Con duc tion ve loc ity of the rab bit fa cial nerve: a noninvasive
func tional eval u a tion
Velocidade de condução no nervo fa cial do coelho: uma avaliação
funcional não invasiva
Belmiro Cavalcanti do Egito Vasconcelos* Cosme Gay Escoda**
Ricardo José de Holanda Vasconcellos*** Riedel Frota Sá Nogueira Neves****
AB STRACT:The aim of this study was to eval u ate stan dard ized con duc tion ve loc ity data for uninjured fa cial nerve and fa cial nerve re paired with autologous graft nerves and syn thetic ma te ri als. An eval u a tion was made mea sur ing the pre op er a tive dif fer ences in the fa cial nerve con duc tion ve loc i ties on ei ther side, and as cer tain ing the ex is tence of a pos-i tpos-ive cor re la tpos-ion be tween fa cpos-ial nerve con duc tpos-ion ve loc pos-ity and the num ber of ax ons re gen er ated post op er a tpos-ively. In 17 rab bits, bi lat eral fa cial nerve mo tor ac tion po ten tials were re corded pre- and post op era tively. The stim u la tion sur face elec trodes were placed on the au ric u lar pa vil ion (fa cial nerve trunk) and the re cord ing sur face elec trodes were placed on thequadratus labii in fe rior mus cle. The fa cial nerves were iso lated, transected and sep a rated 10 mm apart. The gap be tween the two nerve ends was re paired with autologous nerve grafts and PTFE-e (polytetrafluoroethylene) or col la-gen tubes. The mean of max i mal con duc tion ve loc ity of the fa cial nerve was 41.10 m/s. Af ter 15 days no nerve con duc-tion was evoked in the eval u ated group. For the pe riod of 2 and 4 months the mean con duc duc-tion ve loc ity was ap prox i-mately 50% of the nor mal value in the sub groups as sessed. A sig nif i cant cor re la tion was ob served be tween the con duc tion ve loc ity and the num ber of re gen er ated ax ons. Noninvasive func tional eval u ation with sur face elec trodes can be use ful for stim u lat ing and re cord ing mus cle ac tion po ten tials and for as sess ing the func tional state of the fa cial nerve.
DESCRIPTORS: Nerve re gen er a tion; Electrophysiology; Neu ral con duc tion.
RESUMO: O ob je ti vo des te es tu do foi ava li ar os da dos pa dro ni za dos de ve lo ci da de de con du ção para o ner vo fa ci al não le sa do e o ner vo fa ci al re pa ra do com en xer to au tó ge no e com ma te ri a is sin té ti cos. Na ava li a ção fo ram me di das as di fe-ren ças pré-ope ra tó ri as de ve lo ci da de de con du ção do ner vo fa ci al em cada lado e ve ri fi ca da a exis tên cia de uma cor re-la ção po si ti va en tre a ve lo ci da de de con du ção do ner vo fa ci al e o nú me ro de axô nios re ge ne ra dos no pós-ope ra tó rio. O po ten ci al de ação mo to ra bi la te ral do ner vo fa ci al de 17 co e lhos foi re gis tra do no pré e no pós-ope ra tó rio. Os ele tro dos su per fi ci a is de es ti mu la ção fo ram co lo ca dos no pa vi lhão au ri cu lar (tron co do ner vo fa ci al) e os ele tro dos su per fi ci a is de gra va ção fo ram co lo ca dos no mús cu loqua dra tus la bii in fe ri or. Os ner vos fa ci a is fo ram iso la dos, tran sec ci o na dos e se-pa ra dos a 10 mm. O es se-pa ço en tre os dois co tos ner vo sos ter mi na is foi re se-pa ra do com en xer tos ner vo sos au tó lo gos e PTFE-e (po li te tra flu o re ti le no) ou tu bos de co lá ge no. A mé dia da má xi ma ve lo ci dade de con du ção do ner vo fa ci al foi 41,10 m/s. Ne nhu ma con du ção ner vo sa foi ob ser va da no gru po ava li a do após 15 dias. A ve lo ci da de de con du ção mé -dia nos sub gru pos ava li a dos para o pe río do de 2 e 4 me ses foi de apro xi ma da men te 50% do va lor nor mal. A ava li a ção fun ci o nal não in va si va com ele tro dos de su per fí cie pode ser útil para a es ti mu la ção e re gis tro do po ten ci al de ação mus cu lar e para me dir o es ta do fun ci o nal do ner vo fa ci al.
DESCRITORES: Re ge ne ra ção ner vo sa; Ele tro fi si o lo gia; Con du ção ner vo sa.
