Document VKz7gzb5dw77xJrG6r1vmem7K

604 HEINZ SPECHT for the development of local ischemia in the tissues, particularly in the skin.**' and Swindle65 indicate that intravascular bubbles may be secondary- ^ embolism caused by the agglutination of red cells following exposure to con, air, but confirmation of this effect is lacking. In many instances, however;' symptomatic accumulations of gas are found in large quantity, as for ilia in the fascial layers beneath the skin and between the muscles. They...p^ a crepitation during manipulation. The question of whether intra- or extravake bubbles are responsible for such occlusions is an academic point, but on which future prophylactic measures will evolve. # Given the general mechanism of occlusion or embolism the whole gaifi? symptoms presented by decompression sickness can be seen to have asc|m cause. In particular, the effects of central nervous system disorganizatifi' breakdown are directly traceable to the anoxia of motor centers and tfip grating mechanism of the cortex and medulla. Thus the reported "monop paraplegia, M6n$re's complex, apoplectic deafness, vertigo, aphasia, hem etc." are all manifestations of this basic mechanism, throughout the fo, system. In fact, the cause of death in the majority of cases is rather|>Lf attributed to a cerebral embolic accident than to general anoxia from^carai failure or a toxic effect of the exposure on the tissues.68,61 The statistical distribution of symptoms of caisson disease indicate peripheral effects predominate!68 This may be related to the fact that p^fT reservoirs of fat unload their nitrogen slowly and therefore are subject 't'fr$ra formation, while only in case of gross supersaturation of the individi1" chokes and central nervous system disturbances appear. K.1 i It is possible that the caliber of the vessels in the lungs and the'ibralj some part in this distribution, since it is generally estimated that the ciipilftyo are larger here than in other tissues; thus only when large bubbles'r'fofmESi directly o' f- by fusion from smaller bubbles will effects in theseSt;!fe*^>i4oin1 s expected. .y S. Rate of Decompression The problem of desaturating the tissues without causing bubble, form from being initiated. This procedure, however,.resulted in maihtSimhg'^ik, low differential pressure across the interface between tissue and envir|ni^m^' transfer..of-gas.was slow, and bubbles formed .desp.ite..all..pecautiobfcii,H4SS, then instituted the technique of decompressing rapidly to such a"p%iin*{J create a large differential pressure between tissues and environment-blfl " E. End, J. Ind. Hyg. Toxicol., 20, 611 (1938). *P. F. Swindle, Am. J. Physiol, 120, 69 (1937). EFFECTS OF ABNORMAL ATMOSPHERIC PRESSURE 605 .prevent bubble formation in the time used for desaturation. After 2?jfjgffig[|ting,.at this level for an appropriate period the pressure was again a somew^a*' longer period of desaturation followed. By extension |||p9ure will bring the diver to the surface in considerably less time than ||8ormer method and without as great a hazard. It was shown experimeni|p;he..pressure could be safely reduced to one half at each stage, and the ^weiesaturation was calculated from composite data on the different rates BRlfeiltion of various tissues of the body. ffgmgthod outlined above is essentially the one in use in all decompression hut certa'n minor innovations have been applied by subsequent -6^icri'tipnter8.66 The Continental practice is a similar modification introduced isdSjiiP-03 ln which the initial rapid reduction in pressure is made as in jag method, but subsequently a continuous slow ascent is made. This Recording to its originator, maintains the gradient of pressure effected pressure drop throughout the decompression and further reduces yj^Mecomprefflion time. %pving tables in use in this country are constructed on the stage basis jJnej-but include an ascent between stages of not more than 25 feet per ^Acceleration of the ascent schedule has been effected by the introduction Jp|*i}?e breathing of pure oxygen at the later stages when the total pressure "Mbgh to avoid effects of oxygen poisoning, but for economic reasons this Ill-used only in decompressions after recompression following bends or gious decompression symptoms.67 The use of helium in place of nitrogen |P^>cated^ecauie o"f ilsTowir solubility, but its principal contribution Imnation of "nitrogen narcosis" in deep diving.40,64,68,68 Ipractice in decompression for caisson workers is a continuous slow ^o.iPne half the working pressure. Attempts to decrease the incidence of J*9?Orgen breathing have been made with some success.4? Uniform lesion rates have been prescribed by law47 in the past, but changes in have been made to take advantage of more rapid methods, with due Lqii for safety. In many instances there is an'over-all limitation in llpSwP period for decompression without strict interpretation of the initial |gessure reduction. Because of marked fog formation in this practice, of the decompression chamber temperature..during, this pro- iter* r ^^gpiMgcbnaderation i ia ' given in" Continental code's68 to'"moderate re..#a'blowing eah stage of decompression, in order to warm the air m J&M thus avoid chilling the men who have been at hard work in a hot yBoycott.-G, C.-G.-Damant, and J. S. Haldane. J. Hyp., ft, 349 MnnV &M5. der Aue. w. A. White, Jr., R. Hayter, E. S. Brinton, R. J. Keller, and A. R. 'SjgSRmenial Diving Unit, Navy Yard (Washington, D. C.) and Naval Med. Research 'ptft&sda, Md.), Research Project X-44S, Rept. No. I (1945). ----- `"* ipBehnke, R. M. Thomson, E. P. Motley, Am. J. Physiol, 112, 554 (1935). E. End fysiol, 120, 712 (1937). 1