Research in Vestibular Science Vol. 11, Suppl. 1, June 2012 Symposium II pissn 2092-8882, eissn 2093-5501 진동에의한주관적시수직 - 수평의편위 단국대학교의과대학이비인후 - 두경부외과학교실 정재윤 Vibration Induced Shift of Subjective Visual Vertical-Horizontal Jae Yun Jung, MD Department of Otorhinolaryngology-Head and Neck Surgery, Dankook University College of Medicine, Cheonan, Korea Corresponding Author: Jae Yun Jung, MD Department of Otolaryngology-Head and Neck Surgery, Dankook University Medical College, San 29 Anseo-dong, Dongnam-gu, Cheonan 330-715, Korea Tel: +82-41-550-3973 Fax: +82-41-556-1090 E-mail: jjking@dankook.ac.kr Copyrightc 2012 by The Korean Balance Society. All rights reserved. Subject visual vertical-horizontal (SVV-H) is well known as a quick, easy and sensitive otolith function test especially in acute stage and widely used in dizziness clinic. In compensated unilateral vestibulopathy, SVV-H shows decreased deviation losing its clinical role. Vibration applied either to neck muscle or mastoid bone can elicit nystagmus showing vestibular tonic imbalance even after compensation. Likewise, SVV-H test with vibration accentuates abnormal deviation and reveal chronic unilateral vestibular function loss. SVV-H can be sensitive test not only in acute but also after compensation, if used with vibration. Research in Vestibular Science 2012;11 Suppl 1:S47-S51 Key Words: Vibration; Orientation; Dizziness 서론주관적시수직- 수평감에대한조절은시각적정보, 고유수용체감각과전정기능에의해좌우된다. 다양한형태의전정장애에서이러한시수직- 수평의변화를예상할수있으며이는병변의위치와병변의정도, 회복의유무에따라다양한정도의편위를보일수있다. 난형낭과같은이석기관이수직과수평의감지에있어큰역할을담당하고있다고추측되며급성말초성전정기능저하에서는병변측으로정상범위이상의편위를보임으로써민감도높은검사로활용되고있다. 하지만전정보상이이루어지면서급성기이후에는비정상적인편위가감소하기시작하여만성적인전정장애의경우보상의작용으로인하여그진단적가치는떨어진다. 이러한특징은자발안진이보상과정에서보여주는모습과동일하다. 자발안진이소실된말초성전정장애환자의경우에도두부회전 (head shaking) 이나진동자극을가하면좌우전정기능의비대칭성을유발하여많은경우에서병변반대쪽을 향하는안진을관찰할수있으며이러한방법을임상에서많이사용하고있다. 이와같이진동자극을주면서주관적시수직- 수평검사에이용하면역시보상에의해감소된병변측편위를보다뚜렷하게나타나도록유발할수있다. 이에대한관련연구들을통하여진동자극이어떻게전정기능에영향을줄수있는지에대해서알아보고진동에의한주관적시수직- 수평의편위가어떤양상을보이는지기술하여보았다. 유양동진동이말초전정기관에영향을미치는기전 일반적으로진동은두가지형태의파형에의해특정부위에이르게된다. 첫째는진동이전달되는방향으로형성되는 P wave (compressional wave), 두번째는진동이가해지는방향과수직을이루는 S wave (shearing wave) 로이루어진다. 1 진동이유양동에가해졌을때에도이러한복잡한파형의형 S47
Res Vestibul Sci Vol. 11, Suppl. 1, Jun. 2012 A B Figure 1. Effects of vibration on subjective visual vertical-horizontal (SVV-H) in 30 normal healthy subjects. Each line shows SVV-H (A-SVH, B-SVV) value at baseline test and during vibration (sternocleidomastoid muscle [SCM] or mastoid bone of either side). Positive y axis value means clockwise deviation and negative y axis value is counter-clockwise deviation. 태로두개골을통과하며가속을유발하며이러한가속이진동에민감한전정유모세포들을흥분시키게된다. 