SELECTED C10 PERFLUORINATED HYDROCARBONS FOR LIQUID VENTILATION AND ARTIFICIAL BLOOD

Abstract: Perfluorinated alkylcyclohexane and alkyl cyclopentane derivatives of the empirical formula C10F20 boil at atmospheric pressure in the range of 144-146 DEG C and are utilized as mediums for gas transport in liquid ventilation and in artificial blood. Compounds of the C10F20 formula which can exist only as a single stereoisomer are preferred as mediums for gas transport.

Description: ι SELECTED C-10 PERFLUORINATED HYDROCARBONS 2 FOR LIQUID VENTILATION AND ARTIFICIAL BLOOD 3 Background of the Invention 4 1. Field of the Invention 5 The present invention is in the field of biological gas exchange in e mammals using C-10 perfluorinated hydrocarbons (perfluorocarbons) as 7 a medium of the exchange. More particularly, the present invention is β directed to use of those C-10 perfluorinated hydrocarbons in biological 9 gas exchange, primarily in liquid ventilation, which due to their ιo chemical structure can be readily obtained or purified in a state free of ιι isomeric contaminants. 12 2. Brief Description of the Prior Art 13 It has been known for a long time that perfluorocarbons are 14 chemically and biologically inert substances and have the unique is capability of dissolving very large volumes of gases, including oxygen 16 and carbon dioxide. Taking advantage of these properties of the 17 perfluorocarbons, it was demonstrated as early as 1966 that the lives of is experimental animals, such as mice, can be sustained while the animals 19 are submerged in an oxygenated perflurocarbon liquid medium. 20 The above-noted pioneering discovery spurred extensive further 21 research in this field by the present inventor, his coworkers and by other 22 scientists as well. As a result, perfluorocarbons emerged as leading 23 candidates for gas-transporting components of artificial blood, and as 24 mediums of gas exchange in liquid ventilation. 25 Specifically, liquid ventilation is a term used for describing gas 26 exchange, i. e. breathing of a mammal, where a certain volume of gas 27 transporting liquid is added to fill the entire or partial volume capacity 28 of the lungs, and where the presence of the liquid facilitates the 29 breathing process. The term "tidal liquid ventilation" or "total liquid 30 ventilation" is used to describe liquid ventilation where the lungs of the 31 mammal are completely filled with the liquid which is oxygenated by ι bubbling or by passing it through a membrane oxygenator. It is now 2 generally accepted in the art that although the feasibility of using 3 perfluorinated hydrocarbons to sustain the lives of experimental animals 4 was initially demonstrated by this method (the animal was submerged in 5 the liquid medium) "total liquid ventilation" is unlikely to become a 6 medically accepted procedure to be used with humans who need 7 respiratory assistance. β Another form of liquid ventilation where only the functional 9 residual volume of the lung is filled with the perfluorocarbon and where ιo gas exchange is assisted with the use of a mechanical ventilator, is ιι termed "partial liquid ventilation". In partial liquid ventilation 12 approximately 30 milliliters (ml) of the perfluorocarbon (or mixture of 13 perfluorocarbons) is used per kilogram (kg) body weight of the 14 mammal. is Still another form, which has been suggested relatively recently by 16 one of the present inventors is "low volume" or "alveolar" ventilation 17 where the perfluorocarbon (or mixture of perfluorocarbons) is added in is sufficient quantity only to fill the alveoli (air sacs) of the lung and the 19 mammal is allowed to breath normally, or with the assistance of a 20 mechanical ventilator. In this "low volume" method only approximately 21 0.1 to approximately 10 ml of the perfluorocarbon (or mixture of 22 perfluorocarbons) is used per kg body weight of the mammal. 23 The research prompted by the 1966 discovery of the possibility of 24 "liquid breathing" in a perfluorocarbon medium, resulted in voluminous 25 scientific and patent literature on the medical aspects of the subject. It 26 also led to the development of voluminous literature pertaining to the 27 manufacturing and selecting suitable perfluocarbons for "liquid 28 breathing" and "artificial blood" purposes. A substantial list of scientific 29 papers, publications and patents is provided in an Information ι Disclosure Statement, which is filed in connection with this application 2 for patent. An article titled "Liquid Ventilation A State of the Art 3 Review" by Shaffer et al. in Pediatric Pulmonology 14:102-109 (1992) 4 reviews the properties of perfluorocarbons which are pertinent to liquid 5 breathing and provides a long list of references pertinent to the subject, e A publication titled "Response of the rabbit lung as a criterion 7 of safety for flurocarbon breathing and blood substitutes" by Clark Jr. s et al. in Biomat., Art. Cells & Immob. Biotech 20(2-4) 1085-1099 (1992) 9 describes hyperinflated non-collapsible lung syndrome (HNCL) which to has emerged as a serious problem associated with the use of certain ιι perfluorocarbons in liquid breathing and in artificial blood as well. 12 Briefly, it was found in experimental rabbits, and later in other 13 mammals as well, that when perfluorinated decalin (F-decalin) and 14 certain other perfluorocarbons are administered to rabbits either as an is emulsion (artificial blood) or by intratracheal infusion, the animals tend 16 to develop hyperinflated non- collapsible lungs, which can eventually 17 prove to be fatal. The hyperinflated non-collapsible lungs are fatal to 18 the animal because, the lobes completely fill the thorax and are not 19 compliant. 20 The above-noted article in Biomat., Art. Cells J. Immob. Biotech 21 and a poster presented by Clark Jr. et al. at a symposium Hot Topics '95 22 in Neonatology, December 3 - 5, 1995, Washington D. C. , titled 23 "Fluorovent™: A New Perfluorocarbon for Liquid Ventilation", describe 24 the scientific quest for perfluorocarbons which would be ideally suited 25 for use in liquid ventilation and artificial blood as well. The criteria 26 mentioned for ideal, or at least better suitability is avoidance of 27 hyperinflated lung syndrome and an acceptably low "body dwell time" 28 after administration of the perfluorocarbon liquid to the mammal. 