Eliciting constant and prominent waves n34-p44 of vestibular-evoked myogenic potentials.

OBJECTIVE The serial peaks of vestibular-evoked myogenic potentials (VEMPs) have been labeled p13, n23, n34 and p44 according to their latency. Waves p13-n23 have been shown to be of saccular origin, whereas the origin of waves n34-p44 is still unknown. In order to improve the clinical applicability of waves n34-p44, we examine the use of different patterns of acoustic stimuli to evoke constant and prominent VEMPs, especially waves n34-p44. MATERIAL AND METHODS In this prospective study 27 healthy volunteers (54 ears) underwent VEMP tests. Three kinds of click intensity (85, 95 and 105 dB nHL) were presented in a random order to evoke 85-VEMP, 95-VEMP and 105-VEMP, respectively. The response rate, latency of each peak, peak-to-peak interval and amplitude of waves p13-n23 and n34-p44 were measured and analyzed. RESULTS The response rates of waves p13-n23 in 85-VEMP, 95-VEMP and 105-VEMP were 26% (14/54), 89% (48/54) and 98% (53/54), respectively. Significant differences in the response rate existed between 85-VEMP and both 95-VEMP and 105-VEMP (p<0.01), whereas there was a non-significant difference between 95-VEMP and 105-VEMP (p>0.05). In contrast, the response rates for eliciting waves n34-p44 were 19% (10/54), 63% (34/54) and 89% (48/54), using 85, 95 and 105 dB acoustic stimuli, respectively. A significantly higher response rate for waves n34-p44 occurred when the intensity of the stimuli increased (p<0.01). Although neither latencies nor interval exhibited a significant difference between 95-VEMP and 105-VEMP, the amplitude of 105-VEMP was significantly greater than that of 95-VEMP for both waves p13-n23 and n34-p44. CONCLUSION An acoustic stimulus intensity of 105 dB nHL is required to reliably elicit waves n34-p44 in subjects with normal hearing.