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.