29 Out of an abundance of caution it is considered desirable for the ι fluorocarbons to be completely removed from the body after treatment. 2 Alternatively, if complete removal after treatment is impossible, it is in 3 any case desired for the perfluorocarbon to have as short a residual 4 dwell time as possible. In this regard it is noted that the primary 5 mechanism by which the mammalian body eliminates fluorocarbons is 6 through exhalation by the lungs. Although the precise mechanism of 7 this removal by exhalation is not presently known the rate of removal 8 has been recognized to be related to the volatility (vapor pressure at 9 body temperature) of the perfluorocarbon liquid. While, as mentioned ιo above, excessive persistence of the perfluorocarbon in the mammalian ιι body after treatment is undesirable, excessive or too rapid loss by 12 exhalation/evaporation is also undesirable since it requires 13 replenishment of the perfluorocarbon liquid during treatment. As it is 14 readily understood by those skilled in the art, the rate of loss due to is exhalation/evaporation is also related to the volatility (vapor pressure at 16 body temperature) of the perfluorocarbon substance. 1 Finally, as manifested in the above-mentioned article by Clark Jr. is et al. in Biomat, Art. Cells & Immob. Biotech 20(2-4) 1085-1099 (1992) 19 and in the Abstract of the poster presentation by Clark Jr. et al. at a 20 symposium Hot Topics '95 in Neonatology, the prior art recognized that 21 causation of hyperinflated non-collapsible lung syndrome (HNCL) is 22 also related to the volatility of the perfluorocarbon liquid, whether it is 23 used in artificial blood or in liquid ventilation. For example, 2 perfluorinated decalin (F-decalin) having a boiling point of 141-142.5°C 25 is known to cause hyperinflated lung syndrome, while perfluorinated 26 methyldecalin (F-methyldecalin) having a boiling point of 161°C does 27 not. F-methyldecalin, however, persists somewhat longer in the body 28 than what is considered desirable. Thus, the article in Biomat, Art. 29 Cells & Immob. Biotech 20(2-4) 1085-1099 (1992) refers to a search for ι flurocarbons "having boiling points between 140°C and 165°C. "in order 2 to find a perfluorinate with the highest transpiration rate, and hence 3 vapor pressure, compatible with an acceptable body dwell time.". The 4 abstract of the presentation at the above-mentioned symposium refers 5 to an evaluation of the properties of many perfluorocarbons (PFCs) e ... "to find the optimum PFC for liquid ventilation". The abstract 7 mentions "two properties - boiling point related lung hyperinflation and s rapid pulmonary exhalation - ...., as important selection criteria." 9 As it will become apparent from the ensuing description, the ιo present invention provides perfluorocarbons which avoid the ιι hyperinflated lung syndrome and other problems associated with the 12 prior art, and therefore meet the selection criteria mentioned in the 13 above-quoted abstract. Moreover, still another "important selection 14 criterion" has been discovered in accordance with the present invention, 15 and the perfluorocarbons suggested for use in liquid ventilation and for 16 artificial blood also satisfy the newly suggested criterion. 17 As further background to the present invention applicant cites: 18 United States Patent No. Re: 33,451 to one of the present 19 inventors that describes the use of perfluorocarbons as blood substitutes; 20 U. S. Patent No. 3,911,138 to one of the present inventors that 21 pertains to the search for perfluorocarbons having ideal balance of 22 properties for use in liquid ventilation; 23 PCT Patent application No. 92/19232 to Faithful et al. and United 24 States Patent No. 5,437,272 to Fuhrman which pertain to liquid 25 breathing utilizing perfluorocarbons to fill the pulmonary functional 26 residual capacity of the mammal; 27 A publication by Smith et al. in Crit Care Med 1997 Vol. 25, No. 28 7 pρll79 - 1186, titled: Partial liquid ventilation: A comparison using 29 conventional and high frequency techniques in an animal model of ι acute respiratory failure, and 2 A publication by Clark, Jr. et al. in Mat. Res. Soc. Symp. Proc. 3 Vol. 110 (1989) ppl29 - 134, titled "Physiological evaluation of 4 fluorocarbon emulsions with notes on F-decalin and pulmonary 5 inflation in the rabbit." e SUMMARY OF THE INVENTION 7 It is an object of the present invention to provide a 8 perfluorocarbon compound, or several perfluoro compounds which are 9 well suited for use as gas exchange medium in liquid ventilation and as ιo gas exchange medium in artificial blood. ιι More particularly, it is an object of the present invention to 12 provide a perfluorocarbon compound, or several perfluoro compounds 13 which have the appropriate vapor pressure at body temperature so that 14 their use as medium of gas exchange in liquid ventilation or in artificial is blood does not cause hyperinflated lung syndrome, and which 16 nevertheless do not unduly persist in the body after treatment or use of 17 the perfluorocarbon is discontinued. 18 It is a further object of the present invention to provide a 19 perfluorocarbon compound, or several perfluoro compounds which 20 satisfy the foregoing objectives, and which, due to their chemical 21 structure, exist only as single isomers, and can be obtained in a state 22 substantially free of isomeric contaminants. 23 The foregoing and other objects and advantages of the invention 24 are attained by selecting and utilizing perfluorocarbon compounds as 25 gas exchange medium in liquid breathing and in artificial blood which 26 have the empirical formula C 10 F 20 , a molecular weight of approximately 27 500 Daltons, and which have the chemical structure that is selected from 28 the formulas shown below as Formulas 1 through 10. 