Research in Vestibular Science Vol. 8, No. 2 Suppl. 1, December 2009 Symposium ISSN 2092-8882 반고리관기능의이학적검사 고려대학교의과대학이비인후과학교실 채성원 Laboratory Tests for Semicircular Canal Function Sung Won Chae, MD Department of Otorhinolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, Korea Corresponding Author: Sung Won Chae, MD Department of Otorhinolaryngology-Head and Neck Surgery, University Guro Hospital, 97 Gurodong-gil, Guro-gu, Seoul 152-703, Korea Tel: +82-2-2626-3186 Fax: +82-2-868-0475 E-mail: schae@kumc.or.kr Copyrightc 2009 by The Korean Balance Society. All rights reserved. The semicircular canals sense angular acceleration and are arranged in roughly parallel pairs. The vestibuloocular reflex (VOR) is responsible for maintaining binocular fixation and stabilizing binocular foveal images during head movements. The VORs are divided into two types: angular and linear. Angular reflexes are initiated by activation of the semicircular canals. There are several kinds of test for semicircular canal function such as caloric test, rotation test, and pulse step sine test. Caloric testing remains the most useful laboratory test in determining the responsiveness of a labyrinth. It is one of the few tests that allow one labyrinth to be studied independently of the other. The stimulus can be applied relatively easily with techniques that are commonly available. Caloric testing relies on stimulating or cooling the vestibular system by alternately heating and cooling the external auditory canal with water or air. Rotational tests analyze the responses of both labyrinths together. They require a high-torque motor-driven chair and relatively advanced software to analyze the results. Rotatory chair testing is useful in assessing vestibular function in patients with suspected bilateral vestibular hypofunction and children. Step changes in head velocity can be used instead of sinusoidal rotations to identify vestibular hypofunction. Time constant are determined by the time after onset of the stimulus at which slow phase eye velocity has decreased by 67% of its initial value. The use of a novel pulse-step-sine (PSS) rotational stimulus can identify abnormal function of the horizontal semicircular canals in human subjects with unilateral and bilateral vestibular deficits. Research in Vestibular Science 2009;8(2 suppl 1):S22-S30 Key Words: Semicircular canal; Caloric test; Rotational test 서론말초전정기관은머리의회전또는선형가속도를감지한다. 