ㅔ online ML Comm Korean J Otorhinolaryngol-Head Neck Surg 2007;50:846-53 DOI 10.3342/kjorl-hns.2007.50.10.846 보청기를이용한노인성 - 노화성난청의청각재활 가톨릭대학교의과대학이비인후과학교실 노혜일 Rehabilitation for the Elderly or Presbycusis Using Hearing Aids Heil Noh, MD Department of Otorhinolaryngology, The Catholic University of Korea College of Medicine, Seoul, Korea 서론 노령화현대사회에서노인성난청의재활에대한관심은높아지고있다. 일반인들도보청기와관련된많은지식들을지니고있고, 이비인후과의사들은청각사와함께보청기와관련된질문에정확한정보를제공할의무를지니게되었다. 따라서보청기관련정보를정확히이해하여일반인들에게쉽게설명할수있어야하고또잘못알려진관념을수정할수있어야하는데, 이를위해서는청각생리와관련된기초지식을꾸준히연구하고습득하여야한다. 이에저자는이분야를공부할때기초가되는몇가지간단한정보를질문과답변방식으로기술하여, 노인성난청의재활치료시당면하는어려움을해결하기위한방법적정보를제공하고자한다. 본론 난청과증폭된소리자극으로유도된중추청각계의신경가소성 (Hearing loss induced and augmented acoustic stimulus induced neural plasticity of the central auditory system) 질문 1: 보청기를이용한청각재활은중추청각계의어떤생리적현상을바탕으로일어나는가? 나이든뇌의신경세포의뉴런도손상, 퇴행과같은환경변화에대응하여새로운시냅시스를형성하고신경돌기에서가지를내어수지상돌기를수정하는능력을보유하고있다. 1,2) 즉신경계가손상이나퇴행성변화에대응하여신경섬유가가지를내고새로운시냅시스를형성하는데이를 반응성시냅시스형성 (reactive synpatogenesis) 이라하고이는나이가들어도지속되며, 젊은개체에서와같은적응적가소성 (adaptive types of synaptic plasticity) 을형성한다. 차이가있다면변화의속도가느리다는점이다. 3) 이런신경회로를변화시킬수있는능력이나이드는청각뇌안에, 달팽이관의퇴행변화후주파수지도의재배치 (reorganization of central frequency maps in response to age-related cochlear degeneration) 를가져오는현상으로이어지는데성인의뇌에서는이현상이대뇌피질에국한되어나타나며대뇌피질하의재배치는초기발달과정에서만가능하다. 4) 단, 난청으로유도된가소성이청력에이로운지해로운지는확실하지않은데그변화정도는두뇌피질로갈수록더분명해진다. 5) 적절한청각자극과증폭된소리자극이청각뇌의가소성을유도한다는사실은 C57 mice 를이용한음향심리검사에서증명되었다. 6) 이실험은연령별감각병리변화 (agerelated sensory pathology) 가잘나타나는 C57 mice 를이용하여 augmented acoustic environment 즉, 70 db SPL noise burst 소리자극을생후 25~55일사이에 12 hour/night으로받게한후 prepulse inhibition 현상을측정하여이값이나이가들어감에따라감소하지않는다는사실을확인하였다 (Fig. 1). Prepulse inhibition 은청성하구 (inferior colliculus) 를포함한상부중추청각계의매계로이루어지는데, 7) 이런동물실험들을통하여, 2,8-10) 증폭된소리자극은청각가소성에영향을미쳐사람의뇌에서도청각재활이이루어지도록한다는것을유추할수있게되었다. 사람의경우, 노인성난청과같은노화에의해생긴중추청각계의변화가보청기를통해증폭된소리자극에의 846
