Document 3Q4kn7NJgnjqaD097R0o7xmEE

594 HEINZ SPECHT argon, and krypton, is usually thought to be purely physical. Certainly i vital conditions in mammals there is no corroborated evidence that nitrogei can enter into chemical reactions.24 On the other hand, observations af positive pressures, by Behnke and Yarbrough85 and others, have led t| postulation of a quasi-physical or chemical action that may .be involved production of a "narcosis" under these conditions by nitrogen and argon afp by the lighter gases such as helium and hydrogen.36 There does not seem tali present any known cause for these effects except that the behavior of gase|| not follow the usual relations when high pressures exist. Recently similaripuse; vations have been made at atmospheric pressure with xenon and argcnJ,,,j8ii helium and argon86'88 in both man and lower animals. M'S 5 III. Effects of Increased Atmospheric Pressure on the Body A. CHARGING OF THE BODY WITH GASES 1. Mechanical Effects Mechanical effects of compression of the environmental gases on tlS| and solid constituents of the living system are negligible because of ,I|L compressibility of these constituents. On the other hand, since pressure ifpl mitted undiminished throughout these substances of the body, displacemf fluid or tissue into any gas space not continuous with the .atmospher$l| avoidable. Such gas spaces are, unfortunately for those concerned, preseh body,..panticularly..-in-.the-middle-.ear-and-various-sinuses-in-th'e_hea'd7^i^ importance are the included abdominal and other gases. ! .'I'jffi In general the mechanical effects in natural diving aTe only quanJitaL.TM different from those in caisson diving, while suit diving adds a mechanical|l||| called "the squeeze," which is really a macroscopic extension of the ja^^888 ciple, in that here the body is forced into the helmet if air pressure fails-t^M water pressure. It is of considerable practical importance because collapseffi lungs with massive congestive hemorrhage results quite early in such;.\case_; The middle ear, including the mastoid sinus, has only intermittent^J|||| with the external atmosphere through the soft-walled eustachian,;iu||| compression the eardrum and this pharyngeal structure, which'l;is:' .gollaps.edjip...to_the_point_w-here-it-.is-enclosed-in-the-bony-stru'ci6ur^^^^ and thus forms a stopper, are pushed progressively inward. Ifvo1|fnt of this tube is not affected by movement of the adjacent muscles durinf^illi^^ then continued increase in pressure causes a displacement of the eardrumVint^m lumen of the middle ear with varying degrees of trauma, and,.more-inipouaptlv! "A. R. Behnke and 0. D. Yarbrough, V. S. Naval Med. Bull, 36, 549 (1938) ' "E. M. Case and J. B. S. Haldane, J. Hyg., 41, 225 (1941). -1| " J. H. Lawrence el al., J. Physiol., 105, 197 (1940). .,;i "S. F. Cook, J. Cellular Comp. Physiol., 36, 116 (1950). " S. F. Cook el al., Am. J. Physiol., 164, 248 (1951). EFFECTS OF ABNORMAL ATMOSPHERIC PRESSURE 595 mmh`t5c*i'ment of blood into the capillary lining of this cavity, resulting in petechial and massive hemorrhage, and occasionally rupture addition, there is an early dulling of the hearing, which is Efljjjjfjgjf-Helimarked displacement of the incus, malleus, and stapes, preventing ^feffiSjVowtfansmitting sound vibrations to the middle ear properly. According ^fej^^p'eriehpe. of the Royal Navy41 it is found that some degree of acute drum ^j^ff^igjijo'duced in all but the most experienced pressure workers. Iffi^ll'i^ctipn of increased atmospheric pressure on the various sinuses is only JTjii&p'npu* and-painful when, as in the ear, the openings are not patent. In ^f^i^iadiyiduals this is rare, but it is a chronic condition with some individuals, ^fen^Sfl^Ssppiated with infection or malformations. Obviously, acute infection ^^Rii^fp^Kpspiratory tract tends to produce this condition. When the openings hunesfare thus occluded, an increase in atmospheric pressure will result ire pain and varying degrees of trauma even with moderate pressure ^ilfij'Snct^.This seeming disproportionality between cause and effect is due ^fisfi]jiy;.'tthe rather large surface-to-volume ratio of most sinuses, allowing $Sthi?hsion of large areas of capillaries. This distention leads to marked |Ki'mh.atio5vof deep pain receptors, with the observed sequelae of nausea, etc., ili^j^iutSno'mic discharge from this stimulation. As far as can be determined, fpf^'rirtimfthe older literature of mechanical trauma to the vascular system are yJ^iteftW-iHfited more to the various conditions enumerated above than to other ic effects, as was formerly held.42 It is true, however, that the blood ^f^cApntb'the capillaries lining any such rigid-walled, isolated gas space and, g&sgfllftriSthe tonic state, may result in hemorrhage, if we assume a normal of 40 mm. Hg, it takes only 1/lt atm. of positive pressure to |e|||tlfalue in the capillary bed of the ear or sinus. Clinical tests of capillary fttliilie^based on petechial hemorrhages in normal tissue with 50 mm. Hg Stive normal I25 ||||irr!the alimentary traot are, wherever located, subject to compression ^BgssueS and for the most part do not cause any inconvenience beyond mPMement of the viscera, which in most cases tan be of only a benign g|||Pwill be shown subsequently, this does not absolve these gas entities ^^ffleration since, unless passed as flatus, they expand on decompression, ^^^fgihains one more mechanical effect of compression that;;while rare, is giSf^produce drastic sequelae: this concerns the compression of the &|flungs. Offhand, no effect would be expected since almost continuous lollthe breathing passages is assumed. It must be recognized, however, BmUjrapid compression, closure of the glottis in swallowing' or breath BBS------------------ :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ .Dickson, J. E. G. McGibbon, and A. C. P. Campbell, J. Laryngol. Olol., 58, $aval Med. Bull. No. 5, 13 (1943). Abst. in Bull. War Med., 4, 305 (1944). gfioff, A Bibliographical Source-Book oj Submarine and Compressed Aid Medicine. eminent Printing Office, Washington, D. C., 1947. ,