Pure Presbycusis refers to the
hearing loss which occurs with physiological aging. Schuknecht divided
"Pure Presbycusis" into sensory, neural, strial (metabolic)
and cochlear conductive.
- Sociocusis (4) non-work
related noise induced hearing loss.
- Nosocusis (4) refers to hearing loss
caused by other factors than noise and pure presbycusis (aging).
Accounting for presbycusis is not mandatory
but it is often done in the legal setting. What is actually sought
is to account for non-occupational hearing loss. Seven states allow deductions for
presbycusis.
NIOSH does NOT recommend accounting for
presbycusis when looking for Medical Causation of a progressive hearing
loss, NIOSH
states in DHHS (NIOSH) Publication No. 98-126 Section 5.1: "NIOSH
does not recommend that age correction be applied to an individual's audiogram
for significant threshold shift calculations. Although many people experience
some decrease in hearing sensitivity with age, some do not. It is not possible
to know who will and who will not have an age-related hearing loss. Thus,
applying age corrections to a person's hearing thresholds for calculation of
significant threshold shift will overestimate the expected hearing loss for some
and underestimate it for others, because the median hearing loss attributable to
presbycusis for a given age group will not be generalized to that experienced
by an individual in that age group."
1) Measuring Presbycusis:
Two researchers have pooled a variety
of research study data to determine the level of presbycusis and have developed two equations to calculate
presbycusis. Both of these studies found differences in presbycusis
between male and female subjects.
- Robinson Sutton's Equations (6): These
equations were derived by combining a number of studies and are adopted for
the values in ISO-1999 Annex A (3). International Standards
Organization, Annex A estimates hearing levels for an industrial population
that was screened for exposure to gun and intense industrial noise.
- Spoor's Equations (10): Combined data
from 8 different studies. Spoor accounted and controlled for noise in
the derivations of his equations.
 In addition, OSHA (Occupational Safety and
Health Administration) has published correction values for aging. These
values will correct threshold frequencies of 1000 Hz to 6000 Hz. Since no
values are given for 500 Hz, this method can only be used with the NIOSH and
Wisconsin equations. These values are greater than those given by
Robinson Sutton's Equations. However, when used to evaluate hearing loss
progression, they are subtracted from baseline values. For age 20
and below these values are not zero but vary from 3 dB to 8 dB.
In addition, the correction values also do not change above the age of 60,
and there is no noise-presbycusis compression factor. The lack
of a compression factor will tend to cause this method to predict higher
values for aging in audiometric data.
Several researchers have studied primitive
cultures to determine the influence of aging on hearing acuity in the absence of
occupational noise (1,7). These studies found aging effects on hearing,
but observed no sex difference in the hearing loss (1,7). Animal studies
have also found no sex difference (2). It has been proposed that the
difference between male and female thresholds as a function of age, is due to
environmental factors. The most important of which is noise exposure
(4).
Goycoolea (1) studied the natives on
Easter Island and found equal hearing thresholds in males and females of similar
ages. Males, from the island, who
lived and worked in modern society had a greater hearing loss. The natives
on the island, both male and females, had hearing acuity similar to females who
lived in the United States.
However, Spoor's Equations (10)
and Robinson Sutton's (6) Data in ISO-1999 Annex A were derived from populations screened for noise induced hearing
loss and there is still a marked difference between the sexes. Rosenhall (9) also found a gender difference when noise exposure was compensated
for.
Thus, the choosing of a method of compensating
for presbycusis is a complex one and we offer two equations to calculate
presbycusis, both Spoor's and Robinson Sutton's. In addition, if you
believe that the gender difference in male and female subjects is due to noise
exposure, the Master Calculator also offers an option to project male patients
with female presbycusis data. Use the "PROJECT
MALE WITH FEMALE PRESBYCUSIS DATA" check box to accomplish this. I would
only consider doing this if all other risk factors such as hunting, use of
lawn equipment, alcohol or tobacco are not present.
2) Handicap Determination:
Determination of a hearing impairment
from an audiogram is performed by one of the predefined
equations. The percentage of handicap due to presbycusis is usually
determined by ISO-1999 Annex A (Robinson Sutton's Data). It is assumed
that presbycusis and noise trauma are additive but one can argue in severe
hearing losses that this is not true. However, legally this is a mute
point. Since, either the two are additive and the percentage of presbycusis is predicted by Robinson Sutton's Equations or if they are not
additive then some of the noise trauma prevented some presbycusis from taking
place, or visa versa. Thus, this percentage of noise trauma caused no harm and therefore
would still not be compensatible. Therefore the "Calculators"
determine the percentage of the hearing handicap "expected from"
presbycusis and NOT "caused from" presbycusis, the ISO-1999
compression factor or other modifications of the data are not used.