IN TRO DUC TION
Nerve con duc tion data are used rou tinely in the di ag no sis of pe riph eral neuropathies and other conditions1,14,26. Sur face elec trodes have been used
for stim u lat ing and re cord ing the mus cle ac tion po ten tials. Normally three dif fer ent types of electrodes are used in electromyography: sur face, nee
-dle and im planted electrodes15,16,30
. The re cord ing of pe riph eral nerves con duc tion ve loc ity by di rectly stim u lat ing and re cord ing the sur gi cally ex posed nerves is one of the most pre cise ap proaches to nerve re gen er a tion and mus cle reinnervation. How ever, such sin gle brief re cord ings makes it dif-fi cult to eval u ate the nerve re gen er a tion pro cess
* Head Pro fes sor; ***Assis tant Pro fes sor; ****Stu dent of the PhD Pro gram – Oral and Ma xil lofa ci al Sur gery, Scho ol of Den tistry, Uni ver sity of Per nam bu co.
over time20,30
. On the other hand, nee dle elec trodes and elec trodes im planted around pe riph eral nerves for sus tained pe ri ods of time may gen er ate ar ti facts that in ter fere with the in ter pre ta tion of the ef fects of nerve injury15,16,19,20,30
. Fur ther more, in fec tion also may oc cur as a re sult of in va sive punc ture with nee dles or the sur gi cal im plan ta tion of de vices, in par tic u lar when percutaneous con -tacts are used15,30
.
Con trasting with nee dle and im planted elec-trodes, sur face elec trodes re quire no sur gery, and eval u a tions can be re peated over sus tained pe ri-ods of time thereby af ford ing an ac cept able mea-sure ment approach3,9,19,20,25,30. Nerve con duc tion ve
-loc ity is cal cu lated by di vid ing the interelectrode dis tance by the la tency of the first pos i tive de flec-tion in the waveform4,13.
The pres ent ex per i men tal model stud ied nor-mal con duc tion ve loc ity in the rab bit fa cial nerve be fore sur gery, and across fa cial nerve re paired with autologous nerve grafts and syn thetic ma te ri-als, with the aim of es tab lish ing the ef fec tive ness of noninvasive func tional test ing.
MA TE RIALS AND METHODS
The stim u la tion and re cord ing of antidromic evoked mo tor ac tion po ten tials were car ried out in 17 male New Zea land white rab bits (2.5 to 3.0 kg). The an i mals were an es the tized with an in tra mus-cu lar in jec tion of a mix ture of ketamine 50 mg/kg (Ketolar®
, Parke-Da vis, El Prat Llobregat, Bar ce-lona, Spain) and acepromazine maleate 5 mg/kg (Calmo neosan®
, SmithKline-Beechan, Ma drid, Spain), re peated as nec es sary. In ad di tion, lo cal an aes the sia with 3% mepivacaine (Isogaine®
, Clarben, Ma drid, Spain) was ap plied via sub cu ta-ne ous in jec tion in the sur gi cal area. A man dib u lar in ci sion to wards the preauricular area iden ti fied the fa cial nerve. All an i mals were sub jected to noninvasive func tional study be fore and af ter sur -gery.
Nerve le sions
The buccal di vi sion of the fa cial nerve on each side and dis tally to the parotid gland was iden ti fied and iso lated. A 10 mm seg ment was re moved from the buccal di vi sion of the fa cial nerve in all cases (n = 34, nerves) (Fig ure 1). The de fects, in turn, were re paired with autologous nerve grafts, col la-gen and polytetrafluoroethylene (PTFE-e) con duits (Fig ures 2, 3 and 4). The autologous nerve grafts
were ob tained from the left fa cial nerve, of the same an i mal.
The an i mals re cov ered from the sur gery on heated pads and were housed in in di vid ual cages, with free ac cess to food and wa ter. All an i mals sur-vived the sur gery with out prob lems. At the com ple-tion of the study, all rab bits were sac ri ficed with over dose of so dium pentobarbital via an intra-cardiac in jec tion.
Af ter sac ri fice, the anastomotic sites, graft or con duits plus a seg ment of ap prox i mately 5 mm from the prox i mal and dis tal nerve stumps were re moved and marked. All spec i mens were fixed in glutaraldehyde and stained with toluidine blue. Cross-sec tional bi opsy spec i mens were ex am ined un der light mi cros copy (100 X) to as sess intra-neural mor phol ogy. The axon counts were obtained in the sec tions from the mid point of the pri -mary anas to mo sis.
