Errors in Current Alcohol Breath Analysis J. Levett1 and L. Karras On September 29, 1969, Section 11-501 of the Illinois Vehicle Code (Suspension of License Implied Consent) was approved in an effort to curb highway deaths due to consumption of alcoholic beverages by the driver. Section 11.501-1 states that any person operating a vehicle, who is lawfully arrested on the roads of Illinois, must submit to a breath test if he/she is suspected of driving under the influence of alcohol. The breath test will examine a breath sample for alcohol content, which is then expressed in terms of a bood alcohol concentration (BAC). A BAC of 100 mg of ethanol/100 ml of blood or higher is considered proof of driving under the influence in the State of Illinois. The Breathalyzer, model 1000, manufactured by Smith and Wesson is the automated breath analyzing instrument most commonly used in Illinois. Tests were conducted using the Model 1000 Breathalyzer to determine how closely the BAC established via a breath test correlated with the BAC determined via a blood sample. The Breathalyzer, as stated by the manufacturer (4), needs a minimum of 452.5 ml of lung air from a subject to advance the instrument to the analysis stage where the breath sample is automatically analyzed for alcohol content. In the Breathalyzer only the last 52.5 ml of expired air given to the instrument is used for analysis. Thus, if the minimum amount of air, 452.5 ml, is given to the Breathalyzer only the last 52.5 ml of air will be analyzed for alcohol content. Likewise, if a subject expired 2000 ml of air into the instrument it would still be only the last 52.5 ml of air that the Breathalyzer analyzed. In a legal sense, expiring only 452.5 ml of air into the Breathalyzer would be acceptable. The problem is that if a minimum amount of air is given to the Breathalyzer, it will not give an accurate reading indicative of the actual BAC of the person being tested. Tests were conducted which showed that the Breathalyzer could give readings much lower than the expected readings. This problem was brought to the attention of manufacturers, and the instrument was modified to ensure obtaining alveolar air for analysis. The same tests as previously used to determine Breathalyzer accuracy were then repeated on the modified Breathalyzer to determine the improved correlation between the breath sample and blood sample. 1 Dept, o f Biomedical Engineering, Rush-Presbyterian-St. Luke s Medical Centre, Chicago, Illinois 60612, U.S.A. 527
528 J. Levett and L. Karras PROCEDURES AND METHODS The Breathalyzers used in these experiments were examined for accuracy by the Illinois Department of Public Health and each examination showed that the instrument was properly calibrated and usable under the criteria given in the Implied Consent legislation. The experiments involved two phases. The first phase used the Breathalyzer as now used in the field, while the second used an instrument with modified intake controls to guarantee a minimum airflow rate for a specified duration when a breath sample was taken using the Breathalyzer. Twenty-five subjects were used in each phase, and each phase consisted of about 15 sessions. The Breathalyzer was tested before and after each session with a simulator of known value to insure that calibration was proper. In no case did the before-and-after simulator tests differ. All subjects were given one hour to drink an alcoholic beverage of their choice and they were allowed to drink whatever amount they felt they could handle, as long as their predicted BAC did not exceed 250 m g/100 ml. No eating or smoking was allowed during the experiment. A waiting period of one hour followed the drinking hour before automated breath testing began. This hour was necessary to eliminate any differences in the breath and blood-alcohol tests that may have arisen due to the dynamic characteristics of the absorption phase where the breath alcohol level is higher than the venous blood alcohol level (2, 3). After the one-hour wait, subjects were instructed to blow into the Breathalyzer and were told to stop blowing one second after an obvious click was heard coming from the Breathalyzer. This click was due to an electromechanical switch in a cylinder tripped by a piston when 452.5 ml of air had entered the intakes of the Breathalyzer. This breath sample procedure usually lasted about three seconds and met the legal minimum breath sample requirement since it proved sufficient to activate the instrument. This was then defined as the minimum breath sample. The subject s arm was then cleaned with benzykonium chloride and a venous blood sample was taken. After the Breathalyzer analyzed the breath sample the Breathalyzer s ampoule containing a chemical reagent and the saliva trap were changed. The instrument was then immediately recycled for another breath test. The subject was instructed to blow into the Breathalyzer until no more air could be forced out of the lungs. This was the maximum breath sample. The order of obtaining minimum breath tests was reversed in a random fashion. A second venous blood sample was taken from 10 of the 25 subjects. The blood was drawn into a vacutainer containing oxalate, an anti-coagulant, and refrigerated