Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Telecommunications relay service wikipedia , lookup
Olivocochlear system wikipedia , lookup
Lip reading wikipedia , lookup
Sound localization wikipedia , lookup
Hearing loss wikipedia , lookup
Noise-induced hearing loss wikipedia , lookup
Auditory system wikipedia , lookup
Audiology and hearing health professionals in developed and developing countries wikipedia , lookup
The Human Ear: The ear is described in three parts, outer, middle, and inner as shown in figure 1. The outer ear consists of the auricle and the ear canal. The auricle, the immediately visible part of the ear, collects the sound like a funnel and transmits the sound through the ear canal to the tympanic membrane in the middle ear . The tympanic membrane vibrates as the sound hits it; the vibration is tranmitted through the middle ear space by the three bones, the malleus, incus and the stapes, or, in English, the hammer, the anvil, and the stirrups; these are the three smallest bones in the human body. When the vibration reaches the stapes this results in fluid waves in the inner ear and sound is amplified by the hydraulic movement of the ear drum that is relative to the stapes. The hydraulic motion is not at the ear drum, but at the oval window in the cochlea--Alex Szatmary 5/15/08 8:09 PM The Eustachian tube that is connected to the middle ear helps to maintain the equalization of pressure between the middle ear and the outside atmosphere. As vibrations of the stapes reach the inner ear, the cochlea, which is a spiral chamber, like a snail, lined with fine hairs, stereocilia, to detect vibrations in the fluid mediumThis is a sentence fragment--Alex Szatmary 5/15/08 8:12 PM; these vibrations are from sound conducted through the timpanic membrane and the bones in the middle ear. The stereocilia then stimulate the auditory nerve, which sends the signal to the brain. Figure 1. Anatomy of the human ear. Causes of Hearing Loss: There are many causes of hearing loss. Some people lose their hearing slowly as they age- presbycusis; it happens when the tiny hair cells in the inner ear are fall out or are damaged. Another cause of hearing loss is Otosclerosis this is a disease involving the ossicles getting stiff and will not vibrate in response to sound. Some medications are known for their otoxicity if used in large quantities; examples of the ototoxic drugs are aspirin, drugs that are used in chemotherapy regimens, and aminoglycoside antibiotic. An exposure to extremely loud sound can cause hearing loss. A puncture of the ear drum, high changes in pressure and a heavy blow on the ear can all cause a hearing loss. Symptoms: A person with a hearing loss will normally ask the person they are speaking with to repeat themselves, they misunderstand what people say, it sounds like everyone is mumbling to them, they strain to hear and keep up with conversations, they have difficulty hearing on the telephone, they have difficulty hearing environmental sounds like a generator, yelling group of people etc. They read the lips of the person they are speaking with in order to follow what the person is saying. Types of Hearing Loss: The two major types of hearing loss are conductive and sensorineural (1). Conductive hearing loss is the kind of hearing loss where sound is not transmitted efficiently from the auricle through the timpanic membrane, to the ossicular bones (malleus, incus and the stapes). Conductive hearing loss could arise as a result of the fusion of the ossicles to other surrounding parts of the middle ear. Sometimes, it could just be that one of the ossicular bone is damaged or inactive for example, otosclerosis, the hardening of the stapes in the middle ear. Other causes of conductive hearing loss are ear infection, impacted ear wax, or birth defects. Depending on the cause, the condutive hearing loss is easily treatable. Sensorineural hearing loss results from damage to the inner ear or the nerve pathways from it to the brain(1). Most cases of sensorineural hearing losses are inherited; they may not always be apparent at birth, but they show up with age. Other causes of sensorineural hearing loss include certain kinds of antibiotics intravenously (e.g., gentamicin), exposure to loud noise, brain infection, viral infection in the inner ear, inadequate oxygen at birth. Generally, the sensorineural hearing loss cannot be surgically corrected, but can be overcome by the use of cochlea implant. Mixed hearing loss is a combination of the conductive and the sensorineural hearing loss (1). When a person has mixed hearing loss, it means that there are problems in both the middle and inner ear. The conductive part of the mixed hearing loss can be treated, but the sensorineural part could be permanent. II Treatments The Bone-Anchored Hearing Aid (BAHA): BAHA consists of a small titanium fixture, a