29 5 Formula 1 6 11 Formula 2 12 17 Formula 3 18 23 Formula 4 24 29 Formula 5 5 Formula 6 6 11 Formula 7 12 17 Formula 8 18 23 Formula 9 24 25 29 Formula 10 ι In the Formulas 1 - 10 the symbol F in the center of the 5 or 6 2 membered ring represents that all hydrogens of the corresponding 3 cyclohexane or cyclopentane ring have been replaced with fluorine. In 4 other words, F represents that the ring is perfluorinated. The formulas 5 represent all possible positional, stereo (such as cis and trans) and 6 optical isomers (enantiomers) of the compounds depicted in the 7 formulas. In Formula 10 the symbol C 5 F π * represents not only a β perfluorinated pentyl moiety, but any combination of perfluorinated 9 alkyl groups where in the perfluorinated alkyl groups the total number ιo of carbons is 5 and the total number of fluorines is 11. In other words ιι and by way of example in Formula 10 the symbol C 5 F n * represents a 12 CF 3 group in combination with a perfluorinated «-butyl, sec-butyl, iso- 13 butyl or t-butyl group, or five CF 3 groups, or combination of a 14 perfluorinated ethyl group with a perfluorinated n-propyl or wo-propyl 15 group, etc. Moreover, Formula 10 also represents all possible 16 positional, stereo and optical isomers of these compounds. 17 The perfluorinated compounds utilized in accordance with the 18 invention as a gas exchange medium in liquid ventilation and in 19 artificial blood are liquids at ambient temperature and have a vapor 20 pressure at physiological temperature such that the use of these 21 compounds does not result in the development of hyperinflated non- 22 collapsible lung syndrome. Moreover, the vapor pressure and therefore 23 the rate of evaporation/exhalation from the lungs of these 24 perfluorinated compounds is still sufficiently high so that the 25 compounds are satisfactorily cleared from the lungs after use of the 26 compounds (treatment) is discontinued. The boiling point of the 27 compounds is in the range of approximately 144 to 146°C. Preferably 28 those specific perfluorinated compounds are used in accordance with 29 the invention which either can exist only in a single isomeric form and ι can be purified from other contaminants to attain a pure or substantially 2 pure state, or which, although capable of existing in more than one 3 isomeric form, can be readily purified to attain isomeric purity. 4 BRIEF DESCRIPTION OF THE DRAWING 5 Figure 1 is a graph showing the rate of exhalation of F- 1,2,3,5- 6 tetramethylcyclohexane and of F l-methyl-4-isopropylcyclohexane (F- 7 menthane) from the rat. β DETAILED DESCRIPTION OF THE INVENTION 9 DESCRIPTION OF THE PREFERRED EMBODIMENTS ιo The following specification taken in conjunction with the drawings ιι sets forth the preferred embodiments of the present invention. The 12 embodiments of the invention disclosed herein are the best modes 13 contemplated by the inventors for carrying out their invention, although 14 it should be understood that various modifications can be accomplished is within the parameters of the present invention. 16 Referring to the Formulas 1 - 9 shown in the Summary section of 17 the present application, it will be apparent to those skilled in the art 18 that these formulas represent perfluorinated cyclohexane derivatives 19 which have perfluoroalkyl substituents having a total of 4 carbons in the 20 alkyl groups. The term "perfluoro" in this regard has the meaning 21 generally accepted in the art, namely it means that all hydrogens of the 22 hydrocarbon skeleton have been replaced with a fluoro atom. It is well 23 known in the art that perfluorinated hydrocarbons, including the ones 24 used in accordance with the present invention, are biologically inert, 25 non-toxic and as far as is presently known they do not undergo 26 metabolic or catabolic transformation in any known mammal. In 27 addition to their inertness, an important property of these compounds 28 which enables them to be utilized as a medium of biological gas 29 exchange is their ability to dissolve a large quantity of gases, including ι oxygen and carbon dioxide. 2 Formulas 1 through 9 represent all possible positional and stero 3 isomers of the perfluorinated cyclohexyl derivatives having the empirical 4 formula C 10 F 20 . Those skilled in the art will readily understand that 5 numerous positional isomers exist. For example, the 6 tetratrifluoromethyl compounds depicted in Formula 1 can be the 7 following positional isomers: perfluoro 1,2,3,4 tetramethylcyclohexane, 8 perfluoro- 1,2,4,5-tetramethylcyclohexane and perfluoro 1,2,3,5 9 tetramethylcyclohexane. For brevity of description the "perfluoro state" ιo of a compound is sometimes indicated here with the symbol "F". Thus, ιι perfluoro 1,2,3,4 tetramethylcyclohexane can also be written as "F 1,2,3,4 12 tetramethylcyclohexane". For the compounds shown in Formula 2 the 13 following positional isomers are possible: F l,2-dimethyl-3- 14 ethylcyclohexane, F l,2-dimethyl-4-ethylcyclohexane, F l,3-dimethyl-2- 15 ethylcyclohexane, F l,3-dimethyl-4-ethylcyclohexane, F l,3-dimethyl-5- 16 ethylcyclohexane and F l,4-dimethyl-2-ethylcyclohexane. For each of 17 the disubstituted cyclohexanes shown in Formulas 3, 4 and 5 three 18 positional isomers are possible, these are where the substituents are in 19 1,2, 1,3 or in the 1,4 (ortho, meta or para) positions. 20 Because of the nature of the cyclohexane ring depicted in 21 Formulas 1 - 9, and of the cyclopentane ring depicted in Formula 10, cis 22 and trans isomerism (stereoisomerism) and even optical isomerism also 23 exists among the compounds of these formulas, so that the formulas 24 encompass a relatively large number of positional isomers, stereoisomers 25 and for those compounds which include an assymetric or chiral center, 26 optical isomers as well. For example, each of the disubstituted 27 compounds depicted in Formulas 3, 4 and 5 can exist either as cis or as 28 a trans isomer. Therefore, Formulas 3, 4 and 5 represent a total of 18 29 different chemical entities not counting possible optical isomers ι (enantiomers) nor diastereomers. 