F uncao dos Musculos Respirat6riosem Doentes com Insuficiencia

Cardiaca Esquerda*[43]

M IGUEL MOTA CARMO, CRISTINA BARBAHA , TEHESA FERHEIHA, SARA FERREIRA, A NT6 NlO BENSABAT R ENDAS

Service de FisiopatologiaFaeu ldade de Ciencias Medicas da Universidade Nova de LisLoa

Rev I'uo'\ C,mliol 200 1; 20 (5) : 53 :{-5 '~5

R E S UM0

Objectivo: 0 object ivo deste trabalho foi :estudar a funQM dos rmisculos respira t6rios

em doen ies com insuficiencia cardfaca 'esq uercla moderada (ICE), e 0 seu contr ibuto

para a genese do cansaQo e da dispneia.Concepc,;ffo do es tudo:Estuclo prospectivo

coniparati voeutre cloentes com ICE enormais .

Doentes: Es tudamos 10 cloentes clo sexomascu line, com insuficiencia cardfaca

esquerda (GI), classe II e III cia ,NYHA, com

idade media de 6S.6±6.9 anos 'e 10 controlesnorma is, se rn patalogia cardio-pu lmonar

(GIl), ~om idademedia de 64.5±:l-.9 anos.

Mate rial e metodos: Utilizarnos metodosdependentes da vontade 'com determinac,;oes

das pressoes maxi masexpiratorias iff' Mfl) aonfvel tla'Capaeid ade Pulmona r 'fotal e

inspiratorias (PMI) ao nfvel da Capacidad~Hesidual.Funciona l, das pressoes atra ves de

sniff nasal ·(SNIFF-N) e da pressao de sniff.esofagico (SNIFF-E). Determinamos

igualmente as pressoes transdiafragmaticss(TwPDI). Com os metodos independe ntes davontade, ut iliiando a estirnulacao magnetica

cervical do Irenico ao nfvel cia CRFdeterminam os a pressao Twitch esofrigica

(Twf'es) , a Twitch gas trica ( fwGas) e a Twitchtrans diafragmatica (TwPDI ).

Resultados: No que conceme as pressoesdependentes da vontad e nao oLtivemos

ABST R ACTF unction of the Respir atory Musclesin P ati en ts with Left Ventr-icular Failure

Study Objective: The aim of this paper is toevaluate the funct ion os respiratory m usclesin patien tswith moderate left ventricularfailure (LVF), and i ts contribution to the,.pa thophysiology ofdysp nea and fatigu e. '

Design: Prospec tive comparative studybe tween LVF patients and anormal .controlgroup . .

' Patients: We studied 10 male patients withLVF (GI), NYHA class II ancl III/ mean age

'6 5.6±6.9 'years , and 10 'male controls without'cardiopulmonary di seas e (GIl ), mea n ageM .S±4.9 years. .

Methods: We used methods based 'orivolitionalmanellvers: maximal inspiratorypressures at FRe (MIP); maximal'expiratory _.pressures at TLC (MEP); nas al sniff (SNIFF- ~

N); -esophageal sniff (SNIFF-E); andtransdiap hragmatic:press ures (SNIFF-PDI).We also used meth ods based on non- .volitional man euvers, lIs i~g cervicalmagnetic stimulation of the phreni c,n erves, .measuring esophageal twich (Twl'es], gastrictwitch (1wGas) and transdiaphragmeti ctwitch (TwPDl).

Results: With volitional maneuvers we didnol find statistically significant differences inMEP (em H20): GI - 136±38; GIl ­14S.S±36.8; p=NS or in MIP (em H20): GI -

Trabalho subsid iado pelo projecto I'HAXIS/2/2 .1/SA1JI1322/95Work funded by the project I'HAXIS/2/2. I/SAUIl ;,22/95

Rercbido para publicncao: Dezernbro de 2000 • Aceup pnro pI.J.blit urtJo: All/"il de :lOO}Rt'ceiN;~d for publication: December 20nO • Accepted /01 publirntion: April :!OO I

dile ren cas s ignificat ivas cia PME (cmll.O):GI - 13G±38; GII - 14S.S±36 .8 ; p= l S e da

PMI (emII20): GI - 73.720 .7 ; GII ­87 . l ± l l. 7; p= NS; Estas foram no entantoinferi ores its oh tidas atraves cia tecnica do

S;lif!. Ob tive mos urna pressaos ign ifica tivame nte me nor nos doen tes com

ICE do SN IFF-N(cmH20 ): GI - 8 7±lQ.7; GIl- 99 ,4±1 8.5; p<O,Ot/. nao a lingind o

sign ifica ncia para 0 SNIFF- E (cm HzO): GI ­88.9±Il .S; Gil - 9 7.11 7;2; p<O,I; Utilizando

a tecnica nao depcndente da vontadc. rcomest imulacao magneti ca do Irenico nao

enco ntramos dilereneas na pressaolranscliafragmiiti ca TwPDI (emH20 ): GI­19.9±4.42; GIl - 24.2±8 .9; p=NS, mas acomparticipacao clo diafragma para essa

mesma pressao foi s ign ifica tivame nte menornos doentes com ICE, urna vez que se

reg is tou um a diferen ca no TwPes (cmHzO):GI - IO,6±2.4; GIl - lS.6±S.8; p<O,01; Nao

SC regista ram diferen cas entre 0 SNIFF nasale esofagico.

Conclusoes: A compart ic ipacao dodiafragma para a vent ilacao to tal e normal

nos doent es co m ICE mod erad a,uma vezqu e nao ha diferen cas na pressao

tra ns diafragrnatica. Contudo, a suacompart ici pacao para gerar pressoes

ncgativas intru-toraci oas (~ men or um a vezqu e lui uma diminuicao sign ifica tiva do

TwPes e do SNIF F.-N. 0 eliafragma parecepai s , ser 0 prirneiro rmisculo inspiratorio a

ser afectado na ICE moderada, uma vez quea fuucao tola l dos nni sculos inspiraiorios esta .

conse rvada visto nao haver eliferen9as nas. PM I e P ME.

Palavr as-ChaveInsufi ciencia cardiaca csquerda; MLlseulos res pirato rios:

Pressoes maximas resp iratorias; Pressoes de snij]:Pressao transdiafragnuuir-a; Esti-6 I11J a<;ao magnetica cervical

Il 'TROD lI ~:Ao

OS pararnet ros classicam e nte descritos como

ge radores de dispneia em doentes com in­

sufic ie nc ia card fac a esq ue rda tern pouca co rre­

lac ao com Indices de Iu ricao ve ntri c u la r es­q uerela I I. 21. Ultimarnent e, s urgiram na lit eratura

traba lhos qu e referent alteracoes dos rrnis culo s

res pira io rio s como po tencia lme nIe geradores

de dispneia e cansaco neste gm po de doentes ":".