전정유모세포가회전가속이나선형가속이아닌진동에대해반응을보인다는것은잘알려진사실이다. 기도를통한진동에너지의전달 (air conduction stimuli) 에는이석기관특히 saccule의유모세포에시작되는 vestibular afferents들이주로반응하며, 세반고리관에연결된 afferents들은극히드물게반응을보인다는연구와 2 이후유양동진동 (200-1,500 Hz의주파수영역의 bone vibration) 을기니픽에가하면역시주로이석기관에존재하는 irregular nerve fiber의흥분을유발한다는연구를 3 고려하면임상에서사용하는진동이만일전정신경계를직접자극한다면그반응을주로보이는곳이이석기관이라고추정해볼수있다. Young 등 4 은원숭이머리에진동과기도음자극 (50-400 Hz) 을이용하여말초전정신경의반응을조사한연구에서진동과기도음자극에의해주로 irregular nerve fiber가반응을보인다고하였으며다른전정전정기관에비해구형낭 (saccule) 은다른전정기관과비교하였을때진동에대한감수성이없다고보고하기도하였다. 또한진동의의한반응은내림프액의진동을유발하기보다는유모세포를직접자극함으로써일어난다고하였다. 경부진동이전정신경계에영향을미치는기전경부의진동이전정기능에영향을미칠수있는기전들은첫째경부근육의진동도결과적으로유양동진동과마찬가지로골성미로의진동을유발하게되고따라서전정유모세 포의흥분을유발한다. 진동을가하는위치나선택한경부근육의종류에따라차이는있을수있으나유양동진도에비하여 3/4정도의가속을유발하는것으로알려져있다. 5 Karlberg 등 5 은자신들이실험에사용한 vibrator의진동을측정하기위하여 accelerometer (ADXL 150EM-3, Analog Devices, Norwood, MA, USA) 를피험자가입에물고두개골과 subjective visual horizontal (SCM) 근육에진동을가하여그값을측정하였다. 중력가속도를 1 g로하였을때상대적인값으로표시하였으며두부진동시에는평균 0.08 g, SCM 근육진동시에평균 0.06 g의값이나왔으며 ( 두부진동시의 4분의 3정도의크기 ) 이를 db 단위로표시하면 -10에서 -15 db (relative to 1 g) 가되며이는 Young 4 이 squirrel monkey의 SCC afferent 를자극하는데필요한최소한의진동역치 -25 db (relative to 1 g at 80 Hz) 에비하여충분히높은측정치라고하였다. 6 둘째경부근육의진동이자극부위에위치한근육에위치한고유수용체를자극함으로써구심성신호가전정신경핵으로전달되어말초전정기관에서들어오는신호와함께통합처리되는과정에서영향을줄수있다. 진동은선택적으로근육의 spindle receptor를활성화시키기에충분한자극이며 primary endings에흥분을유발하고직경이큰구심성신경섬유에활동전위를유발하는것으로알려져있다. 7-9 경부에존재하는원심성신경정보는머리의위치를유지하는데중요한역할을하며경부체성감각시스템은몸의정위 (orientation) 에특히필수적이다. 6,10 따라서경부의진동자극이경부의감각수용체를자극하여체성감각시스템의균형에변화를유발함으로써주관적시수직- 수평에영향을미칠수도있다. S48
정재윤. 진동에의한주관적시수직 - 수평의편위 A B Figure 2. Effects of vibration on subjective visual vertical-horizontal (SVV-H) in 17 compensated vestibular neuritis (VN) patients (14 right VN, 3 left VN). Each line shows SVV-H (A-SVH, B-SVV) value at baseline test and during vibration (sternocleidomastoid muscle [SCM] or mastoid bone of either side). Positive y axis value means clockwise deviation and negative y axis value is counter-clockwise deviation. 경부자극은근육에위치한고유감각수용체의자극으로설명을하고유양동진동은전정신경의자극으로설명하지만어느하나에진동을가하였을때나머지한쪽에도영향을충분히미치게된다고볼수도있다. 특히흉쇄유돌근의경우한쪽끝이유양돌기에붙어있어근육에가해진진동이유양동의진동과이에따른전정유모세포의영향을줄수있다. 따라서어떤형태의진동이던두가지시스템의자극을모두유발하게된다는것이가능하다고볼수있다. 일측성전정기능저하에서경부진동자극의영향어느부위의진동자극이든일측전정신경절제환자에게서시운동효과 (oculomotor effect) 와체감효과 (perceptual effect) 를보이게된다. 과거의많은연구에서이러한영향을미치는기전으로경부체성감각수용체 (proprioceptor) 에의한다고보고하였다. 6,11-13 진동은경부근육의 spindle의 primary ending 을활성화시키고특히 Ia spindle afferents의 firing rate를증가 시킴으로써근육의 tonic contraction을유발하는것으로알려져있다. 14 경부에는이러한 muscle spindle이풍부하고경부의관절표면에는 mechanoreceptor의밀도가높다. 15,16 이러한고유수용체로부터의신호들은비록전정기관에서기원하지않지만전정신경핵에신경세포들을자극하는것으로알려져있으며심지어 parieto-insular vestibular cortex (PIVC) 에존재하는전정계신경세포도자극한다. 17,18 일측전정기능저하가생기면뇌는균형을잡기위해사용하는다른정보들 ( 특히경부근육에서오는체성감각정보 ) 에비중을높이면서보상기전을진행한다. 19,20 정상인에서경부안반사 (cervico-ocular reflex) 의이득은 0.07 이하로무시할정도이지만 21 전정기능의소실이발생하면 multisensory processing 과정에서경부신호의가중치가변하는일종의보상기전이일어난다. 부족한전정기관으로부터의정보를경부고유수용체에서오는신호로대체 (substitution) 하는과정이일어나는것이다. 원숭이에서양측전정기관의병변을만들면보상과정에서경부안반사의이득이증가되어 S49
