Sandeep Maruthy, G. Nike Gnanateja, Resmitha Ramachandran, Priyanka Thuvassery
(Electrophysiology Lab, Department of Audiology, All India Institute of Speech and Hearing, Mysore, India)
JHS 2015; 5(3):
It is well known that muscle artifacts negatively affect auditory evoked potential (AEP) recordings. However, the precise relation between the set of muscles involved and the specific AEP affected is not clear. Most audiologists believe that increase in the tension of any muscle in the body would affect all AEPs to the same extent, while some believe that only head and neck muscles affect AEPs. Logically, this relation will depend on the frequency characteristics of the muscle artifact. However, to the best of our knowledge, there is no scientific documentation of the extent of interference created by various muscle responses on auditory brainstem responses (ABRs), middle latency responses (MLRs), and late latency responses (LLRs). The present study therefore sought to analyse the minimum artifact rejection threshold required for ABR, MLR, and LLR under various artifact-inducing conditions.
MATERIAL AND METHODS: The present study involved 40 individuals of age 17 to 24 years. For each participant, the effects of muscle artifacts on three popular, clinically relevant AEPs (ABR, MLR, and LLR) were determined. First, recording was done in a rest condition where participants were seated in a reclining chair and asked to close their eyes and maintain a relaxed position. Then the participants were asked to carry out one of the following tasks: blink their eyes continuously; spread their lips; or stiffen their neck, hand, or leg muscles maximally. While tensing each of these set of muscles, the minimum artifact rejection threshold (MART) was noted.
RESULTS: The results showed that each of the artifact-inducing conditions affected the three target AEPs differently. At rest, there was no significant difference in MART across the three AEPs, but artifact-inducing conditions produced different effects.
CONCLUSIONS: Not all artifacts affect every AEP equally. For good AEP recordings one needs to have a clear understanding of various muscle potentials and their relative effect on each AEP.
Keywords: Artifacts, Evoked Potentials, Auditory, signal-to-noise ratio