2 However, it is generally known in the art that compounds of the 3 same molecular weight and of the same type of general structure tend 4 to have similar vapor pressure versus temparature profiles. Vapor 5 pressure is difficult to measure directly, however, it is well known that 6 the boiling temperature of a liquid is directly related to its volatility or 7 vapor pressure. Therefore, compounds of the same molecular weight β and of similar structure tend to have same or closely related boiling 9 temperatures. This is known to be particularly true in the field of ιo perfluorocarbons. Among the compounds within the scope of the ιι present invention boiling temperatures measured at atmospheric 12 pressure have become available for the following specific compounds: 13 F-l-ethyl-2,4-dimethylcyclohexane b. p. 146°C; 14 F-l,2,4,5-tetramethylcyclohexane b. p. 146°C; is F-l,2,3,5-tetramethylcyclohexane b. p. 146°C; 16 F-l-methyl-4-isopropylcyclohexane b. p. 144°C, and 17 F-n-butylcyclohexane b. p. 145°C. 18 As can be seen, the boiling points of the above-noted exemplary 19 compounds, and by analogy of all compounds within the scope of the 20 present invention, are well within the range (approximately 142 to 21 160°C) that is generally considered well suited for compounds utilized 22 as gas exchange medium in liquid ventilation and/or in artificial blood. 23 Perfluoro compounds within this range do not cause hyperinflated lung 24 syndrome, and are transpired from the mammalian body by 25 evaporation/exhalation at an acceptable rate. However, the compounds 26 do not evaporate so rapidly during treatment that undue replenishment 27 would be required. 28 Because measuring boiling points at atmospheric pressure can be 29 difficult or cumbersome, especially when relatively small samples of the ι liquid are available, a more feasible method has been devised in 2 accordance with the present invention to measure the "volatility" of a 3 liquid. In accordance with this method, which is described in more 4 detail below in the experimental section of this application for patent, 5 the compound to be measured (subject compound) is mixed with a 6 known (preferably equal) quantity of a reference perfluorocarbon the 7 volatility (boiling temperature and/or vapor perssure versus β temperature profile) of which is known. A reference compound 9 conveniently employed for this purpose is F- s-decalin which at ιo atmospheric pressure has a boiling point of 141°C. The mixture of the ιι two liquids is maintained in a closed container and the "headspace" 12 above the liquids is allowed to equilibrate with the liquid below. A 13 sample of the saturated gas mixture in the "headspace" is then 14 withdrawn and is analyzed by chromatography to determine the ratios of is the two components in the saturated gas mixture. If the two compounds 16 had the same vapor pressure at the temperature of the measurement 17 (usually ambient temperature) then the quantities of the compounds in 18 the saturated gas mixture would also be equal, provided the liquids were 19 mixed in equal quantities. Thus, the ratios of the two components in 20 the saturated gas mixture in the headspace provide a measure of the 21 volatility/vapor pressure of the liquid to be tested, and provide a basis 22 for extrapolation to obtain a boiling point at atmospheric pressure. 23 "Headspace" saturated gas ratio experiments described in 24 principle above, and detailed below, demonstrated that all 5 exemplary 25 C 10 F 20 perfluorocarbons in accordance with the invention have 26 significantly lower vapor pressure at ambient temperature than F-cis 27 decalin, signaling that the use of these compounds in liquid ventilation 28 and artificial blood would not cause hyperinflated lung syndrome. 29 C 10 F 20 perfluorocarbons which are preferably used in accordance ι with the present invention are selected from among the compounds 2 represented by Formulas 1 - 10 with a view to attaining pure or 3 substantially pure substances substantially free of isomers. This is 4 important for practical purposes because it is well known that isomeric 5 compounds, whether they are positional isomers or stereoisomers (such 6 as cis, trans or diastereomers) are often difficult to separate in 7 substantial quantities. Whereas present day sophisticated analytical β techniques, such as gas chromatography (GC) or high pressure liquid 9 chromatography (HPLC) can often detect the presence of isomers in a ιo substance, separation of the isomers on a preparative scale is often a ιι more difficult task. Moreover, pertinent laws and regulations by the 12 agencies which permit the use of drugs or related pharmaceuticals in 13 therapy or even experimental use in humans, require certain levels of 1 purity and knowledge of the composition of the substances or is compounds to be used. It is much more time consuming and expensive 16 to carry a mixture of isomeric compounds through the appropriate 17 phases of testing in animals and humans, until regulatory approval is 18 obtained, than it is to do the same with pure "single chemical entity" 19 substances. In addition, even during manufacturing and testing phases, 20 quality control of a mixture of isomers is often more difficult than with 21 a single entity compound. 22 For the foregoing and related reasons, use of the following 23 compounds in liquid ventilation and artificial blood is preferred in 24 accordance with the present invention: 25 F-n-butylcyclohexane (Formula 6); 26 F-(2-methylpropyl)cyclohexane (Formula 7, t ø-butyl); 27 F-(l-methylpropyl)cyclohexane (Formula 8, sec -butyl); 28 F-t-butylcyclohexane (Formula 9); 29 F-l,l-diethylcyclohexane (Formula 11); F-1-methyl-l-rt-propylcyclohexane (Formula 12); F-l-methyl-l-iyø-propylcyclohexane (Formula 13); F-1-pentylcyclopentane (Formula 14); F-1-methyl-l-butylcyclopentane (Formula 15); F-1-ethyl-l-propylcyclopentane (Formula 16). In Formulas 14, 15, and 16 the pentyl, butyl and propyl groups represent all possible positional isomers of said groups, for example "propyl" represents «-propyl and irø-propyl as well, and "butyl" represents «-butyl, f-butyl and 1-methylpropyl and 2-methylpropyl groups. However, only the use of single chemical entitles, not the use of mixtures, is preferred. Formula 11 Formula 12 Formula 13 pentyl Formula 14 Formula 15 Formula 16 As it can be readily ascertained from their chemical structure, the preferred compounds of Formulas 6 - 9 and 11 - 16 are single positional isomers and cis and trans isomerism for these compounds is not possible. The compound of Formula 8 and some of the compounds within the scope of Formulas 14 and 15 have one or more chiral centers and therefore exist in enantiomeric