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Context: The use of personal listening devices (PLDs) is becoming increasingly popular, particularly among young people. Numerous studies have demonstrated that being exposed to PLDs can have adverse effects on the auditory system. Owing to the similarities between the auditory and vestibular systems, it is possible that the negative effects of PLD use may extend to the vestibular system, an area that has not been extensively studied. Aim: The study aimed to investigate the impact of exposure to PLDs on the vestibular system, specifically the sacculo-collic reflex assessed by the cervical vestibular-evoked myogenic potential. Settings and Design: The current study used a cross-sectional study design. Materials and Methods: A total of 80 participants were divided into four groups based on the history of PLD exposure. Each group consisted of 20 participants who underwent cervical vestibular-evoked myogenic potential (cVEMP) testing using alternating polarity 500 Hz tone bursts. Statistical Analysis Used: Analysis of variance (ANOVA) and Bonferroni post hoc test were used to obtain the statistically significant difference among the group. Results: The results showed that the amplitude of p1-n1 of cVEMP was significantly reduced in individuals with longer PLD exposure duration. Conclusion: The study suggests that listening to music through a PLD at high levels of volume controls could be deleterious to the vestibular well-being of an individual. The study highlights the importance of being aware of the adverse effects of using PLDs to prevent potential damage to the vestibular systems.
Keywords: Personal listening devices, Cervical vestibular-evoked myogenic potential, Vestibular system, Sacculo-collic reflex, dBA
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Today, one of the most important social concerns is noise exposure. Exposure to noise is known to have deleterious effects on cochlea, resulting in hearing impairment. The literature has well documented the clinical pathophysiology of noise-induced hearing loss (NIHL).[1] Individuals with exposure to noise may also experience balance issues, which are similar to the consequences of acoustic damage on the cochlea.[2] However, unlike NIHL, noise is not known as a common cause of vestibular disturbances. This is most likely a result of how differently the vestibular labyrinth and cochlear hair cells are “tuned.” The cochlea’s hair cells are “tuned” to respond to frequencies between 20 and 20,000 Hz, whereas the vestibular hair cells are “tuned” to react to inputs between 0 and 10 Hz.[3] However, subclinical disturbances of the vestibular system in individuals with NIHL indicate the occurrence of balance-related issues.
Damage to the vestibular system can affect the movement of the eyes, trunk, and limbs, leading to balance problems and a sense of disorientation. There are several electrophysiological tests that can be utilized to determine the extent of the damage caused. The saccular reflex pathways are electrophysiologically assessed using vestibular-evoked myogenic potentials (VEMPs). The cervical VEMP (cVEMP) is measured from the tonically contracted sternocleidomastoid muscle (SCM), and it represents the sacculo-collic reflex pathway, which originates in the saccule and inferior vestibular nerve.[4] Obtaining cVEMP recording is a clinically viable method for the evaluation of otolith end organ (saccule) and subsequent inferior vestibular nerve branches. cVEMP is one such test that assesses the saccular reflex pathway.
Personal Listening Devices (PLDs) have seen significant technological advancements in the recent years, making them more accessible and popular.[5] The new models are more compact, with the ability to store thousands of tracks of music and longer battery life. These devices can be used in a variety of situations for extended periods of time, such as listening in noisy environments (in an aeroplane or a train). In such noisy environments, listeners must turn up the volume in order to draw out the outside noise, and if they are exposed to it for an extended period time, it can put the listeners at the risk of hearing damage.
