SHIMP Findings in Individuals Using Personal Listening Devices

Abstract

Listening to PLD at higher volume levels are known to cause subtle pre-clinical damage to the auditory system and vestibular end organs. Exposure to PLDs may also cause vestibular dysfunction much before the cochlear dysfunction. SHIMP is a newly described tool to assess the vestibulo-ocular reflex (VOR) gain suppression. With the premise that prolonged exposure to PLDs at high volume levels may cause vestibular dysfunction, and SHIMP being an early detector of vestibular dysfunction, the study was undertaken. The study aimed to describe the SHIMP test findings in normal hearing individuals with and without prolonged exposure to PLDs at > 60% of volume. A cross sectional comparative study was carried out on 128 participants with and without history of PLD exposure. Participants within the age range of 15-24 years and history of PLD usage at < 60% volume for < 1 year and at > 60% volume for > 1 year were recruited for the study. Output dBSPLs delivered by PLDs were measured using microphone in the ear method. Further, SHIMP was administered to assess the vestibular function. The dBSPL levels used by the participants of both the groups were within the DRC used for occupational noise exposure. Likewise, no statistically significant difference was observed between the two groups. Participants using PLDs with dBSPLs within the DRC may not be at a crucial risk. However, one must use precautionary measures to prevent any subclinical or long-lasting damage to the inner ear.

Introduction:

The usage of Personal Listening Devices (PLDs) for leisure activities is currently gaining popularity among youngsters. Noise exposure in any form is known to cause damage to the inner ear [1]. Use of PLD might pose a threat to the inner ear. Literature reports a pre-clinical damage to both hearing and vestibular system [2]. According to Shupak, Bar-el, Podoshin, Spitzer, Gordon, Ben-david [3], persons exposed to noise experienced vestibular symptoms long before a hearing impairment was clinically recognised. Today, the use of PLDs is reported to be the most hyped for leisure purposes.

The cochlea and vestibular sensory end organs share a same genesis since they are both situated within the temporal bone and membrane labyrinth of the inner ear. Furthermore, as the tensile strength and breakage point of the saccular membrane are lower than those of the Reissner's membrane, constant noise over stimulation is likely to harm the former before it harms the latter [4]. As a result, vestibular dysfunction may be brought on by PLD exposure considerably earlier than the cochlear loss. This theory was backed by Yilmaz, Soylemez, Ozdek [5], who found that patients with noise-induced hearing loss had significantly poorer VOR gain. Vestibulo-Ocular Reflex (VOR) serves to stabilise the retinal image by rotating the eyes to compensate for head movements thereby maintain the balance.

Although we are aware of how noise affects the auditory system, we know much less about how it affects the vestibular system. Animal studies have revealed a potential rapid degeneration of the vestibular region than the auditory region following loud noise exposure [3]. Occupational noise is harmful to hearing capacities yet recreational noise exposure must not be disregarded [6]. As a result, it is crucial to include a battery of vestibular tests in the clinical setup to rule out vestibular pathology in individuals with any type of noise exposure. A test known as the Suppression Head Impulse Paradigm (SHIMP) can be used to determine the functioning of vestibular system. As there is a paucity of information regarding the SHIMP test findings on PLD users, the study aims to describe the SHIMP test findings in normal hearing individuals with and without prolonged exposure to PLDs at > 60% of volume.

Methods and Materials

Following approval from the institutional ethical committee (Bshrf/RC/IED/D/01/AUD/2021–22 on 17th August 2022), a cross-sectional comparative study was carried out. A total of 128 participants between the ages of 15–24 years were recruited. The inclusion criteria included normal Puretone thresholds (15dBHL at 250–8 kHz) with "A" type tympanogram and present acoustic reflexes at 500–4 kHz. Individuals with history of PLD exposure for at least one hour/day at < 60% volume of the PLD for < one year were taken as the control group; and the individuals with history of PLD exposure at > 60% volume of PLD for > one year were taken as the experimental group. Participants with any history of middle ear or vestibular disorder, those trained in athletics, gymnastics, dance, yoga and/or with intake of immune suppressants within 48 h of the testing were excluded from the study.

Each recruited individual received a two-stage evaluation. First, measurement of output dBSPLs from PLDs using microphone in the ear method (protocol used by Singh, Sasidharan, [4, 7]) was performed using Med Rx probe microphone system. This measurement helps to find the dBSPL used to listen to PLDs near the tympanic membrane. Secondly, Suppression Head Impulse Paradigm (proposed by MacDougall, McGarvie, Halmagyi, Rogers, Manzari, Burgess, et. al, [8]) was administered. In a well-lit room, participants were required to sit in a stationary chair. A target at eye level was fixed at a minimum of one meter. The vestibular function of the horizontal semicircular canal was assessed using video goggles (ICS Impulse, Otometrics, Denmark). This goggle features a laser light, a motion sensor, and an integrated video camera that records the eye movement in real time. Head impulses consisted of random quick horizontal rotating head movements of 5°–10° amplitude with a peak head velocity of 150–250°/sec [9]. For each side, an average of 10 impulses were obtained. Each participant's VOR gain, PR score, Latency of Anti-Compensatory Saccades and Amplitude of Anti-Compensatory Saccades were recorded.

Results

To determine if the data followed a normal distribution, the Kolmogorov–Smirnov and Shapiro–Wilk tests were used. As a result of the data's non-normal distribution, Mann–Whitney U test was employed to determine the statistical difference between the two groups.

In the current study, first, output dBSPL close to the tympanic membrane was compared between the experimental and control groups. This was followed by examining SHIMP parameters between the two groups.