and some in diasteromeric forms. Enantiomers, however are not expected to give rise in the testing and regulatory approval process to problems of the same magnitude as positional isomers, because a racemic mixture of compounds is often considered acceptable for regulatory purposes. Also in chromatographic and many other analytical techniques, unless the chromatography involves a "chiral column", a racemic mixture is not resolved. The C 10 F 20 compounds which are presently most preferred in accordance with the present invention are: F-t-butylcylohexane (Formula 9); F-l,l-diethylcyclohexane (Formula 11), and F-neopentylcyclopentane (Formula 17) Formula 17 The C 10 F 20 compounds used within the scope of the present invention, and particularly the preferred compounds shown in Formulas 6 - 9 and 11 - 16 can be synthesized from homologous hydrocarbons by well-known techniques, such as reaction with cobalt trifluoride in a furnace. A method of manufacture of F- ttαry-butylcyclohexane is described in United States Patent No. 4,453,028, incorporated herein by reference. Further procedures for the synthesis of C 10 F 20 cyclohexane derivatives are described in United States Patent Nos. 5,300,528, 4,105,798, and 5,093,432 which are also specifically incorporated herein by reference. Generally speaking the synthesis of perfluorocarbons is described in detail in the book "Chemistry of Organic Fluorine Compounds II. A Critical Review". Edited by Milos Hudlicky and Attila E. Pavlath, published by the American Chemical Society (1995), incorporated herein by reference. The basic technique for cobalt trifluoride fluorination is set forth in U.S. Patent No. 2,631,170. The basic technique of liquid phase fluorination using diluted fluorine gas is set forth in U.S. Patent No. 5,093,432. United States Patent Nos. 2,631,170 and 5,093,432 are incorporated herein by reference. ι In accordance with the present invention, the C 10 F 20 compounds, 2 and particularly the preferred embodiments of Formulas 6 - 9 and 11 - 3 16 and still more particularly the most preferred embodiments, are 4 utilized as medium of gas exchange in liquid breathing and in artificial 5 blood. These mediums of gas exchange can be employed in accordance e with the present state of the art, namely in "total" or "tidal" liquid 7 ventilation, "partial" liquid ventilation and in "low volume" (alvolear) β ventilation as well. For example, the compounds selected in accordance 9 with the present invention can be used to fill the "pulmonary functional ιo residual capacity" of a mammal, in accordance with the methods and ιι apparatus described in United States Patent No. 5,437,272 (Fuhrman) 12 which is incorporated herein by reference. A recently issued United 13 States Patent by one of the present inventors No. 5,674,913 describes a 14 method of assisting normal breathing in a mammal having a lung is disorder, by introducing a perfluorocarbon into the alveolar sacs of the 16 lung through the trachea. The perfluorocarbons selected in accordance 17 with the present invention can also be used in the method of said is application. United States Patent No. 5,674,913 is also incorporated 19 herein by reference. As a medium of gas exchange in artificial blood 20 the compounds can be used for example as described in United States 21 Patent No. Re: 33,451 (incorporated herein by reference) and as is 22 generally known in the state-of-the-art. 23 The C 10 F 20 compounds, and particularly examples of the 24 preferred embodiments of Formulas 6 - 9 and 11 - 16 selected for use 25 as a medium of gas exchange in accordance with the present invention 26 do not cause hyperinflated lung syndrome in experimental animals 27 (rabbit and baboon) and are exhaled from the body at an acceptable 28 rate. The ensuing "specific embodiments" (experimental) section of this 29 application describes the animal testing conducted with examplary ι compounds, and also experiments wherein the volatility of the 2 compounds selected in accordance with the invention was measured. 3 Description of Animal Tests and Volatility Measurements 4 Animal testing is performed in accordance with Protocols 1, 2, 3 5 and 4, which are described below. e PROTOCOL 1 : Intratracheal administration of perfluorocarbon neat 7 liquids to rats with survival β This protocol is especially useful for the accurate administration 9 of perfluorocarbon neat liquids to the lungs of small animals through a ιo Silastic catheter inserted in the trachea through a tracheotomy. The ιι following protocol and example are specific for rats of the genus Rattus, 12 bred for use in research. Adult Spraque Dawley female rats are is normally used. 14 The nonfasted rat is weighted and anesthetized with a volatile is anesthetic such as enflurane, halothane or similar agent. Surgical plane 16 anesthesia is achieved using an intraperitoneal injection of ketamine 17 hydrochloride in saline (25 mg/ml), at an initial dose of 80 mg/kg. is Additional injections of about 20 mg/kg are given as needed to ensure 19 appropriate anesthesia. A single subcutaneous injection of 20 chlorpromazine in saline (25 mg/ml), as a dose of 5 mg/kg, is used for 21 muscle relaxation. The neck area is shaved, and the skin is cleaned with 22 70% alcohol and scrubbed with betadine. 23 The rat is positioned on her back on a padded surgical platform, 24 and humidified 100% oxygen is administered through a mask loosely 25 covering the rat's head. Core temperature is monitored using a small 26 animal rectal Telethermometer probe and meter from Yellow Springs 27 Instruments, Co. A heat lamp is used to maintain body temperature 2β between 35 and 37 degrees Celsius. 29 Sterilized instruments are used for the surgical procedure. A 2 ι cm midline incision is made in the neck over the trachea. The 2 underlying fat and muscle is dissected to expose the trachea. A narrow 3 piece of sterile umbilical tape is passed beneath the trachea and a small 4 hole is made between rings, below the thyroid, using a 21 gauge needle. 