The usage of PLD in the younger generation is known to cause hearing difficulties. Literature quotes the hazardous effects of PLD usage on the hearing system. A study by Peng et al.[6] reports altered hearing thresholds in the 3 to 8 kHz frequency range. Moreover, this frequency range broadens with prolonged exposure to PLDs at higher intensity levels. Likewise, an Indian study states that listening through PLD at higher volume levels is known to cause subtle preclinical damage to the auditory system and vestibular end organs, which over the years may lead to hazardous effects on the hearing and balance systems.[7]
The impact of noise exposure on the cochlea has been well investigated. However, there are very few studies that specifically address its impact on the vestibular system, presumably because the central nervous system compensates for vestibular abnormalities. When compared to hearing loss, vestibular symptoms include vertigo, imbalance, gait disturbances, and so on. Furthermore, these balance issues pose a greater impact on everyday activities than hearing loss and can even result in disability, leading to poor quality of life. Rehabilitation for these symptoms should commence as soon as possible. Therefore, it is of immense importance to examine the vestibular system of individuals exposed to noise in any form. Among the vestibular system, the saccule is more susceptible to noise. Hence, the present study was taken to investigate the effects of PLD exposure on sacculo-collic reflex pathway using cVEMP.
Subjects and MethodsSubjects
Participants were grouped into four in the age range of 18 to 29 years (Sacco, 2013).[8] Hereafter, the groups were named as follows:
Group A: Participants with <1 year of PLD exposure at a volume level >60% of its maximum limitsGroup B: Participants with 1.1 to 2 years of PLD exposure at a volume level >60% of its maximum limitsGroup C: Participants with 2.1 to 3 years of PLD exposure at a volume level >60% of its maximum limitsGroup D: Participants with 3.1 to 4 years of PLD exposure at a volume level >60% of its maximum limitsEach group consisted of 20 participants with fulfillment of inclusion criteria and after obtaining a written consent form from the participants on a nonpayment basis. Ethical clearance was obtained through the Institutional Ethical Committee on August 17, 2020, with the number BNGRC/T/IEC/05/2020-21. The selection criteria were adopted from the previous studies on the effects of PLD on auditory system.[7],[9],[10] All participants were required to have normal pure tone thresholds within 15 dB HL, “A” type tympanogram with present acoustic reflexes at 500, 1000, 2000, and 4000 Hz and Uncomfortable Loudness Level (UCL) >100 dB HL. Furthermore, professionally trained dancers and trainers, individuals with conductive hearing loss, neuromuscular problems, and autoimmune diseases were excluded from the study after a thorough examination by a trained and experienced practitioner. All participants were instructed to avoid or inform the usage of any vestibulotoxic drugs and muscle relaxants, at least 48 hours before cVEMP testing.
Procedures
All participants underwent a two-stage evaluation after fulfillment of participant inclusion criteria. The initial stage involved utilizing a microphone in the real ear to measure the output decibel sound pressure level (dB SPL) from the PLDs in close proximity to the tympanic membrane. Determining the total dB SPL near the tympanic membrane through PLDs can assist in identifying potential harmful sound levels affecting the vestibular system. The subsequent stage involved conducting cVEMP testing. All the evaluations were performed in a well-illuminated and sound-treated room as per American National Standards Institute (ANSI) standards.[11]
Microphone in the Real Ear Measurement
The measurement of output SPL of PLDs using a probe microphone in the ear near to the tympanic membrane is referred to as “Microphone in the Real Ear (MIRE).” This procedure is adopted from Singh and Sasidharan’s[12] study. It helps in ensuring uniformity in SPL levels used on PLDs >60% of the volume. The output SPL of PLDs was measured using probe microphone. The loudspeaker was placed at an angle of 45° azimuth and at a distance of 30 cm from the participant. The standard reference microphone was placed above the pinna before inserting the probe tube into the ear canal at an insertion depth of 28 mm from the tip of the tube to the intertragal notch. After leveling the system, the real-ear unaided response was measured for an output of a composite signal at 65 dB SPL across the octave frequencies from 200 to 8000 Hz. Furthermore, without changing the position of the probe tube, the earphones of the PLD were placed in the ear. The volume control of the PLD was adjusted to the level that the participants usually set when using the system in the outside environment. Upon obtaining the curve stabilization, the SPLs were measured across the above-mentioned frequencies.
