[Single channel multifocal VEP studies in normal Chinese].

Objective: To investigate the waveform characters of single channel mVEP and its variability in normal Chinese people.

Methods: VERIS Science 4.3 system was used to record and analyze single channel mVEP. The stimulation was performed with a 60 pattern segment dartboard configuration. The Michelson contrast was 99% and the repetition rate 75 Hz. Recording electrodes were placed 3 cm above and 3 cm below the inion. The m-14 sequence required 4 minutes of recording time per eye, which was divided into 8 short segments. The signal was amplified 100 000 times and band-pass filtered between 3 and 100 Hz. The first slices of second kernel at 60 locations were analyzed. The main wave peak-to-trough amplitude and latency from 30 to 130 ms signal window were measured and calculated with the costumed Matlab program. The study included 64 normal subjects (39 women and 25 men). The age range was 13 - 66 years. 7 subjects were tested 2 - 7 times on different occasions for reproducibility. The statistic analysis was performed with Excel and SPSS.

Results: In mVEP trace array, the polarity of upper hemifield traces was usually opposite to lower hemifield traces. However, at near vertical meridian areas and near below horizontal meridian areas, the trace polarity had some variability. The main wave mean amplitudes of 60 location responses in left eye were from 0.177 microV to 0.401 microV. The amplitude CVs for 60 locations were from 36.6% to 60.7%. The mean latencies of 60 location responses were from 100 to 116 ms, and latency CVs were from 8.8% to 18.1%. The smaller signals located in zones of upper periphery, along vertical meridian, below horizontal meridian and the larger signals located in near horizontal meridian areas and near non-axial meridian areas which distribution is like a bow tie. There was smaller amplitude variability in the some upper hemifiled locations with smaller amplitude, and there was larger amplitude variability in the some lower hemifiled locations with larger amplitude. The mean amplitudes of all 60 locations in male subjects were lower than that in female subjects, in which 30 locations were low significantly (P < 0.05). The gender influence on latency was less, in which only at 10 locations the difference was significant (P < 0.05). At 20 locations of all, which were mainly distributed at near vertical meridian of lower hemifiled, there was a significant positive correlation of age with amplitude. The age influence on latency was also less.

Conclusions: The larger variability of main wave peak-to-trough amplitude in single channel mVEP existed in different subjects and different locations of same subject. In analysis of mVEP amplitude, the influence of VEP curve location, gender and age should be considered. The main wave latencies of intersubject and intrasubject have smaller variability, and less effect by gender and age, so latency may be a useful diagnostic parameter.