5 The hole is enlarged with the scalpel, if needed, to accommodate the 6 Silastic catheter. This Silastic catheter, either single or double lumen 7 and fitted with a 23 gauge tubing adapter, is then inserted about 1 cm β into the trachea. The oxygen flow is now directed into, and around, the 9 catheter instead of into the mask. ιo The surgical platform is elevated about 30-40° to facilitate the ιι gravity flow of perfluorocarbon neat liquid into the lungs. The 12 perfluorocarbon neat liquid is then slowly delivered through the catheter 13 from a glass syringe attached to the tubing adapter, at a rate of about 1 14 ml per minute. Oxygen is concomitantly delivered. The rat can also be is rotated to the left and right during dosing to help distribute the liquid. 16 Perfluorocarbon neat liquid doses up to 20 ml/kg have been infused into 7 the lungs by this method. The tracheal catheter is removed, and the is board lowered so that the head and neck are kept slightly above the 19 chest to allow any perfluorocarbon neat liquid in the trachea to drain 20 into the lungs. The small opening in the trachea is closed using a single 21 suture of 5-0 silk, as is the muscle layer. The skin is closed with 22 continuous sutures of 4-0 silk. The rat is then kept on humidified 100% 23 oxygen using the mask, and observed until recovery, when it is returned 24 to its cage in the colony. 25 PROTOCOL 2: Intratracheal administration of perfluorocarbon neat 26 liquids to rabbits with survival 27 1. The fasted animal is sedated with 2.5 mg/kg subcutaneous 28 chlorpromazine (25 mg ml). 29 2. Approximately 30 minutes later the animal is gently ι restrained and the necessary ear blood vessels catheterized with Teflon 2 catheters, such as an Abbocath T-22 Gaxl 1/4", fitted with a 3-way 3 stopcock. Topical 2% Lidocaine may facilitate the cannulation. 4 3. The animal is anesthetized with intravenous sodium 5 pentobarbital (30 mg/ml in normal saline) at a dose of 30 mg/kg. 6 4. The throat is shaved and disinfected with 70% ethyl alcohol 7 and Betadine. β 5. The area of the incision is filtrated with 2% Lidocaine. 9 6. With the animal lying on its back, a 1-2' midline incision is ιo made over the trachea below the laryngeal prominence. ιι 7. The muscle is incised and the area around the trachea is 12 blunt dissected. 13 8. A length of sterile umbilical tape is passed beneath the 14 trachea to help isolate it and to secure the tracheal cannula. is 9. The trachea is then cut between rings and a sterilized 16 Silastic tube (5 mm OD) is inserted in the trachea to a point above the 17 bronchial bifurcation. 18 10. The head and shoulders of the animal are elevated for 19 gravity administration of the perfluorocarbon neat liquid. The 20 perfluorocarbon neat liquid is filtered through a sterile, 0.22 micron 21 filter during administration. 22 11. The Silastic tracheal cannula is removed and the trachea 23 closed with two sutures of 5-0 silk. 24 10. A small piece of Gelfoam is placed over the tracheal 25 incision and the muscle and skin are closed with 4-0 silk. 26 The animal is administered humidified, 100% oxygen during the 27 entire procedure and small maintenance doses of intravenous sodium 28 pentobarbital are given when needed. 29 PROTOCOL 3: Gas chromatographic determination of the Exhalation ι Rate from Rats Having Perfluorocarbon Neat Liquid in the Lungs 2 The rat is placed in a specially designed chamber consisting of a 3 perforated ceramic disk in a 1 liter Pyrex glass dissicator with an oxygen 4 inlet and outlet, and a typical oxygen flow rate of 600ml/min. A 5 magnetic stirring bar below the disk stirs the atmosphere in the 6 dessicator, which has a cover sealed with glycerol. 7 After 20 minutes of equilibration, the gas flow from the outlet of s the rat chamber is measured using a Humonics Optiflow 650 digital 9 flowmeter. Samples are then taken from the flow outlet for GC analysis ιo using a Hamilton side port needle syringe. ιι Samples taken from the outlet are injected onto a 20 foot long x 12 1/8 inch stainless steel packed column (30% SE30 on Chromsorb PAW is 80/100 mesh) in a Hewlett Packard 5890 GC. Head pressure of the 5% 14 methane in argon carrier gas is maintained at 50 pounds/square inch, is with an end flow rate of 25 milliliters/minute. Quantitive measurement 16 is accomplished with an electron capture detector. All data is collected 17 and stored using a Hewlett Packard chemstation data system. 18 Quantitation is done by comparison of the measured value of the 19 rat's exhalation to a known standard. The standard is prepared by 20 injecting a 0.1 to 2 microliter (μL) aliquot of perfluorocarbon neat 21 liquid into a sealed 120 milliter (mL) serum vial. It is allowed to stand 22 at room temperature for at least one hour to completely volatilize. This 23 is referred to as the "Stock standard". A 120μL aliquot of the stock 24 standard vapor is taken and injected into a second sealed 120mL serum 25 vial, producing a 1000:1 dilution of the original; this is referred to as the 26 "working standard". Accurately measured volumes of the working 27 standard, or the oxygen carrier gas from the rat chamber, are alternately 28 injected onto the GC instrument for quantitation. 29 Calculation of the rate of exhalation is performed using the peak ι height (or area) from the chromatogram of the rat's breath, the peak 2 height (or area) from the chromatogram of the working standard, the 3 known concentration of the working standard, and the oxygen flow rate 4 through the chamber to give the exhalation rate of the fluorocarbon 5 vapor as microliters of fluorocarbon per day. e Figure 1 of the appended drawings shows the rate of exhalation 7 of F-l,2,3,5-tetramethylcyclohexane and of F l-ethyl-4- β isopropylcyclohexane (F-menthane) in the rat, substantially as 9 determined in accordance with Protocol 3. Both of these compounds ιo are C 10 F 20 perfluorocarbons the use of which in liquid ventilation is ιι within the scope of the present invention. As it was discussed above, 12 the boiling points of these compounds for practical purposes are 13 virtually the same or very close to the boiling points of all of the 14 perfluorocarbons which are utilized in liquid ventilation and artificial is blood in accordance with the present invention. The rate of exhalation 16 indicated in the graph for both of these C 10 F 20 perfluoro compounds is 17 considered acceptable, and indicates that undue exposure of the animal is to potential long term effect of the perfluorocarbon is likely to be 19 avoided. 