The measured output SPLs were converted to equivalent diffused field SPLs by subtracting the transfer function of the open ear. The transfer function for the open ear were obtained by calculating the difference between reference location at the opening of the ear canal and probe microphone SPL near the eardrum for a sweep frequency tone presented at 65 dB SPL. The output SPLs were converted into dBA values by adding A-weighted adjustment values.[13] The overall dBA was then calculated by logarithmically adding the dBA values at each frequency. Owing to the lack of existing standards for hazardous music level exposure, the transformation of SPL to dBA was carried out to compare the output of the PLDs to the damage risk criteria (DRC) proposed for occupational noise exposure. With reference to the DRC, the standards are reported as A-weighted SPL measurements in its calculations of risk and permissible exposure levels. For these calculations, the same procedure was followed as described formerly.[7] The 8-hour equivalent A-weighted noise exposure level was calculated using the formula given below:
Leq8h = LT + 10 log10 (T/8)
where Leq8h is the 8-hour equivalent continuous noise exposure, “LT” is the level of exposure for the period “T,” and “T” is the exposure time in hours (average music listening duration in hours per day).
Cervical Vestibular-Evoked Myogenic Potential
To acquire cVEMP on all participants, the Bio-logic Navigator Pro Auditory-Evoked Potential System (Natus Medical Incorporated, Illinois, USA) version 7.2.1 was used. First, the participant was seated upright on a chair with back support. Furthermore, gold-plated cup electrodes were placed on the recording sites after cleaning them with abrasive Nuprep gel (Weaver and Company, Colorado, USA) to obtain suitable absolute electrode impedances (<5 kΩ) and interelectrode impedance (<2 kΩ). The electrodes were placed and secured with surgical tape on the recording sites using a conductive paste Ten 20 (Weaver and Company, Colorado, USA). The SCM was first contracted by asking the participant to move his/her head away from the side of stimulation (SCM). The protocol used for cVEMP testing is listed in [Table 1].
To assess interjudge reliability and determine the proper peak marking, two expert audiologists independently examined the obtained cVEMP waveforms. The positive (p1) and negative (p1) peaks were marked, and their individual latencies and peak-to-peak amplitude were obtained. Additionally, the conventional formula provided by Li et al.[17] was used to determine the interaural difference (IAD) ratio, also known as the asymmetry ratio (AR).
Upon obtaining the latencies, peak-to-peak amplitude, and AR, the data were statistically analyzed. Descriptive statistics, one-way repeated measures analysis of variance (ANOVA), and the Bonferroni post hoc test were performed to obtain the statistically significant difference across the groups. Similarly, Pearson correlation analysis was carried out to know if there exists any correlation between the total duration of exposure to PLDs and the parameters of cVEMP across the groups.
ResultsThe objective of the study was to examine the relationship between the output levels of the PLDs near the tympanic membrane and the parameters of cVEMP recording. The study utilized microphone in the ear measurement to determine the mean output dB SPL of four groups: group A, group B, group C, and group D and further converted the obtained dB SPL values to dBA. The study then compared the calculated dBA values across the groups to identify any potential changes in the parameters of cVEMP recording. The mean output dBA obtained from the descriptive statistics is presented in [Table 2].
Table 2 Mean Output dBA Values Used by Individuals to Listen to Personal Listening Devices across Groups.Furthermore, the ANOVA test revealed a statistically significant difference between the groups f(3,76) = 3.007, P = 0.035. The statistically significant difference was mainly observed between groups A and D (P < 0.05).
The cVEMP responses were recorded from all four groups in the study. The responses were observed in both ears across all the groups, resulting in 100% response rate. Three components of the cVEMP waveforms, namely latency of n1 and p1, the peak-to-peak amplitude of p1-n1, and the interaural amplitude AR were analyzed and tabulated.
Furthermore, the obtained data were subjected to descriptive statistics to calculate the mean and standard deviation of the parameters considered in the study. [Table 3] presents the mean and standard deviation of various parameters of all four groups.
Table 3 Mean and Standard Deviation of the Cervical Vestibular-evoked Myogenic Potential Parameters across the Groups.The Shapiro–Wilk test of normality was carried out to check the normality of the data. It was found that the data followed a normal distribution as the P value was >0.05. The parametric test, ANOVA, was used to determine whether there exists any significant differences between the latency of p1, latency of n1, and amplitude of p1-n1 between the right and left across the group’s ears, respectively. There exists no significant difference between the two ears for the mentioned parameters (P > 0.05). Thus, the data obtained in the right ear was added to the left ear making a total of 40 ears available across the groups for statistical analysis.