After the hearing handicap is adjusted
for presbycusis, the remaining handicap may still be accounted for by a variety
of factors including, but not limited to, other sources of acoustic trauma,
smoking, diabetes, heart disease, etc.
3) Projection of Audiogram:
The projection calculators were
programmed to help give guidance to the following question. An employee
enters employment with a preexisting hearing loss. Now he leaves the job
with a more severe hearing loss. Is the increase in his hearing loss due
to the employment or to the effects of aging and his environment?
One must remember that these equations
are looking at LEGAL CAUSATION, what is more likely than not to be true, in
order to reach a legal settlement. The discussions that follows are of
legal arguments and should not be used to determine
MEDICAL CAUSATION.
It is assumed with all of the calculators that
hearing loss due to noise and presbycusis are additive.
-
This hypothesis is supported by Macrae (5) whose findings support the independence
of noise induced hearing loss and presbycusis. He also found
that the maximum hearing loss from noise occurred during the first 10 years of
exposure. After this the hearing level followed the same course as in the
non-exposed group.
- However, Rosler G. (8)
observed that once the frequency hearing threshold, for sensorineural
impairments, reached 50 to 60 dB in individuals that the increase in hearing
loss due to the action of noise and aging shows a smaller than expected
increase, as predicted by non-compressed data from ISO-1999 Annex A.
Because of this the ISO 1999 compression factor is applied when projecting
audiometric data.
Hearing Loss = ARL
+
NIL - (ARL * NIL)/120
The NIH is estimated by following equation: NIH =
120*(HL-PHL)/(120-PHL)
If the hearing loss from NIH is less than expected from presbycusis then
the NIH is set to zero.
ARL: Age Related
Loss, NIL: Noise Induced Loss, HL: Hearing Loss,
PHL: Expected Hearing Loss From Presbycusis
The calculators will apply the ISO
1999 compression factor to all projected thresholds and truncate
all losses at 100 dB. The threshold projection may underestimate the
hearing loss in patients with other risk factors. For example, in patients who hunt without ear protection, since
ISO-1999 Annex A eliminated subjects exposure to gun fire in determining
presbycusis hearing thresholds.
In some cases, the patient's hearing loss will
be less than predicted by the presbycusis calculations (better than average for
his/her age). In this case the projected hearing loss will be that of the
expected hearing loss from presbycusis for the patient's age for the projected
audiogram. One could argue that the expected patient's hearing
should be better than this, however, we know of no studies to guide estimations
of future thresholds in individuals with above average hearing.
References
 1) Goycoolea MV, Goycoolea HG, Farfan
CR, Rodriguez, LLG, Martinez GC, Vidal R. Effect of life in
industrialized societies on hearing in natives of Easter Island.
Laryngoscope 12:1391-1396,1986.
2) Hunter KP Willot JF,
Aging and the auditory brainstem response in mice with severe or minimal
presbycusis. Hear Res 30:207-218.1987.
3) ISO 1999
Acoustics--Determinaton of occupational noise exposure and estimation of noise-induced
hearing impairment (International Standards Organization, Geneva, 1990).
4) Kryter KD Presbycusis,
sociocusis and nosocusis. J Acoustic Society of America.
73:1897-1916,1983.
5) McCrae JH,
Noise-induced hearing loss and presbyacusis. Audiology 10:323-333,1971.
6) Robinson, DW and Sutton, GJ.
Age effects and hearing. A comparative analysis of published threshold
data. Audiology 18:320-334,1979. As also described in Annex A of ISO 1999-01-15.
7) Rosen S, Bergman M, Plester
D, El-Mofty A, Satti MH, Presbycusis study of a relatively noise-free
population in the Sudan. Ann of Otology, Rhinology and Laryngology
71:727-743,1962.
8) Rosler G
Progression of hearing loss caused by occupational noise. Scand Audiol
23:12-37,1994.
9) Rosenhall U, Pedersen K,
Svanborg A. Presbycusis and noise-induced hearing loss. Ear and Hearing
11:257-263,1990.
10) Spoor A. Presbycusis
values in relation to noise induced hearing loss. Int.
Audiology 6:48-57,1967.
Kevin Kavanagh Copyright
2003. All rights reserved. Webpage
last updated: 04/01/2016
Search Website
|