until it could be analyzed. The blood samples were analyzed within 36 hours by a biochemistry laboratory that has facilities certified by the Department of Public Health for such an analysis. The Breathalyzer was modified in an effort to ensure the sampling of only alveolar air reflecting the actual BAC. Originally, the Breathalyzer used in Illinois had an input breath tube which fed directly into a cylindrical chamber with a volume of 52.5 ml. This chamber was in series with another cylindrical chamber of equal size and had a portioning valve to ensure that the subject blows at least 452.5 ml of air to trigger an electromechanical switch. Activation of this switch advanced the Breathalyzer to the analysis stage when a subject had completed his expiratory effort. The contents of the first chamber were then analyzed to determine the BAC of the subject tested (4). The modification of the Breathalyzer consisted of disabling the electro-
Errors in A Icohol Breath A nalysis 5 29 mechanical switch in the second chamber and installing a rated-airflow valve and a timing circuit. The rated airflow valve is inserted in such a way that air blown in by the subject must pass through the valve first before entering the first chamber. When a subject delivers a specified minimum airflow rate (six liters per minute) a switch opens and a timing circuit starts. The timing circuit is set for a maximum of six seconds. Therefore, the Breathalyzer advances to the analysis stage only when the minimum airflow rate (six liters per minute) has been maintained for six seconds, thus a minimum breath sample has a volume of 600 ml. In summary, minimum and maximum breath sample readings taken six minutes apart were compared to corresponding blood sample readings before and after the Breathalyzer was modified. RESULTS AND DISCUSSION During each phase of testing, that is, before and after modifications were made on the Breathalyzer, 10 of the subjects had a blood sample taken immediately after each minimum and maximum breath test was completed. Our findings show that two blood samples taken at a maximum time separation of 10 minutes yielded an average difference in BACs of 5 mg/100 ml. Therefore, it was not necessary to take a blood sample after each maximum and minimum breath test since variations between the blood samples was insignificant. The remaining 15 subjects had only one blood sample taken in the time period (six minutes) between minimum and maximum breath tests. Figure 1 shows the variation in minimum and maximum breath tests at the corresponding BAC determined via blood samples before the modification of the Breathalyzer. Differences in minimum and maximum breath tests were as great as 70 m g/100 ml. Table I indicates that the Breathalyzer was, on the average, 49% below the actual BAC on minimum breath tests and 22% below the actual BAC on maximum breath tests for the BAC ranges shown in Table I. This also is shown in Figure 2 by the slope of the lines as determined by the average error in the breath test as a function of the actual BAC. Minimum breath tests gave errors ranging from 28% to 64% below the actual breath test, whereas maximum breath tests had a range of error from 1% to 37% below the actual BAC. TABLE I Percentage Difference between Breath Test Results and actual BAC BAC Range Breath Tests Before Modifications Breath Tests After Modifications Via Blood Range o f Percentages Average Percentage Range o f Percentage Average Percentage Samples Below Actual BAC Below Actual BAC Below Actual BAC Below Actual BAC m g/100m l Minimum Maximum Minimum Maximum Minimum Maximum Minimum Maximum Breath Breath Breath Breath Breath Breath Breath Breath 1 to 100 39-64 2-33 51 23 14-52 2-37 34 23 101 to 150 28-63 1-35 45 18 17-50 6-36 33 21 151 to 200 35-62 17-28 50 20 34-39 14-29 36 22 201 to 300 43-57 18-37 48 27 25 44 8-31 33 22 Average Percentage Below Actual 49 22 34 22 BAC o f the Four BAC Ranges
530 J- Levett and L. Karras Figure 1 BLOOD ALCOHOL CONCENTRATION VIA A BREATH SAMPLE mfl/10 0 ml BAC via minimum and maximum breath samples given to a Breathalyzer versus the BAC determined via a blood sample. Breathalyzer before modifications. Breath samples were taken six minutes apart, x = maximum, o = minimum. After the intake controls of the Breathalyzer had been modified, differences in minimum and maximum breath tests ranged from 0 m g/100 ml to 40 m g/100 ml. This is a decrease of 30 mg/100 ml in the largest disparity between the minimum and maximum breath tests. After modifications the Breathalyzer was about 34% below the actual BAC for minimum breath tests and 22% below the actual BAC for maximum breath tests for the BAC ranges shown in Table I. This is a decrease of 15% in error for the minimum breath test after the Breathalyzer was modified. The per cent of error below the actual BAC remained the same for maximum breath tests as was expected. Minimum breath tests ranged 14-52% below the actual BAC, while the maximum breath tests were 2-37% below the actual BAC. Figure 2 shows that after modifications there is a decrease in the slope of the minimum breath test error while the slope of the maximum breath test error is essentially the same as before modifications as shown in Figure 2.
