I have mentioned that a primary problem with blood alcohol analysis is that the no two individuals are alike in their physiology and metabolism of alcohol (see, for example, Convicting the Average Person, Racial Differences in the Metabolism of Alcohol and High Blood Alcohol – or a Zinc Deficiency?. Further, many foreign compounds can influence attempts to measure blood alcohol levels (see, for example, Under the Influence…Gasoline?, Asthma Inhalers Can Cause High Breathalyzer Results and Driving Under the Influence of…Paint?.
One of many other factors that render attempts to estimate an individual’s blood alcohol concentration at a given point in time is smoking.
A scientific study has found that cigarette smoking can influence absorption by the body of alcohol – and thus, among other things, attempts to estimate earlier blood alcohol levels when driving based upon tested levels. Johnson et al., "Cigarette Smoking and Rate of Gastric Emptying: Effect on Alcohol Absorption", 302 British Medical Journal 20 (1991).
The researchers reported testing blood samples of a group of smokers for blood alcohol levels both after smoking and after prolonged abstinence. The result was that "areas under the venous blood alcohol concentration-time curves between zero and 30 minutes and 60 minutes and the peak blood alcohol concentrations were significantly less during the smoking period compared with the non-smoking period". (Emphasis added) Gastric emptying was also found to be slower during the smoking evaluation.
The scientists concluded that the effect of smoking on alcohol absorption has "considerable social and medicolegal relevance", and that the ingestion of nicotine should be taken into when dealing with alcohol metabolism.
Non-specific analysis is another problem causing breath machines to give false readings when the subject is a smoker. As I mentioned in an earlier post, Why Breathalyzers Don’t Measure Alcohol, breath machines are actually designed to report the presence of any compound containing the methyl group in its molecular structure, not just alcohol. They cannot distinguish the difference between alcohol and, say, acetaldehyde.
Acetaldehyde? That’s a compound produced in the liver in small amounts as a by-product in the metabolism of alcohol. Unfortunately, alcohol moving from the blood into the lungs has been found to metabolize there as well – and, thus, to produce acetaldehyde there. The amount of acetaldehyde produced in the lungs varies from person to person. However, scientists have found one interesting fact: acetaldehyde concentrations in the lungs of smokers are greater than for non-smokers – far greater. Translated: smokers are more likely to have falsely high readings on a Breathalyzer. "Origin of Breath Acetaldehyde During Ethanol Oxidation: Effect of Long-Term Cigarette Smoking", 100 Journal of Laboratory Clinical Medicine 908.
End result: because breathalyzers can’t tell the difference between alcohol and acetaldehyde, a higher blood-alcohol reading. And if you are a smoker, a much higher reading.