Res Vestibul Sci Vol. 11, Suppl. 1, Jun. 2012 0.4-0.7 정도로증폭된다. 22 경부자극과전정기관자극 (caloric vestibular stimulation with ice water) 을동시에주었을때각각의자극만을주었을때에비하여자극의흥분- 억제조합에따라서로증가시키거나 (additive) 혹은감소시키는 (subtractive) 현상이있음을체감시정면 (perceived straight ahead) 의편위를이용한실험에서보고된바있다. 23 진동에의한주관적시수직-수평의편위공간정위 (spatial orientation) 을올바로감지하기위해시각, 전정, 체성감각에서얻어지는모든정보들을사용하지만정상적인조건에서경부고유수용체에서올라가는신호는상대적으로작은영향을미치고있다고여겨진다. 하지만전정신경염과같이일측전정기능의저하가발생하면세가지감각정보들의상대적가중치에변화가생겨경부고유수용체에서올라오는정보에의한공간정위의편위가보다더증폭되어나타나게된다. 이러한가중치의변화로인해경부근육의진동을병변측에가하면주관적시정면 (subjective visual straight ahead) 의편위가정상인에비하여증가되어나타나게된다. 하지만이러한변화가일측전정기능의소실이일어난직후에는뚜렷하지않으며 60-100일정도에가장큰편위를보이다가서서히감소하는것으로알려져있다. 6 경부근육의진동이정상인에서주관적시수평검사에영향을주는지알아보기위한실험에서는자극의좌우위치에상관없이주관적시수평의값에는변화를주지않는다고하였다. 13 이는건강인에서는흉쇄유돌근진동자극이양측전정신경계에비대칭적인신경활동을유발하지못한다는것을의미한다. 하지만일측성전정기능장애가있는경우에는주관적시수직- 수평에영향을주게되는데 Karlberg 등은 chronic uvd 환자에서 search coil을이용하여시고정상태에서측정한안구의 static torsion을측정하였을때병변측또는반대측경부근육의진동을주었을때모두병변측으로의편위가관찰되었으며그크기가주관적시수평의편위와유사한값을보인다고하였다. 따라서이러한환자에서의주관적시수평의편위는진동에의해일시적으로유발된안구의 torsional shift에의한이차적인현상이라고추정하였다. 6 경부의진동자극에의한 perceptual effects는건측진동보다병변측에적용했을때보다더잘나타난다고알려져있다. 이는 SCM 근육에서도보고되었고, 4 dorsal neck muscle에서도 11 보고되었다. 하지만 Karlberg 등은이러한차이가 SCM근육 이나 mastoid bone의진동시나타나는 ocular torsion shift에서는관찰되지않았다고하였으며 perceptual measure와는다른점이아마도검사시에적용된진동의지속시간이주관적시수평의경우에는수분이걸리는반면자신들의실험에서는 search coil의 slip의가능성을최소화하기위하여측정시간을가능한 10초정도였던것과의차이로설명하였다. 정상인에서주관적시수직에서체성감각에서들어오는정보의가중치가전정기능이소실된환자에서는더욱높아질수있다. 정상인에서는좌우경부근육진동에의한주관적시수직 -수평의편위변화가나타나지않지만양측전정기능저하환자에서는경부근육의진동에의해생기는정보의비대칭성을정상인에서보다많은가중치를부여하기때문인지이에대한추가연구가필요하다. 정상인에서는유양동진동이안진을유발하는경우가드물지만만성일측성말초성전정기능장애환자의유양동에진동을가하면주로병변반대편을향하는회전성분을가지는수평안진이발생하는것은잘알려져있다. 24 또한이보다좀더이후에진동에의한안진발생과유사하게 chronic vestibular deafferentation 환자에서 mastoid bone에진동을가하면주관적시수평 (subjective visual horizontal, SVH) 의 tonic shift가일어남을보고되었다. 25 이러한만성일측성말초성전정기능장애환자의어느쪽이든유양동의진동은밝은환경에서도 tonic ocular torsion을유발하며이것은마치급성기에보이는안구의움직임을보상이이루어진이후에도진동으로인하여유발되기때문이며이전에보고되었던주관적시수평의편위를설명할수있다고하였다. 5 급성전정기능장애환자에서주관적시수직- 수평의편위의방향과크기는안저촬영을통해측정한 ocular torsion의방향과크기와높은상관관계를보인다는사실은잘알려져있다. 26 이러한상관관계가만성전정기능장애환자에서진동에의해유발된 ocular torsion과주관적시수직- 수평의편위에서도성립된다. 결론유양동이나경부근육의진동은말초전정기관과경부고유수용체에모두영향을미치게된다. 또한두가지말초수용기로부터의신호들이전정중추에서 multisensory processing 을통해통합되는과정은일측전정기능의저하유무와이로인한보상, 대체과정의경과에따라다양하게나타날수있다. 진동이보상이이루어진일측성전정기능저하에서주관적시수직- 수평의편위를더욱증폭시켜준다는사실뿐아니 S50
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