Document jgjVeYwRNo19wr7NqOb24Jqn5

580 HEINZ SPECHT seventeenth century that advances in diving technique were made rapidly advances made in that century served to recover the riches sunk with the:Sp_ Armada.3 It was another century before pumps were used to supply air to and it was with this means of prolonging diving time that intimations of ;phy logical factors began to appear in the scientific writings. It was no longer a!'.ml of "fresh air" but the realization that compression and more especially** pression were hazardous and required deliberate and slow schedules attainment of gaseous equilibrium between the body and its envirohrfteifj logical basis for decompression was not discovered until Paul Bert1'2'4-;W i id, *ffil fundamental work on the effects of atmospheric pressure on the body. 3] The effects of rarefied atmospheres were known in ancient timeses only significant deductions were concerned with their geographic distsilVuV Thus, the inhabitants of Alpine, Himalayan, and Andean regions were ' ' * ' be industrious and healthy people casually undifferentiable from the h yet the latter in travels through these regions collapsed or at least w incapable of exertion. However Acosta, in 1590,1|2 wrote that in trans'l trips even the natives were affected by extreme altitude, and he rightiy;o|l that the "fine and thin air" was unsuited to the requirements of respirajpj It was not until abrupt ascent into the atmosphere became fej the pioneer balloonists found--by bitter experience--the necessity f< knowledge of the effects of lowered atmospheric pressure on the bo< again the researches of Paul Bert4 from 1871 to 1883, spurred on by outcome-of-ascents-of-Sivel--0roce"Spinelli-,-and-T-issandier-(T87-5-)y7fcha the analysis of these effects and laid a rational groundwork for the 'eni In essence, the problems in physiology presented by abnormal atmj| pressure deal with the vagaries of the physical solution of gases in the t the pressupe-labile chemical changes of oxygen and carbon dioxide and the concomitant effects of these factors on the complex systems of.fi that the mammalian organism, in particular,-has evolved. ^ Because of certain differences, in various factors, that exist betjv.eg types of abnormal pressure, increased and reduced pressure will each b separately and then followed by a discussion of the common properties: to understand the intimate difficulties encountered by the body jiii.|i two.rangea:vOfpressure4t'is necessary.', to recapitulate the.properfl!eg& the atmosphere, first, with respect to each other and their geographiga tion and, second, with respect to their individual characters. (For. aj;,, treatment of the subject see the excellent work of Humphreys.6) Meyer, Conversations Lexicon. 6th ed., Bibliographisches Institute, Leipzig nd^yi^ 1893. `P. Bert, La pression baromitrique. Available in English as Barometric 'Pressur^ by M. A. and F. A. Hitchcock. College Book Co., Columbus, Ohio, 1943. * W. J. Humphreys, Physics oj the Air. 3rd ed., McGraw-Hill, New York. 1010 V EFFECTS OF ABNORMAL ATMOSPHERIC PRESSURE 581 II. Properties of the Atmosphere A. COMPOSITION jjsgl^tnjjosition of the atmosphere near the earth's surface is given in ' cr1\'V.i(ipage.l43), and therefore the components will not be tabulated here. ffira|jth%fexc'eption of carbon dioxide and ozone, the gases normally present |ij||^fedistributed in relatively unvarying percentages from the level of _ 5i(s4(r^l292 feet in the Dead Sea Basin) to an altitude of about 65,000 altitude there is no thermal mixing of the atmosphere and there iSISSSithaVa' progressive decrease in the concentration of the heavier gases mtjpVesult of gravitational separation. This level is above the altitude flfe|oft*iieoretical grounds, the boiling point of water in the body would be above the level at which pure oxygen will no longer suffice for fie metabolic needs. The composition of the atmosphere at these . JpWaihly of engineering interest in the construction of stratosphere craft ffjjtffii&ambient gases for pressurization of cabins. IpUpfce of such a variable constituent as ozone is accounted for by tera'lfies. Besides local concentrations due to electrical discharges through pffere there is a diffusion of ozone downward from extreme altitudes |lf|en is thought to be converted to ozone by the absorption of energy instability prevents any accumulation to deleterious concen||||lr'a8 is known, in the vital altitude range given above. iHjiioxide is present in appreciable concentration only near the surface may accumulate to a variable extent only in confined or ieajareas in which combustion of carbon or other release of carbon fiking place. In nature it may become a limiting factor for life, for ^certain grottoes where various processes free carbon dioxide from SiScumulate in the air in high concentration.7 Carbon dioxide is also tin; dangerous concentration in caisson work, in mines, and in tunnels.4 Sgelffial'i water vapor in the external air does notHimit the use of the icgl^ryrespiratory purposes, but as will be seen later, at high altitudes ii8an' physically displace other gases from the lungs. As far as can be concentration in air of caissons and tunti'eFheads produces no Sel'eteliops. effects. In' the external atmosphere it attains a very low value the isothermal layer^stratospliereKj^lpfinstances of significant concentrations of abnormal constituents S^efc^sive^concentrations of normal constituents are in situations similar to fewiatsis, in confined or restricted areas. Conditions often are aggravated |plfiSiPth'ese-abnor-mal-constituents-iorm_lay.ers^TChose^:concentEations_ lpto life. In any case, the factor of natural positive atmospheric Ippfiiimportance only because chemical reactions in metabolic systems. Jpf, - ffjyffl&hdH. Strughold, Grundrisse der Flugjahrtmedizin. Barth, Leipzig, 1939. { ^uinn and C. L. Jones, Carbon Dioxide, Reinhold, New York, 1930. w