5:H No e n tan to, e st e s da dos bas eiarn-se na de -

73 .7±20.7; GlI - 8 7 .J ± 11.7; p=NS. However,these values were lower than those obt ain edwith sniff maneu vers. We obtained as ign ifica n tly lowerpressure of SN IFF-N(ern H20): GI - 8 7 ±1O.7; GIl - 99 .4 ±18 .S:p < 0 .05 bUI not of SN IFF-E [ern H20 ):GI - 88.9± 11.S ; GIl - 97.1± 17 .2 : p<·O.Ol.With non- volition al man euvers , using'ce rvical magneti c stimula tion we did not finda s ignifica nt d iffe rence for TwPDI (em H20):GI - I 9.9±4 .42; GIl - 24 .2 ± 8 .9; p= NS, bu tthe contri but ion of the diaphragm totran sd iaphragrnatic pressu re was lower inpatients with LVF when the Twf'es was lower(em (-hO): GI - 1O.6±2.4 ; GlI - I S.6±S.8;p < 0 .01. There were no sign ifican t

·diffe rences between SNIFF-N a nd SNIFF-E.

Conclu sions: The contribution of thediaphragm to tota l ventilation in patientswith mod erate LVF is preserved, as there isno difference in TwPDl. Howe ver, theirabi lity to ge ne ra te negati ve int ra-thorn ·icpr essures dec reases s ince there is as ign ifican t decrease ill TwPes and SNIF F-N .It therefore appears that the d iaphragm is th efirst inspi rat ory muscle to be affec ted in 'moderate LVF, since the total res pira torystren gth is preserved asassessed by MIP andMEP.

Key wordsLeft ventricular failur e; Respi ratory muscles;Maximal res piratory pressures; Sniff pressures;Transd rAphraglllalie pressurc; Cervical magnetic sifmulation

INTRODUCTI ON

The factors class ically described as ca usi ng

dy sp nea in pa ti e nt s with l eft ve n tricula r

fa ilure (LVF) show littl e co rrelat ion with indr­ces of left ven tricula r fu nction ,1. 2,. Re ce n tly

s tudies hav e appeared in the li te rature thal in­

d icat e alte ra tions in the respi ratory muscles as

pot e nti al ca uses of d ysp nea an d fa t ig ue Inthe s e pa tie n ts '2.4'. H ow ev er, th e s e d at a are

based on volitiona! maximal pressures tha t are

termina9ao de pressoes maximas, dependentesda vontade, de diffcil execucao e a sua inter­pretacao levanta reservas, uma vez que nao sepode excluir uma activacao sub-maxima dosmnsculos respirat6rios (2,5). Resultados maisconsistentes s~o obtidos se 0 doente realizarurn curto sniff maximo durante 0 qual e me­dido a pressao nasal, esofagica ou transdiafrag­matica (e. Esta tecnica e de mais facil execucaoe fornece informacao mais especffica do dia­fragrna, que e 0 musculo inspirat6rio mais im­portante.

Quer as pressoes maximas quer 0 sniff saodependentes da vontade, pelo que a aplicacaode tecnicas nao dependentes, como a estimula­9ao magnetica do frenico sao importantes parao estudo da funcao diafragmatica (7). Assim,conduzimos este ensaio com aplicacao de todasestas tecnicas para avaliar a funcao dos mus-

. culos respirat6rios em doentes com insuficien­cia cardfaca esquerda, com 0 objectivo de es­tudar a forca global dos rmisculos respirat6riose em particular 0 diafragma, em doentes cominsuficiencia cardfaca compensada.

MATERIAL E METODOS

Estudamos 10 doentes do sexo masculinocom ICE estavel com idade media de 65.6±6.9anos, seleccionados numa consulta externa decardiologia, sem hist6ria de patologia respira­t6ria e sem qualquer agudizacao no ultimomes, encontrando-se na altura do diagn6stico,7 em Classe II da NYHA e 3 em classe Ill. Aduracao media da doenca era de 3.6±I.2 anos.Todos os doentes estavam sob medicacao comdiureticos, inibidores da enzima de conversaoda angiotensina e digitalicos,

o grupo de controle era composto por 10indivfduos do sexo masculino, com idade me­dia de 64.5±4.9 anos, seleccionados numaconsulta de reumatologia, com 0 diagn6stico deosteoartrose periferica e sem hist6ria de pato­logia cardio-pulmonar. 0 ECG e 0 RX do t6raxeram normais.

Todos deram a seu consentimento pOl' es­crito.

Avalia9ao nutricional

A avaliacao nutricional baseou-se na deter­minacjlo do Indice de Massa Corporal (LM.C.)definido pela razao entre 0 peso em quilogra­mas e 0 quadrado da altura em metros. Sendoos valores da normalidade entre 20 a 24 Kg.m",Valores inferiores a 20 Kg.m" apontavam des-

difficult to determine and to interpret, sincethe possibility of sub-maximal activation ofrespiratory muscles cannot be ruled out (a. 5).

More consistent results are obtained when thepatient performs a brief maximal sniff duringwhich nasal, esophageal and transdiaphragma­tic pressures are measured. This technique iseasier to perform and provides more specificinformation on the diaphragm, which is themost important inspiratory muscle.

Both maximal pressures and sniffs are voli­tional, and non-volitional techniques such asmagnetic stimulation of the phrenic nerve areimportant for the study of diaphragmatic func­tion '". In this study we therefore applied allthese techniques to assess respiratory musclefunction in patients with left ventricular fail­ure, with the aim of studying the overallstrength of the respiratory muscles and, in par­ticular, the diaphragm, in patients with com­pensated heart failure.

METHODS

We studied 10 male patients with stableLVF, mean age 65.6±6.9 years, selected from acardiology outpatient clinic, with no history ofrespiratory pathology and with no worsening ofsymptoms in the previous month. At the timeof diagnosis, 7 were in NYHA class II and 3 inclass III. The mean duration of the disease was3.6±1.2 years. All the patients were being me­dicated with diuretics, angiotensin-convertingenzyme inhibitors and digitalis.