20 PROTOCOL 4: Test of intratracheal neat liquid perflurocarbons for 21 pulmonary hyperinflation in the rabbit 22 Fasted, healthy, Pasteurella-free, young adult female New 23 Zealand white rabbits weighing about 1.8 to 2.2 kilograms, were used. 24 The rabbits were sedated with chlorpromazine, anesthetized with a 25 mixture of ketamine and xylazine, and supported by oxygen breathing. 26 The trachea was cannulated with a soft, sterile Silastic tube stabilized in 27 place with umbilical tape. Filtered, neat liquid fluorocarbon (medical 28 grade) was administered slowly in the doses shown in the table. The 29 cannula was removed, the incision closed and the animal allowed to recover in USDA-approved, air conditioned quarters. The rabbits were observed frequently until sacrifice on the fourth day after infusion. Results of tests conducted substantially as described in Protocol 4, with F-l-ethyl-2,4-dimethylcyclohexane (b. p. 146 °C) and F-1,2,4,5- tetramethylcyclohexane (b. p. 146 °C) caused no pulmonary hyperinflation in the rabbit, whereas F-cw-decalin (b. p. 142.5 C) did. These results are summarized below in Table 1 where the dose of the respective fluorcarbons and the number of animals involved in the test are also indicated. TABLE 1 Tests of intratracheal neat liquid perfluorocarbons for pulmonary hyperinflation in the rabbit. o ra s e n e morn ng o t e ourt ay, s orty a ter e ng remove from their cages. By way of further description of the tests summarized in Table 1 it is noted that several of the animals which received the F-decalin showed signs of pulmonary distress by the second day. These symptoms included rapid and noticeably labored breathing, and, in general, these animals appeared to be hypoxic and hypercapnic. At necropsy the F- ι decalin lungs were pale pink and showed various degrees of 2 hyperinflation. The animals which received the F-1,2,4,5- 3 tetramethylcyclohexane and the F-ethyldimethyl-cyclohexane showed no 4 signs of distress. At necropsy their lungs were found to be normal in 5 appearance and were not hyperinflated. e Test of intratracheal neat liquid perflurocarbons for pulmonary 7 hyperinflation in the baboon 8 To determine if F-l-ethyl-4,4-dimethylcyclohexane caused 9 hyperinflation in the non-human primate, two fasted, normal, healthy ιo juvenile female baboons weighing about 3.5 to 5 kilograms were given ιι intratracheal neat liquid. An IACUC-approved protocol was followed. 12 The procedure, similar to the description in Protocol 4 was performed 13 under sterile conditions in a USDA-approved primate facility. One 14 baboon received 2cc/kg and the other 4cc/kg of F l-ethyl-2,4- 15 dimethylcyclohexane via tracheal cannula. Both animals were observed 16 frequently, and no untoward reactions were observed during, or in the 17 days following, the infusion. The animals gained weight, and behaved in is a normal fashion in their quarters. Both were sacrificed ten weeks after 19 the infusion. At necropsy their lungs were found to be normal in 20 appearance and were not hyperinflated. Laboratory examination of the 21 lung sections revealed no abnormalities. 22 Measurements comparing the vapor phase concentrations of certain 23 perfluoroalkylcvclohexanes (C 10 F 20 ) and cis perfluorodecalin (C 10 F 18 ) 24 with the liquid phase concentration using gas chromatography and 25 electron capture detection 26 A volume (200 microliters) of the perfluorinated liquid under 27 study was mixed with an equal volume of the cis isomer of F-decalin 28 (BP=142.5°C). A stock standard of this mixture was prepared by 29 evaporating two microliters of the liquid in a 120 milliliter glass serum ι vial sealed with a rubber septum and aluminum cap. This volume was 2 chosen so that complete evaporation of the liquid could take place. 3 After volatilization, this stock standard was diluted by transferring 120 4 microliteres of the vapor to a clean, sealed 120 milliliter serum vial to 5 make the working standard. A 20 microliter sample of the working 6 standard was analyzed using a Hewlett-Packard 5880A gas 7 chromatograph with electron capture detector and column temperature β at 80°C. The chromatogram and peak heights were recorded and 9 printed using Hewlett-Packard ChemStation software. This enabled ιo calibration of the electron capture detector for each of the C 10 F 20 ιι compounds tested, and the known concentration in the liquid phase 12 could be used to determine the relative sensitivity, R. in the table, of 13 the detector to the perfluorinates being used. 14 To obtain the relative concentrations of the perfluorinates in the is saturated vapor phase, 30 microliters of the headspace vapor over the 16 50/50 liquid mixture was diluted in a clean, sealed 120 milliliter serum 17 vial. A 20 microliter sample of this diluted headspace was analyzed on is the gas chromatograph. The sample volumes and dilutions were 19 selected so that the F-cis-decalin peaks in the working standard and 20 diluted headspace were of similar height in order to avoid any potential 21 problems with a non-linear detector response. The peak height ratio in 22 the vapor phase, R 2 , was corrected for sensitivity by dividing by R l5 to 23 give the relative concentration of the C 10 F 20 compound to the F-cis- 24 decalin, R2/R1, in the headspace over the liquid; a comparison of the 25 vapor pressures of the liquids in the mixture. ι Table 2: Direct comparison of the vapor phase concentrations of certain perfluoroalkylcyclohexanes 2 (C 10 F 20 ) and cts-perfluorodecalin (C ]0 F 18 ) with the liquid phase concentration using gas cromatography and electron capture detection. 1 F ethyl-2,4-dimethylcyclohexane 2 F 1 ,2,4,5-tetramethylcyclohexane 3 F 1 ,3,4,5-tetramethylcyclohexane 4 F 1-methyl-4-isopropylcyclohexane 5 F n-butylcyclohexane Table 2 above shows the results obtained with five separate C 10 F 20 perfluorocarbons that are utilized in accordance with the present invention. The chemical name of each of the perfluorocarbons measured is indicated by the superscripts over the numerical data. The data of Table 2 clearly demonstrate that the vapor pressure of the 5 C 10 F 20 compounds are significantly lower than that of F cis decalin.

