Positional nystagmus and body sway after alcohol ingestion.

Positional nystagmus and body sway were measured for 8 hours following alcohol ingestion in 27 human volunteers. The intensity of positional alcohol nystagmus phase I (PAN-I) correlated well with blood alcohol concentration (BAC) along the time axis; the correlation coefficient between PAN-I and BAC 1 hour after alcohol ingestion was 0.62 (P less than .01). The minimum threshold BAC resulting in PAN-I was 0.23 mg/mL. Body sway was measured by stabilometry. The circumscribed area of posturography before and after alcohol ingestion was compared. Temporal changes in body sway and BAC were also closely correlated. The BAC threshold for increased body sway was estimated to be somewhere between 0.5 and 0.8 mg/mL, considerably higher than the threshold for PAN-I. Measurements of blood acetaldehyde, the dehydrated product of ethanol metabolism, showed no correlation with either the intensity of PAN or changes in body sway. The intensity of PAN and body sway measured at the time of peak BAC 1 hour after alcohol ingestion, however, showed significant positive correlation (r = .50, n = 25; P less than .01).