**6. Study**

144 Hearing Loss

Taking into account estimates of amplification provided by outer hair cells, complete destruction of OHC'S alone could result theoretically, in a hearing loss of 60 dB. Early investigations in to OAE'S proved that they are not present when the sensorineural hearing

DPOAEs measures have shown excellent intra-subject test reliability which allows

Fig. 3. Basilar membrane displacements produced in cadaveric human cochlea in response

to 200Hz at 4 separate points of time. Envelope of travelling wave is also noted

Fig. 4. Schematic representation of travelling wave along basement membrane

loss exceeds 40-50dB (Collet L, 1989), (Gorga, Michael P, 1997).

monitoring of dynamic changes of cochlear function (V.Rupa, 2001)

In the study done in the ENT department of Christian Medical College India, 60 patients with history suggestive of mild head injury were evaluated over a period of six months.

INCLUSION CRITERIA: All patients with (a) history suggestive of Mild Head injury (MHI) Glasgow coma scale scoring system [GCS] 13 – 15 and improving (b) age between 6 – 60 years,(c) Patients discharged from casualty after observation period of 24 hours,(d) History of loss of consciousness of less than 20 minutes.

EXCLUSION CRITERIA: Patients with past history of ear disease, previous head injury or noise trauma. and patients having family history suggestive of autoimmune disease and hearing loss.

A detailed evaluation of the severity of injury using Glasgow coma scale scoring was done. Radiological investigations like X-Ray of skull (antero-posterior and lateral) and CT scan were used to detect skull fractures.

The external auditory canal and tympanic membrane were assessed to rule out any signs of temporal bone fracture like bleeding from external auditory canal, palpable step deformity, tympanic membrane perforation or haemotympanum. If the external auditory canal was filled with clotted blood patient was called for assessment after a period of one week. Eyes were checked for nystagmus and conjugate deviation. Facial nerve function tests were done and when the patient was cooperative facial nerve function was graded according to House Brackmann scale (House JW, &Brackmann DE 1985)

*Pure tone audiometry was done and Hearing thresholds of 15-25 dB across the frequencies were considered to be as normal.* Tympanometry was done using a probe tone frequency of 226Hz. An ipsilateral stapedial reflex at 1000 Hz was elicited. The ipsilateral acoustic reflex threshold was seen as normal if the level at which it is elicited falls between 70db and 100db.

DPOAE testing was done at 1000Hz, 2000Hz, 3000Hz, 4000Hz, and 6000Hz.

Repeat evaluation was done after a period of three and six months. A detailed otoneurological evaluation was done in all three visits and patients were specifically asked for symptoms of hearing loss tinnitus and vertigo
