Elektro-mehanički model kohlee i analiza odziva modela

Abstract

Pravilan rad svih čula omogućava čoveku normalno funkcionisanje u sredini koja ga okružuje. Oštećenje ili gubitak čula sluha otežava svakodnevni život, smanjuje mogućnosti za rad i društveni život i može dovesti osobu u stanje depresije. Gubitak sluha može biti posledica različitih uzroka, oštećenja različitih delova uva ili auditornih nerava. Poboljšanje sluha je najčešće moguće ostvariti primenom slušnih aparata i slušnih implanata. U zavisnosti od stepena i vrste oštećenja predlaže se odgovarajući implant – pasivni ili aktivni, kohlearni ili implant srednjeg uva, implant koji radi na principu provođenja zvuka kroz vazduh ili zvuka kroz temporalnu kost. Iako doprinose poboljšanju sluha svi implanti se ugrađuju operativnim putem što nosi dozu rizika. O čulu sluha se zna dosta i opet nedovoljno. O uvu, kao organu čula sluha, se zna dosta o njegovoj strukturi i funkciji. Kohlea, koja čini deo unutrašnjeg uva, ima složenu strukturu i dosta procesa se odvija unutar nje. Problem sa izučavanjem kohlee se ogleda u tome što je teško prikupiti eksperimentalne podatke. Kohlea je smeštena duboko u lobanji, gotovo nepristupačna i velika je verovatnoća da će doći do oštećenja prilikom merenja na živom pacijentu. Na taj način eksperimentalni pristup je veoma ograničen. S druge strane, kohlea brzo gubi svoja svojstva po nastupanju smrti, tako da nije moguć u velikoj meri ni rad na mrtvim kohleama. Zbog toga kompjutersko modeliranje kohlee i analiza odziva imaju veliku ulogu u ovoj oblasti istraživanja. Cilj ove teze je razvoj mehaničkih i elektro-mehaničkih modela kohlee koji opisuju normalno funkcionisanje kohlee i omogućavaju analizu odziva – posmatranje promene odziva sa promenom izvesnih parametara. Dovođenje u vezu uzroka oštećenja sa njegovom posledicom, odnosno promenom odgovarajućeg parametra koji utiče na oštećenje sluha, omogućava primenu modela u praksi. Modeliranje kohlee ima za cilj i utvrđivanje postojanja određenih signala koji ukazuju na oštećenje i predlog načina merenja. Na ovaj način je ustanovljena kohlearna mikrofonija i pojava otoakustičnih emisija koje se koriste za detektovanje čula sluha kod novorođenih beba. Modeli kohlee mogu da doprinesu i poboljšanju karakteristika slušnih implanata i njihovom boljem pozicioniranju. U ovom radu su predstavljeni mehanički i elektro-mehanički modeli kohlee koji su rešavani metodom konačnih elemenata i kao modeli u prostoru stanja. Prikazani su osnovni odzivi, izvršeno je poređenje sa određenim eksperimentalnim merenjima i rezultatima drugih modela iz literature i data je analiza dobijenih odziva. Dalji rad na razvoju ovih modela mogao bi da vodi do njihove primene u pretkliničkoj praksi, a nastavak istraživanja je usmeren na primenu u oblasti slušnih implanata.

Proper work of human senses allows normal functioning in the surrounding environment. Damage or hearing loss makes difficult everyday life, decreases possibilities for work and social life and can bring person to the state of depression. Hearing loss can be consequence of different causes, damage of different part of the ear or auditory nerves. Hearing improvement is usually possible to accomplish by applying hearing aids and hearing implants. In dependence of the level and type of damage certain implant is suggested – passive or active, cochlear or middle ear implant, implant that works on principle of air conduction of sound or bone conduction of sound, through the temporal bone. Although all implants contribute to improving of hearing, they are implanted during the surgery, which carrying a dose of risk. About hearing sense is known a lot of, but yet not enough. About ear, as organ of hearing sense, is known a lot about his structure and function. Cochlea, which makes part of the inner ear, has complex structure and a lot of processes are happening inside her. Problem with cochlear research is that it is hard to collect experimental data. Cochlea is placed deep inside the skull, almost unreachable and there is great possibility that it will be harmed during the experimental measurement on alive human. On that way experimental approach is very limited. On the other side, cochlea quickly loses its properties after death occurs, so it is not possible in larger scale to work with dead cochlea. That is the reason why computer modeling of cochlea and response analysis have great role in this research area. The goal of this thesis is to develop mechanical and electro-mechanical cochlea models which describe proper functioning of the cochlea and allow response analysis – observation of the response change with change of certain parameters. By combining cause of damage with his consequence, namely change of the certain parameter which has influence on hearing damage, model can be applied in practice. Modeling of cochlea has as one of the goal to establish existence of certain signals which pointing on damage and to propose way of signals measurement. On this way were established cochlear microphonic and appearance of otoacoustic emissions which are used for detection of hearing in newborn babies. Cochlea models can contribute in improvement of characteristics of hearing implants and their better positioning. In this work are presented mechanical and electro-mechanical cochlea models which were solved with finite element method and as models in state space representation. Most common responses are shown, comparison with specific experimental measurements and with results from other models from literature are performed and analysis of obtained responses is given. Further work on development of these models could lead to their application in preclinical practice, while future investigations in this area are directed to application in area of hearing implants.