AudiologyOnline Phone: 800-753-2160


Shoebox - Learn More - January 2024

Carhart's Notch - New Research Findings

Diana C. Emanuel, PhD, CCC-A

June 8, 2009

Share:

Question

Why does the Carhart notch appear at 2000Hz in otosclerotic patients and at no other frequency?

Answer

An audiometric finding characteristic of otosclerosis is an increase in bone conduction (BC) threshold with a peak at 2,000 Hz known as Carhart's notch (Carhart, 1950). Although the notch occurs at 2,000 Hz, a reduction in bone conduction sensitivity is seen from 500 to 4,000 Hz which is, on average, 5 dB at 500 Hz, 10 dB at 1000 Hz, 15 dB at 2000 Hz, and 5 dB at 4,000 Hz (Carhart, 1971). Carhart attributed this phenomenon to "mechanical factors associated with stapedial fixation." The Carhart notch is not a true indication of "cochlear reserve" and this BC loss may be corrected by successful stapes surgery (Tonndorf, 1971). Carhart (1971) and Tonndorf (1971) provided a review of several theories to explain this phenomenon. Further, Tonndorf (1971) provided a summary of the results of his studies of stapes fixation in various mammals (cats, dogs, guinea pigs, rats, and humans). Tonndorf (1971) explained that the magnitude of the Carhart notch depended on the extent the middle ear contributed to the total BC response in each of the species tested. Further, he explained the frequency of the notch varied depending on the natural (resonance) frequency of the ossicular chain for BC signals.

It has been well established that the resonance frequency of the middle ear for air conducted (AC) stimulation is around 800-1200 Hz (e.g., Margolis et al., 1985). So why is the Carhart notch seen at 2,000 Hz? The answer is because the primary resonance of the ossicular chain for BC signals differs from the primary resonance of the chain for AC signals and is about 1600-1700 Hz (Zwislocki, 1957). Thus, for any BC disorder that decreases the mobility of the ossicular chain, the 1600-1700 Hz frequency range is affected most prominently. The reason that the Carhart notch is seen audiometrically at 2000 Hz is because 2000 Hz is the closest frequency tested in a typical hearing threshold measurement.

Recently Homma and colleagues (2009) published a fascinating study on ossicular chain resonance based on the differences in response to AC and BC stimulation of five human temporal bones. Their research offers additional clarity on the issue of vibration modes of the middle ear. According to their data, the ossicular chain has two basic modes of vibration. The first mode, with a peak around 1200 Hz, is the primary mode for AC stimulation. This mode is associated with a "hinging" motion of the ossicles caused by AC stimulation of the tympanic membrane at the umbo. The second mode, with a peak around 1700 Hz, is described as a "pivoting" motion of the malleus/incus, with an axis of rotation somewhat orthogonal to the axis of rotation associated with the "hinging" motion. The second mode is less robust than the primary mode for AC stimulation, but it is the dominant mode when excited by BC stimulation. A decreased mobility of the ossicular chain at 1700 Hz due to otosclerosis also affects the surrounding frequencies, but is seen most prominently as a BC loss at 2000 Hz in audiometric testing.

References

Carhart, R. (1950). Clinical application of bone conduction audiometry. Archives of Otolaryngology, 51, 798-808.

Carhart, R. (1971). Effects of stapes fixation on bone-conduction response. In I.M. Ventry, J.B. Chailkin, & R.F. Dixon (Eds.), Hearing measurement: A book of readings (pp. 116-129). New York, NY: Appleton-Century-Crofts.

Homma, K., Du, Y., Shizmu, Y., & Puria, S. (2009). Ossicular resonance modes of the human middle ear for bone and air conduction. Journal of the Acoustical Society of America, 125, 968-979.

Margolis, R. H., Van Camp, J., Wilson, R.H., & Creten, W.L. (1985). Multifrequency tympanometry in normal ears. Audiology, 24, 44-53.

Tonndorf, J. (1971). Animal experiments in bone conduction: Clinical conclusions. In I.M. Ventry, J.B. Chaiklin, & R.F. Dixon (Eds.), Hearing measurement: A book of readings (pp. 130-141). New York, NY: Appleton-Century-Crofts.

Dr. Diana Emanuel is a professor and the Audiology Graduate Program Director at Towson University. She can be reached at demanuel@towson.edu.

Dr. Emanuel would like to acknowledge the thoughtful criticism and suggestions of Dr. Tomasz Letowski on the original posting of this ATE in 2002;his suggestions led to this revised answer.


