ReviewArtick

Dyspnea: Pathophysiology and Assessment

l&e Rt+@i&m qflhdhiag The act of breathing is regulated by a corn

plex network of somatic and alltonomir IIC~VCS. Tablr 1 summari?rs the intlcrv&m of the respitatcxy systrm. Normal breathing is controlled by three main corn(nrtmts.“‘~“’ its will be explained here (Figure 1).

RfspiraloTf Chtfo. The neurons that control respiration :II‘C’

located at different Iweb 01.the brainstcm and are responsible for the automatic controt 01 breathing. The most important nrtrvork i* located in the medulla and controls the rcrpi- ratory rhythm. This respirator )’ cater bn the function of integrating all pwipherdl and cm- tral affetmt input and generating the rllcrrnt activity that results in respiration. The central affereenti derive mostly from the cortex that controls voluntary rcspirzrion. This voluntary component of respiration is illustrated by the

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‘/ihh I

itic-reaw of K:O, wi,t\i\\ ,hr pl\yioh#c I-angc, rhrw pallc”,r pr\-crwd an \\\\rll\l\lil~t;lt\IC

“ail- t\\\\\gvr” ii1 abwncr of any dr\\\o\\r,rablc rcspiratry muscl,~ ac,ivir): These lindi\\gs s\lp pm rhc ohwn;\,iol\, wcordrtt in p:\\ic\,,r \vi,h poliomyelitis. ,l\ut changes i\\ P(X), ,a\\ induce dysp\\m.’ ‘.“. In a wcond cxpcrimc\\,. i\\ tl\rrc pa,ie\\w. Ba\\rc\, C, al. found ,ba, ,t\r! wspondcd with dyspnra ,o change* ra\,gi\\g txwrcn 5 mm iig and It mm tlg i,\ IYX),.‘” Tl\r a~\,t,ors clai\\\ rha, <I\;\\\gcs i\\ hr(.a,l,\,\g arc not ncwwar~ to ewkr the scnsc of “air IlUll~“.” but this \nay still dc*pe\\d WI i\\rrc.\ad rftrren, rraffir fro\\\ ,t\c \\\cd\\ll,wv \rrpira,o\-y CC\,,CI‘C warhi\l): ,t\r H’\\uw! co\- ,rx ,l\ro\\gt\ wroll.,ry diwhugc.

111 l \,\\\l\\al-y. atll\o\lgt\ i, is well \-rwg\\in~d tha, both hyt)oxi;a and hype\:;rp\\i;, c.\\\sc wvcrc~ dyp\\ra. i, is \\o\ clr;\r it this o(c\\rs as a diwct percrption of altered chcmorrcq\,~)~- \,i\n\\ta,ion or if rhr dintnw i\ d\\r \o ,t\r conl- bi\\atio\\ 01 ,l\is s,i,nula,ic,\\ and a signilic;,\\, cffcc, ot cffcwn, mu.wlc n,i\,\\\ln,ion. \r-l\icl\ rchul,~ in an incrcaw i,\ vr\\,ita\iv\l.

Tlw IloC of M~ct~amm-rtpor Stimtrlnlion (:\\.~n~\, cvidrnrc indicate that \here is I\(#

