Which of the following procedures measures a patients hearing by using air and bone conduction?

Pure-Tone Air-Conduction Testing

Pure-tone air-conduction thresholds measure the function of the total hearing system, including the external, middle, and inner ear. In typical audiometric testing, pure tones that range in octave spacings from 125 or 250 to 8000 Hz are presented to the listener by headphones or insert earphones. Threshold is usually determined by the use of a version of Hughson-Westlake “ascending method,”4 in which sounds are initially presented well above threshold and are then presented in decreasing steps of 10 to 15 dB, until the sound is inaudible. The tone is then increased in steps that go up 5 dB, then down 10 dB, until the single hearing level at which a response is obtained three times is reached.5

Because air-conduction thresholds measure the acuity of the entire hearing system, when evaluated alone, they provide little information regarding the etiology of hearing loss and specific auditory pathology. However, when examined in conjunction with thresholds obtained by bone-conduction testing, they help determine the type of the hearing loss.

When plotted on an audiogram, pure-tone thresholds also provide information regarding the severity of the hearing loss. Thresholds that fall into the 0- to 25-dB range are considered normal, whereas thresholds above 25 dB represent various levels of hearing loss (seeFig. 134.1).

Pure-Tone Air-Conduction Thresholds

Pure-tone air-conduction thresholds help to appreciate the function of the entire auditory system, including both the auditory peripheral and the central pathways. In typical audiometric testing, pure tones that range in octave spacings from 250 to 8000 Hz are presented to the listener by headphones or insert ear phones. The threshold is usually determined by a version of the Hughson–Westlake ‘ascending method,’ in which sounds are initially presented well above threshold and are then presented in decreasing steps of 10–15 dB until the sound is inaudible. The tone is then increased in ‘up 5-dB, down 10-dB steps’ until the single threshold at which a response is obtained three times is reached. Because air-conduction thresholds measure the acuity of the entire hearing system, when evaluated alone, they provide only limited insight into the etiology of hearing loss and specific auditory pathology. However, when examined in conjunction with thresholds obtained by bone-conduction testing, they help to determine whether an auditory impairment is conductive, cochlear (sensorineural), or both (mixed). Audiometric thresholds are measured in decibels relative to population normative values (0 dB hearing level (HL)). Thresholds that fall into the 0–20-dB range are considered normal. Hearing loss may be termed as mild (20–40 dB), moderate (40–60 dB), severe (60–90 dB), or profound (>90 dB).

Air Conduction.

Pure-tone threshold hearing sensitivity is the subjective procedure by which auditory sensitivity is determined. In the United States, the American National Standards Institute (ANSI) has established standards for the calibration of clinical audiometers. The output sound pressure level for standard circumaural or inserted earphones, or both, is specified when measured in a standard coupler, referred to as anartificial ear. The artificial ear simulates the impedance characteristics of the average human ear at the plane of the tympanic membrane. The decibel levels used in audiometers for the normal threshold for air conduction can be found in other publications.5

To assess hearing loss by air conduction, the examiner determines the magnitude (in decibels) by which the patient's hearing deviates from the 0-dB hearing level (i.e., normal hearing). To determine hearing loss, hearing sensitivity is assessed at octave frequencies between 250 and 8000 Hz. There is increasing interest in assessing hearing between 8000 and 16,000 Hz, but testing in the ultra-audiometric range (10 to 20 kHz) is not routine.

In summary, pure-tone air conduction testing is the initial and critical measurement for subjective hearing loss. The measure provides an indication of the magnitude and configuration of the hearing loss as a function of frequency. However, little differential diagnostic information can be obtained from this description of audiometric configuration because auditory system dysfunction at various anatomic sites may result in similar patterns of loss of sensitivity. Other hearing tests have been developed for the purpose of distinguishing among the various sites of auditory dysfunction.

B. Measurement Issues

Pure-tone air- and bone-conduction audiometry is the standard method to clinically assess hearing loss [93,104]. During this test, tones are presented at various intensities to determine, with a bracketing procedure, the minimum volume detectable (threshold). Hearing loss is measured in decibels with respect to normative data; a 25 dB HL loss means the person does not hear a sound until it is presented at a volume 25 dB louder than that detectable by a person with normal hearing. Usually a series of frequencies is tested from 250 Hz to 8000 Hz, but thresholds for very high frequency sound (9000 Hz and above) can also be measured. The range most important for understanding speech is 500–2000 Hz, with higher frequencies (3000–8000 Hz) contributing to distinguishing some consonant sounds.