The control group was made up of 10 malesubjects, mean age 64.5±4.9 years, selectedfrom a rheumatology clinic, diagnosed with pe­ripheral osteoarthritis and with no history ofcardio-pulmonary pathology. ECG and chest x­ray were normaL

All patients gave their written consent.

" -~Nutritional assessment

Nutritional assessment was based on calcu­lating the Body Mass Index (BMI), defined asthe ratio between weight in kilograms and thesquare of height in meters. Normal values arebetween 20 and 24 Kg.m'. Values lower than20 Kg.nr' suggest under-nutrition, while a BMIof over 25 Kg.m' indicates excess weight, withfigures over 30 Kg.m" indicating obesity.

Assessment of strengthof respiratory muscles

The strength of the respiratory muscles wasassessed indirectly through determination of 535

536

nutricao e acima de 25 Kg.m? excesso de peso,considerando-se existir obesidade quando, napresenca de urn LM.C. superior a 30 Kg.m? (8).

Avalia<;ao da forcados nnisculos respiratoeios

A forea dos ;;;usculos respirat6rios foi ava­liada, de forma indirecta atraves da determina­gao da pressao gerada pela sua contraccao.Para isso recorremos a varios metodos, quediscriminaremos consoante as condicoes e ca­raeterfsticas cia sua realizaeao, em dais grupos:metodos dependentes da vontade e metodosnao dependentes da vontade.

Dentro dos metodos dependentes da von­tade efectuamos a deterrninacao das PressoesMaximas Respirat6rias, a Pressao maxima deSniff Nasal (SNIP) e as Press6es maximas deSniff invasivas (pressao esofagica, pressao gas­trica e pressao transdiafragmatica). Como me­todo nao dependente da vontade recorremos itdeterrninacao das press6es esofagica, gastriea etransdiafragmatiea, resultantes da estimulaeaomagnetics bilateral do nervo frenico.

As press6es foram determinadas mediante autilizacao de dois transdutores de pressoes(MP 45; Validyne, Northridge. CAl, na gama(0-350 cmfl-O). Estes transdutores foram cali­brados diariamente, introduzinclo urn sinal depressao, na gama da medicao, em paralelo comuma coluna de merctirio, fazendo-se posterior­mente a conversao para cmH20. Foram consi­derados lineares para essa gama de pressces.

Os sinais anal6gicos foram digitalizadosatraves da mesma placa anal6gica/digitalsendo os sinais digitais igualmente proces­sados pelo software de aquiaicao de dados(CODAS; DATAQ Instruments Inc., OH), demodo a permitir a visualizacao das curvas depressao em tempo real.

.~.~ ,~~

METODOS DEPENDENTESDA VONTADE

Para a determinacao das press5es maximasrespirat6rias estaticas, a nfvel cia boca, utiliza­mos pecas bocais tipo mergulhador, ligadas aurn via aerea cilfndrica oclufda na Dutra extre­miclade e com urn pequeno orificio de 1 mrn, afim de impedir 0 encerrarnento da glote (9-11). Apega cilrndrica estava conectada a urn dostransdutores de pressao.

Para a determinacao das pressoes de sniffnasal utilizamos 0 mesmo transdutor de pres­sao ja referido para a determinacao das pres-

the pressure generated by their contraction.To this end we used various methods, whichwe divided, according to their characteristicsand the conditions under which they wereperformed, into two groups: volitional and non­volitional methods.

Using volitional methods we determinedmaximal respiratory pressures, maximal nasalsniff pressures (MNSP) and maximal invasivesniff pressures (esophageal pressure, gastricpressure and transdiaphragmatic pressure). Asa non-volitional method we determined eso­phageal, gastric and transdiaphragmatic pres­sures through bilateral magnetic stimulation ofthe phrenic nerve.

The pressures were determined using twopressure transducers (MP 45; Validyne, North­ridge, California), in the range (0-350 cm fLO).These transducers were calibrated daily by intro­ducing a pressure signal from the range beingmeasured in parallel with a mercury column, andsubsequently converting to cm H,O. They wereconsidered linear for this range of pressures.

The analog signals were digitized by thesame analog-to-digital board, with the digitalsignals being processed by data acquisitionsoftware (CODAS; DATAQ Instruments Inc.,Ohio), in order to enable visualization of thepressure curves in real time.

VOLITIONAL METHODS

To determine the maximal static respiratorypressures at the mouth, snorkel-type mouth­pieces were used, linked to a cylindrical air­way occluded at the other end with a smallopening of I mm, in order to prevent the clos­ing of the glottis (9-11). The cylindrical piece wasconnected to one of the pressure 'transducers,

To determine nasal sniff pressures, thesame pressure transducer were used as thatused to determine maximal respiratory pres­sures. The interface between the subject andthe transducer was a Foley n", 12 pediatricprobe (Bardia, Barcelona, Spain).

To determine invasive esophageal and gas­tric pressures, catheters with coupled balloonsconnected to the two pressure transducers wereused, enabling the respective pressure curvesto be observed in real time.

Determination of maximal respiratorypressures at the mouth

For this purpose, the subjects were seatedand wore a nose peg. During the maneuvers,

soes maxirnas respiratorias, A interface entre 0

doente e 0 transdutor foi uma sonda de Folleypediatrica n," 12 (Bardia, Barcelona, Espanha).

Para a determinacao das pressoes invasivasesofagica e gastrica utilizamos cateteres combaloes acoplados, que eram conectados aosdois transdutores de pressao, sendo possiveltambem a visualizaeao, em tempo real, das res­pectivas curvas de pressao,

Determinaeao das pressoes maximasrespirat6rias a nfvel da boca

Para a sua determinacao os doentes encon­travam-se na posicao de sentados e usavam umamola nasal. Durante a realizacso das manobras,eram encorajados verbalmente a Jim de atingi­rem valores maximos, cujas curvas de pressaopodiam visualizar no monitor do computador. Avisualizacao grafica das curvas de pressao fun­cionava como estfmulo visual, a fim de aumen­tar 0 grau de colaboracao do doente (12).

A Pressao Maxima Expirat6ria (PME) foimedida a nfvel da Capacidade Pulmonar Total(CPT) e a Pressao Maxima Inspirat6ria (PMI)foi calculada a mvel da Capacidade ResidualFuncional) segundo metodologia descrita porn6s previamente (13).

Tanto para a PME como para a PMI foramrealizadas, pelo menos tres manobras ate aesta­bilizacao dos valores de pressao, Foi escolhido 0

valor mais elevado, desde que mantido, pelomenos, por urn perfodo de urn segundov- 13). Se adiferenca entre'0 melhor valor e 0 segundo me­lhor fosse superior a 5%, eram realizadas maismanobras ate urn maximo de cinco (14).