난형낭반과구형난반은선형가속도와중력의변화를감지하며반고리관내의팽대부릉은각방향의회전각가속도를감지하여이들정보를전정신경으로전달한다. 반고리관에의한전정안반사는반고리관평면상의안구움직임을유발하게되며, 1,2 이러한전정안반사는머리의회전, 내림프액의움직임, 팽대부릉정의편위, 말초전정신경의활동변화, 동안신경원의활동변화, 외안근의수축및이완, 안구의움직임등을통해작용한다. 3,4 머리의회전속도와관련된정보가동안신경원 (ocular mo- S22
채성원. 반고리관기능의이학적검사 tor neuron) 으로전달되며안구의움직임이유발되며이러한속도정보를이용한안구의반응은세개의신경원궁을거쳐전정안반사로를통해나타난다. 반고리관의자극에의한안구와머리의움직임은반고리관의자극방향과내림프액의흐름방향으로일어나며부동모와운동모의해부학적위치에따라수평반고리관에서는팽대지향성 (ampullopetal) 내림프액흐름에따라일어나며수직반고리관에는이와는반대로팽대반지향성 (ampullofugal) 방향의내림프액흐름에의해자극반응이나타난다. 5,6 좌우측반고리관은측두골내에서해부학적위치상서로쌍을이루므로한쪽반고리관의자극시반대쪽반고리관은억제반응이일어나는형태를갖게된다. 머리회전운동이끝나면안구의위치가고정되어야하며이를위해서는안구위치에대한정보가필요한데이는머리회전속도정보로부터수학적인적분에의해수평성안구운동에있어서는내측전정핵과에서일어나며이를신경적분체 (neural integrator) 라한다. 7,8 양양온안진검사 (sinusoidal bithermal caloric test) 등이있으며, 단일온도자극을사용하는방법으로는 Kobrak ice water test, minimal ice water test, monothermal differential caloric test 등이있다. 1) 검사원리온도안진검사의원리는내림프액의대류, 온도에따른내림프액의부피변화, 전정신경에대한직접적인온도자극등으로설명되고있다. 대류설은체온보다높은온자극이외이도에가해지는경우외이도에가장가까운수평반고리관의중간부위의내림프액이온도가높아지고이로인해팽창한내림프액은밀도가낮아져위쪽 ( 팽대부쪽 ) 으로의흐름이일어나며반대로체온보다낮은냉자극이가해지는경우에는아래쪽 ( 팽대부반대쪽 ) 으로내림프액의흐름이유발된다는가설이다 (Figure 1). 하지만가쪽반고리관의팽대부가아래로향하는역위에서온도안진의강도는정상적인위치 반고리관기능의검사의종류 다양하고정밀한검사가반고리관의기능을진단하기위해이용되고있으며어지럼증환자에서반고리관의이학적검사는환자의증상을객관적으로증명하며병변의방향성을알려주고치료를계획하며경과를파악하기위해시행된다. 반고리관의기능을측정하기위해서는흔히사용되는검사에는온도안진검사, 회전검사등이있으며반고리관의전정안반사를측정한다. 9 1. 온도안진검사 (Caloric test) 온도안진검사는체온보다높거나낮은온도의물혹은공기를외이도에주입하여안진을유발후이를측정하여전정기능을평가하는검사이다. 귀의양쪽을독립적으로자극할수있어병변의국소화가가능한검사로서평형기능검사중제일중요한검사중하나이나일상생활에서경험하지못하는 0.002~0.004 Hz 정도의낮은주파수의자극으로일상생활에서경험하는모든주파수의전정기능을파악하지는못한다. 10,11 냉온수의양온자극을사용하는방법으로는양온교대안진검사 (alternate binaural bithermal caloric test), 동시자극온도안진검사 (simultaneous binaural bithermal caloric test), 진자 Figure 1. Convective flow mechanism of the caloric response. For the warm caloric irrigation shown in this diagram, ampullopetal deflection of the cupula results from this flow of endolymph. Vestibular-nerve afferents innervating the horizontal semicircular are excited, and a horizontal nystagmus with slow phase components directed toward the opposite ear is produced. A cold caloric stimulus results in an oppositely directed response with ampullofugal deflection to the cupula. S23