percutaneous abutment (screw), and an electronic sound processor as shown in figure 2. (2). The titanium fixture is implanted into the mastoid bone (skull) during surgery. The titanium fixture is allowed to bond with the mastoid ( bonding takes a few months) bone before the screw and the processor is attached to it, so that it . After several months, the titanium fixture bonds with the mastoid bone tissue; this process is called osseointegration. The percutaneous abutment and the titanium fixture secure the sound processor. when the sound processor detects a sound, it transmits the sound vibrations through the abutment to the titanium fixture. The sound from the titanium fixture causes a vibration in the skull and stimulates the nerve fibers in the inner ear to allow hearing. BAHA is used for patients with chronic ear infection of the middle and outer ear, which is caused by conductive and mixed hearing loss. These patients cannot use the regular hearing aid that is connected to the ear canal, because the ear canal will be irritated; in order to avoid the irritation of the outer and middle ear, otologic surgeons recommend the BAHA because it bypasses the outer and middle ear to get to the inner ear. In a case where the patient has malformed inner and middle ear from birth, the BAHA can also be used. When a patient gets a hearing aid, they expect to get immediate results after the surgery. After the implantation of BAHA, the surgeons don’t attach the abutment and the processor to the titanium alloy, because it has to bond with the skull. This is not very good because it takes some months before bonding occurs. After the surgery, Since the abutment and the processor are not yet attached, the patient will be as good as deaf. Another downside of the BAHA is that it could be cumbersome; the patient cannot lay on that part of their head on a flat surface without having to detach the abutment and the processor. It is ok to detach them and relax, but in case of emergency, the patient will not respond fast because they are temporarily deaf. While detaching and attaching the abutment and the processor either or both could be misplaced. Figure 2. Bone anchored hearing aid Ossicular Reconstruction: This method of treating hearing loss can involve reconstruction of the ossicles, depending on what part of it is damaged. When the stapes are damaged, the Otologic surgeons may replace them with the patient’s incus. In the case where the more than one ossicular bone is damaged, either an autograft or a homograft is done (3). A homograft involves extracting a bone from genetically non-identical member, while an autograft is when a bone is extracted from one part of a person’s body and used on the same person. There are two major methods that are used during the ossicular reconstruction. In one of the methods the ossicular bones are joined together using a teflon cup and a shaft. The shaft fits into the drilled holes in the homograft or the autograft incus or malleus head; the teflon cup is placed on the stapes capitalum, and the ossicle is placed under the tympanic membrane. In the other method, only a teflon shaft is used. The shaft is fitted into a hole in the incus or malleus head, and the base of the shaft is placed on a footplate. When the bones are connected, the ossicle medial is placed onto the tympanic membrane. Over a decade ago, the choice to correct conductive hearing loss is bone reconstruction (3), but because of the problems associated with them, they are no longer commonly used. The common problem with the bone reconstruction is that when the bones are removed at the time of revision surgery, erosion and thinning of the bone occurs. If the thinning and erosion continues, the amount of sound waves that are being transmitted from the timpanic membrane to the cochlea will reduce, there by leading to a hearing loss all over again. In the case where a homograft is done, there is concern with disease transmission.Is there risk of rejection? -Alex Szatmary 5/15/08 11:11 PM To avoid disease transmission, an autograft can be done, but the patient would have to endure the pain from the extraction point and the ear surgery.Are there other reasons, e.g., length of time in surgery? -Alex Szatmary 5/15/08 11:13 PM This section is very much improved. Great! -Alex Szatmary 5/15/08 11:12 PM Reference: 1)“an overview of Hearing loss”, Patrick J. Antonelli.2002 2) “Bone anchored hearing aid” University of Maryland medical center.www.umm.edu/otolaryngology/baha.htm. 2002 3)“current use of implants in middle ear surgery”, Goldenberg A. Robert, Emmet R. John. Pages 145-152. 2001. 4)Farrier JB, ossicular repositioning and ossicular prosthesis in tympanoplasty. Arch otolaryngol 1960; 443-449 (5) “Required Biocompatibility Training and Toxicology Profiles for Evaluation of Medical Devices” http://www.fda.gov/cdrh/g87-1.html