Other forms of hearing testing include speech understanding tasks that test the ability of the listener to correctly interpret complex sound (speech) [105,106]. These tests usually adjust the presentation level for the person's hearing level in order for the volume to be perceived as similar across subjects. Listening tasks may be made more challenging by degrading the sound of the recording or presenting a competing message to ignore. These tests generally are used in conjunction with air- and bone-conduction audiometry to assess the potential benefit from hearing aids.

In epidemiologic studies, audiometric testing requires a sound-treated room to be in compliance with standards for maximum permissible ambient noise levels, calibrated audiometers, and highly trained personnel. The involvement of experienced, certified audiologists in designing testing facilities, training and supervising technicians, and conducting periodic calibrations (every six months) is essential for high quality data collection. Standard testing techniques such as those recommended by the American Speech Hearing and Language Association are designed to generate reliable and consistent thresholds (within ±5 dB HL) [104].

Although there are reliable standard assessments of hearing sensitivity, epidemiologic studies have been hampered by the lack of a consistent definition of hearing loss. Studies have reported mean (or median) thresholds by frequency, by the percentage of people with abnormal thresholds for each frequency tested using various standards for abnormal (>25 dB HL, >40 dB HL, etc.), or they have applied a cut-point to determine if the average of the pure tone thresholds (PTA) at several frequencies is abnormal [107–112]. While some studies used a three frequency average of thresholds at 500, 1000, and 2000 Hz, and others included 3000 Hz or 4000 Hz, a PTA above 25 dB HL has usually been considered abnormal. Some studies have classified an individual as affected if the better ear PTA was abnormal and some studies have classified people as hearing impaired if the PTA was abnormal in either ear.

Few epidemiologic studies in this country have been able to use audiometric testing to obtain performance-based measures of hearing. Some epidemiologic studies have relied on questionnaires to determine prevalence of hearing loss. Unlike some other areas in chronic disease epidemiology, there have been few attempts to employ validated and standardized questions of hearing loss. Questions have varied from ascertaining mild degrees of hearing loss to profound deafness. One study did compare the sensitivity and specificity of several questionnaire approaches to audiometric measures of hearing loss and found that a simple question, “Do you feel you have a hearing loss,” was the best self-reported measure of hearing loss [113].

The screening versions of the Hearing Handicap Inventory (versions exist for adults and for the elderly), developed by Weinstein and Ventry, are in wide use clinically to detect people who might benefit from amplification [114–116]. This questionnaire was designed to measure self-perceived handicap from hearing loss and has been validated with audiometric data.

The Promise of Implantable Hearing Devices

The limitations of traditional air conduction hearing aids have been the driving force behind a new generation of implantable hearing devices. Implantable hearing devices face most of the same challenges as traditional aids. They also have the added risk of requiring surgery for their placement and are potentially more expensive. Yet their allure includes the possibility of improved signal-to-noise ratios, greater amplification/gain potential, loss of distortion and feedback, elimination of the occlusion effect, greater dynamic range, and improved cosmetics. For some who simply cannot wear a hearing aid because of underlying anatomic problems or extreme discomfort, they may be the only option.

It is widely accepted that implantable hearing devices should provide distinct advantages over conventional hearing aids, including better cosmetics, improved fidelity, broader frequency response, less distortion, reduction or elimination of feedback, and better speech understanding, without reducing residual hearing, limiting patient activities or predisposing patients to infection.12,13 In other words, they should be at least as good as, and preferably better than, the best available noninvasive method of hearing rehabilitation: binaural amplification with the best available aid.14

Although significant strides have been made in many of these areas, implantable hearing devices have yet to deliver on all these features. There also remain questions regarding the candidacy for implantation and willingness of patients to accept the costs and surgical risks. As noted by Junker and colleagues, the number of patients in a fairly typical population of hearing impaired individuals who would be considered realistic candidates is limited, on the order of 0.09%.15 The market for implantable hearing devices may therefore not be sufficiently large to support the current array of device manufacturers. The 2002 financial failing of Symphonix Corp, the first company to clear U.S. Food and Drug Administration (FDA) hurdles and market their implantable middle ear hearing device in the United States, strongly underscores this point, as do the subsequent withdrawal of the Soundtec and TICA (totally implantable communication assistance device), as well as the financial issues surrounding the Carina device described in the review of technologies that follows.