Electrophysiological stud ies
Electrophysiological anal y sis was per formed fol low ing an es the sia. The stim u la tion sur face elec -trodes were placed on the au ric u lar pa vil ion (fa cial nerve trunk) and the re cord ing sur face elec trodes were placed on the quadratus labii in fe rior mus cle. Evoked mus cle ac tion po ten tial was re corded by electromyography (Medelec MS25 Mistro, Sur rey, England). Nor mal con duc tion ve loc ity for the right and left fa cial nerve was re corded pre- and post op-er a tively. Con duc tion ve loc i ties were evoked across the re con structed de fect in the post op er a-tive pe riod, af ter pe riph eral nerve re pair the rab-bits were eval u ated at 15 days and at 1, 2 and 4 months, and cor re lated to the num ber of ax ons re -gen er ated.
Sta tis ti cal Anal y sis
Data anal y sis of the re sults was per formed us -ing the SPSS 7.5 (Sta tis ti cal Pack age for So cial Sci-ence - Microsoft, Il li nois, Chi cago, USA). Con duc-tion ve loc ity com par i sons be tween the two sides (left and right) were made with the Stu dent t-test for paired data. Cor re la tions be tween con duc tion ve loc ity and re gen er ated axon count were in turn eval u ated by Pearson cor re la tion anal y sis.
RE SULTS
Nor mal con duc tion ve loc ity
mean nor mal right con duc ti on ve lo city evo ked pre-o pe ra ti vely was 41.27 ± 3.27 m/s, ver sus
40.92 ± 2.71 m/s on the left side. Ner ve con duc ti-on ve lo city at the peak of the sig nal was 47.05 m/s. The re were no sta tis ti cally sig ni fi cant dif fe ren ces bet we en si des at the 95% con fi den ce le vel (Stu dent
t-test, p = 0.67). The mean glo bal nor mal con duc ti-on ve lo city evo ked be fo re sur gery was 41.10 ± 2.97 m/s.
Post op er a tive nerve con duc tion ve loc ity
No ner ve con duc ti on was evo ked in the ani mals eva lu a ted af ter 15 days, whi le the mean con duc tion ve lo city re cor ded af ter 2 and 4 mtionths was ap -pro xi ma tely 50% of the nor mal va lue. The con duc-ti on ve lo city evo ked at 4 months was 21.21 ± 8.46 m/s (re pa ir with ner ve graft) and 18.26 ± 5.69 m/s (re pa ir with polytetrafluoro-ethylene tube).
The con duc ti on ve lo city at 2 months for the poly te tra flu o ro eth yle ne tube and co la gen groups were 22.95 ± 6.52 m/s and 24.11 ± 6.12 m/s and the re sults at 4 months were 21.68 ± 3.7 m/s (polytetrafluoroethylene tube) and 23.29 ±
2.47 m/s (colagen).
Nor mal axonal nerve
The to tal num ber of myelinated ax ons ranged from 156.37 to 176.21. The mean myelinated nerve count (± stan dard de vi a tion) was 166.29 ± 9.45 myelinated ax ons (oculoreticular area) (Fig ure 5).
Pos to pe ra ti ve axo nal re ge ne ra ti on
15 days af ter PTFE-e, autologous nerve grafts and col la gen repair, an ab sence of axonal re gen er-a tion wer-as ob served (Fig ure 6). How ever, within 4 months, a good axonal re gen er a tion was ob served
FI GU RE 4 - Re pa ir with poly te tra flu o ro eth yle ne e) con du its.
FI GU RE 1 - Seg ment re mo ved from the buc cal di vi si on of the fa ci al ner ve.
FI GU RE 2 - Re pa ir with au to lo gous ner ve grafts.
for all groups (Fig ure 7). In the post op er a tive pe-riod, a sig nif i cant cor re la tion be tween con duc tion ve loc ity and axonal re gen er a tion was ob served for all groups and tech niques (n = 34; 0,002 – Pearson test).
DIS CUS SION
One of the chal lenges of pe riph eral nerve re gen-er a tion is the early and quan ti ta tive as sess ment of the re gen er a tion pro cess in terms of the num ber of ac tive ax ons found in the bun dle. Reinnervation dy nam ics can be stud ied us ing dif fer ent techniques6,17,24,28. In the pres ent study the ef fi cacy
of a noninvasive method was eval u ated in an ap pli-ca tion in a rab bit model.
The use of sin gle-fi ber electromyography for eval u at ing the microphysiology of an in di vid ual mo tor unit has been de scribed in the lit er a ture.
This tech nique can be used to study the denervation and reinnervation oc cur ring as a re-sult of pe riph eral nerve injury29.
