1. Field of the Invention
This invention relates to a method for biochemical assistance in the decompression of divers using a breathing mixture of oxygen and a nitrogen or hydrogen gas diluent and a product for accomplishing the decompression. More particularly, this invention relates to a process for assisting in the removal of hydrogen gas (H.sub.2) or nitrogen gas (N.sub.2) from the systems of divers breathing H.sub.2 or N.sub.2 mixtures under hyperbaric conditions and a product for accomplishing decompression assistance. This product and method supplements and accelerates the removal of hydrogen and nitrogen gas that occurs spontaneously during conventional decompression of divers.
2. Description of the Prior Art
As soon as a diver submerges beneath the water, the diver begins to build a decompression debt. The debt is created by a greater amount of gases dissolving in the blood and cells as the greater depth causes an increase in the partial pressure relative to the conditions prevailing in 1 atm air. When the diver begins to return to the surface these gases leave solution and can create health and life threatening bubbles in the blood stream and tissues. The amount of dissolved gas in the blood and other tissues is a factor of time and pressure. The dissolution of this gas is not instantaneous but happens over time so, until equilibrium is reached, a shallow dive for a long period of time can cause the dissolution of a substantially equal amount of gas as a deep dive for a short period of time. The limits to deep diving by humans are set by factors related to the increasing mass of the water column over the diver as the diver descends.
In order to ventilate the lungs during a dive, a gas mixture containing oxygen must be freely available to the diver at a pressure equal to that of the surrounding environment. This breathing gas cannot be pure oxygen (O.sub.2). If the diver is to spend more than half an hour at a depth greater than 10 m, a pressure equal to 2 atmospheres, the diver might suffer from the cumulative toxic effects of O.sub.2. At depths between 10 and 60 m, it is customary to dilute the O.sub.2 with N.sub.2 as in air. *At depths greater than 60 m, helium is commonly used as the diluent because N.sub.2 exerts narcotic effects at these pressures. However, at extreme depths in excess of 300 m, the density of a helium-O.sub.2 breathing mixture is high enough to make it difficult for divers to ventilate their lungs comfortably, particularly during exercise. At depths greater than 300 m an H.sub.2 -O.sub.2 gas mixture offers the advantage of lower gas density thereby providing a gas that is easier to breathe. An additional difficulty encountered at extreme depths is that divers often experience nausea, tremors, or seizures that appear to be induced by high pressure affecting nervous conduction, a phenomenon known as High Pressure Neurologic Syndrome (HPNS). FNT *All references to gas mixtures with nitrogen are intended to include air.
The diluent gas in the breathing mixture dissolves in the diver's tissues in proportion to the solubility of the gas in tissues and the partial pressure of the diluent gas. As the diver ascends and the partial pressure of the diluent gas decreases this causes a decreasing volume of gas to remain in solution in the tissues. The diver must ascend sufficiently slowly that the excess diluent gas can be eliminated via diffusion across the epidermal tissue, lungs, or other mucous membrane body surfaces, with the residual gas remaining in solution. If this ascent rate is exceeded, gas bubbles may form in the diver. When the gas bubbles are large and numerous, or in particularly vulnerable tissues such as the spinal cord and joints, they may cause a painful and potentially seriously debilitating condition known as decompression sickness (DCS).
The only method of decompression in current use is to carefully control the rate of a diver's ascent. The rate of ascent chosen is based on past history of ascent rates with minimal incidence of DCS. The earliest of these ascent charts were created by the United States Navy and are called the Navy diving tables. Recently, probabilistic models have been generated to assist this process of predicting safe ascent rates for a given dive. In the event that a diver experiences symptoms of DCS, the diver must be recompressed until the symptoms are relieved, and then decompression reinitiated more slowly, again according to past experience. Decompression is thus inherently dangerous because the diver's tissues must remain continuously in a supersaturated state in order to eliminate the burden of excess diluent gas. Decompression sickness cannot be predicted or prevented with absolute certainty because of its probabilistic nature and because each diver reacts differently. The same diver may have a different reaction at different times because of wellness factors. Therefore, the decompression rate necessary to prevent DCS for any individual can only be an approximation based on prior general experience because all the risk factors involved in the off-gassing rate for a given person are not and cannot be known.
Decompression can also be extremely time-consuming; it takes 12 days to safely decompress a diver from a 300 m dive that lasts as little as a few hours. During the ascent, the diver is at high risk of injury just dangling between the surface and the bottom. Thus, a method for shortening decompression would reduce a time of great personal risk to the diver as well as reducing expenses of the dive operation.
The concept of biochemical decompression was first proposed by Dr. Lutz Kiesow, who was a leading scientist in Diving Medicine at the Naval Medical Research Institute. Dr. Kiesow proposed using hydrogenase to cause biochemical decompression. According to this concept, a diver would breathe a gas mixture containing H.sub.2 and O.sub.2. The diver would be supplemented in some fashion with a hydrogenase enzyme, which is found in many bacteria. The hydrogenase enzyme would convert gaseous H.sub.2 to some other molecule or molecules. This process would reduce the diver's burden of excess diluent gas as the diver ascended, thereby shortening the time needed to decompress safely. Dr. Kiesow did not specify any particular means of using the hydogenase or a situs for the interaction. Dr. Milton Axley tried to put this concept in action by trying to put the purified hydrogenase into the red blood cells themselves. Dr. Axley found he could encapsulate the enzyme into red blood cells, but could not devise an animal model in which to test the cells. This work is reported in part in an Abstract for the 5th Meeting of the International Society for the Use of Resealed Erythrocytes as ENCAPSULATION OF HYDOGENASE INTO RED BLOOD CELLS FOR THE PURPOSE OF BIOCHEMICAL DECOMPRESSION, Axley, Kayar, & Harabin 1993, article published in Advances in the Biosciences, Vol 92, pp119-124, 1994 (Elsevier). A study on the kinetics of the concept for use in blood was published as KINETIC MECHANISM STUDIES OF THE SOLUBLE HYDROGENASE FROM ALCALHGENES EUTROPHUS H16, by Keefe, Axley, & Harabin, Archives of Biochemistry and Biophysics, Vol 317, No. 2, pp 449-456, Mar. 10, 1995. The concept of incorporating the hydrogenase into the blood was not further studied because even if the enzyme could be packed into the blood cells and be injected into a diver, the cells could only be circulated for a few weeks before the red blood cells died naturally and were eliminated through the spleen. The foreign protein of the injected enzyme could lead to splenic failure. There remains the concept of biochemical decompression, actually assistance to decompression because normal dissolution of gas continues to occur, without a means of effecting the biochemical decompression.