DISCUSSION:
To the best of our information (based on published literature), present
study is the largest to be conducted in Pakistan among medical students
using PTA for hearing assessment. Our study comprised 221 participants
with age group between 20-24 years (Mean±S.D: 21±0.927). Similar range
was mentioned in comparable studies. (11,12) Male to
female ratio was 1:3. This represents comparative larger number of
female students studying in medical colleges of this region.
We found a high prevalence (96.4%) of electroacoustic device usage
amongst medical students. Rekha et al. reported personal listening
device (PLD) use by medical students with frequency of 86.1% on daily
basis (13). A study from Hamadan University of Medical
Sciences, Iran stated 91.2% prevalence of PLD use.(14) A recent study conducted by Basu et al. narrated
5.4% medical students never used an electroacoustic device.(15) In our study only 3.6% students denied their use
of personal listening devices. This high prevalence of electroacoustic
device use can be attributed to current educational practices followed
by medical students. Such as online lectures and 3D animated content
available for vast academic topics.
Participants of our study preferred insert type earphones. The most
widely used source was smartphone. Parallel studies observed the similar
preferences. (13,14) A study from Jeddah stated that
almost all the medical students used a smartphone.(16) Easy availability of smartphones, comfortable
portability along with broad range compatibility for wide variety of
earphones are the possible attractions making them the first choice
among their users.
Our study showed that hearing impairment was strongly correlated with
the prolonged exposure to listening devices. Near half of our
participants were using electroacoustic devices for more than five
years. However, previous studies reported variable results for
association between hearing loss and listening duration.(11,12) Volume preferences did not vary considerably
from alike studies. (13,14)
We found less prevalence of self-reported hearing symptoms (tinnitus
9.5%, vertigo 2.7%) in comparison with other studies.(8,13,14) Interestingly, we also noted that majority
of medical students who displayed hearing loss in PTA were not
experiencing tinnitus and even not aware of their hearing impairment.
For example, in right ear at 500Hz, 88.4% (n=61) having mild hearing
loss did not complain tinnitus.
Upon PTA, around one third of our medical students showed mild sensory
hearing loss at lower frequencies (250 Hz and 500 Hz). Similar pattern
of low frequency hearing loss was detected in a study conducted among 56
medical students (9). A study was performed among 136
employees of a Malaysian telecommunication company. This revealed
impaired hearing in 21.2% of the personnel. An equal distribution of
hearing loss in low, middle, and high frequencies was noticed.(17) The possible explanation to this distinctive
pattern of low frequency loss might be due to the intensity of noise to
which they were exposed as indicated by McBride et al.(5) The participants of our study were medical
students who might be using electroacoustic devices for educational
purposes mostly. The staff of telecommunication company used headphones
for receiving phone calls which involve conversational frequencies. The
intensity, pitch and bandwidth of sound generated in such content differ
considerably from that produced in music and occupational noise. In
addition, a prolonged exposure up to 8 hours per day over 85dB
(Permissible Exposure Limit) is required to produce characteristic
pattern of NIHL. (18) None of our study participants
reached this limit hence traditional notch at frequency of 4kHz was not
found among most of the users.
In our study we found mild hearing loss (26-40dB) in majority of cases.
Cochlear apex is responsible for perceiving low frequency sounds. Halpin
et al. demonstrated that audiogram inherits some limitations when
assessing low frequency SNHL especially when high frequency thresholds
are within normal range. This is due to asymmetric spread of stimulus
along basilar membrane of cochlea. Healthy hair cells in the middle or
base of cochlea get stimulated and generate the response for lower
frequencies. The upper limit being 50dB in such cases.(19)
This study has certain unavoidable limitations owing to its
cross-sectional study design and non-probability sampling technique.
This was a single centre study hence we cannot generalize the findings.
This study therefore suggests correlation but cannot confirm causation.