Res Vestibul Sci Vol. 8, No. 2 Suppl. 1, Dec. 2009 Figure 2. Average slow phase eye velocity in response to warm (44 C) and cold (30 C) irrigations with subjects oriented in different bed positions. Caloric responses in the face-up positions are consistently greater in intensity than those in the face-down positions. Face-up responses cover a larger segment of the 360-degree arc than the face-down responses. The curves appear to approximate a sine function. (4) The findings are similar for warm and cold irrigations. 에서의온도안진의강도보다약함이관찰되었고, 머리의위치를시상면에서연속적으로변화시킬경우에관찰되는온도안진의강도와방향의변화는대체로 sine 곡선을따르지만, 강도가비대칭으로나타남을보고되어대류요인이외에도비대류적인요인들이있음이증명되었다 (Figure 2). 비대류적인요인에대한가설은온도에따른내림프액의부피변화는온자극시에는수평반고리관내림프액의부피팽창에의해팽대부릉정의난형낭방향으로의변위를유발하고, 12 냉자극에는반대로반고리관방향으로변위를유발한다는가설과전정신경에대한직접적인온도자극은냉자극은전정신경의억제를, 온자극은전정신경의흥분을유발한다는가설이있다. 이러한온도자극에의한반고리관반응기전들중내림프액의대류에의한영향이약 75% 를차지하고있는것으로추정된다. 13 2) 검사방법 (1) 양온교대온도안진검사검사는누운상태에서머리를 30 올린자세나앉은자세에서머리를뒤로 60 누운자세로시행하게된다. 온도자극은양온자극을좌우측귀에교대로가하는방법으로우측온자극 (right warm, RW), 좌측온자극 (left warm, LW), 우측냉자극 (right cold, RC), 좌측냉자극 (left cold, LC) 과 같은순서로시행한다. 온도자극하는방법으로는개방회로법 (open loop system) 과폐쇄회로법 (closed loop system) 으로구분할수있다. 개방회로법은자극매체로물이나공기를사용하며, 외이도에주입된자극매체가다시외이도를통해밖으로흘러나오는방법으로물을이용한개방회로법이가장검사간변동이적어안정적이다. 14 물을이용하는경우 250 ml의냉수 (30 ) 또는온수 (44 ) 를외이도에 40 초간주입한다. 공기를이용하는경우냉자극공기 (24 ) 와온자극공기 (50 ) 8리터를 60초간주입하나이는표준화된방법은아니며검사실조건에따라자극의조건을변화하여사용할수도있다. 폐쇄회로법은외이도염, 고막천공, 중이염과같이외이도나중이에직접자극매체가닿으면안되는상황에서사용되는방법으로외이도에들어가는폐쇄회로를만들어자극매체가직접환자의외이도나고막에닿지않게하는방법이나물을이용한개방회로법에비해자극의강도가일정하지않아검사간변동성이큰단점이있다. 폐쇄회로법에서는 26 의자극과 44 의자극으로 40 초간자극하는것이일반적인방법이며세가지자극방법에의한반응강도는서로유사하다. 안진의기록은전기안진기나영상안진기를이용하며자극시작부터안진이소실될때까지약 3분간기록하게된다. 시고정의영향이없는상태에서기록하여야하며자극과자극간에는직전자극에의한영향을배제하기위해검사사이에 5분이상의간격을주어야하며전기안진기를이용하는경우각검사시마다보정을하여야한다. 15 시고정에의한전정- 시각상호작용을검사하기위해서는온도자극에의한안진의강도 ( 완서상속도 ) 가최대인시점이지난직후시각적목표점을응시하게한상태에서안진을기록한다. (2) 기타온도안진검사자극법 - 빙수자극법 (Ice water test) 얼음물 5 ml를귀에넣어자극하는방법으로온도를일정하게유지하는장치가필요없으나자극이매우커서정상전정기능을가진환자에서는심한현훈을일으킨다는단점이있다. 냉온교대온도안진검사로반응이나타나지않는환자를대상으로얼음물 2 ml를이용하여전정기능이소실되었음을확인하는검사법도있다. 16 - 단일온도자극안진검사검사중유발되는오심, 구토등의증상을줄이기위해 27 의물 5~10 ml를이용하여자극하는법과 40 온수 S24