노혜일 AAE:augmented acoustic environment 100 ms PPI:prepulse inhibition S1: prepulse stimuli 10 ms (1ms) tone burst 70 db SPL S2 : 10 ms (1ms) 4 kh tone burst 100 db SPL Startling response measured by oscilloscope 70 db SPL noise burst (broad band noise rise/fall 10 ms, 200 ms duration) for 12 hr/night 25-55 days A C57 mice : 6-12 months/2-year Age-related sensory pathology B Fig. 1. Illustrations to explain the PPI (prepulse inhibition) experiments. A:C57 mice which show age-related sensory pathology were exposed to AAE (Augmented Acoustic Environment:70 db SPL noise burst of broad band noise rise/fall 10 ms, 200ms duration, for 12 hr/night 25-55 days), when they were 6-12 months of 2-year life span. B:After exposing the mice in AAE, startling response was measured with an oscilloscope to compare the PPI which occurs when a prepulse stimulus (S1) is presented 100 ms prior to an intense, startle-evoking stimulus (S2). 해다시바뀔수있는지를음향심리학적검사와전기신경학적검사를이용하여연구하였는데, 이를통해청각순응현상이실제로일어난다는것을알게되었다. 즉, 일정기간보청기를사용한후소리자극강도의증가에따른주관적크기변화가완만해지고자극크기변화를감지하는능력이보청기사용후 1개월에서 6개월사이에향상된다는것과 ABR의 wave V latency가감소하고 amplitude 가증가하는것을확인하였다. 11) 경중도난청뿐아니라심고도난청에서도보청기사용후한달에서 3개월후에는말소리분별력검사와주관적설문검사에서모두호전을보였다. 12) 보청기와관련된청각가소성 (Neural plasticity related with hearing aids) 질문 2: 임상에서가장흔히볼수있는보청기와관련된청각가소성은어떤것들이있는가? 일측보청기만을착용하는경우에일어나는현상은반대편말소리인지능력의저하로나타나는데, 13,14) 이를 lateonset deprivation effect라하고다시반대편에도보청기를사용하게되면부분적이라도회복이된다. 15,16) 신경세포들은시냅시스를형성하기위해경쟁하는입장이므로자극을받은쪽의입력신호가자극을받지못하는쪽의입력을압도하게된다. 이런현상을환경순응효과 (acclimatization effect) 17) 라고도하고, 이모든현상이중추청각계의가소성에의해일어나는점이며이능력이나이가들어감에도지속된다는사실이다. 임상에서도이현상을바탕으로청각재활이이루어진다. 적당한소리자극이난 청으로유도된가소성에의한중추신경의신호전달의변화와이에따른지각장애를극복하는데도움이된다는사실을알았으므로난청이생긴이후보청기를착용하도록하여청각뇌의가소성을유도하고청각재활이이루어지도록해야한다. 그러나실제임상에서보청기를이용한청각재활에는여러장벽이있다. 사회경제적인장벽과문화적인장벽질문 3: 실제임상에서보청기를이용한청각재활에는여러장벽이있는가? 이런이론적이바탕에도불구하고실제난청환자에서보청기를사용하는비율은미국의보고에의하면 18~20% 정도로추정된다. 18) 스웨덴에서시행한연구중에는실제난청을인식하여도 8% 만보청기를요청한다는보고가있고, 19) 독일의경우 40% 의노인인구가난청이있지만 60 ~69세사이는 4% 만이 70~75 세는 9% 만이보청기를사용한다보고하였다. 20) 우리나라에서는 2006년에발표된보건복지부통계 (2005 장애인실태조사, 서울 ) 에따르면전체청각장애인의 44.7% 가보청기를사용하고있다고는하지만임상에서병원을찾아오는난청환자중에서보청기를실제로착용하고계속사용하는경우는반을넘지못한다. 무엇보다도환자들은기대한것보다보청기기계자체의기능이떨어진다고생각하는데, 최근발전된기계공학의신기술 ( 디지털프로그래밍과디지털기계의압축기술, 다중마이크로폰, 소음억제기술등 ) 에도불구하고대부분기계의성능에만족하지못한다. 또한기계를사용하는것자체를두려워하는데, 20) 한편으로는기계공학의신 847
