In 1919, Sir Edward Mellanby (1884 – 1955) published his monograph, “Alcohol, Its Absorption into and Disappearance from the Blood under Different Conditions.” He instilled various types of alcohol and food into the stomach of dogs and determined the blood alcohol concentration over time using blood obtained from the ears of the dogs. Among other findings, he determined that milk slowed the absorption of alcohol from the stomach and, hence, lowered the BAC. (Remember your mother’s advice when you first started drinking!).
His major finding, however, was that the impairment of sensory and motor functions appeared to be greater when the BAC was increasing than at the same BAC when it was decreasing. This is also known as acute tolerance. This effect is experienced by many drinkers (including myself) when you feel more intoxicated when the BAC is rising. About 20 to 30 minutes later after you stop drinking, you don’t feel as intoxicated even though only a minimal amount of alcohol is eliminated during that time. A recent study has shown the importance of acute tolerance or the Mellanby effect in driving skills and how it increases alcohol’s dangerous effect on driving. The citation is:
WEAFER, J., and M.T. FILLMORE, “Acute Tolerance to Alcohol Impairment of Behavioral and Cognitive Mechanisms Related to Driving: Drinking and Driving on the Descending Limb” Psychopharmacology, 220: 697-706, 2012 (3 figures, 2 tables, 31 references) (WOA502U1)
Ten female and ten male social drinkers (ages 21 to 31years) consumed a placebo or 0.65 g/kg alcohol within six minutes and performed a test battery including computerized simulated driving and go/no go tests. BrACs were determined with an Intoxilyzer Model 400 and testing occurred at 35 minutes (ascending BAC) and 95 minutes (descending BAC) and the mean BrACs were 0.072 and 0.074 g/100mL respectively. Impaired motor coordination and subjective tolerance showed acute tolerance whereas driving performance and inhibitory control did not. The following Table shows several mean simulated driving performance parameters and reaction time for placebo (no alcohol) and on the ascending and descending BAC curve.
Standard deviation of lane position indicates the extent of weaving of the simulated car and the greater the result the more weaving occurs. The willingness to drive ranges from 0 (“not at all), to 100 (“very much”). The reaction time increases or is longer with alcohol, but increases even more on the descending BAC phase, perhaps due in part to tiredness.
One of the dangerous aspects of acute tolerance in driving seen in this study is the increased willingness to drive (and decrease in subjective feelings of intoxication) at the same BAC in the descending phase compared to the rising phase. The authors conclude:
In conclusion, the study highlights the importance of examining alcohol impairment of individual skills related to driving performance and decisions to drive at later time points during a drinking episode. Acute tolerance can result in diminished impairment of some skills, but not others. Moreover, acute tolerance to the subjective effects of alcohol could reduce the ability to accurately appraise one’s fitness to drive. As such, these findings have important implications, particularly in terms of education and prevention of intoxicated driving. Future policy changes could consider education regarding misperception of self-intoxication as well as information about the likelihood of sustained impairment of driving ability and inhibitory control in response to a dose of alcohol.
A recent excellent review on the effects of alcohol on driving published by my colleagues at the Centre of Forensic Sciences also examined acute tolerance and agreed with the Weaver and Fillmore (2012) study. The citation is:
MARTIN, T.L., P.A.M. SOLBECK, D. J. MAYERS, R.M. LANGILLE, Y. BUCZEK, and M.R. PELLETIER, “A Review of Alcohol-Impaired Driving: The Role of Blood Alcohol Concentration and Complexity of the Driving Task”, Journal of Forensic Sciences, 58: 1238-1250, 2013 (124 references) (WOA501U3)
This review consisted of 124 citations and covered topics such as acute and functional tolerance, and the effects of age, gender, and driving proficiency on driving skills. The authors conclude that impairment of driving ability occurs at BACs of 0.05 g/100mL or greater and agrees with the recommendations of the NTSB to lower the illegal BAC from 0.08 to 0.05 g/100mL.
It was also very generous of them to include me in their Acknowledgements, “The efforts of J.G. Wigmore in founding the Centre of Forensic Sciences alcohol literature database are also acknowledged.”
Ontario Mutual Insurance Association
On Tuesday October 29th 2013, I lectured at the wonderful new OMIA building in Cambridge, Ontario (100 km west of Toronto) to a group of Accident Benefits Adjustors on the effects of alcohol on driving ability, breath and blood alcohol tests. I had a great time and enjoyed the luncheon Chinese buffet. Many thanks to Jackie Brouwers, the Training and Research Officer of OMIA for organizing this event.