The focus of the remainder of this chapter will be to critically review the advantages and disadvantages of each of the implantable hearing devices that are either in development or already in clinical use. Lastly, osseointegrated bone-conducting hearing prostheses (OBHPs), which are widely used in hearing rehabilitation for conductive and single sided deafness (SSD), will also be discussed.

10.6.1.3 Rinne Test

The Rinne test compares air conduction to bone conduction. Tap the tuning fork firmly on your palm and place the butt on the mastoid eminence firmly. Tell the patient to say “now” when they can no longer hear the vibration. When the patient says “now”, remove the butt from the mastoid process and place the U of the tuning fork near the ear without touching it.

Tell the patient to say “now” when they can no longer hear anything. Normally, one will have greater air conduction than bone conduction and therefore hear the vibration longer with the fork in the air. If the bone conduction is the same or greater than the air conduction, there is a conductive hearing impairment on that side. If there is a sensorineural hearing loss, then the vibration is heard substantially longer than usual in the air.

Make sure that you perform both the Weber and Rinne tests on both ears. It would also be prudent to perform an otoscopic examination of both eardrums to rule out a severe otitis media, perforation of the tympanic membrane or even occlusion of the external auditory meatus, which all may confuse the results of these tests. If hearing loss is noted, an audiogram is indicated to provide a baseline of hearing for future reference.

Rinne Test

The Rinne test compares air conduction to bone conduction. Tap the tuning fork firmly on your palm and place the butt on the mastoid eminence firmly. Tell the patient to say “now” when they can no longer hear the vibration. When the patient says “now,” remove the butt from the mastoid process and place the U of the tuning fork near the ear without touching it.

Tell the patient to say “now” when they can no longer hear anything. Normally, one will have greater air conduction than bone conduction and therefore hear the vibration longer with the fork in the air. If the bone conduction is the same or greater than the air conduction, there is a conductive hearing impairment on that side. If there is a sensorineural hearing loss, then the vibration is heard substantially longer than usual in the air.

Make certain that you perform both the Weber and Rinne tests on both ears. It would also be prudent to perform an otoscopic examination of both eardrums to rule out a severe otitis media, perforation of the tympanic membrane or even occlusion of the external auditory meatus, which all may confuse the results of these tests. If hearing loss is noted, an audiogram is indicated to provide a baseline of hearing for future reference.

Results

Success is measured by improved air conduction, improved speech discrimination, and more benefit from a hearing aid. In our surgical experience with 72 patients with far advanced otosclerosis, the average hearing gain was 20 dB, and 70% benefited more from a hearing aid.26

Discrimination was improved by more than 15% in 54% of cases. In addition, there is a high correlation of success between ears: a patient who gained hearing after surgery in one ear also did well in the other; a patient who did not achieve a good result in the first ear did not do well in the second ear. The results of stapedectomy for far advanced otosclerosis are often dramatic. They reinforce the surgeon’s resolve to double-check patients with no measurable hearing.

Functional and Structural Airway Zones

•

Conducting zone

Function

Air conduction only

Components

Trachea

Bronchi

Bronchioles

Branching p attern

Dichotomous : Parent airway divides into 2

Asymmetric : Variable diameter

Structure

No alveoli in airway walls

No gas exchanging epithelium

Transitional zone

Function

Air conduction

Respiration

Components

Respiratory bronchioles

Alveolar ducts

Branching pattern

Dichotomous

Symmetric

Frequently trichotomous or quadrivial

Structure

Airway walls contain alveoli

Enable gas exchange

Respiratory zone

Function

Respiration only

Gas exchange

Components

Alveoli

Alveolar sacs

Branching pattern

Dichotomous

Structure

Thin walls

Contact with capillary membrane

Macroscopic Anatomy

•

Tubular structure designed solely for air conduction

a.k.a. windpipe

∼ 10-12 cm long

∼ 2.0-2.5 cm in diameter

Extends from cricoid cartilage to carina

Superior border contiguous with larynx

Branches distally at carina to become mainstem bronchi

Runs directly anterior to esophagus within mediastinum

Protected anteriorly by rings of flexible cartilage

15-20 rings

C- or U-shaped

Prevents collapse or obstruction of airway

Posterior aspect is flat and devoid of cartilage

Instead contains trachealis muscle and membranous fibroelastic connective tissue

Flexible connective tissue allows for expansion of adjacent esophagus during consumption of food and liquid