보청기를이용한노인성 - 노화성난청의청각재활 기술발달은보청기가격상승을가져오고이로인해실제경제적인문제가보청기를선택하는데결정적인역할을하기도한다. 따라서가격대비효율을고려한적절한보청기의선택과정확한맞춤과정이필요하다. 위의조건들이충족하여도보청기를거부하는중요한요인중하나가 stigma effect 이고, 이는보청기를사용하는것자체가난청으로의진입이며, 나이들어보이거나장애인으로보이며보청기를사용하는것은매우성가신일이라는관념이선입관으로작용한다. 이문제를해결하는방법은적절한상담기법의계발이다. 이에대해여러책에서보청기상담을할때여러가지유의할사항을명시하고있다. 이중저자가생각하는가장중요한부분은경중도난청의경우는환자자신이보청기가아직은필요없다고생각이들수있지만주위사람들이환자의난청을느끼고불편해할정도이면이미귀가상당히나빠진상태이며, 무엇보다도보청기착용후재활이잘되기위해서는말소리분별력이더저하되기전에시작해야한다는사실을환자가이해하도록설명해야한다는내용이다. 심고도난청의경우는인공와우수술의방법을같이설명하면서일단은일정기간보청기를사용하여청각수행여부를확인해야한다는것을이해시켜야한다. 일단환자들이보청기를사용하기시작하면서혜택을보게되면처음에가졌던선입관으로보청기사용을중단하지는않는다. 보청기사용과관련된비이과적인요소질문 4: 노인성난청의보청기처방시에고려해야할비이과적인요소들은어떤것이있는가? 노인성난청의환자의고막상태와외이도피부의탄력소실등이과적인요소들외에도환자의시력이나손의감각, 손의미세운동기능을살펴보아혼자서보청기를사용할수있고건전지의교환이나이물질청소를할수있는지판단하여보청기종류를선택하고, 무엇보다도가장중요한환자의사회활동여부와동기유무를고려한다. 인지기능장애를동반하였는지와경제적인문제도임상에서는청각재활을결정하는중요한요소가된다. 청각재활과인지장애와의연관성질문 5: 난청과인지장애가동반된환자의경우보청기를이용한청각재활이가능한가? 사람의음향심리연구결과를통하여청력손실과무관 848 하게나이가들수록시간신호처리 (temporal processing) 와양이신호처리 (binaural processing) 같은고난도의청력기술이저하되는것으로알려져있는데자극이복잡해질수록그정도가더욱분명해진다. 21) 노인성난청을인지과정 (cognitive process) 의장애와연관지어생각한다면말소리인지능력과전체적인인지과정과의역할을완전히분리할수는없다. 22,23) 단지특별한인지장애가없는경우에, 인지적으로건강하다고판단하는경우노인성난청과인지장애와의연관을굳이구분지어생각할필요는없다. 단몇가지말소리인지과정과관련된측면들을생각해볼수있는데첫번째가정보처리속도의저하이다. 인지전반에일어나는현상이기도하지만청력계의시간부호처리속도의저하와연관되어있다. 24) 집중력과단기암기력, 어휘력등과관련된지능이말소리분별력검사결과에영향을미칠수있다. 정리하면한정된인지능력을가지고난청상태에서왜곡된말소리를분석-이해하려면인지능력을충분히사용하여야하는데인지능력의저하가동반된경우결국말소리분별에장애를가져오게된다. 이를 information degradation hypothesis 라한다. 20) 언어처리과정 (speech processing) 과관련된인지요소로많이연구된항목이 working memory capacity 와음성학적인처리과정 (phonological processing) 이다. 25) 이중 working memory capacity 는짧은시간동안, 언어정보의보관과처리과정에할당되는인지시스템으로음성학적인처리과정과유사하며, 수기 (written) 와구기 (spoken) 언어처리과정에관여한다. 이능력이언어인지과정과관련된다는이론인데이를검사하는방법에 working-memory test와 verbal-information processing speed test가있다. 26,27) Working memory test 는주어지는숫자를계속더해가면서마지막에더한숫자들을기억해내는방식의검사들이다. 논리적인문장이냐아니냐를먼저판단하게한후끝에각문장과연관이있었던단어들을기억하는지알아보는검사이며, 22) 철자는다른데운음이같은지를판단하여말소리를인지하는데걸리는시간을측정한다. 23) 좀더간단하게인지기능을측정하는 visual digitmonitoring test는숫자들의나열을보고짝수-홀수-짝수의나열시짧은시간에인지하고반응하는능력을측정한다. 28,29) 이와유사한방식으로여러검사방법들이프로그램으로만들어져사용되고있다. 요약하면난청환자의언어이해에인지기능의역할은매우중요하다. 30) 따라서노화현상에따른인지기능저하의평가를할수있으면개인별청각재활의어려움과문제점을이해하는데많은 Korean J Otorhinolaryngol-Head Neck Surg 2007;50:846-53
