Effects of Secondhand Smoke Exposure on Hearing and Auditory Evoked Potentials, ABR and AMLR in Young Adults.

BACKGROUND: Population health is impacted by environmental secondhand smoke (SHS) exposure. Although the negative health effects of SHS exposure include respiratory problems in children (nonsmokers) as seen in cigarette smokers, other health impacts such as sensory function are not assumed to be the same for both passive nonsmokers and smokers. However, hearing loss was recently reported in adolescents and aging adults with SHS exposure, suggesting that SHS might impact auditory function similarly to cigarette smoking. Specific effects of SHS exposure on the central auditory system have not been fully described.

PURPOSE: To measure auditory function via pure-tone audiometry and evoked potentials in young nonsmoking adults aged 18-23 yr who reported exposure to environmental SHS.

RESEARCH DESIGN: Participants were selected for the SHS-exposed (SHS-E) group first, followed by age and gender matched individuals for the SHS-unexposed (SHS-U) group. Self-reported nonsmoker status was confirmed by biochemical analysis of urine for cotinine level.

STUDY SAMPLE: Potential participants (N = 208) completed a questionnaire about health, smoking history, SHS exposure, and hearing ability. Individuals with any neurological conditions, alcohol/drug dependencies, excessive noise exposure, using certain medications, or current smokers were excluded. Twenty-two nonsmokers in excellent health consented to participate. Participants in the SHS-E group reported SHS exposure in home, work, or social settings for an extensive time period. Participants in the SHS-U group did not live with smokers and reported no SHS exposure, medication use, tinnitus, or any chemical exposures. Statistical analysis was conducted on data from 20 participants, 10 per group with a mean age of 20 yr.

DATA COLLECTION AND ANALYSIS: Participants underwent auditory procedures in one session in an IAC sound-treated room, including otoscopy, tympanometry, pure-tone threshold evaluation, auditory brainstem response per ear, and a three-channel auditory middle latency response in the right ear. The primary study outcomes were hearing thresholds measured (dB HL) at five frequencies, and evoked potential wave latencies (I, III, V, Na, Pa, Nb, Pb) and amplitudes (V-I, Na-Pa, Pa-Nb, Nb-Pb). It was hypothesized that SHS-exposed individuals would have poorer hearing sensitivity (threshold >25 dB HL) and abnormal central auditory function (longer latencies; smaller amplitudes) based on evoked potentials. Statistical analyses focused on identification of group differences in hearing and central auditory function.

RESULTS: All participants had normal hearing sensitivity (thresholds ≤25 dB HL) with no significant group differences. The V/I amplitude ratio in the right ear was significantly decreased in SHS-exposed individuals (p < 0.05). Auditory brainstem response latencies were not significantly different between participant groups or ears. Wave Pb latency was significantly increased in SHS-exposed individuals (p < 0.01). Auditory middle latency response relative amplitudes were significantly different from each other at every electrode site (Cz, Fz, C4) but not between groups. Overall, the Na-Pa complex was highest in amplitude at all three electrode sites.

CONCLUSIONS: This preliminary study indicated toxic effects of SHS exposure by evoked potentials with decreased V/I amplitude ratio and longer (delayed) Pb latency in young adults. Further studies should corroborate these findings to facilitate clinical recommendations.