\u\iq\w peripheral sc\\wry si,r that mrdir\es dyspnca dur ,o mcctlanowcep,or s,i\\\\\la,io\\. Tt\r rev rp,or’i in the n\wosa of ,hc upper ;\ir- WBYS do I\\), t\a\r n nig\\itica\\, role in the WI\- M,io\\ of dynea heca\\sc ,t\r abiliw ,o dlrrcc, rnis,i\,c a,\d clatic Io;\ds lrmains u\\ct\a~~grcl al,rl- Ioc;\l ;\\\cs,t\r,ic hlcnkagc of tl\r .\\-~i\.“‘.‘)~’ \Vi\\ni\\g C, al.” co,\d\\c,cul a : on,\-ottrd trial co\nparing rtie i\\t\ala,io\l 01 \\cw\\\al \;,til\c and ,5B hupivacaine in six paricnlr \$,itt\ inwr- slirisl lu\\g diw:w. ‘Tt\rrc we \\o +\,ilicrl\t i\\\provrn\r\\l af,w placebo 01 b\lpivac:\inc i\\ the w\\\;l,ion of dyspnca. The ti\\di\\gs of ,t\in c,\\dy migh, tw limited hy ,t\r lit, tha, ,I\< int\ala,ion of the Iw.,I a\\chtl\r,ir may \\o, h, ahte ,o block ,t\c rerc,,,ore Ioc;\wd dwpl! within ttw I,IUI~ A ~in~il:~~ I;wL x>f vff,‘r\ frnn\ local a,\cwhe\ir* was +x*ned i\\ p;\,ir,\\s \vi,t\ pulnionar~ fibrosis. “’ hdmi\\is,rd,io\\ of local a\\rs,t\r,ic age,\,” b) arrowl \\\ pafirnts wilt\ variou> pulmonar! diwrdcl-s. i\\rl\,cl\ng cl\ro\\ic ohs,,\\r\\rr air\cavs direaw. s\\t)- prerxd co\\gt\i\\g hu, did \\o, \\\cwtify d!-sp nc;\.“’ This r,qgo,~ rhr, sensors rcrrp,ors in the tasr airw;\)x an’ ,\o, m;ljor con,rihu,ors in the gener;l,io,\ of dyspnca. Thr hlcx&e or

Thrr~~fwe. the nimplt. ~mtput from the I-espira- tory center into the cortex may not he Ihe wlc caw of dyspnra. The input originated in the conducting muscles is complex. Recent cvi- dcnce suggests that the respiratory effort WI- sation that accompanies diaphragm fatigue is not due to perception of increawd diaphrap; matic contraction. but. rather. m-y rcflrct overall respiratory motor output not directed to the diaphragm.”

Moddatm Some modulators amplify or drrreax thr

intensity of the symptom lhal is perceiwcl at llw cortical level. Factors such 3s .xlwral hack- ground. environment, liir experiences. and the psychological state ‘mr’ are ronsidrrcd modula- mrs. which can alter both the rerponrms to stimuli or evems and the subsequent COIISC- quences. Fiptv 2 show the different stages in the production of dyspnea Becauw both the prcducdon and perception of dyspnea cannot be measulrd. the a%ewnent is bavd on the patient’s expression. The expression of the intensity of dyspnea c .m be influenced by a num- kr of Facton described in the figure. The per- ception of drjpnea can be inctra.4 in paienr~ who are anxious or dependent. as compared with rhosr who are adaptiw or nondependent. Moody et aLy’ edualed the complexity of inter- romktions betweet~ dvspnea, diseae severity, mastery, depnz&n. funnional status, and qu&

This should m,t be interpreted as a direct rcprtwntaticm of the intensity of production 01 dynpnca at thr level of merhanoreceptors or , hemorrceptors. In contract to :he level of glucox in a diahrtic patient or the level of blood pressure in a hypertensive patient, which are generally assunxd to be a direct expression of the underljing pathophysiologic mechanism. dyspnea should be interpreted as a multidimensional phenomenon in which the intensity described by a given patient is a result of the interaction bctxwen different fnc- tws at the level of production. perception, and expression.

me-ofDyspnea LIyspnza is a difficult symptom to measure

due to its sul~jcctivc nature and multidimerr sionality. There is ample raiation in the fre- quency of this sympt~m.~~’ This variation may be due to patirnts with different survival times or different awssment methods. Additionally. the awssmem of the symptom is not ;?lwn~ expre.%ed directly by the patient but by the pwxy caregiver or hv the professional staff. In this cav. there is a r&k bias introduced by the stress of the observer who assists a patient with dyspnea. Moreover, there is the possibility of taking tachlpnea as an unpleasam subjective sensation of breathlessness.