Determinacjio das pressdes maximasde sniff

Esta tecnica foi inicialmente descrita (6),

mantendo uma n'l,llina obstrufda, com urn tam­pao de material solido, sendo a pressao colhidaatraves deste tarnpao, enquanto 0 indivtduoefectuava urn sniff maximo atraves da outra na­rina livre.

Efectuamos uma variante desta tecnica, re­correndo a uma sonda de Folley pediatrica quefoi introduzida numa das narinas e que era in­suflada ate obter uma oclusao perfeita, ligandoa outra extremidade ao mesmo transdutor depressao utilizado para a determinacao daspressoes respirat6rias estaticas.

Os sniffs foram realizados a nfvel da FRC,ou seja no final duma expiracao em volumecorrente. Pedia-se aos individuos para, na po-

they were verbally encouraged to reach max­imal values, the pressure curves being visibleon the computer monitor. The graphical imageof the pressure curves acted as a visual stimu­lus, in order to increase the subject's degree ofcollaboration (12).

Maximal Expiratory Pressure (MEP) wasmeasured at total pulmonary capacity (TPC),and Maximal Inspiratory Pressure (MIP) wascalculated at functional residual capacity(FRC) following the methodology previouslydescribed by us (13).

For both MEP and MIl', at least three ma­neuvers were performed, until the pressure va­lues stabilized. The highest value was chosenso long as it was maintained for a period of atleast one second (9. 13). If the difference betweenthe best value and the second best was greaterthan 5%, further maneuvers were carried out,to a maximum of five (14).

Determination of maximal sniff pressures

This technique, as initially described (6),

consisted of blocking one nostril with a plugof solid material, the pressure being readby means of this plug, while the subjectperformed a maximal sniff through the other,open nostril. .

We performed a variation of this technique,using a Foley pediatric probe which was intro­duced into one nostril, and then inflated untilthe nostril was completely blocked; the otherend was connected to the same pressure trans­ducer used to determine the static respiratorypressures.

Sniffs were carried out at FRC, that is atthe end of an expiration of normal volume. Thesubjects, in a seated position, were requestedto perform a maximal sniff maneuver, that is arapid inspiration with the greatest possibleforce through the nose, keeping the mouth

,,"losed. A nose peg was not used, An intervalof 30-45 seconds was left between sniffs.As many sniffs as necessary were performeduntil no increase in the values attained wasobserved, these values being reproducible (15).

Around 15 sniffs on average were made byeach subject. None of the subjects included inthis study were familiar with the sniff maneu­ver. As sniffs are volitional maneuvers, thesniff of greatest amplitude was selected foranalysis (16).

Measurement of esophageal pressure (Pes)is an indirect way of measuring intrathoracicpressure. Simultaneous determination of gas­tric pressure (Pgas) enables transdiaphragmatic 537

sicao sentada, realizarem uma manobra de sniffmaximo, ou seja, uma inspira~ao rapida, com amaior forea possfvel, atraves do nariz e man­tendo a boca fechada. Nao se usou mola nasal.Entre cada sniff esperava-se um intervalo de30-45 segundos, Efectnaram-se tantos sniffsquantos os necessaries ate nao se verificaracrescimo no valor dOB mesmos, havendo re­produtibilidade no valor alcancado (15). Efeetna­ram-se em media cerca de 15 sniffs, em cadadoente. Nenhum dos doentes inclufdos no es­tudo estava familiarizado com a manobra dosniff. Como os sniffs sao manobras dependentesda vontade, para analise seleccionou-se 0 sniffde maior amplitude (16).

A determinacao da pressao esofagica (Pes)representa uma forma indirecta de medicao dapressao intra toracica, A determinacao simulta­nea da pressao gastrica (Pgas) permite, con­forme referido abaixo, a obtencao da pressaotransdiafragmatica, 0 metodo mais vulgar­mente utilizado para a medieao da Pes e daPgas assenta no recurso a baloes de latex aco­plados a cateteres que transmitem a pressao nobalao, a transdutores de pressao,

Utilizamos balaes de latex de paredes finas,. com 10 em de comprimento e acoplados a cate­teres com 0 comprimento de no em (Jaegger,Wiirzburg, Alemanha). Os cateteres foram Iiga­dos por tomeiras de tres vias aos dais transdu­tares de pressao, Os sinais de pressao e volumeforam registados e digitalizados a 100 Hz.

Os cateteres para determinaeao das pressoesesofagicas e gastrioas foram inseridos atravesde uma das narinas, ap6s adrninistraeao deanestesia local, com lidocafna a 2% em gel, anfvel do nariz, e em nebulizacao, a nfvel da fa­ringe e hipofaringe. Foi utilizada a tecnica deMiller v" sendo a 'posicao dos cateteres verifi­cada utilizando os criterios recomendados (17.18).

Uma vez nas respectivas posicoes definiti­vas.jinstilava-se atraves de uma seringa, 0,5cm de ar no balao esofagico e 2 cm, no gas­trico. A amplitude da pressao esofagica e gas"trica foi medida como a diferenca entre 0 valordo pico alcaneado por cada curva de pressao eo valor basal precedente. As pressoes esofagi­cas e as gastrioas foram obtidas ap6s reali­zacao de sniffs nasais. As manobras de sniffmaximo (IS) foram repetidas ate se obterem 3medieoes com menos de 5% de variabilidade,

A pressao transdiafragmatica (SNIFF-PDI)foi obtida por suhtraccao electrica dos SNIFF­Pes e SNIFF-Pgas, tendo sido 0 seu processa­mento posterior a realizacao das manobras que

538 conduziram asua determinaeao.

pressure to be calculated, as described below.The most commonly used method to measurePes and Pgas is based on the use of latex bal­loons coupled to catheters that transmit thepressure in the balloon to pressure trans­ducers.

We used thin-walled latex balloons, 10 cmlong, coupled to catheters with a length of noern (Jaeger, Wiirzburg, Germany). The cathe­ters were linked by three-way taps to two pres­sure transducers. The pressure and volumesignals were recorded and digitized at 100 Hz.

The catheters for measuring esophageal andgastric pressures were inserted via a nostril,after administration of local anesthetic (2% li­docaine gel in the nose and spray on thepharynx and laryngopharynx). Miller's tech­nique (15) was used, with the position of thecatheters being checked using the recommen­ded criteria (17.18).

