Effects of chronic and acute smoking on AMLRs in older and younger listeners.

Chronic and acute smoking effects on the auditory middle latency response (AMLR) were studied in older (55-81 years) and younger (19-30 years) normal-hearing listeners. Forty healthy participants were selected for one of four groups: older smokers, older nonsmokers, younger smokers, or younger nonsmokers. Biochemical urine analyses confirmed participant categorization as smoker or nonsmoker. Click-evoked AMLRs were acquired once from nonsmokers and twice (chronic condition, acute condition) from smokers. Waveform latency (V, Na, Pa) and relative amplitude (V-Na, Na-Pa) were examined with two independent variables (age, smoking) using MANOVA. Results (n=40) revealed no chronic effect of smoking in the AMLR from smokers compared to nonsmokers. However, in both older and younger smokers (n=20), Na-Pa amplitude was significantly larger in the acute compared to the chronic smoking condition, indicating an acute smoking effect. There was no interaction of smoking and aging. This is a first study describing long-term, chronic and acute smoking effects on AMLRs in older compared to younger listeners. Results suggest that cigarette smoking is an important variable for AMLR research and clinical practice.

Neurophysiology of cochlear implant users I: effects of stimulus current level and electrode site on the electrical ABR, MLR, and N1-P2 response.

OBJECTIVE: As the need for objective measures with cochlear implant users increases, it is critical to understand how electrical potentials behave when stimulus parameters are systematically varied. The purpose of this study was to record and evaluate the effects of implanted electrode site and stimulus current level on latency, amplitude, and threshold measures of electrically evoked auditory potentials, representing brainstem and cortical levels of the auditory system. DESIGN: The electrical auditory brainstem response (EABR), electrical auditory middle latency response (EAMLR), and the electrical late auditory response (ELAR) were recorded from the same experimental subjects, 11 adult Clarion cochlear implant users. The Waves II, III, and V of the EABR, the Na-Pa complex of the EAMLR and the N1-P2 complex of the ELAR were investigated relative to electrode site (along the intra-cochlear electrode array) and stimulus current level. Evoked potential measures were examined for statistical significance using analysis of variance (ANOVA) for repeated measures. RESULTS: For the EABR, Wave V latency was significantly longer for the basal electrode (7) compared with the mid (4) and apical (1) electrodes. For the EAMLR and ELAR, there were no significant differences in latency by electrode site. For all subjects and each of the evoked potentials, the apical electrodes tended to have the largest amplitude and the basal electrodes the smallest amplitude, although amplitude differences did not reach statistical significance. In general, decreases in stimulus current level resulted in statistically significant decreases in the amplitude of Wave V, Na-Pa and N1-P2. The evoked potential thresholds for Wave V, Na-Pa, and N1-P2 were significantly higher for the basal Electrode 7 than for Electrodes 4 and 1. CONCLUSIONS: Electrophysiologic responses of Waves II, III, and V of the EABR, Na-Pa of the EAMLR, and N1-P2 of the ELAR were characterized as functions of current level and electrode site. Data from this study may serve as a normative reference for expected latency, amplitude and threshold values for the recording of electrically evoked auditory brainstem and cortical potentials. Responses recorded from cochlear implant users show many similar patterns, yet important distinctions, compared with auditory potentials elicited with acoustic signals.