The phenomenon of enhanced loudness rise (FUNGa)
To identify FUNG, a large number of tests have been proposed, united under the general name suprathreshold audiometry. The most common are the determination of the differential threshold for the perception of sound intensity according to Luscher, the index of small increments of intensity (IMPI, more often referred to as SISI – Short Increment Sensitivity Index), Fowler volume equalization (for unilateral hearing loss) and determining the threshold of discomfort.
The differential threshold (DT) for the perception of sound intensity is determined as follows: the patient is presented with a sound with an intensity of 40 dB above the hearing threshold, modulated in intensity in the range from 0,2 to 6 dB. Normally and with conductive hearing loss, a person distinguishes modulation with a depth of about 1,0-1,5 dB, while with hearing loss of cochlear origin, with an increase in the hearing threshold at the test frequency of at least 40 dB, the threshold of discernible modulation is significantly reduced and is approximately 0,4 dB. It is recommended to carry out the test by gradually increasing the modulation depth.
Determination of the index of small increases in intensity (SIS test) is carried out at a sound intensity of 20 dB above the hearing threshold. Every 4 seconds there is a short-term (200 ms) increase in the intensity of the presented tone by 1 dB. The patient is asked to note the increases in intensity he perceives, and then the percentage of correct answers is calculated.
In order to explain the research methodology to the patient, at the beginning of the test you can increase the amplitude of the intensity increase to 3-6 dB and only after that bring it to 1 dB and start counting. Normally and with impaired sound conduction, a person is able to distinguish from 0 to 20% of intensity increments.
With sensorineural hearing loss, accompanied by a violation of the loudness function, this figure increases significantly and can reach 100% with an increase in hearing thresholds by about 40 dB.
Fowler Loudness Equalization Test most often used for differential diagnosis Meniere’s disease and acoustic neuroma. Typically, this test is performed for unilateral sensorineural hearing loss, but it can also be used for bilateral hearing loss if the difference in hearing thresholds between the ears exceeds 30-40 dB.
First, a sound is delivered to both ears, the intensity of which corresponds to threshold values (for example, 5 dB to the right ear and 45 dB to the left). Then the intensity of the sound supplied to the affected ear is increased by 10 dB, and on the healthy ear the intensity is selected that causes a sensation of equal volume. Next, the sound intensity in the affected ear is again increased by 10 dB, and the procedure is repeated.
In the presence of FUNG, an increase in intensity in the worse hearing ear by 20-30 dB corresponds to an increase of 45-50 dB in the healthy ear. Fowler’s test in this case it is considered positive. Normally or with a retrolabyrinthine lesion, equal loudness is provided by equal increases in intensity in both ears. In this case Fowler’s test is assessed as negative.
The level of auditory discomfort is determined in the frequency range 250-8000 Hz. The sound intensity is gradually increased from a threshold value until the first signs of discomfort appear, i.e. before the patient evaluates his subjective sensations as “unpleasant.” Under no circumstances should the intensity of the sound reach the pain threshold. Normally and with sensorineural hearing loss accompanied by FUNG, the discomfort thresholds are 80-90 dB.
However, it should be taken into account that hearing thresholds in patients with sensorineural hearing loss are increased. Thus, their discomfort thresholds converge with their hearing thresholds. With conductive hearing loss, discomfort thresholds increase to 110 dB and higher or are not detected at all.
In differential diagnosis retrocochlear lesions The tone decay test also plays an important role. It consists of a stepwise (5 dB) increase in tone intensity, starting from a threshold value, until its perception becomes stable.
With intralabyrinthine pathology, stable (within 1 minute) perception of sound is achieved already at 5-10 dB above the threshold, while in patients with retrocochlear lesions, to achieve stable perception it is necessary to gradually increase the tone intensity to 35-40 dB above the threshold of audibility.
It should be emphasized once again that each of the suprathreshold audiometric tests has its own, most optimal, area of application. Due to the ease of implementation, the most widely used SIS test.
If a patient has difficulties analyzing sounds of near-threshold intensity, an adequate replacement for the SISI test can be DP test. Fowler’s test is currently used relatively rarely. However, it may well be used for unilateral or asymmetric hearing loss.
The ability to determine the size and configuration of the auditory field makes the test for determining auditory discomfort thresholds extremely important in hearing aids. The tone decay test, while not being informative regarding the presence and severity of FUNG, is nevertheless very important for the differential diagnosis of retrocochlear lesions of the auditory pathways.
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