Once the catheters were in their correct po­sitions, a syringe was used to introduce 0.5cm' of air into the esophageal balloon and 2cm' into the gastric balloon. The amplitude ofesophageal and gastric pressures was mea­sured as the difference between the peak valuereached by each pressure curve and the preced­ing baseline value. The esophageal and gastricpressures were obtained after the performanceof nasal sniffs. The maximal sniff maneuvers (15)

were repeated until three measurements wereobtained with less than 5% variation.

The transdiaphragmatic pressure (SNIFF­PDI) was obtained by electrical subtraction ofSNIFF-Pes from SNIFF-Pgas, and was calculat­ed after the maneuvers that enabled it to bedetermined.

NON-VOLITIONAL METHODS

Bilateral magnejic phrenic ,$

nerve stimulation

Bilateral magnetic stimulation of the phre­nic nerve was performed with a Magstim 200magnetic stimulator (Magstim Co. Ltd, Whit­land, UK) and a 90 mm coil, using maximumdischarge, This apparatus stimulates the neu­romuscular structures by inducing electric cur­rents (9-19 mNcm', at a frequency of 0.2 Hz)in the tissue within a magnetic field of short(<1 ms) duration. The magnetic field at max­imum discharge is 2.0 Tesla m.

In order to induce bilateral stimulation ofthe phrenic nerve (7), we used a circular 90 mmcoil (PIN 9784-00) connected to the Magstim

METODOSINDEPENDENTESDA VONTADE

Estimulaedo magnetica bilateraldo frenico

A estimulacao magnetioa bilateral do fre­nico foi efectuada utilizando urn estimuladormagnetico Magstim 200 (Magstim Co. Ltd,Whitland, Reino Unido) e uma placa de 90mm, utilizando uma descarga maxima. Esteaparelho estimula as estruturas neuromuscula­res, pOI' inducao de correntes electricas (9-19mA/cm', com uma frequencia de 0,2 Hz) no te­cido abrangido pOI' urn campo magnetico decurta duracao «1 ms de duracao), A nfvel dadescarga maxima 0 campo magnetico e de 2.0Tesla m.

A fim de induairmos a estimulacao magne­tica bilateral do frenico (7', utilizamos umaplaca circular de 90 mm (PIN 9784-00) conec­tada ao Magstim 200, posicionada a nfvel daregiao cervical, sabre as apofises espinhosas.o melhor local para a estimulaeao era procu­rado mobilizando a placa para baixo e paracima entre C5 e C7, com 0 indivrduo sentado emantendo 0 pescogo flectido a cerca de 60°. Azona, atraves cia qual se produziam maiores va­lores de Pdi, correspondia ao melhor local paraestimulaeao. Uma vez determinado esse ponto,procedia-se asua marcacao, sendo as restantesestimulacoes efectuadas a esse nfvel,

Asseguramo-nos de que 0 estfmulo era ma­ximo, por aumentarmos progressivamente a in­tensidade de estimulaoao ate nao se obteremmais aumentos da Pes e Pgas e portanto doPDI (19). Assegurou-se uma estimulaeao supramaxima, em todos as indivfduos accionandoo Magstim com uma descarga de 100%.Aquando da estimulaeao, 0 doente utilizavauma mola nasal e sustinha a respiracao a ntvelda FRC, mantendo a boca fechada. ..1

o registo das pressoes estava acessfvel aooperador, no monitor do computador, de formaque 0 doente era estimulado ate que se obtives­sem cinco estirnulacoes satisfat6rias. As pres­soes produzidas ap6s estimulacao bilateral dosnervos frenicos (TwPes, TwPgas, TwPDI), eramdefinidas pela diferenca entre as linhas depressao basal, imediatamente antes da estimu­lagao e 0 pico de pressao ap6s a estimulacao.

Urna vez que 0 volume pode afectar a am­plitude da pressao de estimulacao ('0>, todas asestimulacoes eram efectuadas a ntvcl da FRC,conforme deduzido pela curva da pressao eso­fagica no final da expiracao, Os valores apre-

200 positioned in the cervical region, over thespinal apophyses. The best site for stimulationwas found by moving the coil upwards anddownwards between C5 and C7, with the sub­ject seated and keeping his neck bent at about60°. The area in which the highest values ofPDI were produced was the best site for stimu­lation. Once this spot was determined, it wasmarked and the remaining stimulations werecarried out at this point.

We ensured that the stimulus was maximumby progressively increasing the intensity of thestimulation until there was no further increasein Pes and Pgas and hence in PDI (19'. A super­maximum stimulation was ensured in all sub­jects by operating the Magstim at a dischargeof 100%. During stimulation, the patient worea nose peg and maintained respiration at FRC,keeping the mouth closed.

The record of pressures was accessible tothe operator on the computer monitor, so thepatient was stimulated until five satisfactorystimulations were obtained. The pressures pro­duced after bilateral phrenic nerve stimulation(~es, TwPgas, TwPDI), were defined as thedifference between the baseline pressure linesimmediately before stimulation and peak pres­sure after stimulation.

As volume can affect the amplitude of sti­mulation pressure (20), all the stimulations wereperformed at FRC, as deduced from the eso­phageal pressure curve at the end of expira­tion. As they are the result of a non-volitionaltechnique, the values presented are the meanof the stimulations accepted for analysis.

Cardiac output

Cardiac output (CO) was determined by 2DDoppler echocardiography. A Toshiba echocar­diograph was used, employing the formula CO= Vmax x Area x HR (}Jm). CO was dividedby body surface area to obtain the cardiac in­dex (CI - Urn/m').

Data analysis

The data were recorded and digitized at100 Hz using a 12-bit analog-digital converterconnected to a Pentium-133 personal computerrunning CODAS software (DATAQ InstrumentsInc., Akron, Ohio).

To analyze the results, the two groups werecompared using the Student's T test for indepen-dent samples, considering significant a confi-dence interval of 95%, that is p<0.05. The cor­relation coefficients were also calculated, using 539

sentados, dado que reflectem uma tecnica in­dependente da vontade, sao a media dos valo­res das estimulacces aceitaveis para analise.

Pearson's method, between the pressures ob­tained and functional class, duration of diseaseand cardiac index. The statistical program usedwas SPSS for Windows, version 5.01, 1989-1992.

BMI- Bodymass index; Min - Minimum; Max _ Ma.ximum.

