The increasing use of mobile communications has raised concerns about possible interactions between electromagnetic radiation and the central auditory system, but research remains limited.

To help fill that gap, we investigated the effects of mobile phone use on the latency of peaks I, III, and V for 500 Hz, 1 kHz, 2 kHz, and 4 kHz in tone-burst auditory brainstem response (ABR).

This preliminary data suggests that prolonged use of cell phones delayed neural information transmission in the central auditory pathway. However, the functional significance of the delay is still to be determined.

SHORT-TERM VS LONG-TERM USE

Guidelines limiting exposure to electromagnetic fields from mobile phones use the specific absorption rate (SAR). The SAR corresponds to the rate at which radiofrequency energy is absorbed in the head of a wireless handset user.

The antenna is the main source of radio waves that produce SAR in the body, although there may also be leakage from the phone body shell.

Commonly, mobile phones are held near the head when in use, keeping the cochlea close to the antenna.

However, mobile phone use has not been extensively investigated in the literature as a cause of cochlear hair cell loss, with most studies examining the effects of short-term rather than chronic exposure.

In one recent study that did look at long-term use, mobile phone users of more than a year had a significantly increased risk of absent distortion product otoacoustic emissions, higher speech frequency thresholds, and lower middle latency response waves Na and Pa amplitudes compared with controls (Otolaryngol Head Neck Surg 2011;144[4]:581-585http://oto.sagepub.com/content/144/4/581.long#ref-11). More than three years of mobile phone usage emerged as a risk factor.

SELECTION CRITERIA

Due to the limited and controversial nature of existing evidence, combined with the widespread use of mobile phones, it is crucial to determine if the electromagnetic fields of mobile phones have adverse effects on the human auditory system.

Therefore, the current study was designed to investigate these potential effects, as determined by changes in tone-burst auditory brainstem response, and to analyze the recovery pattern in case of any aftereffects of these electromagnetic fields on click ABR.

Included in the study were 15 normal-hearing adult volunteers who did not use a cell phone—eight men and seven women between the ages of 18 and 40—comprising Group A, or the mobile nonusers.

Group B, or the mobile users, consisted of 15 normal-hearing adults in the same age range as the Group A participants who had used mobile phones for two hours a day over at least the past three years.

Participants were right-handed postgraduate students and staff members at the Dr. M.V. Shetty College of Speech and Hearing in Mangalore, India, who met the following participation criteria:

Thresholds of 15 dB or better for the octave frequencies 250-8,000 Hz for air conduction and 250-4,000 Hz for bone conduction, and a normal tympanogram (Type A).

No history of audiologic or neurotologic problems, such as vertigo, tinnitus, noise exposure, etc.

No medical problems or use of medications for any reason.

No history of chronic narcotic or alcohol use.

All study participants in Group B used mobile phones produced by a single manufacturer that complied with International Commission on Non-Ionizing Radiation Protection (ICNIRP) Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz; Health Phys 1998;74[4]:494-522http://www.icnirp.de/documents/emfgdl.pdf). They also generally used cell phones in their right ears.

The mobile phones all were recent models from the same year, employed Global System for Mobile communications (GSM) for networking, and had a conformed antenna housed inside the plastic case.

ALTERED ABR LATENCIES

In order to check for any potential deleterious effects on the auditory system of electromagnetic fields emitted by mobile phones, tone-burst ABR was used with two surface cup electrodes that had impedance set lower than 5 k ohms.

The inverting electrode was placed on the right mastoid, the non-inverting electrode over the vertex (Cz of international 10-20 system), and the ground electrode over the left ear mastoid.

Recorded potentials were amplified with high and low-pass filters set at 100 and 300 Hz, respectively. At least 1,000 responses were averaged, with a maximum number of 2,000 and a repetition rate of 13.1/sec.

A 60-dB sPL, 100-µs (alternating) tone-burst (500-, 1,000-, 2,000-, 3,000-, and 4,000-Hz) sound was presented to the right ear with headphones.

We recorded ABRs twice to ascertain their reproducibility under each condition, measuring latencies and amplitudes of waves I, III, and V.

Descriptive statistics were calculated to find the mean and standard deviation of the groups, and the two-way ANOVA test was done to detect any significant differences between the groups. We confirmed normal hearing by pure-tone audio-metry in both groups of participants.

Table 1 shows the ABR results from the right ear for cell phone users versus nonusers.

Table 1: Mean, Standard Deviation (SD), and F Values for Cell Phone Users and Nonusers

For all frequencies tested, peak latencies of waves I, III, and V in the tone-burst ABR were significantly delayed in the right ear of participants who used cell phones for more than three years.

The differences in latencies between cell phone users and nonusers were 27.62 for peak I (P < 0.011), 9.19 for peak III (P < 0.01), and 125.63 for peak V (P < 0.01).

No hearing loss or other symptoms were noted. Pure-tone audiometry and otoacoustic emissions examinations confirmed the absence of these conditions.

Further studies testing for longer-term effects and in larger groups of cell phone users are recommended.