loop at a flow rate calculated to maintain the oxygen needs of a particular diver during the dive. Gas is introduced to the flow loop at a constant fixed flow rate through a valve
32
coupled between the flow loop and the first stage regulator
12
of the gas cylinder
20
. As the breathing gas mix is recirculated, some of the oxygen is necessarily consumed and CO
2
is absorbed, thus perturbing both the total volume and the mix of the gas. A portion of the oxygen is consumed during recirculation, so the diver necessarily breathes a mixture with a lower oxygen concentration than that of the gas mix. Since the amount of oxygen supplied to the system depends on a diver's activity level (oxygen consumption rate), care must be taken to take activity into account as well as selecting the gas mixture composition for a particular diving depth.
A more efficient type of rebreather system is the closed circuit rebreather, illustrated in simplified form in FIG.
3
. Closed circuit rebreathers are generally more sophisticated and effective in their maintenance of oxygen levels in the flow loop. Nonetheless, they share common components with semi-closed circuit rebreather systems such as that depicted in FIG.
2
. The main contrast between fully closed and semi-closed circuit rebrea
Christie Parker & Hale LLP
Dawson Glenn K.
LandOfFree
Rebreather system with optimal PO2 determination does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rebreather system with optimal PO2 determination, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rebreather system with optimal PO2 determination will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2613222