노혜일 도움이된다. 인지장애를동반한경우도보청기를사용하도록권장하는데, 단, 보청기착용을도와줄보호자가반드시필요하며보호자의협조가재활성공의중요한변수로작용한다. 청각재활의수행능력의평가질문 6: 청각재활과정중수행능력의평가는어떤방법으로이루어지는가? 보청기를일정기간착용하고청력재활효과를평가하는방법으로는, 청력검사실에서말소리검사를시행하는객관적인검사방법과환자자신이주관적인평가를내리는설문-답변형보고서가있다. 31) 이두가지평가방법을통하여임상의사는환자로부터직접들어알아내는정보가정확한지알수있고, 이모든정보를통합하여보청기착용후문제점을평가하고재활치료를효율적으로진행할수있게한다. 또한일정기간재활치료후그목적을이루었는지확인하고언제치료를종결할지결정할수있다. 말소리분별력검사를통해서는어떤청취사항에서청취력이얼마나향상되었는지를확인할수있고자가평가방법으로는재활치료에대한환자자신의견해가포함된다 (Fig. 2). 우리나라진료현실상황에서이부분이일반적으로미흡한부분이다. 외국에서많이시행하고있는평가방법을참고하고우리현실에서도시행할수있는평가방법을개발하는작업이필요하다. 일단청각재활을시작한후이를적절히진행하기위해서보청기착용후적응기간을거친후수행능력의평가가이루어져야한다. 청력검사실에서시행하는말소리분별력검사를통해서는어떤청취사항에서청취력이얼마나향 상되었는지를확인할수있다. 문제는어떤청취환경을설정하고검사를시행하는데있다. 즉, 검사의목적이환자의일상생활에서의수행능력을보고싶다면가능한검사환경을일상생활과비슷하게설정하고모의실험상태에서검사를하는것이옳다. 그러나이는각개인의일상생활을그대로재현할수도없고재현한다하더라도이를통해얻는검사결과값의조건이각각다른상태에서이값은개인의절대값으로취급될뿐상대적인비교값의의미는없다. 따라서말소리분별력검사의한계는분명하다. 또한투자한검사시간과노력에비해다른검사방법으로도어느정도결과예측이가능하다. 31) 말소리표의선택은보청기착용자와비착용자에따라구분이있다기보다는검사의목적에따라음소단위의단음절표부터전후문맥파악이가능한문장에이르기까지사용할수있다. 단음절어를이용한경우보다는소음환경에서의문장청취력이주관적불편함을더잘반영하기는하는데, 32) 음소단위의검사를시행하는이유는짧은시간내에고음역청취력에대한정보를얻을수있기때문이다. 소음의영향을알기위해여러종류의소음을추가한다. 즉, 각각의주파수영역과크기를조절하고소리의반사와방향을알맞게설정한사운드필드 (Fig. 3) 에서검사하면된다. 31) 이렇게검사환경을실생활에맞게재현하여도청력검사실에서시행하는말소리검사로환자의청력수행능력을평가하는데는분명히한계가있다. 검사실결과와일상생활에의결과사이의상관관계는 0.61 을넘지못하며이는검사실결과의변화정도는실생활의변화정도를 40% 이 3.0 m Loudspeaker 1 Speaker 2 Evaluation of HA performance Client or patient and family member 3.6 m 45 1.0 m Speech identification test Self-report questionnaires Clinician or audiologist Probe microphone Fig. 2. Schematic drawing to show the relationship between the direct subjective information from the patient, objective report from speech identification test and indirect subjective self-report questionnaires. Fig. 3. Block diagram of equipment and apparatus for verifying HA response in audiology clinic test suite. The subject is 1 m in front of the loud speaker, the azimuth of the loudspeaker relative to the patient can be either 0 or 45 degree. 849
