THE PHARMACODYNAMICS OF ETHANOL - EFFECTS ON PERFORMANCE AND JUDGMENT

The objective and subjective effects produced by increasing and decreasing ethanol concentrations were studied in healthy volunteers on three separate occasions. A randomized, double-blind, placebo-controlled, four-way crossover study was used to determine whether there is any disparity between the time course of blood ethanol concentration and its effects on either objective test performance or self rated impairment. On each study day the subjects received one of four treatments consisting of either placebo or sufficient alcohol to achieve peak estimated blood alcohol concentration (Est.BAC) of 0.07 gm/dL, 0.1 gm/dL or 0.14 gm/dL. Est.BAC determined from breath alcohol concentrations were measured 20 minutes after each 'dose' until peak Est.BAC was achieved, then 1, 2, 3.5, and 4.5 hours after peak Est.BAC. Digit symbol substitution (DSS), simulated driving reaction time (SDRT), choice reaction time (CRT) and self assessment of impairment (SRI) were measured simultaneously with Est.BAC. Changes in objective performance test socres were well correlated with Est.BAC (r2 = 0.60 P<.01). Maximum impairment in test performance occurred at the same time as peak Est.BAC. Threshold Est.BAC needed to produce changes in objective test scores greater than placebo were 0.06 ± 0.01 for DSS, 0.04 ± 0.01 for SDRT, and 0.04 ± 0.02 for CRT. There was no evidence of between dose or within dose tolerance to the effects produced by various Est.BAC on any of these performance tests. Subjects' self rated degrees of impairment at various Est.BAC were influenced by whether alcohol concentrations were rising or falling. Subjective impairment ratings were greater while alcohol concentrations were increasing compared to the same Est.BAC occurring during falling alcohol concentrations. Disparities between self rated degree of impairment and decrements in test performance were greatest 1.0 hour after peak Est.BAC and maximum decrements in test performance. The delay in subjects' ability to accurately rate their impairment relative to peak Est.BAC may be a contributing factor to motorists choosing to drive while their performance is still impaired.