Document B54DoX24dE7M0B1Q8jY0krmDJ

618 HEINZ SPECHT remission of symptoms usually occurs at intermediate altitudes and nearly:a| before reaching ground level. This procedure is not a cure until some tir|| elapsed, since reascent within a reasonably short time will bring almost iniH ate recurrence of symptoms at the same site.11 The reason for this deli! recovery is the same as in diving and caisson recompression: that is, the re-SoJL., of bubbles is slowed down in direct proportion to their loss of surface 'jifliS pression.00 For all practical purposes, recompression and not resaturatiorifW important factor in relief from decompression sickness per se, but eliinina of the hypoxic effects depends upon resaturation of the blood with bxygeiiflli is of course rapidly effected. 'i!l5TM 2. Mechanical Effects oj Recompression The mechanical effects of recompression are as hazardous as under simfi conditions in work at positive pressures. The patency of the eustachean .opeiiihJ and those of the several sinuses must be assured in order to prevent theinjcttfiuf of blood into the capillary bed of the mucosa lining the various cavities!^ question. As stated earlier,25 the pressure necessary to rupture the capillaty|||jl|f is quickly attained in descent, and damage ranging from petechial to{ ma/sSi hemorrhage has been observed regularly in individuals who have diffiruinljl clearing these passages.0,11 ,.{f During descent from altitudes at which oxygen must be usedif.thi'r^ incurred a condition that is called "delayed acute aero-otitis media.";,It iresftlt from-the charging of the middle ear with a high' percentage of oxygetSffiM subsequently lost by absorption into the blood. If the nitrogen influx isismimaM tained at a proper rate, and it seems usually not to be unless the eustachepjjjrm| sage is intermittently opened, then a negative pressure develops imtheitfniflSj ear, sealing the eustachean opening and eventually causing a varyingwcgW*" pain and discomfort, especially in individuals who are asleep. Pracficajg^ phylaxis has been shown by Bowen91 to consist in removing the oxygehlmifjj^p air-breathing levels during descent, and prior to this, if feasible, ventiJ^lirfgSrh ear and sinuses with air during a "stage" descent, while interspersing breathing during halts at each stage. When difficulties of this nature indoctrination and altitude-chamber work a more radical ,procedilrc#;fyij@^ applied--In-this-instance descent "is made with air "from even the. ^igUest^GP| since the time for descent can be made so short that supplementaiy^^gwS^^ not be used. The ability to open the eustachean tubes must be assured^beiorc^Mml maneuvers are attempted, yet it is surprising that with such rapid ^Vscmt^^ viduals having .some difficulty at ordinary rates of desnent. presumably because of the continuous flow of gas into the middle egr'|| 3. Rate oj Recompression The rate of descent that can be effected is limited mainly by thpVs-<v\;ern unquantitative variables and idiosyncrasies of sinus and ear veni ilatiori%a " W. J. Bowen, V. S. Naval Med. Bull., 44, 247 (1944). J 1 , .$u | EFFECTS OF ABNORMAL ATMOSPHERIC PRESSURE 619 and as described for divers and caisson workers. Recompression 4^1^)0()|feet and above has been effected in the space of a minute routinely "'" ^lof-eicperimental work91 without any untoward effect. With these compressional inflow effects described by Bean80 should be " 11|ijectively as well as objectively, yet no mention is made in the :uK'$uch effects on descent from high altitudes. In a preliminary trial, l,ffjjl||gas analysis of respired air indicated temporary carbon dioxide ISs'Kiillnng rapid descent with a corresponding excess for several minutes Iplcent. The respiratory rate also showed an increment in the period __ jfaS^pfollowing the descent.92 The data from experiments and experi- ^>0 fall in parachuting11 indicate that mechanical effects are the v^stnctiiig .factors in rapid descent. It is, of course, necessary to take into ,, 'absolute pressure as well as the rate of descent because of the interf^l^'fhiiff respirab1e air must be available. This is a real difficulty in parachut^n^fio'rSfgreat heights because even in free fall the rate of descent is slow enough mm*TM ma,y develop when an individual is jumping from 40,000 feet. i||||pfeinutes elapse in free fall from this altitude, and an open chute de- l^^Stake 241/2 minutes. Free fall is the method of choice until at least feTm^nfosphere of pressure is attained, not only from the point of view of iSfplIpbxia but also because of the excessively low temperatures at these Ste- . fciiySGomparison of Effects of High and Low Atmospheric Pressure ^TM^Etroduction to this chapter it was pointed out that the effects of baro- M^hanges differed qualitatively as well as quantitatively in the ranges of dl?||ff||p8ure above and below standard atmospheric pressure. The similari- Tan||||merences have been noted in the several sections. In the following lines raef|||||einent is made of the similarities and differences of effects on the normal individuals. The clinical and pathoftigibal features^must be g^ly'anfeirod from their physiological basis, and further^|ftil slibufSSe sought competent reviews, both classical and current,"that are cited in the jgicrenn- . Iframechanical effect of pressure change on the ear and sinuses is qualita- ^^mpr|.qr;bo.thrlow-pressure-and high-pressure-atmdspher'es^THe-prihcipal increase of pressure when for some reason pressure-equalization 'jTajJIppjf air into the lumens cannot be effected. The main result is displace*jS3i|jftqd from the body into the capillary system of the tiss^'lining `these nct'awlh^hemprrhage into the lumen. In the .case..of...the -middiel.ear,-bursting Mf^galso may result. A fall in pressure is usually not attended bv severe may result in driving blood out of the tissues within the cavity and. tnifgJrhtlJ'ear drum outward. The construction of the normal passages connect- WH *^?A;nau|iUshed work by the Aviation Medicine Unit, Ind. Hyg. Research Lab., Natl. Inst. calt'I 'Vlttb'esda, Md. fPi 4 Stiff' mfe