Visual evoked potentials pattern-reversal

Myslobodsky, M.S., Sharon, D., Novis, B.H. Pattern-reversal visual evoked potentials in hepatic cirrhosis. Hepato-Gastroenterol. 1986 33 145-147... 

In contrast to the Hake and Stewart (1977) study, Altmaim et al. (1990) found a statistically significant (p<0.05) increase in latency of pattern reversal visual-evoked potentials in 10 male volunteers exposed to tetrachloroethylene at 50 ppm for 4 hours/day for 4 days, relative to 12 subjects exposed at 10 ppm. No effects on brainstem auditory-evoked potentials were noted. Tests of visual contrast measured in a few individuals showed a tendency for loss of contrast in the low and intermediate spatial frequencies at 50 ppm. In this study, measurements were also completed the day before exposure so each individual served as his own control. The 10-ppm group was considered the control group, and this concentration was used because it is well above the odor threshold of tetrachloroethylene so that there was at least an attempt to blind the subjects to the exposure concentrations. Blood tetrachloroethylene concentrations were measured before, in the middle, and at the end of each day s exposure, and an association between the effect on pattern reversal visual-evoked potentials and blood tetrachloroethylene concentrations was observed (p<0.03). The lack of effect on flash visual-evoked potentials in the Hake and Stewart (1977) study at concentrations up to 100 ppm compared to an effect on pattern reversal visual-evoked potentials at 50 ppm in the Altmann et al. (1990) study may reflect the greater inter- and intrasubject variability of waveforms for flash visual-evoked potentials (Otto et al. 1988). 

In a similar study by Altmann et al. (1990), significant (p<0.05) increased latencies for pattern reversal visual-evoked potentials were observed in 10 male volunteers exposed to tetrachloroethylene at 50 ppm, compared to 12 men exposed at 10 ppm. Exposures in this study were also 4 hours/day for 4 days. Effects on brainstem auditory-evoked potentials were also not observed in the Altmann et al. (1990) study. Tetrachloroethylene in the blood increased with exposure duration, and linear regression to associate blood tetrachloroethylene with pattern reversal visual-evoked... 

An additional study did not reveal any effects on neurological function among 14 persons who lived above or next to dry cleaning facilities for 1-30 years compared to 23 controls matched for age ( 1 year, in two cases 3 and 5 years) and gender when the absolute values of the tests were examined (Altmann et al. 1995). Median tetrachloroethylene exposure concentrations were 0.2 ppm in the apartments of the exposed individuals and 0.0003 ppm in the apartments of control subjects, and blood concentrations were 17.8 46.9 pg/L in exposed individuals and less than the detection limit of 0.5 pg/L in the controls. When multivariate analysis was completed to adjust for age, gender, and education, an increased response time in a continuous performance test (p<0.05), increased simple reaction time to a visual stimuli (p<0.05), and decreased performance in a test of visual memory (p<0.05) were observed. No effect on pattern reversal visual-evoked potentials was... 

ATSDR has derived an acute inhalation MRL of 0.2 ppm with an uncertainty factor of 10, based on increased pattern reversal visual-evoked potential latencies, and deficits for vigilance and eye-hand coordination observed in humans exposed 4 hours/day for 4 days at 50 ppm but not at 10 ppm (Altmaim et al. 1992). A chronic-duration inhalation MRL of 0.04 ppm with an uncertainty factor of 100 was derived based on increased reaction times in workers exposed to tetrachloroethylene in dry cleaning shops at an average concentration of 15 ppm for about 10 years (Ferroni et al. 1992). An acute oral MRL of 0.05 mg/kg/day with an uncertainty factor of 100 was derived based on hyperactivity observed in 60-day-old mice that were treated with tetrachloroethylene for 7 days beginning at 10 days of age (Fredriksson et al. 1993). Additional inhalation and oral MRLs were not derived. 

Boyes, W.K., and Dyer, R.S. 1983a. Pattern reversal visual evoked potentials in awake rats. Br. Res. Bull. 10 817-823. 

Exposure to heavy metals especially during the gestational period may impair development of visual processing, as suggested in a follow-up study in school-age children (mean age = 10.9years). Mercury and lead concentrations in umbilical cord blood (infants) and in blood (children) were negatively correlated with pattern-reversal visual evoked potentials in children that were scalp-recorded at the occipital cortex [190 j. 

Electroencephalogram measures have been shown to be sensitive to some forms of neurological insult, and they have been used in the diagnosis of a variety of neurological disorders. Other neurophysiological measures, such as brainstem auditory evoked potential (BAEP), and pattern-reversal visual evoked potential (PREP), are supposed to be stable, relatively age-independent, and free from social or cultural influences. 

In addition to the experimental conditioning tests, Otto et al (1985) used two clinically validated measures of sensory function, the pattern-reversal visual evoked potential (PREP) and the brainstem auditory evoked potential (BAEP). Exploratory analysis of PREPs revealed increased amplitude and decreased latency of certain components as a linear function of original PbB levels. Although these results were contrary to predictions, the findings are consistent with the results of Winneke et al (1984), who found an association between increased PbB levels and decreased latency in the primary positive component of PREPs in children. BAEP results of the five-year follow-up study also indicated significant associations between original PbB levels and increased latencies of two components (waves III and V), indicative of auditory nerve conduction slowing. 

The effects of lead exposure on visual evoked potentials have been studied in man and animals, but the results of these studies are quite inconsistent. Flash evoked potentials (FEP) have been used in animals, whereas pattern-reversal visual evoked potentials (PREP) have been used in humans. Fox et al (1977) reported increased latencies, Feeney ei ah (1979) found decreased latency, and Winneke (1979) found no latency differences in lead-exposed rats compared with controls. Similar differences were noted in FEP amplitude measures Winneke reported depressed amplitudes, but Fox et al (1979) found increased amplitude recovery (cortical excitability) to paired flashes in lead-exposed rats relative to controls. Fox et al added to the confusion by interpreting the increased latencies as evidence of decreased CNS recovery (1977) and the amplitude effects as evidence of increased CNS recovery (1979). Both Fox et al reports, moreover, were based on the same animals in the same experiment ... 

Figure 6 Pattern-reversal visual evoked potentials recorded binocularly in five girls aged 3 to 7 with varying PbB levels. PIN2 peak-to-peak amplitude decreased significantly with increasing PbB. (Redrawn from Otto et al, 1985)...

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