채성원. 반고리관기능의이학적검사 250 ml나 30 냉수 250 ml를이용하는단일온도자극법등이있다. 냉온교대자극법에비해환자의불편함이적고검사시간은절약되지만위음성률이높다는문제점이있다. 17 - 동시자극온도안진검사양쪽외이도에동시에같은온도의냉수나온수를넣어자극하는방법이다. 한쪽귀의자극으로발생하는심한어지럼을피하고시간을절약할수있으나아직표준온도자극검사를대체하기에는보완이필요하다. 3) 검사의해석및임상적용온도안진검사에서측정되는정량적변수는안진의지속시간, 횟수, 안구운동속도등이있다. 그중에가장간단한방법은발현된안진의지속시간을측정하는방법이며느린성분안구운동속도가가장안정적인변수로전정기능손상을예민하게반영한다. 18 온도안진검사에서측정되는느린성분안구운동속도는 95% 유의수준에서정상범위가 5 ~75 /sec 로사람마다개인차가커서절대적인수치로정상과비정상을판별하기어려운문제가있었다. 이에개인차를없애는방법으로 Jongkees에의해개발된공식이가장널리사용되고있다. 가장많이시행되는표준적인양온교대온도안진검사에서는 RW, RC, LW, LC의값을아래의 Jongkees의공식에넣어반고리관마비 (Canal Paresis, CP) 값과방향우위 (Directional Preponderance, DP) 값을계산한다. 과거에는네개의변수에각각발현된안진의지속시간을대입하였지만현재는느린성분최대안구운동속도를대입하고있다. CP (%)=(LW+ LC)-(RW+ RC)/(LW+ LC)+(RW+ RC) 100 DP (%)=(LW+RC)-(RW+LC)/(LW+LC)+(RW+RC) 100 CP (%) 는 좌측귀의반응 과 우측귀의반응 의차이를 전체반응의합 에대하여비율로나타낸것으로그수치가작을수록양측귀의반응에차이가없음을의미한다. 이차이가 20~30% 이하면정상 ( 좌우대칭 ), 그이상이면비정상 ( 좌우비대칭, 한쪽의가쪽반고리관기능저하 ) 으로판정하지만검사기관마다 CP의판정기준에차이가있다. DP (%) 의공식은 좌측으로향하는안진의반응 (LW와 RC) 과 우측으로향하는안진의반응 (RW와 LC) 의차이를 전체반응의합 에대하여비율로나타낸것으로그수치가작을 Figure 3. Bithermal caloric test in right unilateral vestibular neuritis patient. In acute phase, right side canal weakness is accompanied by directional preponderance to the left due to right beating spontaneous nystagmus. 수록양측으로향하는안진의강도가대칭적임을의미한다. 이차이는 30~40% 이하면정상, 그이상이면비정상으로판정한다. 비정상의경우대개자발안진이나두위안진이반영된것이많다고하나, 임상적인의미는아직불분명하다. 비정상적인방향우위성은주로자발안진이나검사자세에서의두위안진을의미하나, 자발안진없이방향우위성만을보이는경우중추성병변을의심할수도있다. 하지만아직까지그의미는확실히알려져있지않다. 19 반고리관마비가 20~30% 이상인경우, 일측말초성반고리관기능의저하또는일측전정신경기능저하를의미하나 (Figure 3), 8번중추신경근부위의중추성병변시에도나타난다. 또한반고리관마비는양측반응의상대적비율로나타나는값이므로양측반응의절대값을같이비교확인하여야한다. 즉반대측의과잉반응에의해상대적으로반고리관마비를보일수있으며, 양측반응의절대값이정상이하인경우에도상대적으로일측반고리관마비로잘못해석할수있다. 반고리관마비는병변측말초전정기능의회복이없는한중추성전정보상후에도지속적으로비정상소견을나타낸다. 20 따라서어지럼증환자의온도안진검사의판독에는과거전정기능장애에대한병력을참고하여해석하는것이바람직하다. 양측온자극과냉자극에대한반응시최대완서상속도의합이각각 11 /sec와 6 /sec보다작거나, 양측냉온자극모두에대한반응의합이 22 /sec보다작은경우, 양측성수평반고리관기능저하로판정한다. 냉온자극에안진이나타나지않는경우에는얼음물로자극하는 Kobrak ice water test로확인하며, 얼음물에반응을보이지않는경우반고리관기 S25
Res Vestibul Sci Vol. 8, No. 2 Suppl. 1, Dec. 2009 Figure 4. Visual fixation of caloric test. The slow-phase velocities in each time period are averaged to determine the intensity of nystagmus for both before and after fixation conditions. The fixation suppression test is quantified by calculating a Fixation Index. 능소실로판단하게된다. 그러나양온교대안진검사상양측성반고리관마비를보이나얼음물자극에정상반응인최대완서상속도가 40 ~50 /sec 이상인경우에는양온교대안진검사의온도자극이불충분하였거나환자의각성상태가부족했을가능성을고려하여야한다. 온도안진검사는매우낮은자극주파수에의한반응이므로얼음물자극에반응을보이지않는경우에도보다높은자극주파수의회전자극에는반응을보이는경우가있으므로반고리관기능소실을판정하기위해서는회전검사를통해반응여부를확인하는것이필요하다. 