US 3676563 A
An oxygen component of suitable partial pressure for breathing is mixed with an inert component comprising carbon tetrafluoride (CF4), or a mixture of carbon tetrafluoride and helium (He), the inert components having a combined pressure depending upon the pressure of the environment in which breathing is to be sustained. The relative volume percentages of the CF4 and the He are adjusted to optimize certain properties of the breathing mixture to provide improvements over standard compressed air or helium-oxygen mixtures.
Description (OCR text may contain errors)
United States Patent Ormand et a1.
[ 51 July 11,1972
 HYPERBARIC BREATHING MIXTURE  Inventors: lh-ederick T. Ormand; Huey V. Auger,
both of Basking Ridge, N .J
 Assignee: Airco, lnc., New York, NY.
 Filed: April 6, 1970  Appl. No.: 23,101
Related US. Application Data  Continuation of Ser. No. 687,426, Dec. 4, 1967, abandoned.
 US. Cl ..424/366  Int. Cl ..A6lk 13/00, A6lk 27/00  Field of Search ..424/366; 252/372  References Cited UNITED STATES PATENTS 1,473,337 11/1923 Cooke ....424/366 1,644,363 10/1927 Yane et a1 ..424/366 OTHER PUBLICATIONS Merck Index, 7th Ed. Merck & Co., Rahway, N.J., 1960, p. 212
Rochsfort, Anal. Chem. Acta., 29, pp. 350- 357, 1963 Steeng et al.,J. Chem. Phys. 38, 1963, p. 1788 Booth, lnorg. Syn. 1 pp. 34-35, 1939 Primary ExaminerHoward T. Mars Attorney-Edmund W. Bopp and H. Hume Mathews [5 7] ABSTRACT 1 Claim, No Drawings SUMMARY OF THE INVENTION The invention relates to gaseous mixtures for breathing, particularly under pressure materially above normal atmospheric pressure, for example under water, in deep sea diving, in hyperbaric surgical operations, etc.
The invention employs fluorine derivatives of hydrocarbon compounds containing only carbon and fluorineand most particularly carbon tetrafluoride with or without another substantially inert component, for example, helium in admixture with a partial pressure of oxygen suitable for breathing, to form a hyperbaric breathing mixture.
The invention provides non-toxic breathing mixtures that are markedly less narcotic under hyperbaric condition than mixtures in which the inert component is nitrogen as in compressed air. Furthermore, certain of the mixtures disclosed have acoustic properties similar to air, thereby avoiding the high-pitched voices caused by speaking while breathing mixtures in which the significant inert component is helium. Also, the mixtures disclosed have lower thermal conductivities than those in which the inert component is essentially helium, thereby reducing the bodily chilling experienced in breathing helium mixtures. We have found, further, that the mixtures disclosed herein can be used at higher total pressures than mixtures in which the inert component is nitrogen. Furthermore, the tendency of helium to permeate the glass envelopes of vacuum tubes or otherwise to permeate any sensitive electronic devices is'decreased by the admixture of carbon- DESCRIPTION OF THE PREFERRED EMBODIMENTS Breathing mixtures in accordance with the invention contain oxygen at any partial pressure suitable for breathing, usually in the range from about 2 to pounds per square inch and preferably not exceeding 2 atmospheres, the latter limit serving to avoid deleterious physiological effects such as convulsions. To the oxygen there is added an inert gas or a mixture of inert gases selected from halogen derivatives of hydrocarbon compounds,most particularly those containing only fluorine and carbon, with or without an admixture of helium, to bring the total pressure up to a desired value, which may be materially in excess of normal atmospheric pressure.
Preferred mixtures in accordance with the invention are oxygen with carbon tetrafluoride, and oxygen with carbon tetrafluoride-and helium. In the case of mixtures containing carbon tetrafluoride and helium, the relative volume proportions of carbon tetrafluoride and helium are preferably adjusted to suit the particular use, with the object of securing optimum over-all properties, for example, acoustic or thermal properties similar to those of air, or reduction of the tendency of helium to permeate glass, vacuum tubes, or other sensitive electronic devices.
We have tested our preferred mixtures as to their effects upon white mice, in comparison with the effects on the mice of prior art mixtures of oxygen with nitrogen and of oxygen with helium alone. The tests were made using oxygen at about normal atmospheric pressure, for convenience in test procedure, since such pressure is safe for breathing and is well below a level conducive to convulsions. Thetotal pressure of the inert components, carbon tetrafluoride, helium and nitrogen, in each case was carried as high as 150 pounds per square inch. However, there was no indication that 150 pounds per square inch is an upper limit of pressure at which the disclosed mixtures can safely be used.
Specific mixtures tested were (1) 14.7 p.s.i.a. oxygen with up to 150 p.s.i.a. carbon tetrafluoride, and (2) 14.7 p.s.i.a. oxygen with 45 p.s.i.a. carbon tetrafluoride and 105 p.s.i.a. helium. These mixtures were breathed by white mice for test periods up to one hour with no major changes in the behavior of the mice and with no apparent deleterious effects.
Reference mixtures (3) 14.7 p.s.i.a. oxygen with 150 p.s.i.a. nitrogen, and (4) 14.7 p.s.i.a. oxygen with 150 p.s.i.a. helium were breathed by the mice in other tests used as controls.
