ABSTRACT
BACKGROUND: Cervical Vestibular Evoked Myogenic Potentials (cVEMPs) are inhibitory myogenic responses that have commonly been elicited using a variety of stimuli. Yet, the comparison of the effects of multi-frequency tone bursts and narrowband Claus Elberling chirps (NB CE-chirps) on cVEMPs has never been studied in homogeneous age groups. PURPOSE: The present study focused on comparing the effect of multi-frequency NB CE-chirps and tone bursts on the various parameters of cVEMP responses in normal-hearing younger adults. RESEARCH DESIGN: A within-group study design was applied, and purposive sampling was utilized for the collection of the data sample. STUDY SAMPLE: The present study involved the elicitation of NB CE-chirps and tone bursts evoked cVEMPs across four-octave frequencies in 25 normal-hearing younger adults. RESULTS: NB CE-chirps and tone bursts evoked cVEMPs were found to have a 100% response rate for all frequencies except 4000 Hz. Across frequencies, P1 and N1 latencies were seen to be significantly shorter for NB CE-chirps than tone bursts at 500 Hz and 1000 Hz stimulation. No differences were seen in the P1N1 amplitudes and inter-aural asymmetry ratio (IAAR) between the two stimuli across all four-octave frequencies. Further, it was found to have a significantly higher number of ears tuned to NB CE-chirps than tone bursts at 500 Hz. CONCLUSIONS: Comparative differences in the latencies of cVEMP responses between and within stimuli could be due to the variation in stimuli duration. Also, the difference in amplitudes across stimulation frequencies might have resulted due to the predominance of saccular responses at lower mechanical resonance frequencies. Thus, the tuning was also seen at 500 Hz and was relatively higher for NB CE-chirps than tone bursts.
ABSTRACT
PURPOSE: The study aimed to explore the various parameters of multifrequency narrowband Claus Elberling chirp (NB CE-chirp) evoked cervical vestibular evoked myogenic potentials (cVEMPs) in normal-hearing healthy young adults. The study also attempted to define the optimal frequency tuning characteristic of NB CE-chirp evoked cVEMPs. METHOD: cVEMP was performed on 26 young healthy adults using four different NB CE-chirps centered at 500, 1000, 2000, and 4000 Hz. The neck torsion method was applied for electrode placement. To have the acute recording, visual feedback of sternocleidomastoid muscle contraction was provided, and electromyography (EMG) scaling was done. RESULTS: cVEMPs were present for 100% across all frequencies except at 4000 Hz. Amplitudes between each pair of frequencies were significantly different for EMG scaled and unscaled conditions. Frequency tuning was observed at 500 Hz regardless of scaling done. Positive peak 1 of cVEMP (P1) latencies showed no differences between frequencies while both negative peak 1 of cVEMP and the complex of positive peak 1 and negative peak 1 of cVEMP (P1N1) interpeak latency values decreased with increasing frequency. Interaural amplitude asymmetry ratio showed no difference between scaled and unscaled amplitudes. Intraclass correlation revealed a range of test-retest reliability across frequencies. EMG unscaled amplitude were having relatively lower test-retest reliability consistently across frequencies Conclusions: Differences in amplitudes between frequencies with a maximum at 500 Hz can be attributed to the low frequency centered saccular response. No differences in P1 were observed. Yet, N1 latency and P1N1 interpeak latency difference gradually shortened with the decrement in the stimulus duration as the stimulation frequency increased. The lower reliability of EMG unscaled amplitude across frequencies supports the need to use EMG scaling to avoid confounding variables related to muscle contraction.