일측온수와냉수에의한안진의최대완서상속도가각각 80 /sec와 50 /sec를초과하는경우, 온수와냉수에의한양측반응이각각 221 /sec와 146 /sec를초과하는경우에는중추성병변을의심하나, 측두골의해부학적변형이나피검자의긴장상태에의해서도나타날수있다. 21 검사중에시고정을시키면반응이억제되는데이를지수로나타내어중추성병변을감별하는데이용하기도한다 (Figure 4). 시고정지수 (fixation index) 와시고정억제지수 (fixation suppression index) 를측정하는공식은다음과같다. 의방향이온도자극후반응초기에반대방향으로바뀌는경우를 caloric reversal이라하며중추성병변을시사한다. 2. 회전검사 (Rotation test) 회전검사는전정안반사의보상을관찰할수있으며온도안진을시행못하는유아나소아에게유용하며시간이절약된다. 하지만고가의장비가필요하며양측이동시에자극을받으므로전정기능장애의방향성을알기는어렵고강한머리운동을측정못하는단점이있다. 회전검사는머리회전의주체에따라피동회전검사와능동회전검사로구분할수있으며회전축에따라수평반고리관을검사하는수직축수평회전검사방법과, 탈수직축회전검사 (off vertical rotation test) 와편심성회전검사 (eccentric rotation test) 등이있다. 이러한회전검사는임상적으로중저회전주파수 (0.01~1 Hz) 영역의반응을검사하게되며고주파수영역의전정안반사를검사하는방법으로는고주파머리회전검사법 (high frequency head rotation test) 과역동적시력검사법 (dynamic visual acuity test) 등이있다. Fixation index=maximum SPEV with fixation/maximum SPEV without fixation 100 SPEV=slow phase eye velocity Fixation suppression index=100-fixation index 시고정지수가 70% 이상일때는시고정억제실패라고하며소뇌병변의가능성을고려한다. 수평반고리관의온도자극에의해수평성안진대신수직성안진이나오는경우를 caloric perversion이라하며, 안진의완서상속도의변화없이안진마다안진의크기에변동이있는경우를 dysrhythmia, 냉자극과온자극에대한안진의방향이서로바뀌어나오는경우를 caloric inversion, 안진 1) 검사원리회전자극의경우, 수직축에의한수평면상에서시계방향의회전시에는우측수평반고리관의흥분성자극과좌측수평반고리관의억제성자극에의해우향성수평성안진이유발된다 (Figure 5). 정현파회전운동시에는우향성회전에의한우향성안진과, 좌향성회전에의한좌향성안진이나타난다. 22 머리회전과반고리관반응과의관계를보면, 머리회전력은머리회전가속도에비례하며이는관성에의한내림프액의상대적이동에따른팽대부릉정움직임의가속도에비례한힘, 팽대부릉정속도에비례하는팽대부릉정과내림프액의마찰에의한힘, 팽대부릉정의움직임정도에비례하는팽대부릉정탄성에의한힘등과상반된다. 23 이러 S26
채성원. 반고리관기능의이학적검사 Figure 5. Velocity of horizontal slow-phase components of nystagmus. Chair rotations in the counterclockwise (CCW) direction evoke slow phases to the right, whereas rotation in the clockwise (CW) direction evokes slow phases to the left. Gain is determined from the responses by dividing the velocity of the first slow phase in response to the stimulus by the head velocity. Gain measures approximately 0.80 in these data and is symmetric for clockwise and counterclockwise rotations. 한관계에의한경우정현파형회전시머리회전주파수에따른이득과위상으로표현되는머리회전과안구의움직임과의관계있다. 전정안반사는 0.1~5 Hz 회전주파수영역에서작용하게되나, 임상적검사에서는회전의자, 머리고정등의문제로 1 Hz 이하의회전주파수영역에서검사를시행한다. 24 등속도회전운동시에는회전자극에대해팽대부릉정은편위되며이때팽대부릉정의최대편위의 37% 까지의편위에걸리는시간을팽대부릉정의시간상수 (time constant) 라한다. 지속적인등속도운동시구심성전정신경반응시간보다안진은길게나타나게되는데, 중추신경계에서말초전정감수기로부터의반응을저장하였다가방출함으로서저주파수회전이나등속도회전자극에대한반응시간을연장시키는작용을하게되는데이를속도저장이라한다. 속도저장유발에는내측전정핵으로부터의교차섬유 (crossing commissural fiber) 가중요한역할을하는것으로알려져있다. 