Table IIVolitional methods .,

GI Gil p<

MEP (cmH,O) 136.3±38.2 14S.S±36.8 NS

MIP (cmH20) 73.7±24.6 87.1±IS.S NS

Sniff-N (cmILO) 87±10.7 99.4±18.S 0,05

Sniff-E (cmH20) 88.9±II.S 97.I±l7.2 NS

Sniff-G (cmILO) 19.6±8.1 37.4±20.3 0,01

Sniff-TDI 108+11.3 134.3±29.8 0,01

Maximal pressures (Table II):

Although lower in absolute termS in the pa­tients with LVF, maximal pressures did not dif­fer significantly between the two groups: MEP(em H20) was 136.3±38 in group I and145.5±36 in group II, p=NS; !\fIP (em H,O)was 73.7±24.6 in group I and 87.l±15.5 ingroup II, p=NS.

RESULTS

The patients studied were all male, with amean age of 65±6.9 years, and a mean dura­tion of disease of 3.6±1.2 years. The etiologyof heart failure was hypertensive in 6 patientsand ischemic in 4. Seven patients were inNYHA class II and 3 in class III. The BodyMass Index was 28±5.6 Kg.m" and the cardiacindex as determined by echocardiography was2.02±0.6 Urn/m'.

The control group had a similar mean age,64.5±4.9 years, and their anthropometric datadid not differ significantly (Table l).

NS

NSNS

0.05

GilGI

Age (ye",,)) 6S.6±6.9 64.S±4.9BMI (Kg.m') 29.6±6.IS 27.2±3.SDuration of disease 3.6±1.2 99.47±18.5(years) Minoz; Max: 6Cardiax index 2.02±O.6 97.l±17.2

Table IClinical data

Quad,o IDados clinicos

Os doentes estudados, eram todos do sexomasculino, tinham uma idade media de 656.9anos, e uma duracao media de doenca de doen­ga de 3.6±1.2 anos. Quanto a etiologia da in­suficiencia cardfaca, em 6 doentes era hiper­tensiva e em 4 isquemica. 7 doentes estavamem classe II e 3 em classe III da NYHA. 0Jndice de ~assa Corporal era de 285.6 Kg:m-2.

o Indice cardfaco determinado por ecocaiAio­grafia era 2.0±20,6 Urn/m'.

o gmpo de controle tinha uma idade mediasobreponivel 64.5±4.9 anos nao diferindo igual­mente os dados antropometricos (Quadro 1)..

RESULTADOS

Analise dos dados

Os dados foram registados e digitalizados a100 Hz, mediante a utilizacao de urn conversoranal6gico-digital de 12 bits, conectado a urncomputador pessoal com processador Pentium133 apetrechado com 0 programa de softwareCODAS (DATAQ Instruments Inc., Akron, 0lI).

Para a analise dos resultados compararam­se os dois grupos entre si, utilizando 0 teste t

de Student, para amostras independentes, con­siderando-se como significativo, urn intervalode confianca de 95%, ou seja urn p<0,05. Cal­culamos tambem os coeficientes de correlaeao,metodo de Pearson, entre as pressoes obtidas ea classe funcional, duragao da doenca e fndicecardtaco. 0 programa estatfstico utilizado foi 0

SPSS para Windows versao 5.01, 1989-1992.

Debito cardiaco

Determinamoao debito cardfaco (DC) atra­ves de Ecocardiografia 2D-Doppler. Utilizamosurn ecocardi6grafo Toshiba, recorrendo a f6r­mula DC = Vmax x Area x FC (Urn). Dividi­mos 0 DC pela superffcie corporal e obtivemoso fndice cardfaco(IC-Um/m').

IMC- fndice de massa corporal; Min - l\lfnimo; Max - Ma.ximo

6S,6±6.9 64.S±4,929,6±6,15 27,2±3,5

3,6±1,2Min"; Max: 6

2.02±O.6

54·0

Idade {anos)IMC (Kg.m')Duracso dadoence (anos)fndice cardraca(Ilrn/m')

GI Gil p

NSNS

MEP - Maximal expiratory pressure; l\UP _ Maximal [nspiralory pressure;SNIFF· Maximal sniff pressure; N _ Nasal; E _ Esophageal; G - Gastric;

PDI • Transdiaphragmatic pressure.

Maximal sniff pressures (Table II):

Nasal sniffs (em H20) were significantly low­er in group I, 87±10.7, than in group II,

99.47±I8.5, p<O.05. Esophageal sniffs (emH20) did not differ between the two groups: GI88.9±11.5 and GIl 97.I±I7.2, p=NS; while weobtained differences in transdiaphragmaticsniff (em H20): GI I08±11.3, GIl 134.6±29,p<O.Ol.

Electromagnetic stimulation (Table III):

The esophageal twitch (em H20) obtainedwas significantly lower in GI, IO.6±2.4, than inGIl, 15.6±5.88, p<O.OI; transdiaphragmatictwitch (em H20) - GI 19.98±4.4, GIl 24.2±8.9- did not differ significantly.

Pressoes maxtmase (Quadro II)

Embora de valor absoluto menor, as pres­sees maximas naa diferiram significativamenteentre os dois grupos: a PME (cmH20) foi de136338 no groupo I e 145536 no grupo IIp=NS; a PML(cmH20) foi de 73724.6 no<YfUpo I e 87115.5 no grupo II p=NS;

sadroIIdetodos dependentes da vontade

GI GIl p<

PME (cmH,O) 136,3±38,2 145,5±36,8 NS

PMI (cmILO) 73,3±24,6 87,1±IS,S NS

Sniff-N (cmILO) 87±lO,7 99.4±18,S O,OS

Sniff-E (cmH1O) 88,9±Il.S 97,1±17,2 NS

Sniff-G(cmH20) 19,6±8,1 37,4±20,3 0,01

Sniff-TDI lO8±Il,3 134,3±29,8 0,01

Table IIINon-volitional methods

GI GIl p<

PME - Pressao maxima expiratdria; PMI - Pressno maxima inspirat6ria;

Sniff - Pressno maxima de sniff; N - Nasal; E - Esofagico;G - Gastrico; TOI - Transdiagragmatico

TwPes (cmH20)

TwPgas (cmH20)TwPDI

lO.6±2.4

9.38±3

19.98±4.42

IS.6±S.8

8.3±3.7

24.2±8.9

0.01

NS

NS

Pressdes maximas de Sniff: (Quadro II)

o sniff nasal (cmH20) foi signifieativamentemenor no grupo I - 87±10.7, que no grupo II99.47±18.5 p<O.05; 0 sniff esofagico (cmH20)nao diferiu nos dois grupos GI 88.9±II.5 e GI97.1±17.2; p=NS; enquanto obtivemos diferen­yas no Sniff transdiafragrnatico (cmH20) GI108±II.3, GIl 134629; p<O,OI.

