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Doctor, how do my ears conduct sound?

Dear friends, good morning and TGIF!


Welcome back to TGIF Dr Euan's blog.


This week our blog post is a guest post written by Ms Maggie Huang, Principal and Experienced Senior Audiologist of iHear Center Pte Ltd. Let us delve into how ears conduct sound and how we hear.






Helen Keller states that “blindness separates people from things, deafness separates people from people.” Hearing is a fascinating sensory process that enables us to experience the richness of sound and communicate effectively with the world around us. Have you ever wondered how we hear these captivating sounds? Our ears are marvellously designed organs that play a crucial role in conducting and perceiving sounds.


The ear is a complex and delicate organ, divided into three main parts: the outer ear, the middle ear, and the inner ear. The journey of sound begins with the outer ear, which consists of the pinna and the ear canal. The pinna acts as a funnel that captures sound waves from the environment and directs them to the ear canal. Sound waves travel through the ear canal to the eardrum, causing it to vibrate.


The eardrum also known as Tympanic membrane is a thin oval structure that separates the outer ear from the middle ear. The middle ear is an air-filled cavity that amplifies sounds because of the lever and areal ratio advantage. The ossicles (malleus, incus and stapes) in the middle ear form a bridge that transmits the vibrations from the eardrum to the inner ear.


The cochlea in the inner ear has tiny sensory hair cells that convert the vibrations from the middle ear into electrical signals/impulses. These impulses are then transmitted via the auditory nerve to our brain. In the brain, these signals are decoded and interpreted to specific sounds we hear.


Image of the outer, middle and inner ear structure


Now that we have understood how we hear sounds and just how complex our auditory system is, it is important to note that with age or other factors like genetic disposition, medical condition or for idiopathic reasons, our hearing abilities may change over time. Hence, regular hearing assessments (such as audiometry test) is important in monitoring our hearing health to ensure that we never miss out on any precious sounds in our life.


In an audiometry test, our audiologist uses both air conduction (AC) and bone conduction (BC) to evaluate your hearing thresholds and diagnose potential hearing loss, if any. Air conduction (AC) test assesses the entire auditory pathway (from the outer ear all the way up to the auditory cortex in the brain). Hearing thresholds are mapped across different frequencies by our audiologist to understand the hearing sensitivity and determine the severity of hearing loss if any. In bone conduction (BC) test, our audiologist uses a bone vibrator to generate sound vibrations to stimulate the cochlea directly, bypassing the outer and middle ear. Through a comprehensive audiometry test, our audiologist can accurately diagnose the severity, type and site of the lesion causing hearing loss.


Image of an audiologist plotting the patient's hearing thresholds


Damage to any part of the auditory pathway affects sound transmission resulting in hearing loss. Hearing loss is a common condition that can affect people of all ages. A local study reported that in Singapore, more than 60% of people above the age of 60 suffer from hearing loss. Understanding the various types of hearing loss and their unique characteristics is crucial for early detection and appropriate timely management. Let’s now get to know the different types of hearing loss and the potential intervention options that can restore the joy of hearing.


Conductive hearing loss occurs when there is damage or blockage in the outer or middle ear that prevents sound waves from reaching the cochlea. Conductive hearing loss can be reversible depending on the cause of conductive hearing loss. Hence, medical treatment or surgery by the ENT doctor is recommended, such as aural toilet (removing earwax), treating ear infections, patching up the eardrum, repairing middle ear abnormalities, etc. However, for cases where medical intervention is not sufficient, you may consider consulting our audiologist for an alternative solution.


Sensorineural hearing loss results from damage to the cochlea or the auditory nerve. This type of hearing loss is often permanent and irreversible. A few causes that are commonly associated with sensorineural hearing loss include ageing, noise exposure, tinnitus, genetic factors, etc. At the moment, there is no medical intervention for sensorineural hearing loss.


Image of an audiologist selecting hearing aids for the patient


One of the most common and effective management options for sensorineural hearing loss is the use of amplification devices. Based on your hearing profile, lifestyle and listening needs, our audiologist at iHear will provide personalized solutions such as hearing aids, cochlear implants, and/or assistive listening devices to ensure you stay connected to the world of sounds.