속도저장은전정안반사에서반고리관뿐만아니라이석기관의자극에의해서도나타나며, 시운동계에서는시운동후안진으로나타나고체감각기자극에의해서도유발된다. 25 2) 검사방법 (1) 정현파회전검사 (slow harmonic acceleration test) 임상에서가장많이이용되는회전검사방법으로속도와방향을제어할수있는토크모터로움직이는의자에피검 Figure 6. Slow harmonic acceleration test. The gain is the ratio of slow-component eye velocity to the head velocity, which represents the response capability of the vestibular system through the frequencies tested. The phase demonstrates a timing relationship between the head velocity and the slow-component eye velocity through the frequencies tested. The difference between the two is defined as the phase angle and is expressed in a measure of degrees. Symmetry data demonstrates whether slow-component eye velocities are equal on both sides. 자를앉히고여러단계의속도로회전자극을주어나타나는전정안반사의반응을통해전정기능의상태를검사한다. 검사는빛과소리가차단된원통안에설치된의자에앉아실시한다. 26 수평반고리관이회전하는면에오도록피검자의머리를 30 전방으로굴전시킨상태에서의자에앉히고정현파진동으로의자를회전시킨다. 주파수는 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64 Hz로점점빨리자극하며, 최대각속도는 50 /sec이다. 전극을부착하여안구운동을기록하고컴퓨터는안구위치의신호중에서안진의빠른성분을제거하고느린성분의안구속도만을그려서분석한다. (2) 등속회전검사 (velocity step test) 의자를회전시켜나타나는회전중안진과갑자기회전을중지시킨후나타나는회전후안진을분석하는검사이다. 예를들어 1초간 100 /sec 2 로급격히가속회전시킨후 100 /sec로등속회전시킨다. 급격히가속시키면안진이나타나기시작하며점점안구운동의속도가빨라져서최대의초기안진속도 (initial slow component eye velocity) 를가진안구운동이나타나고, 등속운동중에는점차안진의크기가감소하여 1~2분전후에안진이소실된다. 안진이없어진후등속운동을하고있는회전의자를갑자기멈추면반대방향으로회전후안진이발생한다. 27 의자의회전방향이시계방향이면회전중안진은우측으로, 회전후안진은좌측으로나타난다. 반시계방향이면회전중안진은좌측으로, 회전 S27
Res Vestibul Sci Vol. 8, No. 2 Suppl. 1, Dec. 2009 Figure 7. Vestibulo-Ocular reflex to sinusoidal harmonic rotation in right unilateral vestibular neuritis patient. In acute phase, asymmetry shows directional preponderance to the left and phase lead is observed in test frequency. Figure 8. Time constant of right unilateral vestibular neuritis patient. Time constant is determined by the time after onset of the stimulus at which slow phase eye velocity has decreased by 67% of its initial value. 후안진은우측으로나타난다. 3) 검사의해석및임상적용정현파회전검사의검사결과의지표로위상 (Phase), 이득 (gain), 대칭등이있다 (Figure 6). 위상은최고자극속도와안구운동의느린성분의최고속도와의각차이이다. 정상에서안구운동의속도는회전하는의자의자극속도보다빨리나타나는데이를위상차선행 (phase lead) 이라고한다. 이득은회전자극의최고속도와자극의결과나타나는안진의느린성분의최고속도와의비율이며이속도가같으면그값은 1이되고안구운동이없으면 0이된다. 28 이득은피검자의각성상태와관련이많아검사시에각성상태를잘유지해야한다. 이득이 0.1 이하일때신호대잡음비가낮아위상과대칭의계산은의미가없다. 대칭 (symmetry) 은좌측회전으로나타나는안구운동의느린성분과우측회전으로나타나는느린성분의최고속도의비율이다. 