Additionally, the ANOVA showed no statistically significant difference across the groups for the latency of n1 and p1 and AR. However, a statistically significant difference was observed in the peak-to-peak amplitude of p1-n1 (f(3, 156) = 8.58, P = 0.00) across the groups. Furthermore, Bonferroni post hoc test showed a statistically significant difference between groups A and D (P = 0.000) and between groups B and D (0.049).
Since, peak-to-peak amplitude of p1-n1 of cVEMP was the only parameter with a significant difference across the groups, the relationship between the total duration of PLD exposure and the peak-to-peak amplitude of p1-n1 was investigated using Pearson’s correlation analysis. The results of the analysis showed a significant negative correlation between the total duration of PLD exposure and the peak-to-peak amplitude of p1-n1 in the right ear (r = −0.364, P = 0.001) and in the left ear (r = −0.347, P = 0.002), respectively. [Figure 1] and [Figure 2] present the negative correlation observed between the total duration of PLD exposure and the peak-to-peak amplitude of p1-n1.
Figure 1 Scatter plot depicting the relationship between the total duration of personal listening device (PLD) exposure and right ear peak-to-peak amplitude of cervical vestibular-evoked myogenic potential (cVEMP).
Figure 2 Scatter plot depicting the relationship between the duration of personal listening device (PLD) exposure and left ear peak-to-peak amplitude of cervical vestibular-evoked myogenic potential (cVEMP). Discussion The study found a 100% response rate in all participants for both ears, which is consistent with previous research,[4],[18] reporting response rates between 88 and 100%. However, Singh and Sasidhran[12] cautioned that a 100% response rate in PLD users does not necessarily indicate normal functioning of the sacculo-collic pathway but rather suggests a functional pathway due to the bilateral nature of loud sound exposure, as most individuals use binaural earphones.
Numerous studies have investigated the impact of noise on the functionality of the sacculo-collic pathway, with excessively loud music being a form of noise. In this study, no statistically significant difference was observed across the groups for the latency of p1 and n1. Previous research has reported prolonged latencies of both p1 and n1 in individuals exposed to loud noise[19],[20] and a positive correlation between the degree of hearing loss and cVEMP latencies in individuals with occupational noise exposure,[21] indicating a relationship between the cochlea and the sacculo-collic pathway. Similarly, authors reported that patients with NIHL had delayed cVEMP latencies compared to the control group.[21],[22] These results were supported by Zhou et al.[23] who suggested that the delay in cVEMP latencies was due to changes in the nervous pathway responsible for the P13 and N23 responses. This pathway includes the inferior vestibular nerve and nuclei up to the sternocleidomastoid muscle. In addition, Hsu et al.[24] linked the loss of VEMPs in guinea pigs following long-term noise exposure to morphological changes in the saccule. The current study findings are in accordance with the literature suggesting no neural involvement in individuals exposed to PLDs.
Statistically significant variations were observed in the peak-to-peak amplitude across the groups in the present study. A decreasing trend in the peak-to-peak amplitude of p1-n1 was noted with an increase in the years of exposure to PLDs (group A > group B > group C > group D). Several studies have reported a significant decrease in peak-to-peak amplitude over a period of occupational noise exposure.[20],[21] Singh and Sasidharan[12] also reported comparable outcomes in individuals utilizing PLDs. This may be attributed to the irritative macular receptors following acoustic stress to the ears, which typically lasts for a few hours to a few days following exposure to any pathology.[25],[26] As the participants in the current study were exposed to PLDs for a minimum of 1 hour per day, the irritative phase may not have been present long enough to result in a significant reduction in the cVEMP peak-to-peak amplitude.[12]
The observed decrease in amplitudes of p1-n1 in the four groups could be attributed to subclinical vestibular damage caused by recreational noise exposure through PLDs, similar to cochlear damage. Exposure to high levels of noise is known to cause damage to cochlear hair cells, which can also affect the saccular macula due to possible intercommunication between the fluid spaces of the cochlea and the vestibule.[27] Wang and Young[22] suggested that prolonged and intense noise exposure may result in reduced blood flow to both the cochlea and saccule, leading to permanent hearing threshold shifts and abnormal VEMP responses. This is because the cochlea and saccule receive their blood supply from the labyrinthine artery, which also supplies the anterior and posterior vestibular arteries. Additionally, Lamm and Arnold[28] have reported mechanical injury and metabolic damage, such as the generation of toxic-free radicals, metabolic exhaustion, reactive oxygen species, and ionic imbalances in the inner ear fluid.
