Chapter Outline
Chapter Outline
| Process of interpreting the audiogram | Typical hearing loss patterns |
| Noise Induced Hearing Loss |
Educational Aims
After studying this chapter, you should be able to:
Identify different hearing loss patternsIdentify a Noise Induced Hearing Loss pattern
Assess the degree of hearing loss from the audiogram
Record the findings of the interpretation
Key Terms / Abbreviations
| Term / Abbreviation | Definition |
| dB | Decibel |
| DOL | Department of Employment and Labour |
| ENT | Ear Nose and Throat specialist |
| HTL | Hearing Threshold Levels |
| Hz | Frequency |
| NIHL | Noise Induced Hearing Loss |
| OHNP | Occupational Health Nurse Practitioner (Nurse) |
| OHP | Occupational Health Practitioner (Nurse or Doctor) |
| OMP | Occupational Medicine Practitioner (Doctor) |
| PLH | Percentage Loss of Hearing |
| PLHS | Percentage Loss of Hearing Shift |
| PTAC | Pure Tone Air Conduction |
| Term | Definition |
| Acoustic trauma | A common cause of sensory hearing loss. Damage to the hearing mechanisms within the inner ear may be caused by: Explosion near the ear. Firing a gun near the ear. Long-term exposure to loud noises (such as loud music or machinery).¹¹ |
| Air Bone Gap | The difference between the threshold level of air conduction testing and bone conduction testing.² |
| Air conduction Testing | In air-conduction testing, a pure tone is presented via an earphone. The signal travels through the air in the outer ear to the middle ear and then to the cochlea in the inner ear. Air conduction thresholds are usually marked with an O for the right side and an X for the left side. |
| Amplitude | The loudness or intensity (volume) of the sound is determined by the amplitude (height) of the sound wave. Amplitude is measured in decibels (dB)2 |
| Conductive Hearing Loss | Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles). |
| Frequency | Frequency is the speed of the vibration and this determines the pitch of the sound (highness and lowness of the sound). Frequency is measured in Hertz (Hz)2 |
| Hearing Threshold Level Shift | A threshold shift is an increase in the hearing threshold for a particular sound frequency. It means that the hearing sensitivity decreases and that it becomes harder for the listener to detect soft sounds. |
| Hearing Threshold Levels | Hearing thresholds are defined as the lowest level sound that can be heard 50% of the time. |
| Noise Induced Hearing Loss | Noise-induced hearing loss begins at the higher frequencies (3000 to 6000Hz) and develops gradually as a result of chronic exposure to sound levels equal to or above 85dB(A) (continuous exposure to loud noise over an extended period of time, such as noise generated in an engineering workshop). Although the loss is typically symmetric, noise from firearms or sirens may produce an asymmetric loss. NIHL can be caused by a one-time exposure to an intense “impulse” sound, such as an explosion often leading to acoustic trauma. Recreational activities can also cause NIHL such as target shooting and hunting, listening to MP3 players at high volume through earbuds or headphones, playing in band, and attending loud concerts. NIHL is 100% preventable. |
| Percentage Loss of Hearing Shift | Is the change in value of the PLH when compared to the reference value. |
| Percentage Loss of Hearing | Percentage Loss of Hearing (PLH) is a reference value for the hearing status of an individual against which loss can be measured however PLH does not necessarily indicate hearing loss. Instruction 171 introduced a measure of impairment termed percentage loss of hearing (PLH) which is calculated by using a series of tables based on a summation of hearing loss in each ear at the following frequencies: 500, 1000, 2000, 3000 and 4000Hz (COIDA, 2001). The PLH forms the principal criterion for assessing hearing status for compensation claims. |
| Pure tone air conduction (PTAC) | A pure tone is a single sound using one frequency related to one decibel measurement, at a time⁵ . Air conduction refers to tones presented through earmuffs, making use of air in the outer ear as a medium⁵. |
| Pure tone audiometry | Pure tone audiometry is a quantitative hearing screening test done to assess the nature and degree of hearing loss in adults and in children over about four years of age to carefully plan the most appropriate interventions. It is the rapid measurement of the hearing measured against a predetermined limit of normality. Pure tone air conduction and bone conduction tests determine whether or not there is any hearing loss; what type of hearing loss it is; the frequencies that are affected (configuration); and whether hearing loss is unilateral or bilateral. Even though pure tone audiometry is a useful measure of basic hearing function, it does not indicate how well speech is received or understood. |
| Sensorineural Hearing Loss | Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). Sensorineural hearing loss (SNHL) is due to problems of the inner ear, also known as nerve-related hearing loss. |