중추혹은말초전정질환에서는위상차선행이정상보다더많이나타나 며, 비정상이라도병변의위치는알수없다. 29 이득의감소는한쪽의말초병변임을암시하며비정상적인이득의증가는전정억제가감소되는소뇌병변임을의미한다 (Figure 7). 어느쪽에병변이있는지를대칭단독으로판정할수있는가에대해서논란이있으며대칭을통해전정기능의회복의정도를알수있다. 시계방향회전의회전중안진과반시계방향회전의회전후안진은우측수평반고리관기능을나타내며, 반시계방향회전의회전중안진과시계방향회전의회전후안진은좌측수평반고리관의기능을나타낸다. 임상적으로신뢰성이있어많이이용되는지표는시간상수이며, 좌 우측시간상수를비교하여감소가있으면말초전정기능의이상으로생각한다 (Figure 8). 3. Pulse step sine test 평형감각의이상이발견된환자들의말초전정기관의기 S28
채성원. 반고리관기능의이학적검사 Figure 9. Pulse-step-sine (PSS) stimulus. The time course of the pulse, step, and sine rotational acceleration components of the PSS stimulus are shown separately and combined. The PSS acceleration waveform is integrated, the mean velocity is subtracted, and the velocity waveform is shifted in time to form a PSS rotational velocity waveform that begins at zero velocity. 능이상여부확인과병변부위의결정은매우중요한과정이다. 현재까지는앞서설명한두가지검사방법, 즉온도안진검사와회전검사가전정안반사에기초하는전정기능의정량적검사방법이었다. 그러나두검사모두전정기능검사의두가지목적인말초전정기관의이상여부를확인하는것과방향을결정하는것을충족시키지는못한다. 이에최근에소개된두부충돌검사 (head impulse test) 는위두가지목적을모두충족시키는검사법으로빠르게일반화되어가고있지만, 특정한실험환경을제외하고는검사시정량적인안구움직임의기록이어렵다. 이러한두부충돌검사의한계를극복하기위하여두부충돌검사의정성적평가방법이개발되었고이는평형기능의감소가있는쪽을찾아내는매우정확한방법으로생각된다. 두부의회전움직임은움직이지않을때의방전횟수와자 극시의방전횟수의차이에의하여뇌에각인된다. 만약억제방향으로충분히강한회전움직임을받는다면억제자극을받는쪽의신경활성도는완전히사라지게되는데이렇게한번완전히신경활성도를잃게되면더이상회전자극을뇌로각인시킬수없게된다. 양쪽세반고리관이정상기능이라면회전움직임은신경활성도가최고조에이르기전까지 350~400 spikes/sec의높은방전횟수로올라가게되고양쪽세반고리관의차이는방향성을갖는움직임으로뇌에각인시킬수있다 (Figure 9). 그러나한쪽세반고리관이손상되었다면손상된쪽으로의회전시정상쪽의신경활성도는감소되고신경활성도를잃게된다. 반대로정상기능을가진쪽으로회전자극을주면회전움직임은정확히뇌로각인될수있다. 임상적으로두가지요소를갖는주기적회전자극이평형기관의병변측을찾아내는데사용된다. 첫번째요소를 bias component, 두번째요소를 probe component라고하는데 bias component는더낮은빈도와더높은진폭으로회전움직임으로주기적으로방향을크게바꾸어신경활성도를잃게만드는역할을하며 probe component는 bias component한주기의서로다른구간동안평형기관의민감도를측정한다. 이러한두요소를주는방법은다양할수있으나 pulse-step-sine 자극은방향성을결정하는데적합하다. 30 요 반고리관의기능을측정하기위해흔히사용되는온도안진검사는병변의방향성을알려주나검사시간이오래걸리고환자에게심한어지럼증을유발한다. 회전검사는온도안진검사보다생리적인검사이나양쪽이동시에자극을받기때문에방향성에대한정보를주지못한다. Pulse step sine test는환자에게어지럼증, 오심같은검사상의괴로움이적고방향성을알수있는검사이다. 반고리관기능검사를올바르게이해하고임상적으로적절히해석하는것은어지럼증환자의진단과치료및예후관찰에매우중요하다. 약 REFERENCES 1. Torok N. Vestibular decruitment in central nervous system disease. Ann Otol Rhinol Laryngol 1976;85:131-5. 2. Mangabeira-Albernaz PL, Gananca MM, Martinelli MC, Novo NF, Rodrigues de Paiva E. Vestibular decruitment. A study of the phenomenon in a normal population. ORL J S29
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