Mixed hearing loss is a combination of both conductive hearing loss and sensorineural hearing loss. The treatment for mixed hearing loss depends on the specific cause, it may involve both the medical intervention by the ENT doctor and then the further management of residual hearing loss by the audiologist.


When sound transmission to the hearing brain is disrupted, it affects not only the hearing ability but also other aspects of our well-being. Many researches have shown that an undiagnosed or untreated hearing loss can have significant consequences on our life. Communication breakdown or struggling to hear speech clearly can lead to misunderstandings and social withdrawal and isolation. Thus, emotionally, individuals may experience anxiety, stress and even depression. Moreover, untreated hearing loss has been associated with a potential risk for cognitive decline, impacting memory and mental health.


Illustration of cognitive decline due to untreated hearing loss


Professor Frank Lin and his colleagues at Johns Hopkins found that individuals with hearing loss were up to five times more likely to develop dementia. Another study by the Lancet group reported that people with hearing loss without the use of hearing aids had over 42% increased risk of dementia, and up to 8% of dementia cases could be prevented with proper hearing loss management. The World Health Organization (WHO) also highlighted that hearing loss is the largest modifiable risk factor for dementia.


In addition, hearing loss can affect our overall productivity and quality of life. Therefore, it is essential to seek early intervention and treatment for hearing loss to mitigate these consequences and improve our overall well-being.


Image of the audiology clinic - iHear at Royal Square Novena


Don’t let hearing concerns hold you back from enjoying wonderful sounds in your life. Take the first step towards better hearing by scheduling an appointment today at iHear Center Pte Ltd or call 6904 9555 / 8809 1988 to book an appointment to embark on a journey towards improved hearing and quality of life.


If you would like to consult an ENT specialist about hearing loss, or any other Ear, Nose, or Throat related conditions, please feel free to Contact Us at Euan's ENT Surgery & Clinic or call 6694 4282 to make an appointment.


Have a great weekend ahead!


REFERENCES:


1. Durrant, J. D., & Feth, L. (2013). Hearing Sciences: A foundational approach. Pearson.


2. Hamill, T. A., Price, L. L. (2019). Anatomy and physiology of the ear. The Hearing Sciences: Third Edition, 197-248


3.Ho, E. C., Zhang, H., Ong, W., Li, K., Bei, Y., Medapati, S., & Seneviratna, A. (2018). Hearing impairment and hearing aid usage in Singapore. International journal of audiology, 57(4), 291–301.


4. Jiang, F., Mishra, S. R., Shrestha, N., Ozaki, A., Virani, S. S., Bright, T., ... & Zhu, D. (2023). Association between hearing aid use and all-cause and cause-specific dementia: an analysis of the UK Biobank cohort. The Lancet Public Health, 8(5), e329-e338.


5. Katz, J., Chasin, M., English, K. M., Hood, L. J., & Tillery, K. L. (2015). Handbook of Clinical Audiology (7th ed.). Wolters Kluwer.


6. Kral A. (2017). Pathophysiologie des Horverlusts: Klassifikation und Therapieoptionen [Pathophysiology of hearing loss: Classification and treatment options]. HNO, 65(4), 290–297.


7. Lee, J. C., Danker, A. N., Wong, Y. H., & Lim, M. Y. (2017). Hearing Loss amongst the Elderly in a Southeast Asian Population - A Community-based Study. Annals of the Academy of Medicine, Singapore, 46(4), 145–154.


8. Lin, F. R., Metter, E. J., O’Brien, R. J., Resnick, S. M., Zonderman, A. B., & Ferrucci, L. (2011). Hearing loss and incident dementia. Archives of neurology, 68(2), 214-220.


9. Stern, D., & Hilly, O. (2018). The relationship between hearing loss and cognitive decline in the elderly and the efficiency of hearing rehabilitation in preventing cognitive decline. Harefuah, 157(6), 374–377.


10. Zahnert T. (2011). The differential diagnosis of hearing loss. Deutsches Arzteblatt international, 108(25), 433–444.

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