Diana C. Emanuel, PhD, CCC-A

professor and the program director for the Doctor of Audiology (Au.D.) program at Towson University

Diana C. Emanuel, Ph.D. is a professor and the program director for the Doctor of Audiology (Au.D.) program at Towson University. She earned her bachelor’s degree from Towson State University (1988) and her M.S. (1990) and Ph.D. (1993) from Penn State. She teaches in the areas of hearing science, audiology diagnostics, and anatomy and physiology of the auditory system. Her research interests include behavioral auditory processing assessment, hearing science, and pedagogy in Communication Sciences and Disorders. Dr. Emanuel is the co-author of Hearing Science (2009), which provides a student/instructor-friendly approach to learning and teaching hearing science.


Related Courses

Empowerment and Behavioral Insights in Client Decision Making, presented in partnership with NAL
Presented by Simon Alperstein, MSc BE, Paola Incerti, MAudiology, AAudA
Recorded Webinar
AudiologyOnline

Presenters

Simon Alperstein, MSc BEPaola Incerti, MAudiology, AAudA
Course: #37124Level: Intermediate1 Hour
  'The information was relevant, and I was able to relate to example given and found the suggestions to address these could be implemented in clinic'   Read Reviews
Behavioral Insights can be used to understand and support hearing health decision-making, particularly in the appointment setting. An overview of empowering the individual's first awareness of hearing loss to hearing aid fitting and then to becoming an active hearing aid user will be covered.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Innovative Audiologic Care Delivery
Presented by Rachel Magann Faivre, AuD, Lori Zitelli, AuD, Heather Malyuk, AuD, Ben Thompson, AuD
Recorded Webinar
AudiologyOnline

Presenters

Rachel Magann Faivre, AuDLori Zitelli, AuDHeather Malyuk, AuDBen Thompson, AuD
Course: #38661Level: Intermediate4 Hours
  'Clear information, a bit lengthy'   Read Reviews
This four-course series highlights the next generation of audiology innovators and their pioneering approaches to meeting unmet audiologic needs in their communities and beyond. This peer-to-peer educational series highlights researchers, clinicians, and business owners and their pioneering ideas, care delivery models, and technologies which provide desperately needed niche services and audiologic care.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

20Q: Healthy Hearing Over the Lifespan - Effective and Efficient Diagnostic Assessment
Presented by James W. Hall III, PhD
Text/Transcript
AudiologyOnline

Presenter

James W. Hall III, PhD
Course: #37136Level: Intermediate1 Hour
  'Very applicable'   Read Reviews
Accurate diagnosis and effective management of hearing loss is best achieved with a patient-specific test battery that includes sensitive measures of peripheral and central auditory function. Healthy Hearing Over the Lifespan - Effective and Efficient Diagnostic Assessment reviews an approach for selection of auditory test procedures based on patient history and chief complaint, and their likely value in early detection and accurate diagnosis of impaired hearing function and related disorders, such as tinnitus. With careful analysis of the pattern of results for a patient-specific test battery, and consideration of information from patient history including comorbid conditions and lifestyle factors, audiologists have an opportunity to prevent or mitigate hearing loss over the lifespan.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

20Q: Assessing Auditory Wellness in Older Adults
Presented by Larry E. Humes, PhD
Text/Transcript
AudiologyOnline

Presenter

Larry E. Humes, PhD
Course: #37392Level: Intermediate1 Hour
  'The importance of considering the patient's perceived hearing difficulties in determining intervention'   Read Reviews
A discussion of perceived hearing difficulty in adults, including correlation with pure-tone audiometry, relationship to auditory wellness, and effect on candidacy for intervention.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Navigating Case History, Candidacy and Clinical Considerations for Vestibular Evaluations
Presented by Kaitlin Ryan, AuD, CCC-A
Recorded Webinar
AudiologyOnline

Presenter

Kaitlin Ryan, AuD, CCC-A
Course: #38933Level: Intermediate1 Hour
  'Great presentation'   Read Reviews
This course will help audiologists and vestibular providers alike solidify their knowledge of obtaining a case history and other patient information that is useful for vestibular testing. Asking more direct questions, determining candidacy, using functional assessment tools, helping to appropriately counsel, and clinical considerations for testing are covered in this course.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Our site uses cookies to improve your experience. By using our site, you agree to our Privacy Policy.