As I have said in previous posts, the single greatest flaw in breathalyzers is that they are designed to assume that all humans are the same.
You and I are physiologically different, and I am different at this moment from what I will be in an hour. The ratio of alcohol measured on the breath to the amount in the blood, for example, varies widely from time to time and from person to person. Our bodies metabolize alcohol — absorb and eliminate it — at different rates; among other things, this confounds attempts to estimate blood alcohol levels when driving based upon breath/blood tests an hour later. Further, each of us has a different physiological response — tolerance — to alcohol.
An example of this human diversity can be seen in racial differences toward alcohol. The body of scientific literature seems to clearly indicate a racial — i.e., genetic — difference in the metabolism and effects of alcohol. Studies, for example, have found that American Indians metabolize alcohol more than twice as fast as Caucasians. Bennion and Li, “Alcohol Metabolism in American Indians and Whites”, 294 New England Journal of Medicine 9 (1976); Holzbacher, “Elimination of Ethanol in Humans”, 17 Canadian Society of Forensic Science Journal 182 (1984); Fenna et al., “Ethanol Metabolism in Various Racial Groups”, 105 Canadian Medical Association Journal 472 (1971).
The following excerpt is from one of the books I wrote while teaching at a law school some years ago. Entitled Born to Crime (Greenwood Press: London, 1984), it dealt with the sensitive subject of genetic predisposition toward criminal behavior. One chapter addressed the causes of alcoholism:
…This ethnic approach was first used in 1972 in a study of the comparative effects of alcohol on men and women in Japan, Taiwan, Korea and the United States. Wolff, “Ethnic Differences in Alcohol Sensitivity”, 175 Science 449 (1972). Interested by the lower rate of alcoholism among Asians, an American physician selected 38 Japanese, 24 Taiwanese, 20 Koreans and 34 Americans as subjects (all between the ages of 25 and 35). He fed each subject measured amounts of beer, with Americans (that is, Caucasians) receiving more than twice as much per pound of body wieght as the Asians. He then measured the body’s reaction to the alcohol by recording the flushing of the earlobe with an optical densitometer, as well as increases in pulse pressure.
If there were no genetic differences in reactions to alcohol, the physician could expect to find that flushing (an indication of vessel dilation) and pulse pressure — both under the control of the autonomic nervous system — would be consistent among the various ethnic groups. The results, however, clearly indicated a genetic factor in the reaction to alcohol. Fully 83 percent of the Asian subjects responded to the measured amounts of alcohol with a marked flush, but only 6 percent of the Caucasians did, despite the latter having received larger doses. Similarly, increases in pulse pressures were observed in 74 percent of the Asians, with only 3 percent (one adult) of the Caucasians demonstrating such a reaction.
To insure against any possble cultural differences on alcohol consumption, the physician next duplicated the experiment with Japanese, Taiwanese and American infants, giving them small amounts of port wine in a glucose solution. Again, the results showed that heredity rather than environment dictated the body’s automatic reaction to alcohol: Of the Asian babies, 74 percent responded with flushing, but of the Caucasian babies, only 5 per cent (one baby) so reacted. Clearly, the alcohol-induced changes in blood flow were not learned or conditioned responses….
These experiments were repeated by a team of scientists two years later, this time with 24 Chinese and 24 European subjects. Ewing et al., “Alcohol Sensitivity and Ethnic Background”, 131 American Journal of Psychiatry 206 (1974). The results proved to be the same: Skin flushing, increased heart rate and decreased blood pressure in response to alcohol were much more noticeable among the Chinese.
The scientists concluded that physiological rather than cultural factors determined the relatively low rate of alcoholism in Asians….
Humans are a diverse group. Each of us, thankfully, is unique. And it is this uniqueness and variability which will always render unreliable the use of machines to estimate blood alcohol levels by measuring breath, legal presumptions of intoxication based on blood-alcohol levels, and mathematical formulas and presumptions based upon uniform metabolism to estimate earlier levels when driving.