A com par a tive study be tween mag netic nerve stim u la tion with con ven tional elec tric nerve stim -u la tion in nor mal sub jects and in pa tients with dis or ders of the pe riph eral ner vous sys tem has been re ported. In gen eral, both nerve stim u la tion mo dal i ties yielded sim i lar re sults in pa tients with dis or ders and healthy subjects2
.
The lit er a ture re ports an eval u a tion of the in fe-rior al ve o lar nerve func tion us ing a re peated nerve con duc tion test dur ing man dib u lar sagittal split osteotomy. The intraoperative sen sory nerve con-duc tion ve loc ity re corded and the men tal nerve blink re flex tests con ducted two weeks af ter the op er a tion were cor re lated, whereas com par i son of clin i cal neurosensory test ing with the intra-operative events and sen sory con duc tion ve loc i ties was less con sis tent11
.
Anot her re se arch stu di ed con duc ti on ve lo city of the deep tem po ral ner ve and the myloh yo id ner ve mo tor bran ches of the tri ge mi nal ner ve. The se ner-ves were sti mu la ted in tra o rally with a pe di a tric sur fa ce sti mu la tor. Com pound mus cle ac ti on po -ten ti als were re cor ded over the tem po ra lis and myloh yo id mus cles using sur fa ce elec tro des. The mean la tency of the deep tem po ral ner ve was 2.1 m/s ± 0.3 m/s, ver sus 1.9 m/s ± 0.2 m/s for the myloh yo id ner ve. The ma xi mal sidetoside la tency dif fe ren ce was 0.4 m/s. The se aut hors con -clu ded that such tech ni ques should pro ve use ful in pa ti ents with tri ge mi nal ner ve di sor ders5
. A new tech nique for re cord ing sen sory con duc-tion ve loc ity of the in fe rior al ve o lar nerve was
re-FI GU RE 5 -Mye li na ted axons of the nor mal buc cal di vi-si ons of the fa ci al ner ve (to lu i di ne blue, 100 X).
FI GU RE 6 - Absen ce of axo nal re ge ne ra ti on at 15 days af ter PTFE-e con du it re pa ir.
ported by Jaaskelainen12. The sen sory re sponses of
this nerve were ob tained in all 42 nerves ex am ined with sil ver wire or monopolar nee dle elec trodes in -serted be neath the zygomatic arch, an te ri orly to the temporomandibular joint and to a depth of 4 to 4.5 cm, near the oval fo ra men. A small bi po lar sur-face elec trode was used for stim u la tion at the men-tal fo ra men. The mean sen sory con duc tion ve loc ity of the in fe rior al ve o lar nerve was 62.8 m/s ±
6.7 m/s on the right side, and 63.0 m/s ± 5.4 m/s on the left side.
The in flu en ce of tem pe ra tu re7,8,22
, age18,23
, and he ight21,23 upon con duc ti on ve lo city has been des
-cri bed by a num ber of aut hors. Fras senet al.11 re
-por ted dif fe ren ces in evo ked po ten ti al at dif fe rent tem pe ra tu re in hu mans. Our own ob ser va ti ons show mean con duc ti on ve lo city of the fa ci al ner ve (41.10 m/s) at 25°C to be si mi lar to the re sults re -por ted by Fras sen et al. (45.0 m/s)8. In this case,
en vi ron men tal tem pe ra tu re and age of the ani mals were con trol led. In ad di ti on, the mean con duc ti on ve lo city of the fa ci al ner ve was con sis tent with va -lu es pre vi ously re por ted in the li te ra tu re (ran ge
35.0-64.6 m/s)8,10,27. The re were no sig ni fi cant se
ri-al dif fe ren ces bet we en the re sults of con duc ti on ve lo city bet we en the left and right fa ci al ner ves. Ours re sults agree with tho se re por ted by Co linet al.3
.
In this study a sig nif i cant cor re la tion be tween the con duc tion ve loc ity and the num ber of re gen-er ated ax ons in volv ing dif fer ent tech niques was ob served (p < 0.01; r = 0.002). This could ex plain why the study vari ables ex hib ited an in creas ing ten dency dur ing nerve re gen er a tion.
CON CLU SION
In all groups and tech niques, a sig nif i cant cor -re la tion be tween con duc tion ve loc ity and axonal re gen er a tion was ob served.
Noninvasive func tional eval u a tion with sur face elec trodes can be use ful for stim u lat ing and re-cord ing mus cle ac tion po ten tials and for as sess ing the func tional state of the fa cial nerve fol low ing in -jury or sur gery.
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