Document RpVrzzaZzEVLOaBZGZbEq3G7B

608 HEINZ SPECHT Of more fundamental nature is the relation of rate of ascent to the a%g pressure levels attained during ascent. That is, the partial pressure of -SS during ascent falls, and ultimately a point is reached at which the satur^w the hemoglobin of the blood can no longer be effected. This level is general!; fined as about 10,000 feet, since the first disturbances to psychomotor repS become measurable at this level. Thus, the rate of ascent determines the;':piil| time at which the individual arrives at the critical levels. In the case o: " *" ascent cited earlier, advantage was taken of even the limited storage tl: body can effect for oxygen, that is, the reserve time or asphyxiation timep^ the discharge of the pilot's duties needed to be effected over only a ji|f minutes, and for this interval his oxygen reserve could be made to sufficf! doubtful that such close figuring will be resorted to in the future becomes a matter of desperation. S! In general, the influence of rate of ascent can be obviated by thfeN procedure of breathing oxygen from a mask, beginning before ascent to'8! body nitrogen,71 and continuing during ascent to prevent desaturatioiff hemoglobin of the blood. This expedient raises the critical level to abou| feet, at which point the absolute pressure just suffices to maintain propera tion of the hemoglobin of the blood. To obtain independence of these necessary to maintain a pressure differential between the individual altitude environment. Various methods have been devised, but pressuriff||j cabins in aircraft seems to be the most suitable one.11 S. Evolution of Gases from. Solution in Body Tissues during Ascgn, It has been shown empirically that although rate of ascent has soMOTa on the incidence of decompression sickness, there is a delay in tKtffip symptoms that is inversely related to the altitude attained. This correlf^ the fact that bubbles must have a period of growth, either by diffusibnjp by coalescence, before they become effective.' This delay is usually IonfJ|| that no symptoms appear during ascent to altitudes below 45,i.......... reasons for this delay are not known precisely, but it is apparent thaty-wi the cause of the initial delay, the failure of bends to appear in slp$^J|f oxygen-breathing-is -most-probably due to the relatively-good-inetiygL attained. "Irtpr It is known from diving practice and experimental work11 that derpmp'Ttijj sion from two atmosprheres absolute can be carried out without riskit*n f'KerKlsSpS rapid decompression .to one .atmosphere under normal conditions^aaKU thi-yi'a's of pressures was shown to preclude bubble formation at any feasible "A. H. Whitely, W. X>. McElroy, G. H. Warren, and E. N. Harvey, J. Physiol., 24, 257 (1944). . ; V V ''Vwffr ''V'Sft V 'z&j&r EFFECTS OF ABNORMAL ATMOSPHERIC PRESSURE 609 lIOTJ S^raeySfessure. Although- recent work77'78 indicates that abnormal conditions ^^Vitygmay- decrease the ratio markedly, extension of this rule to reduced J^nretsis^'fistified empirically since reports of bends or chokes from decom^.jJjIll^tcrreSuced pressure have not been made below 26,000 feet, or about Vs -B^^imfustice to the facts it must be added that human exposures to reduced such levels were nearly always carried out with added oxygen, although such instances an appreciable partial pressure of nitrogen in the When animals are exposed to reduced pressure, bubbles are rarely fxposure to pressure-altitude equivalents under 15,000 feet,76 even with xtr,,eme conditions of muscular stress. On the other hand, in resting mini-cr-itica1 level is equal to or above that found for man, depending to `'"ty.on the body size of test animals. The physical reasons for the lack formation with saturations below a critical level are not well undergjtfrg-l&fiift it, can be shown that in vitro the lack of properly dimensioned bubble (jyfficiffl-ill prevent bubble formation until the differential pressure has reached ^cffiYiiteVjeyel,69-77 and that at each new level of pressure a new crop of bubbles ^rHo^from nuclei that were ineffective at lower differential pressures. It is there- *" ^ ^'fpfjcd.that the lack of suitable bubble nuclei in the body is one of the g-Var*o^ that allow such high supersaturations to exist without symptoms com'p e-sion sickness. m S. Mechanical Effects EBSEmechanical-.-effeGts--of-- decompression to altitude are identical with ^^ffifiihg on decompression from high-pressure atmospheres. In general fmmbr symptoms only, and these arise from the pressure exerted by Wspfc. when the atmospheric pressure falls. The pressure exerted internally IPfie ear usually falls off readily by displacement of the air through Uplan tube, and a similar discharge from the sinus spaces takes place isHstion from colds or other inflammations closes tiff the openings into the ]!nl?'With such closure, a fall in atmospheric bressure. will allow the tgasfes to displace the blood from the tissues lining the space, and this |||pTus displacement of the yielding portions of the space will cause a Sarris^W. E. Berg, D. M. Whitaker, V.C, Twitty, J. Gen.J^hysiol.,, 28,^241 (1945). ,^^^ffiA^eyyjW^E)rMtElroyi"Ai-tir.'w'iiiteiyi G. 'fe-Warreny-and'D; Cl 'Pease, J. CeU 24, 117 (1944). W. D. McElroy, A. H. Whitely, G. H. Warren, and E. N. *TMtfSi'24, 133 (1944). W. D. McElroy, A. H. Whitely, K. ,W. Cooper, D. C. Pease, |h;and E. N. Harvey, ibid., 24, 273 (1944). e-Kritrier, War Med., 6, 369 (1944). ___a1gjH.'A>8medal and E.-B. -Brown,-V. S. Naval Air Training Bases. Pensacola: Fla.. Project. mmsmfok i (1945). ~ itplrHarris, W. E. Berg, D. M. Whitaker, V. C. Twitty, and L. R. Blinks, J. Gen. Physiol., m- |f|EVvBerg, M. Harris, D. M. Whitaker, and V. C. Twitty, J. Gen. Physiol., 28, 253 m mk,,.