To add on, there was no statistically significant difference in the AR across the four groups. Listening to music or binge watching is a type of noise exposure, and thus the results could be compared with previous studies on the effects of occupational noise exposure on cVEMP. The literature reported normal Interaural Amplitude Asymmetric Ratio (IAAR) (<40%) in about 70% of the participants with NIHL, despite the presence of asymmetrical hearing loss in several participants.[20] Thus, the findings of the present study align with those of Akin et al.[20] The reason for the lack of significant asymmetry in cVEMP between the ears may be attributed to the consistent habit of listening to PLDs through earbud earphones at the same volume level bilaterally, resulting in a symmetrical effect of recreational noise exposure.[12] Further evidence supporting this theory comes from studies examining the effects of PLD use on cochlear function, which have reported bilaterally symmetrical increases in threshold and decreases in the amplitude of otoacoustic emissions.[29],[30]
The total dBA values used by the study participants disclosed a significant increase across the groups (group A < group B < group C < group D). Although the dBA values used by the study participants did not exceed the DRC, they could potentially cause subclinical damage to the vestibular system. Tamura et al.[31] reported peripheral vestibular pathology when exposed to prolonged duration of lower sound levels. This was supported by the findings of a study in which a decrease in the count of vestibular hair cells and an increase in oxidative stress was reported when exposed to a moderate sound level of 70 dB SPL for a period of 1 month. Similarly, McCabe and Lawrence[32] reported detrimental effects within minutes when exposed to higher sound levels.
The study found a negative correlation between the total duration of PLD exposure and the peak-to-peak amplitude of p1-n1 for both right and left ears. These findings are in concordance with the findings of Akdogan et al.[33] The authors reported a peripheral vestibular damage when exposed to continuous noise exposure in comparison to impulse noise exposure of higher intensity. Although the total dBA values used by PLD users in the current study do not cross the DRC, one can assume the presence of subtle preclinical damage to the functioning of sacculo-collic reflex. Therefore, the study findings indicate a detrimental effect on the functioning of the saccule with an increase in the total duration of PLD exposure.
None of the participants reported any vestibular-related symptoms, despite the significant findings of the study. This could be due to the possible bilateral nature of the deficit or the gradual nature of the damage, which may incorporate central compensation. Moreover, the effect of PLDs might not have caused severe trauma to the sacculo-collic pathway, resulting in only diminished cVEMP responses rather than a complete absence. Therefore, although there is pathology to the sacculo-collic pathway, it may not be severe enough to produce symptoms.
ConclusionThe results of the study suggest that prolonged exposure to PLDs may have a negative impact on the sacculo-collic pathway, particularly the saccular function. The investigation explored this impact on four groups with varying durations of PLD exposure, shedding light on the relationship between the years of exposure and damage to the sacculo-collic pathway. It is worth noting that prolonged exposure to PLDs may lead to similar findings as observed in cases of occupational noise exposure. Therefore, caution is advised among younger individuals, and as a preventive measure, it is recommended to limit daily PLD exposure to <1 hour, with volume levels <60%, to minimize potential harm to the saccule and sacculo-collic pathway.
References
Correspondence Address:
Teja Deepak Dessai
Research Scholar, Manipal Academy of Higher Education, Manipal, BSHRF, Bangalore, Dr. S. R. Chandrasekhar Institute of Speech and Hearing, Bangalore
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/nah.nah_13_23
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