TwPes - Esophageal twitch; TwPgas - Gastric twitch;

TwPDI - Transdiaphragmatic twitch.

The values of pressures obtained with thedifferent techniques did not correlate withfunctional class, or duration of disease, or withcardiac index.

DISCUSSION

DlSCUSSAO

TwPes - Twitch esofdgico; TwPgas - Twich gdstrico;

TwPDl- Twitch transdlafragmatico

Quadro 1IlMetodos Independentes da vontade

No nosso estudo, os doentes com insufi­ciencia cardfaca em classes II e III da NYHA,

In our study, patients with heart failure inNYHA classes II and III presented preservedoverall respiratory pressures. However, wefound data that suggest a statistically signi­ficant reduction in the strength of the diaph­ragm.

Measurement of static respiratory pressuresresulting from maximal effort against a blockedairway reflects the overall strength of the respi­ratory muscles ~1.25). When the airway is occlud­ed and the glottis opens, ]ilressure at the mouthequalizes with alveolar p~essure, reflecting thepressure throughout the respiratory system.

We found lower maximal respiratory pressu­res than in the control group, but without reach­ing statistical significance. These results arecomparable to those of other authors (2-4" butthey are difficult to evaluate because of theheavy dependence of this technique on volitionand consequently on the motivation to performit. Other factors, such as adynamia, astheniaand dyspnea (5" may lead to a weakened res­ponse to this technique. Furthermore, patientswith LVF may not wish to cooperate in perform­ing a maximal effort, resulting in sub-maximalpressures (2). 541

p<

0,01

NS

NS

-$GI GIl

TwPes (cmH20) lO,6±2,4 15.6±5,8

TwPgas(cmILO) 9,38±3 8,3±3,7

TwPDI 19,98±4,42 24,2±8,9

Os valores de pressao obtidos com as dife­rentes tecnicas nao se correlacionaram nemcom a classe funcional, nem com a duracao dadoenca nem com mdice cardfaco.

Estimulacao electromagnetieas (Quadro III)

o Twitch Esofagico (cmH20) obtido foi sig­nificativamente inferior no GI 10.6±2.4 que noGIl 15.6±5.88, p<O.OI; e 0 Twitch transdia­fragmatico (cmH20) GI 19.9±84.4; GIl24.2±8.9, nao diferiram significativamente.

apresentam pressoes respirat6rias globais con­servadas. Encontramos, no entanto, dados su­gestivos de uma diminuicao da forea do dia­fragma estatisticamente significativa.

A medicao das press5es respirat6rias estati­cas resultantes de eSfOf(}OS maximos contra umavia aerea oclufclit reflectem a forea global dosmrisculos respirat6rios (21-25). Quando a via aereae ooluida e a glote se abre, a pressao a nfvel daboca iguala-se a pressao alveolar, reflectindo apressao atraves de todo 0 sistema respirat6rio.

Encontramos pressoes maximas respirato­rias maximas inferiores ao grupo de controle,mas sem atingir significado estatfstico. Estesresultados sao sobreponiveis ao de outros auto­res (24), mas sao de diffcil valorizacao devido agrande dependencia desta tecnica da vontade ecia consequente motivaeao para a sua realiza­'.tao. Outros factores como a adinamia, asteniae dispneia (5) podem condicionar uma fracaprestaeao na realizacao desta tecnica. Por ou­tro lado, os doentes com ICE podem nao que­rer colaborar na execueao de urn esforco ma­ximo, gerando press5es sub maximas (2).

Estes valores sao inferiores aos que obtive­mos com os Sniff, que podem ser explicadospela menor dificuldade em realizar esta mano­bra. Em indivfduos normais, foi demonstradoque a pressao maxima de Sniff colhida a nfveldo es6fago era superior a PMI, devendo-seesse facto ao maior recrutamento electromio­grafico do diafragma "6). Contudo, a determina­gao da pressao esofagica toma-se limitada umavez que requer a colocaeao de urn cateter eso­fagico, Foi, no entanto, demonstrado que existeuma estreita correlacao entre a pressao deSniff nasofarfngea e a esofagica (2~, e conse­quentemente pode-se fazer a determinacao dapressao a nfvel nasal (6) (Sniff nasal).

A medicao simultanea da pressao esofagica(pes) e da pftssao gastrica (pgas) permitindofocalculo da pressao transdiafragmatica (PDI)[Pdi = Pgas-Pes], fomece 0 metodo mais fiavelpara avaliacao da forca de contraceao do dia­fragma (28-30). Os valores por n6s obtidos para 0

SNIFF-PDI, e semelhante ao de outros autoresv",tendo-se registado uma diferenca estatistica­mente significativa em relacao ao grupo decontrole. Sugere isto que ha comprometimentodo diafragma neste grupo de doentes. No en­tanto, este metodo e igualmente dependente davontade e embora nos de informaeao da forcado diafragma, reflecte a accao sinergfstica devarios grupos de musculos inspirat6rios e expira-

542 t6rios.

These values are lower than those obtainedwith sniffs, which may be explained by the eas­ier nature of the latter maneuver. In normal in­dividuals, it has been demonstrated that themaximal sniff pressure taken at the esophagusis higher than MIp, which is due to the greaterelectromyographic recruitment of the diaph­ragm ('''. However, determination of esophagealpressure is limited by the fact that it requiresplacement of an esophageal catheter. It hasnevertheless been demonstrated that there is aclose con-elation between nasopharyngeal sniffpressure and esophageal pressure (2~, and COn­sequently the pressure can be determined atthe nose (nasal sniff).

Simultaneous measurement of esophagealpressure (Pes) and gastric pressure (Pgas),enabling calculation of transdiaphragmaticpressure (pDI) [pDI = Pgas-Pes], provides themost reliable method of assessing the contrac­tile strength of the diaphragm (28~O). The valueswe obtained for SNIFF-PDI are similar tothose of other authors (31), with a statisticallysignificant difference being found in relation tothe control group. This suggests that there isimpairment of the diaphragm in this group ofpatients. However, this method is also volitio­nal and, although it provides information onthe strength of the diaphragm, it involves thesynergistic action of several groups of inspira­tory and expiratory muscles.