It was found that the preferred mixtures (l) and (2) were less narcotic in their effects upon the mice than the mixture (3) containing nitrogen, and caused less chilling of the mice than the mixture (4) containing helium as the sole inert component. With the mixtures l and (2) the mice did not appear to be near the threshold of narcosis, while there was evidence of narcosis from the breathing of the mixture (3) containing nitrogen, so that it was clear that the carbon tetrafluoride mixtures (1) and (2) can be used at higher total pressures than nitrogen-containing mixtures.
In general, it was found that breathing mixtures containing carbon tetrafluoride as an inert component are less toxic than mixtures containing nitrogen, and that they reduce undesirable effects caused by breathing helium without accompanying carbon tetrafluoride, such as rapid heat loss due to the high thermal conductivity of helium, helium permeation of sensitive electronic devices and glass as in the envelopes of vacuum tubes, and the high pitch of voice sounds due to the lower atomic weight of helium compared to air.
Breathing mixtures in which the inert component includes both carbon tetrafluoride and helium are further preferred because by adjusting the relative proportions of the two inert gases, certain useful properties of the breathing mixture can be optimized or otherwise adjusted. We have found that when the inert portion of the mixture consists of about 30 volume percent carbon tetrafluoride and volume percent helium, the average molecular weight of the complete mixture is approximately the same as for air. Accordingly, the acoustic properties of the mixture are similar to those of air, resulting in essentially normal voice communication without the high pitch effect usually observed with breathing mixtures high in helium. The thermal conductivity of the preferred breathing mixture, while somewhat higher than for air, is lower than for helium. Consequently, the chilling effect upon the skin, observable with helium, is substantially avoided.
For a combined pressure of the inert gases of p.s.i.a., the preferred mixture of approximately 30 percent by volume of carbon tetrafluoride and 70 percent by volume of helium is equivalent to 45 p.s.i.a. carbon tetrafluoride and 105 p.s.i.a. helium.
Proportioning of the ratio between carbon tetrafluoride and helium content may be employed either to optimize a single parameter of the breathing mixture or to optimize the effect of a combination of two or more such parameters.
The following table shows standard and calculated values for certain pertinent parameters of carbon tetrafluoride, the mixture of 30 volume percent carbon tetrafluoride 70 volume percent helium, straight helium, and air, respectively, at 20 C.
Viscosity (for laminar flow), grams per centimetersecond. x107 201x101 19.61X Thermal conductivity calories per centimeter per second per degree. 3.58X10' As shown by the Table, the average molecular weight, sonic velocity, viscosity for laminar flow, and heat capacity of the 30-70 percent CF -He mixture are quite close to the corresponding values for air, deviating therefrom by less than about i 12 percent. It is evident, therefore, that respiration and voice communication in atmospheres based on this mixture should be essentially the same as in air, although turbulent flow in breathing passages will give higher effective viscosities for a mix containing CF The thermal conductivity of the 30-70 percent CF He mixture, while about 2% times that in air, is still below one half the thermal conductivity of helium. Loss of bodily heat, therefore, is evidently less severe than in helium. The addition of a suitable partial pressure of oxygen to the CF -He mixture tends to bring most of the pertinent properties of the mixture closer to those of air.
In the tests on white mice, the mice were placed in an atmosphere of pure oxygen at 14.7 p.s.i.a. and compressed at a rate of about 30 p.s.i.a. per minute with the test auxiliary gas to a final total pressure of the auxiliary gas of about 150 p.s.i.a., at which resulting pressure the mice were maintained for about one hour. Decompression was carried out over a period of about an hour and a quarter with intermittent addition of oxygen. All the mice tested survived decompression and appeared normal during several days subsequent observation. The mice were tested singly and in pairs. Soda-lime canisters were provided for absorption of metabolic carbon dioxide.
Breathing tests were also made on human subjects at ordinary atmospheric pressure. A mixture of 80 percent by volume of carbon tetrafluoride and percent by volume of oxygen was observed to lower the apparent pitch of the voice somewhat, but it did not impair the intelligibility of the speech. A mixture 80 parts by volume of a mixture of volume percent carbon tetrafluoride and 70 volume percent helium, with 20 parts by volume of oxygen caused no noticeable change in speech. Most subjects reported these mixtures to be odorless and tasteless and none found them to be objectionable.
While in the preferred mixtures disclosed herein helium is used as the second inert gas to be mixed with the oxygen and carbon tetrafluoride, it is to be understood that the invention is not restricted to the use of helium for this purpose. lnert or auxiliary gases which may be used include nitrogen, helium, neon, argon, hydrogen, etc., or any combination of these, even though the use of some of these gases may be less advantageous than the use of helium, and it is to be understood that the use of carbon tetrafluoride as the sole inert gas in a breathing mixture is also covered by the invention.
While illustrative compositions of matter in accordance with the invention have been described and specified herein, it will be understood that numerous changes may be made without departing from the general principles and scope of the invention.
I. A hyperbaric breathing mixture for a hyperbaric environment consisting essentially of oxygen at a partial pressure not less than about two pounds per square inch absolute and not more than about two atmospheres and an inert component consisting essentially of helium and carbon tetrafluoride in which the volumetric proportions of the helium and carbon tetrafluoride are approximately 70 volume percent and 30 volume percent respectively, said inert component at such partial pressure as to provide a breathing mixture having a total pressure sufficient to sustain breathing in the hyperbaric environment.