Errors in Alcohol Breath Analysis 531 Figure 2 AVERAGE VENOUS BLOOD ALCOHOL CONCENTRATION PER 50 mg/l 00 mi RANGE. Breathalyzer error versus BAC via blood samples per 50 m g/100 ml range before and after modifications. ------------ Breathalizer before modifications. ---------------------- Breathalizer after modifications. 0 :=ERROR! mg/100ml = e r r o r 2 mg/100ml = S (B A C -B min) NO. OF Bm;n SAMPLES IN A 50 mg/100ml RANGE = S (B A C -B max) NO. OF Bmax SAMPLES IN A 50mg/100ML RANGE The above results show that to obtain a breath sample that reflects the BAC as accurately as possible the minimum breath sample must be more than the 452 ml now required by Breathalyzers used in Illinois. Using a minimum breath sample on the current Breathalyzer in Illinois one could expect a 49% error in determining the actual BAC. Although the first 452 ml of expired air usually assures that dead-space air has been removed and only alveolar air remains, it is questionable whether the first 452 ml
532 J. Levett and L. Karras of expelled air has reached equilibrium with the blood to contain an alcohol concentration indicative of the actual BAC. The above results confirm that equilibrium had not been reached with a minimum breath sample of 452 ml. Modification of the intake controls as outlined previously ensured a 600 ml minimum breath sample. This reduced the expected error from 49% to 34% when analyzing a minimum breath sample. This indicates that the Breathalyzer needs to have the breath-intake controls adequately modified if it is to make an accurate correlation to the actual blood alcohol levels. It is suggested that the intake controls be modified such that a minimum expiratory effort would have a volume of 800 ml. Although unproven, the minimum 800 ml of expired air would ensure obtaining a Breathalyzer reading of BAC close to that obtained from a maximum expiratory effort which is normally 10-20% below the actual BAC. Caution should be taken in modifying the intake controls such that the flow rate is not too high. Currently, the modified Breathalyzer has a flow rate of six liters per minute and about one-third of the subjects used in these experiments complained about the difficulty of blowing into the Breathalyzer. Several tests could not be completed because a few subjects could not sustain this flow rate for six seconds. A flow rate of five liters per minute for 9.5 seconds would ensure obtaining with ease about 800 ml of air as a minimum breath sample. It should be emphasized that a determined effort to obtain a maximum breath ensures close correlation with the actual BAC (10-20% below the BAC). Therefore, under a strict protocol to obtain a maximum breath sample, the unmodified Breathalyzer is a reasonably accurate and effective instrument for law enforcement, since it measures accurately the alcohol content of whatever breath sample it obtains. REFERENCES 1. Guyton, Arthur C., Pulmonary Ventilation, in Textbook o f Medical Physiology, W. B. Saunders, Philadelphia, 1971. 2. Harger, R. N, Forney, R. B., and Baker, R. S., Estimation o f the Level of Blood Alcohol from Analysis o f Breath, Quarterly Journal of Studies on Alcohol 17, 1-18 (1956). 3. Levett, J., and Karras, L., Implied Consent and Scientific Instrumentation to Make it Work, Lex et Scientia 9, 85 (1973). 4. Smith and Wesson Electronics, Breathalyzer Model 1000 Operator s Manual, Eatontown, New Jersey, 1972.