Claims: WHAT IS CLAIMED IS: 1. A method of facilitating transport of gases in a biological system, comprising using as a medium of gas transport a perfluorocarbon liquid which is selected from the formulas 1 through 10 Formula 1 Formula 2 Formula 3 Formula 4 5 Formula 5 6 11 Formula 6 12 17 Formula 7 18 23 Formula 8 24 29 Formula 9 Formula 10 wherein the cycloalkyl and rings are fully fluorinated and wherein C 5 F π represents any combination of perfluorinated alkyl groups where the total number of carbons is 5 and the total number of fluorines is 11. 2. The method of Claim 1 where the medium of gas transport is a perfluorocarbon liquid selected from the formulas 1 through 9. 3. The method of Claim 1 where the medium of gas transport is a perfluorocarbon liquid selected from the formulas 6 through 9 and 11 through 17. Formula 11 Formula 12 Formula 13 pentyl Formula 14 butyl methyl Formula 15 Formula 16 Formula 17 4. The method of Claim 1 where the medium of gas transport is a perfluorocarbon liquid selected from the following compounds: F-t-butylcyclohexane (Formula 9); F-l,l-diethylcyclohexane (Formula 11), and F-neopentylcyclopentane (Formula 17) 5. The method of Claim 1 comprising the step of instilling the perfluorocarbon liquid into the lungs of a mammal. 6. The method of Claim 5 where a tidal volume quantity of perfluorocarbon is instilled into the lungs of the mammal. 7. The method of Claim 5 where a quantity of perfluorocarbon is instilled into the lungs of the mammal to fill the functional residual volume of the lungs. 8. The method of Claim 5 where a quantity of perfluorocarbon is instilled into the lungs of the mammal to fill the alveoli of the lungs. 9. The method of Claim 1 introducing into the blood stream of a mammal a liquid composition containing a perfluorocarbon defined in Claim 1. 10. A method of assisting breathing in a mammal in need of such assistance, the method comprising introducing into the lungs of the mammal a perfluorocarbon liquid which is selected from the formulas 1 through 10 Formula 1 Formula 2 5 Formula 3 6 7 8 13 Formula 4 14 19 Formula 5 20 25 Formula 6 26 27 28 29 Formula 7 Formula 8 Formula 9 Formula 10 wherein the cycloalkyl rings are fully fluorinated and wherein C 5 F π represents any combination of perfluorinated alkyl groups where the total number of carbons is 5 and the total number of fluorines is 11, and maintaining a quantity of said perfluorcarbon liquid in the lungs while the mammal breathes. 11. The method of Claim 10 where the perfluorocarbon liquid ted from the formulas 1 through 9. 12. The method of Claim 10 where the perfluorocarbon liquid ted from the Formulas 6 through 9 and 11 through 17. Formula 11 Formula 12 CF(CF 3 ) 2 CF, Formula 13 butyl K methyl Formula 15 propyl Formula 16 Formula 17 13. The method of Claim 10 where the perfluorocarbon liquid is selected from the following compounds: F-t-butylcyclohexane (Formula 9); F-l,l-diethylcyclohexane (Formula 11), and F-neopentylcyclopentane (Formula 17) 14. The method of Claim 10 where a tidal volume quantity of perfluorocarbon liquid is introduced into the lungs of the mammal. 15. The method of Claim 10 where a quantity of perfluorocarbon is instilled into the lungs of the mammal to fill the functional residual volume of the lungs. 16. The method of Claim 10 where a quantity of perfluorocarbon is instilled into the lungs of the mammal to fill the alveoli of the lungs. ι 17. A method of assisting breathing in a mammal in need of 2 such assistance, the method comprising introducing into the lungs of the 3 mammal in an amount effective to provide such assistance to breathing 4 a perfluorocarbon liquid selected from the group consisting of 5 F-r-butylcyclohexane (Formula 9); e F-l,l-diethylcyclohexane (Formula 11), and 7 F-neopentylcyclopentane (Formula 17) 8 18. The method of Claim 17 where the perfluorocarbon liquid 9 is F-t-butylcyclohexane (Formula 9). ιo 19. The method of Claim 17 where the perfluorocarbon liquid ιι is F-l,l-diethylcyclohexane (Formula 11). 12 20. The method of Claim 17 where the perfluorocarbon liquid 13 is F-neopentylcyclopentane (Formula 17).

Inventors: CLARK LELAND C, HOFFMANN RICHARD E, CLARK, LELAND, C., HOFFMANN, RICHARD, E.
Applicants: SYNTHETIC BLOOD INTERNATIONAL, SYNTHETIC BLOOD INTERNATIONAL, INC.
Application year: 1998
Main classification: A61K9
IPC codes: A61K9, A61K31, A61P11, A61P43