Assessing thp Cause oJi$spnea Dyspnea is frequently multicausal in patients

with advancrd cancer (Tablr 2). Ilw cause

7irblr ? CalKQs of Dyspnea in cancvcr PakI%e ---

ihili,\ and senri,i\i,y) for thr dwcc, quan,ifirn- lion 01 hrca,hlcwwss induced by wmil;,,w) aimula,ion. both in normal sul+c,sii.i)( and in pa,icnLc with rrrpiratory diwau~.“‘~“” The. VAS is ,,ow frequrndy uwd bo,h in clink-al therapeutir s,,,diesh” and in \,,,dk of ,hc ph+ologic mechanisms undrrl~ing ,hr suna- ,iwLh fkcaure ,bc intrnsity of dyspuea. as

compared with ,Iw ,,ormal rffor, 01 brr;,,bing. i\ ;,n ex,rrn,rh whjrctiw cxpwicncc. ,hc ,,w of ,he V.&S for the compatiwn ol diflcwn, popularions is of lirnkd value. I, i\ mow appropria,e ,o ,,sc the VAS for rrpacd ,,,,‘A- st~rctrtrnts in change% of ,hr disease s,d,us or ,hc efkrcs of diflcxr., ,hrrapeu,ir i.,,rr\cw tivms. Al,hou@ \‘AS is ;, uselid dimcnrional mrawrem~nt OK [be wvrrity UC d\$pnra. i, does no, conrider tbc rct;,,i\e crm,rihu,icm 01 diffrwn, hr,on ,o the patient’s perception of hrea,bl,~ss,wxs.

The rhw,-cerm rc~prod~,rihili,v VT \‘.%.S d\sp nra ,~xaasurc,~~cn,s has her,, ronlirmcd in horh normal suhjec,s and patic,,,? w-i,11 (ZOPD:“,” Sone,l,clrss. tbc modcraw (w long-,erm reprcducibili,~ of rhr VAS \,ill ha\ no, bwn r”a”d.“~‘“-“’ Tbir implies that ,bi meawrenw,~, rwl is indicated only ial xw-e ing ,hrrapeu,ir in,crven,io,l w~po,,xs in ,bc stlclr, ,cr,n.

Grbnl Dcw-t$~lon Roth ;I wrhal ra,i,,g ualc. wcl, AS ahrn,.

mild. modv, aw. wverc. .,nd rxcruri;t,i,lg. and a Lihrrl-,yc sxalr, ’ ” arc mrthcds for dyw! .LU(MIII~,I, ,ha, arc c;lrier IO undrrstand, par- ,icularly in thr raw of rlderly pa,ir,,,s. ‘The. wpport [ran, II\\C\\ITICII, \cbrdulr (RI-AS) record\ a wrk of i,c,t,\ [ha, h.ae been ngrwd cm h! supper, trdnn ,o hc indrpcndc,,, o !‘:.‘.‘T tiws of rdrc*.,hr ,IIC’PSI,~CF ol ,IH. rwdi i ),I. and ,hr needs of dying pa,icnls and thrir I ni- lies. The WAS k a seven-pain, sc&* (O-b,, . +?,,d

tncm~rcs the irnrnsicy of the .ymp,om. &t-c- q,wncy (occdhiollal or ron,inurn,*t, alld 1111

in,erfc,-r,,cr with the a&i,!. This AV’WIN’,I, is prformrd and rrrordcd hy .L I,,~,IIIx r 01 ,tir pallialiw care Wan>, ra,twr ,bla,l ,br p.,,ir,,, himscll.“~““‘-‘”

The 5TA.S i,ls,,-umen, ic a,~ audit ,wl. A: ,I i, ma) rorrrtd,r wi,b the co,didcncr of a pallia- tive care warn in man;llling d>spnr;a. H’i,h thiz type of assessment. it has been porsiblr ,o identify d!npnea a$ ,br mos, lrrqurrl, *)-alp

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