보청기를이용한노인성 - 노화성난청의청각재활 하만반영한다는의미이다. 33) 결국설정한검사환경에수행능력이절대적으로좌우되며환자가실제생활에서본인과가족이느끼는혜택의정도와는차이가있다. 그러므로실제보청기착용후의혜택정도를측정하기위해서는결국설문지형식의주관적보고서를이용한평가가필요하다. 이런목적으로여러종류의설문지가개발되었다. 설문법의분류를보면혜택의정도를직접평가하는 HAPI(hearing aid performance inventory) 처럼 64개의항목에대해 5단계로보청기착용이도움이되는지를평가하는데, 34) 이에비해착용전후를각각모두질문하는 APHAB(Abbreviated Profile of Hearing Aid Benefit) 35) 와 HHIE (Hearing Handicap Inventory of the Elderly) 36) 가있다. 전후비교의장점은환자가등급, 척도기준 (scale-subscale) 을동일하게이용하기때문에비교적정확한정량화가가능하다는점이다. 그러나설문내용이많아질수록환자들은이에답변하기를싫어하고여러상황을총괄하여질문에답변하기어려워하며질문자체를이해못하는경우도있다. 일부항목에대해서는각개인에해당사항이없는경우도많다. 이경우설문에의한측정값의신뢰도가떨어지며, 37) 임상의사도이를관리하고채점하기싫어하므로실용성을잃게된다. 이문제를해결하기위해개발된맞춤형설문방식이 GAS(Goal Attainment Scaling) 38) 와 COSI(Client Oriented Scale of Improvement) 39) 인데초기면접시환자에게어떤청취환경이중요한지를물어봐서일정재활치료기간이지난후다시얼마만큼의변화가있었는지를알아본다. 그런데이방법도각상황에따른환자마다의비중이다르므로정량화를위해서각상황에따른누진법을두도록한것이 GHABP(Glasgow Hearing Aid Benefit Profile) 이다. (40) 이방법이재활전후를비교하는데민감도는높지만설문항목이 56 항목으로늘어나는단점도있다. 또같은검사물 (test material) 과검사구성 (test format) 과측정단위를사용하여가능한객관적주관적평가방법의차이를최소화하기위해계발된 Performance-Perceptual Test(PPT) 는수행능력측정을위한평가방법의개선을위한수많은노력중하나이다. 41) 결국모든조건을충족하는이상적인설문방법은없기때문에알고자하는목적에충족하는설문방법을개발하여사용하면된다. 단설문방법을계발할때참조해야하는통계적지식이있는데, Demorest 와 Walden(1984) 의심리측정학과자가평가설문개발의기본원칙을지키면된다. 42) 설문지를개발하지않더라도외래추적검사시보청기의 1) 사용여부, 2) 사용후혜택정도, 3) 만족도, 4) 불편감, 5) 사회활동유무를질문하면청각재활이잘되는지를간단히확인하고예측도할수있다. 재활치료의추적검사와평가시기질문 7: 청각재활치료중, 적당한추적검사와평가시기는언제인가? 보청기맞춤이잘되었다고판단되는경우 1차적인재활치료의평가는보청기착용후 6주경에시작하고이후 3, 6, 12개월에한다. 일부자가수행평가는일부 3주부터안정된값을보이기시작하는데, 33) 2주는수행평가시점으로너무이르다. 43) 많은경우, 3개월과 6개월에수행능력평가를실시하며, 11,12) 10년의장기간추적검사를실시한연구에서도보청기를잘사용하는경우에처음 6개월때의평가가재활성공측정의시기라하였고, 44,45) 5년까지추적검사한연구에서주로보청기를포기하는경우가 1 년안에발생하므로 46) 이들시점을기준으로추적기간을정한다. 보청기를이용한청각재활의실패요인질문 8: 보청기를착용하다가포기하는경우는어떤이유가가장많은가? 처음부터보청기의적용기준이되지않는말소리분별력저하가심한환자나인지장애가있으면서돌봐주는사람이없는경우가아니라면보청기착용후중도포기하는가장큰이유는잘못된 fitting 등으로인한적응장애이다. 결국큰소리자극과소음환경에서의적응에실패하여중도포기를하는경우는대부분보청기를다시시도하지않기때문에정확한 fitting 의중요함을강조할수밖에없다. 최근 programmable hearing aids 의대중화로인해보청기를컴퓨터에연결하여청력역치값을입력하면자동으로 fitting 이되는 quick fitting(automatic fitting) 을많이사용하는데각보청기회사에서어떤 fitting 방식을사용하는지를명시하여도실제그방법이정확히적용되었는지일일이확인하기가어렵고청력역치값으로정해진 target gain 값이, 실이측정 (Real ear measurement) 을시행하지않으면, 각환자의귀에서정확히도달하였는지는알기가어렵다. 보청기의출력값은 2 cc-coupler를이용하여측정하고확인할수있지만실제귀에서의 SPL(sound pres- 850 Korean J Otorhinolaryngol-Head Neck Surg 2007;50:846-53
