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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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