Phrenic nerve stimulation has the advant­age of being independent of the patient's de­gree of motivation, collaboration and coordina­tion, and thus the resulting transdiaphragmaticpressure measurement is the most specificmethod for assessing the properties of thediaphragm ~2). Although electrical stimulationis considered the reference teclniique for phre­nic nerve stimulation, it has been increasinglyreplaced by magnetic stimhlation, owing to thelatter's advantages in being less painful andmuch easier to perform (32).

Magnetic stimulation is based on the prin­ciple that an electrical field can be induced ina conductor by placing the conductor underthe action of a changing magnetic field. Theamplitude of the resulting electrical field de­pends on the speed of change of the magneticfield and on the geometry of the conductor. Ifthe electrical field is of sufficient intensity, itcan stimulate nerve tissue (33.;H).

Similowski et al. used this principle to de­velop the technique of magnetic stimulation ofthe phrenic nerves (7). This is considered a safe

A estimulaeao do nervo frenico tern a van­tagem de ser independente do grau de motiva­~ao, colaboracao e ooordenacao do doente,sendo a medicao da pressao transdiafragmaticaresultante, 0 metodo mais especffico de avalia­~ao das propriedades do diafragma (32'. Apesarda estimulacao:electrica ser considerada a tee­nica de referencia para a estimulacao do nervofrenico, tern vindo progressivamente a sersubstituida pela estimulaoao magnetica, devidoa algumas vantagens que esta apresenta, comoo facto de ser menos dolorosa e de muito maisfacil execucao (32).

A estirnulacao magnetica e baseada noprincipio de que e possfvel induzir urn campoelectrico num condutor, se este for colocadodebaixo da accao dum campo magnetico emmudanca, A amplitude do campo electrico re­sultante depende da velocidade de mudancado campo magnetico e da geometria do condu­tor. Se tiver suficiente intensidade este campoelectrico pode estimular 0 tecido nervoso {33.34'.

Similowski et al. utilizaram este principia,desenvolvendo a tecnica de estimulacao mag­netica dos nervos frcnicos (7'. E consideradauma tecnica segura {35}, que providencia urnteste nao dependente da vontade, de avaliacaoda Iorca do diafragma (36'. Este metodo deavaliacao da fun~ao diafragmatica e particular­mente importante nas situaeees em que se colo­cam duvidas quanto it capacidade de coopera­93.0 para a realizacao de contraccoes maximas,nas manobras dependentes da vontade.

Os valores por nus obtidos para 0 TwPDInao diferiram do grupo de controle sendo aTwPes significativamente inferior. Significa istoque a comparticipacao do diafragma para aventilacao total e normal nos doentes com ICEmoderada. Contudo, a sua oomparticipacaopara gerar pressoes negativas intra-toracicas emenor, uma vez que se1'encontra uma diminui­~ao significativa do TwPes. 0 diafragma parecepais, sel' 0 primeiro mtisculo inspirat6rio a serafectado na ICE moderada.

Urn dos mecanismos provaveis responsavelpor este facto podera ser a mal nutrieao ~". Noentanto, neste grupo de doentes 0 IMC estaconservado. Outro mecanismo podera ser a di­minuicao do debito cardiaco com atrofia mus­cular, mas nao obtivemos qualquer correlacaoentre as dados hemodinamicos e as pressoes,Estes dados estao de acordo com outros auto­res (2, 38, 39) nao havendo inclusive qualquer cor­relacao com a capacidade ao esforco e com adispneia (39).

technique (35' that enables a non-volitional testto be performed to assess the strength of thediaphragm (36). This method of assessing diaph­ragmatic function is particularly useful in situa­tions where there are doubts concerning theextent of the patient's cooperation in perform­ing maximal contractions in volitional maneu­vers.,

The values we obtained for TwPDI did notdiffer from the control group, while the TwPeswas significantly lower. This means that thecontribution of the diaphragm to total ventila­tion is normal in patients with moderate LVF.However, its contribution in generating nega­tive intra-thoracic pressures is smaller, sincethere is a significant reduction in TwPes. Thediaphragm, then, appears to be the first inspi­ratory muscle to be affected in moderate LVE

One mechanism that is probably respons­ible for this may be malnutrition (3". However,in tbis group of patients, BMI is conserved.Another mechanism may be the reduction incardiac output with muscular atrophy, but wefound no correlation between hemodynamicdata and pressures. These findings are in agree­ment with those of other authors e.38. 39'; there isalso no correlation with exercise capacity orwith dyspnea (39'.

The fact that there is not a greater differencein muscular function, and in particular diaph­ragmatic function, may be due to a remodelingof the diaphragm, with an increase of type I fi­bers (slow oxidative fibers), which are more re­sistant to fatigue, and a reduction in type II fi­bers (40.41'. These alterations may result from lowcardiac output or from the inactivity that is cha­racteristic of many of these patients(1, 42).

On the other hand, all the patients understudy were being treated with angiotensin­converting enzyme inhibitors, which have beendeIl\~nstrated in animals to have a,;>rotectiveeffect on the contractility of the diaphragm (40'.

In conclusion, in this group of patients withmoderate LVF, the overall strength of the respi­ratory muscles is preserved, with a reductionin the strength of the diaphragm but with nor­mal transdiaphragmatic pressure. The respira­tory muscles are not, therefore, responsible forthe dyspnea and fatigue seen in these patients.

543

o facto de nao haver uma diferenea maissignificativa na funcao muscular e em particu­lar do diafragma pode dever-se a urn remodel­ing do diafragma, com aumento das fibras doTipo I (fibras oxidativas lentas) mais resisten­tes afadiga, e diminuicao das fibras tipo II (4(). 41).

Esta variaeao pode dcver-se ao baixo debitocardfaco ou a inactividade que muitos destesdoentes apresentam (1,42).

Por outro lado, todos os doentes estudadosestavam sob terapeutica com Inibidores da En­zima de Conversao da Angiotensina II, medi­camento em relacao ao qual foi demonstradoem animais ter urn efeito protector sabre acontractilidade do diafragma (4()'.

Em conclusso, neste grupo de doentes comICE moderada, a forca global dos rmisculos res­pirat6rios esta preservada, encontrando-se dimi­nutda a forca do diafragma, mas sendo a pres­sao transdiafragmatica normal. Nao sao pois, osmusculos respirat6rios responsaveis pela dis­pneia ou cansaco que estes doentes apresentam.

Pedido de separatas para:Address for reprints:

MIGUEL MOTA CARMaServieo de FisiopatologiaFaculdade de Cisncias Medlcas de LisboaCampo Santana, 1301198 LIBOA CODEXTel: 21 885 3000e-mail: miguelcarmocsnetc.pr

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