노혜일 BTE BTE HA 2 Probe microphone 5 mm Real Ear Analyser SPL measured in the real ear cavity 30 2cc-coupler output recorded in the test box Gain (db) 25 20 15 10 5 0-5 -10 250 500 1000 2000 4000 Frequency (Hz) RECD Fig. 4. Schematic drawing to show how the RECD (real ear to coupler difference) is calculated in the real ear analyzer by simply subtracting the coupler output in the test box from the real ear response of the HA in each subjects ear canal. The probe microphone is placed in the left ear canal approximately 5.0 mm from the tympanic membrane with the HA placed. sure level) 에는분명히차이가있으며이를 RECD(real ear to coupler difference) 라한다 (Fig. 4). 또한환자의주관적판단에의존하여 fitting 을하는경우에도여러문제점이있어전문가의정확한판단에의한 fitting 이환자의결정에의한 fitting 보다재교정하는횟수도적고적응도잘한다고알려져있다. 47) 정확한 fitting 을위해서는어떠한 fitting 방법을사용하느냐의결정은각자의경험과논리에따라다르겠지만 fitting 후환자의주관적인수행능력과객관적인실이측정방법을함께시행하여자신이선택한 fitting 방법이정확하다는것을검증해야한다. 이를위해충분한상담과계획적인정기검사를실시한다. 하이테크놀로지의보청기를처방할때는각환자의의사소통과신체적정신적, 사회적측면을고려하는총제적인방법으로접근해야재활에성공할수있다. 48) 보청기맞춤과정중, 주의사항질문 9: 말소리분별력저하가 50% 이하인경우 fitting 시주의할사항은? 말소리분별력이낮은사람일수록환자에게적응하는데시간이많이걸린다고충분히설명을하고계산된이득값의반이하로시작하여 3~4주간격으로 gain 을증가시켜여러번에걸쳐최종이득값에이르게한다. 이런경우는총적응기간이 1년이되더라도지속적인검사가이루어져야한다. 재활치료성공결정의환자측요소 질문 10: 말소리분별력이 50% 이상이고제대로잘맞춘보청기를착용한경우이를잘사용하여재활치료를성공적으로이루어내는데가장중요한환자측의요소는? 환자의사회활동여부와이에따른재활의필요성을인식하는태도와동기이다. 49,50) 즉환자가보청기의필요성을인식하여충분한적응기간을거쳐잘사용하는데는어느정도인내심이필요한데, 이런성격적인요소와난청을극복해야하는심적동기가중요한결정요소이다. 그러므로이를임상에서처음부터상담과정중미리파악하는능력이필요하다. 결 론 보청기를이용한좀더향상된노인성난청의청각재활을위해이분야의전문가들은지속적인기초지식의습득과상담기법을연마하고객관-주관적인평가방법을계발하며실제환자에서응용하는노력을계속해야한다. 이과정을통해임상에서어려움이많은노인성난청의청각재활을좀더효율적으로진행할수있다고생각한다. REFERENCES 1) Kaas JH. Plasticity of sensory and motor maps in adult mammals. Annu Rev Neurosci 1991;14:137-67. 2) Willott JF, Turner JG. Prolonged exposure to an augmented acoustic 851
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