Output dBSPL level from PLDs near the tympanic membrane

The experimental group listened to PLDs at higher volume levels (61.01dBSPL—95.85dBSPL) in comparison to that of the control group (51.67 dBSPL -72.11dBSPL). The mean output dBSPL near the tympanic membrane from the PLDs was 75.4dBSPL (± 7.77) in the experimental group. Furthermore, Mann Whitney U test revealed a significant difference in mean output dBSPLs from the PLDs near the tympanic membrane between the two groups (p = 0.000). However, these dBSPLs were within the Damage Risk Criteria used for Occupational Noise Exposure.

Examination of SHIMP parameters

The mean VOR gain of the right ear and left ear were compared in control group. No statistically significant difference was observed between the two ears using Mann–Whitney U test (U = 1858.00, p = 0.44) was identified. Likewise, experimental group also did not show any significant difference between the right and left ears (U = 1989.50, p = 0.77). Further, using the same test, control and experimental groups were compared to obtain a statistically significant difference between the two groups. No statistically significant difference between the two groups was observed (U = 7881.00, p = 0.67) (Table 1).

Table 1.

SHIMP findings in Control and Experimental Groups

	Control Group	Experimental Group
Mean VOR Gain	0.78 (±0.11)	0.78 (±0.08)
PR Score	24.6 (±3.56)	24.59 (±4.37)
Latency of Anti-Compensatory Saccades	104.99 (±18.21)	104.96 (±15.9)
Amplitude Of anti-compensatory saccade (°/s)	-133.39 (±26.52)	-133.39 (±27.35)

Further, PR scores were compared between the two ears in control and experimental groups respectively. No statistically significant difference (2025.00, p = 0.91), (U = 2027.00, p = 0.92) was observed between the two ears in both control and experimental groups respectively. Similarly, no statistically significant difference was observed between the two groups (U = 8108.500, p = 0.88). However, the overall PR score observed was higher in the experimental group than in the control group.

Anti-compensatory saccades were obtained for all the participants of the study. The latency of anti-compensatory saccades was found to be higher in the experimental group than the control group. Nevertheless, the non-parametric test result showed no significant difference in the mean latency of the right and left ear of control group (U = 1962.000, p = 0. 682) and experimental group (U = 2001.000, p = 0.823). Similarly, like other SHIMP parameters, the control and experimental groups showed no significant difference between the two groups (U = 7865.500, p = 0.581).

Furthermore, the non-parametric test result showed no significant difference in the mean amplitude of anti-compensatory saccades of the right and left ear of control (U = 1670.500, p = 0.072) and experimental group (U = 1825.500, p = 0.289). Similarly, no statistically significant difference was observed between the two groups (U = 7728.500, p = 0.434).

Discussion

The aim of the study was to describe the SHIMP test findings in normal hearing individuals with and without prolonged exposure to PLDs at > 60% of volume. The findings of the study are in concordance with the findings in the literature. Kim, Shin, Song, Han, [10] reported listening intensity range of 57.32–83.43 dB SPL using PLD in college students. Moreover, in the study conducted by Singh and Sasidharan [4] on the personal music system users 12 out of 32 individuals exceeded the damage risk criteria of 85 dBA given by National Institute for Occupational Safety and Health. The current study revealed an average of 79.78 dBA used in the experimental group.

The experimental group used greater output dBSPLs for leisure purposes, however, below the Damage Risk Criteria levels. Likewise, participants in this study used insert earphones, which increased the output dBSPLs delivered close to the tympanic membrane [4]. Despite this, the levels used by the participants are insufficient to harm the vestibular system when used for shorter durations.

VOR gain is defined as the ratio of slow phase compensatory eye velocity to head impulse velocity during the head impulse. Lower mean VOR values were obtained for the experimental group. However, this finding could be attributed to fatigue in the ocular muscles due to binge watching, fatigue or tiredness.

Similarly, the “PR score” is a numerical score that quantifies the amount of scattered saccadic responses. Higher PR score indicates scattered grouped responses and lower PR score indicates maximum gathered responses [11]. Our study found a lower PR score. Thus, suggesting no significant pathology caused to the vestibular system due to PLD exposure. Literature reports higher PR score in the ears with vestibular pathology. Similar findings are reported in individuals with Meneire’s Disease and Vestibular Migraine. These findings suggest that PR score is more sensitive and is intuitive parameter compared to VOR gain to identify presence of vestibular lesion [12].

Higher mean anti-compensatory saccade amplitude and latency was observed for the experimental group. However, there was no statistically significant difference between the groups. This may be because there was little difference in the overall number of years of PLD exposure between the two groups, the lower dBA values used by the individuals to listen to PLDs below the Damage Risk Criteria and over exertion to the ocular muscles.

Conclusion

The results of the current study emphasise the value of SHIMP test in detecting potential vestibular system impairment. Considering the lower dBSPLs used by the participants and lower difference in PLD exposure between the two groups, a possible significant difference might not have been achieved. However, if the PLD exposure continues for longer durations and at higher dBSPLs crossing the Damage Risk Criteria, one may develop vestibular impairment. Likewise, including vestibular tests and assessing vestibular system will help improve the overall quality of life of an individual exposed to PLD by providing necessary rehabilitation if needed. Thus, emphasizing the need for extending the study on larger population.

Key Message

Current study aimed to identify the VOR gain suppression using SHIMP in PLD users. The findings of the study did not show a significant difference between the two groups of the study. However, if one chooses to continue PLDs at higher volume levels for longer duration may be at a risk for subclinical or permanent damage to the inner ear. Study can be considered for creating awareness and improving overall quality of life of the youngsters using PLDs.

Funding

This study was not funded by any association or organisation.

Declarations

Human or Animals Rights.

Human Participants.

Informed consent.

Informed written consent was taken before recruiting the participants of the study.

Data availability

Available.